全文获取类型
收费全文 | 474496篇 |
免费 | 6367篇 |
国内免费 | 2054篇 |
专业分类
电工技术 | 8858篇 |
综合类 | 393篇 |
化学工业 | 71340篇 |
金属工艺 | 17257篇 |
机械仪表 | 14124篇 |
建筑科学 | 12952篇 |
矿业工程 | 1341篇 |
能源动力 | 12555篇 |
轻工业 | 48373篇 |
水利工程 | 4027篇 |
石油天然气 | 4077篇 |
武器工业 | 54篇 |
无线电 | 60861篇 |
一般工业技术 | 90351篇 |
冶金工业 | 85367篇 |
原子能技术 | 7970篇 |
自动化技术 | 43017篇 |
出版年
2021年 | 3467篇 |
2020年 | 2446篇 |
2019年 | 3139篇 |
2018年 | 5255篇 |
2017年 | 5327篇 |
2016年 | 5744篇 |
2015年 | 4275篇 |
2014年 | 7067篇 |
2013年 | 22251篇 |
2012年 | 12104篇 |
2011年 | 16983篇 |
2010年 | 13230篇 |
2009年 | 15051篇 |
2008年 | 16023篇 |
2007年 | 16344篇 |
2006年 | 14494篇 |
2005年 | 13453篇 |
2004年 | 13019篇 |
2003年 | 12691篇 |
2002年 | 12253篇 |
2001年 | 12444篇 |
2000年 | 11590篇 |
1999年 | 11986篇 |
1998年 | 26896篇 |
1997年 | 19622篇 |
1996年 | 15451篇 |
1995年 | 12173篇 |
1994年 | 10821篇 |
1993年 | 10446篇 |
1992年 | 7922篇 |
1991年 | 7658篇 |
1990年 | 7287篇 |
1989年 | 7002篇 |
1988年 | 6663篇 |
1987年 | 5646篇 |
1986年 | 5612篇 |
1985年 | 6767篇 |
1984年 | 6249篇 |
1983年 | 5479篇 |
1982年 | 5068篇 |
1981年 | 5041篇 |
1980年 | 4765篇 |
1979年 | 4637篇 |
1978年 | 4318篇 |
1977年 | 5210篇 |
1976年 | 6914篇 |
1975年 | 3622篇 |
1974年 | 3506篇 |
1973年 | 3383篇 |
1972年 | 2747篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
992.
993.
994.
Ackerman Steven J.; Hilsenroth Mark J.; Knowles Eric S. 《Canadian Metallurgical Quarterly》2005,42(2):225
The present study examines the concurrent and predictive relationships between therapist psychodynamic-interpersonal activity and therapist-rated alliance. Ratings from 45 patient and therapist dyads engaged in short term psychodynamic psychotherapy from a point early (3rd or 4th session) and late (the session at which 90% of the treatment was completed) in treatment were used. The results suggest that therapists who have positive views of the alliance early in treatment also have positive views of the alliance later in treatment. Therapists who used psychodynamic-interpersonal activities early in treatment also made use of psychodynamic-interpersonal activities later in treatment. Moreover, the use of psychodynamic-interpersonal activities early in treatment was positively related to both global and specific aspects of therapist-rated alliance late in treatment. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
995.
W. Tang H.Z. Shi G. Xu B.S. Ong Z.D. Popovic J.C. Deng J. Zhao G.H. Rao 《Advanced materials (Deerfield Beach, Fla.)》2005,17(19):2307-2311
996.
V. H. Novyts’kyi V. P. Havrylyuk D. D. Panasenko M. O. Kal’chuk V. Ya. Khoruzhyi 《Materials Science》2006,42(6):799-807
The positive influence of lead (2.5%) on the original structure of a cast composite of the Fe-Cr-Cu-C-Ti system, its wear
rate, friction coefficient, and the formation of secondary structures is established under the conditions of dry friction
and friction with boundary lubrication.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 73–80, November–December, 2006. 相似文献
997.
This paper addresses the state estimation of systems with perspective outputs. We derive a minimum-energy estimator which produces an estimate of the state that is "most compatible" with the dynamics, in the sense that it requires the least amount of noise energy to explain the measured outputs. Under suitable observability assumptions, the estimate converges globally asymptotically to the true value of the state in the absence of noise and disturbance. In the presence of noise, the estimate converges to a neighborhood of the true value of the state. These results are also extended to solve the estimation problem when the measured outputs are transmitted through a network. In that case, we assume that the measurements arrive at discrete-time instants, are time-delayed, noisy, and may not be complete. We show that the redesigned minimum-energy estimator preserves the same convergence properties. We apply these results to the estimation of position and orientation for a mobile robot that uses a monocular charged-coupled device (CCD) camera mounted on-board to observe the apparent motion of stationary points. In the context of our application, the estimator can deal directly with the usual problems associated with vision systems such as noise, latency and intermittency of observations. Experimental results are presented and discussed. 相似文献
998.
P Navarro J Sarasa D Sierra S Esteban J L Ovelleiro 《Water science and technology》2005,51(1):113-120
Wine industry wastewaters contain a high concentration of organic biodegradable compounds as well as a great amount of suspended solids. These waters are difficult to treat by conventional biological processes because they are seasonal and a great flow variation exists. Photocatalytic advanced oxidation is a promising technology for waters containing high amounts of organic matter. In this study we firstly investigated the application of H2O2 as oxidant combined with light (artificial or natural) in order to reduce the organic matter in samples from wine industry effluents. Secondly, we studied its combination with heterogeneous catalysts: titanium dioxide and clays containing iron minerals. The addition of photocatalysts to the system reduces the required H2O2 concentration. Although the H2O2/TiO2 system produces higher efficiencies, the H2O2/clays system requires a H2O2 dosage between three and six times lower. 相似文献
999.
A mini spray dryer has been used to investigate morphological changes that occur to milk particles during the spray drying process. We have found that the mini spray dryer is ideal for such investigations, because phenomena such as skin and vacuole formation in particles can be analyzed without the added complication of particle agglomeration, which only occurs in much larger spray dryers where particle number concentrations are higher. We have confirmed observations made by various researchers that the bulk density of spray-dried milk powder is greatly affected by the drying temperature, due to the strong influence of the latter on the porosity of the particles. In addition, we have attempted to explain observations made by various workers that fat accumulates preferentially at the surface of a particle during drying by postulating that fluid fat is transported towards the surface, via a network of cracks and pores, by the development of a vacuole overpressure which is also responsible for the inflation of the particle. Finally, we have shown that milk powders can be spray dried a second time, by reconstitution with water, with no change to the thermodynamic characteristics of the resultant powder. Thus, milk concentrates for spray drying research can be prepared from already-spray-dried milk powders rather than using the more arduous evaporation method to concentrate unprocessed milk. 相似文献
1000.
Goni O. Hossain F. Yusuf S.U. Rahman M. Kaneko E. Takahashi H. 《Power Delivery, IEEE Transactions on》2006,21(4):1778-1786
Simulation of very fast surge phenomena in a three-dimensional (3-D) structure requires a method based on Maxwell's equations, such as the finite-difference time-domain (FDTD) method or the method of moments, because circuit-equation-based methods cannot handle the phenomena. This paper uses a method of thin-wire representation of the vertical conductor system for the FDTD method which is suitable for the 3-D surge simulation. The thin-wire representation is indispensable to simulate electromagnetic surges on wires or steel frames in which the radius is smaller than a discretized space step used in the FDTD simulation. In this paper, a general surge analysis program named the virtual surge test lab based on the Maxwell's equations formulated by the FDTD method, is used to simulate the surge phenomena of a vertical conductor, including the effects of horizontal wave incidence and vertical wave incidence. Experimental results on the reduced scale model have been presented in order to compare among the simulation results by the FDTD method and the results using numerical electromagnetic code based on the MoM. 相似文献