全文获取类型
收费全文 | 332897篇 |
免费 | 5248篇 |
国内免费 | 2248篇 |
专业分类
化学 | 184264篇 |
晶体学 | 5646篇 |
力学 | 14105篇 |
综合类 | 102篇 |
数学 | 33201篇 |
物理学 | 103075篇 |
出版年
2021年 | 2842篇 |
2020年 | 3236篇 |
2019年 | 3415篇 |
2018年 | 4061篇 |
2017年 | 4145篇 |
2016年 | 6181篇 |
2015年 | 4119篇 |
2014年 | 6208篇 |
2013年 | 14986篇 |
2012年 | 11638篇 |
2011年 | 13940篇 |
2010年 | 9871篇 |
2009年 | 9813篇 |
2008年 | 12606篇 |
2007年 | 12234篇 |
2006年 | 11680篇 |
2005年 | 10552篇 |
2004年 | 9446篇 |
2003年 | 8725篇 |
2002年 | 8379篇 |
2001年 | 10537篇 |
2000年 | 7797篇 |
1999年 | 6134篇 |
1998年 | 4681篇 |
1997年 | 4681篇 |
1996年 | 4501篇 |
1995年 | 4200篇 |
1994年 | 4029篇 |
1993年 | 3720篇 |
1992年 | 4609篇 |
1991年 | 4659篇 |
1990年 | 4448篇 |
1989年 | 4410篇 |
1988年 | 4373篇 |
1987年 | 4373篇 |
1986年 | 4092篇 |
1985年 | 5211篇 |
1984年 | 5253篇 |
1983年 | 4166篇 |
1982年 | 4305篇 |
1981年 | 4213篇 |
1980年 | 3977篇 |
1979年 | 4490篇 |
1978年 | 4559篇 |
1977年 | 4620篇 |
1976年 | 4402篇 |
1975年 | 4067篇 |
1974年 | 4015篇 |
1973年 | 4013篇 |
1972年 | 2745篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
995.
996.
M. Okumura K. Fukushi S. N. Willie R. E. Sturgeon 《Fresenius' Journal of Analytical Chemistry》1993,345(8-9):570-574
Summary Atomic fluorescence (AFS), absorption (AAS) and emission (AES) systems were evaluated for the determination of inorganic mercury. Identical vapour generation and amalgamation procedures were used to permit direct comparison of the performance of a commercial long-path AAS instrument to laboratory constructed non-dispersive AFS as well as He-MIP based AES instruments. Instrumental noise-limited detection limits (LOD) were 0.94, 2.4, 2.8 pg for AAS, AES and AFS techniques, respectively. Methodological LOD's were found to be blank controlled and similar for all three instruments, viz. 9, 25 and 16 pg for AAS, AFS and AES, respectively. All three systems produced accurate results at the low ng/l concentration, as verified by the analysis of a certified river water reference material (NRCC ORMS-1). 相似文献
997.
A. L'Esprance J. Nicolas D.K. Wilson D.W. Thomson Y. Gabillet G. Daigle 《Applied Acoustics》1993,40(4)
This paper presents a set of acoustical and meteorological data from an outdoor sound propagation experiment. This experiment was done in a farm field near Rock Springs, Pennsylvania, on 7 July 1990. Meteorological and acoustical measurements were recorded simultaneously during six different times in the day. The meteorological measurements permitted determination of the sound speed profiles during each of the measurement sessions, using a method based on surface-layer similarity scaling. The acoustical measurements allowed precise determination of the relative sound pressure levels for a frequency range up to 3150 Hz at six different distances (66, 88, 125, 175, 250 and 350 m). The results show atmospheric conditions have an important effect on sound propagation. At medium and high frequencies, variations of the relative SPL have been measured at distances as short as 62 m. These effects increased with the distances so that variations as great as 30 dB have been measured during that day. Comparisons with the fast field program predictions are also presented, and amply demonstrate the accuracies of this model, especially for the downward refraction cases. 相似文献
998.
999.
We demonstrate how optimization problems arise in the field of pattern classification, in particular in using piecewise-linear classification and classification based on an optimal linear separator. We motivate the need in this area for a general purpose optimization approach. We discuss ALOPEX, a biased random search approach, from the point of view of this need. While ALOPEX itself failed to fulfil our need, a newly-introduced generalization of it (iterated ALOPEX) was found to be appropriate for the optimization problems of our particular concern. We conclude the paper with a brief critical evaluation of this approach as compared to our original aims. 相似文献
1000.
Vortex-sheet growth is considered. Broken symmetry bifurcations are found in the growth process. The collective elasticity theory for a well-developed vortex sheet is presented, which is similar to that of smectic liquid crystals. The bifurcations in the limit of a much folded vortex sheet correspond to the Helfrich instability in smectics and cholesterics. 相似文献