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   105364篇
  免费   9323篇
  国内免费   5750篇
耳鼻咽喉   780篇
儿科学   2279篇
妇产科学   1725篇
基础医学   12086篇
口腔科学   2249篇
临床医学   10497篇
内科学   18625篇
皮肤病学   1505篇
神经病学   7912篇
特种医学   2059篇
外国民族医学   31篇
外科学   8730篇
综合类   17732篇
现状与发展   13篇
预防医学   8914篇
眼科学   2887篇
药学   10011篇
  33篇
中国医学   4066篇
肿瘤学   8303篇
  2024年   335篇
  2023年   1425篇
  2022年   3286篇
  2021年   4158篇
  2020年   3767篇
  2019年   3307篇
  2018年   3220篇
  2017年   3630篇
  2016年   3892篇
  2015年   3841篇
  2014年   6934篇
  2013年   7349篇
  2012年   6786篇
  2011年   7511篇
  2010年   6231篇
  2009年   5800篇
  2008年   6089篇
  2007年   6054篇
  2006年   5396篇
  2005年   4711篇
  2004年   3968篇
  2003年   3429篇
  2002年   2831篇
  2001年   2434篇
  2000年   2053篇
  1999年   1752篇
  1998年   1535篇
  1997年   1296篇
  1996年   1158篇
  1995年   1054篇
  1994年   851篇
  1993年   680篇
  1992年   604篇
  1991年   459篇
  1990年   426篇
  1989年   318篇
  1988年   259篇
  1987年   204篇
  1986年   169篇
  1985年   260篇
  1984年   217篇
  1983年   129篇
  1982年   184篇
  1981年   102篇
  1980年   116篇
  1979年   68篇
  1978年   45篇
  1977年   33篇
  1976年   29篇
  1975年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
目的 探讨神经生长因子 (NGF)对小脑皮质神经细胞凋亡的影响 ,为临床治疗小脑变性疾病提供新的措施。方法 以原代培养的新生SD乳鼠小脑皮质细胞建立谷氨酸诱导的神经细胞凋亡模型。为观察NGF对受损细胞的保护作用 ,应用MTT法测定细胞的存活率和细胞代谢情况 ;利用光学显微镜技术观察细胞凋亡的形态学改变。结果 Glu (5 0 0 μmol/L)作用 5min可诱导小脑神经细胞凋亡。MTT法计数结果显示 ,NGF高剂量治疗组细胞存活率显著高于模型组 (P <0 0 1) ,光学显微镜观察发现受损细胞的形态学变化也得到明显改善。结论 外源性NGF能够减轻大鼠小脑皮质神经细胞凋亡。  相似文献   
112.
This study aimed to identify risk factors for type 2 diabetes (T2D) in Korea, a rapidly changing country. Data of 5,132 adults aged 20-85 were used from the 2001 Korean Health and Nutrition Examination Survey. Multiple logistic regression was carried out to identify risk factors for T2D. Three models were specified: (i) socioeconomic and demographic factors (model 1: age, gender, education, poverty income ratio, employment), (ii) behavioral risk factors and covariates (model 2: obesity, physical activity, smoking, alcohol drinking, dietary quality, family history of T2D, co-morbidity) and (iii) socioeconomic, demographic, and behavioral factors (model 3). The prevalence of T2D was 7.4%. Less education (OR 1.41, 95% CI 1.08-1.84), age (OR 2.19, 95% CI 1.56-3.08 in 40-59 yrs, OR 4.05, 95% CI 2.76-5.95 in 60 yrs + comparing to 20-39 yrs) and abdominal obesity (OR 2.24, 95% CI 1.79-2.82) were risk factors for T2D even after controlling for other factors simultaneously. There was a significant association of T2D with ever smoking (OR 1.34, 95% CI 1.06-1.67). The relationship of age with T2D was modified by gender in model 1 and the relationship of smoking with T2D was modified by obesity in model 2. Less educated, older, obese or ever smokers were more likely to have T2D. Gender mediated the relationship of age, and obesity mediated the relationship of smoking, with T2D. Intervention programs for T2D in Korea should take the interactions among risk factors into account.  相似文献   
113.
刘佳  吴建维 《中国卒中杂志》2007,15(10):1083-1087
目的 分析急性缺血性卒中患者(acute ischemic stroke,AIS)住院期间消化道出血(gastrointestinal
bleeding,GIB)的发生率、发生时间及危险因素。
方法 本研究纳入首都医科大学附属北京天坛医院急性卒中院内并发症队列(inhospital medical
complication after acute stroke,iMCAS)研究中AIS患者。收集患者临床信息,根据住院期间是否发生
GIB分为GIB组和无GIB组,采用多因素Logistic回归模型,分析AIS患者发生GIB相关危险因素。
结果 共纳入1129例AIS患者,平均年龄58.7±12.5岁,女性230例(20.4%)。47例住院期间发生GIB,
发生率为4.2%,卒中发作至GIB确诊时间为5(3~13)d。合并肝硬化(OR 10.06,95%CI 2.44~41.38)、
高入院NIHSS评分(OR 1.13,95%CI 1.08~1.19)、高白细胞计数(OR 1.25,95%CI 1.13~1.38)、住院时
间长(OR 1.05,95%CI 1.01~1.10)是AIS患者发生消化道出血的独立危险因素。
结论 本单中心研究数据提示合并肝硬化、高入院NI HSS评分、高白细胞计数、住院时间长是AI S患
者住院期间发生GIB的独立危险因素。  相似文献   
114.
Objects We evaluated whether the presence of lacunar skull deformity (LSD) with myelomeningocele is a predictive factor for subsequent hydrocephalus development. Materials and methods We reviewed the clinical and radiological records of 18 infants with myelomeningocele, divided the patients into groups with (group A, n=9) and without (group B, n=9) ventriculomegaly at birth and assessed whether the presence of LSD was predictive of the necessity for ventriculoperitoneal shunt (VPS) placement. Results LSD was present in five group A patients. All nine group A patients underwent VPS placement. Among the group B patients, five had LSD; they underwent VPS placement. A significantly higher proportion of those with ventricle enlargement or LSD at birth required VPS placement (p=0.0001). Conclusion Adding to the ventriculomegaly at birth, the presence of LSD alerts to the necessity to monitor these infants closely to determine the necessity for VPS placement.  相似文献   
115.
Recurrent focal glomerulosclerosis (FSGS) in renal allografts has remained a frustrating and enigmatic disease. Recent studies on gene mutations encoding podocin and other components of the slit-diaphragm in patients with native kidney nephrotic syndrome have underscored the heterogenecity of the idiopathic form of FSGS. While familial FSGS rarely recurs following transplantation, the sporadic variety of FSGS is associated with a 30% recurrence rate. The patients with the sporadic variety of FSGS who have homozygous or complex heterozygous podocin mutations have a low recurrence rate. In the other patients with sporadic FSGS, a more complex and likely multifactorial etiology accounts for the recurrence of FSGS. The role of CD80 expression on podocytes is intriguing but requires confirmation in kidney biopsies of patients with recurrent FSGS. Recent findings on podocin genomics, the permeability factor and CD80 expression may ultimately lead to a better understanding of recurrent FSGS as well as a more effective approach to its prevention and treatment.  相似文献   
116.
目的 探讨转化生长因子β(TGF-β)对人的颈椎关节突关节透明软骨细胞基质金属蛋白酶13(MMP-13)基因表达的作用,旨在阐明颈椎退行性变的相关发生机理。方法 应用逆转录方法PCR及实时荧光定量方法,检测不同浓度TGF-β作用传代培养人的透明软骨细胞MMP-13mRNA的含量。另外3种不同浓度分别与10ng/ml IL-1β组成联合作用组,共计6个实验组及1个正常对照组。结果 正常对照组中透明软骨细胞仅见MMP-13mRNA扩增产物,实验组TGF-β1、10和100ng/ml作用12h后,MMP-13mRNA表达逐渐增强;而联合作用组中,随着TGF-β1浓度的升高,MMP-13mRNA表达逐渐降低,并且各组之间存在明显的差异(P〈0.05)。结论 TGF-β可按剂量依赖方式调节颈椎关节突关节软骨细胞MMP-13mRNA的表达。  相似文献   
117.
Traditional treatments of spectacle magnification for distant objects consider only stigmatic spectacle lenses and they compare the retinal image size in a refractively fully compensated eye with the image size in the uncompensated eye. Spectacle magnification is expressed as a product of two factors, the power and shape factors of the lens. The power factor depends on the position of the entrance pupil of the eye. For an eye with an astigmatic cornea, however, the position of the entrance pupil is not well defined. Thus, the traditional approach to spectacle magnification does not generalize properly to allow for astigmatism. Within the constraints of linear optics and subject to the restriction that the eye's iris remains the aperture stop, this paper provides a complete, unified and exact treatment for optical instruments in general. It compares retinal image size in a generalized sense (including image shape and orientation) for any instrument in front of an eye with that of the eye alone irrespective of whether the instrument compensates or not. The approach does not make use of the concept of the entrance pupil at all and it allows for astigmatism and for non-alignment of refracting elements in the instrument and in the eye. The concept of spectacle magnification generalizes to the concept of instrument size magnification. Instrument size magnification can be expressed as the product of two matrix factors one of which can be interpreted as a power factor (as back-vertex power) and the other factor for which the name dilation factor is more appropriate in general. The general treatment is then applied to a number of special cases including afocal instruments, spectacle lenses (including obliquely crossing thick bitoric lenses), contact lenses, stigmatic systems and stigmatic eyes. In the case of spectacle lenses, the dilation factor reduces to the usual shape factor.  相似文献   
118.
A general expression is derived for the proximity factor in near image size magnification for an arbitrary instrument in front of an arbitrary eye. The proximity factor is a 2 x 2 matrix. The instrument and eye may be astigmatic and have decentred elements. The image on the retina may be blurred or not. The analysis is exact within the limitations of linear optics. The general results are specialized for the case of a stigmatic instrument and a stigmatic eye. The results are applied to the case of a thick, possibly bitoric, spectacle lens. The Appendix treats two numerical examples.  相似文献   
119.
Pathogenesis of diabetic retinopathy and the renin-angiotensin system.   总被引:4,自引:0,他引:4  
Despite the beneficial effects of good glycaemic control, loss of vision because of diabetic retinopathy (DR) still occurs. Recent studies have suggested that hypertension is a risk factor for the development and progression of DR and that blood pressure reduction can delay the progression of retinopathy. The renin-angiotensin system is activated by chronic hyperglycaemia, and the vitreous fluid level of angiotensin II (AII) is elevated in patients with proliferative diabetic retinopathy and diabetic macular oedema. AII increases vascular permeability and promotes neovascularization. It has been suggested that an autocrine-paracrine relationship may exist between AII and vascular endothelial growth factor in the ocular tissues. Accordingly, angiotensin-converting enzyme inhibitors or AII Type 1 (AT1) receptor blockers may be useful therapeutic agents for preventing the progression of DR.  相似文献   
120.
陈勇  崔大祥  孙凯  杨雁灵  戴辉 《医学争鸣》2003,24(8):703-705
目的:克隆sFGFRl(soluble fibroblast growth factors receptor-1)基因,并在RTS(rapid translation system)系统中高效表达相应蛋白.方法:培养Swiss rat 3T3 fibroblast细胞株,提取总RNA,用RT—PCR方法获取鼠sFGFR1 cDNA片段,酶切后克隆到pIVEX2.3d载体并进行序列分析;采用Roche RTS ProteinMaster500系统,高效表达sFGFR1蛋白并用Western Blot鉴定表达的蛋白.结果:克隆了sFGFR1基因,测序证实序列正确;Western Blot证实sFGFR1蛋白在RTS系统中高效表达.结论:克隆了sFGFR1基因并在RTS系统获得高效表达.  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