全文获取类型
收费全文 | 1539篇 |
免费 | 29篇 |
国内免费 | 7篇 |
专业分类
化学 | 1082篇 |
晶体学 | 5篇 |
力学 | 65篇 |
数学 | 237篇 |
物理学 | 186篇 |
出版年
2023年 | 9篇 |
2022年 | 34篇 |
2021年 | 40篇 |
2020年 | 30篇 |
2019年 | 27篇 |
2018年 | 23篇 |
2017年 | 24篇 |
2016年 | 44篇 |
2015年 | 21篇 |
2014年 | 41篇 |
2013年 | 69篇 |
2012年 | 68篇 |
2011年 | 90篇 |
2010年 | 53篇 |
2009年 | 59篇 |
2008年 | 85篇 |
2007年 | 107篇 |
2006年 | 99篇 |
2005年 | 77篇 |
2004年 | 87篇 |
2003年 | 52篇 |
2002年 | 53篇 |
2001年 | 14篇 |
2000年 | 21篇 |
1999年 | 10篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 18篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 19篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 13篇 |
1975年 | 6篇 |
1974年 | 8篇 |
排序方式: 共有1575条查询结果,搜索用时 15 毫秒
101.
F. Tedoldi A. Rigamonti R. Santachiara M. Horvatić L. Linati M. Bini D. Capsoni V. Massarotti 《Applied magnetic resonance》2000,19(3-4):381-389
By means of89Y nuclear magnetic resonance (NMR) spectra direct evidence of staggered magnetization induced by a uniform field has been obtained in the Heisenberg antiferromagneticS = 1 chain Y2BaNi1?xMgxO5. A correspondence between the resonance lines and the lattice positions is established, providing an image of the alternating magnetic moments that develop around the Mg impurities at the chain boundaries. The amplitude of these moments is found to decrease exponentially from the edges, with a characteristic decay distance equal to the magnetic correlation length numerically evaluated for an infinite chain. While the magnetization pertaining to ions far from the boundaries behaves as in typical gapped systems, the edge spins exhibit anS = 1/2 Curie-like deviation. These results promote the NMR approach to access the spin-spin correlation function in antiferro-magnetic quantum spin systems at finite temperatures. 相似文献
102.
103.
104.
Liliana Lamartina Onofrio Migliara Vincenzo Sprio 《Journal of heterocyclic chemistry》1982,19(6):1381-1384
1-Ureido-5-methyl-2,3-dicarbethoxypyrrole under acidic conditions afforded different partially hydrolyzed or decarboxylated products. It has been possible to characterize two isomeric monoethyl esters of dicarboxylic acids of 1-ureidopyrroles by proton gated decoupled carbon-13 nmr spectra on the basis of multiplicities of the carbonyl carbons resonances. 相似文献
105.
Domenico Spinelli Anlonino Corrao Vincenzo Frenna Nicol
Vivona Michele Ruccia Giuseppe Cusmano 《Journal of heterocyclic chemistry》1976,13(2):357-360
The rates of the mononuclear heterocyclic rearrangement of the phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1) into 2,5-diphenyl-4-benzoylamino-1,2,3-triazole (II) have heen measured in dioxane/water (50:50, v:v) in the range of pS+ 3.8–12.2 at various temperatures and the activation parameters determined. On the basis of the results obtained, we present evidence for the occurrence of two different types of reaction: the first, base-catalyzed; the second, pS+ -independent. In the base-catalyzed range the catalysis is of the general type. 相似文献
106.
Alfio Spina Rosaria Saletti Simona Fabroni Antonio Natalello Vincenzo Cunsolo Michele Scarangella Paolo Rapisarda Michele Canale Vera Muccilli 《Molecules (Basel, Switzerland)》2022,27(24)
Among grain pulses, lupins have recently gained considerable interest for a number of attractive nutritional attributes relating to their high protein and dietary fiber and negligible starch contents. The seeds of Lupinus albus (cv. Multitalia and Luxor, and the Modica ecotype); L. luteus (cv. Dukat, Mister, and Taper); and L. angustifolius (cv. Sonet) analyzed in this study were deposited within the germplasm collection of the Research Centre for Cereal and Industrial Crops of Acireale and were sowed in East Sicily in 2013/14. The collected seeds were analyzed for their multielemental micro- and macronutrient profiles, resulting in a wide variability between genotypes. Lupin seed flour samples were subjected to a defatting process using supercritical CO2, with oil yields dependent on the species and genotype. We determined the fatty acid profile and tocopherol content of the lupin oil samples, finding that the total saturated fatty acid quantities of different samples were very close, and the total tocopherol content was about 1500.00 µg/g FW. The proteomic analysis of the defatted lupin seed flours showed substantial equivalence between the cultivars of the same species of Lupinus albus and L. luteus. Moreover, the L. angustifolius proteome map showed the presence of additional spots in comparison to L. albus, corresponding to α-conglutins. Lupin, in addition to being a good source of mineral elements, also contributes vitamin E and, thanks to the very high content of gamma-tocopherols, demonstrates powerful antioxidant activity. 相似文献
107.
Gianfranco Ciani Vincenzo G. Albano Attilio Immirzi 《Journal of organometallic chemistry》1976,121(2):237-248
The structure of the title compound, (NEt4)2[H4Re4(CO)15], is reported in two crystallographic modifications, I and II. Both forms axe monoclinic and the cell constants are as follows: I, a 11.355(2), b 21.204(4), c 17.416(3) Å, β 94.15(2)°, space group P21/c; II, a 21.831(4), b 17.584(3), c 11.446(2) Å, β 96.02(2)°, space group P21,/n. Two sets of 3042 (I) and 2870 (II) independent diffraction intensities, collected by counter methods, were used for the solution and refinement of the two structures. The final conventional R factors have values 5.5% (I) and 6.3% (II), respectively. The crystal packings are compared, showing different conformations of the (NEt4)+ cations. The anions contain a tetrametal cluster formed by an isosceles triangle plus an apically bound metal atom; the carbonyl groups are all terminally bonded to the rhenium atoms. Some differences, present both in the metal atom clusters and in the carbonyl dispositions, are discussed and compared with a third, previously reported, crystallographic modification of the same compound. 相似文献
108.
Vincenzo Ferone Ester Giarrusso Basilio Messano M. Rosaria Posteraro 《Calculus of Variations and Partial Differential Equations》2013,46(3-4):749-768
In this paper we deal with blow-up solutions to an elliptic equation with a nonlinear gradient term. The problem under consideration can be seen as the ergodic limit of a stochastic control problem with state constraints. It is well known that it has a solution only when a parameter which appears in the equation assumes a particular value known as ergodic constant. For such a constant many properties similar to those of an eigenvalue hold true. We show that a Faber–Krahn inequality can be stated for the ergodic constant and that for the corresponding solution a comparison result in terms of the solution to a symmetrized problem can be proved. 相似文献
109.
110.