全文获取类型
收费全文 | 1231篇 |
免费 | 39篇 |
国内免费 | 12篇 |
专业分类
化学 | 833篇 |
晶体学 | 4篇 |
力学 | 40篇 |
数学 | 184篇 |
物理学 | 221篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 36篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 60篇 |
2012年 | 82篇 |
2011年 | 71篇 |
2010年 | 46篇 |
2009年 | 30篇 |
2008年 | 80篇 |
2007年 | 80篇 |
2006年 | 83篇 |
2005年 | 112篇 |
2004年 | 63篇 |
2003年 | 50篇 |
2002年 | 40篇 |
2001年 | 22篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1987年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1973年 | 7篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1881年 | 3篇 |
排序方式: 共有1282条查询结果,搜索用时 15 毫秒
1.
J. -Ph. Jay J. Ben Youssef H. Le Gall 《Journal of magnetism and magnetic materials》2002,240(1-3):287-290
The dynamic response of trilayer magnetoresistive permalloy/Cu/Co films was studied by high-frequency permeability spectra measurements. The resonance frequency is shown to depend on the interlayer copper thickness. This dependence is related to exchange coupling between permalloy and cobalt and the interaction field is estimated using the Landau–Lifschitz–Gilbert model. 相似文献
2.
3.
Sergiy V. Rosokha Jian Jiang Lu Sergey M. Dibrov Jay K. Kochi 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):o464-o466
The title compound, C6H2N6O10·2C2H4Cl2, forms layered stacks of pentanitroaniline molecules, which possess twofold symmetry. The voids between these stacks are occupied by dichloroethane molecules, which reside near a 2/m symmetry element and display pseudo‐inversion symmetry. The C atoms in one of the two solvent molecules are threefold disordered. In the pentanitroaniline molecule, considerable distortion of the benzenoid ring, coupled with the short C—N(H2) bond and out‐of‐plane NO2 twistings, point to significant intramolecular `push–pull' charge transfer at the amino‐ and nitro‐substituted (ortho and para) positions, as theoretically quantified by natural bond orbital analysis of the π‐electron density. 相似文献
4.
We report microscopic observations and a structural determination of actin granules self-assembled in concentrated solutions of actin filaments (F-actin). Optical microscopy shows reproducible formation of numerous and stable granules of densely packed F-actin of variable sizes on the order of 10 microm. These granules coexist with a uniform network of F-actin of a lower concentration. The microscopic segregation of F-actin into two distinct states is assisted by an actin cross-linking protein, alpha-actinin. The rapid on and off rates and temperature sensitivity of the alpha-actinin/F-actin interaction facilitate the formation of multi-micrometer-sized granules of well-defined shapes. Additional physical factors such as the excluded volume effect and the minimization of surface energy act in concert with the specific molecular interactions to define the intriguing granular formation. Both the biochemical specificity of alpha-actinin and the thermodynamics of phase transitions are required for understanding such large scale self-assembly. 相似文献
5.
Baksh MM Dean C Pautot S DeMaria S Isacoff E Groves JT 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10693-10698
We have characterized, in vitro, interactions between hippocampal neuronal cells and silica microbeads coated with synthetic, fluid, lipid bilayer membranes containing the glycosylphosphatidyl inositol (GPI)-linked extracellular domain of the postsynaptic membrane protein neuroligin-1. These bilayer-neuroligin-1 beads activated neuronal cells to form presynaptic nerve terminals at the point of contact in a manner similar to that observed for live PC12 cells, ectopically expressing the full length neuroligin-1. The synthetic membranes exhibited biological activity at neuroligin-1 densities of approximately 1 to 6 proteins/microm(2). Polyolycarbonate beads with neuroligin-1 covalently attached to the surface failed to activate neurons despite the fact that neuroligin-1 binding activity is preserved. This implies that a lipid membrane environment is likely to be essential for neuroligin-1 activity. This technique allows the study of isolated proteins in an environment that has physical properties resembling those of a cell surface; proteins can diffuse freely within the membrane, retain their in vivo orientations, and are in a nondenatured state. In addition, the synthetic membrane environment affords control over both lipid and protein composition. This technology is easily implemented and can be applied to a wide variety of cellular studies. 相似文献
6.
[structure: see text] Derivatives of the highly fluorescent and DNA-binding dye thiazole orange (TO) are described that feature appended peptides. Functionalization of TO can be achieved at either of the endocyclic nitrogens, and the photophysical properties and DNA-binding modes are sensitive to the position of the tethered peptide. A series of TO-peptide conjugates are described, demonstrating the utility of a solid-phase synthesis approach to their preparation and illustrating how the photophysical and DNA-binding properties of the compounds are influenced by chemical structure. 相似文献
7.
Reaction of 2-aminoethanethiol ( 3 ) with trans-3-(p-methoxyplienyl)glycidate ( 4 ) gave the rac.-cis-1,4-thiazepinone 5 and a by-product 6 . The structure of 5 was proven by X-ray crystallography. The X-ray data revealed that this compound adopts the chair conformation in the solid state and the heterocyclic ring is sevenmembered. The structure of the by-product 6 was elucidated on the basis of spectral data. Compounds 9 and 10 were inactive as calcium channel blocking agents. 相似文献
8.
Various phenylsulfonyl allene derivatives were prepared with double bonds tethered either to the alpha-position or the gamma-position of the allene. These substrates underwent a highly regio- and stereospecific thermal [2 + 2]-cycloaddition across the nonactivated cumulene double bond, forming distal cycloadducts (i.e., 57) in the case of alpha-tethered allenes and proximal adducts (i.e., 25) in the case of gamma-tethered allenes. The mechanistic rationale for the observed stereospecificity involves initial diradical formation, followed by a rapid ring closure to the more stable cis-fused ring system. The tether may be equipped with heteroatoms, allowing for the formation of fused heterocycles (e.g., 61), and the cycloaddition can be facilitated by the introduction of sterically bulky groups and/or by conformational rigidity to the tether. Other modes of cyclization were observed in the presence of sodium benzenesulfinate or Lewis acids, in which cases polar mechanisms prevail. The chemoselectivity is reversed for [4 + 2]-cycloadditions, which prefer instead to engage the vinyl sulfone moiety, independent of whether the tether is attached to the alpha- or gamma-position of the allene. 相似文献
9.
A protocol is described for the treatment of molecular polarization in force field calculations. The resulting model is consistent in that both inter- and intramolecular polarization are handled within a single scheme. An analytical formula for removing intramolecular polarization from a set of atomic multipoles for an arbitrary static structure or conformation is given. With the help of the intramolecular polarization, these permanent atomic multipoles can then be applied in modeling alternative conformations of a molecule. Equipped with this simple technique, one can derive transferable electrostatic parameters for peptides and proteins using flexible model compounds such as dipeptides. The proposed procedure is tested for its ability to describe the electrostatic potential around various configurations of the N-methylacetamide dimer. The effect of different intramolecular polarization schemes on the accuracy of a force field model of the electrostatic potential of alanine dipeptide is investigated. A group-based scheme for including direct intramolecular polarization is shown to be most successful in accounting for the conformational dependence of electrostatic potentials. 相似文献
10.