全文获取类型
收费全文 | 1586篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 1075篇 |
晶体学 | 7篇 |
力学 | 43篇 |
数学 | 231篇 |
物理学 | 275篇 |
出版年
2023年 | 8篇 |
2022年 | 34篇 |
2021年 | 40篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 17篇 |
2016年 | 47篇 |
2015年 | 48篇 |
2014年 | 42篇 |
2013年 | 78篇 |
2012年 | 87篇 |
2011年 | 117篇 |
2010年 | 79篇 |
2009年 | 61篇 |
2008年 | 113篇 |
2007年 | 99篇 |
2006年 | 113篇 |
2005年 | 96篇 |
2004年 | 84篇 |
2003年 | 68篇 |
2002年 | 59篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1970年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有1631条查询结果,搜索用时 0 毫秒
91.
Aime S Calabi L Cavallotti C Gianolio E Giovenzana GB Losi P Maiocchi A Palmisano G Sisti M 《Inorganic chemistry》2004,43(24):7588-7590
An innovative MRI contrast agent based on the unprecedented and easily obtained ligand AAZTA is described. The simple and straightforward synthesis of the ligand, together with the potentiometric and relaxometric behavior of the corresponding Gd(III) chelate, is reported. The complex [Gd(AAZTA)]- shows outstanding magnetic properties connected with high thermodynamic stability in aqueous solution and a nearly complete inertness toward the influence of bidentate endogenous anions, placing this compound as one of the most promising candidates for the development of high performance MRI contrast agents. 相似文献
92.
Boiocchi M Fabbrizzi L Foti F Vazquez M 《Dalton transactions (Cambridge, England : 2003)》2004,(17):2616-2620
The spin interconversion equilibrium involving the [Ni(II)(cyclam)]2+ complex has been investigated in a variety of polar solvents, at varying temperatures. The greater the donor tendencies of the solvent, the higher the endothermicity of the high-to-low-spin conversion. In particular, a positive linear relationship exists between DeltaHdegrees and Gutmann's Donor Number (DN). In the same way, higher donor tendencies of the solvent favour the occurrence of the Ni(II)-to-Ni(III) oxidation process and negative linear relationship has been found between the E1/2(Ni(III)/Ni(II)) and DN. General behaviour is related to the intensity of the metal-solvent axial bonds in the octahedrally elongated cyclam complexes (of both Ni(II) and Ni(III)). 相似文献
93.
Sterpone F Pierleoni C Briganti G Marchit M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(11):4311-4314
Hydration of a spherical micelles of C12E6 in solution is studied by molecular dynamics simulation. The interface is found to be separated in an inner part composed of water and hydrophobic and hydrophilic moieties and an outer part with hydrophilic moiety and water only. Hydration numbers in the inner and in the outer parts are in excellent agreement with experimental data from various different methods. Temperature dehydration occurs in the inner region only and is related to the presence of water molecules directly in contact with the hydrophobic core at low temperature. 相似文献
94.
De Napoli M Nardis S Paolesse R Vicente MG Lauceri R Purrello R 《Journal of the American Chemical Society》2004,126(19):5934-5935
In aqueous solution meso-tetrakis(4-phosphonatophenyl)porphyrin shows self-aggregation processes controlled by the "sergeant-soldier rule". After partial protonation of the external phosphonic groups, it is possible (i) to further protonate the inner nitrogen atoms of the molecules or (ii) to allow, over time, the system to aggregate. Therefore, the two procedure lead to a different system evolution, producing species with different chemico-physical properties. 相似文献
95.
Ghedini M Aiello I La Deda M Grisolia A 《Chemical communications (Cambridge, England)》2003,(17):2198-2199
The newly synthesized complexes formed by cyclopalladated 2-phenylpyridine co-ordinated to 5-substituted-8-hydroxyquinolines, are at room temperature and in fluid solution, luminescent with an absolute photoluminescent quantum yield which depends on the nature of the substituent in position 5. 相似文献
96.
The autonomous composition operator is the nonlinear map whichtakes a pair of functions into its composite function. The compositionoperator often appears in problems of nonlinear analysis andto analyse such problems it is often important to know whetherthe composition operator is continuous or differentiable. Afairly large number of papers in the literature have been devotedto the study of composition operators. For fullscale references,we refer the reader to the extensive monographs of Appell andZabrejko [1] and Runst and Sickel [8]. To exemplify a typicalsituation, we consider the semilinear Dirichlet boundary valueproblem
where denotes a sufficiently regular bounded open subset ofRN, and h0 a map of R to R, and where u is the unknown of theproblem. We assume that we know that a certain function u0 belongingto a certain function space X solves (1.1). Then if we wishto know whether by perturbing h0 in a certain function space,say Y, the solutions u depend on h continuously, with differentiability,with analyticity or bifurcate, we could set G[h, u] u+h u,recast problem (1.1) into the abstract form G[h, u] (1.2) and study the solution set of equation (1.2) around the pair(h0, u0) by means of the implicit function theorem or by localbifurcation theorems in a Banach space setting. 相似文献
97.
98.
Marco Apostolo Andrea Tredici Massimo Morbidelli Arvind Varma 《Journal of polymer science. Part A, Polymer chemistry》1997,35(6):1047-1059
Traveling polymerization fronts in unstirred solutions of methylmethacrylate, methacrylic acid, or acrylamide with some free radicals initiators (through thermal decomposition) have been observed experimentally. A local heating of the initial reactant mixture, under suitable conditions, leads to a reaction front that propagates along the space coordinate with a constant velocity. In this article, a physical interpretation of this phenomenon is provided through a mathematical model that accounts for the depolimerization reaction and is based on the constant pattern approach. Moreover, an approximate explicit analytic expression for the velocity of propagation of the polymerization front is proposed. The theoretical values are compared with those measured experimentally as a function of the initiator concentration for different addition polymerization systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35:1047–1059, 1997 相似文献
99.
Marcella Reale Antonia Patruno Maria A De Lutiis Mirko Pesce Mario Felaco Massimo Di Giannantonio Marta Di Nicola Alfredo Grilli 《BMC neuroscience》2011,12(1):13
Background
The exact cause of schizophrenia is not known, although several aetiological theories have been proposed for the disease, including developmental or neurodegenerative processes, neurotransmitter abnormalities, viral infection and immune dysfunction or autoimmune mechanisms. Growing evidence suggests that specific cytokines and chemokines play a role in signalling the brain to produce neurochemical, neuroendocrine, neuroimmune and behavioural changes. A relationship between inflammation and schizophrenia was supported by abnormal cytokines production, abnormal concentrations of cytokines and cytokine receptors in the blood and cerebrospinal fluid in schizophrenia. Since the neuropathology of schizophrenia has recently been reported to be closely associated with microglial activation we aimed to determined whether spontaneous or LPS-induced peripheral blood mononuclear cell chemokines and cytokines production is dysregulated in schizophrenic patients compared to healthy subjects. We enrolled 51 untreated first-episode schizophrenics (SC) and 40 healthy subjects (HC) and the levels of MCP-1, MIP-1α, IL-8, IL-18, IFN-γ and RANTES were determined by Elisa method in cell-free supernatants of PBMC cultures. 相似文献100.
Nicola Arcozzi Enrico Casadio Tarabusi Fausto Di Biase Massimo A. Picardello 《Transactions of the American Mathematical Society》2006,358(6):2781-2798
We establish a potential theoretic approach to the study of twist points in the boundary of simply connected planar domains.