全文获取类型
收费全文 | 12894篇 |
免费 | 1833篇 |
国内免费 | 1221篇 |
专业分类
电工技术 | 1317篇 |
综合类 | 1903篇 |
化学工业 | 675篇 |
金属工艺 | 352篇 |
机械仪表 | 828篇 |
建筑科学 | 846篇 |
矿业工程 | 195篇 |
能源动力 | 275篇 |
轻工业 | 193篇 |
水利工程 | 229篇 |
石油天然气 | 502篇 |
武器工业 | 154篇 |
无线电 | 2301篇 |
一般工业技术 | 1876篇 |
冶金工业 | 158篇 |
原子能技术 | 175篇 |
自动化技术 | 3969篇 |
出版年
2024年 | 61篇 |
2023年 | 203篇 |
2022年 | 401篇 |
2021年 | 397篇 |
2020年 | 461篇 |
2019年 | 389篇 |
2018年 | 380篇 |
2017年 | 422篇 |
2016年 | 502篇 |
2015年 | 565篇 |
2014年 | 733篇 |
2013年 | 866篇 |
2012年 | 947篇 |
2011年 | 970篇 |
2010年 | 768篇 |
2009年 | 797篇 |
2008年 | 792篇 |
2007年 | 895篇 |
2006年 | 789篇 |
2005年 | 698篇 |
2004年 | 586篇 |
2003年 | 498篇 |
2002年 | 454篇 |
2001年 | 365篇 |
2000年 | 333篇 |
1999年 | 288篇 |
1998年 | 226篇 |
1997年 | 196篇 |
1996年 | 169篇 |
1995年 | 163篇 |
1994年 | 139篇 |
1993年 | 106篇 |
1992年 | 87篇 |
1991年 | 59篇 |
1990年 | 68篇 |
1989年 | 59篇 |
1988年 | 41篇 |
1987年 | 19篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 297 毫秒
61.
The treatment of domain integrals has been a topic of interest almost since the inception of the boundary element method (BEM). Proponents of meshless methods such as the dual reciprocity method (DRM) and the multiple reciprocity method (MRM) have typically pointed out that these meshless methods obviate the need for an interior discretization. Hence, the DRM and MRM maintain one of the biggest advantages of the BEM, namely, the boundary-only discretization. On the other hand, other researchers maintain that classical domain integration with an interior discretization is more robust. However, the discretization of the domain in complex multiply-connected geometries remains problematic. In this research, three methods for evaluating the domain integrals associated with the boundary element analysis of the three-dimensional Poisson and nonhomogeneous Helmholtz equations in complex multiply-connected geometries are compared. The methods include the DRM, classical cell-based domain integration, and a novel auxiliary domain method. The auxiliary domain method allows the evaluation of the domain integral by constructing an approximately C
1 extension of the domain integrand into the complement of the multiply-connected domain. This approach combines the robustness and accuracy of direct domain integral evaluation while, at the same time, allowing for a relatively simple interior discretization. Comparisons are made between these three methods of domain integral evaluation in terms of speed and accuracy.
This work was partially supported by the United States Department of Energy (DOE) grants DE-FG03-97ER14778 and DE-FG03-97ER25332. This financial support does not constitute an endorsement by the DOE of the views expressed in this paper. 相似文献
62.
颜力 《太赫兹科学与电子信息学报》2003,1(1):31-36
在频域中推导了适用于差分类数值方法的吸收边界条件的构造方法,并通过选取不同参数导出了几种现有的吸收边界条件。在计算了一般形式的吸收边界条件的反射系数之后,提出了一种简单实用的自适应吸收边界条件。 相似文献
63.
We propose an asymmetric integral imaging method to adjust the resolution and depth of a three‐dimensional image. Our method is obtained by use of two lenticular sheets with different pitches fabricated under the same F/#. The asymmetric integral imaging is the generalized version of integral imaging, including both conventional integral imaging and one‐dimensional integral imaging. We present experimental results to test and verify the performance of our method computationally. 相似文献
64.
一种新的图像水印方案 总被引:1,自引:0,他引:1
目标区域是图像中视觉上最重要的部分。针对现有的水印算法很少考虑图像中确定的目标区域这一问题,提出了一种基于目标区域的水印方案(WIOR)。方案首先利用小波变换分析图像的目标特征,并依据图像的小波高频系数特征对其进行聚类,获得水印的嵌入域,在此嵌入域中,选择小波系数并对其进行量化调制来嵌入二值扩谱水印;同时,通过只在图像的局部区域内嵌入较少的水印信息来改善水印的隐蔽性。实验结果表明,该方案对于一类具有突出目标特征的图像具有较好的效果。嵌入的水印主要优势在于真正把水印嵌入图像的视觉重要部分,从而能有效地抵御剪切攻击,而且可以实现盲检测。 相似文献
65.
A new interaction integral formulation is developed for evaluating the elastic T-stress for mixed-mode crack problems with
arbitrarily oriented straight or curved cracks in orthotropic nonhomogeneous materials. The development includes both the
Lekhnitskii and Stroh formalisms. The former is physical and relatively simple, and the latter is mathematically elegant.
The gradation of orthotropic material properties is integrated into the element stiffness matrix using a “generalized isoparametric
formulation” and (special) graded elements. The specific types of material gradation considered include exponential and hyperbolic-tangent
functions, but micromechanics models can also be considered within the scope of the present formulation. This paper investigates
several fracture problems to validate the proposed method and also provides numerical solutions, which can be used as benchmark
results (e.g. investigation of fracture specimens). The accuracy of results is verified by comparison with analytical solutions. 相似文献
66.
Rafael Gallego Lucia Comino Alberto Ruiz‐Cabello 《International journal for numerical methods in engineering》2006,66(12):1913-1933
In this paper, the material constant sensitivity boundary integral equation is presented, and its numerical solution proposed, based on boundary element techniques. The formulation deals with plane problems with general rectilinear anisotropy. Expressions for the computation of sensitivities for displacements, tractions, strains and stresses are derived, both for boundary and interior points. The sensitivities can be computed with respect to the bulk material properties or to the properties of part of the domain (inclusions, coatings, etc.). To assess the accuracy of the proposed approach, the computed results are compared to analytical ones derived from exact solutions obtained by complex potential theory, when possible, or finite difference derivatives otherwise. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
67.
Periklis E. Ergatis Panagiotis G. Massouros Georgia C. Athanasouli George P. Massouros 《国际能源研究杂志》2003,27(9):795-811
A time‐dependent coefficient of heat transfer is proposed for the computation of thermal power required, so that a room temperature reaches a desired value within a given time. A mathematical formulation of the room heating transient phenomenon is constructed in a dimensionless form. Using an integral approximate solution an analytical expression for this coefficient is provided and it is verified by diagrams adopted by DIN 4701. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
68.
69.
70.
We analyse the Bouchouev integral equation for the deterministic volatility function in the Black–Scholes option pricing model. We areable to reduce Bouchouev's original triple integral equation to a single integral equation and describe its numerical solution. Moreover we show empirically that the most complex term in the equation may often be safely ignored for the purposes of numerical calculations. We present a selection of numerical examples indicating the range of time values for which we would expect the equation to be valid. 相似文献