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   317256篇
  免费   2731篇
  国内免费   1244篇
化学   152987篇
晶体学   4394篇
力学   16400篇
综合类   2篇
数学   57999篇
物理学   89449篇
  2020年   1769篇
  2019年   2051篇
  2018年   12541篇
  2017年   12309篇
  2016年   9702篇
  2015年   3397篇
  2014年   4160篇
  2013年   11424篇
  2012年   11652篇
  2011年   20008篇
  2010年   11934篇
  2009年   12273篇
  2008年   15267篇
  2007年   17444篇
  2006年   8555篇
  2005年   9028篇
  2004年   8418篇
  2003年   8072篇
  2002年   7083篇
  2001年   7413篇
  2000年   5607篇
  1999年   4333篇
  1998年   3706篇
  1997年   3688篇
  1996年   3474篇
  1995年   3247篇
  1994年   3019篇
  1993年   3089篇
  1992年   3345篇
  1991年   3393篇
  1990年   3194篇
  1989年   3156篇
  1988年   3218篇
  1987年   3085篇
  1986年   2981篇
  1985年   4036篇
  1984年   4185篇
  1983年   3438篇
  1982年   3791篇
  1981年   3683篇
  1980年   3566篇
  1979年   3596篇
  1978年   3811篇
  1977年   3625篇
  1976年   3835篇
  1975年   3403篇
  1974年   3528篇
  1973年   3841篇
  1972年   2345篇
  1971年   1793篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied.  相似文献   
83.
Landfill gas, cryotrapped on a loop fashioned from a length of a capillary gas chromatography (GC) column, was examined for volatile organometallic compounds (VOMCs) and for volatile organic compounds (VOCs) by using GC–mass spectrometry (MS). A large number of organic components were present and many were identified, but the only VOMCs present in high enough concentrations to be detected were trimethylstibine and tetramethyltin. The use of inductively coupled plasma (ICP)‐MS as an element‐specific detector allowed the identification of a number of other organometallic species in the landfill gas, including trimethylarsine and trimethylbismuth, and, for the first time, butyltrimethyltin and dibutyldimethyltin. The presence of molybdenum hexacarbonyl was confirmed. Gas from a large‐scale compost heap and from compost incubated in the laboratory contained iodomethane but no common VOMCs (GC–ICP‐MS). Only VOCs were present in forest air (GC–MS). Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
84.
A new parallel storm surge model, the Parallel Environmental Model (PEM), is developed and tested by comparisons with analytic solutions. The PEM is a 2‐D vertically averaged, wetting and drying numerical model and can be operated in explicit, semi‐implicit and fully implicit modes. In the implicit mode, the propagation, Coriolis and bottom friction terms can all be treated implicitly. The advection and diffusion terms are solved with a parallel Eulerian–Lagrangian scheme developed for this study. The model is developed specifically for use on parallel computer systems and will function accordingly in either explicit of implicit modes. Storm boundary conditions are based on a simple exponential decay of pressure from the centre of a storm. The simulated flooding caused by a major Category 5 hurricane making landfall in the Indian River Lagoon, Florida is then presented as an example application of the PEM. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
85.
86.
R.J Hand 《Journal of Non》2003,315(3):276-287
Glass may be strengthened by epoxy coatings although the strengthening mechanisms remain unclear. Possible strengthening mechanisms are reviewed and are used to analyse strength data for both a solvent based and a water based coating system. The coatings either fill (solvent based coatings), or partially fill (water based coatings) surface cracks and it is shown that closure stresses arising from the thermal expansion mismatch of the coating within these cracks can account for the observed degrees of strengthening. It is also demonstrated that other suggested mechanisms such as flaw healing cannot fully account for the observed degree of strengthening.  相似文献   
87.
We prove new theorems on the justification of the averaging method for multifrequency oscillation systems with pulse influence at fixed times.  相似文献   
88.
89.
We prove that the sufficient conditions for the asymptotic stability of impulsive systems obtained by Gurgula and Perestyuk are also necessary conditions.  相似文献   
90.
We construct an integral Newton-type interpolation polynomial with a continual set of nodes. This interpolant is unique and preserves an operator polynomial of the corresponding degree.  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