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   254607篇
  免费   3690篇
  国内免费   1331篇
化学   141772篇
晶体学   3396篇
力学   9594篇
综合类   63篇
数学   30336篇
物理学   74467篇
  2020年   2210篇
  2019年   2202篇
  2018年   2873篇
  2017年   2917篇
  2016年   4533篇
  2015年   3196篇
  2014年   4385篇
  2013年   10720篇
  2012年   9064篇
  2011年   11103篇
  2010年   7562篇
  2009年   7189篇
  2008年   10423篇
  2007年   10500篇
  2006年   9802篇
  2005年   8942篇
  2004年   7862篇
  2003年   6896篇
  2002年   6779篇
  2001年   7312篇
  2000年   5646篇
  1999年   4062篇
  1998年   3392篇
  1997年   3351篇
  1996年   3470篇
  1995年   3026篇
  1994年   3141篇
  1993年   3060篇
  1992年   3241篇
  1991年   3208篇
  1990年   3027篇
  1989年   2896篇
  1988年   2841篇
  1987年   2793篇
  1986年   2766篇
  1985年   3713篇
  1984年   3759篇
  1983年   3194篇
  1982年   3437篇
  1981年   3203篇
  1980年   2972篇
  1979年   3124篇
  1978年   3358篇
  1977年   3380篇
  1976年   3367篇
  1975年   3080篇
  1974年   3188篇
  1973年   3259篇
  1972年   2444篇
  1971年   1979篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
    
  相似文献   
62.
63.
The kinetics of formation of an anomalous phase from a solution with a small 3He impurity was studied in the temperature range 0.2–0.7 K up to a supersaturation of ~30 mbar. The phase diagram was determined for normal and anomalous growths. It is found that, in the presence of impurities, the formation of a fast-growing state is retarded. This experimental fact indicates that the dissipative processes in fluids have an appreciable effect on the phase formation kinetics. The retardation is, possibly, caused by the direct interaction of an impurity with the crystal surface.  相似文献   
64.
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   
65.
The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (Mw) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (Mw/Mn)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with Mw = 12,100 and Mw/Mn = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in Mw of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003  相似文献   
66.
A study of the atmospheric pollution by suspended particulate lead in the city of Seville, Spain, was carried out during the period between March 1983 and February 1984. The results obtained from seven sampling stations allowed us to study the site to site variations; there are two locations with average annual concentrations higher than 2 micrograms X m-3. In one station, the meteorological and traffic effects and relationship with other traffic-related pollutants, were investigated. The regression analyses performed on the average monthly data have shown an inverse correlation with wind speed and temperature and a direct correlation with carbon monoxide and smoke concentrations, but no significant correlation was found with the lead deposition levels.  相似文献   
67.
68.
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 127–134, March–April, 1991.  相似文献   
69.
A generalized relative entropy functional is associated to the evolution of gas in a container with (generally) non-uniform boundary data. A decomposition for its rate in ‘bulk’ and in ‘boundary’ terms is given; for the linear case both have a definite sign. The relation with the strong L1 stability is pointed out.  相似文献   
70.
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