全文获取类型
收费全文 | 359975篇 |
免费 | 21125篇 |
国内免费 | 13021篇 |
专业分类
化学 | 219657篇 |
晶体学 | 4461篇 |
力学 | 15879篇 |
综合类 | 725篇 |
数学 | 43665篇 |
物理学 | 109734篇 |
出版年
2022年 | 4865篇 |
2021年 | 5441篇 |
2020年 | 6368篇 |
2019年 | 6265篇 |
2018年 | 6865篇 |
2017年 | 6386篇 |
2016年 | 9746篇 |
2015年 | 8247篇 |
2014年 | 10426篇 |
2013年 | 18765篇 |
2012年 | 19366篇 |
2011年 | 21464篇 |
2010年 | 14800篇 |
2009年 | 14042篇 |
2008年 | 17755篇 |
2007年 | 17169篇 |
2006年 | 15954篇 |
2005年 | 14343篇 |
2004年 | 12252篇 |
2003年 | 10356篇 |
2002年 | 9871篇 |
2001年 | 9436篇 |
2000年 | 7499篇 |
1999年 | 6086篇 |
1998年 | 5059篇 |
1997年 | 4814篇 |
1996年 | 4910篇 |
1995年 | 4199篇 |
1994年 | 4215篇 |
1993年 | 3862篇 |
1992年 | 4028篇 |
1991年 | 3904篇 |
1990年 | 3592篇 |
1989年 | 3358篇 |
1988年 | 3117篇 |
1987年 | 3019篇 |
1986年 | 3022篇 |
1985年 | 3868篇 |
1984年 | 3838篇 |
1983年 | 3157篇 |
1982年 | 3447篇 |
1981年 | 3150篇 |
1980年 | 2895篇 |
1979年 | 3038篇 |
1978年 | 3230篇 |
1977年 | 3223篇 |
1976年 | 3304篇 |
1975年 | 3007篇 |
1974年 | 3121篇 |
1973年 | 3162篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
The synthesis of polyaniline via the oxidation of aniline with ammonium bisulfate in water and formic acid was monitored potentiometrically by following the yield and changes in the electric conductivity of the polymer. Three basic stages of the process were determined, including the buildup of oligomeric quinone imines, chain propagation via aniline addition of quinone imine groups, and postpolymerization. The oligomeric intermediate products, substituted quinone imines, were isolated. On the basis of IR and NMR data, the presence of tri-and tetrasubstituted aromatic groups and phenazine structural units in the polyaniline chain was revealed. 相似文献
953.
Bart M. J. M. Suijkerbuijk Duncan M. Tooke Anthony L. Spek Gerard van Koten Robertus J. M. Klein Gebbink Prof. Dr. 《无机化学与普通化学杂志》2007,633(15):2649-2653
A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures. 相似文献
954.
S. V. Valueva L. N. Borovikova V. V. Koreneva Ya. I. Nazarkina A. I. Kipper V. V. Kopeikin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(7):1170-1173
Nanostructures formed during the reduction of ionic selenium in the selenite-ascorbate redox system in an aqueous solution of bovine serum albumin (BSA) were studied using static and dynamic light scattering and flow birefringence. It was established that this process results in the formation of stable aggregates of selenium nanoparticles that adsorb BSA molecules. It was found that highly-ordered superhigh-molecular-weight spherical nanostructures with high density and unique morphology are formed. Experiments with a cell culture of promyelocytic leukemia HL-60 showed that BSA adsorbed on selenium nanoparticles can inhibit the growth of tumor cells and deactivate free radicals with an efficiency comparable with that of sodium selenite. 相似文献
955.
We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599. 相似文献
956.
957.
This work deals with the polymer latexes synthesized using zinc-containing monomers. The effect of the ligand environment of the zinc-containing monomers on the colloidal and rheological properties of the latexes, as well as on mechanical properties of their films is studied. Mixed zinc salts containing the residues of saturated and unsaturated carboxylic acids are shown to be more efficient cross-linking agents than the symmetric salts of this metal. 相似文献
958.
属性区间识别理论模型研究及其应用 总被引:15,自引:3,他引:12
根据程乾生教授创立的属性识别理论模型[1] ,提出了属性测度区间的概念 ,建立了属性区间识别理论模型 ,并在自然科学学术期刊质量评价中进行了应用 . 相似文献
959.
We derive a moderate deviation principle for the lower tail probabilities of the length of a longest increasing subsequence in a random permutation. It refers to the regime between the lower tail large deviation regime and the central limit regime. The present article together with the upper tail moderate deviation principle in Ref. 12 yields a complete picture for the whole moderate deviation regime. Other than in Ref. 12, we can directly apply estimates by Baik, Deift, and Johansson, who obtained a (non-standard) Central Limit Theorem for the same quantity. 相似文献
960.
Motivated by Mandelbrot's [The Fractal Geometry of Nature, Freeman, San Francisco, 1983] idea of referring to lacunarity of Cantor sets in terms of departure from translation invariance, we study the properties of these translation sets and show how they can be used for a classification purpose. This first paper of a series of two will be devoted to set up the fundamental properties of Hausdorff measures of those intersection sets. Using the triadic expansion of the shifting number, we determine the fractal structure of intersection of triadic Cantor sets with their translates. We found that the Hausdorff measure of these sets forms a discrete spectrum whose non-zero values come only from those shifting numbers with a finite triadic expansion. We characterize this set of shifting numbers by giving a partition expression of it and the steps of its construction from a fundamental root set. Finally, we prove that intersection of Cantor sets with their translates verify a measure-conservation law with scales. The second paper will take advantage of the properties exposed here in order to utilize them in a classification context. Mainly, it will deal with the use of the discrete spectrum of measures to distinguish two Cantor-like sets of the same fractal dimension. 相似文献