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   48575篇
  免费   8566篇
  国内免费   16225篇
化学   34989篇
晶体学   1626篇
力学   3662篇
综合类   2010篇
数学   7644篇
物理学   23435篇
  2024年   94篇
  2023年   390篇
  2022年   1386篇
  2021年   1296篇
  2020年   1374篇
  2019年   1367篇
  2018年   1275篇
  2017年   1878篇
  2016年   1518篇
  2015年   2053篇
  2014年   2422篇
  2013年   3201篇
  2012年   3188篇
  2011年   4631篇
  2010年   4126篇
  2009年   4289篇
  2008年   4254篇
  2007年   3749篇
  2006年   3864篇
  2005年   3706篇
  2004年   3539篇
  2003年   2447篇
  2002年   2422篇
  2001年   2402篇
  2000年   2261篇
  1999年   1425篇
  1998年   958篇
  1997年   729篇
  1996年   656篇
  1995年   590篇
  1994年   532篇
  1993年   820篇
  1992年   895篇
  1991年   594篇
  1990年   619篇
  1989年   571篇
  1988年   318篇
  1987年   273篇
  1986年   214篇
  1985年   162篇
  1984年   170篇
  1983年   157篇
  1982年   105篇
  1981年   90篇
  1980年   79篇
  1979年   74篇
  1978年   35篇
  1977年   24篇
  1965年   19篇
  1964年   20篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
151.
液体石蜡作分散介质。戊二醛作交联刑,通过反相悬浮聚合制备了微米级的壳聚糖微载体.环氧氟丙烷活化后,乳糖进行修饰.用孔糖修饰的微载体进行原代大鼠肝细胞培养,利用相差显微镜对培养细胞进行形态观察,并测定肝细胞的代谢活性,结果显示,乳糖修饰壳聚糖微载体是一种优良的肝细胞培养支架.  相似文献   
152.
5,6-Dihydro-OSW-1 (1) was synthesized following our previous procedure for the total synthesis of OSW-1. This compound demonstrated slightly stronger potency than that of OSW-1 against the growth of cancer cells.  相似文献   
153.
Introduction In the previous studies on the oxidation reaction,peroxydisulfate was widely used as an oxidizingagent.1-5 One of the advantages of this oxidant lies in itsstability in a wide range of pH values. The reaction be-tween Fe(CN)5L3- (L=N-aromatic heterocyclic li-gands) and S2O8 2- has been proved to proceed throughan outer-sphere electron transfer mechanism.5 For a re-action [(Eq. (1)] to be under an outer-sphere mechanismthe steps involved are the formation of a reactant …  相似文献   
154.
The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular, densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to substrates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined.  相似文献   
155.
A New Triterpene from the Orchid Pholidota yunnanensis   总被引:2,自引:0,他引:2  
A new triterpene, 25-methylenecyclopholidonyl p-hydroxy-trans-cinnamate, was isolated from a orchid Pholidota yunnanensis. The structure elucidation and ^1H, ^13C-NMR assignments were achieved by spectral and chemical method.  相似文献   
156.
For the Na I2 collision system, theoretical study is performed on the QCISD(T) level by using ab initio method. The ab initio potential energy surfaces are got and on them the long-lived complexes are found and optimized. These results verify the crossed molecule beam experimental phenomenon and the detailed geometry structures are given for the first time. The role of the complexes in the reaction path is also described in detail.  相似文献   
157.
Three Novel Eremophilanolides from Ligularia virgaurea spp. oligocephala   总被引:1,自引:0,他引:1  
From the alcoholic extract of the whole plant of Ligularia virgaurea spp. oligocephala, three novel eremophilane sesquiterpene lactones, 6α, 10α-dihydroxy- 1-oxoeremophila-7(11), 8(9)-dien-8, 12-olide, 613, 10α-dihydroxy-1-oxoeremophila-7 (ll), 8 (9)-dien-8, 12-olide and 10α-hydroxy-1-oxoeremophila-7(l 1), 8(9)-dien-8, 12-olide were isolated. Their structures were elucidated by various spectroscopic methods including intensive 2D NMR techniques (COSY,HMQC, HMBC and ^1H-^1H NOESY) and HR-MS.  相似文献   
158.
A new cobalt(Ⅱ) complex with tridentate ligand 2, 6-bis (benzimidazol-2-yl)pyridine has been synthesized by microwave irradiation method and characterized by elemental analysis,electrochemical and spectral methods. The binding of the complex with calf thymus DNA has also been investigated by absorption and fluorescence spectra.  相似文献   
159.
A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported.  相似文献   
160.
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process.  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