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   3891篇
  免费   112篇
  国内免费   10篇
化学   3055篇
晶体学   29篇
力学   46篇
数学   226篇
物理学   657篇
  2022年   23篇
  2021年   33篇
  2020年   44篇
  2019年   60篇
  2018年   39篇
  2017年   28篇
  2016年   70篇
  2015年   54篇
  2014年   82篇
  2013年   175篇
  2012年   158篇
  2011年   234篇
  2010年   80篇
  2009年   107篇
  2008年   200篇
  2007年   203篇
  2006年   191篇
  2005年   227篇
  2004年   186篇
  2003年   144篇
  2002年   160篇
  2001年   119篇
  2000年   145篇
  1999年   52篇
  1998年   42篇
  1997年   40篇
  1996年   61篇
  1995年   29篇
  1994年   50篇
  1993年   38篇
  1992年   54篇
  1991年   44篇
  1990年   43篇
  1989年   40篇
  1988年   53篇
  1987年   43篇
  1986年   62篇
  1985年   60篇
  1984年   64篇
  1983年   32篇
  1982年   40篇
  1981年   39篇
  1980年   30篇
  1979年   34篇
  1978年   29篇
  1977年   27篇
  1976年   23篇
  1975年   35篇
  1974年   31篇
  1972年   23篇
排序方式: 共有4013条查询结果,搜索用时 15 毫秒
41.
42.
43.
An antiviral nucleoside or virazole was synthesized efficiently and regioselectively starting with benzyl cyanoformate.  相似文献   
44.
45.
The adsorbability of pertechnetate ion (TcO 4 ) reached 96% for an active carbon at the 0.1 g/50 ml concentration level, increasing with diminution of acid and its salt concentrations, and depending on the type of anions present. With constant anion concentration, TcO 4 adsorbability rose with decreasing pH in the acidic region, followed in the region around neutrality by a plateau, and in the basic region by an appreciable decline of TcO 4 adsorbability. In the acidic region, part of once-adsorbed TcO 4 appeared to be displaced by other anions. Reversibility was noted between the adsorption and desorption of TcO 4 .  相似文献   
46.
High-speed counter-current chromatography (HSCCC) was used to purify salidroside from an extract of Rhodiola crenulata with two steps using a two-phase solvent system composed of ethyl acetate-n-butanol-water (1:4:5, v/v) in the first run and chloroform-methanol-isopropanol-water (5:6:1:4) in the second run. The method yielded 21.9 mg of salidroside from 1.216 g of the crude sample at 98% purity determined by HPLC analyses. Identification was performed by 1H NMR, 13C NMR, and MS.  相似文献   
47.
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   
48.
Thiazolo[3,2-a]thieno[3,2-d]-, [3,4-d]- and [2,3-d]pyrimidin-5-one derivatives (6, 11 and 16), and polymethylene condensed thieno[3,2-d]-, [3,4-d]- and [2,3-d]pyrimidin-5-one derivatives (19-21), in which the oxygen atom of the oxazolidine moiety in 3 was replaced by a sulfur atom or methylene groups, were synthesized and evaluated for gastric antisecretory activity in pylorus-ligated rats. The structure-activity relationships of these compounds are discussed.  相似文献   
49.
Bromine and chlorine concentrations in some tissues (liver, spleen, thymus) of healthy mice (normal group) and lymphomatous mice (lymphoma group) were determined by neutron activation analysis. There were significant differences in the Br concentrations of the tissues between the normal and lymphomatous group, while the Cl concentrations were found relatively constant in all the tissues. As a result, the Br/Cl ratios in the tissues of the lymphomatous group were significantly higher than those of the normal group. It was difficult to conclude that Br was absorbed into the bodies of lymphomatous mice more easily than was Cl. It is suggested that Br excretion from the body is suppressed.  相似文献   
50.
-Cyclodextrin with two sodium anthranilate moieties (1) has been prepared as a sensor for detecting organic compounds including terpenoids and steroids. Compound1 shows a pure monomer fluorescence whose intensity is increased or decreased upon addition of the guest species examined. In this system, the sodium anthranilate moieties act either as a spacer, which enables the cyclodextrin to form a 1:1 host-guest complex by narrowing the -cyclodextrin cavity, or as a hydrophobic cap.1 recognizes steroids with much higher sensitivity than terpenoids, in which the appended moieties act as a hydrophobic cap for terpenoids and a spacer for steroids, respectively.  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