全文获取类型
收费全文 | 54556篇 |
免费 | 7119篇 |
国内免费 | 5026篇 |
专业分类
化学 | 11248篇 |
晶体学 | 963篇 |
力学 | 10447篇 |
综合类 | 695篇 |
数学 | 18897篇 |
物理学 | 14347篇 |
无线电 | 10104篇 |
出版年
2024年 | 151篇 |
2023年 | 613篇 |
2022年 | 990篇 |
2021年 | 1173篇 |
2020年 | 1549篇 |
2019年 | 1291篇 |
2018年 | 1317篇 |
2017年 | 1896篇 |
2016年 | 2161篇 |
2015年 | 1820篇 |
2014年 | 2985篇 |
2013年 | 3848篇 |
2012年 | 3423篇 |
2011年 | 3879篇 |
2010年 | 3219篇 |
2009年 | 3500篇 |
2008年 | 3507篇 |
2007年 | 3532篇 |
2006年 | 3220篇 |
2005年 | 2950篇 |
2004年 | 2510篇 |
2003年 | 2297篇 |
2002年 | 2054篇 |
2001年 | 1688篇 |
2000年 | 1555篇 |
1999年 | 1393篇 |
1998年 | 1294篇 |
1997年 | 1107篇 |
1996年 | 903篇 |
1995年 | 791篇 |
1994年 | 719篇 |
1993年 | 552篇 |
1992年 | 565篇 |
1991年 | 422篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 214篇 |
1987年 | 151篇 |
1986年 | 101篇 |
1985年 | 132篇 |
1984年 | 134篇 |
1983年 | 64篇 |
1982年 | 89篇 |
1981年 | 73篇 |
1980年 | 42篇 |
1979年 | 50篇 |
1978年 | 41篇 |
1977年 | 44篇 |
1976年 | 19篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This paper has demonstrated that the Schwartz alternating process must converge if D-N alternating process has converged. Its technique is that the overlapping regions in Schwartz alternating process are considered as independent domains, then Schwartz alternating process could be transformed into D-N alter-nating process. Finally the convergence estimation of Schwartz alternating process could be obtained. The results show that its convergence rate is same as that of D-N alternating process. 相似文献
52.
A new parallel storm surge model, the Parallel Environmental Model (PEM), is developed and tested by comparisons with analytic solutions. The PEM is a 2‐D vertically averaged, wetting and drying numerical model and can be operated in explicit, semi‐implicit and fully implicit modes. In the implicit mode, the propagation, Coriolis and bottom friction terms can all be treated implicitly. The advection and diffusion terms are solved with a parallel Eulerian–Lagrangian scheme developed for this study. The model is developed specifically for use on parallel computer systems and will function accordingly in either explicit of implicit modes. Storm boundary conditions are based on a simple exponential decay of pressure from the centre of a storm. The simulated flooding caused by a major Category 5 hurricane making landfall in the Indian River Lagoon, Florida is then presented as an example application of the PEM. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
53.
正交变换在重积分中某些应用 总被引:2,自引:0,他引:2
姚云飞 《数学的实践与认识》2003,33(9):139-144
正交变换是代数学的基本内容 ,其用途十分广泛 .重积分的计算往往存在技术性的困难 ,若利用“正交变换”的有关理论去解决某些重积分的计算问题是颇有功效的 .本文将以“正交变换”为工具 ,简洁的处理重积分的某些问题 相似文献
54.
In this paper, based on the Lame function and Jacobi elliptic function, the perturbation method is appliedto some nonlinear evolution equations to derive their multi-order solutions. 相似文献
55.
L.G. Casado I. García T. Csendes V.G. Ruíz 《Journal of Optimization Theory and Applications》2003,118(1):27-43
Based on the investigation carried out in Ref. 1, this paper incorporates new studies about the properties of inclusion functions on subintervals while a branch-and-bound algorithm is solving global optimization problems. It is found that the relative place of the global minimum value within the inclusion function value of the objective function at the current interval indicates mostly whether the given interval is close to a minimizer point. This information is used in a heuristic interval rejection rule that can save a considerable amount of computation. Illustrative examples are discussed and an extended numerical study shows the advantages of the new approach. 相似文献
56.
We show that functions which are invariant for suitable product semigroups (one of which is a quasi-Poisson semigroup on a general state space) decompose into a singular eigen-function and a mixture of products of minimal eigen-functions. 相似文献
57.
M. I. Gil' 《Proceedings of the American Mathematical Society》2003,131(12):3737-3746
A linear operator in a separable Hilbert space is called a quasinormal one if it is a sum of a normal operator and a compact one. In the paper, bounds for the spectrum of quasinormal operators are established. In addition, the lower estimate for the spectral radius is derived. Under some restrictions, that estimate improves the well-known results. Applications to integral operators and matrices are discussed. Our results are new even in the finite-dimensional case.
58.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important. 相似文献
60.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献