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   237199篇
  免费   3185篇
  国内免费   1343篇
化学   133265篇
晶体学   3339篇
力学   9165篇
综合类   61篇
数学   27402篇
物理学   68495篇
  2020年   2007篇
  2019年   2167篇
  2018年   2831篇
  2017年   2849篇
  2016年   4306篇
  2015年   2913篇
  2014年   4051篇
  2013年   9901篇
  2012年   8710篇
  2011年   10421篇
  2010年   7278篇
  2009年   7055篇
  2008年   9680篇
  2007年   9798篇
  2006年   9207篇
  2005年   8447篇
  2004年   7521篇
  2003年   6586篇
  2002年   6424篇
  2001年   7031篇
  2000年   5370篇
  1999年   3895篇
  1998年   3221篇
  1997年   3164篇
  1996年   3206篇
  1995年   2771篇
  1994年   2883篇
  1993年   2726篇
  1992年   2971篇
  1991年   3019篇
  1990年   2842篇
  1989年   2725篇
  1988年   2662篇
  1987年   2601篇
  1986年   2616篇
  1985年   3431篇
  1984年   3501篇
  1983年   2897篇
  1982年   3140篇
  1981年   2921篇
  1980年   2705篇
  1979年   2865篇
  1978年   3069篇
  1977年   3110篇
  1976年   3130篇
  1975年   2861篇
  1974年   2947篇
  1973年   3003篇
  1972年   2344篇
  1971年   1875篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
    
  相似文献   
63.
64.
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   
65.
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   
66.
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   
67.
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   
68.
69.
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 127–134, March–April, 1991.  相似文献   
70.
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   
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