全文获取类型
收费全文 | 9128篇 |
免费 | 472篇 |
国内免费 | 45篇 |
专业分类
化学 | 6961篇 |
晶体学 | 46篇 |
力学 | 217篇 |
综合类 | 1篇 |
数学 | 1355篇 |
物理学 | 1065篇 |
出版年
2022年 | 49篇 |
2021年 | 65篇 |
2020年 | 85篇 |
2019年 | 128篇 |
2018年 | 78篇 |
2017年 | 85篇 |
2016年 | 245篇 |
2015年 | 276篇 |
2014年 | 280篇 |
2013年 | 518篇 |
2012年 | 419篇 |
2011年 | 452篇 |
2010年 | 353篇 |
2009年 | 336篇 |
2008年 | 466篇 |
2007年 | 407篇 |
2006年 | 391篇 |
2005年 | 368篇 |
2004年 | 388篇 |
2003年 | 289篇 |
2002年 | 376篇 |
2001年 | 189篇 |
2000年 | 186篇 |
1999年 | 109篇 |
1998年 | 94篇 |
1997年 | 111篇 |
1996年 | 142篇 |
1995年 | 101篇 |
1994年 | 111篇 |
1993年 | 107篇 |
1992年 | 94篇 |
1991年 | 77篇 |
1990年 | 75篇 |
1989年 | 71篇 |
1988年 | 72篇 |
1987年 | 68篇 |
1986年 | 62篇 |
1985年 | 98篇 |
1984年 | 116篇 |
1983年 | 99篇 |
1982年 | 133篇 |
1981年 | 135篇 |
1980年 | 138篇 |
1979年 | 132篇 |
1978年 | 136篇 |
1977年 | 120篇 |
1976年 | 111篇 |
1975年 | 119篇 |
1974年 | 118篇 |
1973年 | 82篇 |
排序方式: 共有9645条查询结果,搜索用时 0 毫秒
81.
The optically active methylphenyl-α-naphthylsilane racemises quickly in tetrahydrofuran in the presence of LiAlH4.Kinetic results show a different behaviour of the hydride depending on its concentration. Activation parameters have been obtained and mechanisms proposed. 相似文献
82.
Electron attachment to polar molecules and their non-covalent complexes can lead to different kinds of anions which differ from their excess electron localization. Spectroscopic methods for studying anion structures are reviewed. In many cases, the neutral and anion structures are identical and can be deduced from the electron attachment properties. Examples are given for complexes containing polar solvents or building blocks of biomolecules (nucleobases, amino acid residues...). 相似文献
83.
Jacques Dunoguès Elisabeth Jousseaume Jean-Paul Pillot Raymond Calas 《Journal of organometallic chemistry》1973,52(2):C11-C17
The trimethylchlorosilane/magnesium/hexamethylphosphoric triamide (HMPT) system reacts with some functional polychlorinated compounds (chloral, hexachloroacetone, acetone chloroform) affording a partial reduction accompanied by silylation and leads to new functional silylated derivatives.These reactions exhibit reductive properties of magnesium, in HMPT, towards the CCl bond. 相似文献
84.
A method is presented to reduce the memory requirement of normal mode analysis applied to systems containing two or more large proteins when these systems exhibit symmetry properties. We use a rigid geometry model (i.e., only the dihedral angles of the polypeptide chain are considered as variables). This model allows a reduction by a factor of 8 on average of the number of variables with a concomitant freezing of the high-frequency modes. The symmetry properties of the system are used to reduce further the number of variables that must be considered in the computation. Application of group theory leads to a factorization of the matrices of interest (the coefficient and the Hessian matrices) into independent blocks along the diagonal. The initial, reducible representation is thus transformed into a number of irreducible representations of smaller dimensions. In the case of the C2 symmetry group, the method leads to a reduction of the size of the matrices that must be manipulated during the computation (coefficient matrix, Hessian matrix, and eigenvectors matrix) by a factor of 256 compared with the usual normal mode analysis in Cartesian coordinate space. The method is particularly well adapted to the study of the dynamics of oligomeric proteins because these proteins often display symmetry properties (e.g., virus coat proteins, immunoglobulins, hemoglobin, etc.). In favorable cases, in conjunction with X-ray diffuse scattering data, the study of systems showing allosteric properties might be considered. © 1994 by John Wiley & Sons, Inc. 相似文献
85.
Jean M. J. Tronchet Bernard Gentile Alain P. Bonenfant Olivier R. Martin 《Helvetica chimica acta》1979,62(3):696-699
Further examples of O-isopropylidenaldehydosugars in the furanose series Formyl-bearing furanose derivatives 1–3 (α-D -xylo or α-D -erythro configurations) and 5–8 (configurations α-D -ribo, α-D -lyxo, β-L -threo and D -arabino) have been prepared by classical synthetic steps and their properties mainly spectroscopic, reported. The coupling constant between the formyl and the vicinal proton is always small. Like other members of the series, these new aldehydosugars constitute very useful and flexible synthetic intermediates. 相似文献
86.
Monoanionic tridentate ligands LHa and LHb containing ONSe and ONTe donor sequences and their Pd2+ and Pt2+ derivatives were synthesized and characterized. The formation of a five- and a six-membered ring around the central metal atom and associative phenomena in solutions provide extra stability to the metal complexes. 相似文献
87.
Marfisi S Rodríguez MP Alvarez G Celis MT Forgiarini A Lachaise J Salager JL 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6712-6716
Commercial ethoxylated nonionic surfactant mixtures containing alcohol cosurfactant exhibit a three-phase behavior whose formulation strongly varies with the water/oil ratio. As a consequence, a change in water/oil ratio can result in a sequence of up to three different emulsion inversion processes, through a combination of formulation and composition effects. 相似文献
88.
We describe a versatile, efficient method for the preparation of ether analogues of (S,S)-lysobisphosphatidic acid (LBPA) and its enantiomer from (S)-solketal. Phosphorylation of a protected sn-2-O-octadecenyl glyceryl ether with 2-cyanoethyl bis-N,N-diisopropylamino phosphine and subsequent deprotection generated the bisether LBPA analogues. By simply changing the sequence of deprotection steps, we obtained the (R,R)- and (S,S)-enantiomers of 2,2'-bisether LBPA. An ELISA assay with anti-LBPA monoclonal antibodies showed that the bisether LBPAs were recognized with the same affinity as the natural 2,2'-bisoleolyl LBPA. [reaction: see text] 相似文献
89.
The products of the reaction of butadiene with diethyl malonate catalysed by a palladium complex and of butadiene with acetaldehyde catalysed by a nickel(0) complex have been used in two syntheses of 3,7-dimethylpentadecan-2-ol. 相似文献
90.