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   3294151篇
  免费   266408篇
  国内免费   9394篇
耳鼻咽喉   46859篇
儿科学   104187篇
妇产科学   88737篇
基础医学   459809篇
口腔科学   95032篇
临床医学   301382篇
内科学   649494篇
皮肤病学   72392篇
神经病学   278617篇
特种医学   132545篇
外国民族医学   1111篇
外科学   502425篇
综合类   77340篇
现状与发展   3篇
一般理论   1332篇
预防医学   267510篇
眼科学   75798篇
药学   239910篇
  9篇
中国医学   5899篇
肿瘤学   169562篇
  2018年   34859篇
  2017年   27240篇
  2016年   31324篇
  2015年   34668篇
  2014年   48720篇
  2013年   74786篇
  2012年   96844篇
  2011年   103497篇
  2010年   62128篇
  2009年   59021篇
  2008年   97990篇
  2007年   104316篇
  2006年   105199篇
  2005年   102600篇
  2004年   98359篇
  2003年   95521篇
  2002年   92981篇
  2001年   150051篇
  2000年   155747篇
  1999年   130252篇
  1998年   39452篇
  1997年   35524篇
  1996年   35667篇
  1995年   35096篇
  1994年   32921篇
  1993年   30803篇
  1992年   105290篇
  1991年   101997篇
  1990年   98395篇
  1989年   94314篇
  1988年   87722篇
  1987年   86582篇
  1986年   81900篇
  1985年   78872篇
  1984年   60222篇
  1983年   51289篇
  1982年   31893篇
  1981年   28673篇
  1980年   27019篇
  1979年   55985篇
  1978年   40115篇
  1977年   33859篇
  1976年   31598篇
  1975年   33165篇
  1974年   40355篇
  1973年   38399篇
  1972年   35878篇
  1971年   33258篇
  1970年   31073篇
  1969年   28939篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
93.
94.
95.
96.
97.
98.
Nidogen 1 (NID1) is a glycoprotein found in basement membranes involved in cross-linking collagen IV and laminin. The role of NID in breast cancer has only been evaluated in a small number of studies and the findings of these studies have been inconsistent. Our previous work revealed that highly tumorigenic murine mammary tumor cells express high levels of Nid1 while weakly tumorigenic mammary tumor cells express low levels of Nid1. To investigate Nid1, two stable knockdown lines were created, and Nid1 knockdown was confirmed at both the mRNA and protein level. Nid1 knockdown significantly reduced cell proliferation and migration/invasion and these reductions in proliferation and migration/invasion could be rescued by conditioned media containing NID1 protein. The reduced migration/invasion observed in the Nid1 knockdown cells was not associated with significant alterations in the epithelial gene Cdh1 or the mesenchymal genes Snai1, Snai2, Twist1, Twist2, Zeb1 and Zeb2. Therefore, suppression of Nid1 expression reduces proliferation and migration/invasion in claudin-low murine mammary tumor cells.  相似文献   
99.
The current situation in which the humanities are disparaged affects all university disciplines, including nursing, in whose historical evolution the humanities have always been present in one form or another. Looking beyond this disrepute, this study proposes that nursing renew its attention to classical philosophy. Specifically, it invites a close reading of Xenophon's Anabasis and Plato's Meno, to get three related goals: to show how the use of ancient texts are very valuable tools for the philosophical initiation of nursing students and can help them reflect on their choice of nursing as a practical activity; to reflect on the problem of virtue and the nature of the good life; and to show how the interaction with ancient texts allows students to reflect on questions and issues of life, theirs and others, that are not open to investigation through a purely scientific method. Consequently, both Anabasis and Meno readings strengthen the intellectual relationship between philosophy and nursing, enabling the latter to delve deeper into the key questions of its own thought as a discipline.  相似文献   
100.
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