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   145922篇
  免费   31998篇
  国内免费   23193篇
化学   95144篇
晶体学   1638篇
力学   9990篇
综合类   591篇
数学   18627篇
物理学   75123篇
  2024年   540篇
  2023年   2101篇
  2022年   2671篇
  2021年   2966篇
  2020年   3495篇
  2019年   3827篇
  2018年   3553篇
  2017年   3892篇
  2016年   5129篇
  2015年   5413篇
  2014年   5816篇
  2013年   8834篇
  2012年   10128篇
  2011年   11893篇
  2010年   13231篇
  2009年   13312篇
  2008年   7537篇
  2007年   6641篇
  2006年   6162篇
  2005年   5948篇
  2004年   6126篇
  2003年   4831篇
  2002年   4446篇
  2001年   4596篇
  2000年   3702篇
  1999年   4079篇
  1998年   3438篇
  1997年   3119篇
  1996年   3506篇
  1995年   3746篇
  1994年   3757篇
  1993年   3640篇
  1992年   3150篇
  1991年   2727篇
  1990年   2296篇
  1989年   2309篇
  1988年   2182篇
  1987年   1469篇
  1986年   1462篇
  1985年   1145篇
  1984年   1173篇
  1983年   528篇
  1982年   1030篇
  1981年   840篇
  1980年   853篇
  1979年   574篇
  1978年   586篇
  1977年   685篇
  1976年   1091篇
  1972年   559篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors.  相似文献   
73.
Defects play a central role in controlling the electronic properties of two-dimensional (2D) materials and realizing the industrialization of 2D electronics. However, the evaluation of charged defects in 2D materials within first-principles calculation is very challenging and has triggered a recent development of the WLZ (Wang, Li, Zhang) extrapolation method. This method lays the foundation of the theoretical evaluation of energies of charged defects in 2D materials within the first-principles framework. Herein, the vital role of defects for advancing 2D electronics is discussed, followed by an introduction of the fundamentals of the WLZ extrapolation method. The ionization energies (IEs) obtained by this method for defects in various 2D semiconductors are then reviewed and summarized. Finally, the unique defect physics in 2D dimensions including the dielectric environment effects, defect ionization process, and carrier transport mechanism captured with the WLZ extrapolation method are presented. As an efficient and reasonable evaluation of charged defects in 2D materials for nanoelectronics and other emerging applications, this work can be of benefit to the community.  相似文献   
74.
Chen  Wei  Han  Qi  Liu  Jingbo 《Aequationes Mathematicae》2019,93(2):425-432
Aequationes mathematicae - We discuss equivalence conditions for the non-existence of non-trivial meromorphic solutions to the Fermat Diophantine equation $$f^m(z)+g^n(z)=1$$ with integers $$m,n\ge...  相似文献   
75.
76.
77.
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   
78.
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   
79.
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   
80.
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