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   3772篇
  免费   606篇
  国内免费   551篇
化学   3007篇
晶体学   61篇
力学   176篇
综合类   49篇
数学   496篇
物理学   1140篇
  2024年   4篇
  2023年   37篇
  2022年   76篇
  2021年   86篇
  2020年   114篇
  2019年   147篇
  2018年   123篇
  2017年   96篇
  2016年   183篇
  2015年   197篇
  2014年   221篇
  2013年   259篇
  2012年   282篇
  2011年   305篇
  2010年   243篇
  2009年   230篇
  2008年   306篇
  2007年   267篇
  2006年   241篇
  2005年   208篇
  2004年   184篇
  2003年   198篇
  2002年   238篇
  2001年   193篇
  2000年   115篇
  1999年   87篇
  1998年   52篇
  1997年   30篇
  1996年   26篇
  1995年   18篇
  1994年   15篇
  1993年   18篇
  1992年   12篇
  1991年   9篇
  1990年   4篇
  1989年   4篇
  1988年   10篇
  1987年   5篇
  1986年   5篇
  1985年   17篇
  1984年   9篇
  1982年   4篇
  1980年   6篇
  1979年   4篇
  1977年   4篇
  1975年   3篇
  1974年   3篇
  1973年   4篇
  1972年   3篇
  1936年   5篇
排序方式: 共有4929条查询结果,搜索用时 0 毫秒
991.
The self-assembly of meso-tetra (N-methyl-4-pyridyl) porphyrine tetratosylat (H2TMPyP) on an iodide modified Cu(1 1 1) surface has been studied by means of in situ electrochemical-scanning tunneling microscopy (EC-STM). The I/Cu(1 1 1) surface was found to be a good substrate for the self-assembly of highly ordered layers of porphyrin cations. Furthermore, a reversible structural phase transition within the highly ordered porphyrin layer was observed during variation of the electrode potential, as a consequence of changing electronic properties of the substrate.  相似文献   
992.
The structure of the title compound, [Cu2Cl2(C12H10N2)]n, contains infinite CuCl staircase‐like chains, which lie about inversion centres. The trans‐1,2‐di‐4‐pyrid­ylethyl­ene mol­ecules also lie about inversion centres and connect the CuCl chains through Cu—N coordination bonds into a two‐dimensional organic–inorganic hybrid network. The planar sheets are stacked along the c axis and associated through weak C—H⋯Cl inter­actions. The results show a reliable structural motif with controllable separation of the CuCl chains by variation of the length of the ligand.  相似文献   
993.
Ag-TiO2/TTO film electrode was used as photoanode to investigate the feasibility of a hybrid technology of Ag nanoparticles combined with the application of anodic bias.The results showed that the deposited Ag and applied anodic bias have an apparent additive effect.  相似文献   
994.
A New Sesquiterpene Polyol Ester from Celastrus Angulatus   总被引:1,自引:0,他引:1  
A new sesquiterpene polyol ester, angulatin D, has been isolated from the root bark of Celastrus angulatus. The chemical structure is elucidated on the basis of spectral analysis.  相似文献   
995.
26-O-β-D-Glucopyranosyl-furost-5(6),20(22)-dien-3β,26-diol 1, a new furostanol saponin, was isolated from the water-extract of Dioscorea nipponica Mak., the raw material of a traditional Chinese herbal medicine Wei Ao Xin. The structure of 1 was determined on the basis of its spectral data especially by NMR spectroscopy. The result provides the first example of naturally occurring furostanol saponins with a single saccharide chain at the C-26 position.  相似文献   
996.
林海  赵仁  刘连寿 《中国物理 C》1998,22(6):522-528
利用二维相空间自仿射分形的随机级联α模型,采用蒙特卡罗模拟的方法,研究了阶乘矩、粒子数关联矩在不固定多重数下,对应于多重数相对起伏强度nf的依赖关系,得到:阶乘矩、粒子数关联矩依赖于多重数相对起伏nf,但间歇指数一般不依赖于nf,当nf较小时这种依赖性得以消除.  相似文献   
997.
A novel bifunctional glycolipid which carded a cluster of thiogalactosides as the hepatocyte targeting ligand for gene delivery was prepared. Hexa-antennary alcohol 1 was used as the core scaffold to attach a cholesterol molecule by a poly(ethylene glycol) chain, while its remaining branches were linked with five acetylgalactosides, which would be deacetylated later to produce pentaantennary galactoside. Liposome containing the galactoside showed high affinity and transfection activity in hepatoma cells HepG2.  相似文献   
998.
Daphne tangutica Maxim., a shrub of Thymelaeaceae family, meanly grows in northwest area of China at altitude of 1500-4000 m. The root barks of this plant are utilized as a traditional Tibetan medicine for releasing pain, curing rheumatism and as an abort…  相似文献   
999.
Coordination studies on Zn(II) complexes of 1,3,5‐tri(2,5‐diazahexyl)benzene (L) show that by comparison with the non‐deprotonation of complex ZnL in a 1:1 system, the three‐dimensional complexiaton decreases the pKa of the Zn‐bound water molecule, that is, pKa = 7.47 for trinulclear complex Zn3L in a 3:1 metal–ligand ratio. These two types of zinc(II) complexes have been examined as catalysts for the hydrolysis of 4‐nitrophenyl acetate (NA) in 10% (v/v) CH3CN at 298 K, I = 0.10 mol dm?3 KNO3 at pH range 6.5–8.2 and 8.5–10, respectively. Kinetic studies show that the second‐order rate constants of NA‐hydrolysis catalyzed by complexes ZnL, Zn3L, and Zn3LH?1 are 0.021, 0.0082, and 0.342 mol?1 dm3 s?1, respectively. In all the cases, the pH‐dependent observed first‐order rate constant, kobs, shows sigmoidal pH–rate profile. The 1:1 complex ZnL–H2O undergoes NA hydrolysis by direct rate‐determining hydrolysis to produce 4‐nitrophenol(ate) (NP?) and ZnL(OOCCH3); while in the 3:1 system the oxygen atom of acetic group forms a H‐bond with the Zn(II)‐bound water of the second branch of tripod indicating that the polynuclear centers are associated and bi‐functional. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 41–48 2004  相似文献   
1000.
利用能量为 1 6 7— 1 75MeV的35Cl束流 ,通过16 0 Gd(35Cl,5n)熔合蒸发反应研究了190 Tl的高自旋态能级结构 .实验建立了190 Tl基于πh9/2    νi13/2 组态的转动带 .在束测量结果和194 Biα衰变的α γ测量结果确定地指定了190 Tl的πh9/2    νi13/2 转动带的自旋值 .基于自旋指定 ,发现了190 Tl的πh9/2    νi13/2 扁椭球转动带在低自旋时旋称反转 .这是首次在基于πh9/2    νi13/2 组态的扁椭球转动带中观测到旋称反转 .考虑了质子 -中子剩余相互作用的粒子 -转子模型能够解释πh9/2    νi13/2 扁椭球转动带的低自旋旋称反转 .  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