全文获取类型
收费全文 | 1587篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
化学 | 1103篇 |
晶体学 | 13篇 |
力学 | 28篇 |
数学 | 269篇 |
物理学 | 210篇 |
出版年
2022年 | 15篇 |
2021年 | 16篇 |
2020年 | 25篇 |
2019年 | 15篇 |
2018年 | 12篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 36篇 |
2013年 | 67篇 |
2012年 | 84篇 |
2011年 | 95篇 |
2010年 | 58篇 |
2009年 | 39篇 |
2008年 | 72篇 |
2007年 | 63篇 |
2006年 | 78篇 |
2005年 | 84篇 |
2004年 | 72篇 |
2003年 | 63篇 |
2002年 | 57篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 34篇 |
1992年 | 23篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 17篇 |
1970年 | 9篇 |
排序方式: 共有1623条查询结果,搜索用时 10 毫秒
21.
Gabelica V Galic N Rosu F Houssier C De Pauw E 《Journal of mass spectrometry : JMS》2003,38(5):491-501
A method for determining the equilibrium association constant of a complexation reaction A + B left harpoon over right harpoon AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A-B solutions at different concentrations C(0). The results are fitted by a non-linear least-squares procedure, with the two variable parameters being the equilibrium association constant K(a) and a factor R, defined by I(AB)/I(A) = R x [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexes with alpha,omega-dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different to the response of the free oligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This may be due to the fact that cyclodextrin is neutral in solution, whereas the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1 : 1 complexes. 相似文献
22.
Let (E, (ie63-01),) be a halfordered plane and call
convex if M contains for any two points a,bM all pointsx between a and b. It is shown that segments [a,b] are convex if and only if (E, (ie63-02)) is the affine plane of order 3, (E, (ie63-03),) is an ordered plane or is near-trivial.
Herrn Professor Johannes Böhm zum 70. Geburtstag gewidmet 相似文献
Herrn Professor Johannes Böhm zum 70. Geburtstag gewidmet 相似文献
23.
Alexander Kreuzer 《Geometriae Dedicata》1996,61(3):279-283
Let (P,
) and (P,
) be linear spaces satisfying the exchange axiom with dim P=dim P . Then a bijection :PP which maps collinear points onto collinear points is an isomorphism. Also a surjection :PP which maps any three non-collinear points to non-collinear points is an isomorphism. This assertion is not true if dim P is not finite. 相似文献
24.
Alexander Kreuzer 《Journal of Geometry》1996,56(1-2):87-98
We give a complete and short proof of KAHN's Theorem that every locally projective space (M,M) with dim M3 satisfying the Bundle Theorem is embeddable in a projective space. The central tool of KAHN's proof is the fact that (M,M) is locally projective, while we use mainly the Bundle Theorem.Dedicated to Professor Dr. H. Mäurer on the occasion of his sixtieth birthday 相似文献
25.
26.
Alexander Kreuzer 《Journal of Geometry》1993,47(1-2):86-93
Using the function (x)=cosh x, K-loops on × are constructed. Since every K-loop is a Bruck loop, we have also examples for Bruck loops. Furthermore we investigate the group of the automorphisms a,b of the K-loop which satisfy the equation a(bc)=(ab)a,b(c).Dedicated to Professor Dr. Oswald Giering on the occasion of his 60 th birthday 相似文献
27.
Gerhard Talsky Lothar Mayring Hans Kreuzer 《Angewandte Chemie (International ed. in English)》1978,17(11):785-799
Derivative spectrophotometry has gained increasing importance in the past two years and is currently experiencing vigorous development. Following and introduction the present article provides a review of this extremely effective method. In particular, the advantages of higher-order derivative spectrophotometry (HODS method, n > 2) are discussed on the basis of practical examples from a wide range of analytical fields. The results are achieved with the aid of a newly developed analog computer unit, whereby for the first time readily reproducible, low-noise, on-line spectra can be obtained up to the 7th order and even, in favorable cases, up to the 9th order. In practice it has proved valuable to work with spectra of the 3rd to 5th order; but even higher derivations could be profitable for the separation of strongly superposed signals or for “fingerprinting”. 相似文献
28.
Hjelm J Handel RW Hagfeldt A Constable EC Housecroft CE Forster RJ 《Inorganic chemistry》2005,44(4):1073-1081
The electropolymerization of a series of Ru and Os bis-terpyridine complexes that form rodlike polymers with bithienyl, quaterthienyl, or hexathienyl bridges has been studied. Absorption spectroscopy, scanning electron microscopy, and cyclic voltammetry have been used to characterize the monomers and resulting polymer films. The absolute dc conductivity of the quaterthienyl-bridged {Ru(tpy)2} and {Os(tpy)2} polymers is unusually large and independent of the identity of the metal center at 1.6 x 10(-3) S cm(-1). The maximum conductivity occurs at the formal potential of each redox process, which typically is observed for systems where redox conduction is the dominant charge transport mechanism. Significantly, the dc conductivity of the metal-based redox couple observed in these polymers is 2 orders of magnitude higher thanthat of a comparable nonconjugated system. 相似文献
29.
Fritz Vögtle Edwin Weber 《Journal of inclusion phenomena and macrocyclic chemistry》1992,12(1-4):75-119
We thank the editors of this issue for the opportunity to present the historic development of crown chemistry at the Universities of Wurzburg and Bonn in memory of C. J. Pedersen, the originator of the crown ethers. His legacy of science has tremendously stimulated research at both universities.This paper is dedicated to the memory of the late Dr C. J. Pedersen. 相似文献
30.
Ingeborg Csöregh Mátyás Czugler Anne Ertan Edwin Weber Jochen Ahrendt 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(3):275-287
The crystal structures of four dimethyl sulphoxide (DMSO) inclusion compounds with different carboxylic acid hosts,1–4, have been studied by single crystal X-ray analysis. Crystals of thetrans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid inclusion compound (1a), [1 · DMSO (1: 1)] show monoclinic (P21/n) symmetry with the unit cell dimensionsa = 11.522(4),b = 18.658(2),c = 8.709(1) Å and = 98.92(2)°. The clathrate of the 9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (2a), [2 · DMSO (1: 2)] is triclinic (P) with the cell dimensionsa = 15.043(7),b =9.657(4),c = 8.118(7) Å, = 101.81(5), = 96.05(4) and = 100.04(4)°. Triclinic (P) symmetry is shown also by the inclusion compound of 9,10-dihydro-9,10-ethanoanthracene-11-monocarboxylic acid (3a) [3 · DMSO (1:1)] with the cell dimensionsa=6.3132(1),b=7.9846(2),c=17.5314(4) Å, = 96.46(2), = 87.08(2) and = 106.02(2)°. The 9,9-bianthryl-2-monocarboxylic acid clathrate (4a) [4 · DMSO (1:1)] is monoclinic (P21/n) and the cell dimensions area = 19.625(18),b = 8.817(1),c = 14.076(8) Å and = 97.92(6)°. In all these structures, the hosts show the same basic recognition pattern for the DMSO guest, involving a strong O-H ... O bond from the COON to the S=O group, and a possible C-H ... O type interaction between the carbonyl O atom of the host and a CH3 group of the guest. The crystals consist of discrete host-guest aggregates which are mainly held together by weak intermolecular interactions of the Van der Waals' type. The stoichiometries of the aggregates are, however, different. 相似文献