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   136729篇
  免费   11367篇
  国内免费   8445篇
化学   67427篇
晶体学   1709篇
力学   10010篇
综合类   552篇
数学   38043篇
物理学   38800篇
  2024年   213篇
  2023年   1129篇
  2022年   2055篇
  2021年   2203篇
  2020年   2429篇
  2019年   2533篇
  2018年   12105篇
  2017年   11847篇
  2016年   8706篇
  2015年   3772篇
  2014年   3962篇
  2013年   4960篇
  2012年   9269篇
  2011年   15880篇
  2010年   9541篇
  2009年   9853篇
  2008年   10829篇
  2007年   12343篇
  2006年   3904篇
  2005年   4312篇
  2004年   3870篇
  2003年   3812篇
  2002年   2937篇
  2001年   1799篇
  2000年   1584篇
  1999年   1394篇
  1998年   1129篇
  1997年   990篇
  1996年   1049篇
  1995年   854篇
  1994年   684篇
  1993年   600篇
  1992年   487篇
  1991年   459篇
  1990年   370篇
  1989年   314篇
  1988年   234篇
  1987年   195篇
  1986年   223篇
  1985年   175篇
  1984年   117篇
  1983年   118篇
  1982年   96篇
  1981年   86篇
  1980年   68篇
  1979年   64篇
  1978年   43篇
  1914年   45篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Mass spectrometry (MS) driven metabolomics is a frequently used tool in various areas of life sciences; however, the analysis of polar metabolites is less commonly included. In general, metabolomic analyses lead to the detection of the total amount of all covered metabolites. This is currently a major limitation with respect to metabolites showing high turnover rates, but no changes in their concentration. Such metabolites and pathways could be crucial metabolic nodes (e.g., potential drug targets in cancer metabolism). A stable-isotope tracing capillary electrophoresis–mass spectrometry (CE-MS) metabolomic approach was developed to cover both polar metabolites and isotopologues in a non-targeted way. An in-house developed software enables high throughput processing of complex multidimensional data. The practicability is demonstrated analyzing [U-13C]-glucose exposed prostate cancer and non-cancer cells. This CE-MS-driven analytical strategy complements polar metabolite profiles through isotopologue labeling patterns, thereby improving not only the metabolomic coverage, but also the understanding of metabolism.  相似文献   
52.
In this paper, we propose a sufficient and necessary condition for the boundedness of all the solutions for the equation x¨+n2x+g(x)=p(t) with the critical situation that |02πp(t)e?intdt|=2|g(+)?g(?)| on g and p, where nN+, p(t) is periodic and g(x) is bounded.  相似文献   
53.
54.
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   
55.
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   
56.
57.
58.
Chen  Cui  Wang  Ya-Nan  Yan  Jun 《中国科学 数学(英文版)》2021,64(8):1789-1800
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0.  相似文献   
59.
Lv  Xinyu  Niu  Yugang  Song  Jun 《Nonlinear dynamics》2021,104(1):497-507
Nonlinear Dynamics - This paper seeks to address the problem of finite-time stabilization for a class of uncertain Hamiltonian systems via sliding mode control approach. A novel sliding function in...  相似文献   
60.
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