全文获取类型
收费全文 | 25079篇 |
免费 | 2545篇 |
国内免费 | 1413篇 |
专业分类
电工技术 | 1689篇 |
技术理论 | 2篇 |
综合类 | 2696篇 |
化学工业 | 2486篇 |
金属工艺 | 390篇 |
机械仪表 | 1062篇 |
建筑科学 | 2677篇 |
矿业工程 | 1599篇 |
能源动力 | 914篇 |
轻工业 | 2215篇 |
水利工程 | 1647篇 |
石油天然气 | 1608篇 |
武器工业 | 255篇 |
无线电 | 1870篇 |
一般工业技术 | 2621篇 |
冶金工业 | 913篇 |
原子能技术 | 355篇 |
自动化技术 | 4038篇 |
出版年
2024年 | 85篇 |
2023年 | 311篇 |
2022年 | 760篇 |
2021年 | 772篇 |
2020年 | 816篇 |
2019年 | 701篇 |
2018年 | 687篇 |
2017年 | 828篇 |
2016年 | 1033篇 |
2015年 | 1022篇 |
2014年 | 1629篇 |
2013年 | 1682篇 |
2012年 | 1835篇 |
2011年 | 2074篇 |
2010年 | 1569篇 |
2009年 | 1472篇 |
2008年 | 1428篇 |
2007年 | 1642篇 |
2006年 | 1467篇 |
2005年 | 1279篇 |
2004年 | 1043篇 |
2003年 | 898篇 |
2002年 | 700篇 |
2001年 | 562篇 |
2000年 | 483篇 |
1999年 | 456篇 |
1998年 | 321篇 |
1997年 | 283篇 |
1996年 | 234篇 |
1995年 | 203篇 |
1994年 | 179篇 |
1993年 | 125篇 |
1992年 | 80篇 |
1991年 | 79篇 |
1990年 | 69篇 |
1989年 | 53篇 |
1988年 | 44篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 19篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1961年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
漏斗贮料压力计算公式 总被引:2,自引:0,他引:2
本文从平衡条件和常系数假定出发,建立贮料压力微分方程,导出了正倒锥漏斗、倒锥漏斗贮料压力计算公式。文中说明,圆柱仓筒贮料压力微分方程为上述方程的特殊情形。本文成果可供筒仓工程设计使用,还可供确定斗口给料机贮料荷载参考。 相似文献
62.
Attempts have been made to extend SQL to work with multimedia databases. We are reserved on the representation ability of extended SQL to cope with the richness in content of multimedia data. In this paper we present an example of a multimedia database system, Computer Aided Facial Image Inference and Retrieval system (CAFIIR). The system stores and manages facial images and criminal records, providing necessary functions for crime identification. We would like to demonstrate some core techniques for multimedia database with CAFIIR system. Firstly, CAFIIR is a integrated system. Besides database management, there are image analysis, image composition, image aging, and report generation subsystems, providing means for problem solving. Secondly, the richness of multimedia data urges feature-based database for their management. CAFIIR is feature-based. A indexing mechanism,iconic index, has been proposed for indexing facial images using hierarchical self-organization neural network. The indexing method operates on complex feature measures and provides means for visual navigation. Thirdly, special retrieval methods for facial images have been developed, including visual browsing, similarity retrieval, free text retrieval and fuzzy retrieval. 相似文献
63.
The MSMIE protocol [SBC89] allows processors in a distributed system to communicate via shared memory. It was designed to meet the reliability and efficiency needs of applications such as nuclear safety systems. We present a formal model of the MSMIE protocol expressed in the notation CCS. Desirable properties of the protocol are expressed in the modal mu-calculus, an expressive modal logic. We show that the protocol lacks an important liveness property. In actual operation, additional operating constraints are checked to avoid potential problems. We present a modified protocol and show that it possesses the liveness property even without checking operating constraints. We also show how parts of the analysis were automated with the Concurrency Workbench. 相似文献
64.
通过引入归一化脉宽P和相对脉冲展宽因子q,提出了一个适用于IM/DD系统中各种眼图恶化量x和归一化脉宽P的色散限制改进公式。通过与其它理论的比较、计算机仿真和对实验数据的分析,验证了该公式的正确性,并给出了其它结果的限制条件。研究表明:当眼图恶化量x为1dB左右时,对2.5Gb/;外调制信号(α=0)而言,非色散位移光纤IM/DD系统的色散因子γ约等于0.79,所对应的系统再生中继距离约为900余公里。 相似文献
65.
Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors. 相似文献
66.
67.
68.
适时地选择和培育符合经济发展阶段要求的主导产业,对一个地区的发展具有重要的战略意义。采用层次分析法(AHP法)进行工业主导产业选择可以取得比较好的效果。从评价指标的选择、调查表格的设计及统计整理等方面对采用AHP法进行主导产业的选择进行了探讨,并以娄底市为例进行了论证。 相似文献
69.
针对当前国内长途传输光缆系统在扩容过程中,因光信号色散而影响传输质量的现象,结合实际工程建设,分析了光信号色散的危害及其成因,并提出了相应的解决办法及建议。 相似文献
70.
A practical approach to develop a more realistic fault-tree model with a consideration of various conditions endured by a human operator is proposed. In safety-critical systems, the generation failure of an actuation signal is caused by the concurrent failures of the automated systems and an operator action. These two sources of safety signals are complicatedly correlated. The failures of sensors or automated systems will cause a lack of necessary information for a human operator and result in error-forcing contexts such as the loss of corresponding alarms and indications. It is well known that the error-forcing contexts largely affect the operator's performance. An automated system which consists of multiple processing channels and complex components is also affected by the availability of the sensors. This paper proposes a condition-based human reliability assessment (CBHRA) method in order to address these complicated conditions in a practical way. We apply the CBHRA method to the manual actuation of the safety features such as a reactor trip and auxiliary feedwater actuation in Korean Standard Nuclear Power Plants. Even the human error probability of each given condition is simply assumed, the application results prove that the CBHRA effectively accommodates the complicated error-forcing contexts into the fault trees. 相似文献