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   30746篇
  免费   4992篇
  国内免费   4231篇
化学   21877篇
晶体学   379篇
力学   2032篇
综合类   299篇
数学   3613篇
物理学   11769篇
  2024年   84篇
  2023年   521篇
  2022年   955篇
  2021年   1033篇
  2020年   1063篇
  2019年   1114篇
  2018年   1015篇
  2017年   960篇
  2016年   1515篇
  2015年   1467篇
  2014年   1869篇
  2013年   2270篇
  2012年   2653篇
  2011年   2763篇
  2010年   2032篇
  2009年   2011篇
  2008年   2244篇
  2007年   2006篇
  2006年   1871篇
  2005年   1647篇
  2004年   1246篇
  2003年   1020篇
  2002年   1137篇
  2001年   856篇
  2000年   731篇
  1999年   615篇
  1998年   465篇
  1997年   382篇
  1996年   395篇
  1995年   350篇
  1994年   266篇
  1993年   209篇
  1992年   210篇
  1991年   193篇
  1990年   162篇
  1989年   141篇
  1988年   121篇
  1987年   87篇
  1986年   66篇
  1985年   59篇
  1984年   37篇
  1983年   32篇
  1982年   18篇
  1981年   18篇
  1980年   16篇
  1979年   5篇
  1978年   16篇
  1977年   3篇
  1976年   4篇
  1957年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
为了监测 2型糖尿病人血清钙、镁和甲状腺激素含量 ,分析其临床意义及相关性 ,应用放射免疫分析法测定了 1 1 5例 2型糖尿病及 1 5 0例健康人血清甲状腺激素含量。同时用美国杜邦RXL自动生化仪测定了其血清钙、镁含量。结果表明 ,在 2型糖尿病伴有明显并发症者血镁、FT3水平明显降低 (P <0 0 5 ) ,钙镁两种元素与甲状腺激素水平无明显相关性。 2型糖尿病患者适当补镁对预防其并发症是有益的 ,测定FT3 等可作为判断 2型糖尿病严重程度和估计预后的参考指标。  相似文献   
32.
33.
发生氢化物原子吸收测定农用硝酸稀土中微量砷   总被引:3,自引:0,他引:3  
  相似文献   
34.
Using the method of diagonalization, in which zero-field wavefunctions from a potential model are chosen as a basis, we calculate positions and widths of anticrossings for highly excited Stark states of Rb with principal quantum number n up to 49. We obtain the theoretical positions and widths in good agreement with available experimental values, and we present scaling laws of the field positions and widths of anticrossings that can be used to provide information for future experiments.  相似文献   
35.
The ionic conductivity of polymer electrolytes and their interfacial contact with dye-attached TiO2 particles were enhanced markedly by the addition of amorphous oligomer into polymer electrolytes, resulting in very high overall energy conversion efficiency.  相似文献   
36.
The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples.  相似文献   
37.
Yong He  H.V. Rasika Dias 《Tetrahedron》2006,62(37):8755-8769
N-Alkyl acryloylamides derived from o-aminobenzaldehyde derivatives react with N-alkyl glycine derivatives to provide cis-fused pyrrole[3,2-c]quinolones in moderate yield and high diastereoselectivity. These same substrates engage in a tandem Michael-Mannich pathway on treatment with a secondary amine, providing corresponding quinolone derivatives. The elaboration of a pyrroloquinolone derivative via addition of an in situ generated functionalized copper acetylide to an in situ generated iminium ion provided the C2-substituted derivative. Global deprotection and reduction of the alkyne afford the tricyclic triamine core (as the HCl salt) found in martinellic acid.  相似文献   
38.
Three new β-dihydroagarofuran sesquiterpene polyol esters,one alkaloid andtwo non-alkaloids,were isolated from the MeOH extract of seed oil of Celastrus angulatus.Their structures were elucidated on the basis of UV,IR,mass,NOE difference,~1H-NMR,~(13)C-NMR and ~1H-~(13)C long-range correlation spectroscopy.  相似文献   
39.
Metalloprotein tethered CdSe nanoparticles have been generated to provide selective and reagentless maltose biosensing. As opposed to cell or protein detection by semiconducting nanoparticle bioconjugates, a modular method for small-molecule detection using semiconducting nanoparticle bioconjugates has been difficult. Here we report a method for reagentless protein-based semiconducting nanoparticle biosensors. This method uses Ru(II) complex-CdSe nanoparticle interactions and the maltose-induced conformation changes of maltose binding protein to alter the CdSe nanoparticle fluorescence emission intensity. In this proof-of-principle system, the maltose-induced protein conformation changes alter the Ru(II) complex-CdSe nanoparticle interaction, which increases the CdSe emission intensity. Altered CdSe emission intensity effects are best described as electron transfer from the Ru(II) complex to the CdSe excited state forming the nonfluorescent CdSe anion. Four surface-cysteine, Ru(II) complex-attached maltose-binding proteins have been studied for maltose dependent alteration of CdSe emission intensities. With 3.0-3.5 nm diameter CdSe nanoparticles, all ruthenated maltose-binding proteins display similar maltose-dependent increases (1.4-fold) in CdSe emission intensity and maltose binding affinities (KA = 3 x 106 M-1). For these four systems, the only difference was the sample-to-sample variation in maltose-dependent responses. Thus, very few surface cysteine mutations need to be examined to find a successful biosensor, as opposed to analogous systems using organic fluorophores. This strategy generates a unimolecular, or reagentless, semiconducting nanoparticle biosensor for maltose, which could be applied to other proteins with ligand-dependent conformation changes.  相似文献   
40.
Ni(OH)2 hollow microspheres with beta-Ni(OH)2 nanosheets as the in situ formed building units were fabricated via a novel template-free approach in a strong alkaline solution of glycine, and can be converted into NiO hollow microspheres by a thermal decomposition 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