全文获取类型
收费全文 | 8772篇 |
免费 | 655篇 |
国内免费 | 376篇 |
专业分类
化学 | 3575篇 |
晶体学 | 38篇 |
力学 | 733篇 |
综合类 | 94篇 |
数学 | 2693篇 |
物理学 | 2670篇 |
出版年
2023年 | 82篇 |
2022年 | 109篇 |
2021年 | 153篇 |
2020年 | 175篇 |
2019年 | 209篇 |
2018年 | 166篇 |
2017年 | 210篇 |
2016年 | 216篇 |
2015年 | 151篇 |
2014年 | 280篇 |
2013年 | 399篇 |
2012年 | 312篇 |
2011年 | 472篇 |
2010年 | 467篇 |
2009年 | 618篇 |
2008年 | 573篇 |
2007年 | 450篇 |
2006年 | 421篇 |
2005年 | 351篇 |
2004年 | 259篇 |
2003年 | 251篇 |
2002年 | 195篇 |
2001年 | 172篇 |
2000年 | 150篇 |
1999年 | 133篇 |
1998年 | 120篇 |
1997年 | 96篇 |
1996年 | 79篇 |
1995年 | 48篇 |
1994年 | 61篇 |
1993年 | 41篇 |
1992年 | 46篇 |
1991年 | 42篇 |
1990年 | 34篇 |
1989年 | 24篇 |
1988年 | 27篇 |
1986年 | 24篇 |
1985年 | 417篇 |
1984年 | 286篇 |
1983年 | 236篇 |
1982年 | 211篇 |
1981年 | 156篇 |
1980年 | 122篇 |
1979年 | 136篇 |
1978年 | 78篇 |
1977年 | 86篇 |
1976年 | 89篇 |
1975年 | 89篇 |
1974年 | 116篇 |
1973年 | 131篇 |
排序方式: 共有9803条查询结果,搜索用时 15 毫秒
81.
Two main properties of the subgradient mapping of convex functions are transposed for quasiconvex ones. The continuity of the functionxf(x)–1f(x) on the domain where it is defined is deduced from some continuity properties of the normal coneN to the level sets of the quasiconvex functionf. We also prove that, under a pseudoconvexity-type condition, the normal coneN(x) to the set {x:f(x)f(x)} can be expressed as the convex hull of the limits of type {N(x
n)}, where {x
n} is a sequence converging tox and contained in a dense subsetD. In particular, whenf is pseudoconvex,D can be taken equal to the set of points wheref is differentiable.This research was completed while the second author was on a sabbatical leave at the University of Montreal and was supported by a NSERC grant. It has its origin in the doctoral thesis of the first author (Ref. 1), prepared under the direction of the second author.The authors are grateful to an anonymous referee and C. Zalinescu for their helpful remarks on a previous version of this paper. 相似文献
82.
在H-ZSM-5沸石上甲醇转化为汽油的初始产物分布姜玄珍(浙江大学化学系,杭州310027)R.F.Howe(新南威尔士大学物理化学系,澳大利亚)关键词H-ZSM-5沸石,甲醇转化汽油,产物分布以氢型ZSM-5沸石作催化剂转化甲醇为汽油(MTG),在... 相似文献
83.
An intrinsic principle of least action is presented for the intrinsic dynamism of chemical reactions. Then, as the stationary trajectory, a meta-IRC (intrinsic reaction coordinate) draws a geodesic curve in a rigged Riemannian space. This establishes a geodesic law for the intrinsic dynamism. Moreover, a diagrammatic perturbation theory is formulated for the intrinsic dynamism, and a dynamical interaction between a chemically reacting system and a background system is investigated. Then, the structural stability of the system is discussed using a new concept of the dynamical potential field. An example is given in order to elucidate the present theory.Dedicated to Prof. Hermann Hartmann on the occasion of his 65th birthday. 相似文献
84.
根据出现在质谱中的各种大小的碳原子簇的相对丰度,分析了由激光产生的碳原子簇离子的统计分布,研究了这些统计分布与碳原子簇结构的关联。研究结果表明:相同构型的原子簇的相对丰度可以由同一条对数正态分布曲线来描述,由此能够获得碳原子簇构型的变化情况。质谱中分布曲线的数目对应于具有不同构型或不同结构稳定性的原子簇的数目。如果某些簇离子的谱峰明显地高出分布曲线,它们的结构应特别稳定,其成簇原子数就是所谓的“奇幻数”(magicnumber),例如在石墨质谱中的C_(60)就属于这种情况。原子簇的统计分布还与它们的生成过程有关,由此可能揭示出原子簇的产生机理。 相似文献
85.
86.
WU Xiu-Lan WANG Fen REN Qiang 《结构化学》2007,26(6):732-736
Homogeneous cordierite has been synthesized at low cost by talc-magnesite and coal gangue as the main raw materials. The mechanism of synthesizing cordierite under such a com- posing system of raw materials, and the effect of temperature on the crystal cell parameters and microstructure and thermal expansion coefficient of cordierite crystal have been studied via testing methods of XRD, SEM, etc. The result shows that the homogeneous cordierite can be synthesized by the systematic composing materials of “talc-magnesite—coal gangue—talc” with heat pre- servation at 1350 ℃ for 1 h; as the keeping time is prolonged, Al3+ and Mg2+ in cordierite crystal are replaced by a few impurity ions such as Fe3+, Fe2+, etc., and the crystal cell parameters of cordierite present an increase trend; as the high-temperature heat preservation is prolonged, the content of glassy phase in the sample is increased, its density is improved, and its thermal expansion coeffi- cient presents an increase trend. 相似文献
87.
The ab initio molecular fragment approach is applied to a characterization study of the ground state of the zwitterion of glycine. Included among the properties studied are the — conformational energy surface, the electronic structure, and the magnitude and direction of the dipole moment. The results of the present study are compared to the results of other theoretical and experimental studies.This work was supported in part by the National Science Foundation, the University of Kansas, and the Upjohn Company, Kalamazoo, Michigan 49001.NSF Trainee (1969-1972).Alfred P. Sloan Research Fellow (1971–1973). 相似文献
88.
89.
详细论述了管理评审的基本概念、如何开展管理评审工作以及中国实验室国家认可委员会的有关政策。 相似文献
90.
O. N. Babkina O. M. Chukanova E. E. Faingol"d N. M. Bravaya 《Russian Chemical Bulletin》2004,53(4):785-790
Quantitative characteristics of changes in the energy of charge transfer from -bonded ligands to metal are presented for the series of structurally similar ansa-metallocene complexes of IVB Group elements. The changes are caused by the solvation effect, replacement of -bonded chlorine ligands by methyl groups and of bridging ethylene groups by dimethylsilylene moieties, introduction of the methyl substituent into position 2 and phenyl substituent into position 4 of the indenyl system, variation of the transition metal in metallocene, and formation of complexes with polymethylalumoxane (MAO) at different AlMAO/Zr ratios. These effects are found to be additive. 相似文献