全文获取类型
收费全文 | 1649篇 |
免费 | 66篇 |
国内免费 | 4篇 |
专业分类
化学 | 1463篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 106篇 |
物理学 | 136篇 |
出版年
2023年 | 21篇 |
2022年 | 29篇 |
2021年 | 40篇 |
2020年 | 39篇 |
2019年 | 28篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 60篇 |
2014年 | 71篇 |
2013年 | 91篇 |
2012年 | 105篇 |
2011年 | 103篇 |
2010年 | 61篇 |
2009年 | 56篇 |
2008年 | 95篇 |
2007年 | 98篇 |
2006年 | 89篇 |
2005年 | 81篇 |
2004年 | 59篇 |
2003年 | 47篇 |
2002年 | 58篇 |
2001年 | 15篇 |
2000年 | 29篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 22篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 7篇 |
1981年 | 18篇 |
1979年 | 4篇 |
1969年 | 5篇 |
1964年 | 5篇 |
1963年 | 4篇 |
1962年 | 5篇 |
1954年 | 3篇 |
1947年 | 4篇 |
排序方式: 共有1719条查询结果,搜索用时 203 毫秒
1.
Central European Journal of Operations Research - This paper deals with the dynamic efficiency analysis based on Data Envelopment Analysis (DEA) models. Our aim is to formulate new dynamic DEA... 相似文献
2.
3.
A protocol to correct for intra‐ and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line 下载免费PDF全文
4.
5.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献
6.
Karl Gruber Christoph Kratky 《Journal of polymer science. Part A, Polymer chemistry》2004,42(3):479-486
Hydroxynitrile lyases catalyze the reversible cleavage of α-cyanohydrins to yield hydrocyanic acid and the corresponding aldehyde or ketone. Besides its biological interest, this class of enzymes is also of relevance in industrial biocatalysis for the enantioselective condensation of HCN with a variety of aldehydes and ketones. Several distinctly different types of hydroxynitrile lyases (HNLs) are known, which must have originated through convergent evolution from different ancestral proteins. Three-dimensional structural data are known for three classes of hydroxynitrile lyases. Insights into the reaction mechanisms emerged from a combination of structural, enzyme kinetic, spectroscopic, and molecular modeling data. For all three types of HNLs, mechanisms involving acid–base catalysis were proposed. In members belonging to the α,β-hydrolase type, the amino acid residues of the catalytic triad presumably act as general acid/base, whereas for flavine adenine dinucleotide (FAD)-dependent HNLs a single histidine residue fulfills this function. In the third type of HNL—which is related to carboxypeptidase—acid–base catalysis involves the carboxylate of the C-terminal residue. The catalytic relevance of a positive electrostatic potential in the active site was suggested in some of the mechanistic proposals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 479–486, 2004 相似文献
7.
A computer construction of the Monster is used to prove thatPSL(2, 59) is a subgroup of the Monster. 相似文献
8.
Botjan Japelj Simon Re
nik Petra ebaek Branko Stanovnik Jurij Svete 《Journal of heterocyclic chemistry》2005,42(6):1167-1173
A series of alkyl l‐heteroaryl‐1H‐1,2,3‐triazole‐4‐carboxylates 6a‐u were synthesised in four steps from methyl (Z)‐2‐benzyloxycarbonylarmino‐3‐(dimethylamino)prop‐2‐enoate ( 1 ) and heterocyclic amines 2a‐s. Triazoles 6a‐o were tested against antimycobacterial activity. For the most active compound, n‐pentyl 1‐(6‐phenylpyridazin‐3‐yl)‐1H‐1,2,3‐triazole‐4‐carboxylate ( 6n ), minimum inhibitory concentration 3.13 μg/ml was determined. 相似文献
9.
10.
We use a driving field, of the type first suggested by Evans, to generate a steady heat current in the simplest possible system, a two-dimensional periodic fluid of three hard disks. Hard-disk motion equations can be conveniently derived from repulsive constant-force or linear-force potentials by considering the infinitely repulsive limit of these potentials. We show that the isoenergetic and isokinetic forms of the nonequilibrium equations of motion generate steady-state heat conductivities differing by terms of order 1/N, whereN is the number of particles. The resulting conductivities appear to vary as the logarithm of the driving field strength. Even at low fields, the three-body periodic-system results lie well below Enskog's infinite-system prediction. 相似文献