全文获取类型
收费全文 | 266788篇 |
免费 | 3847篇 |
国内免费 | 833篇 |
专业分类
电工技术 | 5192篇 |
综合类 | 347篇 |
化学工业 | 38920篇 |
金属工艺 | 10414篇 |
机械仪表 | 8613篇 |
建筑科学 | 6400篇 |
矿业工程 | 1100篇 |
能源动力 | 6605篇 |
轻工业 | 23493篇 |
水利工程 | 2655篇 |
石油天然气 | 3928篇 |
武器工业 | 68篇 |
无线电 | 35149篇 |
一般工业技术 | 51529篇 |
冶金工业 | 47556篇 |
原子能技术 | 5436篇 |
自动化技术 | 24063篇 |
出版年
2021年 | 2219篇 |
2019年 | 2207篇 |
2018年 | 3655篇 |
2017年 | 3716篇 |
2016年 | 3953篇 |
2015年 | 2494篇 |
2014年 | 4338篇 |
2013年 | 11801篇 |
2012年 | 6968篇 |
2011年 | 9461篇 |
2010年 | 7387篇 |
2009年 | 8229篇 |
2008年 | 9102篇 |
2007年 | 9000篇 |
2006年 | 8121篇 |
2005年 | 7424篇 |
2004年 | 7118篇 |
2003年 | 6951篇 |
2002年 | 6573篇 |
2001年 | 6568篇 |
2000年 | 6260篇 |
1999年 | 6344篇 |
1998年 | 14323篇 |
1997年 | 10352篇 |
1996年 | 8176篇 |
1995年 | 6481篇 |
1994年 | 5777篇 |
1993年 | 5632篇 |
1992年 | 4611篇 |
1991年 | 4235篇 |
1990年 | 4075篇 |
1989年 | 3817篇 |
1988年 | 3662篇 |
1987年 | 3204篇 |
1986年 | 3097篇 |
1985年 | 3655篇 |
1984年 | 3423篇 |
1983年 | 3067篇 |
1982年 | 2887篇 |
1981年 | 2975篇 |
1980年 | 2786篇 |
1979年 | 2667篇 |
1978年 | 2520篇 |
1977年 | 2960篇 |
1976年 | 3572篇 |
1975年 | 2327篇 |
1974年 | 2320篇 |
1973年 | 2324篇 |
1972年 | 1854篇 |
1971年 | 1748篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
D G Kindack A MacIntosh M Lebelle G Carignan S Sved 《Food Additives & Contaminants》1991,8(6):737-748
During surveillance of hog carcasses from Manitoba for antibiotic residues by the Health of Animals Laboratory, Agriculture Canada, Saskatoon, an unknown substance was found which produced tetracycline-like results with the methods used. This same substance was found in an implicated swine feed premix. Using various HPLC systems and columns, UV spectroscopy, reverse-phase TLC, and mass spectrometry, the substance was isolated from the feed premix, and identified as lumichrome, a photodegradation product of riboflavin. Traces of the same substance were found in riboflavin standard. Analysis of swine kidney, previously found to contain the unknown, showed the same substance was present at a level of about 1 ppm. 相似文献
972.
A Statistical Method for Reconfiguration of Cognitive Radios 总被引:2,自引:0,他引:2
Recent developments in computer technology have enabled radio developers to accomplish in software what traditionally was performed with application-specific integrated circuits. A radio that has the core of its functionality implemented in software is called a software-defined radio. When an SDR has the capability to sense, reason, and dynamically adapt to requirements and environmental change, we call this more capable device a cognitive radio. Many private and public agencies are investing in the promise of CR to improve the utilization of radio frequency spectrum. They envision devices that can sense frequency vacancies and dynamically reconfigure to utilize idle channels. The promise of CR depends on the capability of a radio to change operating frequencies, power, and/or modulation schemes (physical layer flexibility). In addition to this physical layer flexibility, there are a large number of opportunities to capitalize on the interplay of the CR physical layer configuration and other parameters in the radio network protocol stack. At the core of CR functionality is the ability to select from thousands of potential configurations to maximize performance-be it in terms of spectrum use, throughput, or reliability. In this article, we describe a method for selecting from a number of potential configurations to fulfill the communication requirements of a CR network. By using accepted statistical methods, we show how parameters at the physical, data link, network, and application layers interact to affect performance. We build upon this parametric insight with our presentation of a technique for predicting radio performance. 相似文献
973.
I. Ya. Braslavskii A. V. Kostylev D. V. Mezeusheva 《Russian Electrical Engineering》2007,78(11):603-606
The use of prognostic control methods in the digital systems controlling asynchronous electric drives are considered. The methodology for synthesizing predictors on the basis of neural networks is explained. An example of the synthesis of a numeral predictor for a closed control loop is considered. 相似文献
974.
The objective, strategy, and implementation details of a new undergraduate course, Internet-based Instrumentation and Control, are presented. The course has a companion laboratory that is supported by the National Science Foundation and industry. The combination is offered to senior-level undergraduate engineering students interested in sensing, instrumentation, control, and web programming that want to learn more about the integration of these technologies for solving real-world engineering problems. The course will also be offered to gifted high school seniors with similar interests and can serve as a vehicle to attract them to engineering disciplines. Preliminary assessment of the first offering of the course is encouraging and has shown that the course has achieved success in helping students understand concepts and master basic technologies for developing Internet-based automatic systems. 相似文献
975.
The viscometric, turbidimetric and potentiometric properties of copolymers of acrylamide (AM) with 2-acrylamido-2-methylpropanedimethylammonium chloride (AMPDAC) were studied in aqueous solutions. The AMPDAC polymers exhibit poor salt tolerance and large, negative viscosity/temperature coefficients. Furthermore, the polymers were found to be sensitive to changes in pH. The AMPDAC polymers undergo phase separation in the presence of dianions as a function of temperature and AMPDAC composition. 相似文献
976.
Scattering from bandlimited fractal fibers 总被引:2,自引:0,他引:2
The scattering of electromagnetic or optical waves from tenuous dielectric fibers characterized by bandlimited fractal surfaces is considered. The role of several fractal dimensions is noted, and one suitable for this problem is identified. It is found that in the fractal regime, the Rayleigh-Gans differential scattering cross section as a function of the normalized size parameter exhibits a power-law relation reminiscent of that associated with light scattering from fractal clusters and small-angle X-ray and neutron scattering by porous material. This power-law relation is monotonically related to an appropriate fractal dimension and variance of the fiber surface 相似文献
977.
978.
Electric-discharge cleaning of surfaces of manufacturing equipment from foreign nonmetallic deposits
T. D. Denisyuk A. R. Rizun Yu. V. Golen’ 《Surface Engineering and Applied Electrochemistry》2007,43(6):453-454
Processing characteristics of the electric-discharge cleaning of surfaces of manufacturing equipment from foreign nonmetallic deposits of different durability are researched. To expand the capabilities of the cleaning of manufacturing equipment, a complex cleaning method is proposed. 相似文献
979.
A. A. Nechitaĭlov T. K. Zvonareva A. D. Remenyuk V. A. Tolmachev D. N. Goryachev O. S. El’tsina L. V. Belyakov O. M. Sreseli 《Semiconductors》2008,42(10):1249-1254
Catalytic properties of composite amorphous carbon-platinum layers produced by magnetron cosputtering have been studied. The layers were characterized by electron microscopy, IR spectroscopy, ellipsometry, gravimetry, and spectrophotometric chemical analysis. The catalytic activity of the layers was studied in an air-hydrogen fuel cell by measuring its load and power characteristics. 相似文献
980.
With the aim to reduce disorder and improve efficiency, nodes in an ad hoc network run a self-organization scheme to cooperatively organize the network. Although metrics such as complexity or self-stability are commonly used for evaluation, to the best of our knowledge, none of them quantifies the efficiency to build and maintain an organization (order). We henceforth apply the notion of entropy to ad hoc type wireless networks facilitating a quantification of the internal organizational state generated by different self-organization schemes. Invoking node and link failure probabilities, we expose the dependency of the organizational state on the self-organization protocol of choice. 相似文献