全文获取类型
收费全文 | 18025篇 |
免费 | 1146篇 |
国内免费 | 28篇 |
专业分类
耳鼻咽喉 | 188篇 |
儿科学 | 675篇 |
妇产科学 | 464篇 |
基础医学 | 2396篇 |
口腔科学 | 520篇 |
临床医学 | 2044篇 |
内科学 | 3479篇 |
皮肤病学 | 252篇 |
神经病学 | 1454篇 |
特种医学 | 696篇 |
外科学 | 2472篇 |
综合类 | 310篇 |
一般理论 | 29篇 |
预防医学 | 1684篇 |
眼科学 | 271篇 |
药学 | 1119篇 |
2篇 | |
中国医学 | 13篇 |
肿瘤学 | 1131篇 |
出版年
2022年 | 115篇 |
2021年 | 275篇 |
2020年 | 188篇 |
2019年 | 291篇 |
2018年 | 314篇 |
2017年 | 265篇 |
2016年 | 258篇 |
2015年 | 335篇 |
2014年 | 465篇 |
2013年 | 571篇 |
2012年 | 912篇 |
2011年 | 950篇 |
2010年 | 502篇 |
2009年 | 436篇 |
2008年 | 843篇 |
2007年 | 921篇 |
2006年 | 866篇 |
2005年 | 842篇 |
2004年 | 770篇 |
2003年 | 764篇 |
2002年 | 643篇 |
2001年 | 510篇 |
2000年 | 501篇 |
1999年 | 418篇 |
1998年 | 189篇 |
1997年 | 154篇 |
1996年 | 164篇 |
1995年 | 179篇 |
1994年 | 168篇 |
1993年 | 137篇 |
1992年 | 370篇 |
1991年 | 376篇 |
1990年 | 348篇 |
1989年 | 340篇 |
1988年 | 308篇 |
1987年 | 275篇 |
1986年 | 230篇 |
1985年 | 305篇 |
1984年 | 221篇 |
1983年 | 216篇 |
1982年 | 138篇 |
1979年 | 163篇 |
1978年 | 145篇 |
1977年 | 124篇 |
1976年 | 115篇 |
1975年 | 124篇 |
1974年 | 128篇 |
1973年 | 155篇 |
1972年 | 121篇 |
1971年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Public health nurses from 13 local public health agencies and nurse educators from five schools of nursing developed population-based public health nursing competencies for new graduates and novice public health nurses. Educators in one nursing program used a portfolio assignment to measure achievement of the competencies by traditional and RN to BSN students in a community health nursing course. Data were collected from surveys and focus groups to determine students' responses to the portfolio and their use of population-based public health nursing concepts. The assignment enhanced students' critical thinking skills; however, concerns about the structure and evaluation of the portfolio decreased student satisfaction. Recommendations are made for improving the portfolio format, increasing students' valuing of the portfolio, managing the tension between assessment and learning, and orienting clinical agency staff and nursing instructors. 相似文献
62.
Heather Long MD Lewis S. Nelson MD Robert S. Hoffman MD 《Academic emergency medicine》2008,15(7):688-690
Objectives: Many hospitals must send out ethylene glycol (EG) samples to a reference laboratory, and delays in diagnosis and treatment may occur. A qualitative colorimetric test (ethylene glycol test [EGT] kit), already in use by veterinarians, gives results in 30 minutes with little expertise or cost. The EGT reliably detects the presence of EG in spiked human serum samples. The objective of this study was to prospectively assess the sensitivity and specificity of the EGT kit in actual clinical samples submitted for EG testing by the criterion standard gas chromatography (GC).
Methods: Blood samples from patients with suspected toxic alcohol poisoning submitted to a reference laboratory were tested by GC. An investigator blinded to the GC results tested the same sample with the EGT kit following the manufacturer's instructions and using the internal control. Three physicians also blinded to the GC results categorized the sample as positive for EG, negative, or inconclusive. Interrater reliability was assessed with a kappa statistic (κ). Results of the EGT kit testing were then compared to those from GC testing.
Results: Data are reported on 24 samples submitted. By GC, 15 samples were confirmed for EG (range 27–281 mg/dL), 5 were confirmed for methanol (ME; range 64–101 mg/dL), and 4 were negative for both alcohols. The EGT was unanimously positive in all confirmed EG samples and negative in all ME samples. In one of the negative samples, an ambiguous result occurred and was counted as a false-positive. Interobserver agreement with the EGT was high (κ = 0.909; 95% confidence interval [CI] = 0.735 to 1.0). Sensitivity and specificity were 100% (95% CI = 70% to 100%) and 88.8% (95% CI = 52% to 100%), respectively.
Conclusions: The EGT appears to be a reliable qualitative test in cases of suspected human EG poisoning. 相似文献
Methods: Blood samples from patients with suspected toxic alcohol poisoning submitted to a reference laboratory were tested by GC. An investigator blinded to the GC results tested the same sample with the EGT kit following the manufacturer's instructions and using the internal control. Three physicians also blinded to the GC results categorized the sample as positive for EG, negative, or inconclusive. Interrater reliability was assessed with a kappa statistic (κ). Results of the EGT kit testing were then compared to those from GC testing.
Results: Data are reported on 24 samples submitted. By GC, 15 samples were confirmed for EG (range 27–281 mg/dL), 5 were confirmed for methanol (ME; range 64–101 mg/dL), and 4 were negative for both alcohols. The EGT was unanimously positive in all confirmed EG samples and negative in all ME samples. In one of the negative samples, an ambiguous result occurred and was counted as a false-positive. Interobserver agreement with the EGT was high (κ = 0.909; 95% confidence interval [CI] = 0.735 to 1.0). Sensitivity and specificity were 100% (95% CI = 70% to 100%) and 88.8% (95% CI = 52% to 100%), respectively.
Conclusions: The EGT appears to be a reliable qualitative test in cases of suspected human EG poisoning. 相似文献
63.
Immunoglobulin G-induced single ionic channels in human alveolar macrophage membranes. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《The Journal of clinical investigation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D J Nelson E R Jacobs J M Tang J M Zeller R C Bone 《The Journal of clinical investigation》1985,76(2):500-507
While it is well known that the engagement of IgG Fc receptors on the macrophage surface triggers a number of cellular responses, including particle ingestion, secretion, and respiratory burst activity, the mechanism of signal transmission following ligand binding remains poorly understood. To acquire more data in this area, we studied the electrical properties of the macrophage membrane and its response to oligomeric immunoglobulin G (IgG) using the patch-clamp technique on human alveolar macrophages that were obtained by bronchoalveolar lavage and maintained in short-term tissue culture. The results showed that cell resting potentials, as determined from whole-cell tight seal recordings, increased from -15 mV on the day of plating to -56 mV after the first day in culture and remained stable at this hyperpolarized level. Macrophages revealed an input resistance of 3.3 G omega, independent of age in culture. Extracellular application of heat-aggregated human IgG to cells voltage-clamped at -70 mV resulted in peak inward currents of approximately 470 pA. We identified an IgG-dependent, nonselective channel in both cell-attached and isolated membrane patches, with a unitary conductance of approximately 350 pS and a predominant subconductance level of 235 pS in symmetrical NaCl solutions. Single channel open times were observed to be in the range of seconds and, in addition, were dependent upon membrane voltage. Channel opening involved transitions between a number of kinetic states and subconductance levels. Channel events recorded in cell-attached patches showed characteristic exponential relaxations, which implied a variation in membrane potential as a result of a single ion channel opening. These data suggest that the IgG-dependent nonselective cation channel that we have characterized may provide the link between Fc receptor engagement and subsequent cellular activation. 相似文献
64.
G Schonfeld W Patsch L L Rudel C Nelson M Epstein R E Olson 《The Journal of clinical investigation》1982,69(5):1072-1080
The effects of dietary cholesterol and fatty acids on low density and high density lipoproteins (LDL and HDL) were studied in 20 young men. After 2-3 wk of evaluations on ad lib. diets, basal diets, which consisted of 15% protein, 45% carbohydrates, 40% fat, and 300 mg/day of cholesterol, were given for 4-5 wk (Basal). The ratio of dietary polyunsaturated to saturated fatty acids (P/S) for different groups of subjects were 0.25, 0.4, 0.8, or 2.5. 750 and 1,500 mg/d of cholesterol were added to the basal diets as 3 and 6 eggs, respectively. Total cholesterol and LDL cholesterol were lower in all subjects on the basal diets than on the ad lib. diets. Addition of 750 mg cholesterol to the diet with P/S = 0.25-0.4 raised LDL cholesterol by 16 +/- 14 mg/dl to 115% of basal diet values (n = 11, P less than 0.01); 1,500 mg increased LDL cholesterol by 25 +/- 19 mg/dl to 125% (n = 9, P less than 0.01). On the diet with P/S = 0.8, 750 mg produced insignificant increases in LDL cholesterol, but 1,500 mg produced increases of 17 +/- 22 mg/dl to 115% of basal (n = 6, P less than 0.02). On the P/S = 2.5 diet, neither 750 nor 1,500 mg produced significant changes. Thus, both the cholesterol contents and P/S ratios of diets were important in determining LDL levels. The lipid and apoprotein compositions, flotation rates, molecular weights, and binding by cellular receptors of LDL were virtually unchanged by the addition of cholesterol to the diets high in saturated fat. These diets, therefore, caused an increase in the number of LDL particles of virtually unchanged physical and biological properties. On the diet with low P/S ratio, HDL2 rose, whereas this effect was absent on diets with high P/S ratios. The response of LDL to dietary manipulations is consonant with epidemiologic data relating diets high in cholesterol and saturated fat to atherogenesis. The response of HDL2, however, is opposite to that of its putative role as a negative risk factor. Further work is needed to clarify this interesting paradox. 相似文献
65.
Oermann MH Kardong-Edgren S Odom-Maryon T Hallmark BF Hurd D Rogers N Haus C McColgan JK Snelson C Dowdy SW Resurreccion LA Kuerschner DR LaMar J Tennant MN Smart DA 《Nursing education perspectives》2011,32(5):311-315
Our study explored the effects of deliberate practice on the retention ofcardiopulmonary resuscitation (CPR) psychomotor skills among nursing students. The practice sessions were short, six minutes a session one time a month. Differences in performance between students who had deliberate practice and a control group, with no practice beyond the initial training, were compared every three months for one year. The intervention group performed better than the control over the 12 months. There is a need in nursing education for deliberate practice of relevant and high-use skills for students to improve their performance and gradually develop their expertise. 相似文献
66.
Evaluation of the anti-influenza virus activities of 1,3,4-thiadiazol-2-ylcyanamide (LY217896) and its sodium salt.
下载免费PDF全文
![点击此处可从《Antimicrobial agents and chemotherapy》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J M Colacino D C DeLong J R Nelson W A Spitzer J Tang F Victor C Y Wu 《Antimicrobial agents and chemotherapy》1990,34(11):2156-2163
1,3,4-Thiadiazol-2-ylcyanamide (LY217896) and its sodium salt were shown to be effective against influenza A and B viruses in vitro and in the mouse model. In nondividing confluent MDCK cells, the 50% inhibitory concentration of LY217896 ranged from 0.37 to 1.19 micrograms/ml against various strains of influenza A virus and from 0.75 to 1.54 micrograms/ml against various strains of influenza B virus, with no apparent cytotoxicity. However, at a concentration of 0.31 microgram/ml, LY217896 inhibited the replication of dividing MDCK cells. LY217896 (9 mg/m2 of body surface area per day) administered in the diet, in the drinking water, by oral gavage, by intraperitoneal injection, or by aerosolization was well tolerated and protected CD-1 mice infected with a lethal dose of influenza A or B virus. Effective administration of the compound could be delayed for up to 96 h postinfection. Virus titer was reduced by 1 to 2 log10 units in lungs of mice given LY217896 in the drinking water. Mice treated initially with protective levels of LY217896 were resistant to a subsequent challenge of influenza virus in the absence of the compound, indicating that the animals were able to develop immunity to the initial infection. Administration of LY217896 to uninfected mice did not induce interferon-like activity or interfere with natural killer cell function. In the ferret, LY217896 was effective in preventing fever induced by influenza virus. 相似文献
67.
Pharmacokinetics and bacteriological efficacy of cefoperazone, ceftriaxone, and moxalactam in experimental Streptococcus pneumoniae and Haemophilus influenzae meningitis.
下载免费PDF全文
![点击此处可从《Antimicrobial agents and chemotherapy》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The pharmacokinetics and bacteriological efficacy of cefoperazone, cefuroxime, ceftriaxone, and moxalactam were evaluated in the experimental rabbit meningitis model of Haemophilus influenzae type b or Streptococcus pneumoniae infection. The cerebrospinal fluid penetration of these beta-lactam antibiotics was from 3 to 14% and was greater in Haemophilus-infected that in pneumococcus-infected animals. With the exception of moxalactam, the antibacterial activity in cerebrospinal fluid and change in concentration of bacteria during therapy with the test drugs were comparable to those of penicillin G in pneumococcal infection. In animals infected with H. influenzae, cefoperazone, moxalactam, and ceftriaxone were as effective as chloramphenicol in reducing the bacterial counts in cerebrospinal fluid. Moxalactam and ceftriaxone produced the largest cerebrospinal fluid bactericidal titers against this beta-lactamase-producing strain of Haemophilus. On the basis of these data, it was concluded that ceftriaxone and cefoperazone were effective against both pathogens in this meningitis model, whereas moxalactam was effective against only Haemophilus, and cefuroxime was effective against only S. pneumoniae. 相似文献
68.
Using the simple method of protein analysis described here, we could identify thyroxin (T4)-binding-protein abnormalities in euthyroid patients with hyperthyroxinemia or hypothyroxinemia. Serum incubated with [125I]thyroxin was analyzed by agarose gel electrophoresis, with bromphenol blue staining of protein. The relative distribution of radioactive T4 was determined for each binding protein--thyroxin-binding globulin (TBG), transthyretin, albumin, and T4-binding immunoglobulin (when present)--and the mass of T4 bound to each was determined. We also used sensitive immunoassays to quantify TBG, transthyretin, and albumin concentrations, then calculated the mass of T4 (as determined by electrophoresis) bound per unit mass of the respective binding protein. When the concentration of binding proteins was altered (e.g., TBG excess or TBG deficiency), the T4 binding/mass ratio for each protein remained within the expected range; but when the functional affinity of a binding protein was altered--as in dysalbuminemic hyperthyroxinemia and in low-T4 nonthyroidal illness--this ratio was abnormal. This procedure can be used to help identify TBG excess, TBG deficiency, dysalbuminemic hyperthyroxinemia, prealbumin-associated hyperthyroxinemia, variant TBG with reduced affinity for T4, euthyroid sickness, and T4-binding autoantibodies. 相似文献
69.
Palmieri TL Aoki T Combs E Curri T Garma S Kaulkin C Lawless MB Nelson K Sanders J Warden N Greenhalgh DG 《The Journal of burn care & rehabilitation》2004,25(4):381-5; discussion 372-3
Television has become an important tool for learning and socialization in children. Although television violence has been associated with adverse effects, data on depiction of fire and burn injury are lacking. We sought to determine whether Saturday-morning television programming, viewed primarily by children, depicts fire and burn injury as safe or without consequence, thus potentially increasing the incidence of burn injury in children. This was a prospective observational study. Saturday-morning children's television programs were videotaped from 7 AM to 11 AM for eight different television networks during a 6-month period. Tapes were scored for scenes depicting fire or smoke by independent observers. Recorded items included show category, scene type, gender target, context of fire, and outcome after exposure to flame. Fire events were documented during programs and their associated commercials. A total of 108 hours of children's programs, 16 hours per network, were recorded. Scenes depicting fire or smoke were identified 1960 times, with 39% of events occurring during the program itself and 61% in commercials. Fire was depicted as either safe or without consequence in 64% of incidents. Action adventure stories accounted for 56% of flame depictions. Overall, one incident involving flame and fire was portrayed for each 3 minutes of television programming. Saturday-morning television programming frequently depicts fire as safe, empowering, or exciting. The incidence of flame use in programming varies between stations but is most prevalent in action/adventure stories. Television commercials, although brief, provide the majority of the misinformation regarding fire. Medical professional societies should alert the public to this potential hazard and recommend responsible portrayal of fire in children's television programming. 相似文献
70.
Quantitation of basal dyssynchrony and acute resynchronization from left or biventricular pacing by novel echo-contrast variability imaging 总被引:4,自引:0,他引:4
Kawaguchi M Murabayashi T Fetics BJ Nelson GS Samejima H Nevo E Kass DA 《Journal of the American College of Cardiology》2002,39(12):2052-2058
OBJECTIVES: This study sought to test a novel echocardiographic method based on contrast variability imaging (CVI), to quantify cardiac dyssynchrony and magnitude of resynchronization achieved by left ventricular (LV) and biventricular (BiV) pacing therapy. BACKGROUND: Left ventricular or BiV pacing is a promising new therapy for patients with heart failure and intraventricular conduction delay. However, precise quantitation of the extent of resynchronization achieved remains scant. METHODS: Ten patients treated with BiV or LV pacing therapy were studied. Echo-contrast was infused slowly, and gated images were acquired before and during contrast appearance. The temporally normalized variance derived from 30 to 50 sequential beats was determined at each pixel to yield the CVI image-displaying improved wall delineation. Systolic regional fractional area of radial sectors was calculated with active and temporarily suspended (AAI) pacing. All analyses were performed blinded to both patient and treatment. RESULTS: Pacing increased septal inward motion from -20.4 +/- 9.6% to -30.5 +/- 14.0%, whereas lateral wall motion occurred earlier with no net magnitude change. Both spatial and temporal dyssynchrony in the LV declined nearly 40% with LV or BiV pacing (p < or = 0.001), and this correlated with increasing ejection fraction (31% to 39%; p < 0.02; p < 0.004 for correlation with dyssynchrony). CONCLUSIONS: The new imaging and regional dyssynchrony analysis methods provide quantitative assessment of resynchronization analogous to that previously obtained only by tagged magnetic resonance imaging. This could provide a useful noninvasive method for both identifying candidates and following long-term therapy. 相似文献