全文获取类型
收费全文 | 13851篇 |
免费 | 1625篇 |
国内免费 | 1252篇 |
专业分类
电工技术 | 860篇 |
综合类 | 1954篇 |
化学工业 | 527篇 |
金属工艺 | 170篇 |
机械仪表 | 735篇 |
建筑科学 | 632篇 |
矿业工程 | 154篇 |
能源动力 | 310篇 |
轻工业 | 599篇 |
水利工程 | 450篇 |
石油天然气 | 140篇 |
武器工业 | 106篇 |
无线电 | 1523篇 |
一般工业技术 | 1518篇 |
冶金工业 | 595篇 |
原子能技术 | 124篇 |
自动化技术 | 6331篇 |
出版年
2024年 | 74篇 |
2023年 | 192篇 |
2022年 | 282篇 |
2021年 | 317篇 |
2020年 | 380篇 |
2019年 | 379篇 |
2018年 | 366篇 |
2017年 | 450篇 |
2016年 | 490篇 |
2015年 | 523篇 |
2014年 | 694篇 |
2013年 | 955篇 |
2012年 | 934篇 |
2011年 | 1039篇 |
2010年 | 783篇 |
2009年 | 869篇 |
2008年 | 884篇 |
2007年 | 988篇 |
2006年 | 852篇 |
2005年 | 781篇 |
2004年 | 683篇 |
2003年 | 552篇 |
2002年 | 505篇 |
2001年 | 376篇 |
2000年 | 414篇 |
1999年 | 294篇 |
1998年 | 282篇 |
1997年 | 219篇 |
1996年 | 211篇 |
1995年 | 175篇 |
1994年 | 131篇 |
1993年 | 113篇 |
1992年 | 92篇 |
1991年 | 69篇 |
1990年 | 57篇 |
1989年 | 60篇 |
1988年 | 35篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 33篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1965年 | 7篇 |
1960年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Craig S. Long Albert A. Groenwold 《International journal for numerical methods in engineering》2004,61(6):837-855
Reduced integration is frequently used in evaluating the element stiffness matrix of quadratically interpolated finite elements. Typical examples are the serendipity (Q8) and Lagrangian (Q9) membrane finite elements, for which a reduced 2 × 2 Gauss–Legendre integration rule is frequently used, as opposed to full 3 × 3 Gauss–Legendre integration. This ‘softens’ these element, thereby increasing accuracy, albeit at the introduction of spurious zero energy modes on the element level. This is in general not considered problematic for the ‘hourglass’ mode common to Q8 and Q9 elements, since this spurious mode is non‐communicable. The remaining two zero energy modes occurring in the Q9 element are indeed communicable. However, in topology optimization for instance, conditions may arise where the non‐communicable spurious mode associated with the elements becomes activated. To effectively suppress these modes altogether in elements employing quadratic interpolation fields, two modified quadratures are employed herein. For the Q8 and Q9 membrane elements, the respective rules are a five and an eight point rule. As compared to fully integrated elements, the new rules enhance element accuracy due to the introduction of soft, higher‐order deformation modes. A number of standard test problems reveal that element accuracy remains comparable to that of the under‐integrated counterparts. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
32.
Drew Michael R.; Yang Cynthia; Ohyama Tatsuya; Balsam Peter D. 《Canadian Metallurgical Quarterly》2004,30(3):163
Three experiments investigated the effects of varying the conditioned stimulus (CS) duration between training and extinction. Ring doves (Streptopelia risoria) were autoshaped on a fixed CS-unconditioned stimulus (US) interval and extinguished with CS presentations that were longer, shorter, or the same as the training duration. During a subsequent test session, the training CS duration was reintroduced. Results suggest that the cessation of responding during an extinction session is controlled by generalization of excitation between the training and extinction CSs and by the number of nonreinforced CS presentations. Transfer of extinction to the training CS is controlled by the similarity between the extinction and training CSs. Extinction learning is temporally specific. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
33.
This study was motivated by some difficulties encountered by the authors when trying to express temporal knowledge using Sowa's conceptual graph (CG) approach. An overview of Sowa's approach is given and the difficulties encountered when trying to model temporal knowledge are outlined: the disparity of notations allowed by CG theory for expressing temporal information; the ambiguity and incompleteness of tense sspecification; the difficulty of harmonizing tenses and intergraph temporal relations. Various approaches suggested for representing time both in artificial intelligence and linguistics are presented, and an extension to Sowa's approach is proposed in which temporal and nontemporal knowledge are differentiated. In this model points in time are represented as well as time intervals. A semantic interpretation of verbs is provided based on an extension of Reichenbach's model of temporal markers. The authors show how their approach enables the representation of tenses as well as the aspectual properties of natural language sentences. 相似文献
34.
After considering the stabilization of a specific class of stochastic nonlinear systems in a companion paper, in this second part, we address the classical question of when is a stabilizing (in probability) controller optimal and show that for every system with a stochastic control Lyapunov function it is possible to construct a controller which is optimal with respect to a meaningful cost functional. Then we return to the problem from Part I and design an optimal backstepping controller whose cost functional includes penalty on control effort and which has an infinite gain margin. 相似文献
35.
The paper describes a prototype system called HiSQL (Historical SQL) which extends the functionality of SQL in manipulating
historical data, by providing functions for spatial and temporal processing. Conceptually the paper is divided into three
parts: the first part deals with the design and architecture of the system; the second part introduces a case study (the defters);
and the third part describes specific functions for spatial and temporal processing of serial documents. The paper concludes
with a comparison between HiSQL and SQL and suggestions for further work.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
36.
参数三次B样条曲线的一种整体光顺方法 总被引:7,自引:0,他引:7
本文在能量法的基础上,提出了一种新的目标函数,给出了参数三次B样条曲线的一种新的整体光顺方法。利用这种方法得到的曲线不仅具有较小的应变能,而且曲率变化比较均匀,具有很好的光顺效果。该方法能推广到对曲面的光顺。 相似文献
37.
38.
This paper considers the equalisation problem in Quadrature Phase-Shift Keying (QPSK) modulated signals which have been distorted by the passage through a transmission channel. The channel is modelled as a Rician fading channel to simulate the behaviour of the transmission channel in the mobile satellite context. The equalisation is treated as the generalisation of the channel behaviour, and some algorithms with the structure of an artificial neural network using the Multilayer Perceptron, Volterra Series and Radial Basis Function are described. Results for the BER performance of typical transversal equalisers, with Square-Root Kalman adaptation algorithm, and algorithms with artificial neural network structure are also reported and evaluated. Improved performance is exhibited by the artificial neural network approaches. 相似文献
39.
This paper looks into a new area for knowledge-based system application, that of manufacturing modelling. Manual generation of IDEF0 models of manufacturing systems is time-consuming and inconsistent. However, the process can be automated to improve timeliness and consistency. In this paper, a knowledge-based manufacturing modelling system for the automatic generation of IDEF0 models is proposed. The system will not only greatly reduce the IDEF0 modelling time but will also eliminate the inconsistency problem of conventional IDEF0 modelling systems. The paper explains the knowledge-based approach and identifies the kinds of domain knowledge that are required for the construction of the knowledge-based manufacturing modelling system. 相似文献
40.