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   707篇
  免费   16篇
化学   564篇
晶体学   18篇
力学   10篇
数学   33篇
物理学   98篇
  2023年   2篇
  2021年   8篇
  2020年   9篇
  2019年   12篇
  2018年   7篇
  2017年   5篇
  2016年   14篇
  2015年   10篇
  2014年   10篇
  2013年   33篇
  2012年   37篇
  2011年   32篇
  2010年   35篇
  2009年   36篇
  2008年   54篇
  2007年   46篇
  2006年   38篇
  2005年   51篇
  2004年   36篇
  2003年   42篇
  2002年   28篇
  2001年   7篇
  2000年   11篇
  1999年   6篇
  1998年   8篇
  1997年   4篇
  1996年   6篇
  1995年   6篇
  1994年   3篇
  1993年   6篇
  1992年   5篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1988年   6篇
  1987年   2篇
  1986年   3篇
  1985年   6篇
  1984年   6篇
  1983年   10篇
  1982年   8篇
  1981年   11篇
  1980年   11篇
  1979年   10篇
  1978年   5篇
  1977年   8篇
  1976年   9篇
  1975年   2篇
  1974年   6篇
  1973年   3篇
排序方式: 共有723条查询结果,搜索用时 15 毫秒
91.
Effects of a finite ion temperature on the Hall magnetohydrodynamics (MHD), which breaks down for a finite ion temperature, are clarified in terms of a rigorous three-field kinetic dispersion relation. The MHD mode equation becomes anisotropic with respect to the ion pressure because of the double adiabaticity in ion dynamics.  相似文献   
92.
A thermal analyzer consisting of a pair of glass thermistors was coupled with a flowthrough immobilized enzyme reactor for the determination of ATP concentration. Hexokinase was covalently bound to poly(chloromethyl-styrene-divinyl benzene) beads and packed in the reactor. The thermal analyzer was designed so as to respond to heat generation in the reactor. A maximum temperature change was exhibited within 1.5 min after the injection of a sample solution containing ATP together with glucose. Thermal decay occurred within 1 min. The thermal analyzer responded reproducibly to ATP at a constant concentration. Assays could be repeated at 3-min intervals. The effects of sample volume and flow rate on the response were examined with regard to an empirical equation. Concentration of ATP was determined with the thermal analyzer in the range of 0-10 mM. The thermal analyzer may be a simple device for the rapid determination of ATP concentration.  相似文献   
93.
The total synthesis of (±)-11a-methano- 9,11-thiathromboxane A2(1), the sulfur analog of thromboxane A2 is described  相似文献   
94.
The behaviour of adsorbed CO on Ru(001) flat and Ru(l,1,10) stepped surfaces in the CO pressure range between 10?6 and 101 Pa has been investigated by TDS, AES, LEED and UPS. The disproportionation of CO proceeds rapidly on the stepped surface and its apparent activation energy was obtained to be 20 kJ mol?1 at nearly zero coverage. The carbon species produced by CO disproportionation show non-uniform reactivity with 18O2 and provide four CO desorption peaks in TPR spectra, which are assigned to α-C18O,ß-C18O and those derived from carbidic and graphitic carbons. At smaller carbon coverage, only α-CO and β-CO were observed, but with increasing coverage the amount of ß-CO reaches a maximum and carbidic carbon is newly formed. Further increase of carbon deposition gives graphitic carbon. The conversion from carbidic to graphitic carbon and the dissolution into the bulk took place upon heating to 1000 K. It is remarkable that very active carbon species are converted to molecular CO through the reaction with O2 even at low temperature such as 200 K. It was also confirmed that active carbon species are formed on Ru surface during COH2 reaction.  相似文献   
95.
96.
A simple synthetic method of α-arylalkanoic acids was accomplished by the use of a novel 1,2-rearrangement of the aryl group and this method was applied to the syntheses of some biologically important substances.  相似文献   
97.
The dynamics of water molecules in the layered vanadium pentoxide hydrate, V(2)O(5).nH(2)O, were studied by quasi-elastic neutron scattering (QENS) measurements. Heterogeneity of the dynamic properties was confirmed by alpha-relaxation model analysis. Translational diffusion of monolayer and double-layer water molecules is by site-to-site diffusion and is reduced relative to that of bulk water. Water molecules lose their mobility markedly and solidify with decreasing temperature. However, mobile water remains at 253 K. Rotational diffusion coefficients are unaffected by confinement and are very similar to the bulk values determined at temperatures in the range 253-298 K. The dynamic speed characterized by QENS is much faster than that expected from the data determined by deuterium NMR (DNMR) measurements at low temperatures.  相似文献   
98.
The total synthesis of (±)-dithiathromboxane A2 sodium salt 1 was accomplished in 26 steps from methyl 4,4-dimethoxyactoacetate.  相似文献   
99.
(+)-11a-methano-9,11-thiathiromboxane A2(1) was synthesized from prostaglandin A2 and prostaglandin E2.  相似文献   
100.
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