全文获取类型
收费全文 | 18860篇 |
免费 | 1899篇 |
国内免费 | 558篇 |
专业分类
电工技术 | 924篇 |
技术理论 | 1篇 |
综合类 | 772篇 |
化学工业 | 4069篇 |
金属工艺 | 902篇 |
机械仪表 | 1031篇 |
建筑科学 | 920篇 |
矿业工程 | 278篇 |
能源动力 | 810篇 |
轻工业 | 1649篇 |
水利工程 | 210篇 |
石油天然气 | 595篇 |
武器工业 | 112篇 |
无线电 | 2638篇 |
一般工业技术 | 3216篇 |
冶金工业 | 779篇 |
原子能技术 | 226篇 |
自动化技术 | 2185篇 |
出版年
2024年 | 32篇 |
2023年 | 240篇 |
2022年 | 424篇 |
2021年 | 726篇 |
2020年 | 573篇 |
2019年 | 573篇 |
2018年 | 601篇 |
2017年 | 644篇 |
2016年 | 677篇 |
2015年 | 711篇 |
2014年 | 1049篇 |
2013年 | 1249篇 |
2012年 | 1351篇 |
2011年 | 1537篇 |
2010年 | 1307篇 |
2009年 | 1207篇 |
2008年 | 1126篇 |
2007年 | 960篇 |
2006年 | 877篇 |
2005年 | 791篇 |
2004年 | 599篇 |
2003年 | 572篇 |
2002年 | 577篇 |
2001年 | 474篇 |
2000年 | 380篇 |
1999年 | 371篇 |
1998年 | 343篇 |
1997年 | 246篇 |
1996年 | 180篇 |
1995年 | 169篇 |
1994年 | 135篇 |
1993年 | 103篇 |
1992年 | 98篇 |
1991年 | 54篇 |
1990年 | 64篇 |
1989年 | 58篇 |
1988年 | 27篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 11篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Per Hovstad Liching Sung 《International Journal of Satellite Communications and Networking》2005,23(2):91-110
The 1977 Broadcasting‐Satellite Service (BSS) Plan for Region 1 & 3 had been widely acknowledged to be out‐of‐date by the late 1980s. Development of digital modulation in the early 1990s provided an opportunity to update the technical provisions of the Plan to make it more economically viable. After a decade of work and three World Radiocommunication Conferences (WRCs), the revision of Region 1 & 3 BSS Plan was finally completed in 2003. The new Plan increased channel assignments from 5 to 10 analog‐equivalent channels for each country in Region 1, and from 4 to 12 channels for each country in Region 3. Yet, despite the increase in capacity, the new Plan is surprisingly similar to the original one in terms of the technical parameters. It is still based on national coverage, and the channel plan, orbital location, orbital spacing, and polarization are also the same. As a result, the new Plan is no more economically viable to implement than the old. To create economically viable BSS systems would most likely require modifications to the assignment in the Plan. Yet, modification procedures were made more difficult to apply after replanning. Less future implementation of BSS networks than would otherwise have occurred can be expected, and an inefficient usage of these frequency bands will likely result. On the other hand, less implemented systems will mean more capacity set aside for future use. This is important for countries that currently do not have satellite operations. In the end, BSS replanning reflects the eternal conflict between efficient usage and guaranteed future access. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
52.
53.
ISIS全局优化多道反演技术在墩2块岩性油藏描述中的应用 总被引:2,自引:0,他引:2
为进一步落实墩2块戴一段岩性油藏成藏规模及分布规律,针对该储层薄、横向变化快的特点,利用ISIS全局优化多道反演技术,对该构造区岩性储层进行了精细描述,较好的预测出戴一段储层平面分布规律。 相似文献
54.
55.
56.
Ju Han Lee You Min Chang Young-Geun Han Sang-Hyuck Kim Haeyang Chung Sang Bae Lee 《Photonics Technology Letters, IEEE》2005,17(1):34-36
We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range. 相似文献
57.
Metal-based communications between subsystems and chips has become the limiting factor in high-speed computing. Maturing optics-based technologies offer advantages that may unplug this bottleneck. Optical interconnects offer high-speed computers key advantages over metal interconnects. These include (1) high spatial and temporal bandwidths, (2) high-speed transmission, (3) low crosstalk independent of data rates, and (4) high interconnect densities. Although faster device switching speeds will eventually be necessary for future massively parallel computing systems, the deciding factor in determining system performance and cost will be subsystem communications rather than device speed. Free-space optical interconnects, by virtue of their inherent parallelism, high data bandwidth, small size and power requirement, and relative freedom from mutual interference of signals, already show great promise in replacing metal interconnects to solve communication problems 相似文献
58.
This paper presents a novel matrix unit cell scheduler (MUCS) for input-buffered asynchronous transfer mode (ATM) switches. The MUCS concept originates from a heuristic strategy that leads to an optimal solution for cell scheduling. Numerical analysis indicates that input-buffered ATM switches scheduled by MUCS can utilize nearly 100% of the available link bandwidth. A transistor-level MUCS circuit has been designed and verified using HSPICE. The circuit features a regular structure, minimal interconnects, and a low transistor count. HSPICE simulation indicates that using 2-μm CMOS technology, the MUCS circuit can operate at clock frequency of 100 MHz 相似文献
59.
60.