全文获取类型
收费全文 | 223186篇 |
免费 | 3875篇 |
国内免费 | 1910篇 |
专业分类
电工技术 | 4726篇 |
综合类 | 913篇 |
化学工业 | 34966篇 |
金属工艺 | 10715篇 |
机械仪表 | 6851篇 |
建筑科学 | 6070篇 |
矿业工程 | 1288篇 |
能源动力 | 6175篇 |
轻工业 | 19343篇 |
水利工程 | 2282篇 |
石油天然气 | 4642篇 |
武器工业 | 108篇 |
无线电 | 24442篇 |
一般工业技术 | 43396篇 |
冶金工业 | 40036篇 |
原子能技术 | 5063篇 |
自动化技术 | 17955篇 |
出版年
2021年 | 2277篇 |
2020年 | 1606篇 |
2019年 | 1969篇 |
2018年 | 3061篇 |
2017年 | 3034篇 |
2016年 | 3206篇 |
2015年 | 2548篇 |
2014年 | 4042篇 |
2013年 | 10480篇 |
2012年 | 6404篇 |
2011年 | 8638篇 |
2010年 | 6928篇 |
2009年 | 7999篇 |
2008年 | 7759篇 |
2007年 | 7797篇 |
2006年 | 6624篇 |
2005年 | 6037篇 |
2004年 | 5742篇 |
2003年 | 5272篇 |
2002年 | 5245篇 |
2001年 | 5305篇 |
2000年 | 4869篇 |
1999年 | 5060篇 |
1998年 | 12371篇 |
1997年 | 8975篇 |
1996年 | 7051篇 |
1995年 | 5222篇 |
1994年 | 4322篇 |
1993年 | 4301篇 |
1992年 | 3145篇 |
1991年 | 3057篇 |
1990年 | 2912篇 |
1989年 | 2888篇 |
1988年 | 2708篇 |
1987年 | 2477篇 |
1986年 | 2400篇 |
1985年 | 2700篇 |
1984年 | 2467篇 |
1983年 | 2291篇 |
1982年 | 2151篇 |
1981年 | 2215篇 |
1980年 | 2115篇 |
1979年 | 2112篇 |
1978年 | 2043篇 |
1977年 | 2490篇 |
1976年 | 3268篇 |
1975年 | 1837篇 |
1974年 | 1815篇 |
1973年 | 1876篇 |
1972年 | 1582篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Out-of-plane microlenses and microoptical fiber holder are two of the most important components for building an integrated
microoptic system with a precise alignment accuracy. In this paper, a simple and convenient method to fabricate these components
from SU-8 by using inclined UV lithography in water is proposed. It consists of two perpendicular exposures in SU-8 at ±45°.
DI water possesses a low absorption coefficient and a moderate and stable value of refractive index in near UV. Using water,
the exposure angle in SU-8 can be increased to 50° from 35° in air necessary to pattern the desired 45° slope of the sidewalls.
The principle of the proposed technique and the detailed fabrication process of the microoptic components will be presented.
The integratability of the fabricated components was demonstrated by the fabrication of the microoptical fiber holder with
a pre-aligned out-of-plane microlens. 相似文献
92.
93.
94.
F Javier Benítez Ana I Leal Francisco J Real Juan L Acero Gloria Roldán 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):309-316
BACKGROUND: The first stage of the cork industrial process generates great volumes of wastewater with moderate to high organic pollutant content that must be purified using different procedures, such as filtration by membranes. RESULTS: The tangential filtration of these wastewaters was studied using two different laboratory equipments. In the first one, three ultrafiltration (UF) membranes were tested, with molecular weight cut‐off (MWCO) 100 kDa and 30 kDa, and two operating modes were used: total recycling of permeate and retentate streams, and in continuous mode, without recycling both streams. In the total recycling UF experiments, the influence of the operating variables on the permeate flux was first established. The effectiveness of the different membranes was determined by evaluating the rejection coefficients for several parameters that measure the global pollutant content of the effluent. The values found for these rejection coefficients were in the following order: ellagic acid and color > absorbance at 254 nm > tannic content > COD (chemical oxygen demand). In the continuous mode experiments, the fouling mechanism for each membrane was established by fitting the experimental data to various filtration fouling models given in the literature. The operating mode in the second equipment was batch concentration, and additional experiments were carried out with an UF membrane (2 kDa), and with a NF membrane (with MWCO in the range 150–300 Da). CONCLUSIONS: The three operating modes tested provided different rejection levels of organic matter; among them, the most effective procedure tested was batch concentration mode using a NF membrane. Copyright © 2007 Society of Chemical Industry 相似文献
95.
96.
J. Pujara M. A. Siddiqui Z. Liu P. Bjegovic S. S. Takagaki P. Y. Li S. Ramaswamy 《Drying Technology》2008,26(3):341-348
This is part II of a study reported earlier on a method to characterize the air flow and water removal characteristics during vacuum dewatering. This article presents experimental data and analysis of results from the use of a cyclically actuated vacuum dewatering device for removing moisture from wetted porous materials such as paper with the intermittent application of vacuum and accompanying air flow though the material. Results presented include sheet moisture content as a function of residence time and hence water removal rate under a variety of process conditions. Also, experimental results on air flow through the wet porous structure and hence the role and importance of air flow during vacuum dewatering are presented. Vacuum dewatering process conditions include exit solids content between 11 and 20% solid under applied vacuum conditions of 13.5 to 67.7 kPa (4 to 20 in. Hg). Regression analysis indicated that the exit sheet moisture content exhibited a nonlinear relationship with residence time with exit solids reaching a plateau after a certain residence time. Final moisture content correlated linearly with the average overall flow rate of air through the paper sample and the basis weight of the material. 相似文献
97.
Biodiesel has become an attractive diesel fuel substitute due to its environmental benefits since it can be made from renewable resource. However, the high costs surrounding biodiesel production remains the main problem in making it competitive in the fuel market either as a blend or as a neat fuel. More than 80% of the production cost is associated with the feedstock itself and consequently, efforts are focused on developing technologies capable of using lower-cost feedstocks, such as recycled cooking oils and wastes from animal or vegetable oil processing operations. 相似文献
98.
Yu. F. Patrakov E. S. Pavlusha N. I. Fedorova Yu. A. Strizhakova 《Solid Fuel Chemistry》2008,42(1):10-13
The results of the thermal solution of oil shale in benzene in a flow unit under supercritical conditions are reported. It was found that the conversion of shale organic matter into liquid products increased by a factor of 2.5 with an increase in the solvent pressure from 5 to 15 MPa. 相似文献
99.
D. Ballutaud F. Jomard T. Kociniewski E. Rzepka H. Girard S. Saada 《Diamond and Related Materials》2008,17(4-5):451-456
Hot filament and microwave plasma CVD micro- nanocrystalline diamond films are analysed by visible and ultra-violet excitation source Raman spectroscopy. The sample grain size varies from 20 nm to 2 μm. The hydrogen concentration in samples is measured by SIMS and compared to the grain size, and to the ratio of sp2 carbon bonds determined by Raman spectroscopy from the 1332 cm− 1 diamond peak and the sp2 1550 cm− 1 G band. Hydrogen concentration appears to be proportional to the sp2 bonds ratio. The 3000 cm− 1 CHx stretching mode band intensity observed on the Raman spectra is decreasing with the G band intensity. Thermal annealing modifies the sp2 phase structure and concentration, as hydrogen outdiffuses. 相似文献
100.