全文获取类型
收费全文 | 29142篇 |
免费 | 1295篇 |
国内免费 | 111篇 |
专业分类
电工技术 | 378篇 |
综合类 | 228篇 |
化学工业 | 5172篇 |
金属工艺 | 646篇 |
机械仪表 | 613篇 |
建筑科学 | 1003篇 |
矿业工程 | 94篇 |
能源动力 | 955篇 |
轻工业 | 4036篇 |
水利工程 | 254篇 |
石油天然气 | 157篇 |
武器工业 | 6篇 |
无线电 | 2347篇 |
一般工业技术 | 4224篇 |
冶金工业 | 6355篇 |
原子能技术 | 240篇 |
自动化技术 | 3840篇 |
出版年
2023年 | 145篇 |
2022年 | 424篇 |
2021年 | 827篇 |
2020年 | 548篇 |
2019年 | 629篇 |
2018年 | 719篇 |
2017年 | 803篇 |
2016年 | 765篇 |
2015年 | 583篇 |
2014年 | 895篇 |
2013年 | 1485篇 |
2012年 | 1319篇 |
2011年 | 1650篇 |
2010年 | 1202篇 |
2009年 | 1254篇 |
2008年 | 1138篇 |
2007年 | 1001篇 |
2006年 | 808篇 |
2005年 | 856篇 |
2004年 | 920篇 |
2003年 | 822篇 |
2002年 | 806篇 |
2001年 | 702篇 |
2000年 | 551篇 |
1999年 | 545篇 |
1998年 | 2066篇 |
1997年 | 1347篇 |
1996年 | 938篇 |
1995年 | 613篇 |
1994年 | 478篇 |
1993年 | 537篇 |
1992年 | 221篇 |
1991年 | 285篇 |
1990年 | 227篇 |
1989年 | 193篇 |
1988年 | 212篇 |
1987年 | 159篇 |
1986年 | 166篇 |
1985年 | 180篇 |
1984年 | 128篇 |
1983年 | 91篇 |
1982年 | 117篇 |
1981年 | 120篇 |
1980年 | 115篇 |
1979年 | 91篇 |
1978年 | 75篇 |
1977年 | 140篇 |
1976年 | 227篇 |
1975年 | 82篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
de Graaf G. Wolffenbuttel R.F. 《IEEE transactions on instrumentation and measurement》2004,53(2):238-242
An integrated silicon color sensor system has been designed and fabricated in CMOS without extra masks for color filtering. The application is in low-cost measurement of ambient light conditions, e.g., for display control in portable instruments, or for testing the intensity and spectral distribution of light sources. Signals proportional to the intensity and the spectral distribution of the incident light are available at the output in the form of two bit-streams. It is demonstrated that daylight can be distinguished from other light sources, such as incandescent lamps and fluorescent lamps. 相似文献
992.
Rodriguez-Mendez M.L. Arrieta A.A. Parra V. Bernal A. Vegas A. Villanueva S. Gutierrez-Osuna R. de Saja J.A. 《IEEE sensors journal》2004,4(3):348-354
This work represents the first attempt to develop a sensory system, specifically designed for the characterization of wines, which combines three sensory modalities: an array of gas sensors, an array of electrochemical liquid sensors, and an optical system to measure color by means of CIElab coordinates. This new analytical tool, that has been called "electronic panel," includes not only sensors, but also hardware (injection system and electronics) and the software necessary for fusing information from the three modules. Each of the three sensory modalities (volatiles, liquids, and color) has been designed, tested, and optimized separately. The discrimination capabilities of the system have been evaluated on a database consisting of six red Spanish wines prepared using the same variety of grape (tempranillo) but differing in their geographic origins and aging stages. Sensor signals from each module have been combined and analyzed using pattern recognition techniques. The results of this work show that the discrimination capabilities of the system are significantly improved when signals from each module are combined to form a multimodal feature vector. 相似文献
993.
A reconfigurable high-frequency phase-locked loop 总被引:4,自引:0,他引:4
Reconfigurable phase-locked loops (PLLs) present the advantage of fast-frequency acquisition combined with narrow-noise bandwidth, since their parameters can be dynamically adjusted. High-frequency PLLs are generally implemented by means of analog circuits which are not easily reconfigured during operation. However, the five-port technique allows the discrimination of the phase difference between two microwave signals using a mixed circuit. In this paper the design of a PLL comprising a five-port based phase detector is presented. This system benefits from the phase-detector digital circuit to carry out the loop filtering. Simulation results for different conditions of noise and frequency acquisition are shown. We also present measurement results to confirm the simulations. 相似文献
994.
995.
Bond Between Near-Surface Mounted Carbon-Fiber-Reinforced Polymer Laminate Strips and Concrete 总被引:1,自引:0,他引:1
José Manuel de Sena Cruz Joaquim António Oliveira de Barros 《Canadian Metallurgical Quarterly》2004,8(6):519-527
In recent years, a strengthening technique based on near-surface mounted (NSM) laminate strips of carbon-fiber-reinforced polymer (CFRP) has been used to increase the load-carrying capacity of concrete and masonry structures by introducing laminate strips into precut grooves on the concrete cover of the elements to be strengthened. The high experimentally derived levels of strength efficacy with concrete columns, beams, and masonry panels have presented NSM as a viable and promising technique. This practice requires no surface preparation work and, after cutting the groove, requires minimal installation time compared to the externally bonded reinforcing technique. A further advantage associated with NSM CFRP is its ability to significantly reduce the probability of harm resulting from fire, acts of vandalism, mechanical damage, and aging effects. To assess the bond behavior of CFRP to concrete, pullout-bending tests have been carried out. The influences of bond length and concrete strength on bond behavior are analyzed, the tests are described, and the results are presented and discussed in detail. Finally, a local stress-slip relationship is determined based on both experimental results and a numerical strategy. 相似文献
996.
Celso M. F. Lapa Paulo A. B. de Sampaio Cludio M. N. A. Pereira 《Nuclear Engineering and Design》2004,229(2-3):205-212
Reduced scale experiments are often employed in engineering because they are much cheaper than real scale testing. Unfortunately, though, it is difficult to design a thermal-hydraulic circuit or equipment in reduced scale capable of reproducing, both accurately and simultaneously, all the physical phenomena that occur in real scale and operating conditions. This paper presents a methodology to designing thermal-hydraulic experiments in reduced scale based on setting up a constrained optimization problem that is solved using genetic algorithms (GAs). In order to demonstrate the application of the methodology proposed, we performed some investigations in the design of a heater aimed to simulate the transport of heat and momentum in the core of a pressurized water reactor (PWR) at 100% of nominal power and non-accident operating conditions. The results obtained show that the proposed methodology is a promising approach for designing reduced scale experiments. 相似文献
997.
Software engineers of multi‐agent systems (MASs) are faced with different concerns such as autonomy, adaptation, interaction, collaboration, learning, and mobility, which are essentially different from classical concerns addressed in object‐oriented software engineering. MAS developers, however, have relied mostly on object‐oriented design techniques and programming languages, such as Java. This often leads to a poor separation of MAS concerns and in turn to the production of MASs that are difficult to maintain and reuse. This paper discusses software engineering approaches for MASs, and presents a new method for integrating agents into object‐oriented software engineering from an early stage of design. The proposed approach encourages the separate handling of MAS concerns, and provides a disciplined scheme for their composition. Our proposal explores the benefits of aspect‐oriented software development for the incorporation of agents into object‐oriented systems. We also illustrate our aspect‐oriented approach through the Portalware multi‐agent system, a Web‐based environment for the development of e‐commerce portals. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
998.
Müller MC Belei P de la Fuente M Strake M Kabir K Weber O Radermacher K Wirtz DC 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2011,225(5):477-486
Pertrochanteric femoral fractures are common and intramedullary nailing is an accepted method for their surgical treatment. Accurate placement of the implant is essential to ensure fixation. The conventional technique can require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on two-dimensional fluoroscopy for guide wire placement in the femoral neck has been developed, in order to perform intramedullary pertrochanteric fracture fixation using the proximal femoral nail (PFNA). The planning process was supported by a 'zero-dose C-arm navigation' system. The PFNA was inserted into 12, intact, femoral sawbones guided by the computer-based navigation, and into 12, intact, femoral sawbones using a conventional fluoroscopic-assisted technique. Guide wire and subsequent blade placement in the femoral neck was evaluated. The computer-assisted technique achieved a significant decrease in the number of required fluoroscopic images and in the number of guide wire passes. The obtained average blade placement accuracy in the femoral neck was equivalent to the conventional technique. The operation time was significantly longer in the navigation-assisted group. The addition of computer-assisted planning and surgical guidance to the intramedullary nailing of pertrochanteric femoral fractures offers a number of clinical benefits based on the results of this sawbone study. Further studies including fractured sawbones and cadaver models with extension of the navigation process to all steps of PFNA introduction and with the goal of reducing operation time are indispensable before integration of this navigation system into clinical practice. 相似文献
999.
Pastor JF Barbosa M de Paz FJ García M Ferrero E 《Microscopy research and technique》2011,74(10):910-919
The eight current species of bear (Ursidae) are widely distributed throughout Europe, Asia, and America. They are mainly encountered in the northern hemisphere, except for the spectacled bear and the sun bear, which are also found in the south of the equator. Adaptations of the masticatory apparatus (teeth, tongue, and musculature) to diet are one of the factors that imply the greatest structural changes in the cranium. This diet may be carnivorous, herbivorous, melliferous, or insectivorous, with one type of food predominating according to the time of year. The way in which food is eaten determines the morphology of the lingual surface; generally speaking, all bears put their mouth to the food, which, initially, they lick or they let the food stick to their tongue, as occurs when insects are eaten. As in all mammals, a distinction can be made between mechanical and gustatory papillae and the development and distribution of which depend on the species and their eating habits. In this study of the complete tongues of four species of adult bears, we describe the morphology of the lingual surfaces, the different types of papillae, their characteristics, and topographic distribution. It was seen that there were five main types of lingual papillae: filiform, conical, fungiform, foliate, and vallate. Morphology of the microgrooves and pores was similar to that observed in other mammals. In general, there were no great differences among the four species of bears studied, perhaps due to the similarity in the kind of food they consume in captivity. 相似文献
1000.
椭球封头圆柱形爆炸容器振动特性研究 总被引:2,自引:1,他引:2
对椭球封头圆柱形爆炸容器在中心点爆炸状态下的 19次有效炮实验给予了介绍并对实验结果的壳体振动特性进行了分析。理论和实验分析表明 ,在封闭容器内爆炸冲击载荷具有明显的脉冲激励特征 ;容器壳体的振动频谱主要受前 10阶固有频率的影响 ;随着冲击载荷的增加 ,其壳体的主振频率将趋于相应壳体的呼吸频率 ,其应变增长具有减少的趋势 ;联接螺栓的振动模态主要受相应圆柱壳体和封头轴向振动模态的影响 ,并出现了在时域上其振动模态在圆柱壳振动模态和封头轴向振动模态间跳变的现象。 相似文献