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   10638篇
  免费   1735篇
  国内免费   2085篇
化学   8186篇
晶体学   127篇
力学   643篇
综合类   152篇
数学   1358篇
物理学   3992篇
  2024年   40篇
  2023年   263篇
  2022年   475篇
  2021年   486篇
  2020年   529篇
  2019年   515篇
  2018年   399篇
  2017年   417篇
  2016年   578篇
  2015年   585篇
  2014年   626篇
  2013年   862篇
  2012年   786篇
  2011年   884篇
  2010年   660篇
  2009年   618篇
  2008年   711篇
  2007年   589篇
  2006年   549篇
  2005年   512篇
  2004年   422篇
  2003年   361篇
  2002年   411篇
  2001年   327篇
  2000年   279篇
  1999年   238篇
  1998年   182篇
  1997年   137篇
  1996年   155篇
  1995年   115篇
  1994年   135篇
  1993年   101篇
  1992年   74篇
  1991年   95篇
  1990年   90篇
  1989年   42篇
  1988年   40篇
  1987年   30篇
  1986年   35篇
  1985年   38篇
  1984年   15篇
  1983年   20篇
  1982年   9篇
  1981年   8篇
  1980年   4篇
  1979年   3篇
  1971年   1篇
  1957年   3篇
  1936年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Some novel beta-biarylacryl ferrocene derivatives were synthesized via Pd-catalytic Suzuki cross-coupling reactions of beta-(2-bromophenyl)acrylferrocene and arylboronic acids. The structures were determined with elemental analyses, IR spectra, and (1)H-NMR spectra.  相似文献   
152.
The distribution of the chemical states of tellurium isotopes produced by252Cf spontaneous fission, collected separately in the matrixes of NaCl, Kl, NaF, CH3COONa·3H2O, Na2SO4 and NaNO3 crystals have been investigated. Two chemical states of tellurium isotopes maintained in these matrixes are Te(IV) and Te(VI). The relationships between the distribution of the chemical states of tellurium isotopes and the produced mode of tellurium, the chemical properties of collection matrixes, the time for collecting fission fragments are studied and the possible mechanism of the interactions of the fission products and the matrixes is discussed. The results show that the distribution of chemical states of tellurium isotopes depends on the chemical properties of the collection matrixes mainly.  相似文献   
153.
Qi L  Danielson ND 《Electrophoresis》2003,24(12-13):2070-2075
Two reactions, catalyzed by lactate oxidase (LO) and peroxidase, are initiated by a single injection of the enzymes and the substrate 2,2'-azino-bis(3-ethylene-thiazoline-6-sulfonic acid) (ABTS) into the capillary previously filled with the sample (lactate or lactate-oxalate mixture) and the run buffer containing NADH. The oxidized ABTS product upon reaction with NADH is converted to NAD(+) which is separated and detected in less than 2 min at 266 nm with a sample throughput of 7 min (including wash steps between samples). Simplex trade mark software is used to optimize the enzyme concentrations and reaction temperature. Consumption of the more expensive LO enzyme is only 1.4 x 10(-3) U per assay assuming 27 nL per injection. Linearity is established within the range from 0.0025 to 1 mM with R(2) of 0.9982. Recoveries of lactate from five spiked serum samples averaged 101%. Application of this method for the determination of oxalate as an inhibitor of LO is demonstrated.  相似文献   
154.
A series of novel phenoxy-phosphinimine ligands (L): L = 2-(Ph2PNR), 4, 6-(CMe3)2-C6H2OH [2, R = SiMe3; 3, R = Ph] have been prepared in the yield of 65-71%. And bis(phenoxy-phosphinimide) group 4 complexes of the type L2MCl2 [4, M = Ti, R = SiMe3; 5, M = Zr, R = SiMe3; 6, M = Ti, R = Ph; 7, M = Zr, R = Ph] have been synthesized by the reaction of the ligands with TiCl4 and ZrCl4. The structure of complex 7 has been determined by X-ray crystallography. The complexes 4-7 showed inactive to ethylene polymerization in the presence of modified methylaluminoxane (MMAO) and i-Bu3Al/Ph3CB(C6 F5)4. These results should be caused by overdoing the steric congestion around central metal.  相似文献   
155.
A new ursane‐type nortriterpenoid, adenanthusone (=(11α,12α)‐4‐demethyl‐11,12‐epoxy‐3,13‐dihydroxy‐2‐oxoursa‐3,20(30)‐diene‐28‐oic acid γ‐lactone; 1 ) was isolated from Isodon adenanthus. Its structure was determined by NMR spectra and X‐ray crystallographic diffraction analysis. The biogenetic implication of the nortriterpene is discussed.  相似文献   
156.
157.
158.
SnNb2O6 and Sn2Nb2O7 nanosheets were synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. Compared with Sn2Nb2O7 and the previously reported pure Sn-based anode materials, the SnNb2O6 electrode exhibited outstanding cycling performance.  相似文献   
159.
ET is one of the most famous electron-donor molecules, which forms charge-transfer complexes (abbr. CT-complexes) with various types of counterions. These complexes have received intense attention because a wide range of physical properties such as conductivity and superconductivity1, ferromagnetism2-4 and nonlinear optical properties5 was found in these materials. Although the majority of the ET-based CT-complexes were prepared by combining with inorganic counterions, CT-complexes with o…  相似文献   
160.
A new ligand, 2-carboxybenzaldehyde-(4’-hydroxy)benzoylhydrazone(H2L) and its ZnII and NiII complexes have been synthesized and characterized on the basis of elemental analyses, molar conductivities, 1H-NMR, IR spectra and thermal analyses. In addition, DNA-binding properties of these two metal complexes were investigated using spectrometric titrations, ethidium bromide displacement experiments, and viscosity measurements. The results show that the two complexes, especially the NiII complex, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of the ZnII and NiII complexes with DNA are 2.46 × 105 and 7.94 × 105 M −1, 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