全文获取类型
收费全文 | 119136篇 |
免费 | 16757篇 |
国内免费 | 11204篇 |
专业分类
电工技术 | 20725篇 |
技术理论 | 11篇 |
综合类 | 13102篇 |
化学工业 | 4561篇 |
金属工艺 | 2527篇 |
机械仪表 | 6310篇 |
建筑科学 | 4617篇 |
矿业工程 | 2705篇 |
能源动力 | 5005篇 |
轻工业 | 1670篇 |
水利工程 | 2429篇 |
石油天然气 | 2798篇 |
武器工业 | 1098篇 |
无线电 | 23186篇 |
一般工业技术 | 5631篇 |
冶金工业 | 2184篇 |
原子能技术 | 412篇 |
自动化技术 | 48126篇 |
出版年
2024年 | 1016篇 |
2023年 | 2692篇 |
2022年 | 4944篇 |
2021年 | 5500篇 |
2020年 | 5531篇 |
2019年 | 4058篇 |
2018年 | 3373篇 |
2017年 | 4063篇 |
2016年 | 4181篇 |
2015年 | 4785篇 |
2014年 | 8084篇 |
2013年 | 7050篇 |
2012年 | 9156篇 |
2011年 | 9634篇 |
2010年 | 7362篇 |
2009年 | 7743篇 |
2008年 | 7844篇 |
2007年 | 8615篇 |
2006年 | 7184篇 |
2005年 | 6393篇 |
2004年 | 5274篇 |
2003年 | 4623篇 |
2002年 | 3647篇 |
2001年 | 3112篇 |
2000年 | 2513篇 |
1999年 | 2045篇 |
1998年 | 1494篇 |
1997年 | 1212篇 |
1996年 | 1003篇 |
1995年 | 768篇 |
1994年 | 595篇 |
1993年 | 408篇 |
1992年 | 270篇 |
1991年 | 194篇 |
1990年 | 161篇 |
1989年 | 131篇 |
1988年 | 81篇 |
1987年 | 49篇 |
1986年 | 45篇 |
1985年 | 60篇 |
1984年 | 43篇 |
1983年 | 36篇 |
1982年 | 42篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1959年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
基于网络环境的计算机资料室工作 总被引:1,自引:0,他引:1
随着信息技术的迅速发展,基于网络的信息资源共享已成为信息化社会的基本特征。数字化图书馆和电子期刊网的出现,正在改变着人们的阅读习惯,丰富的信息资源和跨时空的浏览方式彻底颠覆了传统的图书馆、资料室的服务模式。同时,数字化图书馆也给资料室管理模式创新带来了新的契机。分析了院系资料室面临的挑战与机遇,探讨了新形势下计算机资料室工作,提出了利用信息技术,改革服务方式,拓展服务内容,提高服务水平,提供有特色的专业服务。 相似文献
42.
A. K. Srivastava Ram M. Shrestha S. C. Srivastava Rabin Shrestha Dharam Paul 《国际能源研究杂志》2003,27(7):671-685
The power sector in India at present comprises of five separate regional electricity grids having practically no integrated operation in between them. This study analyses the utility planning, environmental and economical effects of integrated power sector development at the national level in which the regional electric grids are developed and operated as one integrated system. It also examines the effects of selected CO2 emission reduction targets in the power sector and the role of renewable power generation technologies in India. The study shows that the integrated development and operation of the power system at the national level would reduce the total cost including fuel cost by 4912 million $, total capacity addition by 2784 MW, while the emission of CO2, SO2 and NOx would be reduced by 231.6 (1.9%), 0.8 (0.9%), 0.4 (1.2%) million tons, respectively, during the planning horizon. Furthermore, the study shows that the expected unserved energy, one of the indices of generation system reliability, would decrease to 26 GWh under integrated national power system from 5158 GWh. As different levels of CO2 emission reduction targets were imposed, there is a switching of generation from conventional coal plants to gas fired plants, clean coal technologies and nuclear based plants. As a result the capacity expansion cost has increased. It was found that wind power plant is most attractive and economical in the Indian perspective among the renewable options considered (Solar, wind and biomass). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
43.
Valentina I. Simagina Pavel A. Storozhenko Olga V. Netskina Oksana V. Komova Galina V. Odegova Yury V. Larichev Arcady V. Ishchenko Anna M. Ozerova 《Catalysis Today》2008,138(3-4):253
Catalytic hydrolysis of NaBH4 and NH3BH3 has been studied. It was shown that the nature of the support and the active component of the catalyst affect the H2 generation rate. Despite similar sizes of rhodium particles formed on the surface of different supports (γ-Al2O3, TiO2, carbon), their reactivity is different. Rh/TiO2 with low rhodium concentration (1 wt.%) is the most active catalyst both in the hydrolysis of NaBH4 and NH3BH3. The obtained results show that the rhodium chloride interaction with titania determines the reactivity of rhodium particles formed under action of NaBH4 medium. TEM, DRS UV–vis and XPS were used to characterize the catalysts. 相似文献
44.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results. 相似文献
45.
46.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
47.
Simonetta Balsamo Vittoria De Nitto Person Paola Inverardi 《Performance Evaluation》2003,51(2-4):269-288
A review is carried out on how queueing network models with blocking have been applied so far into the performance evaluation and prediction of Software Architectures (SA). Queueing network models with finite capacity queues and blocking have recently been introduced and applied as more realistic models of systems with finite capacity resources and population constraints. Queueing network models have been often adopted as models for the evaluation of software performance. Starting from our own experience, we observe the need of a more accurate definition of the performance models of SA to capture some features of the communication systems. We consider queueing networks with finite capacity and blocking after service (BAS) to represent some synchronization constraints that cannot be easily modeled with queueing network models with infinite capacity queues. We investigate the use of queueing networks with blocking as performance models of SA with concurrent components and synchronous communication. Queueing theoretic analysis is used to solve the queueing network model and study the synchronous communication and performance of concurrent software components. Our experience is supported by other approaches that also propose the use of queueing networks with blocking. Directions for future research work in the field are included. 相似文献
48.
49.
探讨了中国3G牌照何时发放、发放数量、牌照与标准是否捆绑、3G产业链如何搭建、频率如何分配、市场容量和终端等问题,并对此提出了建设性的意见。 相似文献
50.
Modern methods of determining fracture resistance are analyzed. The necessity of developing a crucially new method based on edge chipping of a brittle material is shown. The results of experimental studies are presented. The applicability of the method to the comparative fracture resistance evaluation of ceramics is substantiated. 相似文献