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   2676篇
  免费   119篇
  国内免费   129篇
系统科学   171篇
丛书文集   62篇
教育与普及   39篇
理论与方法论   12篇
现状及发展   13篇
研究方法   9篇
综合类   2618篇
  2024年   14篇
  2023年   29篇
  2022年   42篇
  2021年   66篇
  2020年   36篇
  2019年   17篇
  2018年   32篇
  2017年   50篇
  2016年   42篇
  2015年   83篇
  2014年   121篇
  2013年   81篇
  2012年   102篇
  2011年   141篇
  2010年   104篇
  2009年   96篇
  2008年   132篇
  2007年   131篇
  2006年   111篇
  2005年   124篇
  2004年   96篇
  2003年   95篇
  2002年   78篇
  2001年   88篇
  2000年   83篇
  1999年   138篇
  1998年   99篇
  1997年   92篇
  1996年   108篇
  1995年   89篇
  1994年   76篇
  1993年   60篇
  1992年   69篇
  1991年   61篇
  1990年   44篇
  1989年   32篇
  1988年   37篇
  1987年   13篇
  1986年   8篇
  1985年   1篇
  1981年   3篇
排序方式: 共有2924条查询结果,搜索用时 500 毫秒
111.
Hu Z  Xia Y  Guo X  Dai J  Li H  Hu H  Jiang Y  Lu F  Wu Y  Yang X  Li H  Yao B  Lu C  Xiong C  Li Z  Gui Y  Liu J  Zhou Z  Shen H  Wang X  Sha J 《Nature genetics》2012,44(2):183-186
Non-obstructive azoospermia (NOA) is one of the most severe forms of male infertility. Its pathophysiology is largely unknown, and few genetic influences have been defined. To identify common variants contributing to NOA in Han Chinese men, we performed a three-stage genome-wide association study of 2,927 individuals with NOA and 5,734 controls. The combined analyses identified significant (P < 5.0 × 10(-8)) associations between NOA risk and common variants near PRMT6 (rs12097821 at 1p13.3: odds ratio (OR) = 1.25, P = 5.7 × 10(-10)), PEX10 (rs2477686 at 1p36.32: OR = 1.39, P = 5.7 × 10(-12)) and SOX5 (rs10842262 at 12p12.1: OR = 1.23, P = 2.3 × 10(-9)). These findings implicate genetic variants at 1p13.3, 1p36.32 and 12p12.1 in the etiology of NOA in Han Chinese men.  相似文献   
112.
113.
防止西藏国有企业政策性寻租对策分析   总被引:1,自引:0,他引:1  
由于特殊的地理环境与政治环境,西藏国有企业自生能力相对较弱,企业生产带有强制的外部经济性,因此政府给予企业政策性优惠与补贴是企业公平发展的需要。文章从西藏国有企业的领导人政策性寻租动机及诱因出发,分析了西藏现实的制度运行环境,从企业领导人的选拔、激励、绩效评价、合作剩余的归宿等多个方面研究了防止西藏国有企业领导人实施政策性寻租的对策措施。  相似文献   
114.
在物理课堂中利用计算机仿真演示实验进行辅助教学一直受到许多关注与研究.已有各种技术被应用到进行物理仿真演示的多媒体教学软件的开发中.本文论述了如何利用3dsMax中的Reactor动力学系统这一新技术进行物理力学现象的仿真演示,这种技术具有不需编程、创作快捷、形象直观且容易学习、实现交互性好等特点.  相似文献   
115.
<正>To detect the deformation of the tunnel structure based on image sensor networks is the advanced study and application of spatial sensor technology.For the vertical settlement of metro tunnel caused by internal and external stress after its long period operation,the overall scheme and measuring principle of tunnel deformation detection system is introduced. The image data acquisition and processing of detection target are achieved by the cooperative work of image sensor,ARM embedded system.RS485 communication achieves the data transmission between ARM memory and host computer.The database system in station platform analyses the detection data and obtains the deformation state of tunnel inner wall,which makes it possible to early-warn the tunnel deformation and take preventive measures in time.  相似文献   
116.
文章介绍了沥青路面常见病害的形式及其成因,并简要探讨了病害防治的对策。  相似文献   
117.
变压器的安装调试运行必须遵循施工顺序和操作方法,达到现行的国家标准和验收规范的规定,方可运行生产.本文主要探讨变压器安装和调试应注意的问题.  相似文献   
118.
Performance of wireless mesh networks can be greatly improved by spatial reuse (SR), therefore, lots of algorithms have been proposed to maximize the number of concurrent transmissions. However, most methods only considered the interference brought by the sender nodes. In this paper, we study the interference model in WiMAX mesh networks and propose a minimal SR-pair interference model to perform concurrent transmissions in both uplink and downlink directions. Simulation results show that our model is more efficient and stable, i.e., it increases the number of concurrent transmissions and its performance is constant and independent of transmission directions. Biography: XIONG Qing(1978–), male, Ph. D., research direction: wireless mesh networks.  相似文献   
119.
Objective: The age-related change is important part of degenerative disc disease. However, no appropriate animal model or objective evaluation index is available. This study aimed to investigate the features of intervertebral disc degeneration in aging process of rats. Methods: 22-month-old Sprague-Dawley (SD) rats were used as spontaneously occurring intervertebral disc degeneration models and 6-month-old rats as young controls. Expression of collagen types II and X was measured by immunohistochemistry. Degenerations of intervertebral discs were scored according to Miyamoto’s method. Numbers and areas of afferent vascular buds were measured. The thicknesses of non-calcified and calcified layers were measured and statistically analyzed. Results: There were less collagen type II expression and more collagen type X expression in the calcified layer of the cartilage endplates and nucleus pulposus in the rats of the aged group than in the young control. There were fewer and smaller afferent vascular buds in the rats of the aged group than in the young control group. The ratio of the non-calcified to the calcified layers in the rats of the aged group significantly decreased, compared with that of the young control group (P<0.01). Conclusion: Rats can spontaneously establish intervertebral disc age-related degeneration. The expression of collagen types II and X, numbers and areas of afferent vascular buds, the ratio of the non-calcified to the calcified layers, and water and glycosaminoglycan contents in the nucleus pulposus are sensitive indexes of intervertebral disc degeneration.  相似文献   
120.
Joint Funds of National Natural Science Foundation of China(NSFC) are initiated by different stakeholders,which aim to play a better guiding role to support basic research in specific areas and directions.They have formed an important part of the national natural science funding system,which is responsible for advancing science and technology in an expanding frontier.The article would briefly summarize the joint funds strategic goals,programs implementation and achievements in the past decade, and provide a perspective on their future development.  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