全文获取类型
收费全文 | 253575篇 |
免费 | 11021篇 |
国内免费 | 6131篇 |
专业分类
化学 | 147182篇 |
晶体学 | 4264篇 |
力学 | 11017篇 |
综合类 | 339篇 |
数学 | 25053篇 |
物理学 | 82872篇 |
出版年
2022年 | 3160篇 |
2021年 | 3509篇 |
2020年 | 3973篇 |
2019年 | 4022篇 |
2018年 | 4050篇 |
2017年 | 4123篇 |
2016年 | 6089篇 |
2015年 | 4800篇 |
2014年 | 6622篇 |
2013年 | 12970篇 |
2012年 | 11266篇 |
2011年 | 12697篇 |
2010年 | 8955篇 |
2009年 | 8705篇 |
2008年 | 10408篇 |
2007年 | 9934篇 |
2006年 | 9269篇 |
2005年 | 8278篇 |
2004年 | 7207篇 |
2003年 | 6448篇 |
2002年 | 6114篇 |
2001年 | 7102篇 |
2000年 | 5484篇 |
1999年 | 4549篇 |
1998年 | 3586篇 |
1997年 | 3492篇 |
1996年 | 3369篇 |
1995年 | 3155篇 |
1994年 | 2938篇 |
1993年 | 2677篇 |
1992年 | 3246篇 |
1991年 | 3115篇 |
1990年 | 2999篇 |
1989年 | 2922篇 |
1988年 | 2877篇 |
1987年 | 2881篇 |
1986年 | 2745篇 |
1985年 | 3438篇 |
1984年 | 3397篇 |
1983年 | 2689篇 |
1982年 | 2763篇 |
1981年 | 2802篇 |
1980年 | 2558篇 |
1979年 | 2893篇 |
1978年 | 2867篇 |
1977年 | 2997篇 |
1976年 | 2835篇 |
1975年 | 2572篇 |
1974年 | 2515篇 |
1973年 | 2479篇 |
排序方式: 共有10000条查询结果,搜索用时 782 毫秒
991.
M. K. Richharia 《Pramana》2007,68(6):1007-1012
The cosmic ray (CR) intensity data recorded in Deep River Neutron Monitoring Station have been investigated on quietest days
(QD) for third harmonics of daily variation during solar cycles 21 and 22. It has been observed that in spite of abrupt change
in the amplitude and phase of tri-diurnal anisotropy in CR intensity, the amplitude is quite significant throughout the period
of investigation with larger amplitude during the years 1980 and 1985. Thus, tri-diurnal anisotropy clearly shows 11-year
variation at the mid latitude neutron monitoring station.
相似文献
992.
993.
Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy was employed to observe the visible absorption spectra of the B^2Σ^+_u-X^2Σ^+_g electronic transition of C^-_2. Four hot bands (0,1), (1,2), (2,3) and (3,4) have been observed and the band (3,4) is measured directly for the first time, so far as we know, by absorption. A rotational analysis was carried out to obtain molecular constants. With the Franck-Condon principle and the vibrational Boltzmann distribution, we have estimated the vibrational temperature of C^-_2 to be about 3000K. 相似文献
994.
995.
C. S. Creaser M. R. S. McCoustra K. E. O'Neill 《Journal of mass spectrometry : JMS》1991,26(4):335-338
Two fibre-optic interfaces were constructed for laser photodissociation/tandem mass spectrometry using an ion trap spectrometer. These interfaces allow sample introduction from a liquid reservoir, solids probe and gas chromatograph. The laser/ion trap configuration was applied to the analysis of a mixture of alkylbenenes separated by gas chromatography using 573 nm photons. 相似文献
996.
An initial boundary value problem for the dynamic system of anisotropic elasticity in a half space is studied in the paper. A novel method of finding an exact solution of this problem for a special polynomial form of initial data and inhomogeneous term of the system is described. On the base of this method the simulation of elastic waves in different homogeneous anisotropic half spaces is implemented. 相似文献
997.
We obtain solutions of new extremal problems of the geometric theory of functions of a complex variable related to estimates
for the inner radii of nonoverlapping domains. Some known results are generalized to the case of open sets.
__________
Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 10, pp. 1313–1321, October, 2007. 相似文献
998.
The last decade has seen a considerable growth in the use of Artificial Intelligence (AI) for operations management with the aim of finding solutions to problems that are increasing in complexity and scale. This paper begins by setting the context for the survey through a historical perspective of OR and AI. An extensive survey of applications of AI techniques for operations management, covering a total of over 1200 papers published from 1995 to 2004 is then presented. The survey utilizes Elsevier's ScienceDirect database as a source. Hence, the survey may not cover all the relevant journals but includes a sufficiently wide range of publications to make it representative of the research in the field. The papers are categorized into four areas of operations management: (a) design, (b) scheduling, (c) process planning and control and (d) quality, maintenance and fault diagnosis. Each of the four areas is categorized in terms of the AI techniques used: genetic algorithms, case-based reasoning, knowledge-based systems, fuzzy logic and hybrid techniques. The trends over the last decade are identified, discussed with respect to expected trends and directions for future work suggested. 相似文献
999.
We exhibit a characteristic structure of the class of all regular graphs of degree d that stems from the spectra of their adjacency matrices. The structure has a fractal threadlike appearance. Points with coordinates given by the mean and variance of the exponentials of graph eigenvalues cluster around a line segment that we call a filar. Zooming-in reveals that this cluster splits into smaller segments (filars) labeled by the number of triangles in graphs. Further zooming-in shows that the smaller filars split into subfilars labeled by the number of quadrangles in graphs, etc. We call this fractal structure, discovered in a numerical experiment, a multifilar structure. We also provide a mathematical explanation of this phenomenon based on the Ihara-Selberg trace formula, and compute the coordinates and slopes of all filars in terms of Bessel functions of the first kind. 相似文献
1000.
K. C. Kiwiel 《Journal of Optimization Theory and Applications》2007,134(3):549-554
We give a linear time algorithm for the continuous quadratic knapsack problem which is simpler than existing methods and competitive
in practice. Encouraging computational results are presented for large-scale problems.
The author thanks the Associate Editor and an anonymous referee for their helpful comments. 相似文献