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   233905篇
  免费   3082篇
  国内免费   1645篇
化学   131054篇
晶体学   3306篇
力学   9273篇
综合类   90篇
数学   26188篇
物理学   68721篇
  2020年   1925篇
  2019年   2069篇
  2018年   2647篇
  2017年   2664篇
  2016年   3949篇
  2015年   2708篇
  2014年   3884篇
  2013年   9595篇
  2012年   8257篇
  2011年   10041篇
  2010年   7120篇
  2009年   6896篇
  2008年   9399篇
  2007年   9546篇
  2006年   8898篇
  2005年   8231篇
  2004年   7379篇
  2003年   6586篇
  2002年   6536篇
  2001年   7073篇
  2000年   5419篇
  1999年   3927篇
  1998年   3233篇
  1997年   3185篇
  1996年   3203篇
  1995年   2825篇
  1994年   2912篇
  1993年   2736篇
  1992年   2969篇
  1991年   3035篇
  1990年   2852篇
  1989年   2743篇
  1988年   2662篇
  1987年   2609篇
  1986年   2613篇
  1985年   3480篇
  1984年   3559篇
  1983年   2943篇
  1982年   3182篇
  1981年   2934篇
  1980年   2728篇
  1979年   2904篇
  1978年   3089篇
  1977年   3166篇
  1976年   3182篇
  1975年   2890篇
  1974年   2995篇
  1973年   3054篇
  1972年   2379篇
  1971年   1878篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
62.
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   
63.
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   
64.
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   
65.
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   
66.
67.
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 127–134, March–April, 1991.  相似文献   
68.
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   
69.
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