全文获取类型
收费全文 | 601877篇 |
免费 | 7197篇 |
国内免费 | 1972篇 |
专业分类
电工技术 | 11362篇 |
综合类 | 625篇 |
化学工业 | 88521篇 |
金属工艺 | 23878篇 |
机械仪表 | 19512篇 |
建筑科学 | 13379篇 |
矿业工程 | 2980篇 |
能源动力 | 16284篇 |
轻工业 | 45983篇 |
水利工程 | 6187篇 |
石油天然气 | 10602篇 |
武器工业 | 80篇 |
无线电 | 74611篇 |
一般工业技术 | 119515篇 |
冶金工业 | 112740篇 |
原子能技术 | 12854篇 |
自动化技术 | 51933篇 |
出版年
2021年 | 5301篇 |
2020年 | 4024篇 |
2019年 | 5142篇 |
2018年 | 8777篇 |
2017年 | 8855篇 |
2016年 | 9420篇 |
2015年 | 5992篇 |
2014年 | 9935篇 |
2013年 | 28416篇 |
2012年 | 15971篇 |
2011年 | 21702篇 |
2010年 | 17274篇 |
2009年 | 19502篇 |
2008年 | 20319篇 |
2007年 | 20072篇 |
2006年 | 18074篇 |
2005年 | 16209篇 |
2004年 | 15496篇 |
2003年 | 15408篇 |
2002年 | 14582篇 |
2001年 | 14444篇 |
2000年 | 13703篇 |
1999年 | 14285篇 |
1998年 | 35397篇 |
1997年 | 24674篇 |
1996年 | 19213篇 |
1995年 | 14509篇 |
1994年 | 12825篇 |
1993年 | 12807篇 |
1992年 | 9572篇 |
1991年 | 8992篇 |
1990年 | 8811篇 |
1989年 | 8299篇 |
1988年 | 7961篇 |
1987年 | 7020篇 |
1986年 | 6851篇 |
1985年 | 7771篇 |
1984年 | 7162篇 |
1983年 | 6438篇 |
1982年 | 5995篇 |
1981年 | 6159篇 |
1980年 | 5731篇 |
1979年 | 5546篇 |
1978年 | 5395篇 |
1977年 | 6250篇 |
1976年 | 7897篇 |
1975年 | 4794篇 |
1974年 | 4616篇 |
1973年 | 4673篇 |
1972年 | 3818篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
91.
92.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
93.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
94.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献
95.
Thirty patients who had undergone either a right or left unilateral temporal lobectomy (14 RTL; 16 LTL) and 16 control participants were tested on a computerized human analogue of the Morris Water Maze. The procedure was designed to compare allocentric and egocentric spatial memory. In the allocentric condition, participants searched for a target location on the screen, guided by object cues. Between trials, participants had to walk around the screen, which disrupted egocentric memory representation. In the egocentric condition, participants remained in the same position, but the object cues were shifted between searches to prevent them from using allocentric memory. Only the RTL group was impaired on the allocentric condition, and neither the LTL nor RTL group was impaired on additional tests of spatial working memory or spatial manipulation. The results support the notion that the right anterior temporal lobe stores long-term allocentric spatial memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
97.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type. 相似文献
98.
99.
A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both the flexibility of clock networks and the relationships between various desirable properties such as robust entrainment, temperature compensation, and stability to environmental variations and parameter fluctuations. We use this to argue that the complexity provides the flexibility necessary to simultaneously attain multiple key properties of circadian clocks. As part of our analysis we show how to quantify the key evolutionary aims using infinitesimal response curves, a tool that we believe will be of general utility in the analysis of regulatory networks. Our results suggest that regulatory and signalling networks might be much less flexible and of lower dimension than their apparent complexity would suggest. 相似文献
100.
Demiguel S. Giraudet L. Joulaud L. Decobert J. Blache F. Coupe V. Jorge F. Pagnod-Rossiaux P. Boucherez E. Achouche M. Devaux F. 《Lightwave Technology, Journal of》2002,20(12):2004-2014
The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes. 相似文献