全文获取类型
收费全文 | 105685篇 |
免费 | 15513篇 |
国内免费 | 10847篇 |
专业分类
电工技术 | 9578篇 |
技术理论 | 11篇 |
综合类 | 10496篇 |
化学工业 | 3111篇 |
金属工艺 | 1653篇 |
机械仪表 | 7007篇 |
建筑科学 | 4106篇 |
矿业工程 | 2460篇 |
能源动力 | 1147篇 |
轻工业 | 5056篇 |
水利工程 | 1771篇 |
石油天然气 | 3866篇 |
武器工业 | 1546篇 |
无线电 | 19878篇 |
一般工业技术 | 5971篇 |
冶金工业 | 1787篇 |
原子能技术 | 1200篇 |
自动化技术 | 51401篇 |
出版年
2024年 | 838篇 |
2023年 | 2277篇 |
2022年 | 4050篇 |
2021年 | 4633篇 |
2020年 | 4695篇 |
2019年 | 3665篇 |
2018年 | 3206篇 |
2017年 | 4048篇 |
2016年 | 4399篇 |
2015年 | 5029篇 |
2014年 | 7859篇 |
2013年 | 6878篇 |
2012年 | 8308篇 |
2011年 | 8845篇 |
2010年 | 6735篇 |
2009年 | 6596篇 |
2008年 | 7112篇 |
2007年 | 7906篇 |
2006年 | 6501篇 |
2005年 | 5697篇 |
2004年 | 4643篇 |
2003年 | 3875篇 |
2002年 | 2926篇 |
2001年 | 2164篇 |
2000年 | 1825篇 |
1999年 | 1347篇 |
1998年 | 1070篇 |
1997年 | 858篇 |
1996年 | 747篇 |
1995年 | 619篇 |
1994年 | 471篇 |
1993年 | 363篇 |
1992年 | 281篇 |
1991年 | 274篇 |
1990年 | 207篇 |
1989年 | 144篇 |
1988年 | 130篇 |
1987年 | 92篇 |
1986年 | 87篇 |
1985年 | 110篇 |
1984年 | 82篇 |
1983年 | 93篇 |
1982年 | 77篇 |
1981年 | 56篇 |
1980年 | 37篇 |
1979年 | 40篇 |
1978年 | 18篇 |
1977年 | 23篇 |
1976年 | 17篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
J. Balakrishnan W. A. Sethares C. R. Johnson 《International Journal of Adaptive Control and Signal Processing》2002,16(4):309-323
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
82.
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
83.
The mirror effect for word frequency refers to the finding that low-frequency words have higher hit rates and lower false alarm rates than high-frequency words. This result is typically interpreted in terms of conventional signal detection theory (SDT), in which case it indicates that the order of the underlying old item distributions mirrors the order of the new item distributions. However, when viewed in terms of a mixture version of SDT, the order of hits and false alarms does not necessarily imply the same order in the underlying distributions because of possible effects of mixing. A reversal in underlying distributions did not appear for fits of mixture SDT models to data from 4 experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
Identification of gaps in mangrove forests with airborne LIDAR 总被引:2,自引:0,他引:2
Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for investigating this issue. Airborne light detection and ranging (LIDAR) technology provides an effective way for identifying gaps by remotely obtaining direct measurements of ground and canopy elevations. A method based on an alternative sequential filter and black top-hat mathematical morphological transformation was developed to extract gap features. Comparison of identified gap polygons with raw LIDAR measurements and field surveys shows that the proposed method successfully extracted gap features in mangrove forests in Everglades National Park. There are 400–500 lightning gaps per square kilometer in mangrove forests at the study sites. The distribution of gap sizes follows an exponential form and the area of gaps with sizes larger than 100 m2 account for 55–61% of the total area of gaps. The area of gaps in the mangrove forest in Everglades National Park is about 4–5% of the total forest area and the average gap formation rate is about 0.3% of the total forest area per year, indicating that lightning gaps play an important role in mangrove forest dynamics. 相似文献
85.
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
86.
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
87.
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
88.
89.
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
90.
针对回转窑在运行过程中窑体变形的情况开发了一种监测与报警系统。完成了系统的前向通道设计、单片机与PC机的串行通讯设计和报警显示。 相似文献