全文获取类型
收费全文 | 3302篇 |
免费 | 107篇 |
国内免费 | 16篇 |
专业分类
化学 | 2375篇 |
晶体学 | 36篇 |
力学 | 30篇 |
数学 | 135篇 |
物理学 | 849篇 |
出版年
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 42篇 |
2019年 | 51篇 |
2018年 | 26篇 |
2017年 | 28篇 |
2016年 | 56篇 |
2015年 | 61篇 |
2014年 | 70篇 |
2013年 | 143篇 |
2012年 | 158篇 |
2011年 | 171篇 |
2010年 | 108篇 |
2009年 | 112篇 |
2008年 | 170篇 |
2007年 | 155篇 |
2006年 | 190篇 |
2005年 | 136篇 |
2004年 | 157篇 |
2003年 | 128篇 |
2002年 | 106篇 |
2001年 | 87篇 |
2000年 | 66篇 |
1999年 | 42篇 |
1998年 | 27篇 |
1997年 | 31篇 |
1996年 | 49篇 |
1995年 | 48篇 |
1994年 | 32篇 |
1993年 | 48篇 |
1992年 | 56篇 |
1991年 | 42篇 |
1990年 | 30篇 |
1989年 | 39篇 |
1988年 | 42篇 |
1987年 | 35篇 |
1986年 | 28篇 |
1985年 | 73篇 |
1984年 | 58篇 |
1983年 | 40篇 |
1982年 | 49篇 |
1981年 | 41篇 |
1980年 | 39篇 |
1979年 | 35篇 |
1978年 | 38篇 |
1977年 | 36篇 |
1976年 | 33篇 |
1975年 | 29篇 |
1973年 | 30篇 |
1966年 | 17篇 |
排序方式: 共有3425条查询结果,搜索用时 62 毫秒
91.
Antianoxic action and active constituents of evodiae fructus 总被引:1,自引:0,他引:1
J Yamahara T Yamada T Kitani Y Naitoh H Fujimura 《Chemical & pharmaceutical bulletin》1989,37(7):1820-1822
In order to develop new drugs from natural products, constituents of natural medicines were examined for their effectiveness in the KCN-induced anoxia model in mice. Methanol extract from a Chinese medicine, evodia (fruits of Evodia rutaecarpa Benth. or E. officinalis Dode), had a significant effect in the KCN-induced anoxia model in mice and therefore the active constituents were further examined. The results indicated that the antianoxic action of evodia was found in the fraction containing evodiamine. Further analysis of the active constituent indicated that evodiamine and rutaecarpine, indole-alkaloids found in large amounts in the Chinese medicine evodia, were mainly responsible for the antianoxic action. 相似文献
92.
93.
Phenotyping of erythrocyte acid phosphatase (EAP) and esterase D (ESD) by cellulose acetate membrane isoelectric focusing (CAM-IEF) under a nonequilibrium condition is described. In an attempt to improve the method of CAM-IEF, we shortened the electrode distance to provide a higher field strength at a given (low) voltage. Various carrier ampholytes for EAP typing and various chemical separators for ESD typing were also tested. Good separations were obtained after 30 min IEF for EAP typing and 25 min for ESD typing. When applied to blood stains and stored for various periods at room temperature, the stains up to 8 months old could still be phenotyped for EAP and those up to 4 weeks old for ESD. CAM-IEF is suitable for routine forensic work of EAP and ESD phenotyping. 相似文献
94.
95.
The effects of the phenyl substituent on the dimerization of copper(II) carboxylate in the solvent extraction of copper(II) with phenylacetic acid using benzene and 1-octanol as a solvent were investigated, at 25 degrees and at the aqueous ionic strength of 0.1M (NaClO(4)). The dimerization of copper(II) phenylacetate has been found to be written as: 2CuA(2)Cu(2)A(4) in 1-octanol, and 2CuA(2)(HA)(2)Cu(2)A(4)(HA)(2) + (HA)(2) in benzene, with the dimerization constants, log K = 2.24 and log K = 4.19, respectively. It was proved that the phenyl group inhibits the formation of the dimeric copper(II) phenylacetate, and its effect is partially shielded by a methylene substituent. 相似文献
96.
Y. Yamada M. Itoh K. Egawa N. Kiriyama K. Komura K. Ueno 《Journal of Radioanalytical and Nuclear Chemistry》1992,164(1):47-57
Various f-elements are separated as anionic complexes from both acidic and alkaline solutions by precipitation with alkylpyridinium salts. The precipitates are also cationic surfactants where the simple counter-ion (e.g. nitrate or chloride) is replaced by the negatively charged complex anion of an actinide or lanthanide. The low solubility of these precipitates is explained by a strong affinity of divalent complex counter-ions of f-elements to the quaternary nitrogen. Precipitations in solutions of nitric acid allow to separate tetravalent f-elements from other metals, in alkaline carbonate solutions tetravalent and hexavalent actinides are precipitated simultaneously. The last procedure yields precipitates, which are very intimate mixtures of hexavalent and tetravalent actinides. This allows to prepare mixed oxides in a simple way. 相似文献
97.
Kotaro Hidea Hiroshi Maezawa Atsushi Ito Katsumi Kobayashi Yoshiya Furusawa Takashi Ito 《Photochemistry and photobiology》1986,44(3):417-419
The spectral throughput of a vacuum-ultraviolet irradiation system at the SOR-RING facility was examined with various combinations of aluminum-and gold-coated optical elements in a 2.2-m modified Wadsworth monochromator. We found that the optimum was a combination of an aluminum-coated collimating mirror, concave grating, and plane deflecting mirror, and a combination of a gold-coated collimating mirror, concave grating and an aluminum-coated plane deflecting mirror in the wavelength regions 190-110 nm and 110-50 nm, respectively. 相似文献
98.
Masayoshi Nakasako Masamitsu Wada Satoru Tokutomi Kotaro T. Yamamoto Jun Sakai Mikio Kataoka Fumio Tokunaga † Masaki Furuya 《Photochemistry and photobiology》1990,52(1):3-12
Abstract— The quaternary structure of pea phytochrome type I (PI) dimer in the red-light-absorbing form was studied by small-angle X-ray scattering (SAXS) technique and rotary-shadowing electron microscopy. Structural parameters for PI 114 kDa chromopeptide dimer and its tryptically digested N-terminal 59 kDa chromopeptide monomer, such as average electron density, molecular volume and the second moment of electron density distribution, were determined in terms of SAXS using the contrast variation method. Furthermore, by means of model simulation for the scattering profiles of the chromopeptides, most plausible structural models for both peptides were constructed. The distance between the chromophoric domains was estimated to be about 70 A in the resultant model for 114 kDa chromopeptide dimer. Furthermore, the model was consistent with the electron-micrographic images of both the intact PI dimer and the PI 114 kDa chromopeptide dimer, so that the N-terminal 7 kDa fragment did not significantly contribute the low-resolution images of the dimer. 相似文献
99.
The ring conformation of 2-O-methyl-1,3,4,5-tetrakis-O-tert-butyldiphenylsilyl-myo-inositol was in a twist form both in solid state and in solution. This is the first observation of a stable twist conformer induced by the introduction of bulky silyl protecting groups. 相似文献
100.
The cyclic voltammetric study of 1,10-phenanthroline—copper(II) complex was carried out in acidic buffer solution. It was found from the current—mole ratio (copper (II): 1,10-phenanthroline) relationship that the maximum coordination number of 1,10-phenanthroline—copper(II) complex was four under the present experimental condition. The reduction mechanism and kinetics of copper(II) was studied in the presence of various concentrations of 1,10-phenanthroline. 相似文献