全文获取类型
收费全文 | 19404篇 |
免费 | 3003篇 |
国内免费 | 1846篇 |
专业分类
电工技术 | 2268篇 |
综合类 | 2328篇 |
化学工业 | 1094篇 |
金属工艺 | 135篇 |
机械仪表 | 996篇 |
建筑科学 | 539篇 |
矿业工程 | 225篇 |
能源动力 | 360篇 |
轻工业 | 168篇 |
水利工程 | 258篇 |
石油天然气 | 279篇 |
武器工业 | 437篇 |
无线电 | 5379篇 |
一般工业技术 | 1496篇 |
冶金工业 | 213篇 |
原子能技术 | 113篇 |
自动化技术 | 7965篇 |
出版年
2024年 | 124篇 |
2023年 | 324篇 |
2022年 | 505篇 |
2021年 | 600篇 |
2020年 | 670篇 |
2019年 | 651篇 |
2018年 | 596篇 |
2017年 | 847篇 |
2016年 | 877篇 |
2015年 | 926篇 |
2014年 | 1266篇 |
2013年 | 1493篇 |
2012年 | 1380篇 |
2011年 | 1614篇 |
2010年 | 1202篇 |
2009年 | 1216篇 |
2008年 | 1319篇 |
2007年 | 1449篇 |
2006年 | 1085篇 |
2005年 | 987篇 |
2004年 | 749篇 |
2003年 | 669篇 |
2002年 | 554篇 |
2001年 | 452篇 |
2000年 | 356篇 |
1999年 | 344篇 |
1998年 | 273篇 |
1997年 | 273篇 |
1996年 | 209篇 |
1995年 | 213篇 |
1994年 | 176篇 |
1993年 | 122篇 |
1992年 | 135篇 |
1991年 | 94篇 |
1990年 | 88篇 |
1989年 | 58篇 |
1988年 | 44篇 |
1987年 | 35篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 49篇 |
1983年 | 21篇 |
1982年 | 38篇 |
1981年 | 35篇 |
1980年 | 23篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1957年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
Cost estimates to guide pre-selection of processes 总被引:2,自引:0,他引:2
A process is a method of shaping, joining or surface-treating a material. Process selection has three steps. The first is to identify from the ‘menu’ of all available processes, the subset, which can give a chosen material the desired shape with the desired detail, precision and finish. The second is to choose, from among these, the ones that will do so at the lowest cost. The final step is to investigate the most promising processes in depth, exploring considerations such as availability, in-house experience, safety and environmental issues. The first two steps can be thought of as process pre-selection. Components have to be assembled and finished to create products. Here too, the ability to rank by cost, however crudely, helps guide pre-selection. Cost models are reviewed from the perspective of material and process selection. An approximate model is useful provided it has generality—that is, it must allow comparison of very different processes. Many approaches fail in this. One that works, based on resource consumption, is developed here and its use for selection is illustrated. It has been implemented as part of a tool that allows rapid pre-selection from a database of 112 processes. 相似文献
83.
一种空间自适应小波门限去噪算法 总被引:3,自引:0,他引:3
提出了一种空间自适应小波门限去噪算法,该算法在小波域对含噪小波系数做两次自适应去噪,两次自适应门限分别基于最大似然(ML)方差估计和最大后验概率(MAP)方差估计.仿真结果表明,该算法与其它自适应门限去噪算法相比,去噪后的图象具有更高的峰值信噪比(PSNR). 相似文献
84.
基于物质平衡方程、产能方程和递减方程的结合,提出了定容气田开发规划的概算法.该法可用于预测地层压力、井底流动压力、井口流动压力和稳产年限.实际应用表明,本文提供的方法是实用有效的. 相似文献
85.
Compositional data occur as natural realizations of multivariate observations comprising element proportions of some whole
quantity. Such observations predominate in disciplines like geology, biology, ecology, economics and chemistry. Due to unit
sum constraint on compositional data, specialized statistical methods are required for analyzing these data. Dirichlet distributions
were originally used to study compositional data even though this family of distribution is not appropriate (see Aitchison,
1986) because of their extreme independence properties. Aitchison (1982) endeavored to provide a viable alternative to existing
methods by employing Logistic Normal distribution to analyze such constrained data. However this family does not include the
Dirichlet class and is therefore unable to address the issue of extreme independence. In this paper generalized Liouville
family is investigated to model compositional data which includes covariates. This class permits distributions that admit
negative or mixed correlation and also contains non-Dirichlet distributions with non-positive correlation and overcomes deficits
in the Dirichlet class. Semiparametric Bayesian methods are proposed to estimate the probability density. Predictive distributions
are used to assess performance of the model. The methods are illustrated on a real data set. 相似文献
86.
87.
The cross-spectral estimation methods are efficient in estimating the parameters of sinusoidal signals embedded in colored noise. But up to now, only FPT and cross-periodogram methods are used in this field, the modern auto-spectral estimation method is introduced into cross-spectral estimation in this paper, meanwhile the cross-correlation based Yule-Walker equation is proposed theoretically and the moment and singular-value decomposition (SVD)) algorithms for cross-spectral estimation have been developed. Finally, a numerical example is given for comparing the presented methods with the well-known Cadzow's SVD method. 相似文献
88.
Robot Pose Estimation in Unknown Environments by Matching 2D Range Scans 总被引:14,自引:0,他引:14
A mobile robot exploring an unknown environment has no absolute frame of reference for its position, other than features it detects through its sensors. Using distinguishable landmarks is one possible approach, but it requires solving the object recognition problem. In particular, when the robot uses two-dimensional laser range scans for localization, it is difficult to accurately detect and localize landmarks in the environment (such as corners and occlusions) from the range scans.In this paper, we develop two new iterative algorithms to register a range scan to a previous scan so as to compute relative robot positions in an unknown environment, that avoid the above problems. The first algorithm is based on matching data points with tangent directions in two scans and minimizing a distance function in order to solve the displacement between the scans. The second algorithm establishes correspondences between points in the two scans and then solves the point-to-point least-squares problem to compute the relative pose of the two scans. Our methods work in curved environments and can handle partial occlusions by rejecting outliers. 相似文献
89.
José Martínez-Aroza Ramón Román-Roldán 《Multidimensional Systems and Signal Processing》1995,6(1):7-35
A multiresolution analysis of digital gray-level images is presented. A gray-level multi-scale framework is determined from two main assumptions: the gray scale is binary at the finest spatial resolution, and the gray levels of composed regions are obtained additively. In order to interrelate the gray-level histograms of the same image at different resolutions, probabilistic linear models are developed, which are then applied for estimation. Linear-optimization theory is used as a way of constructing such models. A general procedure for image processing is sketched, based on gray-level estimation. A versatile algorithm for nonlinear filtering is derived. Some examples of prospective applications are given.This work was partially supported by grant TIC91-646 from the DGYCIT of the Spanish Government. 相似文献
90.
对应状态原理与基团贡献法结合,提出一个新的蒸气压估算方程(RLYM)。通过对烷烃、烯烃、炔烃、环烷烃、环烯烃、醇、环醇、酮、醚、芳烃、酚、萘在内的174种有机物质蒸气压实验数据的关联,获得了30种基团的贡献参数值。新模型的预测精度优于现有的对应状态法,并且对高碳分子仍有较好的估算精度。总的关联误差小于1.17%。 相似文献