全文获取类型
收费全文 | 957篇 |
免费 | 20篇 |
国内免费 | 5篇 |
专业分类
化学 | 658篇 |
晶体学 | 5篇 |
力学 | 38篇 |
数学 | 80篇 |
物理学 | 201篇 |
出版年
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 32篇 |
2012年 | 42篇 |
2011年 | 53篇 |
2010年 | 32篇 |
2009年 | 22篇 |
2008年 | 39篇 |
2007年 | 56篇 |
2006年 | 61篇 |
2005年 | 62篇 |
2004年 | 54篇 |
2003年 | 34篇 |
2002年 | 37篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 25篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 5篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有982条查询结果,搜索用时 250 毫秒
1.
2.
3.
Dmitry I. Belov Ronald D. Armstrong 《Computational Optimization and Applications》2006,33(2-3):319-332
This paper introduces a novel approach for extracting the maximum number of non-overlapping test forms from a large collection
of overlapping test sections assembled from a given item bank. The approach involves solving maximum set packing problems
(MSPs). A branch-and-bound MSP algorithm is developed along with techniques adapted from constraint programming to estimate
lower and upper bounds on the optimal MSP solution. The algorithm is general and can be applied in other applications including
combinatorial auctions. The results of computer simulations and experiments with an operational item bank are presented.
An erratum to this article is available at . 相似文献
4.
For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of
the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of
this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an
example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a
C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat
ambient metric in the sense of Fefferman and Graham.
Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse
9, 1090 Vienna, Austria
Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany 相似文献
5.
6.
KL Britton HF Rogers Y Asano T Dairi Y Kato TJ Stillman DW Rice 《Acta crystallographica. Section D, Biological crystallography》1998,53(4):124-126
The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres. 相似文献
7.
8.
9.
N-Alkoxycarbonyl- and N-carboxamido-oxaziridines are shown to react with aromatic alkenes to give epoxide, aziridine or hydro-oxidation products, in ratios depending on the oxaziridine structure. Chiral oxaziridines can effect epoxidation and hydro-oxidation with promising levels of asymmetric induction. 相似文献
10.
Jaime L. Matta Juan M. Ramos Roy A. Armstrong Hector D'Antoni 《Photochemistry and photobiology》2005,81(3):563-568
Apoptosis involves a highly organized and programmed series of events aimed at maintaining genomic stability by eliminating defective host cells. The purpose of this study was to determine the threshold doses and environmental UV‐A and UV‐B exposure times necessary to produce apoptosis and necrosis in the normal cells of a human fibroblast cell line. Enviromental UV‐A and UV‐B doses were measured over a 6 year period with a four‐channel UV radiometer. The fibroblasts were irradiated once using an Oriel UV Solar Simulator with six doses of environmentally‐based UV. Doses corresponded to 0,11,19,23 and 45 min of average environmental UV‐A and UV‐B radiation at solar noon in Puerto Rico. The Annexin‐V binding method was used to differentiate between normal fibroblasts and apoptotic or necrotic fibroblasts. The threshold dose from apoptosis to necrosis was found between 24–28 kJ/m2, which corresponded to 19 and 23 min of environmental UV‐A and UV‐B exposure. This study provides the first data that specify the environmental threshold doses of UV‐A and UV‐B at which human fibroblasts undergo apoptosis and necrosis. These results may provide valuable dose‐response thresholds for apoptosis and necrosis for future mechanistic studies and baseline data for skin cancer prevention programs. 相似文献