全文获取类型
收费全文 | 404075篇 |
免费 | 4686篇 |
国内免费 | 1364篇 |
专业分类
电工技术 | 7570篇 |
综合类 | 316篇 |
化学工业 | 59837篇 |
金属工艺 | 16430篇 |
机械仪表 | 13498篇 |
建筑科学 | 8353篇 |
矿业工程 | 2164篇 |
能源动力 | 11533篇 |
轻工业 | 28477篇 |
水利工程 | 4272篇 |
石油天然气 | 7916篇 |
武器工业 | 17篇 |
无线电 | 49265篇 |
一般工业技术 | 83033篇 |
冶金工业 | 75130篇 |
原子能技术 | 9184篇 |
自动化技术 | 33130篇 |
出版年
2022年 | 2552篇 |
2021年 | 3891篇 |
2020年 | 2941篇 |
2019年 | 3804篇 |
2018年 | 6483篇 |
2017年 | 6475篇 |
2016年 | 6922篇 |
2015年 | 4319篇 |
2014年 | 7136篇 |
2013年 | 20049篇 |
2012年 | 11414篇 |
2011年 | 15271篇 |
2010年 | 12156篇 |
2009年 | 13717篇 |
2008年 | 14065篇 |
2007年 | 13820篇 |
2006年 | 12420篇 |
2005年 | 11124篇 |
2004年 | 10510篇 |
2003年 | 10426篇 |
2002年 | 9834篇 |
2001年 | 9736篇 |
2000年 | 9137篇 |
1999年 | 9533篇 |
1998年 | 24360篇 |
1997年 | 16741篇 |
1996年 | 12813篇 |
1995年 | 9531篇 |
1994年 | 8374篇 |
1993年 | 8388篇 |
1992年 | 6059篇 |
1991年 | 5696篇 |
1990年 | 5686篇 |
1989年 | 5326篇 |
1988年 | 5047篇 |
1987年 | 4425篇 |
1986年 | 4302篇 |
1985年 | 4818篇 |
1984年 | 4424篇 |
1983年 | 3995篇 |
1982年 | 3660篇 |
1981年 | 3733篇 |
1980年 | 3435篇 |
1979年 | 3327篇 |
1978年 | 3335篇 |
1977年 | 3752篇 |
1976年 | 4860篇 |
1975年 | 2858篇 |
1974年 | 2664篇 |
1973年 | 2731篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A new sensitive method for imaging of the spatial distribution of microwave intensity is proposed. The method is based on the imaging of the 6P-recombination continuum of cesium, emitted from a nonequilibrium plasma of the positive column of gas discharge in a cesium vapor-xenon mixture. It is demonstrated that the spatial distribution of intensity of 35-GHz microwave radiation measured by this method in a focal plane of a lens well coincides with the pattern obtained with the aid of a movable microwave detector. The time resolution of the proposed microwave imaging system reaches 1 ms. 相似文献
992.
SiC-based field-effect gas sensors with catalytic platinum electrodes (Pt-MOSiC) have been subjected to a series of gas response measurements. Structural analysis of the Pt electrodes revealed that the gas sensitivity and the selectivity of Pt-MOSiC gas sensors depend on two major parameters: the porosity and the catalytic activity of the Pt electrodes. Pt-MOSiC gas sensors with thick, dense Pt electrodes only exhibit hydrogen sensitivity, whereas Pt-MOSiCs with thin porous gates exhibit a broad range of gas sensitivities similar to resistive metal-oxide gas sensors. A model is put forward that explains the nonhydrogen gas response of Pt-MOSiC devices and of conventional polycrystalline metal-oxide materials on a common basis. 相似文献
993.
994.
995.
Recent developments on fiber-optic devices are reviewed from the local area network (LAN) application viewpoint. Future technical trends are also discussed, along with current research activities. In local area network systems, low device cost and easy maintenance or maintenance-free devices are especially required. Light sources and photodetectors suitable for the systems are described. InGaAsP/InP light emitting diodes can cover a broad application field, up to a gigabits per second super high-speed network region. Optical passive devices, which include branching couplers, switches and connectors, are mentioned as essential components. Compact transmitter/receiver module technology is a key factor in realizing optical-fiber local area network systems. An example of 200-Mbit/s transmitter/receiver module is reported. 相似文献
996.
B L Sergeev S P Bogovski? T I Ve?debaum R Kh Tanner I N Shevchuk 《Eksperimental?nai?a onkologii?a》1985,7(5):27-30
The UV irradiation (lambda = 362 nm) of aflatoxin B1 (AfB1) dissolved in water resulted in the formation of an oxidized product. The process was not inhibited by ionol, a routine inhibitor of the radical processes. The oxidized product was not found in the system where AfB1 was metabolized by the 3-methylcholanthrene-activated rat liver microsomes. It is suggested that the product is identical with 2,3-dihydrodiol of AfB1. 相似文献
997.
S. Taye 《Computers & Structures》1991,41(6):1341-1347
An approximate structural reanalysis method that is based on a binomial series expansion and that employs operations of matrix scaling and norm minimization is presented in this paper. It is shown that the scaling operation significantly reduces several unfavourable effects of the magnitude and nature of design changes on the prediction quality of the model. Norm minimization provides a very effective and optimal scaling factor in a simplified manner. The most significant achievement of the work is the development of an effective and efficient reanalysis model that provides near-exact response quantities even when large and strongly dispersed changes are introduced in the design. The potential capacity of the proposed method of improvement is demonstrated using numerical examples. Graphical interpretation of the concept is also provided. 相似文献
998.
K.W. Allen S.M. Smith W.C. Wake A.O. van Raalte 《International Journal of Adhesion and Adhesives》1985,5(1):23-32
The effect of cyclic stressing on the strength of single lap adhesive joints has been studied and a considerable reduction in strength observed when the maximum stress exceeds about 40% of the ultimate tensile strength, but whether or not a true endurance limit exists is not proven. Fallacies are shown in some of the techniques which have been proposed for studying the fatigue behaviour of adhesive joints. 相似文献
999.
S. Vaidyanathan K. M. Kavadia L. P. Borkar S. P. Mahajan 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):121-128
With a view to evaluate the effects of hydraulic retention time and volatile solids loading rate on methane production using water hyacinth, experiments were conducted in a 160 dm3 capacity, well-mixed continuous digestion unit at ambient temperature. The optimal design of biogas plant using water hyacinth was elucidated, to provide a unit giving a maximum methane yield of 0.16 nm3 kg?1 volatile solids added, which was 60% greater than the conventional plant using cowdung. The calculations of optimal design factors were based on reactor size, hydraulic retention time and volatile solids loading rate; considerations were made of capital cost, running costs and operational revenue. 相似文献
1000.
A concept is proposed for utilizing artificial neural networks to enhance the high-speed tracking accuracy of robotic manipulators. Tracking accuracy is a function of the controller's ability to compensate for disturbances produced by dynamical interactions between the links. A model-based control algorithm uses a nominal model of those dynamical interactions to reduce the disturbances. The problem is how to provide accurate dynamics information to the controller in the presence of payload uncertainty and modeling error. Neural network payload estimation uses a series of artificial neural networks to recognize the payload variation associated with a degradation in tracking performance. The network outputs are combined with a knowledge of nominal dynamics to produce a computationally efficient direct form of adaptive control. The concept is validated through experimentation and analysis on the first three links of a PUMA-560 manipulator. A multilayer perceptron architecture with two hidden layers is used. Integration of the principles of neural network pattern recognition and model-based control produces a tracking algorithm with enhanced robustness to incomplete dynamic information. Tracking efficacy and applicability to robust control algorithms are discussed. 相似文献