全文获取类型
收费全文 | 58621篇 |
免费 | 7550篇 |
国内免费 | 5930篇 |
专业分类
电工技术 | 5089篇 |
技术理论 | 9篇 |
综合类 | 6389篇 |
化学工业 | 1370篇 |
金属工艺 | 691篇 |
机械仪表 | 3583篇 |
建筑科学 | 2250篇 |
矿业工程 | 1535篇 |
能源动力 | 777篇 |
轻工业 | 725篇 |
水利工程 | 1363篇 |
石油天然气 | 2899篇 |
武器工业 | 793篇 |
无线电 | 9110篇 |
一般工业技术 | 2847篇 |
冶金工业 | 1081篇 |
原子能技术 | 736篇 |
自动化技术 | 30854篇 |
出版年
2024年 | 316篇 |
2023年 | 851篇 |
2022年 | 1744篇 |
2021年 | 2151篇 |
2020年 | 2295篇 |
2019年 | 1776篇 |
2018年 | 1599篇 |
2017年 | 1981篇 |
2016年 | 2222篇 |
2015年 | 2545篇 |
2014年 | 4037篇 |
2013年 | 3629篇 |
2012年 | 4309篇 |
2011年 | 4636篇 |
2010年 | 3585篇 |
2009年 | 3539篇 |
2008年 | 4009篇 |
2007年 | 4527篇 |
2006年 | 3825篇 |
2005年 | 3449篇 |
2004年 | 2976篇 |
2003年 | 2506篇 |
2002年 | 1922篇 |
2001年 | 1455篇 |
2000年 | 1247篇 |
1999年 | 904篇 |
1998年 | 692篇 |
1997年 | 587篇 |
1996年 | 484篇 |
1995年 | 434篇 |
1994年 | 344篇 |
1993年 | 247篇 |
1992年 | 173篇 |
1991年 | 178篇 |
1990年 | 132篇 |
1989年 | 106篇 |
1988年 | 85篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 71篇 |
1982年 | 60篇 |
1981年 | 37篇 |
1980年 | 20篇 |
1979年 | 34篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1976年 | 13篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Non-redundant data clustering 总被引:6,自引:6,他引:0
Data clustering is a popular approach for automatically finding classes, concepts, or groups of patterns. In practice, this
discovery process should avoid redundancies with existing knowledge about class structures or groupings, and reveal novel,
previously unknown aspects of the data. In order to deal with this problem, we present an extension of the information bottleneck
framework, called coordinated conditional information bottleneck, which takes negative relevance information into account by maximizing a conditional mutual information score subject to
constraints. Algorithmically, one can apply an alternating optimization scheme that can be used in conjunction with different
types of numeric and non-numeric attributes. We discuss extensions of the technique to the tasks of semi-supervised classification
and enumeration of successive non-redundant clusterings. We present experimental results for applications in text mining and
computer vision. 相似文献
102.
金永杰 《核电子学与探测技术》1989,9(1):10-17
本文所提出的投影域重建——再投影迭代算法可以恢复不完整的扇形束投影数据,从而实现从有限的投影数据重建图象。这种算法把滤波——反投影图象重建过程和再投影的过程纳入一个公式,仅在投影域上估算未知的投影数据,因此避免了重建过程和反投影过程中的插值运算,改善了收敛性,提高了计算精度,缩短了运算时间。模拟实验表明:即使有70%的投影数据丢失,经过两次迭代就能以令人满意的精度恢复丢失的投影数据。 相似文献
103.
Experimentally determined p,V,T data are reported for toluene, trichloromethane, dichloromethane, acetonitrile, aniline, and n-dodecane at 278, 288, 298, 313, and 323 K, except for dichloromethane, for which the highest temperature was 298 K. At each temperature, measurements were done at pressures up to about 280 MPa or (for aniline and n-dodecane) at a lower pressure slightly below the freezing pressure at the temperature of measurement. Values of the isobaric expansivity isothermal compressibility and (for toluene, trichloromethane, dichloromethane, and acetonitrile) internal pressure, derived from the p,V,T data, are presented. 相似文献
104.
Transport problems typically involve at least two types of constraints, on income and on time. Therefore, the indirect utility
function depends either on the income available after having subtracted the cost of the discrete alternative and on the free
time left after having worked and travelled by each competing option. In the typical linear-in-the-attributes and in-the-parameters
specification, that represents the first grade approximation of the indirect utility function, the effect of income and time
constraints cancel out and only the cost and time of the alternatives matter in the comparison between them. From a microeconomic
point of view this is equivalent to assume that income and time effects could be disregarded; which is not always the case.
To account for these effects the utility function should include second order attributes; however, in non-linear utility functions
it may not be easy to distinguish among several effects that could be relevant: direct preferences for good and leisure, and
simple interactions between attributes other than income and time effects. This paper analyses these effects from a theoretical
point of view focusing on the possible confounding problem in detecting income and time effects. We use a dataset collected
for a modal choice context and containing both revealed and stated preference data, and estimate several NL models examining
the effect of the different second-order terms on detecting income and time effects. We compared specifications including
square cost and time attributes, interactions between time and cost, cost divided by the income available to be spent on free
time, and time multiplied by free time. Our results confirm the strong effect of direct preferences for goods and leisure
time on choice, and the potential confounding effect between quadratic attributes and other non-linear omitted terms. Finally,
we also found that care should be taken in highlighting income and time effects using mixed data sources, since confounding
effects can occur when non-linearities are accounted for in both data sets. 相似文献
105.
106.
This paper presents Bayes estimators for the reliability measures of the individual components in a multi-component systems in the presence of masked system life test data. The life time distributions of the system components are assumed to be geometric with different parameters. Two-sided Bayesian probability intervals of the parameters are also derived. Numerical simulation study is given in order to: (i) explain how one can apply the theoretical results obtained, (ii) study the influence of the sample size and masking level on the accuracy of point estimates. 相似文献
107.
Excel在大学物理实验中的应用 总被引:1,自引:0,他引:1
利用Excel的强大功能,对实验数据进行处理、分析,对实验过程及实验结果的监控。 相似文献
108.
Interventions for a variety of emotional and behavioral problems are commonly delivered in the context of treatment groups, with many using rolling admission to sustain membership (i.e., admission, dropout, and discharge from group are perpetual and ongoing). The authors present an overview of the analytic challenges inherent in rolling group data and outline commonly used (but flawed) analytic and design approaches to addressing (or sidestepping) these issues. Moreover, the authors propose use of latent class pattern mixture models (LCPMMs) as a statistically and conceptually defensible approach for modeling treatment data from rolling groups. The LCPMM approach is illustrated with rolling group data from a group-based alcoholism pilot treatment trial (N = 128). Different inferences were made with regard to treatment efficacy under LCPMM vs. the commonly used standard group-clustered latent growth model (LGM); coupled with other preliminary findings in this area, inferences from LGMs may be overly liberal when applied to data from rolling groups. Continued work on data analytic difficulties in groups with membership turnover is critical for furthering the ecological validity of research on behavioral treatments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
109.
110.
对自动化在选矿工业中应用的意义进行了论述。结合堆浸选矿的工艺特点,介绍了金矿选厂自动化系统的构成和自动化系统实现的基本功能。 相似文献