全文获取类型
收费全文 | 41229篇 |
免费 | 2444篇 |
国内免费 | 1086篇 |
专业分类
电工技术 | 1351篇 |
技术理论 | 2篇 |
综合类 | 3357篇 |
化学工业 | 5464篇 |
金属工艺 | 1657篇 |
机械仪表 | 2211篇 |
建筑科学 | 3712篇 |
矿业工程 | 1736篇 |
能源动力 | 1529篇 |
轻工业 | 2484篇 |
水利工程 | 778篇 |
石油天然气 | 1855篇 |
武器工业 | 244篇 |
无线电 | 3433篇 |
一般工业技术 | 5155篇 |
冶金工业 | 1563篇 |
原子能技术 | 303篇 |
自动化技术 | 7925篇 |
出版年
2024年 | 55篇 |
2023年 | 386篇 |
2022年 | 622篇 |
2021年 | 548篇 |
2020年 | 674篇 |
2019年 | 821篇 |
2018年 | 702篇 |
2017年 | 878篇 |
2016年 | 1053篇 |
2015年 | 1001篇 |
2014年 | 1434篇 |
2013年 | 1517篇 |
2012年 | 2127篇 |
2011年 | 2327篇 |
2010年 | 1588篇 |
2009年 | 1879篇 |
2008年 | 1738篇 |
2007年 | 1932篇 |
2006年 | 1804篇 |
2005年 | 1619篇 |
2004年 | 2234篇 |
2003年 | 1920篇 |
2002年 | 2503篇 |
2001年 | 2132篇 |
2000年 | 1888篇 |
1999年 | 1621篇 |
1998年 | 1072篇 |
1997年 | 1050篇 |
1996年 | 1873篇 |
1995年 | 1150篇 |
1994年 | 804篇 |
1993年 | 298篇 |
1992年 | 267篇 |
1991年 | 257篇 |
1990年 | 208篇 |
1989年 | 124篇 |
1988年 | 97篇 |
1987年 | 73篇 |
1986年 | 87篇 |
1985年 | 94篇 |
1984年 | 72篇 |
1983年 | 45篇 |
1982年 | 47篇 |
1981年 | 39篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
重金属(以铅计)含量测定方法的改进 总被引:1,自引:0,他引:1
探讨了用硫化钠-丙三醇溶液代替饱和硫化氢水溶液进行重金属(以铅计)测定的分析方法。此法简单、快速,并在实际应用中取得了满意的结果。 相似文献
82.
83.
在不同频率流量和阻水程度条件下,采用一维明渠非恒定流网河数学模型,分析规划中的佛山市桥梁群对区间河道洪季行洪、枯季水环境的影响,计算洪季不同频率洪峰流量下规划桥梁群对区间河道行洪洪水位、分流比的影响,枯季时规划桥梁群对区间河道过流量、分流比的影响,结果表明,利用一维网河数学模型计算佛山市中心组团规划桥梁群对区间河道断面平均水位、流量和流速的影响,结果有足够的数值精度,是可信的。 相似文献
84.
Colour Centres and Energy Transfer in BaF2-xClx:Eu2+ Phosphors 总被引:1,自引:1,他引:0
The optical absorption spectra of BaF2-xClx:Eu2 after ultraviolet (UV) light excitation were investigated.The differences between the absorption spectra after and before excitation (DAS) were observed.The DAS increase at both the high and the low energy side of F band in BaF2-xClx:Eu2 after 245 nm UV light excitation.The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres (association of F(Cl-) centres), whose absorption band matches the HeNe laser better, may explain the latter.In the write-in process, the transfer of electrons is via tunneling.In the readout process, the transfer of electrons captured in F(F-) and Fa centres is more likely via tunneling, and that of F(Cl-) centres is more likely via conduction band. 相似文献
85.
86.
We report on the use of pulsed plasma-enhanced chemical vapor deposition (P-PECVD) technique and show that “state-of-the-art” amorphous silicon (a-Si:H) materials and solar cells can be produced at a deposition rate of up to 15 Å/s using a modulation frequency in the range 1–100 kHz. The approach has also been developed to deposit materials and devices onto large area, 30 cm×40 cm, substrates with thickness uniformity (<5%), and gas utilization rate (>25%). We have developed a new “hot wire” chemical vapor deposition (HWCVD) method and report that our new filament material, graphite, has so far shown no appreciable degradation even after deposition of 500 μm of amorphous silicon. We report that this technique can produce “state-of-the-art” a-Si:H and that a solar cell of p/i/n configuration exhibited an initial efficiency approaching 9%. The use of microcrystalline silicon (μc-Si) materials to produce low-cost stable solar cells is gaining considerable attention. We show that both of these techniques can produce thin film μc-Si, dependent on process conditions, with 1 1 1 and/or 2 2 0 orientations and with a grain size of approx. 500 A. Inclusion of these types of materials into a solar cell configuration will be discussed. 相似文献
87.
M. Loidl E. Leblanc T. Branger H. Rotzinger T. Daniyarov M. Linck A. Fleischmann C. Enss 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):73-75
We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a 55Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology. 相似文献
88.
B. A. Young J. R. Williams S. W. Deiker S. T. Ruggiero B. Cabrera 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):307-310
We summarize a continuing investigation into using ion implantation to alter the transition temperature of superconducting thin films. The primary motivation for the work presented here was to study the feasibility of using magnetic ion doping to replace the bi-layer Tc control process currently used for certain cryogenic detector applications at National Institute for Standards and Technology. The results from work with various ion species implanted into aluminum, molybdenum, titanium and tungsten host films are presented. 相似文献
89.
Roberto Leoni Bruno Buonomo Gabriella Castellano Francesco Mattioli Guido Torrioli Luciana Di Gaspare Florestano Evangelisti 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):44-47
We discuss the performance, of a normal metal hot electron bolometer (NHEB) that we have measured at 0.3 K. We found that the noise equivalent power was limited by the amplifier noise. To improve the NHEB power response and to make it more robust and reliable we propose to substitute the normal metal with heavily doped silicon. The heavily doped silicon behaves like a metal with lower carrier concentration and has a smaller electron–phonon thermal coupling. We have fabricated superconductor-doped silicon-superconductor contacts (S-Sm-S) and we have used them as thermometers and coolers. 相似文献
90.
Photoluminescence features in a commercial grade cured DGEBA-based epoxy resin have been investigated with as objective to determine which of the material compounds are responsible for cured resin emissions. The origin of the bands has been approached by considering photoluminescence of base resin and hardener taken separately, of their mixture, and in the course of curing. Most of the bands observed in the cured resin could be interpreted based on those found in the components taken separately. Fluorescence of the cured resin appears dominated by two broad bands that are characteristic of the hardener and exhibits a blue shift by up to 30 nm in the course of curing which could be used for cure monitoring purpose of the investigated system. Fluorescence of the base resin is clearly detected in the resin cured with tertiary amine as catalyser. However, it is very weak if the catalyser is not added. Two phosphorescence processes have been isolated in the cured resin, one of them being related to the base resin. Finally, a chemiluminescence spectrum has been recorded in the course of curing, which has been related to either curing-related reactions or to an oxidation process. 相似文献