全文获取类型
收费全文 | 38792篇 |
免费 | 5058篇 |
国内免费 | 3075篇 |
专业分类
电工技术 | 4093篇 |
综合类 | 4170篇 |
化学工业 | 3776篇 |
金属工艺 | 1036篇 |
机械仪表 | 2038篇 |
建筑科学 | 2513篇 |
矿业工程 | 910篇 |
能源动力 | 1086篇 |
轻工业 | 2003篇 |
水利工程 | 842篇 |
石油天然气 | 1619篇 |
武器工业 | 629篇 |
无线电 | 5327篇 |
一般工业技术 | 3713篇 |
冶金工业 | 1560篇 |
原子能技术 | 576篇 |
自动化技术 | 11034篇 |
出版年
2024年 | 189篇 |
2023年 | 512篇 |
2022年 | 979篇 |
2021年 | 1117篇 |
2020年 | 1422篇 |
2019年 | 1347篇 |
2018年 | 1176篇 |
2017年 | 1547篇 |
2016年 | 1709篇 |
2015年 | 1797篇 |
2014年 | 2411篇 |
2013年 | 2795篇 |
2012年 | 2758篇 |
2011年 | 2884篇 |
2010年 | 2133篇 |
2009年 | 2278篇 |
2008年 | 2183篇 |
2007年 | 2570篇 |
2006年 | 2409篇 |
2005年 | 1978篇 |
2004年 | 1627篇 |
2003年 | 1527篇 |
2002年 | 1330篇 |
2001年 | 1151篇 |
2000年 | 985篇 |
1999年 | 735篇 |
1998年 | 589篇 |
1997年 | 522篇 |
1996年 | 392篇 |
1995年 | 327篇 |
1994年 | 271篇 |
1993年 | 225篇 |
1992年 | 156篇 |
1991年 | 151篇 |
1990年 | 107篇 |
1989年 | 90篇 |
1988年 | 65篇 |
1987年 | 67篇 |
1986年 | 47篇 |
1985年 | 54篇 |
1984年 | 40篇 |
1983年 | 29篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1964年 | 12篇 |
1956年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This paper derives the admissible decompositions for a time series dynamic linear model, assuming only that the model is observable. The decompositions depend on factorizations of the characteristic polynomial of the state evolution matrix G into relatively prime factors. This generalizes the method of West (1997 ) which considers one decomposition in the particular case where G is diagonalizable. Conditions are derived for a decomposition to be independent. These results show that no autoregressive process of order d has an independent decomposition for any integer d . Two illustrations of this procedure are discussed in detail. 相似文献
102.
Sarrazin Jean-Christophe; Giraudo Marie-Dominique; Pailhous Jean; Bootsma Reinoud J. 《Canadian Metallurgical Quarterly》2004,30(3):411
In 3 experiments, the authors studied the organization of spatiotemporal information in memory. Stimuli consisted of configurations of dots, presented sequentially. The stimuli were either proportional, with interdot distances corresponding to interdot durations, or not proportional, with interdol distances not corresponding to interdot durations. After a learning phase, participants reproduced the spatial (Experiment 1), temporal (Experiment 2), or spatial and temporal (Experiment 3) characteristics of the target 60 times in succession. In the nonproportional conditions, effects of variable interdot durations or distances on the reproduction of, respectively, constant distances (tau effect) or durations (kappa effect) were observed, whereas no such effects were observed when variable distances or durations were to be produced. Tau and kappa effects influenced the accuracy but not the variability of responses. The results are discussed in light of the distinction between properties of the stabilized mental image and the process of stabilization. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Verhaeghen Paul; Cerella John; Basak Chandramallika 《Canadian Metallurgical Quarterly》2004,30(6):1322
Five individuals participated in an extensive practice study (10 1-hr sessions, 11,000 trials total) on a self-paced identity-judgment n-back task (n ranging from 1 to 5). Within Session 1, response time increased abruptly by about 300 ms in passing from n = 1 to n > 1, suggesting that the focus of attention can accommodate only a single item (H. Caravan, 1998; B. McElree, 2001). Within Session 10, response time was dramatically reduced and increased linearly with n for n ≤ 4, with a slope of about 30 ms. The data suggest that working memory consists of a focus of attention governed by a limited-capacity search, expandable through practice, and a content-addressable region outside the focus of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
105.
中国海上时移地震技术应用的可行性研究 总被引:8,自引:0,他引:8
赵伟 《勘探地球物理进展》2003,26(1):30-34
针对中国海上油田的具体情况,参照国外风险评估方法,进行了一些初步的时移地震可行性研究。总的来说,在中国海上开展时移地震是基本可行的,是必然的发展趋势,但中国海上油田的储层结构和成分比较复杂,因此必须针对不同油田的具体问题,做好各种风险性研究及相应的技术和策略,才能最大限度地降低风险,发挥时移地震技术的效益。 相似文献
106.
阐述了一个全新的聚丙烯腈高聚物溶解理论,取代了以往人们思维中的高聚物大分子必须经过先溶胀再溶解的漫长的静态溶解过程。对于年产50kt/a腈纶装置可减少一次性投资约1500万元,减少运转费用360万元/a,在现有腈纶大装置上实施,经济效益十分可观。 相似文献
107.
塔巴庙区块气藏属于低压、低渗气藏,储集层物性差异大、含气级别高,但含气非均质性强,录井解释评价困难。针对这一问题,开展了综合判断储集层物性和含气性方面的研究,分别探讨了钻时与全烃、钻井液性能与全烃、钻井液粘度与全烃、气测显示与测井参数和烃组分与气显示之间的关系,分析了其相关性及其在塔巴庙区块气层解释评价中的意义及作用。通过相关性研究,不但摸索出定性解释评价气层的方法,同时为今后深入研究录井相关参数关系,探索其内在规律,为实现准确解释评价储集层奠定了基础。 相似文献
108.
We propose a simulation-based algorithm for inference in stochastic volatility models with possible regime switching in which the regime state is governed by a first-order Markov process. Using auxiliary particle filters we developed a strategy to sequentially learn about states and parameters of the model. The methodology is tested against a synthetic time series and validated with a real financial time series: the IBOVESPA stock index (São Paulo Stock Exchange). 相似文献
109.
Review of book: Stephen Mitchell. Can Love Last? The Fate of Romance Over Time. New York: Norton, 2002, 223 pp. Reviewed by Timothy J. Zeddies. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
110.
Yu. F. Smirnov 《Measurement Techniques》2007,50(3):293-297
Metrological characteristics of active hydrogen frequency standards are investigated on the basis of internal and external
comparisons. The stability of random changes and drift of hydrogen frequency standards and also the potential capabilities
of time scale preservation with effective consideration of systematic changes in their frequency are demonstrated.
__________
Translated from Izmeritel’naya Tekhnika, No. 3. pp. 42–45, March, 2007. 相似文献