全文获取类型
收费全文 | 517篇 |
免费 | 9篇 |
专业分类
化学 | 292篇 |
晶体学 | 3篇 |
力学 | 33篇 |
数学 | 88篇 |
物理学 | 110篇 |
出版年
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 5篇 |
2013年 | 17篇 |
2012年 | 29篇 |
2011年 | 22篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 30篇 |
2007年 | 19篇 |
2006年 | 31篇 |
2005年 | 20篇 |
2004年 | 15篇 |
2003年 | 16篇 |
2002年 | 18篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1971年 | 4篇 |
1966年 | 3篇 |
1919年 | 2篇 |
1906年 | 2篇 |
排序方式: 共有526条查询结果,搜索用时 19 毫秒
71.
Non-empirical SCF-MO molecular wavefunctions were computed for the two limiting structures of C2H2F+ with full geometry optimization using double-zeta quality atomic orbital basis sets. The bridged structure (fluorenium ion) was found to be an energy maximum (transition state) about 31 kcal/mole higher than the open structure (fluoro-vinyl cation). The latter, contrary to the unsubstituted vinyl cation, is slightly (4.5 °) bent away from fluorine at the electron deficient centre. 相似文献
72.
We construct quantum stochastic processes whose multi-time correlation functions, with suitable time ordering, can be obtained from a quantum dynamical semigroup. We prove that such a process defines a stationary Markov dilation of the associated semigroup if and only if (up to technicalities) the semigroup satisfies the quantum detailed balance condition with respect to its stationary state. 相似文献
73.
Taglienti A Cellesi F Crescenzi V Sequi P Valentini M Tirelli N 《Macromolecular bioscience》2006,6(8):611-622
[Chemical structure: see text] The interactions between a biomaterial and biomolecules present in body fluids often determine the fate of the biomaterial. This paper presents a study on hyaluronan (HA)-containing materials (in soluble or colloidal form) that focuses on their interactions with lipids and proteins and for the first time uses PFG NMR as an analytical technique for probing these events. The interactions of HA-based polymers with phospholipids (DPPC and DPPG liposomes) are shown to depend both on charge and hydrophobicity factors. Despite the difference in behavior between albumin (substantially non-adhesive) and fibrinogen (adhesive), the interactions of the polymers with proteins do not seem to be based on hydrophobic effects but on surface polar interactions. 相似文献
74.
Palmisano G Addamo M Augugliaro V Caronna T García-López E Loddo V Palmisano L 《Chemical communications (Cambridge, England)》2006,(9):1012-1014
Experimental results are reported showing that the photocatalytic oxidation of aromatic compounds containing an electron-donor group (EDG) gives rise mainly to ortho- and para-monohydroxy derivatives while in the presence of an electron-withdrawing group (EWG) all the monohydroxy derivatives are obtained. 相似文献
75.
We propose a cheat sensitive quantum protocol to perform a private search on a classical database which is efficient in terms of communication complexity. It allows a user to retrieve an item from the database provider without revealing which item he or she retrieved: if the provider tries to obtain information on the query, the person querying the database can find it out. The protocol ensures also perfect data privacy of the database: the information that the user can retrieve in a single query is bounded and does not depend on the size of the database. With respect to the known (quantum and classical) strategies for private information retrieval, our protocol displays an exponential reduction in communication complexity and in running-time computational complexity. 相似文献
76.
V. Errico A. Salhi C. Giordano M. De Giorgi A. Passaseo M. De Vittorio 《Superlattices and Microstructures》2008,43(5-6):507
In this work, the analysis, fabrication and optical characterization of a two-dimensional circular photonic crystal (2D-CPC) nano-resonator based on an air/GaAs/air slab waveguide are presented. Four InAs/InGaAs quantum dots (QDs) stacked layers emitting around 1300 nm at room temperature were embedded in a GaAs waveguide layer grown on an Al0.7Ga0.3As layer and GaAs substrate. The patterning of the structure and the membrane release were achieved by using electron beam lithography, ICP plasma etching and selective wet etching of the AlGaAs sacrificial layer. The micro-luminescence spectrum recorded from the fabricated nano-cavity shows a narrow optical transition at the resonance wavelength of about 1282 nm with a FWHM and Q-factor of 6.2 Å and more than 2000, respectively. 相似文献
77.
Ali Maalaoui Vittorio Martino 《Calculus of Variations and Partial Differential Equations》2014,50(3-4):599-614
We consider a family of tight contact forms on the three-dimensional torus and we compute the relative Contact Homology by using the variational theory of critical points at infinity. We will also show local stability. 相似文献
78.
Laura Castoldi Laura Ielo Pilar Hoyos María J. Hernáiz Laura De Luca Andrés R. Alcántara Wolfgang Holzer Vittorio Pace 《Tetrahedron》2018,74(18):2211-2217
An effective stereocontrolled synthesis of the HIV protease inhibitor Nelfinavir is reported. Two transformations were identified crucial for achieving success: the formation of a densely functionalized α-chloroketone via the homologation of a Weinreb amide with chloromethyllithium (LiCH2Cl), followed by its erythro selective reduction into the corresponding chiral chlorohydrin. A commercially available enzyme P2-C02 was particularly well suited for this purpose, affording the key alcohol (in an excellent 99% de), which was then smoothly converted into the active biologically active agent. 相似文献
79.
A relativistic equation for free fields whichtake their values in the Clifford algebra associatedwith the Minkowski metric is shown to be interpretableas the equation of the nucleon. The internal symmetry group SU(2) arises naturally from theassociative algebra structure of the representationspace. The latter structure can be used to constructcoupling terms consistent with the transformationproperties of the interacting fields; in particular, itallows the familiar couplings of the nucleon field withthe electromagnetic field and with the -mesonfield. 相似文献
80.
A superior, mild, high-yielding one-pot process for rapid access to oxo anilides has been developed that involves three cascade reactions: iodine-magnesium exchange, regiospecific ortho N-Fries rearrangement, and in situ trapping of the formed aniline anion. Coupled with McMurry cyclization, the two-step process allows ready synthesis of strained 1,2,3-trisubstituted indoles regioselectively. 相似文献