全文获取类型
收费全文 | 430597篇 |
免费 | 4868篇 |
国内免费 | 1392篇 |
专业分类
电工技术 | 7702篇 |
综合类 | 255篇 |
化学工业 | 67977篇 |
金属工艺 | 18184篇 |
机械仪表 | 12718篇 |
建筑科学 | 10546篇 |
矿业工程 | 2538篇 |
能源动力 | 10646篇 |
轻工业 | 39039篇 |
水利工程 | 4556篇 |
石油天然气 | 9332篇 |
武器工业 | 18篇 |
无线电 | 47385篇 |
一般工业技术 | 83713篇 |
冶金工业 | 78163篇 |
原子能技术 | 10591篇 |
自动化技术 | 33494篇 |
出版年
2021年 | 3156篇 |
2019年 | 3000篇 |
2018年 | 5374篇 |
2017年 | 5326篇 |
2016年 | 5671篇 |
2015年 | 3790篇 |
2014年 | 6425篇 |
2013年 | 18602篇 |
2012年 | 10505篇 |
2011年 | 14407篇 |
2010年 | 11719篇 |
2009年 | 13414篇 |
2008年 | 13708篇 |
2007年 | 13515篇 |
2006年 | 11824篇 |
2005年 | 11029篇 |
2004年 | 10352篇 |
2003年 | 9929篇 |
2002年 | 9933篇 |
2001年 | 9793篇 |
2000年 | 9336篇 |
1999年 | 9501篇 |
1998年 | 23072篇 |
1997年 | 16873篇 |
1996年 | 13161篇 |
1995年 | 10038篇 |
1994年 | 8849篇 |
1993年 | 8701篇 |
1992年 | 6578篇 |
1991年 | 6488篇 |
1990年 | 6241篇 |
1989年 | 6271篇 |
1988年 | 6173篇 |
1987年 | 5313篇 |
1986年 | 5292篇 |
1985年 | 6072篇 |
1984年 | 5742篇 |
1983年 | 5269篇 |
1982年 | 4955篇 |
1981年 | 5111篇 |
1980年 | 4853篇 |
1979年 | 4808篇 |
1978年 | 4877篇 |
1977年 | 5592篇 |
1976年 | 7197篇 |
1975年 | 4375篇 |
1974年 | 4190篇 |
1973年 | 4263篇 |
1972年 | 3701篇 |
1971年 | 3403篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The emerging software defined radio technologies will be an enabler for a new generation of dynamic wireless systems. It will also open up the possibility of allocating frequencies in a, more dynamic way than today. From an intersystem-interference point of view, this can cause unforeseen problems to occur due to the increased complexity in such applications. In such applications, a measure indicating whether or not a frequency band is possible to use from an electromagnetic interference point of view, must be found. A simple approach is to use the measured total average interference power within the receiver band. Since the interference impact on modern digital communication systems from an interference signal does not only depend on the power but also on the actual waveform of the interference signal, some kind of quality measure of the average-power approach would be convenient to use. In this paper, we introduce a simple quality measure of the average-power approach so that a rough adjustment for the interference-waveform properties can be done. 相似文献
92.
Solar cells based on SnO2/Cd0.4Zn0.6S/CdTe heterostructures are fabricated by electrochemical deposition, and the dependences of their electrical and photoelectric properties on the thermal annealing conditions are studied. It is shown that thermal annealing reduces the tunnel currents by almost two orders of magnitude. The best conditions of thermal annealing are determined (t = 300°C and τ = 9 min). These conditions provide the highest photosensitivity of the heterostructures under study (I sc ≈ 21.2 mA/cm2, U oc ≈ 813 mV, and η = 14.7%). 相似文献
93.
This paper provides an overview of the main aspects of modern fluorescence microscopy. It covers the principles of fluorescence and highlights the key discoveries in the history of fluorescence microscopy. The paper also discusses the optics of fluorescence microscopes and examines the various types of detectors. It also discusses the signal and image processing challenges in fluorescence microscopy and highlights some of the present developments and future trends in the field. 相似文献
94.
Seidel A.R. Bisogno F.E. Pinheiro H. do Prado R.N. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1267-1274
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out. 相似文献
95.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
96.
N.S. Chen S.F. Yu 《Photonics Technology Letters, IEEE》2004,16(7):1610-1612
The effect of external optical feedback on the transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is studied. It can be shown that the proper design of ARROW can suppress the excitation of high-order transverse leaky mode as well as increase the critical feedback strength so that stable high-power single-mode operation of VCSELs can be obtained even under the influence of strong external optical feedback. 相似文献
97.
Scale Up from Small Oven-Drying Tests of Mineral Concentrate to Pilot-Scale Drying with a Heated Pad
While Fickian diffusion models are commonly used in other applications, there are few reports of them being applied to the batch drying of a mineral concentrate. Diffusion coefficients estimated from small-scale oven-drying tests were used to predict the drying behavior of a concentrate sample 1 m × 1 m in area and 50 cm deep, with a heated bottom pad. These pilot-scale tests included both daily turning of the sample and turning every three days. The excellent quantitative agreement between the predicted and observed pilot-scale behavior gives a high level of confidence in the model predictions and suggests that a Fickian diffusion model is adequate to predict the behavior of mineral concentrates at the low moisture contents used here. 相似文献
98.
99.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
100.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献