全文获取类型
收费全文 | 207335篇 |
免费 | 20999篇 |
国内免费 | 12379篇 |
专业分类
电工技术 | 16551篇 |
技术理论 | 7篇 |
综合类 | 16800篇 |
化学工业 | 29672篇 |
金属工艺 | 12459篇 |
机械仪表 | 13779篇 |
建筑科学 | 17107篇 |
矿业工程 | 6745篇 |
能源动力 | 6149篇 |
轻工业 | 15426篇 |
水利工程 | 4978篇 |
石油天然气 | 10699篇 |
武器工业 | 2380篇 |
无线电 | 25136篇 |
一般工业技术 | 21324篇 |
冶金工业 | 8442篇 |
原子能技术 | 2308篇 |
自动化技术 | 30751篇 |
出版年
2024年 | 1071篇 |
2023年 | 3521篇 |
2022年 | 6969篇 |
2021年 | 9538篇 |
2020年 | 7141篇 |
2019年 | 5493篇 |
2018年 | 6187篇 |
2017年 | 7208篇 |
2016年 | 6173篇 |
2015年 | 9169篇 |
2014年 | 11620篇 |
2013年 | 13617篇 |
2012年 | 15817篇 |
2011年 | 16580篇 |
2010年 | 15280篇 |
2009年 | 14101篇 |
2008年 | 14081篇 |
2007年 | 13211篇 |
2006年 | 12082篇 |
2005年 | 9611篇 |
2004年 | 6641篇 |
2003年 | 5618篇 |
2002年 | 5393篇 |
2001年 | 4751篇 |
2000年 | 3938篇 |
1999年 | 3456篇 |
1998年 | 2334篇 |
1997年 | 1883篇 |
1996年 | 1768篇 |
1995年 | 1495篇 |
1994年 | 1227篇 |
1993年 | 781篇 |
1992年 | 656篇 |
1991年 | 480篇 |
1990年 | 373篇 |
1989年 | 309篇 |
1988年 | 228篇 |
1987年 | 150篇 |
1986年 | 134篇 |
1985年 | 76篇 |
1984年 | 68篇 |
1983年 | 52篇 |
1982年 | 54篇 |
1981年 | 63篇 |
1980年 | 63篇 |
1979年 | 37篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Fan Zhang To-yat Cheung 《IEEE transactions on pattern analysis and machine intelligence》2003,29(1):1-14
The fault-state detection approach for blackbox testing consists of two phases. The first is to bring the system under test (SUT) from its initial state to a targeted state t and the second is to check various specified properties of the SUT at t. This paper investigates the first phase for testing systems specified as observable nondeterministic finite-state machines with probabilistic and weighted transitions. This phase involves two steps. The first step transfers the SUT to some state t' and the second step identifies whether t' is indeed the targeted state t or not. State transfer is achieved by moving the SUT along one of the paths of a transfer tree (TT) and state identification is realized by using diagnosis trees (DT). A theoretical foundation for the existence and characterization of TT and DT with minimum weighted height or minimum average weight is presented. Algorithms for their computation are proposed. 相似文献
33.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
34.
LaNiO3 was synthesized by sol-gel method in which lanthanum nitrate and nickel nitrate were used as start materials and citric acid was used as complex for gel formation.The precursor was dried and subsequently heated at elevated temperature to form the desired product.XRD analysis shows that pure LaNiO3 was synthesized.Electrical conductivity and electrochemical performance of the material were tested.The electrical conductivity decreases from 34.5that there are current peaks in the curve, which is the evidence of the electrochemical activity of LaNiO3. 相似文献
35.
Kubat M. Hafez A. Raghavan V.V. Lekkala J.R. Wei Kian Chen 《Knowledge and Data Engineering, IEEE Transactions on》2003,15(6):1522-1534
Association mining techniques search for groups of frequently co-occurring items in a market-basket type of data and turn these groups into business-oriented rules. Previous research has focused predominantly on how to obtain exhaustive lists of such associations. However, users often prefer a quick response to targeted queries. For instance, they may want to learn about the buying habits of customers that frequently purchase cereals and fruits. To expedite the processing of such queries, we propose an approach that converts the market-basket database into an itemset tree. Experiments indicate that the targeted queries are answered in a time that is roughly linear in the number of market baskets, N. Also, the construction of the itemset tree has O(N) space and time requirements. Some useful theoretical properties are proven. 相似文献
36.
37.
Yi‐Hung Chen Ching‐Yuan Chang Wei‐Ling Su Chun‐Yu Chiu Yue‐Hwa Yu Pen‐Chi Chiang Chiung‐Fen Chang Je‐Lueng Shie Chyow‐San Chiou Sally IM Chiang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(1):68-75
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry 相似文献
38.
用宏观断口分析、化学检验、力学性能测定、低倍检查、金相组织及夹杂物评定鉴别、受力分析及强度寿命定量估算的方法,对人字轮被动齿轴端断裂失效原因进行分析,并提出改进措施。 相似文献
39.
Huai Wen-xin Wuhan University of Hydraulic & Electric Engineering Wuhan Hubei P.R.China Prof.Li Wei 《水动力学研究与进展(B辑)》1993,(3)
Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu-lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.Thevertical turbulent jets,plumes and buoyant jets discharging into static environment is one of themost important and basic flow patterns related with the environment pollution.These flows havenumerous important applications,for example,thrust augmentors,waste disposal plumes fromstacks and combustion systems,and significant problems of turbulent diffusion. 相似文献
40.