全文获取类型
收费全文 | 1263篇 |
免费 | 58篇 |
国内免费 | 137篇 |
专业分类
化学 | 368篇 |
晶体学 | 8篇 |
力学 | 19篇 |
综合类 | 12篇 |
数学 | 896篇 |
物理学 | 155篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 19篇 |
2021年 | 28篇 |
2020年 | 43篇 |
2019年 | 57篇 |
2018年 | 42篇 |
2017年 | 54篇 |
2016年 | 33篇 |
2015年 | 25篇 |
2014年 | 34篇 |
2013年 | 318篇 |
2012年 | 31篇 |
2011年 | 43篇 |
2010年 | 27篇 |
2009年 | 53篇 |
2008年 | 48篇 |
2007年 | 69篇 |
2006年 | 61篇 |
2005年 | 46篇 |
2004年 | 42篇 |
2003年 | 46篇 |
2002年 | 89篇 |
2001年 | 37篇 |
2000年 | 30篇 |
1999年 | 30篇 |
1998年 | 26篇 |
1997年 | 21篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1458条查询结果,搜索用时 15 毫秒
51.
Angelika B. Boeer David Collison Prof. Christopher A. Muryn Dr. Grigore A. Timco Dr. Floriana Tuna Dr. Richard E. P. Winpenny Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(47):13150-13160
The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4‐DiMe‐ImidH][Cr7NiIIF8(O2CtBu)16] 1 (2,4‐DiMe‐ImidH=the cation of 2,4‐dimethylimidazole), [ImidH]2[Cr6NiII2F8(O2CCtBu)16] 2 (ImidH=the cation of imidazole), and [1‐Bz‐ImidH]2 [Cr7NiII2F9(O2CtBu)18] 3 (1‐Bz‐ImidH=the cation of 1‐benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3 . In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X‐ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J≈?5.8 cm?1, and it is not possible to differentiate the exchange between two CrIII centers (JCrCr) from the exchange between a CrIII and a NiII center (JCrNi). For 2 there is evidence for the presence of at least two, possibly four, linkage isomers of the heterometallic ring, caused by the presence of two divalent metal centers in the ring. The EPR spectroscopy of 3 suggests an S=1/2 ground state of the ring and that it is likely that only one linkage isomer is present. 相似文献
52.
In this article, we present some commutativity theorems for a ring R equipped with a generalized derivation satisfying certain differential identities on Jordan ideals of R. Some related results for prime rings are also discussed. Finally; we provide examples to show that the assumed restrictions are not superfluous. 相似文献
53.
《Journal of Pure and Applied Algebra》2019,223(11):4888-4900
We construct families of prime ideals in polynomial rings for which the number of associated primes of the second power (or higher powers) is exponential in the number of variables in the ring. 相似文献
54.
Vincenzo de Filippis 《数学学报(英文版)》2009,25(12):1965-1974
Let R be a prime ring, L a non-central Lie ideal of R and g a non-zero generalized derivation of R. If g acts as a Jordan homomorphism on L, then either g(x) = x for all x ∈ R, or char(R) = 2, R satisfies the standard identity s4(x1, x2, x3, x4), L is commutative and u2 ∈ Z(R), for any u C L. We also examine some consequences of this result related to generalized derivations which act as Jordan homomorphisms on the set [I, I], where I is a non-zero right ideal of R. 相似文献
55.
56.
This communication describes a convenient synthesis of fused bicyclic pyrazolones in a one-pot reaction procedure. Modified protocols are also developed to access 5,5-bicyclic and bulky pyrazolones in good yields. The method reported herein represents a practical approach to structurally diversified bicyclic pyrazolones. 相似文献
57.
O.A. Shegai V.I. Mashanov H.-H. Cheng O.P. Pchelyakov 《Physica E: Low-dimensional Systems and Nanostructures》2009,42(1):22-24
At low temperatures a lateral photoconductivity (PC) of Ge/Si (1 0 0) self-organized quantum rings (QRs) structures as a function of interband light intensity has been investigated for different values of lateral voltage and temperature. In contrast to self-organized Ge/Si quantum dots (QDs) structures (grown at the same conditions) where the stepped PC was registered, for QRs structures essential smoothing of PC steps was observed. Such behavior is determined by decreasing of strain potential around QRs in conductive Si matrix due to a transfer of Ge atoms from the center of QDs to its periphery accompanied by Ge/Si intermixing. 相似文献
58.
Hélio A. Stefani Jesus M. PenaFlávia Manarin Rômulo A. AndoDaiana M. Leal Nicola Petragnani 《Tetrahedron letters》2011,52(34):4398-4401
A functional group tolerant palladium-catalyzed Negishi coupling of diaryl tellurides with organozinc has been developed. This methodology permits efficient preparation of biaryls, aryl acetylenes and diaryl acetylenes in moderate to good yields. A preliminary study to gain further insight into the reaction was performed using in situ ReactIR technology. 相似文献
59.
An analogue of the Kunz–Frobenius criterion for the regularity of a local ring in a positive characteristic is established for general commutative semigroup rings. 相似文献
60.