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   92184篇
  免费   15434篇
  国内免费   10407篇
化学   64447篇
晶体学   1112篇
力学   5735篇
综合类   600篇
数学   10254篇
物理学   35877篇
  2024年   309篇
  2023年   1836篇
  2022年   3164篇
  2021年   3458篇
  2020年   3700篇
  2019年   3620篇
  2018年   3115篇
  2017年   2913篇
  2016年   4341篇
  2015年   4331篇
  2014年   5121篇
  2013年   6605篇
  2012年   8401篇
  2011年   8357篇
  2010年   5790篇
  2009年   5600篇
  2008年   6104篇
  2007年   5367篇
  2006年   5056篇
  2005年   4314篇
  2004年   3382篇
  2003年   2670篇
  2002年   2546篇
  2001年   2094篇
  2000年   1881篇
  1999年   1924篇
  1998年   1539篇
  1997年   1469篇
  1996年   1456篇
  1995年   1189篇
  1994年   1071篇
  1993年   883篇
  1992年   748篇
  1991年   668篇
  1990年   553篇
  1989年   426篇
  1988年   379篇
  1987年   293篇
  1986年   274篇
  1985年   237篇
  1984年   160篇
  1983年   117篇
  1982年   92篇
  1981年   83篇
  1980年   75篇
  1979年   45篇
  1978年   37篇
  1977年   47篇
  1976年   32篇
  1973年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
144.
145.
146.
Synthesis, single-crystal structure determination, and magnetic properties are reported for manganese carbodiimide, MnNCN. The presumably unstable but inert phase adopts the trigonal system (R3m) with a = 3.3583(4) A, c = 14.347(2) A, V = 140.13(3) A3, and Z = 3. Divalent manganese is octahedrally coordinated by nitrogen atoms at 2.26 A, and the NCN(2-) unit adopts the linear [N=C=N](2-) carbodiimide shape with two C=N double bonds of 1.23 A. MnNCN contains high-spin Mn(II) with five unpaired electrons and behaves like an antiferromagnet with an ordering temperature below 30 K.  相似文献   
147.
An Y  Ji M  Baiyin M  Liu X  Jia C  Wang D 《Inorganic chemistry》2003,42(14):4248-4249
A novel layered K(4)Ag(2)Sn(3)S(9) x 2KOH was synthesized solvothermally. A mixture of ethanol and HSCH(2)CH(SH)CH(2)OH was used for the synthesis. The HSCH(2)CH(SH)CH(2)OH plays an important role and appears to serve as a mineralizer for the solvothermal reaction. A layer comprises Sn(3)S(9)(6)(-) clusters linked by Ag(+) ions and possesses two types of 1D channels in which potassium ions are located. The compound crystallizes in the monoclinic P2(1)/m space group [a = 7.8071(2) A, b = 27.3508(1) A, c = 10.5008(2) A, alpha = 90 degrees, beta = 103.874(1) degrees, gamma = 90 degrees, Z = 4]. Its crystal structure, composition analysis, and IR are presented.  相似文献   
148.
The occupational health impact of atmospheric pollution on exposed workers at one iron and steel complex was studied by instrumental neutron activation analysis of workers' hair samples and medical examination. The experimental results indicate that there is a positive correlation between the high inhalation amounts of iron and other trace elements by the exposed workers and the symptom of their high blood pressure and hypoglycemia, which implies that the atmospheric environment polluted by iron and steel industry has an adverse health impact on the exposed workers. The measures to relieve and abate the occupational diseases caused by air-borne particulate matter should be taken  相似文献   
149.
Hai-Xia Liu 《Tetrahedron letters》2005,46(20):3525-3528
Annonaceous acetogenins are a series of potent naturally occurring anticancer agents, which act as inhibitors of complex I in mitochondria. AA005, a mimicry of acetogenins, has been found as active as those natural products and to present high selectivities between cancer and normal cells. In order to investigate the further cell-based mechanism induced by AA005, a d4-labeled derivative of AA005 (AA005-d4) was designed to detect the drug permeation ability into the membranes. In this letter, the synthesis is reported of this deuterium-labeled compound, wherein a ethylene-d4 glycol unit is incorporated efficiently into the molecule skeleton by simple etherifications.  相似文献   
150.
A submicron light-emitting device (LED) was fabricated from lithographically fabricated parallel indium-tin oxide (ITO) finger electrodes (0.9 mum wide) separated by a 1.1 mum gap. A single layer of an amorphous (a) Ru(bpy)3(ClO4)2 film ( approximately 100 nm thick) was spin-coated on the electrode array. Ga:In or carbon paste was employed as a liftable upper contact electrode. Films ( approximately 1.5 mum thick) of single-crystal Ru(bpy)3(ClO4)2 (xyl) between two ITO electrodes in a sandwich cell were also prepared and produce electroluminescence. As with larger cells of this type, the high-resolution electroluminescence produced showed a high external efficiency ( approximately 3.4%), a low turn-on voltage (2.3 V), and reasonable stability. The single-crystal cells also behaved as photovoltaic devices and a short-circuit photocurrent was observed when they were irradiated without a bias voltage.  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