全文获取类型
收费全文 | 76709篇 |
免费 | 9940篇 |
国内免费 | 4474篇 |
专业分类
电工技术 | 9756篇 |
技术理论 | 7篇 |
综合类 | 6865篇 |
化学工业 | 7926篇 |
金属工艺 | 5052篇 |
机械仪表 | 6261篇 |
建筑科学 | 6285篇 |
矿业工程 | 4218篇 |
能源动力 | 4090篇 |
轻工业 | 5788篇 |
水利工程 | 2660篇 |
石油天然气 | 6299篇 |
武器工业 | 967篇 |
无线电 | 7793篇 |
一般工业技术 | 5772篇 |
冶金工业 | 5272篇 |
原子能技术 | 768篇 |
自动化技术 | 5344篇 |
出版年
2024年 | 396篇 |
2023年 | 1298篇 |
2022年 | 2583篇 |
2021年 | 2883篇 |
2020年 | 3189篇 |
2019年 | 2465篇 |
2018年 | 2307篇 |
2017年 | 2812篇 |
2016年 | 3100篇 |
2015年 | 3322篇 |
2014年 | 5116篇 |
2013年 | 4491篇 |
2012年 | 6134篇 |
2011年 | 6374篇 |
2010年 | 4529篇 |
2009年 | 4317篇 |
2008年 | 3760篇 |
2007年 | 4831篇 |
2006年 | 4353篇 |
2005年 | 3784篇 |
2004年 | 3013篇 |
2003年 | 2872篇 |
2002年 | 2344篇 |
2001年 | 2157篇 |
2000年 | 1824篇 |
1999年 | 1457篇 |
1998年 | 1004篇 |
1997年 | 839篇 |
1996年 | 720篇 |
1995年 | 596篇 |
1994年 | 505篇 |
1993年 | 347篇 |
1992年 | 276篇 |
1991年 | 218篇 |
1990年 | 192篇 |
1989年 | 158篇 |
1988年 | 96篇 |
1987年 | 77篇 |
1986年 | 49篇 |
1985年 | 51篇 |
1984年 | 50篇 |
1983年 | 29篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 27篇 |
1966年 | 10篇 |
1964年 | 18篇 |
1962年 | 11篇 |
1959年 | 14篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
121.
O. Gravrand E. De Borniol S. Bisotto L. Mollard G. Destefanis 《Journal of Electronic Materials》2007,36(8):981-987
This paper aims at studying the feasibility of very long infrared wavelength (VLWIR) (12–18 μm) focal plane arrays using n-on-p planar ion-implanted technology. To explore and analyze the feasibility of such VLWIR detectors, a set of four Cd
x
Hg1−x
Te LPE layers with an 18 μ cutoff at 50 K has been processed at Defir (LETI/LIR–Sofradir joint laboratory), using both our “standard” n-on-p process and our improved low dark current process. Several 320 × 256 arrays, 30-μm pitch, have been hybridized on standard Sofradir readout circuits and tested. Small dimension test arrays characterization
is also presented. Measured photonic currents with a 20°C black body suggest an internal quantum efficiency above 50%. Typical
I(V) curves and thermal evolution of the saturation current are discussed, showing that standard photodiodes remain diffusion
limited at low biases for temperatures down to 30 K. Moreover, the dark current gain brought by the improved process is clearly
visible for temperatures higher than 40 K. Noise measurements are also discussed showing that a very large majority of detectors
appeared background limited under usual illumination and biases. In our opinion, such results demonstrate the feasibility
of high-performance complex focal plane arrays in the VLWIR range at medium term. 相似文献
122.
123.
变频器在暖通空调行业中的应用 总被引:1,自引:0,他引:1
本文提出中央空调系统的一种变频调速改造方案,介绍了该系统的结构组成及运行原理,对系统各部分的作用进行了讨论。 相似文献
124.
低渗透油田合理注采井距的确定--以纯41块沙4段低渗透油田为例 总被引:3,自引:1,他引:2
以纯41块沙4段低渗透油田为例,从低渗透油田渗流机理出发,分析了造成低渗透油田开发效果差的主要原因。在计算注水井最大井底流压、油井最小井底流压、油水井之间可建立的最大注采压差的基础上,结合室内试验确定的最小启动压力梯度公式计算油田技术极限注采井距,并结合经济合理井距计算结果,确定了油田合理注采井距,并提出了下二步调整方案,实施后取得了显著的效果。该方法为低渗透油田合理井距的确定、提高低渗透油田的开发效果提供了理论依据。 相似文献
125.
系统阐述了全集成自动化理念的内涵,指出其特点在于统一的数据管理、统一的编程组态、统一的通讯以及无与伦比的开放性,其中采用WINCC与STEP7两个软件进行了说明,井提出全集成自动化应用将是今后自动化技术发展应用的方向。 相似文献
126.
Ring‐opening polymerization of D,L ‐lactide (LA) has been successfully carried out by using rare earth 2,6‐dimethylaryloxide (Ln(ODMP)3) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)3 exhibits higher activity to prepare poly(D,L ‐lactide) (PLA) with a viscosity molecular weight of 4.5 × 104 g mol?1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)3 has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)3 is 69.6 kJ mol?1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ‘coordination–insertion’ mechanism with selective cleavage of the acyl–oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry 相似文献
127.
An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb2S3). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test. 相似文献
128.
高速逆流色谱(HSCCC)在食品色素制备中的应用 总被引:1,自引:0,他引:1
综述了高速逆流色谱在食品色素制备中的应用情况,包括溶剂选择、色素种类等。 相似文献
129.
Organic photovoltaic solar cells bear an important potential of development in the search for low-cost modules for the production of domestic electricity. One of the main differences between inorganic and organic solar cells is that photo-excitation in these materials does not automatically lead to the generation of free charge carriers, but to bind electron–hole pairs (exciton) with a binding energy of about 0.4 eV. Till now various numerical methods using approximations have been reported to study different aspects of organic solar cells. For the first time an accurate method using Lambert W-function is presented to study different parameters of organic solar cells. 相似文献
130.