全文获取类型
收费全文 | 31713篇 |
免费 | 809篇 |
国内免费 | 179篇 |
专业分类
化学 | 21486篇 |
晶体学 | 271篇 |
力学 | 772篇 |
综合类 | 1篇 |
数学 | 4987篇 |
物理学 | 5184篇 |
出版年
2022年 | 273篇 |
2021年 | 311篇 |
2020年 | 334篇 |
2019年 | 424篇 |
2018年 | 342篇 |
2017年 | 316篇 |
2016年 | 652篇 |
2015年 | 491篇 |
2014年 | 623篇 |
2013年 | 1643篇 |
2012年 | 1546篇 |
2011年 | 1951篇 |
2010年 | 1031篇 |
2009年 | 901篇 |
2008年 | 1763篇 |
2007年 | 1789篇 |
2006年 | 1719篇 |
2005年 | 1681篇 |
2004年 | 1499篇 |
2003年 | 1237篇 |
2002年 | 1201篇 |
2001年 | 459篇 |
2000年 | 389篇 |
1999年 | 304篇 |
1998年 | 330篇 |
1997年 | 366篇 |
1996年 | 460篇 |
1995年 | 345篇 |
1994年 | 324篇 |
1993年 | 320篇 |
1992年 | 308篇 |
1991年 | 254篇 |
1990年 | 243篇 |
1989年 | 259篇 |
1988年 | 277篇 |
1987年 | 267篇 |
1986年 | 258篇 |
1985年 | 408篇 |
1984年 | 460篇 |
1983年 | 329篇 |
1982年 | 452篇 |
1981年 | 423篇 |
1980年 | 359篇 |
1979年 | 342篇 |
1978年 | 361篇 |
1977年 | 346篇 |
1976年 | 286篇 |
1975年 | 283篇 |
1974年 | 277篇 |
1973年 | 246篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Summary Transfer chemical potentials have been determined from measured solubilities for four uncharged encapsulated iron(II) complexes containing three diimine ligating moieties and O3BOBu-n and O3BF capping groups, in H2O–MeOH andt-BuOH–H2O solvent mixtures, The trends in transfer chemical potentials are discussed in terms of the natures of the encapsulating ligands, and are compared with those for a selection of other iron(II)-diimine complexes. 相似文献
102.
结合声表面波和光致发光谱在低温(15K)下对非故意掺杂的GaAs(110)量子阱结构的发光特性进行了研究.实验结果表明,由于声表面波的作用GaAs(110)量子阱的发光强度减弱,并且其对应的重空穴能级出现了分裂的现象,当施加的声波强度Prf达到20dBm时,能级分裂ΔE达到了10meV.进一步讨论了声表面波对GaAs(110)量子阱圆偏振光自旋注入的影响.
关键词:
发光
GaAs量子阱
声表面波
自旋极化 相似文献
103.
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
104.
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
105.
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
106.
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
107.
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
108.
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
109.
110.
Patrick Mather Nino Grizzuti Glenn Heffner Mathias Ricker Willie E. Rochefort Markus Seitz Hans-Werner Schmidt Dale S. Pearson 《Liquid crystals》1994,17(6):811-826
In this paper, we report on the synthesis and detailed characterization of a new semiflexible nematic liquid crystalline polyester which could serve as a 'model' polyester for a variety of physical and physico-chemical investigations. The polymer is a nematic liquid over a wide temperature range-from the glass transition temperature at ∼95°C to the isotropic transition at ∼240°C. We expect this polyester to be particularly useful for studying the effect of flow on the orientation of liquid crystalline polymers, as well as the production and removal of disclinations. 相似文献