全文获取类型
收费全文 | 93102篇 |
免费 | 1649篇 |
国内免费 | 712篇 |
专业分类
电工技术 | 1132篇 |
综合类 | 2685篇 |
化学工业 | 12941篇 |
金属工艺 | 5283篇 |
机械仪表 | 3621篇 |
建筑科学 | 2668篇 |
矿业工程 | 732篇 |
能源动力 | 1407篇 |
轻工业 | 4030篇 |
水利工程 | 1422篇 |
石油天然气 | 639篇 |
武器工业 | 30篇 |
无线电 | 10667篇 |
一般工业技术 | 17794篇 |
冶金工业 | 3516篇 |
原子能技术 | 346篇 |
自动化技术 | 26550篇 |
出版年
2024年 | 42篇 |
2023年 | 136篇 |
2022年 | 263篇 |
2021年 | 353篇 |
2020年 | 279篇 |
2019年 | 291篇 |
2018年 | 14676篇 |
2017年 | 13596篇 |
2016年 | 10201篇 |
2015年 | 949篇 |
2014年 | 633篇 |
2013年 | 792篇 |
2012年 | 3677篇 |
2011年 | 9971篇 |
2010年 | 8740篇 |
2009年 | 6036篇 |
2008年 | 7205篇 |
2007年 | 8212篇 |
2006年 | 526篇 |
2005年 | 1599篇 |
2004年 | 1388篇 |
2003年 | 1433篇 |
2002年 | 790篇 |
2001年 | 343篇 |
2000年 | 388篇 |
1999年 | 317篇 |
1998年 | 322篇 |
1997年 | 251篇 |
1996年 | 226篇 |
1995年 | 172篇 |
1994年 | 147篇 |
1993年 | 114篇 |
1992年 | 105篇 |
1991年 | 102篇 |
1990年 | 62篇 |
1989年 | 67篇 |
1988年 | 68篇 |
1987年 | 46篇 |
1986年 | 38篇 |
1985年 | 42篇 |
1982年 | 35篇 |
1968年 | 44篇 |
1967年 | 37篇 |
1966年 | 43篇 |
1965年 | 48篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 64篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
2.
Jan van Eijck 《Formal Aspects of Computing》1994,6(1):766-787
Presuppositions of utterances are the pieces of information you convey with an utterance no matter whether your utterance is true or not. We first study presupposition in a very simple framework of updating propositional information, with examples of how presuppositions of complex propositional updates can be calculated. Next we move on to presuppositions and quantification, in the context of a dynamic version of predicate logic, suitably modified to allow for presupposition failure. In both the propositional and the quantificational case, presupposition failure can be viewed as error abortion of procedures. Thus, a dynamic assertion logic which describes the preconditions for error abortion is the suitable tool for analysing presupposition. 相似文献
3.
4.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen 相似文献
5.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach. 相似文献
6.
7.
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
8.
9.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献
10.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献