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   8266篇
  免费   658篇
  国内免费   607篇
  9531篇
  2024年   16篇
  2023年   105篇
  2022年   266篇
  2021年   435篇
  2020年   310篇
  2019年   347篇
  2018年   370篇
  2017年   251篇
  2016年   357篇
  2015年   503篇
  2014年   573篇
  2013年   600篇
  2012年   760篇
  2011年   634篇
  2010年   384篇
  2009年   369篇
  2008年   408篇
  2007年   378篇
  2006年   349篇
  2005年   276篇
  2004年   239篇
  2003年   207篇
  2002年   175篇
  2001年   142篇
  2000年   114篇
  1999年   133篇
  1998年   79篇
  1997年   89篇
  1996年   80篇
  1995年   74篇
  1994年   85篇
  1993年   60篇
  1992年   73篇
  1991年   69篇
  1990年   60篇
  1989年   33篇
  1988年   36篇
  1987年   25篇
  1986年   19篇
  1985年   23篇
  1984年   9篇
  1983年   11篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1978年   1篇
排序方式: 共有9531条查询结果,搜索用时 15 毫秒
21.
腹腔注射链脲佐霉素(65mg/kg)诱发Wistar大鼠糖尿病。糖尿病发病4周后,向饲料中加尼群地平(30mg·kg-1·d-1)。结果表明,糖尿病4周时大鼠心室舒张功能首先受损,8周后心室舒张和收缩功能均明显受累。尼群地平处理对糖尿病大鼠的心肌收缩性有一定的改善作用。提示尼群地平对大鼠糖尿病性心肌病有一定有益作用。  相似文献   
22.
报道了缢蛏碱性磷酸酶(简称ALP)经不同浓度盐酸胍处理时酶的分子构象所发生的变化以及酶变化和失活的动力学过程。在胍中酶荧光发射峰强度下降,紫外差光谱在246nm和285nm处出现2个负峰,CD谱中酶的α螺旋度下降,且随浓度增大,变化程度也加大。动力学研究表明,酶在0.5mol/L、1.0mol/L、2.0mol/L3.0mol/L、4.0mol/L盐酸胍中的变性速度常数分别为3.21×10~(-4)s~(-1)、6.38×10~(-4)s~(-1)、2.17×10~(-3)s~(-1)、2.33×10~(-3)s~9-1)、5.17×10~(-3)s~(-1);而酶在相应盐酸胍中的失活速度常数分别为2.33×10~(-4)s~(-1)、3.57×10~(-4)s~(-1)、5.86×10~(-4)s~(-1)、1.14×10~(-3)s~(-1)、3.45×10~(-3)s~(-1);表现为失活与构象伸展变化基本平行。  相似文献   
23.
The localization of neuropeptide Y (NPY) and atrial natriuretic peptide (ANP) in the endothelial cells of human umbilical blood vessels was studied using the pre-embedding peroxidase-antiperoxidase (PAP) technique for electron microscopy and avidin-biotin-complex (ABC) immunostaining for endothelial cells cultured from umbilical vein. Subpopulations of NPY- and ANP-immunoreactive endothelial cells were present in term umbilical vein and artery. The umbilical vein contained more positive cells than the artery. The percentage of NPY- and ANP-immunoreactive umbilical vein cells in culture was 32% and 44%, respectively, out of a total of 3013 cells examined. The possibility that these potent vasoactive substances located in the endothelial cells of the non-innervated umbilical vessels are involved in the local regulation of blood flow is discussed.  相似文献   
24.
25.
We have investigated the relationship between hydrolysis of phosphatidylcholine (PC) and activation of the Raf-1 protein kinase in Ras-mediated transduction of mitogenic signals. As previously reported, cotransfection of a PC-specific phospholipase C (PC-PLC) expression plasmid bypassed the block to cell proliferation resulting from expression of the dominant inhibitory mutant Ras N-17. In contrast, PC-PLC failed to bypass the inhibitory effect of dominant negative Raf mutants, suggesting that PC-PLC functions downstream of Ras but upstream of Raf. Consistent with this hypothesis, treatment of quiescent cells with exogenous PC-PLC induced Raf activation, even when normal Ras function was blocked by Ras N-17 expression. Further, activation of Raf in response to mitogenic growth factors was blocked by inhibition of endogenous PC-PLC. Taken together, these results indicate that hydrolysis of PC mediates Raf activation in response to mitogenic growth factors.  相似文献   
26.
Now is the time to refocus efforts in urban research and design. A changing climate and extreme weather events are presenting unique challenges to urban systems around the world. These challenges illuminate the social barriers that accompany disruptive events such as resource inequities and injustices. In this perspective, we provide three research priorities for just and sustainable urban systems that help to address these matters. The three research priorities are: (1) social equity and justice, (2) circularity, and (3) digital twins. Conceptual context and future research directions are provided for each. For social equity and justice, the future directions are mandatory equity analysis and inclusionary practices, understanding and reconciling historical injustices, and intentional integration with diverse community stakeholders. For circularity applications, they are better metrics for integration, more robust evaluation frameworks, and dynamic modeling at multiple spatial and temporal scales. Future directions for digital twins include developing principles to reduce complexity, integrating model and system components, and reducing barriers to data access. These research priorities are core to meeting several of the United Nations Sustainable Development Goals (i.e., 1—No Poverty, 8—Decent Work and Economic Growth, 10—Reduced Inequalities, and 11—Sustainable Cities and Communities). Useful social and technical matters are discussed throughout, where we highlight the importance of prioritizing localized research efforts, provide guidance for community-engaged research and co-development practices, and explain how these priorities interact to align with the evolving field of industrial ecology.  相似文献   
27.
汉族ABO血型的皮纹特征分析   总被引:2,自引:1,他引:1  
作者对芜湖地区382例(男220人;女162人)汉族ABO血型的皮纹特征进行了分析,其中O型130人,A型113人,B型101人,AB型38人。分析比较了指纹类型、指纹组合格局、指嵴纹计数、掌嵴纹计数、atd角,掌部真实花纹,掌褶纹和拇趾球纹等项参数,结果表明,ABO各血型的皮纹参数间有若干统计学差异。  相似文献   
28.
This work firstly reported a new polycaprolactone based material functionalized with guanidinium ionic liquid (PCL-GIL) as the stationary phase with high resolution performance for capillary gas chromatography (GC). It is composed of polycaprolactone (PCL) and guanidinium ionic liquid (GIL) with amphiphilic conformation. The PCL-GIL capillary column coated by static method exhibited high column efficiency of 3942 plates/m and moderate polarity. As a result, the PCL-GIL column exhibited high-resolution capability. For a mixture of 27 analytes with a wide ranging polarity and outperformed the PCL-2OH and HP-35 columns, showing its advantageous separation capability for analytes of diverse types. Moreover, the PCL-GIL column showed high resolving capability for various positional isomers and cis-/trans-isomers, including alkylbenzenes, chlorobenzenes, naphthalenes, bromonitrobenzenes, chloronitrobenzenes, benzaldehydes, phenols, alcohols, respectively. In a word, PCL derivatized by GIL units as a new type of stationary phase has a promising future in GC separations.  相似文献   
29.
30.
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