全文获取类型
收费全文 | 1379篇 |
免费 | 7篇 |
国内免费 | 21篇 |
学科分类
数理化 | 1407篇 |
出版年
2016年 | 9篇 |
2014年 | 10篇 |
2013年 | 59篇 |
2012年 | 42篇 |
2011年 | 42篇 |
2010年 | 36篇 |
2009年 | 22篇 |
2008年 | 35篇 |
2007年 | 49篇 |
2006年 | 57篇 |
2005年 | 52篇 |
2004年 | 47篇 |
2003年 | 34篇 |
2002年 | 47篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 23篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 32篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 15篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 41篇 |
1980年 | 32篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 36篇 |
1976年 | 33篇 |
1975年 | 30篇 |
1974年 | 28篇 |
1973年 | 33篇 |
1972年 | 16篇 |
1971年 | 10篇 |
1970年 | 10篇 |
1969年 | 9篇 |
1968年 | 23篇 |
1967年 | 10篇 |
1966年 | 7篇 |
排序方式: 共有1407条查询结果,搜索用时 0 毫秒
1.
Harold Steinacker 《Communications in Mathematical Physics》1998,192(3):687-706
We study irreducible unitary representations of U
q
(SO(2,1)) and U
q
(SO(2,?3)) for q a root of unity, which are finite dimensional. Among others, unitary representations corresponding to all classical one-particle
representations with integral weights are found for , with M being large enough. In the “massless” case with spin bigger than or equal to 1 in 4 dimensions, they are unitarizable only
after factoring out a subspace of “pure gauges” as classically. A truncated associative tensor product describing unitary
many-particle representations is defined for .
Received: 27 November 1996 / Accepted: 28 July 1997 相似文献
2.
Harold A. Scheraga 《International journal of quantum chemistry》1992,42(5):1529-1536
Various methods are used to surmount the multiple-minima problem that is encountered in the multidimensional conformational energy surface of a polypeptide. A summary is given here of two of these methods: (i) The build-up procedure that is modified to include statistical data on the positional frequencies of occurrence of amino acid residues along the chain, and (ii) the diffusion equation method that smoothes out the potential surface, leaving only the potential well containing the global minimum. 相似文献
3.
An algorithm has been developed for packing polypeptide chains by energy minimization subject to regularity conditions, in which regularity is maintained without the addition of pseudoenergy terms by defining the energy as a function of appropriately chosen independent variables. The gradient of the energy with respect to the independent variables is calculated analytically. The speed and efficiency of convergence of the algorithm to a local energy minimum are comparable to those of existing algorithms for minimizing the energy of a single polypeptide chain. The algorithm has been used to reinvestigate the minimum-energy regular structures of three-stranded (L -Ala)8, three-stranded (L -Val)6, five-stranded (L -Ile)6, and the regular and truncated three-stranded (Gly-L -Pro-L -Pro)4 triple helices. Local minima with improved packing energies, but with essentially unchanged geometrical properties, were obtained in all cases. The algorithm was also used to reinvestigate the structures proposed previously for the I and II forms of crystalline silk fibroin. The silk II structure was reproduced with slightly improved packing and little other change. The orthorhombic silk I structure showed more change and considerably improved packing energy, but the new regular monoclinic silk I structure had considerably higher energy. The results support the structure proposed previously for silk II and the orthorhombic structure, but not the monoclinic structure proposed for silk I. © 1994 by John Wiley & Sons, Inc. 相似文献
4.
5.
6.
A necessary and sufficient condition for regularity of the
-Neumann operator on (0,q)-forms in a smooth bounded pseudoconvex domain in Cn is that the orthogonal projections onto
-closed forms of degrees (0,q−1), (0,q), and (0,q+1) all be regular.
The first author partially supported by NSF Grant DMS-8701038 相似文献
7.
8.
Michael J. Costanzo Harold R. AlmondJr. A. Diane Gauthier Bruce E. Maryanoff 《Tetrahedron: Asymmetry》1994,5(12)
The conformational preferences for 2,3-O-isopropylidene-α-
-sorbopyranose derivatives 3–6 were determined by using 1H NMR data and empirical force field calculations. Proton NMR studies of 3–6 indicate that a twist-boat (or skew) conformation (3S0) prevails over possible chair forms for each compound. Force-field calculations (MM2, MNDO, AM1) on a model 2,3-O-isopropylidene-α-
-sorbopyranose system (18) indicate that the 3S0 conformation is among the low-energy structures. X-Ray crystallographic analysis of α-
-sorbopyranose sulfamate 3, a compound with potent anticonvulsant activity, demonstrates that the 3S0 skew conformation is manifested in the solid state, as well. 相似文献
9.
Background
Kynureninase is a key enzyme on the kynurenine pathway of tryptophan metabolism. One of the end products of the pathway is the neurotoxin quinolinic acid which appears to be responsible for neuronal cell death in a number of important neurological diseases. This makes kynureninase a possible therapeutic target for diseases such as Huntington's, Alzheimer's and AIDS related dementia, and the development of potent inhibitors an important research aim. 相似文献10.
A new algorithm is presented for performing molecular dynamics simulations of peptides with fixed geometry, with the aim of simulating conformational changes and of exploring conformational space. The principle of the method is to expand the potential energy as a Taylor's series in the coordinates around the current point, retaining the force and its first two derivatives, and obtain a series solution of the resulting differential equations using a method due to Lyapunov. By choosing the time step so that the second term in the series is small compared to the first, the true solution can in principle be approximated to any desired degree of accuracy. The algorithm has been used to solve numerically Lagrange's equations of motion for N-acetyl alanine amide and N-acetyl methionide amide, regarded as fixed at their C-termini, under the influence of the ECEPP/2 potential energy function, and time steps of 15–30 fsec have been achieved with little variation in the total energy. Possible directions for future development are discussed. 相似文献