全文获取类型
收费全文 | 389103篇 |
免费 | 30963篇 |
国内免费 | 17639篇 |
专业分类
电工技术 | 22999篇 |
技术理论 | 47篇 |
综合类 | 28268篇 |
化学工业 | 64524篇 |
金属工艺 | 22555篇 |
机械仪表 | 24490篇 |
建筑科学 | 30109篇 |
矿业工程 | 12863篇 |
能源动力 | 10642篇 |
轻工业 | 26477篇 |
水利工程 | 7426篇 |
石油天然气 | 24682篇 |
武器工业 | 3056篇 |
无线电 | 42419篇 |
一般工业技术 | 42991篇 |
冶金工业 | 20089篇 |
原子能技术 | 4006篇 |
自动化技术 | 50062篇 |
出版年
2024年 | 1574篇 |
2023年 | 6010篇 |
2022年 | 10709篇 |
2021年 | 15070篇 |
2020年 | 11339篇 |
2019年 | 9353篇 |
2018年 | 10721篇 |
2017年 | 12025篇 |
2016年 | 11048篇 |
2015年 | 15117篇 |
2014年 | 19019篇 |
2013年 | 22868篇 |
2012年 | 24790篇 |
2011年 | 27281篇 |
2010年 | 24283篇 |
2009年 | 22910篇 |
2008年 | 22481篇 |
2007年 | 21399篇 |
2006年 | 21739篇 |
2005年 | 19130篇 |
2004年 | 13089篇 |
2003年 | 12053篇 |
2002年 | 11721篇 |
2001年 | 10415篇 |
2000年 | 9720篇 |
1999年 | 10134篇 |
1998年 | 7655篇 |
1997年 | 6522篇 |
1996年 | 6138篇 |
1995年 | 5073篇 |
1994年 | 4128篇 |
1993年 | 2779篇 |
1992年 | 2223篇 |
1991年 | 1697篇 |
1990年 | 1313篇 |
1989年 | 1066篇 |
1988年 | 888篇 |
1987年 | 554篇 |
1986年 | 433篇 |
1985年 | 277篇 |
1984年 | 216篇 |
1983年 | 168篇 |
1982年 | 139篇 |
1981年 | 84篇 |
1980年 | 118篇 |
1979年 | 52篇 |
1978年 | 22篇 |
1977年 | 29篇 |
1976年 | 32篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection. 相似文献
22.
23.
Yung Ting Liang-Chiang Chen Chun-Chung Li Jeng-Lin Huang 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(4):847-853
A new type of piezoelectric linear motor incorporating a traveling wave has been developed. The linear motor is comprised of a stator and a carriage. The stator design, which consists of a meander-line structure and gear teeth mounted on the meander-line structure, is the focus of this article. The meander-line structure is constructed with bimorph actuators arranged in a line. These actuators are driven by two phased sets of alternating current (ac) in order to generate a traveling wave. The traveling wave is transferred to the gear teeth, by which the carriage is driven. Modeling of the stator is derived by use of a strain energy method. The performance of various materials is evaluated by analytical and experimental methods. The analytical and the experimental results are quite approximate. Modal analysis is investigated using ANSYS. Appropriate modes associated with ultrasonic levels of resonant frequency are selected to obtain desired motion and to enhance the output performance. Surface speed for various applied input voltage are studied and indicate a nearly linear relationship. The stator in combination with the carriage makes up the linear motor. 相似文献
24.
Qing Li 《Computer Standards & Interfaces》1991,13(1-3):99-103
The term ‘object-oriented database’ has been used to refer to different characteristics and mechanisms supported by semantic databases and (behaviorally) object-oriented ones. While this indicates the current confusion due to the lack of a common model, it also suggests the potential desirability of combining these two kinds of modeling facilities into the same nutshell. This paper summarizes from these two paradigms the features common to both, the features influenced/adopted by each other, and the features which are presented in one paradigm but missing from the other. After a brief analysis and discussion of these features, we conclude this paper by proposing our major theme: a complete object data model should take the union of the facilities offered by these two kinds of models. 相似文献
25.
26.
27.
报道了4,4′-硫代双[2-(1,1-二甲基乙基)-5一甲基苯酚]的合成方法及结构鉴定。 相似文献
28.
Sien Chi Jeng-Cherng Dung Senfar Wen 《Lightwave Technology, Journal of》1995,13(6):1121-1126
The maximum bit rate of a soliton communication system with lumped amplifiers and optical filters is considered. When the dispersion of the fiber varies from one amplifier spacing to another amplifier spacing, the maximum bit rate is significantly reduced. To overcome the effect, the amplitude of the soliton is amplified so that it is still the average soliton corresponding to the fiber dispersion for an amplifier spacing. Thus, the maximum bit rate is only slightly less than that without the dispersion variations. For a given distance, the maximum bit rate limited by the stability and soliton interaction is obtained. The result is compared with that limited by the Gordon-Haus effect. For shorter transmission distance, the maximum bit rate is limited by the stability and soliton interaction. For longer transmission distance, the maximum bit rate is limited by the Gordon-Haus effect 相似文献
29.
30.
Li Pen Yuan 《Quantum Electronics, IEEE Journal of》1993,29(1):171-174
Two coupled-mode theories based on individual waveguide modes and compound system modes, respectively, are briefly reviewed with proper modification and new comments. The relation between these two theories is built and it is found that one theory is actually an efficient approximation of the other. Also, the reason why the results obtained with the first more accurate than those obtained with the second is found. The constraint on both approaches is shown 相似文献