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   13385篇
  免费   938篇
  国内免费   52篇
耳鼻咽喉   77篇
儿科学   398篇
妇产科学   297篇
基础医学   1872篇
口腔科学   405篇
临床医学   1113篇
内科学   2863篇
皮肤病学   530篇
神经病学   1800篇
特种医学   719篇
外国民族医学   2篇
外科学   1474篇
综合类   174篇
预防医学   983篇
眼科学   170篇
药学   767篇
中国医学   2篇
肿瘤学   729篇
  2023年   75篇
  2022年   99篇
  2021年   248篇
  2020年   195篇
  2019年   203篇
  2018年   229篇
  2017年   187篇
  2016年   267篇
  2015年   304篇
  2014年   377篇
  2013年   507篇
  2012年   896篇
  2011年   840篇
  2010年   527篇
  2009年   465篇
  2008年   839篇
  2007年   864篇
  2006年   806篇
  2005年   783篇
  2004年   710篇
  2003年   637篇
  2002年   630篇
  2001年   260篇
  2000年   208篇
  1999年   231篇
  1998年   158篇
  1997年   125篇
  1996年   86篇
  1995年   89篇
  1994年   59篇
  1993年   85篇
  1992年   175篇
  1991年   160篇
  1990年   146篇
  1989年   152篇
  1988年   157篇
  1987年   136篇
  1986年   122篇
  1985年   112篇
  1984年   111篇
  1983年   82篇
  1982年   59篇
  1981年   55篇
  1980年   57篇
  1979年   91篇
  1977年   69篇
  1974年   65篇
  1973年   72篇
  1971年   48篇
  1969年   56篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.

Objective

To determine whether differences in combination DTaP vaccine types at 2, 4 and 6?months of age were associated with mortality (all-cause or non-specific), within 30?days of vaccination.

Design

Observational nationwide cohort study.

Setting

Linked population data from the Australian Childhood Immunisation Register and National Death Index.

Participants

Australian infants administered a combination trivalent, quadrivalent or hexavalent DTaP vaccine (DTaP types) between January 1999 and December 2010 at 2, 4 and 6?months as part of the primary vaccination series. The study population included 2.9, 2.6, & 2.3?million children in the 2, 4 and 6?month vaccine cohorts, respectively.

Main outcome measures

Infants were evaluated for the primary outcome of all-cause mortality within 30?days. A secondary outcome was non-specific mortality (unknown cause of death) within 30?days of vaccination. Non-specific mortality was defined as underlying or other cause of death codes, R95 ‘Sudden infant death syndrome’, R96 ‘Other sudden death, cause unknown’, R98 ‘Unattended death’, R99 ‘Other ill-defined and unspecified cause of mortality’ or where no cause of death was recorded.

Results

The rate of 30?day all-cause mortality was low and declined from 127.4 to 59.3 deaths per 100,000 person-years between 2 and 6?month cohorts. When compared with trivalent DTaP vaccines, no elevated risk in all-cause or non-specific mortality was seen with any quadrivalent or hexavalent DTaP vaccines, for any cohort.

Conclusion

Use of routine DTaP combination vaccines with differing disease antigens administered during the first six months of life is not associated with infant mortality.  相似文献   
3.
1. Rhesus monkeys were equipped with a novel intracerebroventricular (i.c.v.) cannula system and trained to respond under operant schedules of food presentation or termination of stimuli associated with the delivery of shock (escape). 2. CRH decreased food-maintained behavior in a dose-related manner over the range of (0.3-10 micrograms/kg) but did not affect escape responding, demonstrating a selective effect on food-maintained responding. 3. This selective effect was related to the tendency for responding to stop after delivery of a food pellet when higher doses of CRH were given, consistent with the notion that a conditioned aversion to food was established in the presence of CRH. 4. This may suggest that in hyperaroused clinical states such as depression and anorexia nervosa, focus is shifted away from appetitive tasks as a result of increased levels of CRH.  相似文献   
4.
Many polycyclic aromatic hydrocarbons containing peripherallyfused cyclopenta rings are believed to be activated primarilyby epoxidation of the cyclopenta ring. The cyclopenta epoxidesof a series of four cyclopenta benzanthracene derivatives, benz[e]aceanthrylene-5,6-oxide,benz[j]ace-anthrylene-1,2-oxide, benz(l)anthrylene-1,2-oxideand benz[k]acephenaceanthrylene-4,5-oxide were synthesized fromtheir parent hydrocarbons by formation of the bromohydrin followedby dehydrobromination, and characterized by u.v. – vis,and 1H n.m.r. spectroscopy and mass spectrometry. The mutagenicityof these compounds was investigated in the Ames plate incorporationassay with Salmonella typhimurium strain TA98. All the oxideswere active without exogenous metabolic activation (170–320His+ revertants per nanomole) and also toxic above 0.5 µg/plate.Addition of S9 protein did not increase, and generally decreased,the mutagenicity of the oxides, while toxicity was largely unchanged.These results are consistent with the postulated role of cyclopentaoxides as major contributors to the mutagenicity of the parentcompounds in the Ames assay.  相似文献   
5.
6.
7.
8.
9.
Growth of malignant tumors is dependent on sufficient blood supply. Thus, inhibition of tumor angiogenesis is emerging as a promising target in the treatment of malignancies. Human angiostatin (hANG) is one of the most potent inhibitors of endothelial cell proliferation, angiogenesis, and tumor growth in vivo. However, its mechanisms operating in vivo are not well understood. METHODS: To obtain more information about functional changes in the angiogenic process, we established Morris hepatoma (MH3924A) cell lines expressing hANG (hANG-MH3924A). The effects of hANG expression on proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs) were measured in coculture experiments in vitro. To evaluate changes in tumor perfusion and blood volume, H2 15O and 68Ga-DOTA-albumin (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid) were used for PET studies in vivo. Additionally, immunohistologic quantification of vascularization, apoptosis, and proliferation as well as gene array analyses were performed. RESULTS: Our in vitro experiments demonstrate reduced proliferation and increased apoptosis in HUVECs when being cocultured with hANG-MH3924A. In support, tumor growth of hANG-MH3924A is diminished by 95% in vivo. However, tumor perfusion and blood volume are increased in hANG-MH3924A corresponding to an increased microvessel density. Furthermore, hANG-transfected tumors show changes in expression of genes related to apoptosis, stress, signal transduction, and metabolism. CONCLUSION: hANG expression leads to inhibition of tumor growth, increased apoptosis, and changes in the expression of multiple genes involved in stress reactions, signal transduction, and apoptosis, which indicates a multifactorial reaction of tumors. An enhanced microvessel density is seen as part of these reactions and is associated with increased perfusion as measured by PET.  相似文献   
10.
Purpose To evaluate prospectively our experience with transjugular intrahepatic portosystemic shunt (TIPS) using four different metallic stents. Methods Between November 1991 and April 1995, 57 patients (41 men and 16 women; age 35–72 years, mean 54 years) underwent the TIPS procedure. Techniques for portal vein localization before and during TIPS were fluoroscopy, computed tomography (CT) studies, wedged hepatic venography, arterial portography, and ultrasound. After predilation we deployed balloon-expandable (n=48) and self-expanding (n=45) metallic stents. Fifteen patients underwent variceal embolization. Initial follow-up angiograms (mean 6.9 months, range 3–24 months) were obtained in 39 of these patients. Results Fifty-three patients (93%) had successful TIPS placement. The mean decrease in portal pressure was 42.7%. Besides fluoroscopy, the most helpful techniques for portal vein localization were venography and CT. Residual stenosis (n=1) and late shortening (n=4) of Wallstents resulted in shunt dysfunction. The technical problems encountered with the Palmaz stent resulted from its lack of flexibility. We combined balloon-expandable and self-expanding stents in 12 patients. The 30-day and late follow-up (mean 11.9 months) percutaneous reintervention rates were 11.3% and 64.2%, respectively. There were no clinically significant complications related to the TIPS insertions. Conclusion An ideal stent does not exist for TIPS, and the authors recommend combining a Palmaz stent with a flexible self-expanding stent.  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