全文获取类型
收费全文 | 7957篇 |
免费 | 1562篇 |
国内免费 | 501篇 |
专业分类
化学 | 4886篇 |
晶体学 | 655篇 |
力学 | 299篇 |
综合类 | 47篇 |
数学 | 127篇 |
物理学 | 4006篇 |
出版年
2024年 | 17篇 |
2023年 | 54篇 |
2022年 | 121篇 |
2021年 | 153篇 |
2020年 | 243篇 |
2019年 | 210篇 |
2018年 | 222篇 |
2017年 | 273篇 |
2016年 | 480篇 |
2015年 | 348篇 |
2014年 | 416篇 |
2013年 | 1127篇 |
2012年 | 456篇 |
2011年 | 483篇 |
2010年 | 398篇 |
2009年 | 457篇 |
2008年 | 422篇 |
2007年 | 528篇 |
2006年 | 460篇 |
2005年 | 415篇 |
2004年 | 343篇 |
2003年 | 328篇 |
2002年 | 301篇 |
2001年 | 197篇 |
2000年 | 184篇 |
1999年 | 200篇 |
1998年 | 206篇 |
1997年 | 146篇 |
1996年 | 139篇 |
1995年 | 133篇 |
1994年 | 93篇 |
1993年 | 71篇 |
1992年 | 53篇 |
1991年 | 38篇 |
1990年 | 54篇 |
1989年 | 25篇 |
1988年 | 42篇 |
1987年 | 20篇 |
1986年 | 24篇 |
1985年 | 15篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Chemical bonding in isolated molecules and crystals of zwitterionic pentacoordinate silicon chelates
The electronic structures of a number of zwitterionic pentacoordinate silicon chelates were investigated using the results of X-ray diffraction studies and quantum-chemical calculatoins by the MPW1PW91/6-311G(d) method. The topological analysis of the electron density distribution function and the study in the framework of the natural bond orbital partitioning scheme showed that the character of chemical bonding in the axial fragments of the molecules under consideration changes from dative to three-center, four-electron as the silicon atom assumes a trigonal-bipyramidal coordination. 相似文献
14.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
15.
We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen–Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non‐linear. We employ two‐scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
T. K. Solovykh 《Journal of Applied Spectroscopy》1997,64(5):654-657
The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra
of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on
the optical absorption of orthoferrites that are promising for magnetooptics is studied.
Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072,
Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997. 相似文献
17.
18.
《Journal of Chemical Sciences》2005,117(5):525-531
The silicon atom may increase its coordination number to values greater than four, to form pentacoordinated compounds. It
has been observed experimentally that, in general, pentacoordinated compounds show greater reactivity than tetracoordinated
compounds. In this work, density functional theory is used to calculate the global softness and the condensed softness of
the silicon atom for SiH
n
F4−n
and SiH
n
F
5−n
1−
. The values obtained show that the global and condensed softness are greater in the pentacoordinated compounds than in the
tetracoordinated compounds, a result that explains the enhanced reactivity. If the results are analysed through a local version
of the hard and soft acids and bases principle, it is possible to suggest that in nucleophilic substitution reactions, soft
nucleophiles preferably react with SiH
n
F
5−n
1−
, and hard nucleophiles with SiH
n
F4−n
. 相似文献
19.
20.