全文获取类型
收费全文 | 7427篇 |
免费 | 1333篇 |
国内免费 | 1721篇 |
专业分类
化学 | 4755篇 |
晶体学 | 46篇 |
力学 | 671篇 |
综合类 | 9篇 |
数学 | 796篇 |
物理学 | 4204篇 |
出版年
2024年 | 2篇 |
2023年 | 133篇 |
2022年 | 227篇 |
2021年 | 228篇 |
2020年 | 251篇 |
2019年 | 206篇 |
2018年 | 157篇 |
2017年 | 171篇 |
2016年 | 170篇 |
2015年 | 254篇 |
2014年 | 365篇 |
2013年 | 539篇 |
2012年 | 628篇 |
2011年 | 728篇 |
2010年 | 611篇 |
2009年 | 694篇 |
2008年 | 559篇 |
2007年 | 670篇 |
2006年 | 604篇 |
2005年 | 476篇 |
2004年 | 394篇 |
2003年 | 335篇 |
2002年 | 266篇 |
2001年 | 301篇 |
2000年 | 229篇 |
1999年 | 275篇 |
1998年 | 181篇 |
1997年 | 166篇 |
1996年 | 142篇 |
1995年 | 105篇 |
1994年 | 93篇 |
1993年 | 86篇 |
1992年 | 104篇 |
1991年 | 66篇 |
1990年 | 29篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
991.
In this paper, the transformations of generating systems of Euclidean space are examined in connection with the Drazin inverse of their Gram matrices and the notion of biorthogonal systems is generalized. The results obtained in this paper can be considered as the extension of some recent results concerning Moore-Penrose biorthogonal systems and reflexiveg-inverse systems in Euclidean spaces. 相似文献
992.
Influence of relaxation effects on probabilities of the 2s2p35S2-2s22p2 3P1,2 intercombination transitions in NII 下载免费PDF全文
Transition probabilities of the 2s2p^3 {}^5S_2-2s^22p^2 {}^3P_{1,2} intercombination transitions in NII have been calculated by using a large-scale multiconfiguration Dirac-Fock method. In the calculation the most important effects of relativity, correlation, and relaxation are considered. From the calculated transition probabilities, the lifetime of the 2s2p^3 {}^5S_2 metastable state is derived. The result is in excellent agreement with the latest experimental result. In the meantime the influence of anomalously strong relaxation effects on probabilities of the 2s2p^3 {}^5S_2-2s^22p^2 {}^3P_{1,2} lines in NII have been found. 相似文献
993.
A highly stereoselective synthesis of the side Chain enantiomers of brassinolide and dolicholide through an aldol reaction of 2-(4-methoxy benzyloxyl) proplonylaldehyde (5) with the anion of 1- ( tert -butyldimethylsiloxy )-3-methyl-2-butanone ( 6 ) is described. 相似文献
994.
995.
996.
An efficient total synthesis of (±)-isocembrene via an intramolecular Stille cross-coupling reaction is described. A novel strategy towards the 1,3-diene-based cembrane-type macrocyclic diterpenoids has been realized. 相似文献
997.
The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular, densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to substrates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined. 相似文献
998.
This paper introduces a bi-virus model with time-varying susceptibility. The model describes the case that there coexist two viruses and the time-varying susceptibility due to repeated infections. For different parameters, we investigate the stability of various equilibriums. Under appropriate conditions the two viruses show competitive relationship, that is, one virus will eventually become a pandemic, and the other virus will eventually disappear. For this case, we further study the dynamical behavior of virus transmission. The model shows some new phenomena, that is, the outbreak of the virus will be delayed appropriately, giving people an illusion. Finally, we present a numerical example to illustrate the effectiveness of the theoretical results. 相似文献
999.
Abstract The two 1-aryl-5-methyl-1,2,3-triazole derivatives were prepared by the 1-aryl-5-methyl-1,2,3-triazol-4-carboxylic acids 3. The yielded products 4a–b were confirmed by NMR, MS, IR spectra. We investigated the crystalline structure of compounds 4a and 4b. Compound 4a, C9H8BrN3, Mr = 238.09, crystallizes in the monoclinic space group P2(1)/n with unit cell parameters a = 11.660(2), b = 7.668(2), c = 11.818(2) ?, α = 90.00, β = 116.01(3), γ = 90.00o. V = 949.6(3) ?3, Z = 4, Dx = 1.665 Mg m−3. The final R was 0.0477. Compound 4b, C13H11N3, Mr = 209.25, crystallized in the orthorhombic space group Pbca with unit cell parameters a = 10.373(2) ?, b = 11.691(2) ?, c = 17.579(4) ?, α = 90.00o, β = 90.00o, γ = 90.00o, V = 2131.8(7) ?3, Z = 8, D
m = 1.304 Mg m−3. The final R was 0.0565.
Index Abstract The two 1-aryl-5-methyl-1,2,3-triazole derivatives were prepared by the 1-aryl-5-methyl-1,2,3-triazol-4-carboxylic acids 3. The yielded products 4a–b were confirmed by NMR, MS, IR spectra. We investigated the crystalline structure of compounds 4a and 4b. Compound 4a, C9H8BrN3, Mr = 238.09, crystallizes in the monoclinic space group P2(1)/n with unit cell parameters a = 11.660(2), b = 7.668(2), c = 11.818(2) ?, α = 90.00, β = 116.01(3), γ =90.00o. V = 949.6(3) ?3, Z = 4, Dx = 1.665 Mg m−3. The final R was 0.0477. Compound 4b, C13H11N3, Mr = 209.25, crystallized in the orthorhombic space group Pbca with unit cell parameters a = 10.373(2) ?, b = 11.691(2) ?, c = 17.579(4) ?, α = 90.00o, β = 90.00o, γ = 90.00o, V = 2131.8(7) ?3, Z = 8, D
m = 1.304 Mg m−3. The final R was 0.0565.
相似文献
1000.