全文获取类型
收费全文 | 6273篇 |
免费 | 769篇 |
国内免费 | 941篇 |
专业分类
化学 | 5522篇 |
晶体学 | 67篇 |
力学 | 65篇 |
综合类 | 54篇 |
数学 | 320篇 |
物理学 | 1955篇 |
出版年
2024年 | 12篇 |
2023年 | 96篇 |
2022年 | 93篇 |
2021年 | 125篇 |
2020年 | 171篇 |
2019年 | 173篇 |
2018年 | 153篇 |
2017年 | 141篇 |
2016年 | 197篇 |
2015年 | 203篇 |
2014年 | 269篇 |
2013年 | 429篇 |
2012年 | 443篇 |
2011年 | 392篇 |
2010年 | 345篇 |
2009年 | 425篇 |
2008年 | 428篇 |
2007年 | 456篇 |
2006年 | 431篇 |
2005年 | 364篇 |
2004年 | 364篇 |
2003年 | 297篇 |
2002年 | 192篇 |
2001年 | 194篇 |
2000年 | 223篇 |
1999年 | 200篇 |
1998年 | 171篇 |
1997年 | 141篇 |
1996年 | 134篇 |
1995年 | 128篇 |
1994年 | 107篇 |
1993年 | 84篇 |
1992年 | 82篇 |
1991年 | 88篇 |
1990年 | 51篇 |
1989年 | 45篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有7983条查询结果,搜索用时 15 毫秒
101.
102.
Zhang JJ Sheng TL Hu SM Xia SQ Leibeling G Meyer F Fu ZY Chen L Fu RB Wu XT 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(16):3963-3969
The first successful attempt to construct 3D supramolecular frameworks with high-nuclear 3d-4f heterometallic clusters as a node is reported. The self-assembly of Ln3+, Cu2+ and amino acid in solution leads to the formation of two polymers, 35-nuclear complex [Sm6Cu29] 1 with a primitive cubic net-like structure and 36-nuclear complex [Nd6Cu30] 2 with a face-centred cubic network type structure. Glycine and L-proline, respectively, were used as ligands. It should be noted that 2 has a chiral framework. X-ray structure analyses show that 1 crystallizes in the triclinic P1 space group (a=19.6451(8), b=20.4682(8), c=20.7046(8) A, alpha=89.453(1), beta=66.290(1), gamma=68.572(1) degrees, V=7003.0(5) A3 and Z=1) and 2 belongs to the cubic P2(1)3 space group (a=b=c=32.4341(3) A, V=34 119.7(5) A3 and Z=4). Both complexes utilize Ln6Cu24 octahedral clusters as nodes and trans-Cu(amino acid)2 groups as bridges. Electrical conductivity measurements reveal that both polymers behave as semiconductors. 相似文献
103.
The geometries of the most stable isomers of gold telluride systems AuTe, Au2Te, and AuTe2 are determined using the MP2 method. The aspect of gold—telluride interaction, the electron correlation, and relativistic
effects on geometry and stability are investigated at the MP2 and CCSD(T) theoretical levels. The results show that the electron
correlation and relativistic effects are responsible not only for gold—gold attraction but also for additional gold—telluride
interaction. The gold—telluride interaction is strong enough to modify the known pattern of bare gold clusters. Both effects
are essential for determining the geometry and relative stability of this type of systems. 相似文献
104.
本文首次利用碳基钴簇合物PhPCo_3(CO)_9催化剂,在常压和-20℃-0℃,用苯乙烯和重氮乙酸乙酯进行环丙烷化反应,合成了菊酸酯,重氮乙酸乙酯可全部转化,酯的选择性可达85%。产物经减压分馏后,由IR和 ̄1HNMR分析,确证了产物为菊酸酯,表明了羰基钴簇合物对苯乙烯的环丙烷化反应有良好的催化性能,为四面体异核簇合物用于不对称催化反应打下了基础。 相似文献
105.
Zareen Ahkter Andrew J. Edwards Scott L. Ingham Jack Lewis Ana M. Martin Castro Paul R. Raithby Gregory P. Shields 《Journal of Cluster Science》2000,11(1):217-226
The reaction of the di-gold cation [Au2(dppx)]2+ with the heptanuclear cluster dianion [Os7(CO)20]2– affords the mixed metal cluster [Os7(CO)20{Au2(dppx)}] (x=m (1), e (2), b (3)). On standing, in solution, this complex undergoes decarbonylation to give the cluster [Os7(CO)19{Au2(dppx)}] (x=m (4), e (5), b (6)). The complexes have been characterised spectroscopically, and an X-ray structure determination of the dppm derivative shows that it contains a metal core based on an Os7 edge-bridged bicapped tetrahedron with the two
3-Au atoms capping adjacent triangular Os3 faces of the central tetrahedron. In an analogous reaction, the carbido anion [Os7(H)C(CO)19]– affords the neutral cluster [Os7C(CO)19{Au2(dppm)}] (7) when treated with [Au2(dppm)]2+ in the presence of base. 相似文献
106.
107.
108.
The localized molecular orbitals and their energy levels for the clusters [Fe3S4(SH)3]2–, [(HS)3Fe3S4·Ni(PH3)]2–, [Mo3S4(OH2)9]4+, and [Mo3S4·Ni]4+ have been calculated by mean of the Edmiston-Ruedenberg energy localization technique under the CNDO/2 approximation in order to reveal the resemblance between [Fe3S4]+ and [Mo3S4]4+ in the geometrical configurations and the addition reactivities with heterometal atoms. It is shown that in these two cluster species with core {M
3(3-S)(-S)3} of similar structure (M = Mo, Fe) there exist three synergically connected three-centered two-electron (M-S-M) -bonds around the puckered six-membered {M3S3} rings on account of delocalization of a lone electron pair on each bridging S atom; these (M-S-M) -bonds are thus capable of forming cubane-like heterometal clusters with intruder metal atoms through the ( M) bonding. It is therefore seen that unlike the [Mo3S4]4+ with appreciable bonding between the Mo atoms, the extra d-electrons on the metal atoms in the [Fe3S4]+ cluster are localized on the Fe atoms, exhibiting an electronic structure significantly different from that of the [Mo3S4]4+ cluster. 相似文献
109.
110.