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   326573篇
  免费   3872篇
  国内免费   1744篇
化学   181413篇
晶体学   5007篇
力学   13221篇
综合类   66篇
数学   35514篇
物理学   96968篇
  2018年   3012篇
  2017年   3016篇
  2016年   4699篇
  2015年   3279篇
  2014年   4670篇
  2013年   13115篇
  2012年   10424篇
  2011年   12937篇
  2010年   8870篇
  2009年   8524篇
  2008年   11996篇
  2007年   12141篇
  2006年   11659篇
  2005年   10871篇
  2004年   9661篇
  2003年   8597篇
  2002年   8489篇
  2001年   9475篇
  2000年   7244篇
  1999年   5517篇
  1998年   4658篇
  1997年   4606篇
  1996年   4550篇
  1995年   4160篇
  1994年   4040篇
  1993年   3898篇
  1992年   4341篇
  1991年   4380篇
  1990年   4147篇
  1989年   4082篇
  1988年   4005篇
  1987年   3960篇
  1986年   3857篇
  1985年   5168篇
  1984年   5353篇
  1983年   4470篇
  1982年   4991篇
  1981年   4598篇
  1980年   4433篇
  1979年   4616篇
  1978年   4922篇
  1977年   4873篇
  1976年   4902篇
  1975年   4572篇
  1974年   4558篇
  1973年   4817篇
  1972年   3458篇
  1971年   2742篇
  1968年   2645篇
  1967年   2626篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
    
  相似文献   
83.
84.
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   
85.
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   
86.
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   
87.
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   
88.
89.
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 127–134, March–April, 1991.  相似文献   
90.
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