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   4213篇
  免费   83篇
  国内免费   11篇
化学   2972篇
晶体学   55篇
力学   66篇
数学   225篇
物理学   989篇
  2021年   25篇
  2020年   49篇
  2019年   54篇
  2018年   42篇
  2017年   24篇
  2016年   56篇
  2015年   59篇
  2014年   73篇
  2013年   206篇
  2012年   157篇
  2011年   205篇
  2010年   132篇
  2009年   134篇
  2008年   213篇
  2007年   230篇
  2006年   211篇
  2005年   167篇
  2004年   148篇
  2003年   163篇
  2002年   162篇
  2001年   112篇
  2000年   134篇
  1999年   86篇
  1998年   62篇
  1997年   54篇
  1996年   48篇
  1995年   43篇
  1994年   47篇
  1993年   55篇
  1992年   52篇
  1991年   52篇
  1990年   40篇
  1989年   54篇
  1988年   54篇
  1987年   46篇
  1986年   38篇
  1985年   67篇
  1984年   68篇
  1983年   58篇
  1982年   59篇
  1981年   44篇
  1980年   59篇
  1979年   71篇
  1978年   62篇
  1977年   69篇
  1976年   21篇
  1975年   39篇
  1974年   36篇
  1973年   23篇
  1967年   18篇
排序方式: 共有4307条查询结果,搜索用时 15 毫秒
41.
42.
To sophisticate the nuclear fuel recycling processes, the transfer percentages for Pd, Mo, Te, and Sb should be determined. Each element solution containing NaNO3 or HNO3 was fed consistently into the thin film evaporator regulated in vac and at 50 °C. The analyte percentages in the inside of the lid, in the condenser, and in the distillate were 10-1%/m2, 10-3%/m2, and 10-3% (DF = 105), respectively. The Mo percentage in the condenser was lower by a factor of 10 than those of other elements investigated. The NO3 - percentages were nearly constant despite increasing HNO3 concentrations, however, the ratios decreased with increasing NaNO3 concentrations.  相似文献   
43.
44.
45.
A chiral HWE reagent reacted with an alternative carbonyl group of meso-α-diketones of bicyclo[2.2.1] system to give non-racemic (Z)- and (E)-olefins, respectively.  相似文献   
46.
Oxovanadium(V)(salen) complex 4 was found to catalyze Meerwein-Ponndorf-Verley cyanation of aliphatic aldehydes with good to high enantioselectivity. This cyanation showed a positive nonlinear effect.  相似文献   
47.
48.
The bioassay-guided fractionation of the cytotoxic constituents of the Japanese sea hare Dollabella auricularia led to the isolation of aurilide (1), a 26-membered cyclodepsipeptide. The gross structure of 1 was established by spectroscopic analysis including 2D NMR techniques. The absolute stereostructure was determined by chiral HPLC analysis of acid hydrolysates of 1 and by the enantioselective synthesis of a degradation product arising from a dihydroxylated fatty acid portion. The enantioselective synthesis of 1 was achieved in 12% overall yield (16 steps) and confirmed the absolute stereostructure of 1. The cytotoxicity of 1 was evaluated using a synthetic sample, which was found to exhibit potent cytotoxicity against HeLa S3 cells with an IC50 of 0.011 μg/mL. Further biological and pharmacological studies of 1 have been carried out by using synthetic 1.  相似文献   
49.
In supercritical water the rate of methanol oxidation was controlled by ionic behavior as follows: the oxidation rate of methanol decreased with increasing proton and hydroxide ion concentration, possibly due to stabilization of the reactant, while that of CO was suppressed by added protons and enhanced by added hydroxide ions.  相似文献   
50.
Six analogues of 1 alpha,25-dihydroxy-22-oxavitamin D3 (OCT) (2), 26,27-dimethyl OCT (5), 26,27-diethyl OCT (6), 24-norOCT (7), 24-homoOCT (8), 24-dihomoOCT (9), and 24-trihomoOCT (10) were synthesized from the 20(S)-alcohol (11) as the common starting material. In the activity inducing differentiation of human myeloid leukemia cells (HL-60) into macrophages, 26,27-dimethyl OCT (5) and 24-homoOCT (8) showed the highest activities. The binding properties of these analogues to the chick embryonic intestinal 1 alpha,25-dihydroxyvitamin D3 (1) receptor are also described.  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