全文获取类型
收费全文 | 409319篇 |
免费 | 5069篇 |
国内免费 | 1725篇 |
专业分类
电工技术 | 8232篇 |
综合类 | 380篇 |
化学工业 | 59597篇 |
金属工艺 | 17129篇 |
机械仪表 | 11832篇 |
建筑科学 | 9759篇 |
矿业工程 | 1188篇 |
能源动力 | 10353篇 |
轻工业 | 36247篇 |
水利工程 | 3246篇 |
石油天然气 | 4057篇 |
武器工业 | 10篇 |
无线电 | 53374篇 |
一般工业技术 | 76282篇 |
冶金工业 | 85054篇 |
原子能技术 | 6764篇 |
自动化技术 | 32609篇 |
出版年
2021年 | 2752篇 |
2019年 | 2673篇 |
2018年 | 4312篇 |
2017年 | 4191篇 |
2016年 | 4525篇 |
2015年 | 3350篇 |
2014年 | 5636篇 |
2013年 | 17922篇 |
2012年 | 9498篇 |
2011年 | 13233篇 |
2010年 | 10713篇 |
2009年 | 12096篇 |
2008年 | 12800篇 |
2007年 | 12881篇 |
2006年 | 11784篇 |
2005年 | 10918篇 |
2004年 | 10615篇 |
2003年 | 10471篇 |
2002年 | 10380篇 |
2001年 | 10618篇 |
2000年 | 9807篇 |
1999年 | 10733篇 |
1998年 | 28067篇 |
1997年 | 19360篇 |
1996年 | 15076篇 |
1995年 | 11233篇 |
1994年 | 9887篇 |
1993年 | 9698篇 |
1992年 | 6831篇 |
1991年 | 6686篇 |
1990年 | 6306篇 |
1989年 | 6079篇 |
1988年 | 5785篇 |
1987年 | 4819篇 |
1986年 | 4855篇 |
1985年 | 5627篇 |
1984年 | 5015篇 |
1983年 | 4537篇 |
1982年 | 4184篇 |
1981年 | 4339篇 |
1980年 | 3968篇 |
1979年 | 3728篇 |
1978年 | 3678篇 |
1977年 | 4554篇 |
1976年 | 6479篇 |
1975年 | 3151篇 |
1974年 | 3004篇 |
1973年 | 2973篇 |
1972年 | 2494篇 |
1971年 | 2192篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
T P?usa P Górski H Frank-Piskorska M Kowalski J Kruszewski P Kuna M Kurek R Kurzawa W Silny E Zawisza 《Canadian Metallurgical Quarterly》1996,1(4):292-293
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre. 相似文献
62.
63.
A method is described for experimentally determining the dose rate created in building bricks by incorporated natural radionuclides.
It was established using the thermoluminescence dosimetry method that the measured dose rate depends on the detector thickness,
the mass of the ceramic product investigated, and the irradiation geometry. The contributions to the measured dose of weakly
penetrating α and β radiation and hard ψ radiation are separated, the ratio between them depending on the experimental conditions.
Translated from Izmeritel'naya Tekhnika, No. 7, pp. 62–66, July, 1996. 相似文献
64.
Test Case Generation as an AI Planning Problem 总被引:6,自引:0,他引:6
Adele E. Howe Anneliese von Mayrhauser Richard T. Mraz 《Automated Software Engineering》1997,4(1):77-106
While Artificial Intelligence techniques have been applied to a variety of software engineering applications, the area of automated software testing remains largely unexplored. Yet, test cases for certain types of systems (e.g., those with command language interfaces and transaction based systems) are similar to plans. We have exploited this similarity by constructing an automated test case generator with an AI planning system at its core. We compared the functionality and output of two systems, one based on Software Engineering techniques and the other on planning, for a real application: the StorageTek robot tape library command language. From this, we showed that AI planning is a viable technique for test case generation and that the two approaches are complementary in their capabilities. 相似文献
65.
Development of a recurrent Sigma-Pi neural network rainfall forecasting system in Hong Kong 总被引:1,自引:1,他引:0
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead. 相似文献
66.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
67.
68.
Large-scale simulation studies in image pattern recognition 总被引:1,自引:0,他引:1
Tin Kam Ho Baird H.S. 《IEEE transactions on pattern analysis and machine intelligence》1997,19(10):1067-1079
Many obstacles to progress in image pattern recognition result from the fact that per-class distributions are often too irregular to be well-approximated by simple analytical functions. Simulation studies offer one way to circumvent these obstacles. We present three closely related studies of machine-printed character recognition that rely on synthetic data generated pseudo-randomly in accordance with an explicit stochastic model of document image degradations. The unusually large scale of experiments - involving several million samples that makes this methodology possible have allowed us to compute sharp estimates of the intrinsic difficulty (Bayes risk) of concrete image recognition problems, as well as the asymptotic accuracy and domain of competency of classifiers 相似文献
69.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
70.
A beam propagation method (BPM) based on the finite element method (FEM) is described for longitudinally varying three-dimensional (3-D) optical waveguides. In order to avoid nonphysical reflections from the computational window edges, the transparent boundary condition is introduced. The present algorithm using the Pade approximation is, to our knowledge, the first wide-angle finite element beam propagation method for 3-D waveguide structures. To show the validity and usefulness of this approach, numerical results are shown for Gaussian-beam excitation of a straight rib waveguide and guided-mode propagation in a Y-branching rib waveguide 相似文献