全文获取类型
收费全文 | 5398篇 |
免费 | 695篇 |
国内免费 | 339篇 |
专业分类
化学 | 4193篇 |
晶体学 | 15篇 |
力学 | 730篇 |
综合类 | 63篇 |
数学 | 564篇 |
物理学 | 867篇 |
出版年
2024年 | 12篇 |
2023年 | 66篇 |
2022年 | 332篇 |
2021年 | 325篇 |
2020年 | 248篇 |
2019年 | 158篇 |
2018年 | 187篇 |
2017年 | 173篇 |
2016年 | 278篇 |
2015年 | 285篇 |
2014年 | 317篇 |
2013年 | 522篇 |
2012年 | 324篇 |
2011年 | 302篇 |
2010年 | 221篇 |
2009年 | 283篇 |
2008年 | 263篇 |
2007年 | 285篇 |
2006年 | 266篇 |
2005年 | 264篇 |
2004年 | 219篇 |
2003年 | 213篇 |
2002年 | 149篇 |
2001年 | 95篇 |
2000年 | 96篇 |
1999年 | 63篇 |
1998年 | 64篇 |
1997年 | 74篇 |
1996年 | 73篇 |
1995年 | 47篇 |
1994年 | 34篇 |
1993年 | 27篇 |
1992年 | 38篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 8篇 |
1988年 | 20篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有6432条查询结果,搜索用时 0 毫秒
1.
In this work, the natural convection in a concentric annulus between a cold outer square cylinder and a heated inner circular cylinder is simulated using the differential quadrature (DQ) method. The vorticity‐stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation. It is shown in this paper that the outer square boundary can be approximated by a super elliptic function. As a result, the coordinate transformation from the physical domain to the computational domain is set up by an analytical expression, and all the geometrical parameters can be computed exactly. Numerical results for Rayleigh numbers range from 104 to 106 and aspect ratios between 1.67 and 5.0 are presented, which are in a good agreement with available data in the literature. It is found that both the aspect ratio and the Rayleigh number are critical to the patterns of flow and thermal fields. The present study suggests that a critical aspect ratio may exist at high Rayleigh number to distinguish the flow and thermal patterns. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
Alexander Yu. Gelfgat 《国际流体数值方法杂志》2004,44(2):135-146
The global Galerkin method is applied to the benchmark problem that considers an oscillatory regime of convection of air in a tall two‐dimensional rectangular cavity. The three most unstable modes of the linearized system of the Boussinesq equations are studied. The converged values of the critical Rayleigh numbers together with the corresponding oscillation frequencies are calculated for each mode. The oscillatory flow regimes corresponding to each of the three modes are approximated asymptotically. No direct time integration is applied. Good agreement with the previously published results obtained by solution of the time‐dependent Boussinesq equations is reported. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
X. H. Li Y. Z. Meng S. J. Wang A. Varada Rajulu S. C. Tjong 《Journal of Polymer Science.Polymer Physics》2004,42(4):666-675
The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004 相似文献
4.
5.
The implementation of a nonzero-order joint transform correlator using the double port Mach-Zehnder interferometric technique is proposed and demonstrated. This approach provides on-line processing for directly removing the zero-order components of a joint power spectrum in one step and performs the nonzero-order optical correlation. Experimental results are presented and discussed. 相似文献
6.
Youssef Randjiou 《Journal of Theoretical Probability》2006,19(3):701-720
Let μ+(t) and μ−(t) be the locations of the maximum and minimum, respectively, of a standard Brownian motion in the interval [0,t]. We establish a joint integral test for the lower functions of μ+(t) and μ−(t), in the sense of Paul Lévy. In particular, it yields the law of the iterated logarithm for max(μ+(t),μ−(t)) as a straightforward consequence. Our result is in agreement with well-known theorems of Chung and Erdős [(1952) Trans. Amer. Math. Soc. 72, 179–186.], and Csáki, F?ldes and Révész [(1987) Prob. Theory Relat. Fields
76, 477–497].
相似文献
7.
用三个关系式与Mathematica软件求第二类自然数幂和公式 总被引:1,自引:1,他引:0
首先介绍三个第二类自然数幂和关系式并对其中的两式给出证明,接着利用这些关系式与数学软件M athem atica4.0,给出求解第二类自然数幂和公式的若干机械计算方法. 相似文献
8.
Nis Halland Tore Hansen Karl Anker Jrgensen 《Angewandte Chemie (International ed. in English)》2003,42(40):4837-4837
9.
The hydrocarbon discovery prediction problem is important to firms having to make decisions about the deployment of scarce exploration resources. Traditional methods for estimating the discovery rate rely on the completion of time consuming simulation experiments. A rapid approximation that does not require the completion of simulation exists and has been shown to have some promise as a prediction tool. This paper investigates the accuracy of the approximation method under a wide variety of distributional and drilling efficiency assumptions. The results indicate that the approximation produces predictions close to those of simulation under most of the tested conditions. This suggests that resource exploration firms could conveniently use the method for a wide variety of planning purposes without incurring the same costs in time and personnel required for simulation. 相似文献
10.
This contribution discusses the phenomena of retrograde condensation of one or two liquids. It w1 be shown that both phenomena can be well understood. Also the relation of retrograde condensation of one liquid phase with the condensation behavior of natural gas will be discussed. Similarly that of two liquid phases with multiple phase behavior occurring in low temperature reservoir fluids will be pointed out. 相似文献