全文获取类型
收费全文 | 749篇 |
免费 | 17篇 |
国内免费 | 6篇 |
专业分类
化学 | 413篇 |
晶体学 | 1篇 |
力学 | 19篇 |
数学 | 105篇 |
物理学 | 234篇 |
出版年
2023年 | 13篇 |
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 25篇 |
2015年 | 13篇 |
2014年 | 26篇 |
2013年 | 33篇 |
2012年 | 43篇 |
2011年 | 41篇 |
2010年 | 28篇 |
2009年 | 25篇 |
2008年 | 43篇 |
2007年 | 35篇 |
2006年 | 32篇 |
2005年 | 33篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有772条查询结果,搜索用时 546 毫秒
11.
Arijit BanerjeeSamir Kumar Maji Michael G.B. DrewDebasish Haldar Arindam Banerjee 《Tetrahedron letters》2003,44(4):699-702
A single-crystal X-ray diffraction study of the terminally protected tetrapeptide Boc-β-Ala-Aib-Leu-Aib-OMe 1 (Aib: α-aminoisobutyric acid; β-Ala: β-Alanine) reveals that it adopts a new type of double turn structure which self-associates to form a unique supramolecular helix through intermolecular hydrogen bonds. Scanning electron microscopic studies show that peptide 1 exhibits amyloid-like fibrillar morphology in the solid state. 相似文献
12.
Dipendra C. Sengupta 《Journal d'Analyse Mathématique》1994,63(1):1-17
Let Γ be a non-elementary finitely generated Kleinian group with region of discontinuity Ω. Letq be an integer,q ≥ 2. The group Λ acts on the right on the vector space Π2q?2 of polynomials of degree less than or equal to 2q ? 2 via Eichler action. We note by Aqq(Ω, Λ) the space of cusp forms for Λ of weight (?2q) and the space of parabolic cohomology classes by PH1 (Λ, Π2q?2). Bers introduced an anti-linear map $$\beta _q^* :A^q \left( {\Omega ,\Gamma } \right) - - - \to PH^1 \left( {\Gamma ,\Omega _{2q - 2} } \right)$$ . We try to determine the class of Kleinian groups for which the Bers map is surjective. We show that the Bers map is surjective for geometrically finite function groups. We also obtain a characterization of geometrically finite function groups. As an application, we reprove theorems of Maskit on inequalities involving the dimension of the space of cusp forms supported on an invariant component and the dimension of the space of cusp forms supported on the other components for finitely generated function groups. We also show all these inequalities are equalities for geometrically finiteB-groups. 相似文献
13.
14.
15.
Tapan Kumar Sengupta 《Journal of polymer science. Part A, Polymer chemistry》1989,27(6):2065-2070
In the complete absence of a systematic polymer nomenclature, a scheme of nomenclature based on structure is proposed. The problem of naming a “mer” has been solved for an addition polymer by adding “ne” to the monomer name, the justification being on withdrawal of a π bond a monomer becomes a mer. To furnish completeness to the nomenclature, condensation polymers were included in the system. The present nomenclature system of polymers is very arbitrary. Some polymers are not chemically named, some named incorrectly, and there are some fantastic names. After pointing these out, the possible solutions were shown, encompassing a systematic discussion on nearly every type of polymer–linear, branched, or crosslinked–and copolymer (including block or graft), and plastic, fiber, or rubber, and stereospecific polymer. One or more names were proposed for different cases. 相似文献
16.
Sengupta Soumitra K. Pandey Om P. Srivastava Bimal K. Sharma Vinod K. 《Transition Metal Chemistry》1998,23(4):349-353
The reactions of bis(cyclopentadienyl)titanium(IV)/zirconium(IV) dichloride with a new class of organometallic thiosemicarbazones (LH), derived by condensing acetylferrocene with substituted thiosemicarbazides, have been studied and two types of bimetallic products, viz. [Cp2M(L)Cl] (M = Ti or Zr) and [CpZr(L)3], have been isolated. On the basis of various physicochemical and spectral studies, five- and seven-coordinate structures have been assigned to these derivatives, respectively. Attempts have been made to establish a correlation between biological activity and the structures of the products. 相似文献
17.
Preparation and properties of the salts of the series MVO2F4, where M = NH, Na+, K+, 1/2 Ni2+, and 1/3 [Co(NH3)6]3+ are described. Molecular conductivity of Na3VO2F4 at different dilutions indicates that Na3VO2F4 dissociates into 3 Na+ and VOaF ions. Ion exchange study of (NH4)3VO2F4 solution through cation exchange resin (H+ form) suggests that the corresponding acid decomposes partly to vanadium pentoxide. Reaction between (NH4)3VO2F4 with BaCl2 and AgNO3 solutions shows the formation of BaVO2F3 and AgVO3 respectively. Thermogravimetric study of (NH4)3VO2F4 shows the formation of impure vanadium pentoxide as the ultimate product on heating up to 450°C. X-ray powder diffraction data are given for (NH4)3VO2F4 and Na3VO2F4. 相似文献
18.
The kinetics of the interaction of DL-methionine with [Pt(en)(H2O)2]2+ have been studied spectrophotometrically as a function of [Pt(en)(H2O)22+], [DL-methionine], PH and temperature. The reaction proceeds via a rapid outer sphere association followed by two slow consecutive steps having first order dependence on the aqua ion and methionine concentrations. Activation parameters have been evaluated using the Eyring equation. The low H1 (15.6 kJ mol–1) and large negative value of S1 (–230 J K–1 mol–1) as well as H2 (19.5 kJ mol–1) and S2 (–226 J K–1 mol–1) indicate an associative mode of activation for both the aqua ligand substitution processes in the two consecutive steps. 相似文献
19.
Vinod K. Sharma Om P. Pandey Soumitra K. Sengupta Dost M. Halepoto 《Transition Metal Chemistry》1989,14(4):263-266
Summary The reactions of MCl3·3H2O (M=Ru, Rh or Ir) with hydrazones have been studied by three different methods and complexes of the types [M(LH2)(H2O)2]Cl3, [M(L)Cl(H2O)] and [M(LH2)Cl2]Cl·H2O have been isolated. Tentative structural conclusions are drawn for these products based upon elemental analysis, electrical conductance, magnetic moment, and i.r. and1H n.m.r. data. The thermal stability and mode of decomposition for the complexes have been studied by t.g.a., d.t.g. and d.s.c. techniques. 相似文献
20.
Acylation of heteroatoms (O, N and S) with acetyl chloride based on the use of a catalytic amount of the moisture stable, inexpensive ZrOCl2·8H2O, proceeds efficiently producing the corresponding acylated products in excellent yields. 相似文献