全文获取类型
收费全文 | 42286篇 |
免费 | 3211篇 |
国内免费 | 2602篇 |
专业分类
化学 | 25160篇 |
晶体学 | 225篇 |
力学 | 1456篇 |
综合类 | 711篇 |
数学 | 7805篇 |
物理学 | 12742篇 |
出版年
2023年 | 286篇 |
2022年 | 1757篇 |
2021年 | 1559篇 |
2020年 | 850篇 |
2019年 | 935篇 |
2018年 | 712篇 |
2017年 | 827篇 |
2016年 | 1062篇 |
2015年 | 1089篇 |
2014年 | 1501篇 |
2013年 | 2556篇 |
2012年 | 1672篇 |
2011年 | 1948篇 |
2010年 | 1790篇 |
2009年 | 2262篇 |
2008年 | 2366篇 |
2007年 | 2531篇 |
2006年 | 2028篇 |
2005年 | 1323篇 |
2004年 | 1271篇 |
2003年 | 1279篇 |
2002年 | 3660篇 |
2001年 | 1363篇 |
2000年 | 871篇 |
1999年 | 791篇 |
1998年 | 733篇 |
1997年 | 590篇 |
1996年 | 628篇 |
1995年 | 542篇 |
1994年 | 535篇 |
1993年 | 552篇 |
1992年 | 551篇 |
1991年 | 379篇 |
1990年 | 324篇 |
1989年 | 285篇 |
1988年 | 307篇 |
1987年 | 216篇 |
1986年 | 217篇 |
1985年 | 333篇 |
1984年 | 265篇 |
1983年 | 163篇 |
1982年 | 306篇 |
1981年 | 482篇 |
1980年 | 432篇 |
1979年 | 478篇 |
1978年 | 385篇 |
1977年 | 285篇 |
1976年 | 241篇 |
1974年 | 110篇 |
1973年 | 190篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Karol Jankowski Danuta Rutkowska Andrzej Rutkowski 《Theoretical chemistry accounts》1978,48(2):119-125
It is shown that the Galerkin-Petrov method if applied in a controlled way yields reliable results for excited states of the
same symmetry classifications as the ground state. Computations are performed for the 21
S and 31
S states of He. The problem of optimizing nonlinear parameters of the basis functions by means of the GP method is discussed.
A special optimization scheme is suggested and numerically illustrated for someS states of He. 相似文献
972.
Peter D. Dacre 《Theoretical chemistry accounts》1976,43(2):197-205
The direct CI method, which avoids explicit calculation of the Hamiltonian matrix, is presented in a new form. The method is linked with Davidson's algorithm for iterative evaluation of the ground state eigenvector. The viability of the method is indicated by the test calculations on water which are described. 相似文献
973.
In contrast to the high precision with which masses of atoms and molecules can be specified, their external dimensions remain intrinsically fuzzy. Attention is directed to the difference between measurements of interatomic separations within molecules, that in many instances are cited with error bars of +/– 0.002 Å, and the available approximate magnitudes of over-all sizes, needed for estimating packing densities (in solids or liquids). The following account, is a critical examination of the underlying concepts and of the diversity of data in the literature, regarding internal dimensions (bond lengths), overall extensions, cross-sectional areas, and volumes of molecules that may be derived from a variety of experiments. Historical markers of the evolution of the underlying theories and experiments are included. 相似文献
974.
The kinetic features of radical polymerization of styrene in the presence of primary and secondary aliphatic amines combined
with benzoyl peroxide and the molecular-mass characteristics of the resulting polymers were studied. In the presence of peroxide
initiators, aliphatic amines, as potential sources of stable aminoxyl radicals, provide the synthesis of polystyrene with
a controlled molecular mass without gel effect at a relatively high rate.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 159–164, January, 2007. 相似文献
975.
J.S. Yadav B.V.Subba Reddy B. Padmavani Ch. Venugopal A.Bhaskar Rao 《Tetrahedron letters》2007,48(26):4631-4633
Enzymatic kinetic resolution of (±)-hydroxytetrahydropyrans has been achieved for the first time by means of lipase-mediated transesterification to afford optically active (2S,4R)-tetrahydropyranyl acetates and (2R,4S)-tetrahydropyranols in excellent yields with high enantioselectivity. Absolute configurations of the tetrahydropyranyl acetates were assigned as (S) by chemical correlation. 相似文献
976.
Veronika Gemmer-Colos und Rolf Neeb 《Fresenius' Journal of Analytical Chemistry》1978,293(4):290-294
Zusammenfassung Kleine Mengen Ni, Cu und Zn in wäßrigen Lösungen können nach Ausschütteln ihrer Dipropyldithiocarbamatochelate gas-chromatographisch bestimmt werden. Arbeitsbedingungen für den 0,01–1 ppm-Bereich werden angegeben. Die Reproduzierbarkeit der Bestimmung wird durch Zusatz eines inneren Standards verbessert.
Dialkyldithiocarbamates as reagents for the gas-chromatographic determination of metalsII. Determination of zinc, copper and nickel as dipropyldithiocarbamato chelates after extraction from aqueous solution
Summary Small amounts of Ni, Cu and Zn in aqueous solutions can be determined by gas chromatography after extraction of their dipropyldithiocarbamatochelates. Working details for the 0.01–1 ppm range are reported. Reproducibility is markedly improved by addition of an inner standard.
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbands der chemischen Industrie unterstützt. 相似文献
977.
The Saccharomyces strains uvarum, montuliensis, bayanus, capensis and florentinus were grown in liquid media prepared from a 1% aqueous glucose solution to which 0.05% of ammonium sulfate or urea were added as the only nitrogen supply. The amino acids exuded during incubation were isolated by cation exchange and derivatized as the corresponding N,O-heptafluorobutyryl isopropyl esters. Separation was achieved on a highly deactivated glass capillary column coated with OV-101. A characteristic amino acid profile was obtained for each of the species studied, allowing the construction of a chemotaxonomic tree, on the basis of present or absent acids. 相似文献
978.
979.
The isolation and structure elucidation of xyloccensin L from the stem bark of Xylocarpus granatum is described. Xyloccensin L is a highly oxidized heptacyclic A, B, D-seco limonoid with an α-8, 30-epoxy ring and a rare 1, 29 oxygen bridge. 相似文献
980.
自行研制了电子碰撞离子化的飞行时间型质量分析器(TOFMS),用于物质的化学分析。用研制的TOFMS测量了Ar离子化的飞行时间谱和离子的部分电离截面积比与碰撞电子能量的依赖关系,将它与Stepshan等人的实验结果进行了比较。 相似文献