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   33004篇
  免费   2413篇
  国内免费   55篇
耳鼻咽喉   304篇
儿科学   1182篇
妇产科学   980篇
基础医学   4278篇
口腔科学   430篇
临床医学   4339篇
内科学   5908篇
皮肤病学   472篇
神经病学   3540篇
特种医学   596篇
外国民族医学   4篇
外科学   2969篇
综合类   327篇
一般理论   45篇
预防医学   4583篇
眼科学   504篇
药学   2207篇
中国医学   23篇
肿瘤学   2781篇
  2024年   32篇
  2023年   263篇
  2022年   433篇
  2021年   1120篇
  2020年   679篇
  2019年   1035篇
  2018年   1157篇
  2017年   832篇
  2016年   979篇
  2015年   1006篇
  2014年   1329篇
  2013年   1871篇
  2012年   2737篇
  2011年   2953篇
  2010年   1547篇
  2009年   1297篇
  2008年   2381篇
  2007年   2378篇
  2006年   2173篇
  2005年   2044篇
  2004年   1825篇
  2003年   1577篇
  2002年   1595篇
  2001年   210篇
  2000年   170篇
  1999年   204篇
  1998年   307篇
  1997年   239篇
  1996年   168篇
  1995年   178篇
  1994年   134篇
  1993年   119篇
  1992年   70篇
  1991年   47篇
  1990年   48篇
  1989年   40篇
  1988年   39篇
  1987年   37篇
  1986年   35篇
  1985年   19篇
  1984年   19篇
  1983年   29篇
  1982年   27篇
  1981年   18篇
  1980年   13篇
  1979年   9篇
  1978年   5篇
  1977年   4篇
  1973年   5篇
  1942年   4篇
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
81.
82.
Objective. To synthesize information about nurse migration in and out of Canada and analyze its role as a policy lever to address the Canadian nursing shortage.
Principal Findings. Canada is both a source and a destination country for international nurse migration with an estimated net loss of nurses. The United States is the major beneficiary of Canadian nurse emigration resulting from the reduction of full-time jobs for nurses in Canada due to health system reforms. Canada faces a significant projected shortage of nurses that is too large to be ameliorated by ethical international nurse recruitment and immigration.
Conclusions. The current and projected shortage of nurses in Canada is a product of health care cost containment policies that failed to take into account long-term consequences for nurse workforce adequacy. An aging nurse workforce, exacerbated by layoffs of younger nurses with less seniority, and increasing demand for nurses contribute to a projection of nurse shortage that is too great to be solved ethically through international nurse recruitment. National policies to increase domestic nurse production and retention are recommended in addition to international collaboration among developed countries to move toward greater national nurse workforce self sufficiency.  相似文献   
83.
84.
We describe the pattern and progression of atrophy delineated using fluid registration of serial magnetic resonance imaging scans in a case of multiple system atrophy (MSA). The in vivo findings were consistent with those found at postmortem, including significant supratentorial atrophy concurrent with an unusual degree of cognitive impairment for MSA.  相似文献   
85.
Cognitive models of depression propose that negative schemas contribute to depressive symptoms. Early experiences, particularly parenting, have been proposed to influence cognitive schemas and have also been shown to correlate with depression. This study explores the concurrent relationship between retrospective reports of parenting, Early Maladaptive Schemas (EMSs) described by J. E. Young (1994), and symptoms of depression in a sample of undergraduate students (N = 194). The EMSs of defectiveness/shame, insufficient self-control, vulnerability, and incompetence/inferiority were associated with perceptions of parenting and depressive symptomatology. There was evidence that these four EMSs partially mediate the relationship between parental perceptions and depressive symptomatology. Results are discussed in relation to previous findings, theory, and the measurement of EMSs.  相似文献   
86.
87.
A multiplex polymerase chain reaction (PCR) procedure was adapted for the rapid and efficient evaluation of deletions of the hypoxanthine guanine phosphoribosyltransferase (hprt) gene in human T-lymphocytes. The hprt clonal assay was used to isolate in vivo-arising hprt-deficient T-cells from six healthy males. Mutant frequencies ranged from 9-27 × 10?6. Simple crude cellular extracts from 223 mutants were analyzed for hprt gene deletion. Sixteen (7.2%) were found to be due to total gene deletion and 22 (9.9%) were due to partial gene deletion. The relatively high frequency of total gene deletions was caused by replicate isolates of a single mutational event as shown by single-strand conformation polymorphism (SSCP) analysis of rearranged T-cell receptor (TCR)-γ genes. Eighteen of the 22 partial hprt gene deletion mutants were determined to be of independent origin based on a unique hprt mutation or SSCP-TCR-γ pattern. One-half (9/18) of the partial deletion mutants involved all or part of exon 4 alone, suggesting that this region of the hprt gene is prone to deletion. The small deletions effecting exon 1 (1 mutant), exon 2 (2 mutants), and exon 4 (6 mutants) would not have been detected by conventional Southern blot analysis and may represent a new, previously unrecognized class of mutations. The ready isolation of such intragenic deletions will allow the characterization of breakpoint junctions and may provide insights into the important processes of DNA breakage and rejoining. © 1994 Wiley-Liss, Inc.  相似文献   
88.
Abstract: The purpose of this paper is to determine whether divorced parents exhibit a diminished capacity to parent in the period following divorce. Using 2 waves of data from a national survey of Canadian children, the current study prospectively follows 5,004 children living in 2–biological parent households at initial interview and compares changes in parenting practices between households that subsequently divorce and those that remain intact. Results show that divorce is unrelated to changes in parenting behavior, suggesting that there are more similarities than differences in parenting among recently divorced and continuously married parents.  相似文献   
89.
Differential screening-selected gene aberrative in neuroblastoma (DAN) is a member of a cystine knot protein family that includes Cerberus and Gremlin. First isolated in a screen to identify genes down-regulated in transformed rat fibroblasts, DAN has subsequently been cloned in Xenopus, mouse, and human. Overexpression of DAN suppresses the transformed phenotype and retards the cell's entry into S phase. Biochemical analyses have demonstrated DAN's ability to bind bone morphogenetic proteins and antagonize their signaling activity. In this study, chick DAN was cloned and sequenced, revealing a conserved cystine knot region as well as an N-glycosylation site. A riboprobe was designed from the 3' chick DAN coding sequence and used for analysis of DAN in the developing chick embryo by in situ hybridization. Chick DAN was expressed beginning at stage 10 in the developing somites and the medial otic epithelium. Expression in the neural layer of the eye became apparent at stage 14. By stage 17, expression had expanded to the base of the hindbrain. Limb bud labeling began at stage 20, whereas expression in the branchial arches appeared at stage 25. Chick DAN expression generally corresponded to that of mouse DAN expression as shown by comparative in situ hybridization. However, chick DAN was found in the otic epithelium and notochord, whereas mouse DAN was restricted to the overlying otic ectomesenchyme and was absent from the notochord. This observation suggests that DAN may play different roles in chick and mouse otic and notochord development.  相似文献   
90.
The literature addressing the mental health of homeless children is critically reviewed. Higher rates of behavioral, emotional, and cognitive problems have been reported for this population, but research results are qualified by significant methodological problems. Minimal attention has been given to the development and evaluation of specific intervention and prevention strategies. Recommendations are made for conducting research that will overcome previous methodological problems and focus more directly on identifying risk and protective mechanisms within the population of children exposed to homelessness.  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