全文获取类型
收费全文 | 750篇 |
免费 | 11篇 |
国内免费 | 10篇 |
专业分类
化学 | 436篇 |
晶体学 | 4篇 |
力学 | 15篇 |
数学 | 138篇 |
物理学 | 178篇 |
出版年
2020年 | 7篇 |
2019年 | 6篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2014年 | 10篇 |
2013年 | 27篇 |
2012年 | 20篇 |
2011年 | 39篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 33篇 |
2007年 | 22篇 |
2006年 | 37篇 |
2005年 | 36篇 |
2004年 | 23篇 |
2003年 | 28篇 |
2002年 | 32篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 11篇 |
1969年 | 5篇 |
1939年 | 5篇 |
排序方式: 共有771条查询结果,搜索用时 46 毫秒
91.
J. Hoffman 《国际流体数值方法杂志》2009,59(11):1241-1258
General Galerkin (G2) is a new computational method for turbulent flow, where a stabilized Galerkin finite element method is used to compute approximate weak solutions to the Navier–Stokes equations directly, without any filtering of the equations as in a standard approach to turbulence simulation, such as large eddy simulation, and thus no Reynolds stresses are introduced, which need modelling. In this paper, G2 is used to compute the drag coefficient cD for the flow past a circular cylinder at Reynolds number Re=3900, for which the flow is turbulent. It is found that it is possible to approximate cD to an accuracy of a few percent, corresponding to the accuracy in experimental results for this problem, using less than 105 mesh points, which makes the simulations possible using a standard PC. The mesh is adaptively refined until a stopping criterion is reached with respect to the error in a chosen output of interest, which in this paper is cD. Both the stopping criterion and the mesh‐refinement strategy are based on a posteriori error estimates, in the form of a space–time integral of residuals times derivatives of the solution of a dual problem, linearized at the approximate solution, and with data coupling to the output of interest. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
92.
93.
Communicated by J. C. C. Nitsche 相似文献
94.
C. Boekema I. M. Suarez J. C. Lam T. J. Hoffman E. N. La Joie S. F. Weathersby J. A. Flint R. L. Lichti C. P. Wang D. W. Cooke 《Hyperfine Interactions》1991,64(1-4):467-475
Transverse-field (TF) muon-spin-relaxation (μSR) and Mössbauer experiments on the uniaxial insulating spin glass Fe2?xTi1+xO5 (x=0.25) have been performed near and below the spin-glass temperature (T g). The effect of a transverse field on the spin-freezing process and spin-glass state has been investigated by measuring the field-and temperature-dependencies of the μSR parameters. Spin-cluster effects signaled by anomalous μ-spin relaxation have been observed in a temperature region just aboveT g. An interpretation supported by recently developed theoretical models addressing non-linear relaxation in an intermediate Griffiths phase is offered. 相似文献
95.
Raman optical activity (ROA) of magnons and phonons in antiferromagnetic FeF2 (TN=78 K) has been studied as a function of temperature and in applied magnetic field. For exciting light incident along the rutile-structure c-axis, ROA is observed for magnons but not phonons. In zero field, the small anisotropy-induced splitting (0.09 cm−1) of the two acoustic-magnon branches is observed by light scattering for the first time. The splitting in applied magnetic field is found to reduce with increasing temperature in accordance with theory. No ROA was detected for two-magnon excitations. 相似文献
96.
The research described in this paper was supported by research grant DE-FG02-86ER250125 of the Applied Mathematical Science subprogram of Office of Energy Research, U.S. Department of Energy, and National Science Foundation grants DMS-8611574 and DMS-8802858 相似文献
97.
We investigated site specific reactivity of the α-Cu-Al(17 at.%)(1 0 0) alloy surface versus that of Al and Cu by measuring neutralisation of Li+ ions. Experiments show that Li+ neutralisation on the α-CuAl(1 0 0) alloy surface does not occur efficiently on Al and is somewhat more efficient on Cu as compared to a pure Cu sample, indicating depletion of electron density on Al and transfer to neighboring Cu. It can thus be concluded that Cu sites in presence of Al are more reactive in the sense that processes involving electron capture from the surface would proceed more efficiently on these. 相似文献
98.
Christopher Hoffman Douglas Rizzolo Erik Slivken 《Random Structures and Algorithms》2017,50(3):394-419
Permutations that avoid given patterns are among the most classical objects in combinatorics and have strong connections to many fields of mathematics, computer science and biology. In this paper we study the scaling limits of a random permutation avoiding a pattern of length 3 and their relations to Brownian excursion. Exploring this connection to Brownian excursion allows us to strengthen the recent results of Madras and Pehlivan [25] and Miner and Pak [29] as well as to understand many of the interesting phenomena that had previously gone unexplained. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 50, 394–419, 2017 相似文献
99.
Cho DS Gibson SC Bhandari D McNally ME Hoffman RM Cook KD Song L 《Rapid communications in mass spectrometry : RCM》2011,25(23):3575-3580
Batch slurry reactions are widely used in the industrial manufacturing of chemicals, pharmaceuticals, petrochemicals and polymers. However, onsite monitoring of batch slurry reactions is still not feasible in production plants due to the challenge in analyzing heterogeneous samples without complicated sample preparation procedures. In this study, direct analysis in real time mass spectrometry (DART-MS) has been evaluated for the onsite monitoring of a model batch slurry reaction. The results suggested that automation of the sampling process of DART-MS is important to achieve quantitative results. With a sampling technique of manual sample deposition on melting point capillaries followed by automatic sample introduction across the helium beam, relative standard deviation (RSD) of the protonated molecule signals from the reaction product of the model batch slurry reaction ranged from 6 to 30%. This RSD range is improved greatly over a sampling technique of manual sample deposition followed by manual sample introduction where the RSDs are up to 110%. Furthermore, with the semi-automated sampling approach, semi-quantitative analysis of slurry samples has been achieved. Better quantification is expected with a fully automated sampling approach. 相似文献
100.
An efficient molybdenum-catalyzed asymmetric allylic alkylation (Mo-AAA) of cyanoester nucleophiles is reported. A number of highly functionalized branched cyanoesters containing a quaternary carbon stereocenter with a vicinal tertiary stereocenter are obtained. This method generates a number of functionalized cyanoesters in excellent yield and chemoselectivity in good to excellent diastereoselectivity and enantioselectivity. 相似文献