全文获取类型
收费全文 | 2782篇 |
免费 | 94篇 |
国内免费 | 13篇 |
专业分类
化学 | 1955篇 |
晶体学 | 118篇 |
力学 | 58篇 |
数学 | 209篇 |
物理学 | 549篇 |
出版年
2023年 | 26篇 |
2022年 | 69篇 |
2021年 | 53篇 |
2020年 | 51篇 |
2019年 | 66篇 |
2018年 | 47篇 |
2017年 | 65篇 |
2016年 | 109篇 |
2015年 | 54篇 |
2014年 | 75篇 |
2013年 | 227篇 |
2012年 | 145篇 |
2011年 | 173篇 |
2010年 | 109篇 |
2009年 | 83篇 |
2008年 | 154篇 |
2007年 | 136篇 |
2006年 | 134篇 |
2005年 | 113篇 |
2004年 | 85篇 |
2003年 | 75篇 |
2002年 | 63篇 |
2001年 | 32篇 |
2000年 | 49篇 |
1999年 | 27篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 22篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 23篇 |
1992年 | 29篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 31篇 |
1985年 | 25篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 31篇 |
1981年 | 35篇 |
1980年 | 25篇 |
1979年 | 25篇 |
1978年 | 23篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1975年 | 22篇 |
1973年 | 19篇 |
排序方式: 共有2889条查询结果,搜索用时 31 毫秒
801.
[reaction: see text] Aldehydes, in the presence of methanol, undergo oxidative transformation to the corresponding esters upon treatment with catalytic amounts of vanadium pentoxide in combination with oxidant hydrogen peroxide. Mild reaction conditions, shorter reaction times, high efficiencies, cost-effectiveness, and facile isolation of the desired products make the present methodology a practical alternative. 相似文献
802.
Resource allocation in the North Sea demersal fisheries: A goal programming approach 总被引:1,自引:0,他引:1
Simon Mardle Sean Pascoe Mehrdad Tamiz Dylan Jones 《Annals of Operations Research》2000,94(1-4):321-342
The management of a fishery is a complex task generally involving multiple, often conflicting, objectives. These objectives typically include economic, biological and social goals such as improving the income of fishers, reducing the catch of depleted species and maintaining employment.Multicriteria decision making (MCDM) techniques appear wellsuited to such a management problem, allowing compromises between conflicting objectives to be analysed in a structured framework. In comparison to other fields, such as water resource planning, forestry and agriculture, there have been few applications of MCDM to fisheries.In this paper, a goal programming model of the North Sea demersal fishery is presented. The model is used to demonstrate the potential applicability of this type of approach to the analysis and development of fisheries management plans with multiple objectives. Alternative scenarios are considered for the problem, and tradeoffs between given objectives are also highlighted and discussed. 相似文献
803.
Brandenburg G Ershov A Gao YS Kim DY Wilson R Browder TE Li Y Rodriguez JL Yamamoto H Bergfeld T Eisenstein BI Ernst J Gladding GE Gollin GD Hans RM Johnson E Karliner I Marsh MA Palmer M Plager C Sedlack C Selen M Thaler JJ Williams J Edwards KW Janicek R Patel PM Sadoff AJ Ammar R Bean A Besson D Davis R Kwak N Zhao X Anderson S Frolov VV Kubota Y Lee SJ Mahapatra R O'Neill JJ Poling R Riehle T Smith A Stepaniak CJ Urheim J Ahmed S Alam MS Athar SB Jian L Ling L Saleem M Timm S Wappler F 《Physical review letters》2000,85(15):3095-3099
Using 13.4 fb(-1) of data collected with the CLEO detector at the Cornell Electron Storage Ring, we have observed 300 events for the two-photon production of ground-state pseudoscalar charmonium in the decay eta(c)-->K(0)(S)K-/+pi(+/-). We have measured the eta(c) mass to be [2980.4+/-2.3 (stat)+/-0.6 (syst)] MeV and its full width as [27.0+/-5.8 (stat)+/-1.4 (syst)] MeV. We have determined the two-photon partial width of the eta(c) meson to be [7.6+/-0.8 (stat)+/-0.4 (syst)+/-2.3 (br)] keV, with the last uncertainty associated with the decay branching fraction. 相似文献
804.
In this paper we present a novel technique for the computation of orthonormal polynomial expansions. The proposed method is very straightforward; given a function to be expanded in a polynomial series, we first use the FFT to compute a vector of Fourier coefficients. Then, using a change of basis transformation, we go from the Fourier coefficients to the polynomial coefficients. Convergence properties for this new approach are investigated. 相似文献
805.
The nitrosation of monophenylamido substituted quadridentate Schiff base complexes of copper(II) are observed to adopt N-bonded
isonitroso coordination whereas the phenylisocyanation of the corresponding mononitrosated quadridentate complexes are found
to prefer O-bonded isonitroso coordination. 相似文献
806.
807.
Alan R. Katritzky George de Ville Ranjan C. Patel Richard Harlow 《Tetrahedron letters》1982,23(12):1241-1242
1-Aryl-2-(2′-benzimidazolyl)-4,6-diphenyl-pyridiniums are converted photochemically into 2-[2′-(1′-arylbenzimidazolyl)]-4,6-diphenylpyridines. X-Ray crystal analysis comfirms the structure for the -chlorophenyl derivative. 相似文献
808.
809.
Lattice entrapment of glycolytic enzymes 总被引:1,自引:0,他引:1
810.
It is shown that in junction lasers containing absorbing traps the onset of stimulated emission is followed by a reduction of spontaneous emission such as observed by Nicoll and Brosson et al. Detailed agreement with the latter's experimental results is obtained. 相似文献