全文获取类型
收费全文 | 10016篇 |
免费 | 198篇 |
国内免费 | 35篇 |
专业分类
化学 | 5598篇 |
晶体学 | 183篇 |
力学 | 223篇 |
数学 | 1733篇 |
物理学 | 2512篇 |
出版年
2022年 | 45篇 |
2021年 | 189篇 |
2020年 | 118篇 |
2019年 | 168篇 |
2018年 | 169篇 |
2017年 | 190篇 |
2016年 | 302篇 |
2015年 | 249篇 |
2014年 | 331篇 |
2013年 | 772篇 |
2012年 | 485篇 |
2011年 | 568篇 |
2010年 | 437篇 |
2009年 | 414篇 |
2008年 | 497篇 |
2007年 | 484篇 |
2006年 | 418篇 |
2005年 | 358篇 |
2004年 | 346篇 |
2003年 | 313篇 |
2002年 | 270篇 |
2001年 | 199篇 |
2000年 | 177篇 |
1999年 | 133篇 |
1998年 | 140篇 |
1997年 | 118篇 |
1996年 | 111篇 |
1995年 | 124篇 |
1994年 | 83篇 |
1993年 | 83篇 |
1992年 | 94篇 |
1991年 | 70篇 |
1990年 | 93篇 |
1989年 | 91篇 |
1988年 | 83篇 |
1987年 | 71篇 |
1986年 | 78篇 |
1985年 | 128篇 |
1984年 | 146篇 |
1983年 | 84篇 |
1982年 | 87篇 |
1981年 | 96篇 |
1980年 | 98篇 |
1979年 | 79篇 |
1978年 | 79篇 |
1977年 | 95篇 |
1976年 | 76篇 |
1975年 | 68篇 |
1974年 | 57篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Tomasz Stawski Janusz Szklarzewicz Krzysztof Lewiński 《Transition Metal Chemistry》2006,31(3):353-361
The single crystal X-ray structure of (AsPh4)[W(bpy)(CN)6] is described. The structure of octa- and hepta-coordinated intermediates of substitutional photolysis of [Mo(CN)8]4− ion in aqueous media were determined by performing semi-empirical calculations. On the basis of obtained results as well
as on empirical data the photolysis scheme has been postulated. 相似文献
42.
Zdzisław Denkowski Leszek Gasiński Nikolaos S. Papageorgiou 《Journal of Global Optimization》2006,34(3):317-337
We study a resonant semilinear elliptic hemivariational inequality. Under some assumptions of strong resonance on the Clarke
subdifferential of the superpotential, and using nonsmooth critical point theory, the existence of a nontrivial solution of
the problem is shown.
This paper has been partially supported by the State Committee for Scientific Research of Poland (KBN) under research grants
no. 2 P03A 003 25 and no. 4 T07A 027 26. 相似文献
43.
The internal conical refraction of a Bessel beam of arbitrary order is studied theoretically. It is shown that a beam of the order m of arbitrary polarization in the general case is partially converted to Bessel beams of the order m ± 1 with orthogonal circular polarizations. Conditions for complete conversion of a beam of the order m to a Bessel beam of the order m?1 or m+1 are determined. 相似文献
44.
45.
Andrzej Wi?nicki 《Journal of Mathematical Analysis and Applications》2002,267(1):158-172
We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory. 相似文献
46.
We give characterizations of continuous distributions in terms of moments of order statistics when the sample size is random.
In particular, we characterize uniform, exponential, Pareto, and logistic distributions. Special cases of a random sample
size (logarithmic series, geometrical, truncated binomial, truncated negative binomial, and truncated Poisson distribution)
are also considered.
Proceedings of the XVII Seminar on Stability Problems for Stochastic Models, Kazan, Russia, 1995, Part I. 相似文献
47.
Stephen L. Howard Joyce E. Newberry Rosario C. Sausa Andrzej W. Miziolek 《Journal of the American Society for Mass Spectrometry》1993,4(2):152-158
A recently developed research apparatus for characterization of low-pressure premixed flames has been developed and was used to characterize the C2H4/N2O/Ar flame at 20 torr. This instrument incorporates several diagnostic techniques in one apparatus so that individual techniques can be quantitatively compared and the usable detection range (both in terms of resolution and species detection) expanded. Results discussed in this report include mass analysis by triple quadrupole mass spectrometer and temperature measurement by thermocouple. Concentration profiles in the one-dimensional flame include CO, N2, and C2H4, at nominal m/z 28 as well as CO2 and N2O at m/z 44. 相似文献
48.
Janusz Mierczyński Wenxian Shen Xiao-Qiang Zhao 《Journal of Differential Equations》2004,204(2):471-510
The purpose of this paper is to investigate uniform persistence for nonautonomous and random parabolic Kolmogorov systems via the skew-product semiflows approach. It is first shown that the uniform persistence of the skew-product semiflow associated with a nonautonomous (random) parabolic Kolmogorov system implies that of the system. Various sufficient conditions in terms of the so-called unsaturatedness and/or Lyapunov exponents for uniform persistence of the skew-product semiflows are then provided. Among others, it is shown that if the associated skew-product semiflow has a global attractor and its restriction to the boundary of the state space has a Morse decomposition which is unsaturated or whose external Lyapunov exponents are positive, then it is uniformly persistent. More specific conditions are discussed for uniform persistence in n-species, particularly 3-species, random competitive systems. 相似文献
49.
Andrzej Kaim 《Journal of polymer science. Part A, Polymer chemistry》2007,45(2):232-241
The competitiveness of the combination and disproportionation reactions between a 1‐phenylpropyl radical, standing for a growing polystyryl macroradical, and a 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) radical in the nitroxide‐mediated free‐radical polymerization of styrene was quantitatively evaluated by the study of the transition geometry and the potential energy profiles for the competing reactions with the use of quantum‐mechanical calculations at the density functional theory (DFT) UB3‐LYP/6‐311+G(3df, 2p)//(unrestricted) Austin Model 1 level of theory. The search for transition geometries resulted in six and two transition structures for the radical combination and disproportionation reactions, respectively. The former transition structures, mainly differing in the out‐of‐plane angle of the N? O bond in the transition structure TEMPO molecule, were correlated with the activation energy, which was determined to be in the range of 8.4–19.4 kcal mol?1 from a single‐point calculation at the DFT UB3‐LYP/6‐311+G(3df, 2p)//unrestricted Austin Model 1 level. The calculated activation energy for the disproportionation reaction was less favorable by a value of more than 30 kcal mol?1 in comparison with that for the combination reaction. The approximate barrier difference for the TEMPO addition and disproportionation reaction was slightly smaller for the styrene polymerization system than for the acrylonitrile polymerization system, thus indicating that a β‐proton abstraction through a TEMPO radical from the polymer backbone could diminish control over the radical polymerization of styrene with the nitroxide even more than in the latter system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 232–241, 2007 相似文献
50.
JPC – Journal of Planar Chromatography – Modern TLC - Emodin and twelve phenolic acids (ellagic, gallic, protocatechuic, homoprotocatechuic, caffeic, p-hydroxybenzoic, p-coumaric,... 相似文献