全文获取类型
收费全文 | 35866篇 |
免费 | 1549篇 |
国内免费 | 1483篇 |
专业分类
化学 | 27087篇 |
晶体学 | 348篇 |
力学 | 685篇 |
综合类 | 10篇 |
数学 | 5237篇 |
物理学 | 5531篇 |
出版年
2023年 | 227篇 |
2022年 | 194篇 |
2021年 | 958篇 |
2020年 | 660篇 |
2019年 | 785篇 |
2018年 | 674篇 |
2017年 | 671篇 |
2016年 | 1371篇 |
2015年 | 1193篇 |
2014年 | 1296篇 |
2013年 | 2677篇 |
2012年 | 2534篇 |
2011年 | 2768篇 |
2010年 | 1679篇 |
2009年 | 1832篇 |
2008年 | 2211篇 |
2007年 | 2138篇 |
2006年 | 1820篇 |
2005年 | 1731篇 |
2004年 | 1888篇 |
2003年 | 1397篇 |
2002年 | 1301篇 |
2001年 | 627篇 |
2000年 | 527篇 |
1999年 | 400篇 |
1998年 | 384篇 |
1997年 | 327篇 |
1996年 | 375篇 |
1995年 | 291篇 |
1994年 | 239篇 |
1993年 | 230篇 |
1992年 | 206篇 |
1991年 | 196篇 |
1990年 | 169篇 |
1989年 | 182篇 |
1988年 | 177篇 |
1987年 | 147篇 |
1986年 | 159篇 |
1985年 | 242篇 |
1984年 | 254篇 |
1983年 | 161篇 |
1982年 | 179篇 |
1981年 | 170篇 |
1980年 | 159篇 |
1979年 | 125篇 |
1978年 | 117篇 |
1977年 | 101篇 |
1976年 | 98篇 |
1975年 | 80篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Lévy processes in matrix Lie groups are studied. Subordination (random time change) is used to show that quasi-invariance of the Brownian motion in a Lie group induces absolute continuity of the laws of the corresponding pure jump processes. These results are applied to several examples which are discussed in detail. 相似文献
93.
D.L. Skuratov Yu.L. Ratis I.A. Selezneva J. Pérez P. Fernández de Córdoba J.F. Urchueguía 《Applied Mathematical Modelling》2007
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method. 相似文献
94.
Adam Kiersnowski Jochen S. Gutmann Jacek Pigłowski 《Journal of Polymer Science.Polymer Physics》2007,45(17):2350-2367
ε‐caprolactone was polymerized in the presence of neat montmorillonite or organomontmorillonites to obtain a variety of poly(ε‐caprolactone) (PCL)‐based systems loaded with 10 wt % of the silicates. The materials were thoroughly investigated by different X‐ray scattering techniques to determine factors affecting structure of the systems. For one of the nanocomposites it was found that varying the temperature in the range corresponding to crystallization of PCL causes reversible changes in the interlayer distance of the organoclay. Extensive experimental and literature studies on this phenomenon provided clues indicating that this effect might be a result of two‐dimensional ordering of PCL chains inside the galleries of the silicate. Small angle X‐ray scattering and wide angle X‐ray scattering investigation of filaments oriented above melting point of PCL revealed that polymer lamellae were oriented perpendicularly to particles of unmodified silicate, while in PCL/organoclay systems they were found parallel to clay tactoids. Calorimetric and microscopic studies shown that clay particles are effective nucleating agents. In the nanocomposites, PCL crystallized 20‐fold faster than in the neat polymer. The crystallization rate in nanocomposites was also significantly higher than in microcomposite. Further research provided an insight how the presence of the filler affects crystalline fraction and spherulitic structure of the polymer matrix in the investigated systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2350–2367, 2007 相似文献
95.
In this Note, we give a necessary and sufficient condition for Lagrangians in a symplectic vector bundle to be deformed stably into transversal Lagrangians. In the case of three Lagrangians, we show that the associated Grothendieck group can be identified with a Hermitian K-theory group. To cite this article: M. Karoubi, M.L. Lapa de Souza, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
96.
Sajewicz Mieczysław Hauck Heinz-E. Drabik Gabriela Namysło Ewa Głód Bronisław Kowalska Teresa 《平面色谱法杂志一现代薄层色谱法》2006,19(4):278-281
JPC – Journal of Planar Chromatography – Modern TLC - We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of... 相似文献
97.
Maria Chudnovsky Jim Geelen Bert Gerards Luis Goddyn Michael Lohman Paul Seymour 《Combinatorica》2006,26(5):521-532
Let G=(V,E) be an oriented graph whose edges are labelled by the elements of a group Γ and let A⊂V. An A-path is a path whose ends are both in A. The weight of a path P in G is the sum of the group values on forward oriented arcs minus the sum of the backward oriented arcs in P. (If Γ is not abelian, we sum the labels in their order along the path.) We are interested in the maximum number of vertex-disjoint
A-paths each of non-zero weight. When A = V this problem is equivalent to the maximum matching problem. The general case also includes Mader's S-paths problem. We prove that for any positive integer k, either there are k vertex-disjoint A-paths each of non-zero weight, or there is a set of at most 2k −2 vertices that meets each of the non-zero A-paths. This result is obtained as a consequence of an exact min-max theorem.
These results were obtained at a workshop on Structural Graph Theory at the PIMS Institute in Vancouver, Canada. This research
was partially conducted during the period the first author served as a Clay Mathematics Institute Long-Term Prize Fellow. 相似文献
98.
In the present work, the effect of the oxidizing treatment with nitric acid on three activated carbon samples has been studied. The influence of the acid treatment on the surface groups of the different samples has been investigated by means of FT-IR spectroscopy. The pore size distributions of the different samples were determined by means of the HK and DFT methods. The HK method points out a moderate increment of the microporosity due to the action of the nitric acid, whereas the DFT method shows an increase in the microporosity range above 17 Å. Finally, the values of the fractal dimension reveal that the treatment of the samples with nitric acid leads to chemical reactions of a limited extent. 相似文献
99.
100.
Maria Conceição A. Silva Portela Emmanuel Thanassoulis 《Annals of Operations Research》2006,145(1):129-147
This paper re-assesses three independently developed approaches that are aimed at solving the problem of zero-weights or non-zero
slacks in Data Envelopment Analysis (DEA). The methods are weights restricted, non-radial and extended facet DEA models. Weights
restricted DEA models are dual to envelopment DEA models with restrictions on the dual variables (DEA weights) aimed at avoiding
zero values for those weights; non-radial DEA models are envelopment models which avoid non-zero slacks in the input-output
constraints. Finally, extended facet DEA models recognize that only projections on facets of full dimension correspond to
well defined rates of substitution/transformation between all inputs/outputs which in turn correspond to non-zero weights
in the multiplier version of the DEA model. We demonstrate how these methods are equivalent, not only in their aim but also
in the solutions they yield. In addition, we show that the aforementioned methods modify the production frontier by extending
existing facets or creating unobserved facets. Further we propose a new approach that uses weight restrictions to extend existing
facets. This approach has some advantages in computational terms, because extended facet models normally make use of mixed
integer programming models, which are computationally demanding. 相似文献