全文获取类型
收费全文 | 5560篇 |
免费 | 176篇 |
国内免费 | 15篇 |
专业分类
化学 | 3140篇 |
晶体学 | 42篇 |
力学 | 166篇 |
数学 | 783篇 |
物理学 | 1620篇 |
出版年
2022年 | 59篇 |
2021年 | 78篇 |
2020年 | 83篇 |
2019年 | 96篇 |
2018年 | 102篇 |
2017年 | 74篇 |
2016年 | 141篇 |
2015年 | 120篇 |
2014年 | 143篇 |
2013年 | 348篇 |
2012年 | 313篇 |
2011年 | 380篇 |
2010年 | 228篇 |
2009年 | 212篇 |
2008年 | 321篇 |
2007年 | 290篇 |
2006年 | 289篇 |
2005年 | 254篇 |
2004年 | 212篇 |
2003年 | 156篇 |
2002年 | 150篇 |
2001年 | 89篇 |
2000年 | 96篇 |
1999年 | 71篇 |
1998年 | 59篇 |
1997年 | 50篇 |
1996年 | 63篇 |
1995年 | 59篇 |
1994年 | 57篇 |
1993年 | 67篇 |
1992年 | 51篇 |
1991年 | 41篇 |
1990年 | 57篇 |
1989年 | 46篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 32篇 |
1985年 | 53篇 |
1984年 | 50篇 |
1983年 | 44篇 |
1982年 | 40篇 |
1981年 | 45篇 |
1980年 | 48篇 |
1979年 | 41篇 |
1978年 | 55篇 |
1977年 | 37篇 |
1976年 | 43篇 |
1975年 | 38篇 |
1974年 | 41篇 |
1973年 | 43篇 |
排序方式: 共有5751条查询结果,搜索用时 156 毫秒
31.
N. Chai W.D. Kulatilaka S.V. Naik N.M. Laurendeau R.P. Lucht J.P. Kuehner S. Roy V.R. Katta J.R. Gord 《Applied physics. B, Lasers and optics》2007,88(1):141-150
We report the application of electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) for measurements
of nitric oxide concentration ([NO]) in three different atmospheric pressure flames. Visible pump (532 nm) and Stokes (591 nm)
beams are used to probe the Q-branch of the Raman transition. A significant resonance enhancement is obtained by tuning an
ultraviolet probe beam (236 nm) into resonance with specific rotational transitions in the (v’=0, v”=1) vibrational band of
the A2Σ+–X2Π electronic system of NO. ERE-CARS spectra are recorded at various heights within a hydrogen-air flame producing relatively
low concentrations of NO over a Hencken burner. Good agreement is obtained between NO ERE-CARS measurements and the results
of flame computations using UNICORN, a two-dimensional flame code. Excellent agreement between measured and calculated NO
spectra is also obtained when using a modified version of the Sandia CARSFT code for heavily sooting acetylene-air flames
(φ=0.8 to φ=1.6) on the same Hencken burner. Finally, NO concentration profiles are measured using ERE-CARS in a laminar,
counter-flow, non-premixed hydrogen-air flame. Spectral scans are recorded by probing the Q1 (9.5), Q1 (13.5) and Q1 (17.5) Raman transitions. The measured shape of the [NO] profile is in good agreement with that predicted using the OPPDIF
code, even without correcting for collisional effects. These comparisons between [NO] measurements and predictions establish
the utility of ERE-CARS for detection of NO in flames with large temperature and concentration gradients as well as in sooting
environments.
PACS 07.88.+y; 42.62.Fi; 42.65.Dr 相似文献
32.
The decision problem for positively quantified formulae in the theory of linearly ordered Heyting algebras is known, as a special case of work of Kreisel, to be solvable; a simple solution is here presented, inspired by related ideas in Gödel-Dummett logic. 相似文献
33.
P. C. Roy 《等离子体物理论文集》1992,32(2):101-107
By using the two-point space correlation function an equation for the power spectral density for a random Langmuir field has been derived. The dispersion relation for a monochromatic wave is regained for a delta spectrum. For a Gaussian spectrum, the maximum growth rate is less than that for a monochromatic wave. For a “meander spectrum”, the growth rate is increased with the width of the spectrum in the first stage then decreased for further increase of the width. 相似文献
34.
The complexification of a semi-algebraic set is the smallest complex algebraic set containing S. Let S be defined by s polynomials of degrees less than d. We prove that the geometric degree of the complexification is less than .
Received: 9 January 1997; in final form: 11 August 2000 / Published online: 17 May 2001 相似文献
35.
The analysis in this paper looks at two important elements in modelling the market for timber in the United States. First, the issue of directional causality between price and quantity and its implications in a modelling effort is investigated. Second, the extent of the geographic market for timber is discussed and a method of detecting it is suggested. The method for detecting the extent of the geographical market is tractable and can be applied in a straightforward way. Both considerations are applied to the softwood lumber market in the United States. 相似文献
36.
This paper presents an algorithm and the supporting theory for solving a class of nonlinear multiple criteria optimization problems using Zionts—Wallenius type of interaction. The Zionts—Wallenius method, as extended in this paper, can be used for solving multiple criteria problems with concave objective and (implicit) value functions and convex feasible regions. Modifications of the method to handle nonconvex feasible regions and general nonlinear objective functions are also discussed.This research was supported, in part, by a Faculty Research Development Award and by a Council of 100 Research Grant from Arizona State University (Roy), and by a grant from Y. Jahnsson Foundation, Finland (Wallenius). The research was performed while the second author was a Visiting Professor at Arizona State University. 相似文献
37.
Communicated by Charles A. Micchelli. 相似文献
38.
We have calculated total and differential cross-sections for 1s →ns (n = 2, 3, 4) electron impact excitation of hydrogen and hydrogenic ions at various energies in Coulomb-projected Born approximation.
Distortion due to static interactions, target polarization and exchange effects has been incorporated in the initial channel.
The present calculations have been compared with other theoretical and experimental results. 相似文献
39.
We study the behavior of dynamic programming methods for the tree edit distance problem, such as [P. Klein, Computing the edit-distance between unrooted ordered trees, in: Proceedings of 6th European Symposium on Algorithms, 1998, p. 91–102; K. Zhang, D. Shasha, SIAM J. Comput. 18 (6) (1989) 1245–1262]. We show that those two algorithms may be described as decomposition strategies. We introduce the general framework of cover strategies, and we provide an exact characterization of the complexity of cover strategies. This analysis allows us to define a new tree edit distance algorithm, that is optimal for cover strategies. 相似文献
40.
Serge Zhuiykov 《Ionics》2005,11(5-6):352-361
An impedance method for periodic“in-situ” diagnostics of the solid electrolyte/liquid-metal electrode interface during the lifespan of yttria-stabilized zirconia (YSZ)-based
sensors measuring oxygen partial pressure in melts was developed. It was found that the impact of polarization effects on
YSZ, stipulated by corrosive measuring environments (molten alkaline metals), is increasing with increase of the working temperature,
which may lead to the appearance blocking reaction layers at the electrolyte/liquid-metal electrode interface. The proposed
impedance method allows obtaining necessary information about the electrolyte/liquid-metal electrode interface and about the
character and the level of polarization of the liquid-metal electrode. 相似文献