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   92825篇
  免费   1066篇
  国内免费   513篇
化学   34441篇
晶体学   883篇
力学   7114篇
数学   34466篇
物理学   17500篇
  2023年   139篇
  2022年   141篇
  2021年   328篇
  2020年   402篇
  2019年   387篇
  2018年   10600篇
  2017年   10402篇
  2016年   6611篇
  2015年   1304篇
  2014年   841篇
  2013年   1162篇
  2012年   4841篇
  2011年   11688篇
  2010年   6249篇
  2009年   6571篇
  2008年   7490篇
  2007年   9608篇
  2006年   1130篇
  2005年   2113篇
  2004年   2227篇
  2003年   2446篇
  2002年   1512篇
  2001年   416篇
  2000年   427篇
  1999年   299篇
  1998年   306篇
  1997年   271篇
  1996年   361篇
  1995年   220篇
  1994年   186篇
  1993年   212篇
  1992年   137篇
  1991年   155篇
  1990年   120篇
  1989年   130篇
  1988年   142篇
  1987年   129篇
  1986年   124篇
  1985年   145篇
  1984年   145篇
  1983年   96篇
  1982年   155篇
  1981年   160篇
  1980年   142篇
  1979年   127篇
  1978年   147篇
  1977年   110篇
  1976年   89篇
  1975年   87篇
  1973年   93篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Traditionally, due to different hardware requirements, nuclear magnetic resonance (NMR) has developed as two separate fields: one dealing with solids, and one with solutions. Comprehensive multiphase (CMP) NMR combines all electronics and hardware (magic angle spinning [MAS], gradients, high power Radio Frequency (RF) handling, lock, susceptibility matching) into a universal probe that permits a comprehensive study of all phases (i.e., liquid, gel-like, semisolid, and solid), in intact samples. When applied in vivo, it provides unique insight into the wide array of bonds in a living system from the most mobile liquids (blood, fluids) through gels (muscle, tissues) to the most rigid (exoskeleton, shell). In this tutorial, the practical aspects of in vivo CMP NMR are discussed including: handling the organisms, rotor preparation, sample spinning, water suppression, editing experiments, and finishes with a brief look at the potential of other heteronuclei (2H, 15N, 19F, 31P) for in vivo research. The tutorial is aimed as a general resource for researchers interested in developing and applying MAS-based approaches to living organisms. Although the focus here is CMP NMR, many of the approaches can be adapted (or directly applied) using conventional high-resolution magic angle spinning, and in some cases, even standard solid-state NMR probes.  相似文献   
12.
13.
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   
14.
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   
15.
16.
17.
18.
19.
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   
20.
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