全文获取类型
收费全文 | 3421篇 |
免费 | 85篇 |
国内免费 | 23篇 |
专业分类
化学 | 2142篇 |
晶体学 | 10篇 |
力学 | 131篇 |
数学 | 693篇 |
物理学 | 553篇 |
出版年
2023年 | 16篇 |
2022年 | 31篇 |
2021年 | 67篇 |
2020年 | 54篇 |
2019年 | 61篇 |
2018年 | 50篇 |
2017年 | 32篇 |
2016年 | 115篇 |
2015年 | 59篇 |
2014年 | 74篇 |
2013年 | 162篇 |
2012年 | 159篇 |
2011年 | 231篇 |
2010年 | 123篇 |
2009年 | 128篇 |
2008年 | 186篇 |
2007年 | 194篇 |
2006年 | 174篇 |
2005年 | 163篇 |
2004年 | 127篇 |
2003年 | 119篇 |
2002年 | 82篇 |
2001年 | 39篇 |
2000年 | 52篇 |
1999年 | 49篇 |
1998年 | 33篇 |
1997年 | 46篇 |
1996年 | 50篇 |
1995年 | 40篇 |
1994年 | 49篇 |
1993年 | 41篇 |
1992年 | 38篇 |
1991年 | 20篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 23篇 |
1985年 | 40篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1974年 | 17篇 |
1973年 | 12篇 |
排序方式: 共有3529条查询结果,搜索用时 250 毫秒
61.
Guido Audisio Maria Grassi Piero Traldi Sergio Daolio 《Journal of mass spectrometry : JMS》1985,20(5):327-330
The positive ion chemical ionization (CI (isobutane)), negative ion chemical ionization (NICI) electron attachment (CH4, He) and NICI (OH?) spectra of the title compounds have been studied in detail with the aid of deuterium-labelled derivatives. The obtained results show that under CI conditions the stereospecificity is retained. Interesting correlations with the condensed phase epimerization yields are emphasized. 相似文献
62.
Enkhtsetseg Dashjav Guido Kreiner Walter Schnelle Frank R. Wagner Rüdiger Kniep 《无机化学与普通化学杂志》2004,630(5):689-696
Carbometalates: Complex Anions equation/tex2gif-stack-4.gif [MoC4/26—] in the Crystal Structure of Pr equation/tex2gif-stack-5.gif [MoIIC2] Criteria for the existence of carbometalates are established and discussed in a broader context. The concept is then applied to the novel compound Pr2[MoC2], which is characterized by chemical analyses, X‐ray diffraction and metallography. The crystal structure (tetragonal, P42/mnm, Z = 4, a = 581.29(8) pm, c = 1032.53(14) pm) consists of layered polyanions equation/tex2gif-stack-6.gif[MoC4/26—] of distorted vertex and edge sharing MoC4 tetrahedra. Praseodymium is also in a distorted tetrahedral coordination by carbon. The physical properties show “bad metal” behaviour and localized magnetic 4f‐moments in agreement with the existence of Pr3+‐species. A detailed bonding analysis using both the electron localization function ELF and the COHP method justifies the interpretation of the title compound as a carbomolybdate(II). 相似文献
63.
Quagliotto P Viscardi G Barolo C D'Angelo D Barni E Compari C Duce E Fisicaro E 《The Journal of organic chemistry》2005,70(24):9857-9866
[reaction: see text] In this work, we report the synthesis of a new series of glucocationic surfactants, a class of surfactants we introduced very recently. The preparation of the surfactants is based on the synthesis of the 2-bromoethyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside, whose preparation was studied in order to improve yields and stereoselectivity of this key intermediate. These glucocationic amphiphiles were prepared and studied as a model of cationic surfactants marked with a carbohydrate moiety. The use of carbohydrates as markers on cationic lipids was recently introduced to induce recognition by specific receptors, present on the surface of cell membranes. The chemicophysical characterization of these model structures can give more insight on the aggregation behavior. Conductivity and surface tension measurements were performed in order to characterize the compounds from the amphiphilic point of view. The results showed a different effect of the glucosidic moiety on the cmc value with respect to the glucopyridinium cationic surfactants. The surfactants also showed the tendency to form premicellar aggregates in solution when the hydrophobicity is raised. 相似文献
64.
65.
Urs P. Wild Tae-Kyu Ha Guido A. Raggio Hans U. Keller Peter O. Brunner 《Helvetica chimica acta》1975,58(3):696-706
An ab initio SCF calculation of 42 points of the energy hypersurface of the fluoronium ion is presented using a contracted F(5s/3p), H(2s) gaussian basis set. In its equilibrium structure a bond length of 1.812 a.u. and a HFH bond angle of 127.2° are predicted. The calculated vibrational frequencies for H2F+, HDF+, and D2F+ are in good agreement with the experimental data. 相似文献
66.
Enrico Jabara 《Rendiconti del Circolo Matematico di Palermo》1995,44(1):107-112
An automorphism σ of order (a divisor of)n of the groupG is calledn-splitting if
for everyg∈G.
In this paper we prove that a 2-group admitting a 4-splitting automorphism, is locally finite. 相似文献
67.
68.
69.
Guido Schneider 《Communications in Mathematical Physics》1994,164(1):157-179
The so-called Ginzburg-Landau formalism applies for parabolic systems which are defined on cylindrical domains, which are, close to the threshold of instability, and for which the unstable Fourier modes belong to non-zero wave numbers. This formalism allows to describe an attracting set of solutions by a modulation equation, here the Ginzburg-Landau equation. If the coefficient in front of the cubic term of the formally derived Ginzburg-Landau equation has negative real part the method allows to show global existence in time in the original system of all solutions belonging to small initial conditions, inL
. Another aim of this paper is to construct a pseudo-orbit of Ginzburg-Landau approximations which is close to a solution of the original system up tot=. We consider here as an example the socalled Kuramoto-Shivashinsky equation to explain the methods, but it applies also to a wide class of other problems, like e.g. hydrodynamical problems or reaction-diffusion equations, too. 相似文献
70.
Raffaele P. Bonomo Vincenzo Cucinotta Franca D' Allessandro Giuseppe Impellizzeri Giuseppe Maccarrone Enrico Rizzarelli Graziella Vecchio 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(2):167-180
The functionalized cyclodextrin 6-deoxy-6-[1-(2-amino)ethylamino]--cyclodextrin was synthesized, and an NMR, EPR, pH-metric, and calorimetric investigation was carried out in aqueous solution in order to ascertain its behaviour towards protonation and copper(II) complex formation. The thermodynamic parameters of the ternary complex formation with alanine, phenylalanine and tryptophan enantiomeric pairs were also determined (25° C andI=0.1 mol dm–3). No thermodynamic enantioselectivity was observed in these systems, while a chiral, though poor, discrimination was observed in LEC: c.d. spectra also show enantiomeric stereoselectivity. The results of the present investigation, compared with previously reported results, suggest the occurence of acis-complex trans-complex equilibrium in such systems. 相似文献