全文获取类型
收费全文 | 125295篇 |
免费 | 6158篇 |
国内免费 | 12610篇 |
专业分类
化学 | 78816篇 |
晶体学 | 2213篇 |
力学 | 3386篇 |
综合类 | 947篇 |
数学 | 30177篇 |
物理学 | 28524篇 |
出版年
2023年 | 787篇 |
2022年 | 1675篇 |
2021年 | 2052篇 |
2020年 | 2462篇 |
2019年 | 3017篇 |
2018年 | 2602篇 |
2017年 | 3288篇 |
2016年 | 3300篇 |
2015年 | 2789篇 |
2014年 | 4116篇 |
2013年 | 8427篇 |
2012年 | 7142篇 |
2011年 | 6831篇 |
2010年 | 5843篇 |
2009年 | 7521篇 |
2008年 | 7966篇 |
2007年 | 8242篇 |
2006年 | 7490篇 |
2005年 | 6093篇 |
2004年 | 6131篇 |
2003年 | 5305篇 |
2002年 | 6697篇 |
2001年 | 4448篇 |
2000年 | 4078篇 |
1999年 | 3972篇 |
1998年 | 3437篇 |
1997年 | 2579篇 |
1996年 | 2138篇 |
1995年 | 1871篇 |
1994年 | 1673篇 |
1993年 | 1375篇 |
1992年 | 1289篇 |
1991年 | 839篇 |
1990年 | 703篇 |
1989年 | 671篇 |
1988年 | 489篇 |
1987年 | 410篇 |
1986年 | 396篇 |
1985年 | 498篇 |
1984年 | 417篇 |
1983年 | 257篇 |
1982年 | 371篇 |
1981年 | 445篇 |
1980年 | 382篇 |
1979年 | 271篇 |
1978年 | 293篇 |
1977年 | 235篇 |
1976年 | 211篇 |
1975年 | 123篇 |
1974年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Andrea Blunck 《Monatshefte für Mathematik》1997,123(2):93-107
In this note we show that the chain space belonging to a quadric can be embedded into the chain geometry over a Clifford algebra via a generalized stereographic projection. 相似文献
62.
Summary. Let be a square matrix dependent on parameters and , of which we choose as the eigenvalue parameter. Many computational problems are equivalent to finding a point such that has a multiple eigenvalue at . An incomplete decomposition of a matrix dependent on several parameters is proposed. Based on the developed theory two new algorithms are
presented for computing multiple eigenvalues of with geometric multiplicity . A third algorithm is designed for the computation of multiple eigenvalues with geometric multiplicity but which also appears to have local quadratic convergence to semi-simple eigenvalues. Convergence analyses of these methods
are given. Several numerical examples are presented which illustrate the behaviour and applications of our methods.
Received December 19, 1994 / Revised version received January 18, 1996 相似文献
63.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework. 相似文献
64.
65.
Addition of functionalized zinc-copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts 3d were determined by single X-ray diffraction analysis. 相似文献
66.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2]
n
·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993. 相似文献
67.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
68.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
69.
计算全息检测非球面干涉场的理论分析与实验结果 总被引:2,自引:0,他引:2
本文应用光学全息术及傅里叶光学的理论对计算全息图干涉检测非球面面形的光路及干涉场进行了理论分析,提出了其干涉场为不定域干涉的观点,并在实验中予以证实. 相似文献
70.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献