全文获取类型
收费全文 | 6969篇 |
免费 | 179篇 |
国内免费 | 6篇 |
专业分类
化学 | 4195篇 |
晶体学 | 35篇 |
力学 | 135篇 |
数学 | 1415篇 |
物理学 | 1374篇 |
出版年
2022年 | 52篇 |
2021年 | 83篇 |
2020年 | 93篇 |
2019年 | 87篇 |
2018年 | 180篇 |
2017年 | 149篇 |
2016年 | 247篇 |
2015年 | 188篇 |
2014年 | 231篇 |
2013年 | 554篇 |
2012年 | 375篇 |
2011年 | 521篇 |
2010年 | 270篇 |
2009年 | 241篇 |
2008年 | 396篇 |
2007年 | 396篇 |
2006年 | 371篇 |
2005年 | 274篇 |
2004年 | 238篇 |
2003年 | 166篇 |
2002年 | 153篇 |
2001年 | 107篇 |
2000年 | 89篇 |
1999年 | 64篇 |
1998年 | 54篇 |
1997年 | 51篇 |
1996年 | 52篇 |
1995年 | 52篇 |
1993年 | 48篇 |
1992年 | 55篇 |
1991年 | 43篇 |
1990年 | 48篇 |
1989年 | 52篇 |
1988年 | 48篇 |
1987年 | 47篇 |
1986年 | 41篇 |
1985年 | 61篇 |
1984年 | 68篇 |
1983年 | 65篇 |
1982年 | 61篇 |
1981年 | 41篇 |
1980年 | 56篇 |
1979年 | 48篇 |
1978年 | 70篇 |
1977年 | 41篇 |
1976年 | 52篇 |
1975年 | 41篇 |
1974年 | 48篇 |
1973年 | 40篇 |
1972年 | 34篇 |
排序方式: 共有7154条查询结果,搜索用时 31 毫秒
21.
22.
23.
24.
25.
26.
Marijana ?aković Zora Popović 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):m507-m509
In the title compound, [Ni(N3)2(C6H6N2O)2], the NiII atom lies on an inversion centre. The distorted octahedral nickel(II) coordination environment contains two planar trans-related N,O-chelating picolinamide ligands in one plane and two monodentate azide ligands perpendicular to this plane. Molecules are linked into a three-dimensional framework by N—H...N hydrogen bonds. 相似文献
27.
Miodrag M. Spalević 《Numerical Algorithms》2007,46(3):253-264
We have recently proposed a very simple numerical method for constructing the averaged Gaussian quadrature formulas. These
formulas exist in many more cases than the real positive Gauss–Kronrod formulas. In this note we try to answer whether the
averaged Gaussian formulas are an adequate alternative to the corresponding Gauss–Kronrod quadrature formulas, to estimate
the remainder term of a Gaussian rule. 相似文献
28.
We consider a four-dimensional generalization of Hess–Appel’rot system and costruct its Lax pair. Both classical and algebro-geometric integration procedure are proceeded. The algebro-geometric integration is based on deep facts from geometry of Prym varieties such as the Mumford relation and Mumford-Dalalyan theory. The integration is similar to the integration of Lagrange bitop which has recetly been performed by the authors. 相似文献
29.
Xingping Qiu Svetlana A. Sukhishvili 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):183-191
Free‐radical copolymerizations of N‐vinylcaprolactam (VCL) and glycidyl methacrylate (GMA) were investigated to synthesize temperature‐responsive reactive copolymers with minimized compositional heterogeneity. The average copolymer composition was determined by Fourier transform infrared and nuclear magnetic resonance techniques. The reactivity ratios for VCL and GMA were found to be 0.0365 ± 0.0009 and 6.44 ± 0.36 by the Fineman–Ross method and 0.039 ± 0.006 and 6.75 ± 0.29 by the Kelen–Tudos method, respectively. When prepared by batch polymerization, VCL–GMA copolymers had a highly heterogeneous composition and fractions of different solubilities in water. The use of a gradual feeding technique, which included the sequential addition of more reactive GMA monomer into the reaction, yielded copolymers with much more homogeneous composition. The produced copolymers with 0.9 and 0.11 fractional GMA contents preserved their temperature‐responsive properties and precipitated from aqueous solutions when the temperature exceeded 31 °C. The GMA units in the VCL–GMA copolymers were capable of reacting with amino end‐functionalized poly(ethylene oxide) at room temperature to produce poly(N‐vinylcaprolactam)–poly(ethylene oxide) graft copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 183–191, 2006 相似文献
30.
Monoclinic (N2H6)3Zr2F13·F crystallizes in space group P21-C
2
2
(No. 4) with unit cell dimensionsa=5.670(1),b=10.984(2),c=10.601(2) Å,=93.88(1)°,V=658.7(4) Å3 andZ=2. Two different types of N2H6
2+ ions are present. One is involved in strong H-bonds to F– ions in infinite chains running along the a axis (the shortest N-F distance is 2.437(5) Å), and the other links the structure through weaker bi- and trifurcated H-bonds to fluorine ligands of the Zr2F13
5– ions. The N-N bond lengths range from 1.430(5) to 1.446(5) Å with apparently no meaningful correlation to the type of N2H2
2+ ions. The Zr2F13
5– ions have very nearly C2 point symmetry and are formed by joining two distorted bicapped trigonal prisms of ZrF8-units through a common face. Distances of Zr-F terminal bonds range from 2.015(2) to 2.112(2) Å and of bridging bonds from 2.133(2) to 2.212(2) Å. (N2H6)3Hf2F13·F is isomorphous. The vibrational spectra of the two compounds are nearly identical, with the exception of a strong infrared band, which is assigned to a stretching mode with the moving central atom within the anion. The anion part of the spectrum is simple, showing broad unresolved bands. The cation part shows two types of N2H6
– ions. H-Bonding is strongly present in the spectra, but no simple correlations with the H-bond strength is evident. 相似文献