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   3458964篇
  免费   282438篇
  国内免费   13948篇
耳鼻咽喉   48337篇
儿科学   110896篇
妇产科学   90607篇
基础医学   547168篇
口腔科学   93465篇
临床医学   306651篇
内科学   612503篇
皮肤病学   91374篇
神经病学   293091篇
特种医学   136788篇
外国民族医学   391篇
外科学   540042篇
综合类   102647篇
现状与发展   23篇
一般理论   2207篇
预防医学   288336篇
眼科学   79167篇
药学   239550篇
  23篇
中国医学   9794篇
肿瘤学   162290篇
  2021年   55063篇
  2020年   35131篇
  2019年   58187篇
  2018年   71395篇
  2017年   54336篇
  2016年   59974篇
  2015年   74240篇
  2014年   108550篇
  2013年   173897篇
  2012年   90475篇
  2011年   90666篇
  2010年   116581篇
  2009年   121180篇
  2008年   78778篇
  2007年   82264篇
  2006年   93061篇
  2005年   88970篇
  2004年   90681篇
  2003年   82020篇
  2002年   72418篇
  2001年   104502篇
  2000年   97236篇
  1999年   97465篇
  1998年   65347篇
  1997年   63025篇
  1996年   60990篇
  1995年   56413篇
  1994年   50702篇
  1993年   47174篇
  1992年   69644篇
  1991年   66867篇
  1990年   64254篇
  1989年   63402篇
  1988年   59377篇
  1987年   57814篇
  1986年   55157篇
  1985年   55119篇
  1984年   49710篇
  1983年   45749篇
  1982年   42195篇
  1981年   39676篇
  1980年   37379篇
  1979年   41828篇
  1978年   36475篇
  1977年   33435篇
  1976年   30787篇
  1975年   30037篇
  1974年   31260篇
  1973年   30064篇
  1972年   28340篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
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   
102.
103.
104.
105.
106.
107.
108.
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   
109.
110.
Abstract

Supporting patients in making informed healthcare decisions is a cornerstone of ethical medical practice. Surgeons frequently draw for and show images to patients when consenting them for operations but the value of this practice in informed decision-making is unclear. An audit was conducted in a General Surgery Department. 244 patients completed questionnaires on the value of visual materials when giving consent for surgery. The complexity of the operations was classified into “simple”, “moderate” or “complex”. 100% of patients felt they had given informed consent to surgery. 62% of patients received at least one form of visual material during the consenting process. All patients who received a drawing, and 99% of those provided with other images, valued these resources. Visual materials were considered more useful to patients when giving consent for moderate or complex operations than simple ones. Approximately one third of patients who did not receive visual materials would have appreciated these when making an informed decision. This research highlights the value of surgeons drawing for, and providing other visual resources to, their patients as part of the consent process. There is a role for further research and training materials in drawing skills for surgeons.  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