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   84788篇
  免费   541篇
  国内免费   409篇
化学   29441篇
晶体学   853篇
力学   6789篇
数学   32266篇
物理学   16389篇
  2021年   69篇
  2020年   80篇
  2019年   100篇
  2018年   10483篇
  2017年   10303篇
  2016年   6160篇
  2015年   963篇
  2014年   424篇
  2013年   637篇
  2012年   4097篇
  2011年   10898篇
  2010年   5832篇
  2009年   6283篇
  2008年   6986篇
  2007年   9143篇
  2006年   615篇
  2005年   1660篇
  2004年   1823篇
  2003年   2248篇
  2002年   1274篇
  2001年   428篇
  2000年   468篇
  1999年   269篇
  1998年   288篇
  1997年   256篇
  1996年   298篇
  1995年   189篇
  1994年   157篇
  1993年   196篇
  1992年   151篇
  1991年   144篇
  1990年   126篇
  1989年   139篇
  1988年   125篇
  1987年   135篇
  1986年   116篇
  1985年   148篇
  1984年   132篇
  1983年   89篇
  1982年   92篇
  1981年   112篇
  1980年   107篇
  1979年   133篇
  1978年   99篇
  1977年   65篇
  1976年   67篇
  1975年   59篇
  1974年   64篇
  1973年   54篇
  1914年   45篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
2.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
3.
4.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
5.
6.
7.
8.
The Pd‐catalyzed polycondensation of 4‐octylaniline with various dibromoarylenes was carried out under microwave heating. Microwave heating led to a decrease in the reaction time and an increase in the molecular weight of the polymers as compared to conventional heating. Microwave heating also allowed the catalyst loading to be reduced to 1 mol %, yielding polymerization results that were comparable to those under conventional heating and 5 mol % catalyst. Investigations regarding field‐effect transistors and organic photovoltaic cells using the obtained poly(arylamine) with azobenzene units revealed that increasing the molecular weight of the polymer led to improved device performance, including hole mobility and power conversion efficiency. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 536–542  相似文献   
9.
Strategies for the formation of amide bonds, that is, one of the most basic and important transformations in organic synthesis, have so far focused predominantly on dehydration reactions. Herein, we report and demonstrate the practical utility of a novel decarboxylative amidation of α-ketoacids by using inexpensive tert-butyl hydroperoxide (TBHP), which is characterized by high yields, a broad substrate scope, mild reaction conditions, and a unique chemoselectivity. These features enable the synthesis of peptides from amino acid derived α-ketoacids under preservation of the stereochemical information.  相似文献   
10.
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   
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