全文获取类型
收费全文 | 4273篇 |
免费 | 165篇 |
国内免费 | 37篇 |
专业分类
化学 | 2747篇 |
晶体学 | 9篇 |
力学 | 170篇 |
数学 | 932篇 |
物理学 | 617篇 |
出版年
2023年 | 25篇 |
2022年 | 95篇 |
2021年 | 95篇 |
2020年 | 103篇 |
2019年 | 90篇 |
2018年 | 89篇 |
2017年 | 66篇 |
2016年 | 180篇 |
2015年 | 148篇 |
2014年 | 180篇 |
2013年 | 275篇 |
2012年 | 314篇 |
2011年 | 325篇 |
2010年 | 157篇 |
2009年 | 198篇 |
2008年 | 272篇 |
2007年 | 260篇 |
2006年 | 217篇 |
2005年 | 202篇 |
2004年 | 205篇 |
2003年 | 145篇 |
2002年 | 102篇 |
2001年 | 47篇 |
2000年 | 38篇 |
1999年 | 35篇 |
1998年 | 39篇 |
1997年 | 37篇 |
1996年 | 49篇 |
1995年 | 22篇 |
1994年 | 28篇 |
1993年 | 16篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 34篇 |
1984年 | 28篇 |
1983年 | 27篇 |
1982年 | 30篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 19篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1974年 | 11篇 |
1967年 | 4篇 |
排序方式: 共有4475条查询结果,搜索用时 31 毫秒
71.
Hereditarily finite sets and hypersets are characterized both as algorithmic data structures and by means of a first-order axiomatization which, despite being rather weak, suffices to make the following two problems decidable:
- (1) Establishing whether a conjunction r of formulae of the form: ? y1 ?? ym((y1?W1& ?&ym ?Wm) ←q), with q quantifier-free and involving only the relators =, ? and propositional connectives, and each yi distinct from all wj's, is satisfiable.
- (2) Establishing whether a formula of the form ? y q, q quantifier-free, is satisfiable.
72.
We study the topological structure of all 3-manifolds obtained by surgery along principal fibers of a closed orientable
-manifold. As a consequence, we give alternative proofs of some classical results due to W. Heil and L. Moser. Moreover, we completely specify the Seifert invariants for the considered manifolds. Finally we classify the manifolds obtained by surgery along certain Seifert links and determine geometric presentations of their fundamental groups.Work performed under the auspices of C.N.R. (National Research Council) of Italy and partially supported by Ministero della Ricerca Scientifica e Tecnologica within the projects Geometria Reale e Complessa and Topologia. 相似文献
73.
Krull-Schmidt fails for serial modules 总被引:1,自引:0,他引:1
Alberto Facchini 《Transactions of the American Mathematical Society》1996,348(11):4561-4575
We answer a question posed by Warfield in 1975: the Krull-Schmidt Theorem does not hold for serial modules, as we show via an example. Nevertheless we prove a weak form of the Krull-Schmidt Theorem for serial modules (Theorem 1.9). And we show that the Grothendieck group of the class of serial modules of finite Goldie dimension over a fixed ring is a free abelian group.
74.
The gauging of free differential algebras (FDA's) produces gauge field theories containing antisymmetric tensors. The FDA's extend the Cartan-Maurer equations of ordinary Lie algebras by incorporating p-form potentials (p>1). We study here the algebra of FDA transformations. To every p-form in the FDA, we associate an extended Lie derivative l generating a corresponding gauge transformation. The field theory based on the FDA is invariant under these new transformations. This gives geometrical meaning to the antisymmetric tensors. The algebra of Lie derivatives is shown to close and provides the dual formulation of FDA's. 相似文献
75.
76.
Thomas Andre´s Wolcan Ezequiel Fe´liz Mario R. Capparelli Alberto L. 《Transition Metal Chemistry》1997,22(6):541-544
The kinetics of the complexation of NiII by pteroylglutamic acid have been studied in the 545 ∘C range, the ionic strength
(0.6 M) being regulated with KNO3, in the 5.5–7.0pH range, using the stopped-flow method. Under the experimental conditions
two processes were observed. The faster process was detected in the millisecond range and is associated with the reaction
between NiII and the ligand. The slower is observed within a few seconds. Complementary equilibrium studies were made at 25
∘C. The results are consistent with the formation of a 1:1 complex between the reactants, and a mechanism is proposed to account
for the observed behaviour. Equilibrium constants for the NiII plus pteroylglutamic acid system, as well as activation parameters,
are reported.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
77.
New Hg2+ and Cu2+ selective chromo- and fluoroionophore based on a bichromophoric azine 总被引:1,自引:0,他引:1
[graph: see text] A new probe, 1,4-bis(1-pyrenyl)-2,3-diaza-1,3-butadiene, selectively senses Hg2+ and Cu2+ through two different channels: the yellow-deep-pink color change and the enhancement of the fluorescence with the red shift of the excimer emission, which can visually be discernible by a green fluorescence in the presence of Hg2+ and an orange fluorescence in the presence of Cu2+. 相似文献
78.
Lorenzo Testaferri Marcello Tiecco Marco Tingoli Donatella Bartoli Alberto Massoli 《Tetrahedron》1985,41(7):1373-1384
The reactions of 2,6- and 2,5-dibromopyridines and of 2,3- and 3,5-dichloropyridines with sodium isopropanethiolate and methanethiolate afforded the products of mono- or of bis-substitution depending on the experimental conditions. The same pyridines reacted with sodium methoxide to give good yields of the mono-substituted products; bis-substitution occurred easily only in the case of the 2,6-dibromo- and of the 3,5-dichloropyridine. The syntheses of some methoxy thiomethoxypyridine, starting from the halogeno methoxypyridines or from the halogeno thiomethoxypyhdines are also described. The bis-(alkylthio)pyridines can be fragmented by sodium in HMPA to give the bis(mercapto)pyridines. 相似文献
79.
Fiammengo R Wojciechowski K Crego-Calama M Timmerman P Figoli A Wessling M Reinhoudt DN 《Organic letters》2003,5(19):3367-3370
[structure: see text] Water-soluble models of heme-protein active sites are obtained via the self-assembly of cationic porphyrins 1 and tetrasulfonato calix[4]arene 2 (K(1.2)() = 10(5) M(-)(1)). Selective binding of ligands either outside or inside the cavity of assemblies 1.2 via coordination to the zinc center has been observed. Small ligands such as 4-methylpyridine and 1-methylimidazole are encapsulated, while the bulkier caffeine is bound outside. Assemblies Co-1.2, in which the Zn porphyrin moiety has been replaced by a Co(II) porphyrin, can act as O(2) carriers. 相似文献
80.
We introduce a new Monte Carlo algorithm for the self-avoiding walk (SAW), and show that it is particularly efficient in the critical region (long chains). We also introduce new and more efficient statistical techniques. We employ these methods to extract numerical estimates for the critical parameters of the SAW on the square lattice. We find=2.63820 ± 0.00004 ± 0.00030=1.352 ± 0.006 ± 0.025v=0.7590 ± 0.0062 ± 0.0042 where the first error bar represents systematic error due to corrections to scaling (subjective 95% confidence limits) and the second bar represents statistical error (classical 95% confidence limits). These results are based on SAWs of average length 166, using 340 hours CPU time on a CDC Cyber 170–730. We compare our results to previous work and indicate some directions for future research. 相似文献