全文获取类型
收费全文 | 4773篇 |
免费 | 286篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 64篇 |
综合类 | 8篇 |
化学工业 | 934篇 |
金属工艺 | 56篇 |
机械仪表 | 76篇 |
建筑科学 | 177篇 |
矿业工程 | 5篇 |
能源动力 | 161篇 |
轻工业 | 332篇 |
水利工程 | 53篇 |
石油天然气 | 35篇 |
无线电 | 404篇 |
一般工业技术 | 1199篇 |
冶金工业 | 598篇 |
原子能技术 | 13篇 |
自动化技术 | 952篇 |
出版年
2024年 | 13篇 |
2023年 | 59篇 |
2022年 | 96篇 |
2021年 | 140篇 |
2020年 | 114篇 |
2019年 | 122篇 |
2018年 | 127篇 |
2017年 | 139篇 |
2016年 | 162篇 |
2015年 | 134篇 |
2014年 | 190篇 |
2013年 | 338篇 |
2012年 | 310篇 |
2011年 | 388篇 |
2010年 | 298篇 |
2009年 | 283篇 |
2008年 | 311篇 |
2007年 | 247篇 |
2006年 | 216篇 |
2005年 | 188篇 |
2004年 | 154篇 |
2003年 | 136篇 |
2002年 | 130篇 |
2001年 | 68篇 |
2000年 | 64篇 |
1999年 | 60篇 |
1998年 | 54篇 |
1997年 | 49篇 |
1996年 | 49篇 |
1995年 | 45篇 |
1994年 | 40篇 |
1993年 | 35篇 |
1992年 | 38篇 |
1991年 | 21篇 |
1990年 | 27篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 27篇 |
1986年 | 17篇 |
1985年 | 28篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 20篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1964年 | 4篇 |
排序方式: 共有5067条查询结果,搜索用时 0 毫秒
21.
Mechanisms in damping of mechanical vibration by piezoelectric ceramic-polymer composite materials 总被引:5,自引:0,他引:5
The piezoelectric ceramic (piezoceramic) component of a polymer-piezoelectric ceramic composite converts mechanical energy
into electrical energy and this electrical energy is dissipated as heat in a load resistance, R
x, simulated by a shunted resistance, but provided in practice by a conductive polymer composite matrix. The composite therefore
dissipates the input mechanical energy via the damping mechanism provided by piezoelectric ceramic-conductive matrix material,
as well as the conventional viscoelastic damping provided by the polymer. Mathematical models have been developed to characterize
the damping behaviour of the composites, and the maximum damping ratio of composites can be as high as 23%. A two degrees-of-freedom
(2DOF) experimental setup was developed to test the validity of the models. The experimental results are in good agreement
with the theoretical predictions. 相似文献
22.
An important aspect of the vehicle routing problem (VRP) that has been largely overlooked is the use of satellite facilities to replenish vehicles during a route. When possible, satellite replenishment allows the drivers to continue making deliveries until the close of their shift without necessarily returning to the central depot. This situation arises primarily in the distribution of fuels and certain retail items. When demand is random, optimizing customer routes a priori may result in significant additional costs for a particular realization of demand. Satellite facilities are one way of safeguarding against unexpected demand. This paper presents a branch and cut methodology for solving the VRP with satellite facilities subject to capacity and route time constraints. We begin with a mixed-integer linear programming formulation and then describe a series of valid inequalities that can be used to cut off solutions to the linear programming relaxation. Several separation heuristics are then outlined that are used to generate the cuts. Embedded in the methodology is a VRP heuristic for finding good feasible solutions at each stage of the computations. Results are presented for a set of problems derived from our experience with a leading propane distributor. 相似文献
23.
Peter J. Bentley Jonathan P. Wakefield 《Computer-Aided Civil and Infrastructure Engineering》1996,11(3):153-161
Abstract: This paper examines the first stage of using genetic algorithms in design—how to encode designs as chromosomes. Generic representations capable of describing the geometry of any solid object to eliminate the unnecessary duplication of work at this stage are explored. A suitable low-parameter, spatial-partitioning representation is then proposed, using partitions consisting of six-sided polyhedra intersected by planes. Finally, the coding of the representation is examined, with the conclusion that allelic coding with control genes and user-definable, fixed-value alleles would provide the most flexible system. 相似文献
24.
25.
A classification of models of visual word recognition is presented that facilitates formal comparisons between models of different formats. In light of the theoretical contributions to this special section, sets of criteria for the evaluation of models and strategies for model construction are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
Michael Vermut William R. Widner Jonathan D. Dinman Reed B. Wickner 《Yeast (Chichester, England)》1994,10(11):1477-1479
MKT1 is required for m aintenance of K2 above 30°C in strains with the L-A-HN variant of the L-A double-stranded RNA virus of Saccharomyces cerevisiae. We report that MKT1 encodes a 92 979 Da protein with serine-rich regions and the retroviral protease signature, DTG, but with no substantial homology to proteins presently in the databases. This sequence is available from GenBank under Accession Number U09129. 相似文献
27.
A dual read-out model of context effects in letter perception is described that predicts forced-choice accuracy in the Reicher paradigm and its relation to word reportability. It is hypothesized that a correct choice to a letter in a word context is made when either the correct letter representation or a word representation containing the correct letter in the correct position reaches a response threshold (a criterion level of activation). This hypothesis was implemented using the basic architecture of the interactive activation model (J. L. McClelland & D. E. Rumelhart, 1981) in its semistochastic variant (A. M. Jacobs & J. Grainger, 1992). The model successfully captures the data of J. C. Johnston (1978), otherwise thought to be critically damaging for this type of model, and accurately predicts performance in a series of new experiments using the Reicher paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
Joannie W. Chin Eric Byrd Ned Embree Jonathan Martin J. D. Tate 《Journal of Coatings Technology》2002,74(929):39-44
Laboratory ultraviolet (UV) chambers are widely used to obtain weathering data for a wide range of commercial polymer products
including coatings, textiles, elastomers, plastics, and polymeric composites. Although numerous improvements have been made
in the design of UV chambers over the last 80 years, the reproducibility of the exposure results from these chambers has remained
elusive. This lack of reproducibility is attributed to systematic errors in their design, operation, and control which prevent
direct comparisons of the performance of materials exposed in the same environment, comparisons of the performance of the
same material exposed in different laboratories, and the comparison of field and laboratory results. This paper describes
an innovative UV chamber design based on integrating sphere technology that greatly reduces the magnitude of these errors,
as well as provides additional experimental capabilities.
Presented at the 79th Annual Meeting of the Federation of Societies for Coatings Technology, on November 4–7, 2001, in Atlanta,
GA.
Building Materials Division. Gaithersburg, MD.
Freeport, TX. 相似文献
29.
Jonathan Cherneff Robert Logcher Jerome Connor Nicholas Patrikalakis 《Research in Engineering Design》1992,3(4):195-210
A method for machine interpretation of architectural (or other) schematic drawings is presented. The central problem is to build an efficient drawing parser (i.e., a program that identifies the semantic entities, characteristics, and relationships that are represented in the drawing). The parser is built from specifications of the drawing grammar and an underlying spatial model. The grammar describes what to look for, and the spatial model enables the parser to find it quickly. Coupled with existing optical recognition technology, this technique enables the use of drawings directly as: (1) a database to drive various Architecture-Engineering-Construction (AEC) applications; (2) a communication protocol to integrate CAD systems; (3) a traditional user interface. 相似文献
30.
Courtney Marrett Alexandre Moulart Jonathan Colton Abbas Tcharkhtchi 《Polymer Engineering and Science》2003,43(4):822-830
The dielectric properties of a ceramic powder (BaTiO3) filled thermoplastic elastomer (EPDM TPE) were investigated for use in a flexible electromagnetic crystal. Materials were produced that had a high dielectric constant (approximately 9) and low loss tangent (less than 0.01). Materials were extruded and injection molded so as to povide low‐cost processing. Mechanical and electromagnetic test results showed the effect of processing conditions on the final quality of the composite. The shear rate during processing and the number of mixing cycles were found to affect the final material characteristics significantly. An electromagnetic crystal woven from extruded rods showed good reflectivity in the 10–15 GHz region. 相似文献