全文获取类型
收费全文 | 130507篇 |
免费 | 11996篇 |
国内免费 | 6695篇 |
专业分类
电工技术 | 8605篇 |
技术理论 | 10篇 |
综合类 | 10826篇 |
化学工业 | 20671篇 |
金属工艺 | 7529篇 |
机械仪表 | 8150篇 |
建筑科学 | 10161篇 |
矿业工程 | 3582篇 |
能源动力 | 3640篇 |
轻工业 | 12533篇 |
水利工程 | 2572篇 |
石油天然气 | 6472篇 |
武器工业 | 1231篇 |
无线电 | 14019篇 |
一般工业技术 | 14289篇 |
冶金工业 | 5110篇 |
原子能技术 | 1470篇 |
自动化技术 | 18328篇 |
出版年
2024年 | 635篇 |
2023年 | 2273篇 |
2022年 | 4354篇 |
2021年 | 5689篇 |
2020年 | 4358篇 |
2019年 | 3411篇 |
2018年 | 3697篇 |
2017年 | 4398篇 |
2016年 | 3825篇 |
2015年 | 5494篇 |
2014年 | 6923篇 |
2013年 | 8045篇 |
2012年 | 9230篇 |
2011年 | 10103篇 |
2010年 | 8956篇 |
2009年 | 8455篇 |
2008年 | 8384篇 |
2007年 | 7823篇 |
2006年 | 7511篇 |
2005年 | 6182篇 |
2004年 | 4292篇 |
2003年 | 3655篇 |
2002年 | 3623篇 |
2001年 | 3053篇 |
2000年 | 2667篇 |
1999年 | 2469篇 |
1998年 | 1921篇 |
1997年 | 1485篇 |
1996年 | 1414篇 |
1995年 | 1094篇 |
1994年 | 895篇 |
1993年 | 649篇 |
1992年 | 529篇 |
1991年 | 416篇 |
1990年 | 284篇 |
1989年 | 244篇 |
1988年 | 189篇 |
1987年 | 141篇 |
1986年 | 104篇 |
1985年 | 62篇 |
1984年 | 48篇 |
1983年 | 39篇 |
1982年 | 36篇 |
1981年 | 36篇 |
1980年 | 42篇 |
1979年 | 18篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1972年 | 4篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
作为太赫兹技术中的重要组成部分,太赫兹脉冲焦平面成像一经问世就引起了行业内的广泛关注,人们引入了各种方法去提升此成像技术的测量性能,同时也尝试将此成像技术应用于不同的工业和基础研究领域。本文综述了近年来人们对太赫兹脉冲焦平面成像的技术改良和应用研究,包括提升成像系统的空间分辨率、信噪比、信息获取能力,以及将此成像技术应用于光谱识别检测、超表面器件功能验证、太赫兹特殊光束测量、太赫兹表面波观测等,希望该综述能够推动太赫兹脉冲焦平面成像的进一步技术革新和应用拓展。 相似文献
2.
针对流体输送埋地管道泄漏问题,设计了一种利用管道机器人携带封堵气囊进行快速应急封堵修复的埋地管道泄漏内封堵装置。采用矩阵变换方法建立了牵引系统驱动轮过弯方程,利用MATLAB软件对过弯方程进行了验证,同时利用ADAMS软件仿真分析过弯路径与驱动轮转角对牵引系统行走速度的影响。研究结果表明:由两个串联封堵器组成的应急封堵系统可满足复杂工况下的管道泄漏封堵要求;牵引系统驱动轮在弯管内部行走时,单轮速度呈周期性变化,但三个驱动轮整体周期运动特性一致;驱动轮转角在25°~40°时,牵引系统行走速度与驱动轮转角成正比,且转角为30°时驱动效果最好。该内封堵装置的结构设计可为管道泄漏应急封堵领域装备的研发提供重要参考。 相似文献
3.
Ye Wan Jun Tan Guangling Song Chuanwei Yan 《Metallurgical and Materials Transactions A》2006,37(7):2313-2316
The focused ion beam technique was employed to investigate the atmospheric corrosion morphology of AZ91D. It was found that
the α matrix of the alloy was preferentially corroded in the areas adjacent to intermetallic phases. The most interesting
finding was that the corrosion products in corrosion cavities were pelletlike, which has never been reported before. 相似文献
4.
5.
管道风险管理方法研究 总被引:6,自引:0,他引:6
按照管道风险管理的流程分别对管道风险评价、风险控制和决策支持、效能测试和响应进行了论述。针对目前国内管道行业的情况,提出了进行管道风险评价的有效方法及维护措施。着重介绍了国外管道风险可接受标准的情况,作为国内制定管道风险评价标准的参考。 相似文献
6.
Qin Song Zou Xubiao Zhong Yan Zhang Zhongdong 《中国炼油与石油化工》2006,(1):31-35
1 Introduction Propylene as an important feedstock for organic chemicals is mainly originated from steam cracking and catalytic cracking processes. During the FCC process the propylene content varies with the FCC catalyst and process technology adopted, resulting in significant difference in propylene concentration in the cracked product——LPG. The conventional FCC pro- cess generally gives a propylene yield of around 4%, while the FCC process with maximization of propylene yield can in… 相似文献
7.
Chong D. Y. R. Lim B. K. Rebibis K. J. Pan S. J. Sivalingam K. Kapoor R. Sun A. Y. S. Tan H. B. 《Advanced Packaging, IEEE Transactions on》2006,29(4):674-682
The recent advancement in high- performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip ball grid array (BGA) package with high pin count and targeted reliability has emerged as a popular choice. The flip chip technology can accommodate an I/O count of more than five hundreds500, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. None the less, greater expectations on these high-performance packages arose such as better substrate real estate utilization for multiple chips, ease in handling for thinner core substrates, and improved board- level solder joint reliability. A new design of the flip chip BGA package has been looked into for meeting such requirements. By encapsulating the flip chip with molding compound leaving the die top exposed, a planar top surface can be formed. A, and a flat lid can then be mounted on the planar mold/die top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process development of the new package and its advantages for improved solder joint fatigue life, and being a multichip package and thin core substrate options. Finite-element simulations have been employed for the study of its structural integrity, thermal, and electrical performances. Detailed package and board-level reliability test results will also be reported 相似文献
8.
9.
By exploiting a general cyclostationary (CS) statistics-based framework, this letter develops a rigorous and unified asymptotic (large sample) performance analysis setup for a class of blind feedforward timing epoch estimators for linear modulations transmitted through time nonselective flat-fading channels. Within the proposed CS framework, it is shown that several estimators proposed in the literature can be asymptotically interpreted as maximum likelihood (ML) estimators applied on a (sub)set of the second- (and/or higher) order statistics of the received signal. The asymptotic variance of these ML estimators is established in closed-form expression and compared with the modified Crame/spl acute/r-Rao bound. It is shown that the timing estimator proposed by Oerder and Meyr achieves asymptotically the best performance in the class of estimators which exploit all the second-order statistics of the received signal, and its performance is insensitive to oversampling rates P as long as P/spl ges/3. Further, an asymptotically best consistent estimator, which achieves the lowest asymptotic variance among all the possible estimators that can be derived by exploiting jointly the second- and fourth-order statistics of the received signal, is also proposed. 相似文献
10.
燕善敏 《徐州工程学院学报》2003,(6)
行政法学的研究应该尽量放宽视角,适应将来法治建设的需要。我们必须把行政行为的概念放到整个法治体系中甚至整个社会的发展中去研究。 相似文献