全文获取类型
收费全文 | 2258篇 |
免费 | 93篇 |
国内免费 | 7篇 |
专业分类
化学 | 1609篇 |
晶体学 | 25篇 |
力学 | 56篇 |
数学 | 318篇 |
物理学 | 350篇 |
出版年
2022年 | 18篇 |
2021年 | 25篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2017年 | 10篇 |
2016年 | 53篇 |
2015年 | 50篇 |
2014年 | 61篇 |
2013年 | 145篇 |
2012年 | 115篇 |
2011年 | 142篇 |
2010年 | 87篇 |
2009年 | 67篇 |
2008年 | 121篇 |
2007年 | 123篇 |
2006年 | 138篇 |
2005年 | 119篇 |
2004年 | 127篇 |
2003年 | 96篇 |
2002年 | 86篇 |
2001年 | 21篇 |
2000年 | 28篇 |
1999年 | 22篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 34篇 |
1995年 | 25篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 19篇 |
1990年 | 18篇 |
1989年 | 26篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 20篇 |
1985年 | 34篇 |
1984年 | 33篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 28篇 |
1980年 | 30篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 15篇 |
1975年 | 21篇 |
1974年 | 12篇 |
1973年 | 20篇 |
排序方式: 共有2358条查询结果,搜索用时 15 毫秒
181.
Fenaille F Morgan F Parisod V Tabet JC Guy PA 《Rapid communications in mass spectrometry : RCM》2003,17(13):1483-1492
Glycation of beta-lactoglobulin (beta-Lg) with either lactose or galactose in a solid-state medium was monitored using gel electrophoresis techniques and liquid chromatography coupled to electrospray ionisation mass spectrometry (LC/ESI-MS). The kinetics of glycation monitored by SDS polyacrylamide gel electrophoresis showed a molecular weight increase over time of the beta-Lg bands for both sugars, but no significant amounts of aggregated proteins were observed. The isoelectric point of the protein, observed by isoelectric focusing gel electrophoresis, was dramatically affected by galactosylation. LC/MS measurements of beta-Lg variants A and B, over the whole glycation reaction time, showed a larger extent of glycation with galactose (from 4 up to 22 adducts) as compared with lactose (from 0 up to 14 adducts), and confirmed that early Maillard reaction products were the main species observed. Based on the relative abundances obtained from the deconvoluted mass spectra after a 8 h 15 min incubation time at 60 degrees C, the mean values of lactose and galactose molecules bound to the protein species were calculated to be 10.4 and 17.9, and 10.5 and 18.6, for variants A and B, respectively. Furthermore, the charge state distribution data obtained by ESI-MS was studied using different methanol percentages, and indicated that adduct formation with lactose, but more significantly galactose, tends to improve the stability properties of the native protein towards denaturation. 相似文献
182.
Carreño MC Des Mazery R Urbano A Colobert F Solladié G 《The Journal of organic chemistry》2003,68(20):7779-7787
The stereocontrolled formation of cis-2,5-disubstituted tetrahydrofurans and cis-2,6-disubstituted tetrahydropyrans is achieved from enantiopure ketosulfinyl esters by reduction, Weinreb's amide, and ketone formation, followed by the reductive cyclization (Et3SiH/TMSOTf) of the resulting hydroxysulfinyl ketones. The sulfoxide-bearing heterocycles were transformed into two natural products, (-)-centrolobine (1) and both enantiomers of cis-(6-methyltetrahydropyran-2-yl)acetic acid (2). 相似文献
183.
An evaluation of alpha-aryl-alpha-diazodiones in tandem carbonyl ylide formation-enantioselective [3 + 2]-cycloaddition reactions is described. Such substrates were designed to allow investigation of the electronic characteristics of the dipole upon asymmetric induction. Intramolecular cycloadditions (with a tethered alkene dipolarophile) were found to occur in good to quantitative yields, with a difference in ee exhibited by the two electronically different diazodiones 8 and 9. Intermolecular cycloadditions using diazodiones 12 and 13 with DMAD and arylacetylenes 16-18 again demonstrated that electronics play a key role in determining the outcome of the cycloaddition reactions. Enantioselectivities of up to 76% were observed. 相似文献
184.
Miqueu K Despagnet-Ayoub E Dyer PW Bourissou D Bertrand G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5858-5864
Density functional calculations are reported for complexes of general formula [(carbene)RhClL(2)] featuring model phosphino- and aminocarbenes. Both the cis and trans isomers of the rhodium(I) eta(1)-complexes (1-9) were investigated, and the influence of the rhodium co-ligands (L=ethylene, phosphine, or carbon monoxide) was evaluated. In the case of phosphinocarbenes and carbon monoxide as a ligand, a somewhat unusual coordination mode was observed, in which a significant intramolecular Cl-->C(carbene) interaction is present. The propensity of phosphino- and aminocarbenes to behave as four electron donors was also investigated both structurally and energetically on the related eta(2)-complexes 10-18. These results as a whole emphasize the structural versatility of phosphino- compared with aminocarbene complexes. 相似文献
185.
186.
187.
Alonso MA Casares JA Espinet P Soulantica K Orpen AG Phetmung H 《Inorganic chemistry》2003,42(12):3856-3864
The stereochemistry of the chelate rings of a number of rhodium aminophosphine complexes is studied by NMR spectroscopy. The similarity in the variable-temperature behavior for the different compounds is consistent with them having in common highly preferred chelate ring conformations. The six-membered metallacycle of coordinated (R)-PN (PN = o-diphenylphosphino-alpha-methyl-N,N-dimethylbenzylamine) adopts a delta conformation in the solid state. NMR experiments indicate that this conformation is strongly favored in solution as well. The preferred sense of helicity is imposed by the absolute configuration of the stereogenic carbon atom on the ligand, which exerts an important steric control. The complex [Rh(TFB)((C(6)H(4)CHMeNMe(2))(2)P(C(6)H(4)CHMeNHMe(2)))](BF(4))(2).H(2)O.Me(2)CO crystallizes in the monoclinic space group P2(1) with a = 12.0548(11) A, b = 16.139(2) A, c = 12.1804(10) A, beta = 100.742(9) degrees, Z = 4. 相似文献
188.
189.
We deal with variational problems on varying manifolds in ℝn. We represent each manifold by a positive measure μ, to which we associate a suitable notion of tangent space Tμ, of mean
curvature H(μ), and of Sobolev spaces with respect to μ on an open subset Ω ⊆ ℝn. We introduce the notions of weak and strong convergence for functions defined on varying manifolds, that is defined μh -a.e., being {μh} a weakly convergent sequence of measures. In this setting, we prove a strong-weak type compactness theorem for the pairs
(Pμ
h H(μh)), where Pμ
h are the projectors onto the tangent spaces Tμ
h. When μh belong to a suitable class of k-dimensional measures, having in particular a prescribed (k−1)-manifold as a boundary, we
enforce this result to study the convergence of energy functionals, possibly with a Dirichlet condition on ∂Ω. We also address
a perspective for optimization problems where the control variable is represented by a manifold with a prescribed boundary. 相似文献
190.