全文获取类型
收费全文 | 92606篇 |
免费 | 1335篇 |
国内免费 | 423篇 |
专业分类
电工技术 | 869篇 |
综合类 | 2325篇 |
化学工业 | 13406篇 |
金属工艺 | 4994篇 |
机械仪表 | 3194篇 |
建筑科学 | 2496篇 |
矿业工程 | 589篇 |
能源动力 | 1310篇 |
轻工业 | 4381篇 |
水利工程 | 1375篇 |
石油天然气 | 379篇 |
武器工业 | 2篇 |
无线电 | 9867篇 |
一般工业技术 | 17951篇 |
冶金工业 | 4598篇 |
原子能技术 | 334篇 |
自动化技术 | 26294篇 |
出版年
2022年 | 89篇 |
2021年 | 186篇 |
2020年 | 148篇 |
2019年 | 140篇 |
2018年 | 14592篇 |
2017年 | 13509篇 |
2016年 | 10119篇 |
2015年 | 734篇 |
2014年 | 452篇 |
2013年 | 689篇 |
2012年 | 3523篇 |
2011年 | 9868篇 |
2010年 | 8577篇 |
2009年 | 5879篇 |
2008年 | 7163篇 |
2007年 | 8164篇 |
2006年 | 461篇 |
2005年 | 1515篇 |
2004年 | 1402篇 |
2003年 | 1417篇 |
2002年 | 798篇 |
2001年 | 216篇 |
2000年 | 304篇 |
1999年 | 191篇 |
1998年 | 239篇 |
1997年 | 184篇 |
1996年 | 211篇 |
1995年 | 157篇 |
1994年 | 157篇 |
1993年 | 167篇 |
1992年 | 130篇 |
1991年 | 129篇 |
1990年 | 135篇 |
1989年 | 106篇 |
1988年 | 95篇 |
1987年 | 129篇 |
1986年 | 98篇 |
1985年 | 133篇 |
1984年 | 129篇 |
1983年 | 134篇 |
1982年 | 104篇 |
1981年 | 93篇 |
1980年 | 79篇 |
1979年 | 77篇 |
1978年 | 96篇 |
1976年 | 76篇 |
1975年 | 79篇 |
1974年 | 83篇 |
1955年 | 97篇 |
1954年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
51.
52.
Cynicism and Social Trust in the New Media Environment 总被引:1,自引:0,他引:1
Joseph N. Cappella 《The Journal of communication》2002,52(1):229-241
This article, with minor modifications, was the author's presidential speech to the International Communication Association conference, May 2001. It summarizes trends in social trust, trust in government, media, and other social institutions and evaluates the news and entertainment media's roles in these trends. Alternatives to causal accounts are proposed, including variations on genetic or "memetic" forms of explanation for media influences on macrosocial trends. 相似文献
53.
George Ter-Stepanian 《Bulletin of Engineering Geology and the Environment》2002,61(3):197-205
The paper discusses the postulated suspension force, by which it is possible to explain some enigmatic phenomena observed
in different types of mass movements. This force is generated in thick suspensions as a result of friction between sinking
solid particles and static water. The suspension force is related to the seepage force but they have opposite directions.
Both forces form flow networks. Having explained the suspension force, the paper describes how this influences the movement
of material, particularly in debris flows. Enigmatic features and the mechanism of debris flows and lahars are explained by
virtue of the suspension force.
Electronic Publication 相似文献
54.
We consider the problem of rescheduling trains in the case where one track of a railway section consisting of two tracks
in opposing directions is closed due to construction activities. After presenting an appropriate model for this situation
we derive a polynomial algorithm for the subproblem of finding an optimal schedule with minimal latenesss if the subsequences
of trains for both directions outside the construction site are fixed. Based on this algorithm we propose a local search procedure
for the general problem of finding good schedules and report test results for some real world instances.
Received: December 8, 1999 / Accepted: May 2, 2001 相似文献
55.
Three interesterified vegetable oils (IVOs) prepared from palm, cottonseed, and olive oil, respectively, have been studied for application to Frankfurters. Beef fat (10%) was replaced by one of the IVOs at 20, 60 or 100%. Fatty acid composition of the lipid fraction in the Frankfurters and saturated/unsaturated ratios were established for all batches. We found that total or partial replacement of beef fat by IVOs did not lead to significant changes in appearance, colour, texture, flavour or sensory score. We conclude that IVOs may be successfully applied as beef fat substitutes in Frankfurters. 相似文献
56.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
57.
58.
Joseph A Wehrmeyer Zhongxian ChengDavid M Mosbacher Robert W PitzRobin Osborne 《Combustion and Flame》2002,128(3):232-241
Several opposed jet flames, produced by a lean H2-air jet opposing a rich or lean C3H8-air jet, are investigated. Spontaneous Raman spectroscopy is used for major species concentration and temperature measurements along the opposed jet centerline. The hot products of the H2-air flame simulate the burnt gases of strong-burning near-stoichiometric reactants as they impinge upon a weak-burning lean or rich hydrocarbon-fueled reactant mix, a situation encountered in stratified charge operation of direct injection spark ignition engines. In addition the H2-air flame hot products facilitate experimental data interpretation through the absence of carbon-bearing species. Good agreement between numerical and experimental data are obtained for a rich (equivalence ratio, φ = 1.25) C3H8-air jet versus a lean (φ = 0.4) H2-air jet. Two lean C3H8-air jets (φ = 0.64 or 0.60), versus the φ = 0.4 H2-air jet, are also investigated. For both of these flames, the amount of CO2 production strongly depends upon φ, with the φ = 0.64 flame having a peak CO2 mole fraction an order of magnitude higher than for the φ = 0.60 flame, and the C3H8 flames burning either as a normal flame (high CO2) or as a “negative flame speed” flame producing little CO2 and then only through diffusion of C3H8 into the hot products jet. The numerically predicted and experimental CO2 profiles agree well for the positive flame speed flame, but the large discrepancy between predicted and measured peak CO2 in the negative flame speed flame suggests modeling improvements are needed for this type of flame. 相似文献
59.
Less may not be more,but it still counts: The state of social capital in Yeoville,Johannesburg 总被引:2,自引:2,他引:0
Kirsten Harrison 《Urban Forum》2002,13(1):67-84
60.
Yanqiu Shao Jiqing Han Ting Liu Yongzhen Zhao 《International Journal of Speech Technology》2007,10(1):45-55
In real speech, not like lexical words (LWs), prosodic words (PWs) are basic rhythmic units. The naturalness of a Text-to-Speech
(TTS) system is directly influenced by the segmentation of the PWs. Most of the PWs are the combination of several LWs. In
this paper, three Lexical Combination Models are proposed to combine LWs into PWs, including a Directed Acyclic Graph Model,
a Segmentation Model and a Markov Model (MM). To cope with the situation where some long LWs should be segmented into two
or more PWs, a Lexical Split Model (LSM) is applied to the long LWs. Experimental results prove that relatively constant results
with various training data can be obtained from a MM. The Transformation-Based Error Driven Learning (TBED) algorithm, for
its high performance of individual property, is applied in combination with the MM to improve the precision of PW segmentation.
Experiments show that among the three proposed models, the MM combined with TBED and LSM, leads to the best performance, in
which a precision of 93.00% and a recall of 93.23% are achieved. The perception test indicates that by using PWs as the lowest
prosodic units a speech sounds more natural and acceptable than by using LWs.
This paper is supported by NSFC Project (60503071); 973 Natural Basic Research Program of China (2004CB318102); Postdoctor
Science Foundation of P. R. China (20070420275). 相似文献