全文获取类型
收费全文 | 6218篇 |
免费 | 163篇 |
国内免费 | 134篇 |
专业分类
化学 | 4769篇 |
晶体学 | 18篇 |
力学 | 144篇 |
综合类 | 11篇 |
数学 | 600篇 |
物理学 | 973篇 |
出版年
2024年 | 8篇 |
2023年 | 75篇 |
2022年 | 94篇 |
2021年 | 72篇 |
2020年 | 88篇 |
2019年 | 130篇 |
2018年 | 94篇 |
2017年 | 114篇 |
2016年 | 77篇 |
2015年 | 70篇 |
2014年 | 150篇 |
2013年 | 185篇 |
2012年 | 110篇 |
2011年 | 151篇 |
2010年 | 125篇 |
2009年 | 132篇 |
2008年 | 98篇 |
2007年 | 125篇 |
2006年 | 79篇 |
2005年 | 77篇 |
2004年 | 86篇 |
2003年 | 56篇 |
2002年 | 49篇 |
2001年 | 42篇 |
2000年 | 25篇 |
1999年 | 37篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1986年 | 2篇 |
1985年 | 685篇 |
1984年 | 466篇 |
1983年 | 410篇 |
1982年 | 436篇 |
1981年 | 330篇 |
1980年 | 252篇 |
1979年 | 221篇 |
1978年 | 195篇 |
1977年 | 205篇 |
1976年 | 241篇 |
1975年 | 212篇 |
1974年 | 194篇 |
1973年 | 187篇 |
排序方式: 共有6515条查询结果,搜索用时 21 毫秒
131.
Yaujen Wang Krishnan Rajeshwar Richard N. Nottenburg Joel B. Dubow 《Thermochimica Acta》1979,30(1-2):141-151
The thermal diffusivity values of eight minerals that are commonly associated with oil shales of the Green River formation have been measured by the laser flash technique. Data are presented in the temperature range 25–500°C for quartz, dolomite, calcite, plagioclase, analcite, pyrite, potassium feldspar and low albite. A comparison of the thermal conductivities of some of these minerals, calculated from experimentally measured thermal diffusivity and density, with the experimental values reported in the literature reveals good agreement. Trends in the variation of thermal diffusivity with temperature and anisotropic effects in thermophysical parameters are discussed from the point of view of grain boundary effects in these polycrystalline mineral aggregates. 相似文献
132.
The enzyme catalysed oxidation of ferrocene and some substituted ferrocenes to the corresponding ferricinium ions by hydrogen peroxide in the presence of native or immobilized horseradish peroxidase has been studied. Initial and maximum rates of oxidation have been determined. It was found that the oxidation was independent of the hydrogen peroxide concentration. The oxidation of ferrocene was effected also by horseradish peroxidase in a coupled system with glucose oxidase in the absence of any added hydrogen peroxide. 相似文献
133.
The reaction of KCN with Al(CH3)3 to form K[Al(CH3)3CN] is greatly facilitated by the presence of an aromatic solvent: for p-xylene a solid complex, K[Al(CH3)3CN]·C6H4(CH3)2, has been isolated. The crystal structure of potassium cyanotrimethylaluminate has been determined from three-dimensional X-ray data measured by counter methods. K[Al(CH3)3CN] crystallizes in the monoclinic space group C2/c with cell dimensions a = 19.902(7), b = 9.211(4), c = 9.615(4) Å, β = 107.74(5)°, and pcalcd. = 1.09 g cm?1 for Z = 8. Least squares refinement gave a conventional weighted R factor of 4.9% for 807 independent reflections. The monomeric [Al(CH3)3CN]? units possess no crystallographic symmetry, and the packing in the unit cell is such that the nitrogen atoms on three such units approach the potassium atom to within 3.11 Å. The average aluminum-methyl carbon bond distance is 1.971 (7) Å, while the aluminum-cyano carbon distance is 2.047 (7) Å. This significant lengthening is attributed to partial electron deficiency in the aluminum-cyano carbon bond. 相似文献
134.
The infrared spectra, transmittance, and polarized reflectance of Cs3CoCl5 are reported. The group theoretical analysis was executed and a vibrational assignment proposed on the basis of D4h symmetry. Factor group and site effects are discussed. 相似文献
135.
Sorin Staicu Ilie G Dinulescu Filip Chiraleu Margaret Avram 《Journal of organometallic chemistry》1976,113(4):C69-C72
Coupling of diarylacetylenes with alkenes in the presence of dichlorobis(benzonitrile)palladium gives chloro(syn-1-chloro-anti-1-aryl-syn-3-alkyl)-π-allylpalladium complexes. 相似文献
136.
The theory of first-order kinetic collection efficiencies at the double channel electrode is developed for the following two schemes: (I) A±n1e→B (at the generator electrode), B→kP (in solution), B±n2e→Y (at the detector electrode), (II) A±n1e→B, B→kA, B±n2e→Y. The exact expressions for the kinetic collection efficiencies are obtained as ascending and asymptotic series with respect to the kinetic parameter. Further, approximate formulae in exponential forms are given, which hold within an error of about 2% for conventional electrode geometry. Finally, the validity of the approximate procedure, which has been used previously to obtain the kinetic collection efficiencies for fast homogeneous reactions, is discussed in comparison with the present theory. 相似文献
137.
The technique of three-phase partitioning (TPP) was used to purify the green fluorescent protein (GFP) in a single step. TPP uses a combination of ammonium sulphate and tert-butanol to precipitate proteins from their crude extracts. In the first round of TPP with 20% ammonium sulphate saturation at the ratio of crude to tert-butanol 1:1 (v/v), most of the GFP remains in the lower aqueous phase. When subjected to a second round of TPP with 60% ammonium sulphate saturation at the ratio of crude to tert-butanol 1:2 (v/v) gives 78% recovery of GFP with a 20-fold purification. The sodium dodecyl sulphate-polyacrylamide gel electrophoretic (SDS-PAGE) analysis of purified preparation shows single band. The fluorescence excitation and emission spectra agreed with values reported in literature. 相似文献
138.
Solutions of CoII salts of organic acids in primary amines absorb molecular oxygen rapidly and irreversibly forming μ-dioxygen—cobalt complexes. Thermolysis leads to a homopolar cleavage of the OO bond with subsequent radical reactions involving ligand amine. After thermolysis the capacity of oxygen uptake is reestablished (catalysis). 相似文献
139.
The proton chemical shift tensor of the hydroxyl proton in calcium hydroxide has been measured using multiple pulse NMR techniques. The tensor is axially symmetric with susceptibility corrected components σtT = ?9.3 ± 1 ppm and ppm relative to TMS. 792 79 相似文献
140.
A flame atomic-absorption spectroscopy method for determination of nickel in the serum of occupationally exposed subjects has been developed. Trichloroacetic add is utilized for precipitating proteins and freeing bound nickel; sodium diethyldithiocarbamate is used as complexing agent and isopropyl acetate as the solvent for extraction. The method is characterized by good accuracy, precision and sensitivity, over a concentration range up to about 20 ng/ml. Calcium, which is present in serum in great excess with respect to typical nickel concentrations, does not interfere in the determination of the latter. 相似文献