全文获取类型
收费全文 | 309761篇 |
免费 | 3719篇 |
国内免费 | 714篇 |
专业分类
电工技术 | 6193篇 |
综合类 | 560篇 |
化学工业 | 46745篇 |
金属工艺 | 10323篇 |
机械仪表 | 8820篇 |
建筑科学 | 7899篇 |
矿业工程 | 862篇 |
能源动力 | 8570篇 |
轻工业 | 31081篇 |
水利工程 | 2532篇 |
石油天然气 | 3669篇 |
武器工业 | 8篇 |
无线电 | 39697篇 |
一般工业技术 | 58445篇 |
冶金工业 | 56633篇 |
原子能技术 | 5458篇 |
自动化技术 | 26699篇 |
出版年
2021年 | 2278篇 |
2019年 | 2138篇 |
2018年 | 3607篇 |
2017年 | 3448篇 |
2016年 | 3539篇 |
2015年 | 2540篇 |
2014年 | 4440篇 |
2013年 | 14272篇 |
2012年 | 7363篇 |
2011年 | 10115篇 |
2010年 | 7900篇 |
2009年 | 9131篇 |
2008年 | 9601篇 |
2007年 | 9578篇 |
2006年 | 8505篇 |
2005年 | 7888篇 |
2004年 | 7759篇 |
2003年 | 7496篇 |
2002年 | 7333篇 |
2001年 | 7543篇 |
2000年 | 7205篇 |
1999年 | 7545篇 |
1998年 | 17656篇 |
1997年 | 12831篇 |
1996年 | 10097篇 |
1995年 | 7872篇 |
1994年 | 7203篇 |
1993年 | 6903篇 |
1992年 | 5286篇 |
1991年 | 5066篇 |
1990年 | 4933篇 |
1989年 | 4781篇 |
1988年 | 4673篇 |
1987年 | 3886篇 |
1986年 | 4007篇 |
1985年 | 4717篇 |
1984年 | 4275篇 |
1983年 | 4021篇 |
1982年 | 3601篇 |
1981年 | 3761篇 |
1980年 | 3456篇 |
1979年 | 3418篇 |
1978年 | 3226篇 |
1977年 | 3814篇 |
1976年 | 4848篇 |
1975年 | 2780篇 |
1974年 | 2660篇 |
1973年 | 2675篇 |
1972年 | 2215篇 |
1971年 | 1963篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Control law design for rotorcraft fly-by-wire systems normally attempts to decouple the angular responses using fixed-gain crossfeeds. This approach can lead to poor decoupling over the frequency range of pilot inputs and increase the load on the feedback loops. In order to improve the decoupling performance, dynamic crossfeeds should be adopted. Moreover, because of the large changes that occur in the aircraft dynamics due to small changes about the nominal design condition, especially for near-hovering flight, the crossfeed design must be ‘robust’. A new low-order matching method is presented here to design robust crossfeed compensators for multi-input, multi-output (MIMO) systems. The technique minimizes cross-coupling given an anticipated set of parameter variations for the range of flight conditions of concern. Results are presented in this paper of an analysis of the pitch/roll coupling of the UH-60 Black Hawk helicopter in near-hovering flight. A robust crossfeed is designed that shows significant improvement in decoupling perfomance and robustness over the fixed-gain or single point dynamic compensators. The design method and results are presented in an easily used graphical format that lends significant physical insight to the design procedure. This plant precompensation technique is an appropriate preliminary step to the design of robust feedback control laws for rotorcraft. 相似文献
82.
Matthew R. James 《国际强度与非线性控制杂志
》1994,4(6):791-806
》1994,4(6):791-806
In this paper we present a numerical method for estimating the current state of a nonlinear control system. We use finite differences to discretize a modified version of the finite-time observer equations in James. The discretized equations are simple and easily programmed. The convergence and accuracy of the scheme is proved, and the scheme enjoys a number of important properties: availability of rate of convergence estimates, good robustness characteristics, and the ability to handle certain types of discontinuities in the observations. The major disadvantage is that the number of grid points required increases exponentially with the number of state dimensions. 相似文献
83.
Low temperature wafer direct bonding 总被引:11,自引:0,他引:11
Qin-Yi Tong Cha G. Gafiteanu R. Gosele U. 《Journal of microelectromechanical systems》1994,3(1):29-35
A pronounced increase of interface energy of room temperature bonded hydrophilic Si/Si, Si/SiO2, and SiO2/SiO 2 wafers after storage in air at room temperature, 150°C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and/or silicon at the interface at temperatures below 110°C and the formation of stronger siloxane bonds above 110°C appear to be the main mechanisms responsible for the increase in the interface energy. After prolonged storage, interface bubbles are detectable by an infrared camera at the Si/Si bonding seam. Desorbed hydrocarbons as well as hydrogen generated by a reaction of water with silicon appear to be the major contents in the bubbles. Design guidelines for low temperature wafer direct bonding technology are proposed 相似文献
84.
Silicon nitride corrugated diaphragms of 2 mm×2 mm×1 μm have been fabricated with 8 circular corrugations, having depths of 4, 10, or 14 μm. The diaphragms with 4-μm-deep corrugations show a measured mechanical sensitivity (increase in the deflection over the increase in the applied pressure) which is 25 times larger than the mechanical sensitivity of flat diaphragms of equal size and thickness. Since this gain in sensitivity is due to reduction of the initial stress, the sensitivity can only increase in the case of diaphragms with initial stress. A simple analytical model has been proposed that takes the influence of initial tensile stress into account. The model predicts that the presence of corrugations increases the sensitivity of the diaphragms, because the initial diaphragm stress is reduced. The model also predicts that for corrugations with a larger depth the sensitivity decreases, because the bending stiffness of the corrugations then becomes dominant. These predictions have been confirmed by experiments. The application of corrugated diaphragms offers the possibility to control the sensitivity of thin diaphragms by geometrical parameters, thus eliminating the effect of variations in the initial stress, due to variations in the diaphragm deposition process and/or the influence of temperature changes and packaging stress 相似文献
85.
Although not well known, the University of Toronto had a very early computer-development program and in 1952 was one of the first few institutions with an operable computer in North America. This article describes the university's initial attempt to build the UTEC computer and how it acquired the pioneering Ferut machine 相似文献
86.
É. R. Smolyakov 《Cybernetics and Systems Analysis》1994,30(1):10-17
Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 24–33, January–February, 1994. 相似文献
87.
In the editorial by J.C. Bezdek (ibid., p.1), an example is presented to demonstrate differences between fuzzy membership and probability. The authors argue that probability can be used in a way much more closely analogous to this use of fuzzy membership, weakening the argument for the latter 相似文献
88.
R Thomas 《Canadian Metallurgical Quarterly》1993,15(4):285-289
The purpose for this study was to evaluate the results of silicone oil use in patients who have undergone vitrectomy for proliferative vitreoretinopathy (PVR). The authors reviewed the 5-year results of 50 consecutive patients (52 eyes) with grade C1/D3 PVR operated on in 1987. Silicone oil has been removed in 42 eyes. The retina remained attached in 38 eyes. Visual acuities were finger counting in 12 eyes and 0.1 or greater in 19 eyes. Glaucoma was thought to be the major cause of loss of visual acuity after an initial improvement (9 eyes), as well as the most frequent complication of surgery (13 eyes). Silicone oil was deemed nonremovable in 10 operated eyes. A questionnaire was developed to determine the patients' perceptions of the use of silicone oil, and 46 patients responded to the questionnaire. Four patients indicated that they would not have elected to have surgery again. Six patients thought that surgery was not worthwhile, but would permit treatment again. Most patients thought that a modest amount of improvement had taken place and that vision was stable. Subjectively, most patients believed that surgery was worthwhile. 相似文献
89.
Variations in lipid profile and incidence of vascular events were evaluated. Group 1 had a 29.3% reduction of total and a 38.3% reduction of LDL cholesterol as against reductions of 9% and 9.6% respectively in group 2. No significant difference was observed between the two groups as far as the vascular events considered were concerned. Pravastatin is an effective and safe drug. The lack of influence on the evolution of vascular disease would appear to be correlated to the small number of subjects studied and the short follow-up. 相似文献
90.