全文获取类型
收费全文 | 1828篇 |
免费 | 98篇 |
国内免费 | 22篇 |
专业分类
化学 | 1360篇 |
晶体学 | 16篇 |
力学 | 36篇 |
数学 | 303篇 |
物理学 | 233篇 |
出版年
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 42篇 |
2020年 | 51篇 |
2019年 | 49篇 |
2018年 | 41篇 |
2017年 | 50篇 |
2016年 | 86篇 |
2015年 | 74篇 |
2014年 | 80篇 |
2013年 | 124篇 |
2012年 | 132篇 |
2011年 | 164篇 |
2010年 | 102篇 |
2009年 | 82篇 |
2008年 | 122篇 |
2007年 | 107篇 |
2006年 | 105篇 |
2005年 | 82篇 |
2004年 | 76篇 |
2003年 | 48篇 |
2002年 | 46篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 22篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 28篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1958年 | 6篇 |
1957年 | 2篇 |
排序方式: 共有1948条查询结果,搜索用时 203 毫秒
171.
172.
Ivan Poto?ňák Michal Dunaj-Jur?o Du?an Miklo? Lothar J?ger 《Monatshefte für Chemie / Chemical Monthly》2001,22(6):315-327
The structure of the new compound [Cu(bpy)2N(CN)2]C(CN)3 (6) is compared with thestructures of six copper(II) coordination compounds with phenanthroline or bipyridine ligands and N-donor pseudohalide anions: [Cu(phen)2NCS]C(CN)3 (1), [Cu(bpy)2NCS]C(CN)3 (2), [Cu(phen)2NCS]ONC(CN)2 (3), [Cu(phen)2N(CN)2]C(CN)3 (4), [Cu(bpy)2C(CN)3]C(CN)3 (5), and [Cu(bpy)2NCO]C(CN)3 (7). The Cu(II) atoms in all above compounds are five-coordinated with an N-donor atom of the pseudohalide anion located in the equatorial plane of a deformed trigonal bipyramid. The shape of the coordination polyhedra and the degree of trigonal bipyramidal distortion towards a tetragonal pyramid are discussed and described using one electronic and several structural criteria which are discussed and compared. 相似文献
173.
A Heuristic for Moment-Matching Scenario Generation 总被引:1,自引:0,他引:1
Kjetil Høyland Michal Kaut Stein W. Wallace 《Computational Optimization and Applications》2003,24(2-3):169-185
In stochastic programming models we always face the problem of how to represent the random variables. This is particularly difficult with multidimensional distributions. We present an algorithm that produces a discrete joint distribution consistent with specified values of the first four marginal moments and correlations. The joint distribution is constructed by decomposing the multivariate problem into univariate ones, and using an iterative procedure that combines simulation, Cholesky decomposition and various transformations to achieve the correct correlations without changing the marginal moments.With the algorithm, we can generate 1000 one-period scenarios for 12 random variables in 16 seconds, and for 20 random variables in 48 seconds, on a Pentium III machine. 相似文献
174.
A direct tetraalkylation of thiacalix[4]arenes using procedures well established in ‘classical’ calixarene chemistry usually gives the 1,3-alternate conformers as the main product (n-PrI/K2CO3/acetone) while the cone conformers are obtained only in very poor yields (n-PrI/NaH/DMF). Surprisingly, the so far almost inaccessible cone conformers can be prepared in high yields using the two-step procedure: dialkylation-dialkylation, opening the way for their further utilisation in supramolecular chemistry. 相似文献
175.
Summary Part I of this paper is concerned with the theory of differential invariants of a symmetric affine connection and a general
linear connection of theK?nig type. Part II deals with a geometry in which the components of the affine connection areChristoffel symbols, and the general linear connection is of a special sort. This section can be considered in part as an extension of
theEinstein-Mayer (5) geometry, 相似文献
176.
Michal Fećkan 《Applications of Mathematics》1997,42(5):369-393
Ordinary differential inclusions depending on small parameters are considered such that the unperturbed inclusions are ordinary differential equations possessing manifolds of periodic solutions. Sufficient conditions are determined for the persistence of some of these periodic solutions after multivalued perturbations. Applications are given to dry friction problems. 相似文献
177.
178.
Ale Ricka Libor Dostl Roman Jambor Vladimír Buchta Jirí Brus Ivana Císarov Michal Holcapek Jaroslav Holecek 《应用有机金属化学》2002,16(6):315-322
A set of seven [2,6‐bis(dimethylaminomethyl)phenyl]diphenyltin(IV) ({[(CH3)2NCH2]2(C6H3)}(C6H5)2Sn+X?) ionic organotin(IV) compounds (X = Br, NO3, CN, SCN, SeCN, BF4 and PF6) has been prepared and characterized by electrospray ionization mass spectrometry, 1H NMR spectroscopy in CDCl3,119Sn NMR in CDCl3 and DMSO‐d6 solution, as well as by 13C and 119Sn CP/MAS NMR spectroscopy and X‐ray diffraction techniques in the solid state. The in vitro antifungal activity of these water‐soluble ionic organotin(IV) compounds was compared with starting compounds and the antifungal drugs currently in clinical use. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
179.
Michal Maymon Erez Michal Yerushalmy 《International Journal of Computers for Mathematical Learning》2006,11(3):271-299
This paper describes a study of the cognitive complexity of young students, in the pre-formal stage, experiencing the dragging
tool. Our goal was to study how various conditions of geometric knowledge and various mental models of dragging interact and
influence the learning of central concepts of quadrilaterals. We present three situations that reflect this interaction. Each
situation is characterized by a specific interaction between the students’ knowledge of quadrilaterals and their understanding
of the dragging tool. The analyses of these cases offer a prism for viewing the challenge involved in changing concept images
of quadrilaterals while lacking understanding of the geometrical logic that underlies dragging. Understanding dragging as
a manipulation that preserves the critical attributes of the shape is necessary for constructing the concept images of the
shapes. 相似文献
180.
Proteinaceous microspheres of BSA (Bovine Serum Albumin) containing an anticancer drug, Taxol (paclitaxel) were fabricated using a sonochemical procedure and then assayed for chemical and biological activity. The sonochemical reaction did not compromise the drug, which became encapsulated in the BSA microspheres. The amount of the anticancer drug in the microspheres was determined by HPLC. Anticancer activity of the proteinaceous microspheres encapsulating the Taxol was tested on Mouse Multiple Myeloma cell line MPC-11. The influence of the Taxol microspheres on the cancer cells was different from pristine Taxol. It was found that Taxol in combination with the organic solvent causes the death of cancer cells. 相似文献