全文获取类型
收费全文 | 193808篇 |
免费 | 2872篇 |
国内免费 | 721篇 |
专业分类
电工技术 | 3521篇 |
综合类 | 110篇 |
化学工业 | 31261篇 |
金属工艺 | 8050篇 |
机械仪表 | 5401篇 |
建筑科学 | 5424篇 |
矿业工程 | 982篇 |
能源动力 | 5168篇 |
轻工业 | 17633篇 |
水利工程 | 1855篇 |
石油天然气 | 3318篇 |
武器工业 | 3篇 |
无线电 | 20916篇 |
一般工业技术 | 36050篇 |
冶金工业 | 37084篇 |
原子能技术 | 4441篇 |
自动化技术 | 16184篇 |
出版年
2021年 | 1512篇 |
2019年 | 1455篇 |
2018年 | 2350篇 |
2017年 | 2317篇 |
2016年 | 2489篇 |
2015年 | 1792篇 |
2014年 | 3076篇 |
2013年 | 8845篇 |
2012年 | 5173篇 |
2011年 | 7191篇 |
2010年 | 5686篇 |
2009年 | 6507篇 |
2008年 | 6682篇 |
2007年 | 6677篇 |
2006年 | 5663篇 |
2005年 | 5370篇 |
2004年 | 5017篇 |
2003年 | 4694篇 |
2002年 | 4583篇 |
2001年 | 4443篇 |
2000年 | 4216篇 |
1999年 | 4351篇 |
1998年 | 10681篇 |
1997年 | 7683篇 |
1996年 | 5947篇 |
1995年 | 4601篇 |
1994年 | 3874篇 |
1993年 | 3848篇 |
1992年 | 2863篇 |
1991年 | 2695篇 |
1990年 | 2643篇 |
1989年 | 2703篇 |
1988年 | 2577篇 |
1987年 | 2326篇 |
1986年 | 2266篇 |
1985年 | 2614篇 |
1984年 | 2425篇 |
1983年 | 2224篇 |
1982年 | 2085篇 |
1981年 | 2141篇 |
1980年 | 1957篇 |
1979年 | 1991篇 |
1978年 | 1938篇 |
1977年 | 2280篇 |
1976年 | 2822篇 |
1975年 | 1732篇 |
1974年 | 1704篇 |
1973年 | 1725篇 |
1972年 | 1453篇 |
1971年 | 1327篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
van Dick Rolf; Wagner Ulrich; Pettigrew Thomas F.; Christ Oliver; Wolf Carina; Petzel Thomas; Castro Vanessa Smith; Jackson James S. 《Canadian Metallurgical Quarterly》2004,87(2):211
Furthering G. W. Allport's (1954) contentions for optimal contact, the authors introduce a new construct: the perceived importance of contact. They propose that perceived importance is the best proximal predictor of contact's reduction of prejudice. If individuals have opportunities for contact at work or in the neighborhood, their chances to have intergroup acquaintances and friends increase. Intergroup contact among acquaintances and friends can be perceived as more or less important, which in turn determines intergroup evaluations. A 1st study shows that the new measure of perceived importance is indeed distinct from established quantity and quality indicators. The results are cross-validated in a 2nd study that also sheds light on the meaning of importance. In 3rd and 4th studies, structural equation analyses and a meta-analysis support the hypotheses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
152.
D. Vignolles D. Smirnov G. Rikken B. Raquet H. Rakoto C. Proust M. Nardone J. Léotin F. Lecouturier M. Goiran O. Drachenko J. M. Broto L. Brossard A. Audouard 《Journal of Low Temperature Physics》2003,133(1-2):97-120
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned. 相似文献
153.
A key performance parameter of a manufacturing network or supply chain is its cycle time; the time that a typical item spends in the network. A previous simulation study on a semiconductor assembly and test facility showed that cycle times could be reduced by having smooth input and service rates. This suggested that there is a “cycle time principle” that, for a system with a specified throughput or input rate, the shortest cycle times are obtained when the input and service rates do not vary over time. We prove that this principle is true for the M/G/1 and M/M/s queueing systems and Jackson networks. The analysis involves establishing several results on the concavity of waiting time probabilities and the convexity of expected waiting times and queue lengths, as functions of input and service rates. These results also have natural uses in other optimization problems. 相似文献
154.
Three different vanadium-modified Pd/Al2O3 catalysts were prepared and tested as catalysts for the deep oxidation of methane. Vanadium was added to the palladium catalyst by incipient wetness of palladium catalyst in order to modify its properties and improve its thermal stability and thioresistance. The behaviour of vanadium-modified catalysts depends on the concentration of this compound, being 0.5 wt.% the optimum amount. However, when strong catalyst poisons are present in the gas (SO2), these modified catalysts do not show a better performance than unmodified catalyst. Bimetallic catalysts were tested with and without further reduction, being observed that reduced bimetallic catalysts perform worse than the non-reduced ones. 相似文献
155.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
156.
157.
Albul V. I. Bychkov V. B. Gusev K. E. Demidov V. S. Demidova E. V. Kurchanov A. F. Luk'yashin V. E. Sokolov A. Yu. 《Measurement Techniques》2003,46(8):810-814
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec. 相似文献
158.
Analogue switch for very low-voltage applications 总被引:2,自引:0,他引:2
Munoz F. Ramirez-Angulo J. Lopez-Martin A. Carvajal R.G. Torralba A. Palomo B. Kachare M. 《Electronics letters》2003,39(9):701-702
A new analogue switch suitable for operation at very low-voltage supply in a standard CMOS technology is presented. The proposed switch is based on 'quasi-floating-gate' transistors and has a simple and compact structure. For illustrative purposes, two sample-and-hold circuits operating from a single supply voltage close to the threshold voltage of a transistor, and using the proposed technique, are presented. Experimental results obtained from prototypes in a 1.5 /spl mu/m CMOS technology are provided. 相似文献
159.
Summary. A solution is presented for the contact problem with a smooth circular elastic insert in an infinite, linearly elastic plate under thermal load. The thermal load considered here includes the temperature gradient applied at infinity and a uniform temperature change. One of the major difficult parts in solving the present problem is that separation may occur between an insert or inclusion and the surrounding matrix under a nonuniform expansion of the matrix and the insert due to a temperature change. Based on the complex potential theory and the method of analytical continuation, the problem is reduced to a singular integro-differential equation which is solved numerically. Results are presented for the contact angle and for the normal and circumferential stresses at the plate-insert interface. Exact solutions are found for the current problem for a special case when the material properties of the plate and the insert are identical. 相似文献
160.
Pinpoint injection of microtools for minimally invasive micromanipulation of microbe by laser trap 总被引:1,自引:0,他引:1
F. Arai H. Maruyama T. Sakami A. Ichikawa T. Fukuda 《Mechatronics, IEEE/ASME Transactions on》2003,8(1):3-9
This paper reports transportation of the target microbe by the laser trapped microtools with minimum laser irradiation to the target. The size of a microtool (MT) is around micrometer. The MTs are manipulated by the focused laser under the microscope to manipulate the target microbe. Here we propose a pinpoint injection method of MTs at the desired location in the microchamber, which is filled with liquid. At first, we classified the injection method of the MTs in four categories. Here we employed a new method to install the MTs inside the microchamber. We developed a MT holding chip to install the MTs. The MTs were injected in the microchamber, and were manipulated successfully by the laser scanning micromanipulator to transport the target microbe for separation. The proposed method is useful for the pinpoint injection of MTs and separation by the indirect micromanipulation. 相似文献