全文获取类型
收费全文 | 2318篇 |
免费 | 104篇 |
国内免费 | 17篇 |
专业分类
化学 | 1574篇 |
晶体学 | 6篇 |
力学 | 51篇 |
数学 | 349篇 |
物理学 | 459篇 |
出版年
2024年 | 5篇 |
2023年 | 30篇 |
2022年 | 73篇 |
2021年 | 84篇 |
2020年 | 72篇 |
2019年 | 117篇 |
2018年 | 76篇 |
2017年 | 73篇 |
2016年 | 92篇 |
2015年 | 84篇 |
2014年 | 104篇 |
2013年 | 126篇 |
2012年 | 169篇 |
2011年 | 190篇 |
2010年 | 114篇 |
2009年 | 81篇 |
2008年 | 158篇 |
2007年 | 137篇 |
2006年 | 138篇 |
2005年 | 122篇 |
2004年 | 106篇 |
2003年 | 62篇 |
2002年 | 57篇 |
2001年 | 22篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有2439条查询结果,搜索用时 31 毫秒
71.
72.
Natalia V. Kuratieva Marina I. Naumova Dmitry Yu. Naumov 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):i129-i131
The title compounds, hexaaquacobalt(II) bis(hypophosphite), [Co(H2O)6](H2PO2)2, and hexaaquacobalt(II)/nickel(II) bis(hypophosphite), [Co0.5Ni0.5(H2O)6](H2PO2)2, are shown to adopt the same structure as hexaaquamagnesium(II) bis(hypophosphite). The packing of the Co(Ni) and P atoms is the same as in the structure of CaF2. The CoII(NiII) atoms have a pseudo‐face‐centred cubic cell, with a = b~ 10.3 Å, and the P atoms occupy the tetrahedral cavities. The central metal cation has a slightly distorted octahedral coordination sphere. The geometry of the hypophosphite anion in the structure is very close to ideal, with point symmetry mm2. Each O atom of the hypophosphite anion is hydrogen bonded to three water molecules from different cation complexes, and each H atom of the hypophosphite anion is surrounded by three water molecules from further different cation complexes. 相似文献
73.
74.
Vyacheslav Z. Grines Dmitry S. Malyshev Olga V. Pochinka Svetlana Kh. Zinina 《Regular and Chaotic Dynamics》2016,21(2):189-203
It is well known that the topological classification of structurally stable flows on surfaces as well as the topological classification of some multidimensional gradient-like systems can be reduced to a combinatorial problem of distinguishing graphs up to isomorphism. The isomorphism problem of general graphs obviously can be solved by a standard enumeration algorithm. However, an efficient algorithm (i. e., polynomial in the number of vertices) has not yet been developed for it, and the problem has not been proved to be intractable (i. e., NPcomplete). We give polynomial-time algorithms for recognition of the corresponding graphs for two gradient-like systems. Moreover, we present efficient algorithms for determining the orientability and the genus of the ambient surface. This result, in particular, sheds light on the classification of configurations that arise from simple, point-source potential-field models in efforts to determine the nature of the quiet-Sun magnetic field. 相似文献
75.
76.
- Download : Download high-res image (110KB)
- Download : Download full-size image
77.
Dmitry E. Siyutkin Alexander S. Kucherenko Larisa L. Frolova Alexander V. Kuchin Sergei G. Zlotin 《Tetrahedron: Asymmetry》2013,24(12):776-779
Novel stereoisomeric natural pinane-derived bifunctional catalysts 3a–d bearing a pyrrolidine unit have been synthesized and examined in the asymmetric conjugate additions of carbonyl compounds to α-nitroalkenes. Six-membered cyclic ketones react with β-nitrostyrene derivatives in the presence of (1R,2R,3R,5R)-2-hydroxy-3-((S)-pyrrolidin-2-ylmethylamino) pinane 3b (10 mol %) with high conversion to afford with diastereoselectivity (dr (syn/anti) up to 97/3), the corresponding Michael adducts with enantiomeric purities of up to 88% ee. 相似文献
78.
Mudaris N. Dimukhametov Vladimir F. Mironov Dmitry B. Krivolapov Igor A. Litvinov Rashid Z. Musin 《Mendeleev Communications》2012,22(2):98-100
Keeping of O,O’-bis(2-benzylideneaminophenyl) phenylphosphonite in a CCl4 solution for 50 days resulted in its spontaneous rearrangement into 1,6,7-triphenyl-3,4:9,10-dibenzo-2,11-dioxa-5,8-diaza-1-phosphatricyclo[6.3.0.01,5]undeca-3,9-diene, a representative of spirophosphoranes with P–N bonds. 相似文献
79.
80.
We consider stability of periodic travelling waves in the generalized reduced Ostrovsky equation with respect to co-periodic perturbations. Compared to the recent literature, we give a simple argument that proves spectral stability of all smooth periodic travelling waves independent of the nonlinearity power. The argument is based on the energy convexity and does not use coordinate transformations of the reduced Ostrovsky equations to the semi-linear equations of the Klein–Gordon type. 相似文献