全文获取类型
收费全文 | 14535篇 |
免费 | 1138篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 242篇 |
综合类 | 19篇 |
化学工业 | 3429篇 |
金属工艺 | 583篇 |
机械仪表 | 809篇 |
建筑科学 | 252篇 |
矿业工程 | 4篇 |
能源动力 | 667篇 |
轻工业 | 1404篇 |
水利工程 | 52篇 |
石油天然气 | 13篇 |
武器工业 | 3篇 |
无线电 | 2368篇 |
一般工业技术 | 3434篇 |
冶金工业 | 892篇 |
原子能技术 | 144篇 |
自动化技术 | 1402篇 |
出版年
2023年 | 185篇 |
2022年 | 230篇 |
2021年 | 487篇 |
2020年 | 365篇 |
2019年 | 368篇 |
2018年 | 492篇 |
2017年 | 515篇 |
2016年 | 605篇 |
2015年 | 504篇 |
2014年 | 712篇 |
2013年 | 973篇 |
2012年 | 1066篇 |
2011年 | 1286篇 |
2010年 | 914篇 |
2009年 | 929篇 |
2008年 | 798篇 |
2007年 | 685篇 |
2006年 | 560篇 |
2005年 | 471篇 |
2004年 | 435篇 |
2003年 | 382篇 |
2002年 | 328篇 |
2001年 | 283篇 |
2000年 | 295篇 |
1999年 | 248篇 |
1998年 | 373篇 |
1997年 | 246篇 |
1996年 | 191篇 |
1995年 | 135篇 |
1994年 | 110篇 |
1993年 | 94篇 |
1992年 | 62篇 |
1991年 | 41篇 |
1990年 | 44篇 |
1989年 | 44篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1974年 | 8篇 |
1971年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
31.
T.J. ChungJ.H. Park C.K. Choi D.-Y. Yoon 《International Journal of Heat and Mass Transfer》2002,45(14):3061-3064
The onset of convective instability in a fluid-saturated porous layer between the two horizontal plates heated isothermally from below has been analyzed theoretically by using propagation theory. In the analysis the thermal dispersion coefficient is assumed to be proportional to the streamwise velocity. The results show that both inertia and thermal dispersion stabilize the system. 相似文献
32.
33.
The transmission mode of holographic polymer‐dispersed liquid crystals (HPDLCs) was developed an under electric field. It is reported that orientation of LC molecules under an electric field induces orientation of oligomer molecules giving rise to low off‐state diffraction and small grating shrinkage. Copyright © 2005 Society of Chemical Industry 相似文献
34.
Erv J. Kuhlmann Dick Y. Jung Richard P. Guptill Charles A. Dyke Hyung K. Zang 《Fuel》1985,64(11):1552-1557
The presence of hydroaromatic, hydrogen donor components in a coal-derived solvent is one of the more important factors in the successful operation of a non-catalytic coal liquefaction process. Various hydrogen donor species present in a hydrogenated creosote oil have been identified. Their rate of disappearance under conditions that are consistent with a short residence time coal liquefaction process has been used to rank the reactivities of the various hydrogen donors. 1,2,3,10b-Tetrahydrofluoranthene was found to be an exceptional donor while 4,5-dihydropyrene, the hexahydropyrenes and 9,10-dihydrophenanthrene were found to be quite active. Sym.-octahydrophenanthrene and 2a,3,4,5-tetrahydroacenaphthene exhibited moderate activity. Tetralin and the four methyltetralin isomers were found to be unreactive under the coal liquefaction conditions employed. 相似文献
35.
Temperature and pH‐responsive interpenetrating polymer network (IPN) hydrogels, constructed with poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA), by a sequential IPN method, were studied. The characterization of IPN hydrogels was investigated by Fourier‐transform infrared spectroscopy, differential scanning calorimetry (DSC) and swelling under various conditions. The IPN hydrogels exhibited relatively high swelling ratios, in the range 230–380 %, at 25 °C. The swelling ratios of the PMAA/PVA IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the amounts of freezing and non‐freezing water. The amount of free water increased with increasing PMAA content in the IPN hydrogels. Copyright © 2004 Society of Chemical Industry 相似文献
36.
37.
S H Yoon J H Collins D Musale S Sundararajan S P Tsai G A Hallsby J F Kong J Koppes P Cachia 《Water science and technology》2005,51(6-7):151-157
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works. 相似文献
38.
Dielectric reliability in Al2O3(2–3.1nm)–HfO2(3nm) stack capacitor with Metal–Insulator–Si(MIS) structure is investigated in this paper. We propose an optimized capacitor process through the Time–Dependent Dielectric Breakdown (TDDB) data under various process conditions. Furthermore, due to asymmetric current at both negative and positive voltage stress polarities, we show different lifetime extrapolation by a fluence–driven model. As a result, the maximum allowed operating voltage is projected to be 1.7V (failure rate 10ppm during 10year @ 85°C) for Data “0” retention lifetime. 相似文献
39.
Design and practical implementation of multifrequency RF front ends using direct RF sampling 总被引:1,自引:0,他引:1
Psiaki M.L. Powell S.P. Hee Jung Kintner P.M. 《Microwave Theory and Techniques》2005,53(10):3082-3089
The use of direct RF sampling has been explored as a means of designing multifrequency RF front ends. Such front ends will be useful to multifrequency RF applications such as global navigation satellite system receivers that use global positioning system (GPS) L1, L2, and L5 signals and Galileo signals. The design of a practical multifrequency direct RF sampling front end is dependent on having an analog-to-digital converter whose input bandwidth accommodates the highest carrier frequency and whose maximum sampling frequency is more than twice the cumulative bandwidth about the multiple carrier signals. The principle of direct RF sampling is used to alias all frequency bands of interest onto portions of the Nyquist bandwidth that do not overlap. This paper presents a new algorithm that finds the minimum sampling frequency that avoids overlap. This design approach requires a multifrequency bandpass filter for the frequency bands of interest. A prototype front end has been designed, built, and tested. It receives a GPS coarse/acquisition code at the L1 frequency and GPS antispoofing precision code at both L1 and L2. Dual-frequency signals with received carrier-to-noise ratios in excess of 52 dB-Hz have been acquired and tracked using this system. 相似文献
40.
Shinsook Yoon Mi-Kyoung Kim In-Young Lee Mikyung Yun Jeong E. Nam Shin 《Journal of Industrial and Engineering Chemistry》2008,14(6):759-764
We have developed a mutant strain derived from Agrobacterium sp. ATCC 31750, which produces a water-soluble polysaccharide having potential utility to the food, feed, pharmaceutical and cosmetic industries. A high concentration of product (15 g/L) is obtained by 48 h cultivation of the mutant strain under optimized fermentation conditions. The water-soluble polysaccharide obtained from cultures of the mutant strain beta82 has Glc:Man:Gal in approximate molar ratios of 5.8:6.7:1.0. The molecular weight of the polysaccharide was determined to be approximately 1000 kDa by HPSEC analysis. Linkage analysis contained 3-Glcp, 3-Manp, terminal Glcp and terminal Manp, as well as a small proportion of 3- and 3,4-Galp, and 4,6-Manp residues. Based on analyses using FT-IR and 13C NMR spectrometers, most glycosidic bonds joining these sugar residues are of the α-type, and acetyl groups are apparently attached to the polymer chain at random. 相似文献