全文获取类型
收费全文 | 65060篇 |
免费 | 8682篇 |
国内免费 | 3050篇 |
专业分类
电工技术 | 3849篇 |
技术理论 | 2篇 |
综合类 | 3211篇 |
化学工业 | 13330篇 |
金属工艺 | 2460篇 |
机械仪表 | 3095篇 |
建筑科学 | 4918篇 |
矿业工程 | 2048篇 |
能源动力 | 1377篇 |
轻工业 | 6728篇 |
水利工程 | 1549篇 |
石油天然气 | 1779篇 |
武器工业 | 341篇 |
无线电 | 7055篇 |
一般工业技术 | 6278篇 |
冶金工业 | 2826篇 |
原子能技术 | 636篇 |
自动化技术 | 15310篇 |
出版年
2024年 | 140篇 |
2023年 | 1112篇 |
2022年 | 2265篇 |
2021年 | 4142篇 |
2020年 | 2125篇 |
2019年 | 2090篇 |
2018年 | 2244篇 |
2017年 | 2938篇 |
2016年 | 4087篇 |
2015年 | 4655篇 |
2014年 | 5211篇 |
2013年 | 5186篇 |
2012年 | 4010篇 |
2011年 | 3488篇 |
2010年 | 2823篇 |
2009年 | 2793篇 |
2008年 | 2826篇 |
2007年 | 4015篇 |
2006年 | 4154篇 |
2005年 | 3562篇 |
2004年 | 2463篇 |
2003年 | 2322篇 |
2002年 | 1689篇 |
2001年 | 1156篇 |
2000年 | 1042篇 |
1999年 | 711篇 |
1998年 | 453篇 |
1997年 | 410篇 |
1996年 | 344篇 |
1995年 | 287篇 |
1994年 | 291篇 |
1993年 | 206篇 |
1992年 | 164篇 |
1991年 | 148篇 |
1990年 | 140篇 |
1989年 | 126篇 |
1988年 | 87篇 |
1987年 | 71篇 |
1986年 | 91篇 |
1985年 | 78篇 |
1984年 | 89篇 |
1983年 | 59篇 |
1982年 | 42篇 |
1981年 | 42篇 |
1980年 | 51篇 |
1966年 | 25篇 |
1964年 | 35篇 |
1962年 | 65篇 |
1959年 | 22篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
111.
112.
113.
A real-time distributed database system (RTDDBS) must maintain the consistency constraints of objects and must also guarantee
the time constraints imposed by each request arriving at the system. Such a time constraint of a request is usually defined
as a deadline period, which means that the request must be serviced on or before its time constraint. Servicing these requests
may incur I/O costs, control-message transferring costs or data-message transferring costs. As a result, in our work, we first
present a mathematical model that considers all these costs. Using this cost model, our objective is to service all the requests
on or before their respective deadline periods and minimize the total servicing cost. To this end, from theoretical standpoint, we design
a dynamic object replication algorithm, referred to as Real-time distributed dynamic Window Mechanism (RDDWM), that adapts to the random patterns of read-write requests. Using competitive analysis, from practical perspective,
we study the performance of RDDWM algorithm under two different extreme conditions, i.e., when the deadline period of each
request is sufficiently long and when the deadline period of each request is very short. Several illustrative examples are
provided for the ease of understanding.
Recommended by: Ashfaq Khokhar 相似文献
114.
随着3G时代的到来,移动网络将步入重大的转型期。本文通过对河北移动网络运维的实例分析说明,集中化是移动网络发展的要求,信息化支撑了集中化的实施,区域化是县区保证网络运维、支撑市场发展的有效途径。文中最后对集中化、信息化、区域化的运维发展趋势做了展望。 相似文献
115.
116.
117.
W. Wang J. Dai J. Tang D.-T. Jiang Y. Chen J. Fang J. He W. Zhou L. Spinu 《Journal of Superconductivity》2003,16(1):155-157
Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO2). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO2 films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed. 相似文献
118.
Kuniaki Honjo 《Carbon》2003,41(5):979-984
Fracture toughness (KIC) of representative high-strength type PAN (polyacrylonitrile)-based carbon fibers, Torayca™ T300 and T800H, with or without artificial surface defects, were estimated to be ca. 1 MPam1/2 from the tensile strength vs. fracture mirror size relation, assuming a constant crack-to-mirror size ratio. The corresponding critical energy release rate (Γ) was ca. 7.4 J m−2, which was close to the value derived from the reported surface energies for a graphite crystal. Similar KIC values were obtained for the old-type PAN-based carbon fibers from the reported data by the use of the present estimation procedure. 相似文献
119.
Field Static Load Test on Kao-Ping-Hsi Cable-Stayed Bridge 总被引:1,自引:0,他引:1
Field load testing is an effective method for understanding the behavior and fundamental characteristics of a cable-stayed bridge. This paper presents the results of field static load tests on the Kao-Ping-Hsi cable-stayed bridge, the longest cable-stayed bridge in Taiwan, before it was open to traffic. A total of 40 loading cases, including the unit and distributed bending and torsion loading effects, were conducted to investigate the bridge behavior. The atmospheric temperature effect on the variations of the main girder deflections was also monitored. The results of static load testing include the main girder deflections, the flexural strains of the prestressed concrete girder, and the variations of the cable forces. A three-dimensional finite-element model was developed. The results show that the bridge under the planned load test conditions has linear superposition characteristics and the analytical model shows a very good agreement with the bridge responses. Further discussion of deflection and cable forces of the design specifications for a cable-stayed bridge is also presented. 相似文献
120.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %. 相似文献