全文获取类型
收费全文 | 277165篇 |
免费 | 4132篇 |
国内免费 | 1303篇 |
专业分类
电工技术 | 5174篇 |
综合类 | 292篇 |
化学工业 | 41991篇 |
金属工艺 | 11550篇 |
机械仪表 | 7747篇 |
建筑科学 | 8116篇 |
矿业工程 | 593篇 |
能源动力 | 7276篇 |
轻工业 | 26795篇 |
水利工程 | 2239篇 |
石油天然气 | 1445篇 |
武器工业 | 8篇 |
无线电 | 33306篇 |
一般工业技术 | 50532篇 |
冶金工业 | 56125篇 |
原子能技术 | 4105篇 |
自动化技术 | 25306篇 |
出版年
2021年 | 2198篇 |
2020年 | 1497篇 |
2019年 | 2009篇 |
2018年 | 3057篇 |
2017年 | 2872篇 |
2016年 | 3228篇 |
2015年 | 2615篇 |
2014年 | 4136篇 |
2013年 | 12998篇 |
2012年 | 7019篇 |
2011年 | 9730篇 |
2010年 | 7818篇 |
2009年 | 8410篇 |
2008年 | 9215篇 |
2007年 | 9290篇 |
2006年 | 8512篇 |
2005年 | 7852篇 |
2004年 | 7337篇 |
2003年 | 7300篇 |
2002年 | 7207篇 |
2001年 | 7025篇 |
2000年 | 6318篇 |
1999年 | 6971篇 |
1998年 | 17094篇 |
1997年 | 12131篇 |
1996年 | 9458篇 |
1995年 | 7229篇 |
1994年 | 6387篇 |
1993年 | 6197篇 |
1992年 | 4490篇 |
1991年 | 4260篇 |
1990年 | 3951篇 |
1989年 | 3857篇 |
1988年 | 3733篇 |
1987年 | 3239篇 |
1986年 | 3121篇 |
1985年 | 3795篇 |
1984年 | 3436篇 |
1983年 | 3028篇 |
1982年 | 2818篇 |
1981年 | 2823篇 |
1980年 | 2676篇 |
1979年 | 2515篇 |
1978年 | 2466篇 |
1977年 | 3016篇 |
1976年 | 4356篇 |
1975年 | 2080篇 |
1974年 | 1950篇 |
1973年 | 1937篇 |
1972年 | 1569篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Computer graphics in art history and archaeology 总被引:2,自引:0,他引:2
142.
Brian M. Louie Thomas Franaszek Tina Pho Wen Yen Chiu David S. Soong 《应用聚合物科学杂志》1985,30(9):3841-3856
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate. 相似文献
143.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed. 相似文献
144.
H. Koizumi 《International Journal of Heat and Mass Transfer》2002,45(5):937-949
I have experimentally studied the influence of the buoyancy force and inlet flow conditions on the laminar-turbulent transition process of fully developed air flow in a heated horizontal tube with uniform wall heat flux at modified Rayleigh number 3.1×106. Eight time-series of the air temperature were simultaneously obtained using eight thermocouples positioned within the tube along a vertical line passing through the tube's axis. I have studied the time and space dependence of the transition behavior by analyzing these instantaneous time-series. By calculating a set of Lyapunov exponents and the correlation dimension of the time-series of a single thermocouple, these transitional flows are found to be chaotic. 相似文献
145.
Chen H.H. Huang T.S. 《IEEE transactions on pattern analysis and machine intelligence》1991,13(9):872-878
The specific problem addressed by the authors is how to detect the true match of a fourth point from among candidate matches in a situation in which three points have already been matched. The two sets of points to be matched are both subject to measurement errors. The depth error is more dominant than errors in the other two coordinates; however, the exact statistical distribution of the measurement errors is not known. The authors present a new method for solving the problem. The method is based on the technique of motion analysis using orthographic views. It discards the noisy z (depth) coordinates and uses only the x and y coordinates of the points to verify the match. The effect of depth errors on the motion estimate is completely prevented. Results show that this method is substantially more effective than previous methods that use all three coordinates 相似文献
146.
The carrier sense multiple access with collision detection (CSMA-CD) protocol cannot be applied directly to radio channels because of the difficulty in sensing remote carrier in the presence of local transmission. Only recently, a new protocol called the CSMA with timesplit collision detection (CSMA-TCD) was introduced to overcome this problem on radio channels. This paper presents an extension of the CSMA-TCD protocol, called CSMA-TCD with multitone tree search (CSMA-TCD-MTTS). In CSMA-TCD, a preamble is transmitted before data transmission. For CSMA-TCD-MTTS, the preamble is modulated with one out ofN tones. In case of a collision, a resolution algorithm splits the terminals involved into anN -degree tree according to the tone chosen. This paper presents the throughput and approximate delay analysis of the CSMA-TCD-MTTS protocol. 相似文献
147.
In this paper, the authors present the results of experiments which clearly demonstrate a technical basis confirming that the carrier frequency harmonics data can be used for diagnostics relative to motor stator insulation degradation. 相似文献
148.
Tang Helen H. Y.; McNally Gavan P.; Richardson Rick 《Canadian Metallurgical Quarterly》2007,121(6):1421
The authors studied the role of gamma-aminobutyric acid (GABA) in 2 types of forgetting of fear in the developing rat. One type of forgetting studied was that observed after an intermediate retention interval (the "Kamin effect"); the other type studied was that observed after a longer interval (infantile amnesia). Rats were given pairings of an auditory conditioned stimulus with shock, and learned fear was assessed by freezing. Forgetting at an intermediate retention interval (1 hr) was not alleviated by the GABAA receptor partial inverse agonist FG7142 (0, 1, 5, or 10 mg/kg), whereas forgetting at a longer retention interval (48 hr) was alleviated. These results suggest that in the developing rat, forgetting observed at different retention intervals is mediated by different physiological mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
149.
Linking Entrepreneurship to Growth: The Case of West Germany 总被引:1,自引:0,他引:1
150.
MetaModel is a user-friendly program for calculating steady-state fluxes and metabolite concentrations of metabolic systems on the IBM PC and compatible computers. For any steady state that is obtained, one can then calculate a matrix of elasticity coefficients at that steady state, or a matrix of control and response coefficients. It thus offers a simple way to calculate the control structure of a pathway: it provides not only an educational tool that allows the student to verify empirically the classic summation relationships of metabolic control analysis but also a research tool for addressing 'what if?' questions about the behaviour of metabolic systems. Results can not only be printed or stored in a file, but can also be written to a special file that can be read by popular spreadsheet programs, thereby giving access to rapid, flexible and powerful methods for subsequent analysis and plotting of these results. 相似文献