全文获取类型
收费全文 | 62439篇 |
免费 | 3340篇 |
国内免费 | 752篇 |
专业分类
化学 | 40511篇 |
晶体学 | 363篇 |
力学 | 2244篇 |
综合类 | 41篇 |
数学 | 9321篇 |
物理学 | 14051篇 |
出版年
2023年 | 555篇 |
2022年 | 547篇 |
2021年 | 786篇 |
2020年 | 1046篇 |
2019年 | 976篇 |
2018年 | 1351篇 |
2017年 | 1123篇 |
2016年 | 2042篇 |
2015年 | 1884篇 |
2014年 | 1975篇 |
2013年 | 3827篇 |
2012年 | 4312篇 |
2011年 | 4436篇 |
2010年 | 2726篇 |
2009年 | 2336篇 |
2008年 | 3808篇 |
2007年 | 3783篇 |
2006年 | 3386篇 |
2005年 | 3266篇 |
2004年 | 2757篇 |
2003年 | 2245篇 |
2002年 | 1968篇 |
2001年 | 1191篇 |
2000年 | 1042篇 |
1999年 | 821篇 |
1998年 | 614篇 |
1997年 | 557篇 |
1996年 | 719篇 |
1995年 | 492篇 |
1994年 | 536篇 |
1993年 | 523篇 |
1992年 | 537篇 |
1991年 | 451篇 |
1990年 | 417篇 |
1989年 | 422篇 |
1988年 | 326篇 |
1987年 | 326篇 |
1986年 | 277篇 |
1985年 | 463篇 |
1984年 | 405篇 |
1983年 | 281篇 |
1982年 | 385篇 |
1981年 | 362篇 |
1980年 | 330篇 |
1979年 | 304篇 |
1978年 | 288篇 |
1976年 | 298篇 |
1975年 | 280篇 |
1974年 | 277篇 |
1973年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
New tricyclic spacers, readily available through fourfold Mannich reaction of substituted dibenzyl ketones, were introduced into a series of ten H2O-soluble cyclophanes with spacious preorganized cavity binding sites. These spacers provide H2O-solubility with amine or crown-ether functionality remote from the cyclophane cavity while directing functional groups such as keto or OH groups in a precise geometrical array inside the cavity. The cyclophanes were designed to include organic substrates via a combination of apolar and specific polar functional group interactions. The X-ray crystal-structure analysis of the tritopic receptor 18 with one potential neutral-molecule and two cation-binding sites showed a large rectangular open cavity with dimensions of roughly 9 × 14 Å and a spacing of 9.7 Å between the O-atoms of two convergent C?O groups. Despite the binding-site preorganization, cyclophanes incorporating two of the new spacers did not show any substrate binding in aqueous solutions. The failure of these systems to function as receptors is mainly due to steric hindrance to important cyclophane aromatic ring-guest interactions. Also, the favorable solvation of the intracavity functionality may prevent the formation of complexes. Hybrid receptors constructed from the novel spacers and diphenylmethane units were found to bind flat aromatic substrates as well as bulky [4.2]paracyclophanes. The observed large differences in stability (ΔΔG°> 2 kcal mol?1) of the complexes formed by three structurally closely related hybrid receptors with convergent C?O, OH or CH2 groups and 6-hydroxynaphthalene-2-carbonitrile as guest can be explained by a strong solvation effect of the convergent functional groups on apolar inclusion complexation. 相似文献
32.
33.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
34.
35.
36.
We study the asymptotic properties of the Bayes estimator in models differentiable in quadratic mean (DQM) in the case of
independent and identically distributed observations. The goal is to define weak assumptions on the model under which this
estimator is asymptotically efficient, regular, and asymptotically of minimal risk. The results of the paper are applied to
models based on a mixture distribution, the Cauchy distribution with location and scale parameter, and the Weibull distribution.
Bibliography: 10 titles.
Published in Zapiski Nauchnykh Seminarov POMI, Vol. 328, 2005, pp. 114–146. 相似文献
37.
A. I. Magunov A. Ya. Faenov I. Yu. Skobelev T. A. Pikuz E. Biémont P. Quinet F. Blasco C. Bonte F. Dorchies T. Caillaud F. Salin C. Stenz 《Journal of Experimental and Theoretical Physics》2002,95(6):998-1005
The satellite structure of 1s2p 1,3 P 1-1s 21 S 0 lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters. 相似文献
38.
Michel Hébert 《Archive for Mathematical Logic》1991,31(2):133-143
Summary We give a syntactic characterization of (finitary) theories whose categories of models are closed under the formation of connected limits (respectively the formation of pullbacks and substructures) in the category of all structures. They are also those theories whose consistent extensions by new atomic facts admit in each component an initial structure (respectively an initial term structure), and also thoseT for whichM(T) is locally finitely multi-presentable in a canonical way. We also show that these two properties of theories are nonuniform. 相似文献
39.
We analyze the dynamics of an AdS5 braneworld with matter fields when gravity is allowed to deviate from the Einstein form on the brane. We consider exact five-dimensional warped solutions which are associated with conformal bulk fields of weight –4 and describe on the brane the following three dynamics: those of inhomogeneous dust, of generalized dark radiation, and of homogeneous polytropic dark energy. We show that, with modified gravity on the brane, the existence of such dynamical geometries requires the presence of non-conformal matter fields confined to the brane. 相似文献
40.