全文获取类型
收费全文 | 6824篇 |
免费 | 829篇 |
国内免费 | 150篇 |
专业分类
化学 | 5395篇 |
晶体学 | 90篇 |
力学 | 191篇 |
综合类 | 2篇 |
数学 | 113篇 |
物理学 | 2012篇 |
出版年
2024年 | 13篇 |
2023年 | 70篇 |
2022年 | 182篇 |
2021年 | 224篇 |
2020年 | 352篇 |
2019年 | 239篇 |
2018年 | 166篇 |
2017年 | 171篇 |
2016年 | 298篇 |
2015年 | 308篇 |
2014年 | 340篇 |
2013年 | 436篇 |
2012年 | 394篇 |
2011年 | 359篇 |
2010年 | 270篇 |
2009年 | 380篇 |
2008年 | 404篇 |
2007年 | 493篇 |
2006年 | 364篇 |
2005年 | 285篇 |
2004年 | 221篇 |
2003年 | 261篇 |
2002年 | 201篇 |
2001年 | 178篇 |
2000年 | 143篇 |
1999年 | 152篇 |
1998年 | 157篇 |
1997年 | 68篇 |
1996年 | 74篇 |
1995年 | 73篇 |
1994年 | 47篇 |
1993年 | 57篇 |
1992年 | 47篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 33篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 30篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有7803条查询结果,搜索用时 46 毫秒
91.
D. Fennell Evans Martin Allen B. W. Ninham Abdel Fouda 《Journal of solution chemistry》1984,13(2):87-101
Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol–1. 相似文献
92.
Deo SK 《Analytical and bioanalytical chemistry》2004,379(3):383-390
Reassembly of protein from its peptide fragments is a technique that can have many applications in the bioanalytical field. Typically, a reporter protein fragmented into its two peptides is employed as a label in this study. This fragments of peptide can reassemble yielding an active functional reporter. This reassembly of the protein can be assisted by non-covalently interacting peptides or proteins, which are attached to the fragmented reporter. This technique has been employed in several applications including study of protein–protein interactions, antibody screening, immunoassays, and high-throughput screening. This review focuses on different reporters employed in the study of reassembly of proteins and applications of this strategy in bioanalysis. 相似文献
93.
The structures, energies, and natural atomic charges of 2-dimethylaminophenol oxide, 2-Me2N-(O)C6H4OH, and 2-dimethylphosphinylphenol, 2-Me2P(O)C6H4OH, in three different conformations were computed at the ab initio MP2/6-31G* level. Computed natural charges indicate distributions of electron density in amine oxides and phosphine oxides that are quite different from what is normally assumed on the basis of the formal charges in the usual representations of these compounds. The charges on nitrogen and phosphorus in these compounds are typically computed to be approximately zero on nitrogen and +2 on phosphorus, and the oxygen is considerably more negative in the phosphine oxide than in the amino oxide. Electronegativity differences thus play a larger role and formal charges a smaller one in determining atomic charges in these compounds than is generally believed. Despite the more negative oxygen in phosphine oxides, amine oxides are computed to be considerably more basic when participating in hydrogen bonding. Calculations treating the computed natural charges on these six conformations as point charges for classical approximations of the coulombic energies support the idea that the quantum mechanically computed relative energies are largely determined by coulombic interactions. 相似文献
94.
95.
Balamurugan V Hundal MS Mukherjee R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(7):1683-1690
Using a group of six neutral M(II)Cl(2)-containing coordination compounds as building blocks, the first systematic investigation of C-H...Cl hydrogen-bonding interactions was performed. Single-crystal X-ray structural analyses of four new compounds (pseudo-tetrahedral Co(II) and Zn(II); distorted trigonal bipyramidal Zn(II)) authenticate the metal coordination geometry. To provide a unified view of the presence of noncovalent interactions in this class of compounds, we have re-examined the packing diagram of two previously reported compounds (a distorted square-pyramidal Cu(II) complex and a trans-octahedral Co(II) complex). The organic ligands of our choice comprise bidentate/tridentate pyrazolylmethylpyridines and an unsymmetrical tridentate pyridylalkylamine. This systematic investigation has allowed us to demonstrate the existence of versatile C-H...Cl(2)M interactions and to report the successful application of such units as inorganic supramolecular synthons. Additional noncovalent interactions such as C-H...O and O-H...Cl hydrogen bonding and pi-pi stacking interactions have also been identified. Formation of novel supramolecular architectures has been revealed: 2D lamellar (p-cyclophane) and 3D lamellar, 3D "stitched staircase" (due to additional hydrogen-bonding interactions by water tetramers, with an average O-O bond length in the tetramer unit of 2.926 A, acting as "molecular clips" between staircases), 3D linked ladder, and single-stranded 1D helix. 相似文献
96.
Summary Molecular surface areas accessible to a 4 ? diameter spherical probe were calculated from crystallographic data for five proteins:
α-chymotrypsinogen A, lysozyme, trypsinogen, ribonuclease A and ribonuclease S. The retention factors of various proteins
were measured on stationary phases having polyether- and phenylligates and with aqueous eluents containing (NH4)2SO4, Na2SO4 or NaCl at pH 7.0. The logarithmic retention factors were plotted against the salt molality and the hydrophobic interaction
parameters evaluated from the limiting slopes of the plots at high salt concentrations for the proteins in the chromatographic
systems investigated. The hydrophobic interaction parameters thus obtained were linear in both the molecular surface areas
of the proteins and the molal surface tension increments of the salts. The experimental results obtained with these relatively
simple proteins of known molecular structure, which were available in high purity, support earlier theoretical predictions
for the dependence of the hydrophobic interaction parameter on the surface area of the protein and the surface tension raising
effect of the salt. 相似文献
97.
C. E. I. Carneiro M. J. de Oliveira W. F. Wreszinski 《Journal of statistical physics》1995,79(1-2):347-376
We show rigorously that the ground state of a quantum chain with competing ferromagnetic nearest and antiferromagnetic next nearest interactions undergoes a transition from ferromagnetic to helical type, in the isotropic case, for a certain value of the relevant ratio of coupling constants. Boundaries of the phase diagram are also determined in the anisotropic case. The stability of a special quantum state (corresponding to a classical modulated phase of =/3) is analyzed by an extension of Holstein-Primakoff arguments, along a line of constant ratio of couplings, showing in particular a sequence of (instability) gaps. Finally, a natural adaptation of a variational wave function due to Huse and Elser is used to study several portions of the phase diagram, with very good agreement with previous theoretical results. 相似文献
98.
99.
We assess several models for the environment of the P
b
center (Si dangling bond center) at the interface of Si(111) with its oxide. The comparison of hyperfine constants observed with those predicted using large cluster models favors a local structure in which there is an Si-Si bond within the oxide close to the Si dangling bond. Such Si-Si bonds are also suggested by a number of other experiments and are consistent with the reactive layer model proposed to rationalize a range of oxidation studies. 相似文献
100.
George Adomian 《Foundations of Physics Letters》1993,6(6):603-605
In mathematical approaches to elementary particle theory, the equation [2 -
2/t2]=m2
;+g
3 has been of interest [1,2]; it describes a quartically self-coupled neutral scalar meson field. This paper applies the decomposition method [3-6] to obtain accurate non-perturbative timedevelopment of the field for this equation, or variations involving other nonlinear interactions, without the use of cutoff functions or truncations. 相似文献