全文获取类型
收费全文 | 2296篇 |
免费 | 393篇 |
国内免费 | 273篇 |
专业分类
电工技术 | 121篇 |
综合类 | 342篇 |
化学工业 | 131篇 |
金属工艺 | 38篇 |
机械仪表 | 103篇 |
建筑科学 | 48篇 |
矿业工程 | 6篇 |
能源动力 | 21篇 |
轻工业 | 18篇 |
水利工程 | 20篇 |
石油天然气 | 3篇 |
武器工业 | 25篇 |
无线电 | 490篇 |
一般工业技术 | 261篇 |
冶金工业 | 37篇 |
原子能技术 | 13篇 |
自动化技术 | 1285篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 26篇 |
2021年 | 30篇 |
2020年 | 58篇 |
2019年 | 56篇 |
2018年 | 50篇 |
2017年 | 79篇 |
2016年 | 103篇 |
2015年 | 91篇 |
2014年 | 138篇 |
2013年 | 209篇 |
2012年 | 187篇 |
2011年 | 222篇 |
2010年 | 176篇 |
2009年 | 198篇 |
2008年 | 193篇 |
2007年 | 189篇 |
2006年 | 139篇 |
2005年 | 130篇 |
2004年 | 109篇 |
2003年 | 80篇 |
2002年 | 61篇 |
2001年 | 66篇 |
2000年 | 54篇 |
1999年 | 32篇 |
1998年 | 33篇 |
1997年 | 30篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 22篇 |
1993年 | 22篇 |
1992年 | 12篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2962条查询结果,搜索用时 15 毫秒
1.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
2.
3.
Participants' usage of informational variables in learning visual relative-mass discrimination in collisions was tracked by means of PROBIT correlations. Four groups received feedback that was true or accorded with either of three nonspecificational cue variables. A majority in each group adopted the feedback, but several participants defied the false feedback. Unlike in previous research, the fit to data of the relative-mass invariant could not be bettered by post hoc linear combinations of the cues. Discriminability was lower in the use of the invariant. Analytic complexity was rejected as an explanation for discriminability differences. A "smart mechanism" for pickup of the relative-mass invariant was developed as an extension of G. Johansson's (1950/1994) vector model. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
基于DFT插值的宽带波束形成器设计 总被引:6,自引:0,他引:6
本文提出一种基于DFT插值的宽带波束形成器设计方法。首先推导了具有频率不变波束图的连续线阵的灵敏度函数与离散线列阵加权系数之间的关系;接着给出了基于DFT插值的宽带波束形成器设计的两个步骤:(1)使用窄带波束形成器的设计方法计算在参考频率下基阵的加权系数;(2)根据参考频率下基阵的权系数与其它子带权系数之间的关系,利用DFT插值的方法求出其它子带的加权系数。最后,给出了一个设计实例说明本文方法的有效性。 相似文献
5.
Abstract. A pth‐order random coefficient integer‐valued autoregressive [RCINAR(p)] model is proposed for count data. Stationarity and ergodicity properties are established. Maximum likelihood, conditional least squares, modified quasi‐likelihood and generalized method of moments are used to estimate the model parameters. Asymptotic properties of the estimators are derived. Simulation results on the comparison of the estimators are reported. The models are applied to two real data sets. 相似文献
6.
Legendre orthogonal moments have been widely used in the field of image analysis. Because their computation by a direct method is very time expensive, recent efforts have been devoted to the reduction of computational complexity. Nevertheless, the existing algorithms are mainly focused on binary images. We propose here a new fast method for computing the Legendre moments, which is not only suitable for binary images but also for grey level images. We first establish a recurrence formula of one-dimensional (1D) Legendre moments by using the recursive property of Legendre polynomials. As a result, the 1D Legendre moments of order p, Lp=Lp(0), can be expressed as a linear combination of Lp-1(1) and Lp-2(0). Based on this relationship, the 1D Legendre moments Lp(0) can thus be obtained from the arrays of L1(a) and L0(a), where a is an integer number less than p. To further decrease the computation complexity, an algorithm, in which no multiplication is required, is used to compute these quantities. The method is then extended to the calculation of the two-dimensional Legendre moments Lpq. We show that the proposed method is more efficient than the direct method. 相似文献
7.
8.
R. C. Ecob 《Journal of microscopy》1985,137(3):313-337
Whereas models of the structure and periodicity of CSL or near CSL high angle grain boundaries are relatively well developed and have been to some extent verified by experiment, the nature of more general (e.g. fcc/bcc) interfaces is very imperfectly understood. One of the major differences between homo- and heterophase boundaries is the occurrence, in the latter case, of reproducible orientation relationships due to the crystallographic requirements of phase transformation (e.g. a glissile interface for martensitic growth, low energy interfaces for classical nucleation). A review is given of the relationships commonly observed to obtain between fcc and bcc crystals (as well as ordered phases based upon these structures). Within a given relationship, it is possible to use models of the available interfaces to predict their dislocation content; the success of the various approaches is considered. It is shown that the dislocation arrays identified on fcc/bcc boundaries are consistent with the occurrence of a primary structural relaxation, but that the latter does not appear to be complete. Possible reasons for this are discussed, together with the extent to which secondary structural models may be applicable. Attempts to rationalize the observed orientation relationships and morphologies are discussed, and it is pointed out that these all rely on searches for situations of minimum primary misfit, but that the way in which the latter is quantified determines the results of the analyses. Nevertheless, the implication is that the primary misfit does appear to determine the actual behaviour, though no structural or mechanistic conclusions can safely be drawn from this observation. 相似文献
9.
10.
Alvaro Realpe 《Powder Technology》2006,169(2):108-113
A large part of pharmaceutical manufacturing involves the use of particulate materials. It is well known that both particle size and shape affect the physical characteristics of tablets. An image processing and analysis algorithm based on the invariant image moment technique was developed in this work to determine the particle shape by comparing features (moments) extracted from templates to those extracted from each of the objects in the image. First it determines the particle shape (rectangle, circle, etc.) and then calculates its specific dimensions (diameter, aspect ratio).The statistical validation of the vision system obtained a repeatability of 0.0012 in and 0.5% relative standard deviation and accuracy within 0.1 to 0.9% of the average value considered as true value. Also the pattern recognition technique indicated high precision and accuracy for images containing particles with some level of contact between them. The shape recognition of microcrystalline cellulose (MCC) indicated that particles of equant and acicular shape as defined by USP are predominant. The results suggest that image processing and analysis would be a suitable tool for pharmaceutical process analytical technologies (PAT) and process optimization. 相似文献