全文获取类型
收费全文 | 23431篇 |
免费 | 2509篇 |
国内免费 | 1624篇 |
专业分类
电工技术 | 3193篇 |
技术理论 | 1篇 |
综合类 | 2145篇 |
化学工业 | 2193篇 |
金属工艺 | 522篇 |
机械仪表 | 1648篇 |
建筑科学 | 870篇 |
矿业工程 | 398篇 |
能源动力 | 1396篇 |
轻工业 | 607篇 |
水利工程 | 417篇 |
石油天然气 | 593篇 |
武器工业 | 285篇 |
无线电 | 3426篇 |
一般工业技术 | 2610篇 |
冶金工业 | 437篇 |
原子能技术 | 159篇 |
自动化技术 | 6664篇 |
出版年
2024年 | 101篇 |
2023年 | 361篇 |
2022年 | 592篇 |
2021年 | 727篇 |
2020年 | 713篇 |
2019年 | 725篇 |
2018年 | 698篇 |
2017年 | 829篇 |
2016年 | 963篇 |
2015年 | 1048篇 |
2014年 | 1459篇 |
2013年 | 1467篇 |
2012年 | 1607篇 |
2011年 | 1911篇 |
2010年 | 1349篇 |
2009年 | 1498篇 |
2008年 | 1566篇 |
2007年 | 1660篇 |
2006年 | 1333篇 |
2005年 | 1105篇 |
2004年 | 920篇 |
2003年 | 769篇 |
2002年 | 646篇 |
2001年 | 495篇 |
2000年 | 473篇 |
1999年 | 398篇 |
1998年 | 392篇 |
1997年 | 261篇 |
1996年 | 264篇 |
1995年 | 232篇 |
1994年 | 182篇 |
1993年 | 166篇 |
1992年 | 115篇 |
1991年 | 112篇 |
1990年 | 73篇 |
1989年 | 81篇 |
1988年 | 53篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1963年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
A new surface characterization technique: RIMAPS (Rotated Image with Maximum Average Power Spectrum)
This work introduces a new imaging technique, Rotated Image with Maximum Average Power Spectrum (RIMAPS), for use in determining orientation and characteristics of surface topography. It consists of computing the maximum value of the averaged power spectrum, given by one step of the two‐dimensional Fourier transform, for each angle of rotation of a digitized image. The basic measurement science of this technique is described and different cases are studied. The characterization of simple geometrical figures explains the meaning of peaks and their angular positions given by RIMAPS analysis. A known surface pattern made on a sample of pure copper, mechanically ground, is used to study reproducibility, dependence on image quality and topography scale relative to pixel size and magnification. Samples of pure zinc, mechanically ground and chemically etched, were used to show the main features of RIMAPS analysis when characterizing a more complicated pattern on a real surface. All the studies performed under different conditions for observation and acquisition of images give strong evidence of the stability and robustness of RIMAPS as a technique for the characterization of topography. 相似文献
32.
New accurate two-noded shear-flexible curved beam elements 总被引:2,自引:0,他引:2
There are two purposes of this work. One is to present two accurate two-noded finite elements which are derived from the
potential energy principle and the Hellinger–Reissner functional principle respectively. The second is to show the successful
application of the internal displacement parameters in developing a high-order related displacement-rotation interpolation
field. Because the derived interpolation field is capable of accurately modeling deformation modes in extreme thin curved
beams and nearly straight beams, both shear locking and membrane shocking are avoided. Several standard numerical tests display
superior behaviors of the present elements.
Received: 5 February 2002 / Accepted: 16 September 2002 相似文献
33.
邹光远 《水动力学研究与进展(A辑)》1993,8(2):219-226
对于用层平均速度势(或速度)与波高给出的非线性等水深Boussinesq方程,与KdV方程一样,存在两类永形波—孤立波和周期波。不同的是,对于Boussinesq方程,孤立波和周期波一样,是以反函数的积分形式给出的,这在使用上是不方便的。本文对这两类波,分别给出了相应的级数形式的正函数解。对于孤立波,级数的收敛速度是十分快的,且文中还给出了一个具有高精度的十分简单的近似解,对于周期波,只要有关参数选得合适,解的收敛速度也是相当快的。这就有效地克服了反函数形式解在使用上的不方便。 相似文献
34.
The inherently nonlinear phenomenon of fatigue crack propagation is modeled as a linear random process. To a first approximation, simple, nonstationary time series models are introduced and standard techniques for determining the parameters of autoregressive integrated moving-average processes are applied. Multiplicative time series models are next utilised for the representation of a group of crack history curves. Implementation of the models on the Virkler experimental data set yields satisfactory results. Reliable Gaussian approximations to the distribution of the time required by a crack to reach a specified critical length are obtained, and the usefulness of the approach is demonstrated when updating lifetime predictions after periodic inspections. 相似文献
35.
David A. Carlson 《The Journal of supercomputing》1992,6(2):107-116
In this paper a set of techniques for improving the performance of the fast Fourier transform (FFT) algorithm on modern vector-oriented supercomputers is presented. Single-processor FFT implementations based on these techniques are developed for the CRAY-2 and the CRAY Y-MP, and it is shown that they achieve higher performance than previously measured on these machines. The techniques include (1) using gather/scatter operations to maintain optimum length vectors throughout all stages of small-to medium-sized FFTs, (2) using efficient radix-8 and radix-16 inner loops, which allow a large number of vector loads/stores to be overlapped, and (3) prefetching twiddle factors as vectors so that on the CRAY-2 they can later be fetched from local memory in parallel with common memory accesses. Performance results for Fortran implementations using these techniques demonstrate that they are faster than Cray's library FFT routine CFFT2. The actual speedups obtained, which depend on the size of the FFT being computed and the supercomputer being used, range from about 5 to over 300%. 相似文献
36.
A stochastic model is proposed for a basic mechanism in the formation of uncertainties in physical quantity measurements.
__________
Translated from Izmeritel'naya Tekhnika, No. 1, pp. 12–17, January, 2006. 相似文献
37.
基于数字化二次曝光干涉的光学元件波前畸变测量 总被引:1,自引:1,他引:0
将傅立叶变换条纹分析方法与二次曝光全息干涉计量相结合,提出了数字化二次曝光干涉术,用于测量光学元件引入的波前畸变。文中给出了理论分析,模拟与光学实验结果证实提出的方法具有高精度、快速的波前测量特点,可应用于激光系统中光学元件的波前畸变在线检测。 相似文献
38.
This paper derives the admissible decompositions for a time series dynamic linear model, assuming only that the model is observable. The decompositions depend on factorizations of the characteristic polynomial of the state evolution matrix G into relatively prime factors. This generalizes the method of West (1997 ) which considers one decomposition in the particular case where G is diagonalizable. Conditions are derived for a decomposition to be independent. These results show that no autoregressive process of order d has an independent decomposition for any integer d . Two illustrations of this procedure are discussed in detail. 相似文献
39.
准噶尔盆地三台-北三台地区第三系勘探潜力分析 总被引:1,自引:0,他引:1
从沉积及储层组合、油气运移系统等方面全面剖析了准噶尔盆地三台-北三台地区第三系油气成藏条件,建立了成藏模式,对未钻探区勘探潜力进行了预测;通过分析,认为该区第三系储层物性主体差,断裂更多地表现为封闭性,导致沟通深部油气源的运移体系不畅,致使第三系圈闭不能有效捕获和储集油气。圈闭又比较匮乏,主体勘探潜力不大。北25井西背斜紧邻多期活动的甘诃子北断裂,第三系可能发育较好的储层,相对有利,北25井西背斜应是钻探第三系的首选目标。 相似文献
40.
A new efficient numerical method and the dynamic analysis of composite laminates with piezoelectric layers 总被引:1,自引:0,他引:1
Firstly, a numerical method for the inversion of Laplace transform is developed and its accuracy is shown through examples. Then, a state-vector equation for the dynamic problems of piezoelectric plates is deduced directly from a modified mixed variational principle for piezoelectric bodies and its exact solution for the dynamic problems of simply supported rectangle piezoelectric plate is simply given. For multilayered hybrid plates, we derive the solution in terms of the propagator matrices. The techniques accounts for the compatibility of generalized displacements and generalized stresses on the interface both the elastic layers and piezoelectric layers, and the transverse shear deformation and the rotary inertia of laminate are also considered in the global algebraic equation of structure. Meanwhile, there is no restriction on the thickness and the number of layers. As an application of the numerical inversion of Laplace transform presented in this paper, typical numerical examples of the harmonic vibration and transient response are proposed and discussed. Since the highly accurate numerical results, they can serve as benchmarks to test various thick plate theories and various numerical methods, such as the finite and boundary element methods for transient response problems. 相似文献