全文获取类型
收费全文 | 111772篇 |
免费 | 1890篇 |
国内免费 | 1251篇 |
专业分类
电工技术 | 2049篇 |
综合类 | 156篇 |
化学工业 | 12761篇 |
金属工艺 | 5625篇 |
机械仪表 | 3393篇 |
建筑科学 | 2350篇 |
矿业工程 | 195篇 |
能源动力 | 3180篇 |
轻工业 | 6456篇 |
水利工程 | 762篇 |
石油天然气 | 696篇 |
武器工业 | 15篇 |
无线电 | 16685篇 |
一般工业技术 | 24005篇 |
冶金工业 | 26214篇 |
原子能技术 | 1460篇 |
自动化技术 | 8911篇 |
出版年
2023年 | 378篇 |
2022年 | 807篇 |
2021年 | 1106篇 |
2020年 | 796篇 |
2019年 | 916篇 |
2018年 | 1420篇 |
2017年 | 1344篇 |
2016年 | 1517篇 |
2015年 | 1219篇 |
2014年 | 1924篇 |
2013年 | 5209篇 |
2012年 | 3106篇 |
2011年 | 4451篇 |
2010年 | 3514篇 |
2009年 | 4128篇 |
2008年 | 4317篇 |
2007年 | 4493篇 |
2006年 | 4011篇 |
2005年 | 3570篇 |
2004年 | 3398篇 |
2003年 | 3222篇 |
2002年 | 2857篇 |
2001年 | 3092篇 |
2000年 | 2831篇 |
1999年 | 3193篇 |
1998年 | 9622篇 |
1997年 | 6307篇 |
1996年 | 4862篇 |
1995年 | 3244篇 |
1994年 | 2858篇 |
1993年 | 2811篇 |
1992年 | 1681篇 |
1991年 | 1642篇 |
1990年 | 1568篇 |
1989年 | 1359篇 |
1988年 | 1214篇 |
1987年 | 901篇 |
1986年 | 921篇 |
1985年 | 958篇 |
1984年 | 839篇 |
1983年 | 730篇 |
1982年 | 726篇 |
1981年 | 708篇 |
1980年 | 590篇 |
1979年 | 495篇 |
1978年 | 442篇 |
1977年 | 557篇 |
1976年 | 1015篇 |
1975年 | 326篇 |
1974年 | 292篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
44.
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
45.
PURPOSE: To report the disappearance of traumatic macular hole in three eyes of three patients. METHODS: Clinical data of the patients were reviewed. RESULTS: The three patients were relatively young, ranging in age from 12 to 18 years old. In one eye of each patient, a small traumatic macular hole was observed at the first visit. Visual acuities ranged from 20/100 to 20/40. The macular holes resolved spontaneously 3 to 4 months after the trauma, and final visual acuity improved to 20/20 in all patients. CONCLUSION: Small traumatic macular holes in young patients can resolve spontaneously, and this can be associated with good visual recovery. 相似文献
46.
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
47.
Phase contrast magnetic resonance imaging (MRI) can provide in vivo myocardial velocity field measurements. These data allow densely spaced material points to be tracked throughout the whole heart cycle using, for example, the Fourier tracking algorithm. To process the tracking results for myocardial deformation and strain quantification, we developed a method that is based on fitting the tracking results to an appropriate local deformation model. We further analyzed the accuracy and precision of the method and provided performance predictions for several local models. In order to validate the method and the theoretical performance analysis, we conducted controlled computer simulations and a phantom study. The results agreed well with expectations. Human heart data were also acquired and analyzed, and provided encouraging results. At the signal-to-noise ratio (SNR) level and spatial resolution expected in clinical settings, the study predicts strain quantification accuracy and precision that may allow the technique to become a practical and powerful noninvasive approach for the study of cardiac function, although clinically acceptable data acquisition strategies for three-dimensional (3-D) data are still a challenge. 相似文献
48.
Dopamine receptors influence vasoactive intestinal peptide release from turkey hypothalamic explants
Amongst the elements which contributed to the success of the early lung transplants at the beginning of the 1980's we feel that the careful selection of candidates probably played a predominant role. If some of the selection criteria initially described remain somewhat intangible, others have either been eased or have been invalidated. The experience acquired over the last 15 years has enabled to precise the optimal moment to include patients on the waiting list and to refine the choice for the type of surgical procedure according to the underlying disease. This article aims to review the different selection criteria for candidates for transplantation and stresses those which have recently undergone change. 相似文献
49.
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
50.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 相似文献