全文获取类型
收费全文 | 1448篇 |
免费 | 42篇 |
国内免费 | 9篇 |
专业分类
化学 | 797篇 |
晶体学 | 18篇 |
力学 | 50篇 |
数学 | 212篇 |
物理学 | 422篇 |
出版年
2022年 | 14篇 |
2021年 | 14篇 |
2020年 | 25篇 |
2019年 | 24篇 |
2018年 | 20篇 |
2017年 | 21篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 39篇 |
2013年 | 91篇 |
2012年 | 78篇 |
2011年 | 99篇 |
2010年 | 38篇 |
2009年 | 38篇 |
2008年 | 78篇 |
2007年 | 60篇 |
2006年 | 69篇 |
2005年 | 78篇 |
2004年 | 46篇 |
2003年 | 38篇 |
2002年 | 38篇 |
2001年 | 30篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 22篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1972年 | 10篇 |
1971年 | 9篇 |
排序方式: 共有1499条查询结果,搜索用时 15 毫秒
211.
212.
213.
Stefano Starita M. Paola Scaparra Jesse R. O’Hanley 《The Journal of the Operational Research Society》2017,68(1):74-88
This paper focuses on the problem of identifying optimal protection strategies to reduce the impact of flooding on a road network. We propose a dynamic mixed-integer programming model that extends the classic concept of road network protection by shifting away from single-arc fortifications to a more general and realistic approach involving protection plans that cover multiple components. We also consider multiple disruption scenarios of varying magnitude. To efficiently solve large problem instances, we introduce a customised GRASP heuristic. Finally, we provide some analysis and insights from a case study of the Hertfordshire road network in the East of England. Results show that optimal protection strategies mainly involve safeguarding against flooding events that are small and likely to occur, whereas implementing higher protection standards are not considered cost-effective. 相似文献
214.
Waldo JP Mehta S Neuenswander B Lushington GH Larock RC 《Journal of combinatorial chemistry》2008,10(5):658-663
The iodocyclization of O-methyloximes of 2-alkyn-1-ones affords 4-iodoisoxazoles, which undergo various palladium-catalyzed reactions to yield 3,4,5-trisubstituted isoxazoles. The palladium-catalyzed processes have been adapted to parallel synthesis utilizing commercially available boronic acid, acetylene, styrene, and amine sublibraries. Accordingly, a diverse 51-member library of 3,4,5-trisubstituted isoxazoles has been generated. 相似文献
215.
216.
217.
An experimental method for simultaneously measuring the velocity fields on the air and water side of unsteady breaking waves
is presented. The method includes a novel technique for seeding the air flow such that the air velocity can be resolved in
the absence of wind. Low density particles that have large Stokes drag and ability to respond to high-frequency flow fluctuations
are used to seed the air flow. Multi-camera, multi-laser particle image velocimetry setups are applied to small-scale unsteady
breaking waves, yielding fully time-resolved velocity fields. The surface tension of the fluid is altered and controlled to
form spilling breaking waves. Results for the velocity and vorticity fields of representative spilling breakers, which show
shedding of an air-side vortex and well-documented generation of water-side vorticity, are presented and discussed. 相似文献
218.
In this study, a coupled regional air quality modeling system is applied to investigate the time spatial variations in airborne particulate matters (PM10), originating from Mentougou to Beijing municipal area in the period of April 1-7, 2004, and the influences of complex terrain and meteorological conditions upon boundary layer structure and PM10 concentration distributions. An intercomparison of the performance with CALPUFF against the observed data is presented and an examination of scatter plots is provided. The statistics show that the correlation coefficient and STD between the modeled and observed data are 0.86 and 0.03, respectively. Analysis of model results illustrates that the pollutants emitted from Mentougou can be transported to Beijing municipal area along certain transport pathways, and PM10 concentration distributions show heterogeneity characteristics. Contributions of the Mentougou sources to the PM10 concentrations in Beijing municipal area are up to 0.1-15 μg/m^3. 相似文献
219.
Improved understanding of in-cylinder flows requires knowledge from well-resolved experimental velocimetry measurements and flow simulation modeling. Engine simulations using large eddy simulations (LES) are making large progress and the need for well documented velocimetry measurements for model validation is high. This work presents velocimetry measurements from PIV, high-speed PIV, stereoscopic PIV, and tomographic PIV to extensively describe the in-cylinder flow field in a motored optical engine operating at 800 RPM. These measurements also establish a comprehensive database designed for LES model development and validation. Details of the engine, engine accessory components, and well-controlled boundary conditions and engine operation are presented. The first two statistical moments of the flow field are computed and show excellent agreement among the PIV database. Analysis of statistical moments based on limited sample size is presented and is important for modeling validation purposes. High-speed PIV resolved the instantaneous flow field throughout entire engine cycles (i.e. 719 consecutive crank-angles), while tomographic PIV images are further used to investigate the 3D flow field and identify regions of strong vortical structures identified by the Q-criterion. Principle velocity gradient components are computed and emphasize the need to resolve similar spatial scales between experimental and modeling efforts for suitable model validation. 相似文献
220.