全文获取类型
收费全文 | 20330篇 |
免费 | 3062篇 |
国内免费 | 1926篇 |
专业分类
电工技术 | 2285篇 |
综合类 | 2409篇 |
化学工业 | 1106篇 |
金属工艺 | 137篇 |
机械仪表 | 1004篇 |
建筑科学 | 543篇 |
矿业工程 | 228篇 |
能源动力 | 361篇 |
轻工业 | 171篇 |
水利工程 | 259篇 |
石油天然气 | 286篇 |
武器工业 | 460篇 |
无线电 | 6034篇 |
一般工业技术 | 1534篇 |
冶金工业 | 236篇 |
原子能技术 | 113篇 |
自动化技术 | 8152篇 |
出版年
2024年 | 159篇 |
2023年 | 372篇 |
2022年 | 554篇 |
2021年 | 645篇 |
2020年 | 708篇 |
2019年 | 707篇 |
2018年 | 653篇 |
2017年 | 904篇 |
2016年 | 939篇 |
2015年 | 963篇 |
2014年 | 1330篇 |
2013年 | 1542篇 |
2012年 | 1421篇 |
2011年 | 1656篇 |
2010年 | 1246篇 |
2009年 | 1260篇 |
2008年 | 1367篇 |
2007年 | 1497篇 |
2006年 | 1125篇 |
2005年 | 1016篇 |
2004年 | 779篇 |
2003年 | 692篇 |
2002年 | 568篇 |
2001年 | 469篇 |
2000年 | 363篇 |
1999年 | 353篇 |
1998年 | 287篇 |
1997年 | 279篇 |
1996年 | 214篇 |
1995年 | 215篇 |
1994年 | 178篇 |
1993年 | 122篇 |
1992年 | 135篇 |
1991年 | 94篇 |
1990年 | 89篇 |
1989年 | 60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 15 毫秒
101.
Banaji and Crowder (see record 1990-00387-001) contend "that the movement to develop an ecologically valid psychology of memory has proven itself largely bankrupt" (p. 1185). The authors have two primary concerns. First, they believe that it is rare for studies of real-world cognition to support conclusions that generalize broadly. Second, they are concerned that such studies may be inherently incapable of making significant theoretical or methodological contributions. The research program outlined here can be viewed as a response (in the form of a case study) to the Banaji and Crowder position. Specifically, this project has adopted both theoretical and methodology perspectives from the study of real-world memory to address a long-standing issue in the mainstream memory literature. The project itself was designed to characterize the strategies used to estimate event frequency and the conditions that foster the use of these strategies. A valid model of the estimation process is necessary in order to understand the encoding and representation of event frequency. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
车号定位识别与可信度估计 总被引:2,自引:0,他引:2
以车号的定位与识别为例,应用行投影法对车号图片进行倾斜行定位,证明了模拟与场景的二维互相关系数近拟等于一维投影互相关系数,在此基础上提列投影法快速行扫描识别算法及相应的可信度估计方法,这种方法对于室外拍摄的有复杂背景,光照变化,字体微倾,字符排列疏密不均及噪声干扰的车牌图像具有很好的识别效果。 相似文献
103.
104.
105.
Previous work on transmitter antenna diversity has shown that the use of multiple transmitter antennas at the base station results in improved performance due to increase of diversity (path diversity). This happens with no bandwidth cost, even when the signal quality along several paths is poor, but the receiver estimates the channel with accuracy. This paper evaluates the effects of channel estimation errors in the performance of the schemes designated as Space-Time Transmitter Diversity (STTD) and Selective Transmitter Diversity (STD). We consider low to medium signal to noise ratios characteristic of Wideband Code Division Multiple Access (WCDMA) networks. Different fading channel models are considered for comparison between the two schemes. The improvement due to convolutional coding associated with these techniques is also evaluated. 相似文献
106.
数字混沌扩频序列的盲估计 总被引:1,自引:0,他引:1
混沌序列具有非线性、宽带类噪声、大的码族、任意长的周期且容易产生的特性,因此在扩频通信系统中很有实用价值。本文将文献[1]中对伪随机扩频序列盲估计的方法推广应用到混沌扩频通信中,并对其不足提出了改进方法。在只知道扩频码周期而无其它任何先验知识的条件下,利用特征值分析的方法可以对数字混沌直扩序列进行盲估计,仿真实验证明了该方法的有效性。 相似文献
107.
Christine Di Massimo Paul A. Lant Aidan Saunders Gary A. Montague Ming T. Tham A. Julian Morris 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,53(3):265-277
The last decade has seen the development of a number of approaches for estimating those variables which are difficult to measure on-line in industrial process situations. Whilst a range of techniques is available, a common element is the use of process knowledge in the form of a system model. In the case of bioprocess systems, although a large range of models has been presented in the literature, their use in estimation schemes on an industrial scale has been limited. A number of reasons can be identified for their low level of utilisation. Of particular significance is the uncertainty which exists in quantifying system performance and the process-model mismatch which inevitably results. The level of ‘pre-defined model’ uncertainty, together with the knowledge gained during the course of the fermentation, serves to dictate estimator structure. The paper considers a range of estimation strategies and contrasts, through industrial applications, their performance characteristics and utility. 相似文献
108.
European intercomparison on electron spin resonance identification of irradiated foodstuffs 总被引:1,自引:0,他引:1
J. RAFFI † M. H. STEVENSON M. KENT J. M. THIERY J.-J. BELLIARDO 《International Journal of Food Science & Technology》1992,27(2):111-124
The results of a co-trial organized by the Community Bureau of Reference on the use of Electron Spin Resonance spectroscopy for the identification of irradiated food in 21 laboratories are presented. The trial was qualitative on beef and trout bones, sardine scales, pistachio nut shells, dried grapes, and papaya, and quantitative on poultry bones. There was no difficulty in identifying irradiated meat bones, dried grapes, and papaya. In the case of fish bones there is a need for further kinetic study on different species. Identification of irradiation in pistachio nuts is more complicated and additional research is needed before further trials. All laboratories were able to distinguish between chicken bones irradiated at 1 to 3 kGy or 7 to 10 kGy although there was a partial overlap between the results. 相似文献
109.
Two elements enter the choice between 2 and 3SLS for full-system estimation: statistical efficiency and computational cost. 2SLS always has the computational edge, but 3SLS can be more efficient, a relative advantage that increases with the strength of the interrelations among the error terms. A measure of these interrelations is thus helpful in making the choice, and, when there are only two equations, this has suggested using a high pairwise error correlation as an indicator of when to use 3SLS. In larger systems of equations, however, these pairwise correlations can remain small even though more general interrelations give 3SLS the relative advantage. More general indicators are therefore needed, and this paper suggests three such and demonstrates their efficacy.Professor of Economics, Boston College, and Principal Research Associate, Center for Computational Research in Economics and Management Science, MIT. All computation was done on the TROLL system at MIT. My thanks go to Josh Charap for his able research assistance. This research was sponsored in part by the National Science Foundation under grant #IST-8420614. 相似文献
110.
Improved Estimates for the Accuracy of Small Disjuncts 总被引:2,自引:0,他引:2
Learning systems often describe a target class as a disjunction of conjunctions of conditions. Recent work has noted that small disjuncts, i.e., those supported by few training examples, typically have poor predictive accuracy. One model of this accuracy is provided by the Bayes-Laplace formula based on the number of training examples covered by the disjunct and the number of them belonging to the target class. However, experiments show that small disjuncts associated with target classes of different relative frequencies tend to have different error rates. This note defines the context of a disjunct as the set of training examples that fail to satisfy at most one of its conditions. An empirical adaptation of the Bayes-Laplace formula is presented that also makes use of the relative frequency of the target class in this context. Trials are reported comparing the performance of the original formula and the adaptation in six learning tasks. 相似文献