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   1695277篇
  免费   123718篇
  国内免费   3781篇
耳鼻咽喉   21732篇
儿科学   55638篇
妇产科学   46168篇
基础医学   241224篇
口腔科学   48741篇
临床医学   151311篇
内科学   333500篇
皮肤病学   38655篇
神经病学   131145篇
特种医学   63873篇
外国民族医学   242篇
外科学   257231篇
综合类   38946篇
现状与发展   4篇
一般理论   531篇
预防医学   124226篇
眼科学   40212篇
药学   123608篇
  7篇
中国医学   4475篇
肿瘤学   101307篇
  2021年   12785篇
  2019年   13523篇
  2018年   19950篇
  2017年   15213篇
  2016年   16615篇
  2015年   18965篇
  2014年   26212篇
  2013年   37945篇
  2012年   52729篇
  2011年   55418篇
  2010年   32770篇
  2009年   30692篇
  2008年   51518篇
  2007年   54797篇
  2006年   55260篇
  2005年   52540篇
  2004年   50741篇
  2003年   48150篇
  2002年   46371篇
  2001年   91783篇
  2000年   93608篇
  1999年   76963篇
  1998年   19718篇
  1997年   17267篇
  1996年   17391篇
  1995年   16742篇
  1994年   15290篇
  1993年   14073篇
  1992年   57381篇
  1991年   55272篇
  1990年   52971篇
  1989年   50748篇
  1988年   46134篇
  1987年   44940篇
  1986年   42227篇
  1985年   39987篇
  1984年   29349篇
  1983年   24908篇
  1982年   13899篇
  1979年   25535篇
  1978年   17575篇
  1977年   14910篇
  1976年   13878篇
  1975年   14564篇
  1974年   17631篇
  1973年   16944篇
  1972年   15676篇
  1971年   14456篇
  1970年   13432篇
  1969年   12517篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
A lawsuit directed by parents at a day care program following an outbreak of infectious disease would most likely be based on the legal theory of negligence--the failure to exercise due care as required by circumstances. In the determination of liability for infectious diseases in child day care, the element of causation is most critical. Did the day care facility's actions or failure to act cause the harm? Another important question is whether an infectious disease can be occupational and under what circumstances. Although worker's compensation laws initially had no provisions for occupational disease, now all states recognize responsibility for them. Awareness of potential problems with legal liability and establishment of procedures to minimize risk are important for day care providers, public health officials, clinicians, and parents.  相似文献   
962.
963.
964.
Indirect evidence suggests that amphetamine (AMPH) releases dopamine (DA) from an extravesicular, cytoplasmic pool. Disruption of vesicular DA storage by reserpine has been hypothesized to increase the concentration of extravesicular DA available for release by AMPH, which is consistent with the observation that reserpine does not prevent but augments the behavioral response to AMPH. In order to more directly test this hypothesis, the in vivo microdialysis technique was used to concurrently examine the behavioral and striatal dopaminergic response to AMPH (1.25 or 2.5 mg/kg) 24 h following reserpine pretreatment (2.5 mg/kg). Reserpine decreased tissue levels of DA by approximately 90% and reduced baseline dialysate DA concentrations by approximately 80%. Reserpine augmented the behavioural effects of AMPH, particularly increasing the occurrence and intensity of stereotypies. In contrast, reserpine did not alter the amount or duration of AMPH-induced DA release. This observation confirms that DA release by AMPH does not depend on vesicular stores but is inconsistent with the hypothesis that augmentation or behaviour by reserpine results from increased striatal DA release.  相似文献   
965.
Although England/Wales, Italy, and the United States share a common policy of deinstitutionalization, their mental health systems differ considerably. Each country's civil commitment standards define patient eligibility criteria along one of two primary dimensions--need for treatment or degree of dangerousness. These differential selection criteria result in mental health systems serving different subgroups of the total population. The criteria in England/Wales target older women; in the United States, younger men; and in Italy, a group balanced in age and sex. Implications for the current debate on civil commitment policies are considered.  相似文献   
966.
967.
968.
969.
Site-directed mutagenesis of the vaccinia virus gene encoding a type I DNA topoisomerase implicates Tyr-274 as the active-site residue that forms a covalent adduct with DNA during cycles of DNA-strand breakage and reunion. Replacement of Tyr-274 by phenylalanine results in loss of the ability of the enzyme to relax negatively supercoiled DNA as well as to form the covalent DNA-protein intermediate. Substitution of phenylalanine for tyrosine at nine other sites in the protein has no apparent effect on enzyme activity. Amino acid sequence alignment reveals Tyr-274 to be homologous to Tyr-727 and Tyr-771, respectively, of the type I topoisomerases from Saccharomyces cerevisiae and Saccharomyces pombe; Tyr-727 and Tyr-771 have been shown to represent the active-site tyrosines of those enzymes. Sequence comparison of the active-site regions defines a motif Ser-Lys-Xaa-Xaa-Tyr common to the viral and cellular type I topoisomerases, including the human enzyme.  相似文献   
970.
S Bilancini  M Lucchi 《Phlébologie》1989,42(1):151-156
The subject of enlarged legs is vast and complex. Up to now there has been no organic classification of the clinical picture involved. The basic problem is that of the criterion on which to base the classification. Literature on this subject has opted for the pathogenic criterion because it seems to facilitate the formulation of a classification which is of use to the doctor. One possibility would be to divide the syndrome into vascular and non-vascular swollen legs. The first group could in turn be separated into macro-circulating and micro-circulatory. The micro-circulatory forms can be primitive or secondary. Amongst the secondary micro-circulatory forms, two other groups can be singled out: secondary forms with local cause and secondary forms caused by organic pathology. However, there are clinical forms which are on the periphery of these different groups and these forms are subject to discussion regarding nosographic localization.  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