全文获取类型
收费全文 | 358989篇 |
免费 | 42090篇 |
国内免费 | 34217篇 |
专业分类
电工技术 | 32372篇 |
技术理论 | 10篇 |
综合类 | 33940篇 |
化学工业 | 58068篇 |
金属工艺 | 14443篇 |
机械仪表 | 23195篇 |
建筑科学 | 28282篇 |
矿业工程 | 9371篇 |
能源动力 | 11424篇 |
轻工业 | 23625篇 |
水利工程 | 9364篇 |
石油天然气 | 11465篇 |
武器工业 | 4363篇 |
无线电 | 43665篇 |
一般工业技术 | 41070篇 |
冶金工业 | 11040篇 |
原子能技术 | 5864篇 |
自动化技术 | 73735篇 |
出版年
2024年 | 1759篇 |
2023年 | 5524篇 |
2022年 | 10165篇 |
2021年 | 11710篇 |
2020年 | 12148篇 |
2019年 | 10853篇 |
2018年 | 10191篇 |
2017年 | 13419篇 |
2016年 | 14747篇 |
2015年 | 16068篇 |
2014年 | 19750篇 |
2013年 | 22693篇 |
2012年 | 26978篇 |
2011年 | 28993篇 |
2010年 | 21565篇 |
2009年 | 21843篇 |
2008年 | 22250篇 |
2007年 | 25938篇 |
2006年 | 23895篇 |
2005年 | 20318篇 |
2004年 | 17005篇 |
2003年 | 14018篇 |
2002年 | 11282篇 |
2001年 | 8980篇 |
2000年 | 7714篇 |
1999年 | 6472篇 |
1998年 | 5193篇 |
1997年 | 4388篇 |
1996年 | 3563篇 |
1995年 | 3074篇 |
1994年 | 2624篇 |
1993年 | 1950篇 |
1992年 | 1643篇 |
1991年 | 1267篇 |
1990年 | 1046篇 |
1989年 | 901篇 |
1988年 | 661篇 |
1987年 | 421篇 |
1986年 | 363篇 |
1985年 | 334篇 |
1984年 | 298篇 |
1983年 | 198篇 |
1982年 | 257篇 |
1981年 | 170篇 |
1980年 | 148篇 |
1979年 | 80篇 |
1978年 | 44篇 |
1977年 | 46篇 |
1975年 | 33篇 |
1959年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
Jeong Ho Moon Hak Soo Han Yong Gun Shul Do Hoon Jang Muyng Do Ro Du Suk Yun 《Progress in Organic Coatings》2007
This study relates to the development of coatings for optical discs in high-density digital versatile disc systems (HD-DVD or blue lay disk) that use a high numerical aperture of 0.85 at 405 nm wavelength and have a protective top layer over a primer layer for protection against damage and dust. Ultraviolet-curable raw materials of two acrylic monofunctional monomers ( isobornylacrylate, IBA and tetrahydrofurfurylacrylate, THFA) and two kinds of urethaneacrylate oligomers (OUMD and OUME) have been easily mixed with photoinitiators. Curing rate of these materials was characterized by FT-IR. In case of top coats, VTES (vinyltriethoxysilane) and acrylic acid were added to enhance the abrasion resistance. These two kinds of UV-curable resinous materials having no solvent were synthesized and investigated as means for making a blue ray disk having good optical and mechanical properties. In addition, dynamic characteristics including reflectivity, fluctuation of RF signal and noise level were also investigated. 相似文献
943.
A finite-difference Total Variation Diminishing (TVD) numerical simulation model for coupling the Reynolds Averaged Navier-Stokes (RANS) equations, pressure-relative continuity equation and various k-ε turbulence models was developed to solve the incompressible flow based on the pseudo-compressibility method. The hyperbolicity of all these equations was studied and the discretization of the fully coupling equations with all the primal variables and source terms were made in this article. Numerical simulation for modeling the flow around a ground-mounted square rib was implemented and validated by comparing with the published wind tunnel experimental data. It is shown that such a numerical simulation method with a proper turbulence model has a very good accuracy to simulate the flow around a surface-mounted rib. It is concluded that the Renormalization Group (RNG) and Chen-Kim k-ε turbulence models have much better ability to predict the characteristics of the vortex structure and flow separation than the standard k-ε model. 相似文献
944.
为了解在惰气环境Pu(OH)4(am)与碳酸盐溶液中HCO-3,CO2-3的配位行为,考察了放置时间对Pu总浓度的影响;同时也考察了pH值、碳酸根总浓度变化对碳酸盐溶液中Pu的主要存在形态及溶解总浓度的影响。实验结果表明,HCO-3离子与Pu(OH)4(am)生成[Pu(OH)4(HCO3)2]2-(lg K=-2.61±0.18, lgβ=54.25±0.18)或[Pu(OH)2(CO3)2]2-(lgK=-2.61±0.18, lgβ=46.91±0.18);CO2-3离子与Pu(OH)4(am)生成[Pu(OH)4(CO3)2]4-(lgK=-3.52±0.11, lgβ=53.33±0.11)。可能的配位反应方程式为: Pu(OH)4(am)+2HCO-3 = [Pu(OH)4(HCO3)2]2-, Pu(OH)4(am)+2HCO-3 =[Pu(OH)2(CO3)2]2-+2H2O, Pu(OH)4(am)+2CO2-3=[Pu(OH)4(CO3)2]4-。 相似文献
945.
During the 1997 winter season, shipborne polarimetric backscatter measurements of Great Lakes (freshwater) ice types using the Jet Propulsion Laboratory C-band scatterometer, together with surface-based ice physical characterization measurements and environmental parameters, were acquired concurrently with Earth Resource Satellite 2 (ERS-2) and RADARSAT Synthetic Aperture Radar (SAR) data. This polarimetric data set, composed of over 20 variations of different ice types measured at incident angles from 0° to 60° for all polarizations, was processed to radar cross-section to establish a library of signatures (look-up table) for different ice types. The library is used in the computer classification of calibrated satellite SAR data. Computer analysis of ERS-2 and RADARSAT ScanSAR images of Great Lakes ice cover using a supervised classification technique indicates that different ice types in the ice cover can be identified and mapped, and that wind speed and direction can have an influence on the classification of water as ice based on single frequency, single polarization data. Once satellite SAR data are classified into ice types, the ice map provides important and necessary input for environmental protection and management, ice control and ice breaking operations, and ice forecasting and modeling efforts. 相似文献
946.
947.
以Bi(NO3)3·5H2O和Ti(OC4H9)4为原料,NaOH为矿化剂,采用水热法制备了形貌规则的单晶Bi4Ti3O12纳米片。X射线衍射(XRD)结果表明,所合成的产物为正交相层状钙钛矿结构的Bi4Ti3O12。场发射扫描电子显微镜(FESEM)研究显示:样品是由大量边缘尺寸接近200nm,厚度约为15nm的片状结构组成。利用X射线光电子能谱(XPS)研究产物的化学组分和价态分布。室温拉曼光谱研究表明,Bi4Ti3O12纳米片的声子寿命和热稳定性低于相应的块体材料。 相似文献
948.
The reliability of a system is the probability that the system will perform its intended mission under given conditions. This
paper provides an overview of the approaches to reliability modelling and identifies their strengths and weaknesses. The models
discussed include structure models, simple stochastic models and decomposable stochastic models. Ignoring time-dependence,
structure models give reliability as a function of the topological structure of the system. Simple stochastic models make
direct use of the properties of underlying stochastic processes, while decomposable models consider more complex systems and
analyse them through subsystems. Petri nets and dataflow graphs facilitate the analysis of complex systems by providing a
convenient framework for reliability analysis. 相似文献
949.
Pierre Hadaya 《Electronic Commerce Research》2006,6(2):173-185
Based on the literature dealing with the diffusion of innovation and with information systems, and building on the emerging
concepts in electronic commerce (e-commerce), this paper aims at assessing the influence of various factors on firms’ future
level of use of electronic marketplaces (e-marketplaces). This theoretical model is tested on data collected from 1,200 senior
managers in Canadian firms. Findings indicate that a firm’s past experience in e-commerce, as well as the factors relating
to its business relationships ultimately affect its future use of e-marketplaces. Results of TOBIT regressions also show that
the complexity of sophisticated e-commerce implementations is negatively correlated with the future level of use of e-marketplaces,
and that consultants and other experts play an essential role in encouraging and facilitating the use of this new type of
electronic platform. Finally, our survey data demonstrate that the relative influence of some determinants differs according
to the firms’ size.
Pierre Hadaya is an assistant professor of MIS at the Faculté d’administration of the Université de Sherbrooke (Canada). He holds a Ph.D.
in Management of Technology from the école Polytechnique de Montréal. His research interests lie at the intersection of information
technology management, business strategy and interorganizational design. 相似文献
950.
连续、高强度、快速施工既是碾压混凝土坝的施工特点,也是层间结合质量的根本保证。龙滩水电站碾压混凝土浇筑采用了合理的入仓手段和机械设备配置,通过配套的碾压混凝土施工技术的应用和健全的管理体系,有效地提高了碾压混凝土施工强度,保证了施工进度和施工质量。 相似文献