首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   9275篇
  免费   818篇
  国内免费   80篇
耳鼻咽喉   156篇
儿科学   239篇
妇产科学   285篇
基础医学   1153篇
口腔科学   135篇
临床医学   1043篇
内科学   2143篇
皮肤病学   184篇
神经病学   869篇
特种医学   232篇
外科学   1257篇
综合类   258篇
一般理论   6篇
预防医学   974篇
眼科学   283篇
药学   584篇
中国医学   8篇
肿瘤学   364篇
  2023年   40篇
  2021年   133篇
  2020年   68篇
  2019年   148篇
  2018年   158篇
  2017年   127篇
  2016年   129篇
  2015年   139篇
  2014年   214篇
  2013年   392篇
  2012年   454篇
  2011年   561篇
  2010年   298篇
  2009年   308篇
  2008年   509篇
  2007年   538篇
  2006年   523篇
  2005年   585篇
  2004年   564篇
  2003年   501篇
  2002年   499篇
  2001年   208篇
  2000年   158篇
  1999年   180篇
  1998年   134篇
  1997年   127篇
  1996年   113篇
  1995年   79篇
  1994年   108篇
  1993年   87篇
  1992年   143篇
  1991年   92篇
  1990年   103篇
  1989年   96篇
  1988年   90篇
  1987年   68篇
  1986年   86篇
  1985年   102篇
  1984年   89篇
  1983年   80篇
  1982年   84篇
  1981年   69篇
  1980年   88篇
  1979年   62篇
  1978年   64篇
  1977年   39篇
  1976年   49篇
  1975年   35篇
  1974年   46篇
  1973年   33篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
There is increasing evidence that the assessment of eosinophilic airway inflammation using induced sputum and measurement of airway hyperresponsiveness provides additional, clinically important information concerning asthma control. The aim of this study was to directly compare the effects of different treatments on these markers in patients with asthma and persistent symptoms, despite the use of low-dose inhaled corticosteroids. A double-blind four-way crossover study was performed, which compared a 1-month treatment with budesonide 400 mug b.i.d., additional formoterol, additional montelukast and placebo in 49 patients with uncontrolled asthma despite budesonide 100 mug b.i.d., with each treatment separated by a 4-week washout period. The change in sputum eosinophil count with formoterol (2.4 to 3.8% change, 0.6-fold reduction, 95% confidence interval (CI) 0.5-0.9) differed significantly from placebo (2.8 to 2.5% change, 1.1-fold reduction, 95% CI 0.7-1.6) and high-dose budesonide (2.7 to 1.6% change, 1.6-fold reduction, 95% CI 1.2-2.2). The effects of montelukast did not differ from placebo. The changes in methacholine airway responsiveness were small and did not differ between treatments. High-dose budesonide had the broadest range of beneficial effects on other outcomes, including symptom scores, morning peak expiratory flow and forced expiratory volume in one second. In conclusion, treatment given in addition to low-dose inhaled corticosteroids results in modest benefits. Formoterol and high-dose budesonide have contrasting effects on eosinophilic airway inflammation.  相似文献   
2.
3.
Background: General anesthetics inhibit evoked release of classic neurotransmitters. However, their actions on neuropeptide release in the central nervous system have not been well characterized.

Methods: The effects of representative intravenous and volatile anesthetics were studied on the release of sulfated cholecystokinin 8 (CCK8s), a representative excitatory neuropeptide, from isolated rat cerebrocortical nerve terminals (synaptosomes). Basal, elevated KCl depolarization-evoked and veratridine-evoked release of CCK8s from synaptosomes purified from rat cerebral cortex was evaluated at 35[degrees]C in the absence or presence of extracellular Ca2+. CCK8s released into the incubation medium was determined by enzyme-linked immunoassay after filtration.

Results: Elevation of extracellular KCl concentration (to 15-30 mm) or veratridine (10-20 [mu]m) stimulated Ca2+-dependent CCK8s release. Basal, elevated KCl- or veratridine-evoked CCK8s release was not affected significantly by propofol (12.5-50 [mu]m), pentobarbital (50 and 100 [mu]m), thiopental (20 [mu]m), etomidate (20 [mu]m), ketamine (20 [mu]m), isoflurane (0.6-0.8 mm), or halothane (0.6-0.8 mm).  相似文献   

4.
Performance characteristics of pooled rabbit IgG polyclonal anti-C3d are compared with one mouse IgM and three mouse IgG monoclonal anti-C3d antibodies (MAs). IgG MA,s employed singly or in combination, failed to precipitate C3d; by contrast, IgM MA and polyclonal anti-C3d precipitated C3d. Measurements of polyclonal anti-C3d concentration by chemical means and by 125I-C3d radioimmunoassay (RIA) agreed closely. RIA values were 50% of chemical measurement values for three of the four MAs. Use of sucrose density gradient ultracentrifugation to assess MA C3d/anti-C3d molar combining ratios for soluble anti-C3d/C3d was not possible because fast-sedimenting multimeric C3d/anti-C3d complexes did not form. Dissociation and competitive binding studies indicate that (1) two MAs had substantially lower affinities than the other anti-C3d antibodies, and (2) polyclonal anti-C3d recognizes more C3d epitopes than are recognized by individual MAs. The results demonstrate antigenic complexity of C3d fragment and illustrate the difficulties of predicting individual MA performance based on prior experience with polyclonal antibodies.  相似文献   
5.
A method of uretero-intestinal implantation of the intact ureters in two stages, combined with total cystectomy at the second stage, has been described. When properly done it usually is followed by no permanent obstruction to the upper urinary tract. In my series of 29 cases in which both stages of the ureteral transplantation have been completed, there were only 3 patients who died as the specific result of the uretero-intestinal anastomosis. The causes in 2 of these cases have been determined and subsequently eliminated by improvement in the surgical technique. In 4 other elderly patients with advanced carcinoma there were 2 deaths from coronary occlusion, 1 from pulmonary embolus, and 1 from volvulus. Radical surgery no.w is limited to patients who are good surgical risks, and in whom there is a reasonable chance of cure. To be suitable for radical cure by total cystectomy, metastases must be absent, and the tumor must be completely confined to the bladder wall and freely movable. This latter condition is best determined pre-operatively by recto-abdominal palpation under anaesthesia. The opposition to total cystectomy for cancer of the bladder which is otherwise incurable has been based on two principal considerations: (1) The results of the rerouting of the urinary stream have been too uncertain, and (2) a surgical procedure which contemplates two laparotomies has seemed too formidable. These objections should be largely eliminated by the results obtained in this series of 29 cases. Certain authors have also objected to cystectomy because the incidence of radical cures of the cancer has not been impressive. I believe the principal reason for this is that ureteral transplantation previously has been so hazardous that this operation and cystectomy usually have been postponed until the cancer has become advanced and the patient's condition desperate. When this stage is reached the opportunity for obtaining a radical cure has been missed. The restriction of total cystectomy to cases without metastases in which the primary tumor is completely confined to the bladder wall and freely movable should increase the incidence of radical cures.  相似文献   
6.
OBJECTIVE: To assess the impact of activity restriction (AR) on the incidence of preterm birth in women treated for preterm labor testing negative for fetal fibronectin (fFN). STUDY DESIGN: Women who were diagnosed with preterm labor and tocolyzed with magnesium sulfate were concurrently screened with fFN for the purpose of subsequent management. Included were consenting patients with negative fFN, gestational age 23 0/7-33 6/7 weeks, cervical dilation < or =3 cm, and minimal vaginal bleeding. Patients were randomized to AR or no AR. Primary study outcome was incidence of preterm delivery and interval from randomization to delivery. RESULTS: A total of 73 women with negative fFN were randomized (36 with AR, 37 without AR). The overall preterm birth rate was 40%, with 44.4% of patients with AR and 35.1% of patients without AR delivering preterm, p=0.478. CONCLUSION: Maternal AR did not impact pregnancy outcome. The incidence of preterm birth in symptomatic women testing fFN negative was higher than previously reported.  相似文献   
7.
BACKGROUND: The reconstruction of small defects of the alar groove can be a unique challenge owing to the importance of maintaining its concave structure. OBJECTIVE: To present a report of a patient with a small alar groove defect that was repaired using a combination of partial primary closure and second-intention healing. METHODS: A 73-year-old female was referred for the treatment of a basal cell carcinoma of the right nasal ala and underwent Mohs micrographic surgery with clearance of the lesion. The final defect, less than 1 cm, extended to the subcutaneous fat. Two absorbable subcutaneous sutures were placed in the defect, and the wound was then allowed to heal by second intention. RESULTS. This closure yielded a good cosmetic result, with preservation of the alar groove. CONCLUSION: A combination of primary closure and second-intention healing is a time-efficient, low-risk option for nonperforating, small alar groove defects.  相似文献   
8.
Metabolism is one of the major determinants for age-related changes in susceptibility to chemicals. Aldehydes are highly reactive molecules present in the environment that also can be produced during biotransformation of xenobiotics and endogenous metabolism. Although the lung is a major target for aldehyde toxicity, early development of aldehyde dehydrogenases (ALDHs) in lung has been poorly studied. The expression of ALDH in liver and lung across ages (postnatal day 1, 8, 22, and 60) was investigated in Wistar-Han rats. In adult, the majority of hepatic ALDH activity was found in mitochondria, while cytosolic ALDH activity was the highest contributor in lung. Total aldehyde oxidation capability in liver increases with age, but stays constant in lung. These overall developmental profiles of ALDH expression in a tissue appear to be determined by the different composition of ALDH isoforms within the tissue and their independent temporal and tissue-specific development. ALDH2 showed the most notable tissue-specific development. Hepatic ALDH2 was increased with age, while the pulmonary form did not. ALDH1 was at its maximum value at postnatal day 1 (PND1) and decreased thereafter both in liver and lung. ALDH3 increased with age in liver and lung, although ALDH3A1 was only detectible in lung. Collectively, the present study indicates that, in the case of aldehyde exposure, the in vivo responses would be tissue and age dependent.  相似文献   
9.
As a part of our ongoing study on Alzheimer's disease (AD) in elderly African Americans, we obtained clinical assessment and apolipoprotein E (ApoE) genotype data on 288 individuals (including 60 with AD). The ApoE σ4 allele frequency was significantly increased in AD patients compared with controls. The age-adjusted odds ratio (OR) for AD in σ4 homozygotes was 4.83 (95% confidence interval [CI], 1.71–13.64) compared with the σ3/σ3 genotype, but the OR for AD with the σ3/σ4 genotype did not reach significance (1.20; 95% CI, 0.58–2.45). These findings suggest that the association between ApoE σ4 and AD is weaker in African Americans than in whites.  相似文献   
10.
There is little agreement about the methodology of clinical trials of antipsychotic drugs in patients with negative symptoms. A literature review revealed wide variation in experimental design, rating scales and study duration. This reflects differing views as to the definition and response to treatment of negative symptoms. Some degree of standardization would improve comparability of studies and aid the development of new compounds. Patients included in such studies should have displayed negative symptoms for at least 6 months. Depressive symptoms, positive schizophrenic symptoms and extrapyramidal signs may all influence or be confused with negative symptoms and may respond to treatment; they should be at a low level at baseline and should be measured during the study period. Studies should last at least 8 weeks. Several scales are available for measuring negative symptoms and are reviewed; a global impression score should be used additionally.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号