全文获取类型
收费全文 | 1723篇 |
免费 | 39篇 |
国内免费 | 8篇 |
专业分类
化学 | 1010篇 |
晶体学 | 8篇 |
力学 | 80篇 |
数学 | 306篇 |
物理学 | 366篇 |
出版年
2019年 | 13篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 30篇 |
2015年 | 33篇 |
2014年 | 34篇 |
2013年 | 84篇 |
2012年 | 69篇 |
2011年 | 62篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 68篇 |
2007年 | 61篇 |
2006年 | 74篇 |
2005年 | 61篇 |
2004年 | 57篇 |
2003年 | 53篇 |
2002年 | 65篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 23篇 |
1990年 | 35篇 |
1989年 | 12篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 32篇 |
1982年 | 26篇 |
1981年 | 26篇 |
1980年 | 32篇 |
1979年 | 30篇 |
1978年 | 31篇 |
1977年 | 34篇 |
1976年 | 43篇 |
1975年 | 20篇 |
1974年 | 17篇 |
1973年 | 13篇 |
1972年 | 15篇 |
1971年 | 9篇 |
1966年 | 9篇 |
排序方式: 共有1770条查询结果,搜索用时 578 毫秒
1.
Lithium Insertion Mechanism in Iron-Based Oxyfluorides with Anionic Vacancies Probed by PDF Analysis
Dr. Damien Dambournet Dr. Karena W Chapman Dr. Mathieu Duttine Dr. Olaf Borkiewicz Dr. Peter J Chupas Dr. Henri Groult 《ChemistryOpen》2015,4(4):443-447
The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal–tungsten–bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties. 相似文献
2.
Steven D. Bull Simon W. Epstein Nadeam Mujtaba Edward D. Savory Juan A. Tamayo 《Tetrahedron》2006,62(33):7911-7925
Enolates of (S)-N,N′-bis-(p-methoxybenzyl)-3-iso-propylpiperazine-2,5-dione exhibit high levels of enantiodiscrimination in alkylations with (RS)-1-aryl-1-bromoethanes and (RS)-2-bromoesters, affording substituted diketopiperazines containing two new stereogenic centres in high de. Deprotection and hydrolysis of the resultant substituted diketopiperazines provides a route to the asymmetric synthesis of homochiral methyl 2-amino-3-aryl-butanoates and 3-methyl-aspartates in high de and ee. 相似文献
3.
A method has been developed for the determination of melengestrol acetate in bovine tissues at lower levels than previously reported. Liquid-liquid extraction of tissue homogenates provided crude clean-up while final isolation, screening, and quantification was done on-line with an automated, normal-phase, coupled-column high-performance liquid chromatographic system. The chromatographic system included phenyl and silica analytical columns for the purposes of isolation and final separation, respectively. These columns provided a large difference in selectivity when operated under normal-phase conditions which allowed for the efficient isolation of melengestrol acetate from the complex tissue extracts. Mobile phases were composed of hexane and dichloromethane modified with methanol and water. Transfer and enrichment of the analyte from the primary phenyl column to the silica column was via a short (12 mm x 4 mm I.D.) silica column. Regeneration and equilibration of the phenyl column was performed after the injection of each tissue extract and was accomplished simultaneously while analytical separation occurred on the final silica column. Routing of the mobile phases and regeneration solvent was performed with automated switching valves. The total time required for each analysis was 12 min. Quantification is demonstrated using external standards with UV detection at 287 nm. The overall recovery of the method was 86% with a coefficient of variation of 9.84% at the 10 ppb [the American billion (10(9] is used in this article] level in bovine liver extracts. 相似文献
4.
5.
A new approach to the robust handling of non‐linear constraints for GAs (genetic algorithms) optimization is proposed. A specific feature of the approach consists of the change in the conventional search strategy by employing search paths which pass through both feasible and infeasible points (contrary to the traditional approach where only feasible points may be included in a path). The method (driven by full Navier–Stokes computations) was applied to the problem of multiobjective optimization of aerodynamic shapes subject to various geometrical and aerodynamic constraints. The results demonstrated that the method retains high robustness of conventional GAs while keeping CFD computational volume to an acceptable level, which allowed the algorithm to be used in a demanding engineering environment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
6.
Processing-induced residual strains in solid cylinders of Nickel 200 were investigated using phase shifting moiré interferometry. Two different experimental approaches were used to study the strains produced during Tungsten-inert gas spot welding. A comparison of results for a ‘hot/fast’ and a ‘cool/slow’ weld demonstrate the capabilities of the general approach. Both experimental methods revealed distinct differences in the residual displacement and strain fields between the two types of welds. 相似文献
7.
8.
Labour scheduling plays an important and critical role in Sainsburys day to day operations and profitability. The integrated
workforce management solution for Sainsburys is an intelligent solution for the operational deployment of human resources,
integrated business forecasting, generation and calculation of workload and staff scheduling. The workforce management technology
has provided Sainsburys with a fully web-based and centralised system that produces optimised schedules for all employees
satisfying the forecasted demand of work with granularity of fifteen minutes. The system is configured to respect all operational
and business requirements as well as employee contractual constraints. This paper introduces the workforce management solution
system designed, developed and implemented for Sainsburys. We concentrate on two modelling structures, namely the work pattern
model and optimisation model, and briefly discuss the optimisation process. 相似文献
9.
10.