全文获取类型
收费全文 | 14351篇 |
免费 | 1335篇 |
国内免费 | 1075篇 |
专业分类
化学 | 5192篇 |
晶体学 | 35篇 |
力学 | 932篇 |
综合类 | 266篇 |
数学 | 7280篇 |
物理学 | 3056篇 |
出版年
2024年 | 26篇 |
2023年 | 134篇 |
2022年 | 199篇 |
2021年 | 276篇 |
2020年 | 400篇 |
2019年 | 369篇 |
2018年 | 373篇 |
2017年 | 463篇 |
2016年 | 593篇 |
2015年 | 433篇 |
2014年 | 696篇 |
2013年 | 1218篇 |
2012年 | 629篇 |
2011年 | 852篇 |
2010年 | 802篇 |
2009年 | 876篇 |
2008年 | 891篇 |
2007年 | 957篇 |
2006年 | 824篇 |
2005年 | 781篇 |
2004年 | 685篇 |
2003年 | 648篇 |
2002年 | 560篇 |
2001年 | 444篇 |
2000年 | 416篇 |
1999年 | 332篇 |
1998年 | 314篇 |
1997年 | 260篇 |
1996年 | 222篇 |
1995年 | 189篇 |
1994年 | 142篇 |
1993年 | 131篇 |
1992年 | 109篇 |
1991年 | 87篇 |
1990年 | 48篇 |
1989年 | 58篇 |
1988年 | 45篇 |
1987年 | 30篇 |
1986年 | 38篇 |
1985年 | 36篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A conjugate-gradient method is developed for computing the Moore-Penrose generalized inverseA
of a matrix and the associated projectors, by using the least-square characteristics of both the method and the inverseA
. Two dual algorithms are introduced for computing the least-square and the minimum-norm generalized inverses, as well asA
. It is shown that (i) these algorithms converge for any starting approximation; (ii) if they are started from the zero matrix, they converge toA
; and (iii) the trace of a sequence of approximations multiplied byA is a monotone increasing function converging to the rank ofA. A practical way of compensating the self-correcting feature in the computation ofA
is devised by using the duality of the algorithms. Comparison with Ben-Israel's method is made through numerical examples. The conjugate-gradient method has an advantage over Ben-Israel's method.After having completed the present paper, the author received from Professor M. R. Hestenes his paper entitledPseudo Inverses and Conjugate Gradients. This paper treated the same subject and appeared in Communications of the ACM, Vol. 18, pp. 40–43, 1975. 相似文献
62.
Mass determination by mass spectrometric methods (electrospray ionization mass spectrometry (ESI-MS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS)) of sodiumdodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE)-separated proteins is a well known procedure and reliable protocols are available. In our efforts to use the established methods to determine the molecular mass of the disulfide bridged, heterodimeric glycoprotein GP3 and to determine the carbohydrate content of each protein subunit we developed an in-gel chemical deglycosylation method. For this purpose we established experimental conditions that allow maximum extraction of the high molecular mass protein subunits and developed a routine method to apply the HF-pyridine deglycosylation protocol to proteins isolated from polyacrylamide gel pieces. The novel protocol and extraction procedure described can be used to analyze O-glycosylated proteins up to 150 kDa after SDS-PAGE separation. 相似文献
63.
Bruce R. McGarvey 《Coordination chemistry reviews》1998,170(1):75-92
Using a newly proposed approach involving an internally consistent set of equations, the ligand field parameters Δ/ξ, V/ξ and k are obtained from literature values of the g matrix for strong field d5 systems of various conformations in which |Δ/ξ|≤10. Qualitative analysis of the observed results is done using the Angular Overlap Model, AOM. 相似文献
64.
65.
综述了近年来利用一些新型的含氟砌块,通过它们的环加成反应来高效地合成 含氟杂环化合物的研究,其中包括以下两个部分:(1)用1,3—偶极环加成反应合 成五元含氟杂环化合物;(2)用杂原于Diels-Alder反应合成六元含氟杂环化合物. 相似文献
67.
In this paper, the photochemistry of glyoxal–hydroxylamine (Gly–HA) complexes is studied using FTIR matrix isolation spectroscopy and ab initio calculations. The irradiation of the Gly–HA complexes with the filtered output of a mercury lamp (λ > 370 nm) leads to their photoconversion to hydroxyketene–hydroxylamine complexes and the formation of hydroxy(hydroxyamino)acetaldehyde with a hemiaminal structure. The first product is the result of a double hydrogen exchange reaction between the aldehyde group of Gly and the amino or hydroxyl group of HA. The second product is formed as a result of the addition of the nitrogen atom of HA to the carbon atom of one aldehyde group of Gly, followed by the migration of the hydrogen atom from the amino group of hydroxylamine to the oxygen atom of the carbonyl group of glyoxal. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structures and vibrational spectra of the identified species. 相似文献
68.
LI De-Sheng LUO Cheng-Xin 《理论物理通讯》2006,46(8)
In this paper, we improve the method for deriving Jacobi elliptic function solutions of nonlinear evolution equations given in Ref. [12] and apply it to the integrable higher-order Broer-Kaup system in (2 1)-dimensional spaces.Some new elliptic function solutions are obtained. 相似文献
69.
In this paper, a quantum secure direct communication protocol using ensembles with the same density matrix is proposed. The two communication parties can realize the message transmission using this method through a quantum channel, each bit of information can be transmitted using an ensemble and read out through global measurement.The eavesdropping behavior can be detected through the channel diagnoses. 相似文献
70.