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   96203篇
  免费   3783篇
  国内免费   2791篇
化学   37812篇
晶体学   1011篇
力学   7728篇
综合类   127篇
数学   33759篇
物理学   22340篇
  2024年   55篇
  2023年   460篇
  2022年   631篇
  2021年   768篇
  2020年   879篇
  2019年   837篇
  2018年   10990篇
  2017年   10749篇
  2016年   6950篇
  2015年   1783篇
  2014年   1404篇
  2013年   1725篇
  2012年   5462篇
  2011年   12033篇
  2010年   6771篇
  2009年   7077篇
  2008年   7717篇
  2007年   9787篇
  2006年   1214篇
  2005年   2183篇
  2004年   2150篇
  2003年   2504篇
  2002年   1553篇
  2001年   678篇
  2000年   661篇
  1999年   591篇
  1998年   546篇
  1997年   489篇
  1996年   525篇
  1995年   393篇
  1994年   308篇
  1993年   305篇
  1992年   215篇
  1991年   206篇
  1990年   216篇
  1989年   175篇
  1988年   138篇
  1987年   112篇
  1986年   118篇
  1985年   108篇
  1984年   74篇
  1983年   68篇
  1982年   71篇
  1981年   57篇
  1980年   56篇
  1979年   46篇
  1914年   45篇
  1912年   40篇
  1909年   42篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Acta Mathematica Sinica, English Series - We are interested in the existence and asymptotic behavior for the least energy solutions of the following fractional eigenvalue problem $$\left({\rm{P}}...  相似文献   
22.
23.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  相似文献   
24.
Ni–Co alloys have a wide range of applications in various fields owning to their excellent physical, chemical, and mechanical properties. In this paper, we prepare Ni–Co alloy coatings on 316L stain steel surfaces by electroplating. We present a novel approach utilizing a nanosecond laser to induce microtextures on Ni–Co alloy coatings. We study experimentally the effects of laser power and scanning rate on the surface morphologies of Ni–Co alloy coatings. The results indicate that the shape and size of induced microtextures can be controlled by the laser power and scanning rate. The size of grains increases with increase in the work current of the laser (WCL) at a certain scanning rate. With the WCL constant, the size of grains decreases with increase in scanning rate while their average height increases. It is a simple and easily-controlled method for the fabrication of microstructures on Ni–Co alloy coatings, which has promising applications in investigations of the properties of microtextured surfaces, such as friction, adhesion, and wetting.  相似文献   
25.
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
26.
27.
28.
29.
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.  相似文献   
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