全文获取类型
收费全文 | 28436篇 |
免费 | 652篇 |
国内免费 | 176篇 |
专业分类
化学 | 19207篇 |
晶体学 | 240篇 |
力学 | 698篇 |
综合类 | 1篇 |
数学 | 4820篇 |
物理学 | 4298篇 |
出版年
2021年 | 195篇 |
2020年 | 248篇 |
2019年 | 321篇 |
2018年 | 260篇 |
2017年 | 220篇 |
2016年 | 494篇 |
2015年 | 401篇 |
2014年 | 510篇 |
2013年 | 1404篇 |
2012年 | 1322篇 |
2011年 | 1649篇 |
2010年 | 857篇 |
2009年 | 690篇 |
2008年 | 1494篇 |
2007年 | 1528篇 |
2006年 | 1521篇 |
2005年 | 1530篇 |
2004年 | 1347篇 |
2003年 | 1160篇 |
2002年 | 1094篇 |
2001年 | 408篇 |
2000年 | 336篇 |
1999年 | 266篇 |
1998年 | 305篇 |
1997年 | 345篇 |
1996年 | 422篇 |
1995年 | 327篇 |
1994年 | 309篇 |
1993年 | 303篇 |
1992年 | 292篇 |
1991年 | 264篇 |
1990年 | 242篇 |
1989年 | 261篇 |
1988年 | 296篇 |
1987年 | 285篇 |
1986年 | 266篇 |
1985年 | 429篇 |
1984年 | 469篇 |
1983年 | 364篇 |
1982年 | 467篇 |
1981年 | 437篇 |
1980年 | 382篇 |
1979年 | 356篇 |
1978年 | 376篇 |
1977年 | 353篇 |
1976年 | 292篇 |
1975年 | 293篇 |
1974年 | 275篇 |
1973年 | 256篇 |
1972年 | 155篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We see that the entropy method yields strong concentration results for general self‐bounding functions of independent random variables. These give an improvement of a concentration result of Talagrand much used in discrete mathematics. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
92.
A mean-field model of nonlinearly coupled oscillators with randomly distributed frequencies and subject to independent external white noises is analyzed in the thermodynamic limit. When the frequency distribution isbimodal, new results include subcritical spontaneous stationary synchronization of the oscillators, supercritical time-periodic synchronization, bistability, and hysteretic phenomena. Bifurcating synchronized states are asymptotically constructed near bifurcation values of the coupling strength, and theirnonlinear stability properties ascertained. 相似文献
93.
Claire Cates Haulk John Drew Charles R. Johnson J. Hunter Tart 《Linear and Multilinear Algebra》1997,43(1):35-51
For a given n-by-n matrix A, we consider the set of matrices which commute with A and all of whose principal submatrices commute with the corresponding principal submatrices of A. The properties of this set are examined, with particular attention to its dimension. 相似文献
94.
The fluorescence dynamics parameters of the fluorescent transient flavin-luciferase species from the typesVibrio fischeri andPhotobacterium leiognathi are presented. The fluorescence anisotropy decay is a single exponential function for both types. The correlation time is 70 ns for theP. leiognathi fluorescent transient intermediate (2°C, aqueous buffer, pH 7.0), consistent with the rotational correlation time of the luciferase macromolecule (77 kD) to which the flavin fluorophore is rigidly attached. In contrast, for theV. fischeri species the observed correlation time for the anisotropy decay function is 133 ns. This suggests that protein self-association occurs in theV. fischeri case and this is confirmed by filtration, where the fluorescent transient fromV. fischeri does not pass through a 100,000 molecular weight cutoff membrane, whereas theP. leiognathi species does. The filtration method also demonstrates self-association in the luciferase peroxyflavin and photoflavin fromV. fischeri. A monomer-dimer equilibrium also explains the previously reported high correlation times for theV. harveyi luciferase-flavin species. It is proposed that the self-association competes with the lumazine protein interaction in the bioluminescence reaction. 相似文献
95.
Using a scanning tunneling microscope, quantum dots with diameters of order 25 Å have been fabricated on the cleaved InSb (110) surface in UHV. Both In and Sb atoms were clearly resolved on the cleaved surface. 相似文献
96.
A new heuristic for the vehicle routeing problem which makes use of repeated matching is described. The numerical results are comparable to or better than the best published for most of the 14 benchmark problems commonly used to evaluate VRP heuristics. 相似文献
97.
In this paper a statistical multiplexer that processes a mixture of real-time and non-real-time traffic is studied under bursts of traffic. Different scheduling algorithms are compared under conditions when one of the classes of traffic has a sudden increase in its arrival rate during a short period of time. The results show a difference in the way the scheduling disciplines studied behave under short overloads of traffic even though the scheduling algorithms had been set up to give similar performance under steady-state arrivals. The lifetime of real-time packets is shown to have a great effect on the way in which the performance of the scheduling algorithms compare.Robert Lackman is an IBM employee in the IBM Resident Study Program. 相似文献
98.
99.
Joel M. Kauffman Ali Khalaj Peter T. Litak John A. Novinski Gurdip S. Bajwa 《Journal of heterocyclic chemistry》1994,31(4):957-965
To improve the solubility, photostability and fluorescence quantum yield (Φ) of 2-arylbenzimidazolium ions the N-1 hydrogen was replaced by an alkyl group before N-3 was quatemized; this substitution did not reduce Φ, proving the absence of steric inhibition to attainment of coplanarity in the excited state. A related symmetrical 2,2′-arylenebis(1,3-dimethyldibenzimidazolium ion) had Φ = 0.86. The related 2,5-bis(1-methyl-2-benzimidazolyl)phenol had Φ = 0.38 at 22° as well as a very large Stokes' shift due to proton-transfer. These findings supported a new insight into the electron distribution of the first excited singlet state of oligophenylenes. The compounds are of interest as laser dyes and scintillation fluors. 相似文献
100.
Christopher J. Booth John W. Goodby Judith P. Hardy Olwen C. Lettington Kenneth J. Toyne 《Liquid crystals》1994,16(6):925-940
The synthesis and characterization of seven novel (R)-2-(4-substituted-phenoxy)propanonitriles are described. The propanonitriles were prepared to evaluate their potential use as thermochromics and ferroelectric dopants, as well as to determine their twist sense properties. The materials exhibit smectic and chiral nematic phases of high thermal stability; the mesogenic behaviour of the nitriles is directly related to the type of two-ring core unit employed. The effects of the different molecular geometries and polarizabilities of the liquid crystalline cores on mesophase stability are discussed, particularly in relation to other members of this series. The chiral nematic phase of the propanonitriles is assigned as having a left-handed twist sense from contact preparation studies, and this is in agreement with rules relating absolute configuration and molecular structure to helical twist sense. 相似文献