全文获取类型
收费全文 | 2251篇 |
免费 | 243篇 |
国内免费 | 96篇 |
专业分类
化学 | 389篇 |
力学 | 119篇 |
综合类 | 57篇 |
数学 | 1133篇 |
物理学 | 892篇 |
出版年
2024年 | 6篇 |
2023年 | 34篇 |
2022年 | 68篇 |
2021年 | 56篇 |
2020年 | 69篇 |
2019年 | 77篇 |
2018年 | 78篇 |
2017年 | 100篇 |
2016年 | 89篇 |
2015年 | 55篇 |
2014年 | 119篇 |
2013年 | 136篇 |
2012年 | 98篇 |
2011年 | 111篇 |
2010年 | 101篇 |
2009年 | 118篇 |
2008年 | 138篇 |
2007年 | 118篇 |
2006年 | 131篇 |
2005年 | 110篇 |
2004年 | 93篇 |
2003年 | 94篇 |
2002年 | 82篇 |
2001年 | 67篇 |
2000年 | 66篇 |
1999年 | 50篇 |
1998年 | 35篇 |
1997年 | 46篇 |
1996年 | 32篇 |
1995年 | 33篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 18篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1982年 | 7篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2590条查询结果,搜索用时 46 毫秒
131.
132.
《光谱学快报》2013,46(3):303-318
Abstract Open‐path Fourier transform infrared (FTIR) spectrometry was used to continuously monitor 11 chlorinated hydrocarbon species in the region connecting two different industrial complexes for 24 hr. The single‐beam spectra obtained from open‐path FTIR were analyzed by newly developed software named COL1SB, which generates site‐specific background spectra as well as path‐averaged water vapor concentrations in addition to performing regression analyses. The path‐averaged water vapor concentrations calculated by the COL1SB agreed very well with those measured by a thermo‐hygrometer. In addition, site‐specific background spectra were generated by accounting for chemical absorption of 50 chemical species. The accurate estimation of path‐averaged water vapor concentrations, as well as the usage of site‐specific background spectra, enables chlorinated hydrocarbons to be measured by open‐path FTIR spectrometry at the ppb level. Among 11 chlorinated hydrocarbons considered here, trichlorofluoromethane, carbon tetrachloride, trichloroethylene, and tetrachloroethylene were identified as major chlorinated hydrocarbons having concentrations above 1 ppb. Wind affected the temporal variations of these chlorinated hydrocarbons, indicating the importance of local transport. However, the effect of wind differed from one species to another because of different source characteristics. 相似文献
133.
134.
135.
J.S. Lee M. Ortolani J. Kouba A. Firsov Y.J. Chang T.W. Noh U. Schade 《Infrared Physics & Technology》2008,51(5):443-445
We investigated the effect of an electric-pulse on the insulator–metal phase transition of VO2/Al2O3 films using synchrotron-based infrared microspectroscopy. By monitoring the time-resolved optical response, we could demonstrate that local conducting areas are formed under the influence of the electric-pulse, and the Joule heat generated from the local current flow drives a consecutive thermal phase transition in the adjacent sample area. 相似文献
136.
In the real-world application of face recognition system, owing to the difficulties of collecting samples or storage space of systems, only one sample image per person is stored in the system, which is so-called one sample per person problem. Moreover, pose and illumination have impact on recognition performance. We propose a novel pose and illumination robust algorithm for face recognition with a single training image per person to solve the above limitations. Experimental results show that the proposed algorithm is an efficient and practical approach for face recognition. 相似文献
137.
The predictor-corrector method for following a reduced gradient (RGF) to determine saddle points [Quapp, W. et al., J Comput Chem 1998, 19, 1087] is further accelerated by a modification allowing an implied corrector step per predictor but almost without additional costs. The stability and robustness of the RGF method are improved, and the new version in addition reduces the number of gradient and Hessian calculations. 相似文献
138.
In this paper we study the relationship between Constraint Programming (CP) and Shortest Path (SP) problems. In particular, we show that classical, multicriteria, partially ordered, and modality-based SP problems can be naturally modeled and solved within the Soft Constraint Logic Programming (SCLP) framework, where logic programming is coupled with soft constraints. In this way we provide this large class of SP problems with a high-level and declarative linguistic support whose semantics takes care of both finding the cost of the shortest path(s) and also of actually finding the path(s). On the other hand, some efficient algorithms for certain classes of SP problems can be exploited to provide some classes of SCLP programs with an efficient way to compute their semantics. 相似文献
139.
140.
A. Y. Lee 《Journal of Optimization Theory and Applications》1988,57(3):519-536
Neighboring extremals of dynamic optimization problems with path equality constraints and with an unknown parameter vector
are considered in this paper. With some simplifications, the problem is reduced to solving a linear, time-varying two-point
boundary-value problem with integral path equality constraints. A modified backward sweep method is used to solve this problem.
Two example problems are solved to illustrate the validity and usefulness of the solution technique.
This research was supported in part by the National Aeronautics and Space Administration under NASA Grant No. NCC-2-106.
The author is indebted to Professor A. E. Bryson, Jr., Department of Aeronautics and Astronautics, Stanford University, for
many stimulating discussions. 相似文献