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   24086篇
  免费   1810篇
  国内免费   81篇
耳鼻咽喉   394篇
儿科学   839篇
妇产科学   379篇
基础医学   2455篇
口腔科学   540篇
临床医学   2183篇
内科学   5269篇
皮肤病学   563篇
神经病学   1280篇
特种医学   1276篇
外国民族医学   1篇
外科学   4572篇
综合类   362篇
一般理论   15篇
预防医学   1165篇
眼科学   827篇
药学   2046篇
中国医学   39篇
肿瘤学   1772篇
  2023年   224篇
  2022年   405篇
  2021年   986篇
  2020年   475篇
  2019年   817篇
  2018年   947篇
  2017年   612篇
  2016年   648篇
  2015年   681篇
  2014年   1013篇
  2013年   1191篇
  2012年   1744篇
  2011年   1717篇
  2010年   878篇
  2009年   823篇
  2008年   1289篇
  2007年   1213篇
  2006年   1131篇
  2005年   988篇
  2004年   884篇
  2003年   757篇
  2002年   655篇
  2001年   596篇
  2000年   560篇
  1999年   494篇
  1998年   180篇
  1997年   174篇
  1996年   165篇
  1995年   163篇
  1994年   128篇
  1993年   111篇
  1992年   274篇
  1991年   289篇
  1990年   256篇
  1989年   221篇
  1988年   222篇
  1987年   238篇
  1986年   213篇
  1985年   191篇
  1984年   121篇
  1983年   132篇
  1982年   96篇
  1981年   84篇
  1980年   71篇
  1979年   131篇
  1978年   84篇
  1977年   76篇
  1975年   63篇
  1974年   65篇
  1973年   88篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Cystic fibrosis (CF) is the most common autosomal recessive disorder in Caucasian populations with an approximate frequency of one in 2,500 live births and a carrier frequency of one in 25. We studied 400 individuals seen at The Nebraska Regional Cystic Fibrosis Center that included 139 CF patients, 206 parents, and 55 unaffected siblings to determine the frequency of the ΔF508, R117H, G542X, S549R/N, G551D, R553X, R560T, and W1282X mutations. In addition, we determined haplotypes on each of these individual's chromosomes using four markers that included XV-2c, KM-19, pMP6d.9, and G2. Results from this study showed that the ΔF508 mutation was present in 70% of CF chromosomes. Of the 139 CF patients 74 (53%) were homozygous for the ΔF508 deletion, 47 (34%) were heterozygous for the ΔF508 deletion and an unknown mutation, and 18 (13%) carried two unknown mutations. Four additional-mutations were also found in our population and included G542X (6%), G551D (5%), R553X (4%), and R560T (1%). One patient was documented to be a compound heterozygote for G542X/G551D. A polymorphism, F508C, that has previously been reported in several families was also present in our study. The most common haplotype associated with the ΔF508 deletion in our CF patients was the E haplotype (CF Consortium B) while other mutations were associated with a variety of haplotypes. © 1993 Wiley-Liss, Inc.  相似文献   
992.
ObjectivesMesoporous fillers have been investigated for use in dental composites because of their potential for creating micromechanical filler/resin matrix interphase bonding. Such a micromechanical bonding could eliminate the need for the silane treatment of fillers for interfacial chemical bonding that is prone to hydrolysis in the oral environment. In the case of micromechanical bonding, dental polymer chains are threaded mechanically (like a “necklace”) through nanosized channels in the fillers.MethodsA combination of mesoporous silica, which was synthesized using the non-surfactant templating method, and nonporous spherical silica (500 nm) was used to prepare experimental dental composites. The porous silica used in this study contained interconnected pores and channels as opposed to porous fillers containing surface pores. The compressive strength, compressive modulus, flexural modulus, and flexural strength of these composites were evaluated.ResultsThe results showed that composites containing a combination of mesoporous and nonporous fillers have better mechanical properties than the composites having either of these fillers alone.SignificanceThe results showed that a combination of mesoporous and nonporous materials can be used to prepare stronger dental materials that may resist hydrolysis and wear.  相似文献   
993.
Patel  K. R. 《Lung》1990,168(1):210-218
β 2-agonists have been shown to induceβ 2-adrenoceptor down-regulation in vivo and in vitro. Whether this has any functional relevance remains unclear. Tulobuterol is a new syntheticβ 2-agonist with potent and prolonged bronchodilator activity when given by oral and inhaled routes. The effect of tulobuterol aerosol (400μg q.i.d.) and tulobuterol tablets (2 mg b.i.d.) was studied in patients with chronic asthma and reversible airways obstruction in two separate trials. Tulobuterol produced significant bronchodilatation after the first and final dose over a 6-h period and the effects were comparable. The bronchodilator activity of tulobuterol given by inhalation and oral routes was not attenuated after 6 months of continuous treatment. There was significant improvement in symptom score and lung function measurements. Side effects, predominantly tremors, were observed at the start of treatment with tablet formulation but the incidence and severity of tremors decreased after 6 months. The changes in BP and pulse rate were not clinically significant. These results confirm the potent bronchodilator activity of tulobuterol and the lack of tachyphylaxis after prolonged treatment.  相似文献   
994.
IntroductionErectile dysfunction is a serious complication of diabetes mellitus. Apart from the peripheral actions, central mechanisms are also responsible for penile erection.AimThis study aims to determine the contribution of angiotensin (ANG) II in the dysfunction of central N-methyl-D-aspartic acid (NMDA)- and nitric oxide (NO)-induced erectile responses in streptozotocin-induced type 1 diabetic (T1D) rats.MethodsThree weeks after streptozotocin injections, rats were randomly treated with the angiotensin-converting enzyme inhibitor-enalapril, or the ANG II type 1 receptor blocker, losartan, or the superoxide dismutase mimetic, tempol, or vehicle via chronic intracerebroventricular infusion by osmotic mini-pump for 2 weeks.Main Outcome MeasureCentral NMDA receptor stimulation or the administration of the NO donor, sodium nitroprusside (SNP)-induced penile erectile responses and concurrent behavioral responses were monitored in conscious rats.ResultsTwo weeks of enalapril, losartan, or tempol treatment significantly improved the erectile responses to central microinjection of both NMDA and SNP in the paraventricular nucleus (PVN) of conscious T1D rats (NMDA responses—T1D+enalapril: 1.7 ± 0.6, T1D+losartan: 2.0 ± 0.3, T1D+tempol: 2.0 ± 0.6 vs. T1D+vehicle: 0.6 ± 0.3 penile erections/rat in the first 20 minutes, P < 0.05; SNP responses—T1D+enalapril: 0.9 ± 0.3, T1D+losartan: 1.3 ± 0.3, T1D+tempol: 1.4 ± 0.4 vs. T1D+vehicle: 0.4 ± 0.2 penile erections/rat in the first 20 minutes, P < 0.05). Concurrent behavioral responses including yawning and stretching, induced by central NMDA and SNP microinjections, were also significantly increased in T1D rats after enalapril, losartan, or tempol treatments. Neuronal NO synthase expression within the PVN was also significantly increased, and superoxide production was reduced in T1D rats after these treatments.ConclusionsThese data strongly support the contention that enhanced ANG II mechanism/s within the PVN of T1D rats contributes to the dysfunction of central NMDA-induced erectile responses in T1D rats via stimulation of superoxide. Zheng H, Liu X, and Patel KP. Centrally mediated erectile dysfunction in rats with type 1 diabetes: Role of angiotensin II and superoxide. J Sex Med 2013;10:2165–2176.  相似文献   
995.
IntroductionErectile dysfunction (ED) is more common in men with type 2 diabetes mellitus (T2DM), obesity, and/or the metabolic syndrome (MetS).AimThe aim of this study is to investigate the associations among proxy measures of diabetic severity and the presence of MetS with ED in a nationally representative U.S. data sample.MethodsWe performed a cross‐sectional analysis of adult participants in the 2001–2004 National Health and Nutrition Examination Survey.Main Outcome MeasuresED was ascertained by self‐report. T2DM severity was defined by calculated measures of glycemic control and insulin resistance (IR). IR was estimated using fasting plasma insulin (FPI) levels and the homeostasis model assessment of IR (HOMA‐IR) definition. We classified glycemic control using hemoglobin‐A1c (HbA1c) and fasting plasma glucose (FPG) levels. MetS was defined by the American Heart Association and National Heart, Lung, and Blood Institute criteria. Logistic regression models, adjusted for sociodemographics, risk factors, and comorbidities, were fitted for each measure of T2DM severity, MetS, and the presence of ED.ResultsProxy measures of glycemic control and IR were associated with ED. Participants with FPG between 100–126 mg/dL (5.6–7 mmol/L) and ≥126 mg/dL (>7 mmol/L) had higher odds of ED, odds ratio (OR) 1.22 (confidence interval or CI, 0.83–1.80), and OR 2.68 (CI, 1.48–4.86), respectively. Participants with HbA1c 5.7–6.4% (38.8–46.4 mmol/mol) and ≥6.5% (47.5 mmol/mol) had higher odds of ED (OR 1.73 [CI, 1.08–2.76] and 3.70 [CI, 2.19–6.27], respectively). When FPI and HOMA‐IR were evaluated by tertiles, there was a graded relation among participants in the top tertile. In multivariable models, a strong association remained between HbA1c and ED (OR 3.19 [CI,1.13–9.01]). MetS was associated with >2.5‐fold increased odds of self reported ED (OR 2.55 [CI, 1.85–3.52]).ConclusionsPoor glycemic control, impaired insulin sensitivity, and the MetS are associated with a heightened risk of ED. Weinberg AE, Eisenberg M, Patel CJ, Chertow GM, and Leppert JT. Diabetes severity, metabolic syndrome, and the risk of erectile dysfunction. J Sex Med 2013;10:3102–3109.  相似文献   
996.
Objective: To determine whether inflammatory bowel disease (IBD) is associated with increased risk for adverse perinatal outcome.

Methods: A case–control study of 116 singleton pregnancies with IBD compared to 56?398 singleton controls delivered between 1986 and 2001.

Results: Patients with IBD were slightly older (32.8 vs. 30.6 years, p <?0.001), more likely to be Caucasian or Asian than Black or Latino (92% vs. 57%, p <?0.001) and have private health insurance (33% vs. 3%, p <?0.001). IBD was associated with an increased risk for labor induction (32% vs. 24%, p?=?0.002), chorioamnionitis (7% vs. 3%, p?=?0.04) and Cesarean section (32% vs. 22%, p?=?0.007), but there were no differences in neonatal outcomes. Subgroup analysis demonstrated an increased risk for low birth weight (LBW) in the ulcerative colitis group vs. the Crohn's disease group (19% vs. 0%, p?=?0.002). Patients with prior surgery for IBD had a lower incidence of LBW (0% vs. 12%, p?=?0.03). Flares during pregnancy were associated with an increased risk for preterm delivery (27% vs. 8%, p?=?0.02) and LBW (32% vs. 3%, p?=?0.003).

Conclusion: IBD was an independent risk factor for Cesarean section but there was no increase in adverse perinatal outcome. Crohn's disease, prior IBD surgery and quiescent disease were associated with a lower risk for LBW.  相似文献   
997.
The objective of this study was to identify risk factors for pancreatic fistula (PF) after stapled transection in distal pancreatectomy (DP). Patients undergoing DP using a stapler for transection between 2005 and 2009 were identified from a pancreatic resection database. Variables examined included patient and tumor characteristics, staple size, and the use of mesh reinforcement. Univariate and multivariate regression analyses were performed to identify risk factors for postoperative PF. One hundred forty-nine had stapled transection, and of these, 25 (17%) had mesh reinforcement. The overall morbidity and mortality rates were 28 per cent and less than 1 per cent; 34 (23%) were diabetic. The rate of clinically significant PF was 14 per cent. On univariate analysis, diabetes (P = 0.04), a firm pancreas (P = 0.03), use of mesh staple line reinforcement (P = 0.02), use of a 4.1-mm staple cartridge (P = 0.01), and blood loss greater than 100 mL (P = 0.01) were associated with higher pancreatic fistula rates. On multivariate analysis, only the presence of diabetes (OR, 4.17; 95% CI, 1.1-15.3; P = 0.03) and the use of a 4.1-mm cartridge (OR, 8.57; 95% CI, 1.2-60.2; P = 0.03) were independently associated with pancreatic fistula formation. Stapled pancreatic transection provides an acceptable PF rate after DP. Diabetes and staple size influence PF rates. In our experience, use of mesh staple line reinforcement did not reduce the incidence of PF after stapled transection.  相似文献   
998.
A new tray has been designed for use during procedures involving needles and other sharp objects. The tray includes a foam adhesive pad, marked into 10 sections, into which the sharp objects can be placed point first. After the procedure, the objects can be safely withdrawn by their handles and then discarded. The tray has been used in more than 250 procedures.  相似文献   
999.
Maintenance of independent living is the top health priority among patients with advanced chronic kidney disease (CKD). Mobility limitation is often the first sign of functional limitation leading to loss of independence. Regular assessments of physical capacity can help provide kidney health providers identify patients at risk of frailty and other adverse health‐related outcomes that contribute to the loss of functional independence. These physical capacities can be measured with commonly used self‐reported measures of physical function or by objective physical performance testing. The current review describes commonly used assessments of self‐reported physical function and physical performance. First, we describe the disablement process and how these assessments can be performed with commonly used quality of life instruments measuring self‐reported physical function or objective physical performance tests. Second, we identify the determinants and correlates of self‐reported physical function and physical performance and their contribution to the frailty phenotype. Third, we describe the association of physical capacities with clinical outcomes. We conclude with on possible approach to identifying and intervening on persons with CKD at high risk of functional decline.  相似文献   
1000.
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