全文获取类型
收费全文 | 252907篇 |
免费 | 2797篇 |
国内免费 | 871篇 |
专业分类
电工技术 | 4808篇 |
综合类 | 198篇 |
化学工业 | 36134篇 |
金属工艺 | 9518篇 |
机械仪表 | 7545篇 |
建筑科学 | 6075篇 |
矿业工程 | 881篇 |
能源动力 | 7226篇 |
轻工业 | 21089篇 |
水利工程 | 2206篇 |
石油天然气 | 3231篇 |
武器工业 | 16篇 |
无线电 | 34283篇 |
一般工业技术 | 49980篇 |
冶金工业 | 48556篇 |
原子能技术 | 5077篇 |
自动化技术 | 19752篇 |
出版年
2021年 | 2173篇 |
2020年 | 1567篇 |
2019年 | 1921篇 |
2018年 | 3273篇 |
2017年 | 3310篇 |
2016年 | 3399篇 |
2015年 | 2218篇 |
2014年 | 3955篇 |
2013年 | 11475篇 |
2012年 | 6232篇 |
2011年 | 8574篇 |
2010年 | 6904篇 |
2009年 | 7884篇 |
2008年 | 8402篇 |
2007年 | 8297篇 |
2006年 | 7363篇 |
2005年 | 6497篇 |
2004年 | 6284篇 |
2003年 | 6553篇 |
2002年 | 6036篇 |
2001年 | 6514篇 |
2000年 | 5973篇 |
1999年 | 6389篇 |
1998年 | 16489篇 |
1997年 | 11410篇 |
1996年 | 8797篇 |
1995年 | 6609篇 |
1994年 | 5901篇 |
1993年 | 5845篇 |
1992年 | 4133篇 |
1991年 | 4022篇 |
1990年 | 3858篇 |
1989年 | 3649篇 |
1988年 | 3561篇 |
1987年 | 3019篇 |
1986年 | 2941篇 |
1985年 | 3208篇 |
1984年 | 2928篇 |
1983年 | 2829篇 |
1982年 | 2637篇 |
1981年 | 2543篇 |
1980年 | 2463篇 |
1979年 | 2305篇 |
1978年 | 2108篇 |
1977年 | 2605篇 |
1976年 | 3563篇 |
1975年 | 1765篇 |
1974年 | 1729篇 |
1973年 | 1666篇 |
1972年 | 1466篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Programming and Computer Software - In the biomedical domain, diagrammatical models have been extensively used to describe and understand the behaviour of biological organisms (biological agents)... 相似文献
992.
Programming and Computer Software - This paper is devoted to automating the development of standalone scientific visualization modules based on systems on chips with custom tangible user... 相似文献
993.
Knowledge-based recognition and analysis of high dimensional data such as aerial images often has high computational complexity. For most applications time and computational resources such as memory are limited. Therefore approximately correct interpreters with any-time capability are proposed. In this contribution a special software architecture is published, which can handle the administration of complex knowledge-based recognition and analysis in a tractable manner. 相似文献
994.
In this paper we have proposed a dynamic pricing scheme for the contributing peers in the Video on Demand (VoD) system. The
scheme provides an effective mechanism to maximize the profit through the residual resources of the contributing peers. A
utilization function is executed for each contributing peer to estimate the utility factor based on the parameters such as
initial setup cost, holding cost, chaining cost and salvage cost. In this paper, we urge an effective dynamic pricing algorithm
that efficiently utilizes a range of parameters with a varying degree of complexity. The key findings of the algorithm are
(i) each contributing peers are benefitted by the monetary based on its resource contributions to the VoD system and (ii)
a high degree of social optimum is established by proficiently aggregating the contributing peer’s resources with the overall
resources of the VoD system. We validate our claim by simulating the proposed dynamic pricing scheme with other standard pricing
schemes such as altruism, cost model and game theory perspective. The result of our dynamic pricing scheme shows the best
utility factor than other standard pricing schemes. 相似文献
995.
Scale-up and control of droplet production in coupled microfluidic flow-focusing geometries 总被引:1,自引:1,他引:0
A single microfluidic chip consisting of six microfluidic flow-focusing devices operating in parallel was developed to investigate the feasibility of scaling microfluidic droplet generation up to production rates of hundreds of milliliters per hour. The design utilizes a single inlet channel for both the dispersed aqueous phase and the continuous oil phase from which the fluids were distributed to all six flow-focusing devices. The exit tubing for each of the six flow-focusing devices is separate and individually plumbed to each device. Within each flow-focusing device, the droplet size was monodisperse, but some droplet size variations were observed across devices. We show that by modifying the flow resistance in the outlet channel of an individual flow-focusing device it is possible to control both the droplet size and frequency of droplet production. This can be achieved through the use of valves or, as is done in this study, by changing the length of the exit tubing plumbed to the outlet of the each device. Longer exit tubing and larger flow resistance is found to lead to larger droplets and higher production frequencies. The devices can thus be individually tuned to create a monodisperse emulsion or an emulsion with a specific drop size distribution. 相似文献
996.
Nikos K. Flevaris 《Journal of Materials Science》1989,24(1):313-320
Systems with a coherently modulated composition are considered with regard to their elastic properties. The (stress-free) coherency strains are considered in a new frame where the standard state is redefined on the basis of the property under study. These strains are used in the study of the thermodynamics of spinodal decomposition in solids with a (generally) anisotropic distortion into a cubic matrix. Finally, the influence of these strains is considered in the study of magnetostrictive effects in such modulated systems or strained-layer superlattices. 相似文献
997.
998.
G. P. Dmitrieva Z. B. Krasnokutskaya N. N. Belyavina A. K. Shurin 《Powder Metallurgy and Metal Ceramics》1989,28(3):233-238
Conclusions The eutectic in the Co-VC system corresponds to the composition with 14% VC and a temperature of 1340 ± 20°C and the maximum solubility of vanadium carbide in cobalt is 6%. The Co-VC section is not a quasibinary section of the Co-V-C phase diagram.The eutectic in the Co-NbC system melts at 1360°C and contains 11–12% NbC.The as-cast alloys of the Co-VC-NbC system are in the metastable two-phase condition and the only carbide phase is a carbide of complex composition which is a three-component solid solution of vanadium and niobium monocarbides.The fusibility diagram of the equilibrium phase diagram of the Co-VC-NbC system is characterized by the four-phase eutectic equilibrium L Co + VC + NbC with the point of the ternary eutectic at 1330 ± 20°C and a composition of 11% VC, 4% NbC, and 85% Co. The Co-VC-NbC equilibrium phase diagram does not contain ternary compounds and the equilibrium phases are cobalt- and vanadium- and niobium carbide-base solid solutions. The total volume share of the carbide constituents of the ternary eutectic somewhat exceeds the share of carbide phases in the boundary eutectics Co-VC and Co-NbC.The total solubility of the carbides in cobalt does not exceed 2–3%.Translated from Poroshkovaya Metallurgiya. No. 3(315), pp. 80–87, March, 1989. 相似文献
999.
Smith PM Campbell CK 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(1):10-15
A study of low-loss surface-acoustic-wave (SAW) interdigitated interdigital transducer (IIDT) structures is presented. A model based on mixed scattering matrices was used in the analysis. It is shown that the inherent comb frequency response of the IIDT can be smoothed by slanting the transducers in the structure. Alternatively, the combs can be enhanced to produce a compact low-loss feedback element for potential application in multimode oscillators. Experimental verification of the analysis is provided by a 3:2 slanted-finger IIDT filter with a 10% relative bandwidth of 5.9-dB insertion loss, and a comb filter with 13.4-dB insertion loss and comb spacing of about 3 MHz. The measured responses agree quite well with the theory. 相似文献
1000.
The evolution with temperature of the deformation mechanisms responsible for yielding in polypropylene (PP) and a PP-based blend is correlated to the molecular mobilities associated to glass transitions processes occurring in these materials. It is shown that the elementary local deformation event remains the same throughout the whole temperature range and that the onset of mobility only affects the average internal stress field \(\bar \sigma \) i in which this thermally activated event takes place. 相似文献