全文获取类型
收费全文 | 183616篇 |
免费 | 18241篇 |
国内免费 | 10350篇 |
专业分类
电工技术 | 15065篇 |
技术理论 | 8篇 |
综合类 | 18846篇 |
化学工业 | 19249篇 |
金属工艺 | 7534篇 |
机械仪表 | 16621篇 |
建筑科学 | 20439篇 |
矿业工程 | 6820篇 |
能源动力 | 8417篇 |
轻工业 | 12913篇 |
水利工程 | 7612篇 |
石油天然气 | 8646篇 |
武器工业 | 2331篇 |
无线电 | 11102篇 |
一般工业技术 | 17972篇 |
冶金工业 | 6928篇 |
原子能技术 | 2603篇 |
自动化技术 | 29101篇 |
出版年
2024年 | 655篇 |
2023年 | 2226篇 |
2022年 | 4582篇 |
2021年 | 5486篇 |
2020年 | 5691篇 |
2019年 | 4788篇 |
2018年 | 4618篇 |
2017年 | 5734篇 |
2016年 | 6895篇 |
2015年 | 7299篇 |
2014年 | 11744篇 |
2013年 | 11879篇 |
2012年 | 13797篇 |
2011年 | 15247篇 |
2010年 | 10909篇 |
2009年 | 11165篇 |
2008年 | 10394篇 |
2007年 | 12478篇 |
2006年 | 10804篇 |
2005年 | 9049篇 |
2004年 | 7634篇 |
2003年 | 6569篇 |
2002年 | 5322篇 |
2001年 | 4352篇 |
2000年 | 3760篇 |
1999年 | 3098篇 |
1998年 | 2685篇 |
1997年 | 2259篇 |
1996年 | 1866篇 |
1995年 | 1531篇 |
1994年 | 1389篇 |
1993年 | 1015篇 |
1992年 | 959篇 |
1991年 | 697篇 |
1990年 | 584篇 |
1989年 | 498篇 |
1988年 | 408篇 |
1987年 | 286篇 |
1986年 | 241篇 |
1985年 | 227篇 |
1984年 | 271篇 |
1983年 | 251篇 |
1982年 | 207篇 |
1981年 | 101篇 |
1980年 | 96篇 |
1979年 | 66篇 |
1978年 | 55篇 |
1977年 | 48篇 |
1976年 | 43篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
991.
无源软开关电路拓扑的研究 总被引:1,自引:0,他引:1
提出一个研究无源软开关电路的新技术方法;其特征是对基本的单管隔离型PWM DC/DC变换器进行类比分析,由此直接导出可行的缓冲能量再生复位电路.该新方法能使DC/DC PWM硬开关变换器转变为软开关变换器.以新型Boost无源软开关变换器为例,进行了电路理论分析与中功率样机的实验测试;结果表明此新变换器具有较宽的软开关工作范围、较低的电应力、较小的缓冲元件量值等特点.由此认为,这种研究方法推导简单、物理意义清晰,还能深入地研究无源软开关的新电路拓扑. 相似文献
992.
在对比分析了传统辅助水刹车与气控盘式辅助刹车的特性后,重点对气控盘式辅助刹车进行了数学分析,得到了该辅助刹车的制动扭矩取决于施加的气体压力,与钻具质量无关,冷却液的流量应同钻柱质量保持正比关系,可精确控制下钻速度并易于实现自动送钻功能。得出了气控盘式辅助刹车更适用于车载钻机的结论。 相似文献
993.
三峡蓄水初期水库近坝区水环境特性分析 总被引:3,自引:0,他引:3
通过现场观测和数值模拟的方法,对三峡水库近坝区在蓄水初期的水流和水环境特性进行了
分析。对蓄水初期的溶解氧、BOD、COD和NH3-N、Cu等水质参数进行了观测,将蓄水初期水质资料与蓄水之前的结果进行了对比,分析了近坝区水环境变化趋势。采用大涡模拟紊流模型,考虑水体表面的热交换,对三峡近坝区的流动和水温分布特性进行了模拟。研究结果表明,三峡水库蓄水初期近坝区水流特性明显改变,主要表现为水深增加、流速变缓,部分地段有回流区出现。水质指标变化不明显,坝前断面溶解氧浓度、悬浮物浓度有所降低,和悬浮物密切相关的污染物总磷、重金属也随之降低;蓄水初期139m水位时坝前水域尚没有出现温度分层现象。 相似文献
994.
Numerical simulations of acoustic scattering in the frequency domain based on hybrid methods coupling finite elements and boundary elements are the most suited for dealing with problems involving wave propagation in inhomogeneous media. Furthermore, it is necessary to resort to high performance computing to effectively solve the large size problems. However, the direct coupling yields a linear system with a matrix which is partly dense and partly sparse and thus not adapted to high performance computing. To avoid this difficulty, we present a new iterative method constructed from a non overlapping domain decomposition technique. 相似文献
995.
Xu Qianjun Li Xu Chen Zuyu 《Frontiers of Architecture and Civil Engineering in China》2007,1(2):217-221
It is usually difficult to determine the actual safety factors of rock masses in an ordinary two-dimensional stability analysis
if the safety factors of the different cross sections in the rock mass vary significantly. In addition to the actual slope,
arch dam abutment, and the actual foundation of a high building, another example is that the different cross sections of the
foundation in the monolith of a gravity dam vary significantly, just like the condition at the overflow dam in the Baise project.
A three-dimensional stability analysis method based on the upper-bound theorem was employed to solve this problem. The parameters
used in the analysis were obtained from geomechanics tests, as well as continuity simulations of the randomly distributed
joints. Two failure patterns against sliding are analyzed. One pattern is the foundation slide along deep-seated planes which
were determined by calculations. The other pattern is the foundation slide along the planes across the bottom of the high
steps in the foundation pit. The results indicate that a special overflow dam monolith can be considered to be safe in case
of considering the three dimensional effect. However, a key wall with a depth of 5m must be constructed at the upper side
of this monolith in order to ensure the safety of the foundation.
Translated from Chinese Journal of Rock Mechanics and Engineering, 2006, 25(3): 533–538 [译自: 岩土力学与工程学报] 相似文献
996.
Yvon Maday Frédéric Magoulès 《Computer Methods in Applied Mechanics and Engineering》2007,196(8):1541-1553
In this paper an original variant of the Schwarz domain decomposition method is introduced for heterogeneous media. This method uses new optimized interface conditions specially designed to take into account the heterogeneity between the sub-domains on each sides of the interfaces. Numerical experiments illustrate the dependency of the proposed method with respect to several parameters, and confirm the robustness and efficiency of this method based on such optimized interface conditions. Several mesh partitions taking into account multiple cross points are considered in these experiments. 相似文献
997.
A method of processing complex signals in passive multi-element antenna arrays based on an analysis of the natural values of the correlation matrix of the signal is considered. By means of the method it is possible to substantially increase the output signal-to-noise ratio. An iterational process by means of which optimal estimators of both the signal and the amplitude-phase distribution may be obtained, is proposed. Theoretical estimators of the efficiency of the method are given. It is proved that, in terms of the efficiency, the approach considered in the article comes close to the technique of matched filtration. Results of statistical modeling that confirm the statistical results are presented. 相似文献
998.
B. E. Rytsar 《Cybernetics and Systems Analysis》2007,43(2):192-207
The paper considers the set-theoretical approach to the joint decomposition of systems of Boolean functions of variables specified
in different representation forms. The approach is based on the method of q-partitions of conjuncterms and concept of decomposition
clones. Theorems on joint decomposition of a system of full and partial functions are formulated. The approach is illustrated
by examples.
Parts I and II of this article are published in No. 5 (2001) and No. 1 (2002).
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 39–58, March–April 2007. 相似文献
999.
赵波 《水资源与水工程学报》2006,17(5):58-60
塌方是隧洞施工过程中经常遇到的难题,本文针对引红济石工程1#支洞在施工过程中出现的两次塌方原因进行分析,总结出隧洞施工过程中避免塌方的主要方法和策略,具有普遍的借鉴意义。 相似文献
1000.
S. Kumar Author Vitae Author Vitae S. Ranganath Author Vitae Author Vitae F.T. Chew Author Vitae 《Pattern recognition》2006,39(6):1088-1098
This paper presents a robust rule-based approach for the splitting of binary clumps that are formed by objects of diverse shapes and sizes. First, the deepest boundary pixels, i.e., the concavity pixels in a clump, are detected using a fast and accurate scheme. Next, concavity-based rules are applied to generate the candidate split lines that join pairs of concavity pixels. A figure of merit is used to determine the best split line from the set of candidate lines. Experimental results show that the proposed approach is robust and accurate. 相似文献