全文获取类型
收费全文 | 2853篇 |
免费 | 187篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 52篇 |
综合类 | 9篇 |
化学工业 | 827篇 |
金属工艺 | 90篇 |
机械仪表 | 121篇 |
建筑科学 | 120篇 |
矿业工程 | 12篇 |
能源动力 | 178篇 |
轻工业 | 183篇 |
水利工程 | 47篇 |
石油天然气 | 28篇 |
无线电 | 285篇 |
一般工业技术 | 465篇 |
冶金工业 | 98篇 |
原子能技术 | 18篇 |
自动化技术 | 535篇 |
出版年
2024年 | 5篇 |
2023年 | 51篇 |
2022年 | 84篇 |
2021年 | 193篇 |
2020年 | 141篇 |
2019年 | 198篇 |
2018年 | 229篇 |
2017年 | 209篇 |
2016年 | 193篇 |
2015年 | 130篇 |
2014年 | 225篇 |
2013年 | 307篇 |
2012年 | 198篇 |
2011年 | 214篇 |
2010年 | 169篇 |
2009年 | 121篇 |
2008年 | 78篇 |
2007年 | 44篇 |
2006年 | 46篇 |
2005年 | 33篇 |
2004年 | 23篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 5篇 |
1998年 | 20篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 3篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有3068条查询结果,搜索用时 16 毫秒
1.
Mehdi Hosseini Abadshapoori 《亚洲传热研究》2021,50(2):1056-1072
Increasing the heat capacity of heat exchangers is a crucial need for modern devices. The thermal conductivity of the usual fluids and the Nusselt (Nu) number of flows containing such fluids are two bottlenecks in the way of increasing heat delivery in the heat exchangers. For this reason, nanofluids have been introduced. The effect of utilizing a Cu-water nanofluid as a coolant of two hot pipes in a square cavity is investigated numerically with a two-component lattice Boltzmann method. The volume fraction of nanoparticles is assumed to be constant (0.03) while the Richardson (Ri) number varies from 0.02 to 20. Results show that the effectiveness of nanoparticles is better observed in the natural convection mode. However, sedimentation is also very probable at high Ri numbers, which significantly reduces the effectiveness of the nanoparticles. Configurations which produce a natural convection stream similar to the forced convection one as well as the configurations with high spacing and hence, low heat stream interactions, are the best choices for a uniform heat rate from the pipes. 相似文献
2.
Amini Amir Jafari Azin Vafaei Mostafa Mahmoodian Mehrnoosh 《Journal of Materials Science: Materials in Electronics》2022,33(3):1293-1306
Journal of Materials Science: Materials in Electronics - The main weakness of polymer gas sensors is its stability. Here, we report stability enhancement of a 100 nm polypyrrole (PPy) thin... 相似文献
3.
Sama Rezasoltani Reza Ghanbari Mehdi Azizmohammad Looha Ehsan Nazemalhosseini Mojarad Abbas Yadegar Delisha Stewart Hamid Asadzadeh Aghdaei Mohammad Reza Zali 《International journal of molecular sciences》2020,21(23)
Abnormal activation of Toll-like receptor (TLRs) signaling can result in colon cancer development. The aim of this study was to investigate the expression of important TLRs in different histological types of colorectal polyps and evaluate their relationship with intestinal microbiota. The expression levels of TLR2, 3, 4, and 5 were analyzed in intestinal biopsy specimens of 21 hyperplastic polyp (HP), 16 sessile serrated adenoma (SSA), 29 tubular adenoma (TA), 21 villous/tubulovillous (VP/TVP) cases, and 31 normal controls. In addition, selected gut bacteria including Streptococcus bovis, Enterococcus faecalis, Enterotoxigenic Bacteroides fragilis (ETBF), Fusobacterium nucleatum, Porphyromonas spp., Lactobacillus spp., Roseburia spp., and Bifidobacterium spp. were quantified in fecal samples using absolute qRT PCR, and, finally, the association between TLRs and these gut microbiota- was evaluated by Spearman’s correlation coefficient. Higher expression of TLR2 and TLR4 in VP/TVP and TA, and lower expression levels of TLR3 and TLR5 in all type of polyps were observed. The differences in TLR expression patterns was not only dependent on the histology, location, size, and dysplasia grade of polyps but also related to the intestinal microbiota patterns. TLR2 and TLR4 expression was directly associated with the F. nucleatum, E. faecalis, S. bovis, Porphyromonas, and inversely to Bifidobacterium, Lactobacillus, and Roseburia quantity. Furthermore, TLR3 and TLR5 expression was directly associated with Bifidobacterium, Roseburia, and Lactobacillus quantity. Our results suggest a possible critical role of TLRs during colorectal polyp progression. An abnormal regulation of TLRs in relation to gut microbial quantity may contribute to carcinogenesis. 相似文献
4.
5.
Porkar Rezaeiye Payam Sharifi Arash Rahmani Amir Masoud Dehghan Mehdi 《The Journal of supercomputing》2021,77(12):14207-14229
The Journal of Supercomputing - With the expansion in the use of IoT, increasing the efficiency of these networks has become even more significant. Objects need reliable communications at suitable... 相似文献
6.
Imaging of the optic disc and retinal nerve fiber layer: the effects of age, optic disc area, refractive error, and gender. 总被引:3,自引:0,他引:3
Christopher Bowd Linda M Zangwill Eytan Z Blumenthal Cristiana Vasile Andreas G Boehm Parag A Gokhale Kourosh Mohammadi Payam Amini Timothy M Sankary Robert N Weinreb 《Journal of the Optical Society of America. A, Optics, image science, and vision》2002,19(1):197-207
We cross-sectionally examined the relationship between age, optic disc area, refraction, and gender and optic disc topography and retinal nerve fiber layer (RNFL) measurements, using optical imaging techniques. One eye from each of 155 Caucasian subjects (age range 23.0-80.8 y) without ocular pathology was included. Measurements were obtained by using the Heidelberg Retina Tomography (HRT), the GDx Nerve Fiber Analyzer, and the Optical Coherence Tomograph (OCT). The effects of age were small (R2 < 17%) and were limited to specific HRT, GDx, and OCT parameters. Disc area was significantly associated with most HRT parameters and isolated GDx and OCT parameters. Refraction and gender were not significantly associated with any optic disc or RNFL parameters. Although effects of age on the optic disc and RNFL are small, they should be considered in monitoring ocular disease. Optic disc area should be considered when cross-sectionally evaluating disc topography and, to a lesser extent, RNFL thickness. 相似文献
7.
Weekly storage of coolness in heavy walls (walls with large thermal inertia or large characteristic time constants or low Fourier numbers) was investigated numerically by considering one-dimensional heat conduction through the walls. The study consisted of first analyzing the heat flow through a single wall and considering various boundary conditions on the inside. The boundary conditions were: constant inside air tempeture throughout the day, variable inside air temperature on a 24-hour cycle, and variable inside air temperature on a 48-hour cycle. Next, the heat flow through walls was studied through a thermal network analysis of a simple building. In this case it was assumed that the ambient air temperature (following a periodic distribution) was increased suddenly and followed this new distribution for many days thereafter.It was concluded that walls with high thermal inertia or time constant can store coolness for several days. The larger the time constant of the wall (for example adobe as compared with brick) the longer it takes for the wall temperature to reach a steady periodic distribution after the change has occurred. However, because of low thermal conductivity of adobe, the retrieval of the stored coolness in these walls is slow, and the mean daily temperature of the room air in the adobe building does not change appreciably beyond seven days after the change. Increase of the wall thickness beyond 50 cm does not improve the thermal performance of the building significantly. 相似文献
8.
Kirby P.L. Pukala D. Manohara H. Mehdi I. Papapolymerou J. 《Microwave and Wireless Components Letters, IEEE》2006,16(6):366-368
We present the first characterization of a micromachined silicon rectangular waveguide at 400GHz. The silicon waveguide has an average loss of 0.086dB/mm for a range of 350-460GHz. The waveguides are formed using well known microfabrication techniques and demonstrate a successful first step towards the use of silicon waveguides as a viable option for THz systems. 相似文献
9.
Ahmad Nozad Golikand Elaheh Lohrasbi Mohammad Ghannadi Maragheh Mehdi Asgari 《Journal of Applied Electrochemistry》2008,38(6):869-874
The effect of carbon surface oxidation on platinum supported carbon particles (Pt/C) with nitric acid was investigated by
cyclic voltammetry, electrochemical impedance spectroscopy, polarization experiments and chronoamperometry. Cyclic voltammograms,
polarization curves and electrochemical impedance spectra showed that the treated catalyst had much larger active surface
area and higher ionic conductivity than the untreated catalyst, and provided enhanced performance for oxygen reduction. The
formation of acidic groups was examined by IR spectra. The Pt/C surface oxidation had a large effect on the performance of
a gas diffusion electrode for oxygen reduction reaction. 相似文献
10.
Khalid Mahmood Zia Mehdi Barikani Ijaz Ahmad Bhatti Mohammad Zuber Haq Nawaz Bhatti 《应用聚合物科学杂志》2008,109(3):1840-1849
A series of polyurethane (PU) elastomers was prepared by the reaction of poly(?‐caprolactone) and 4,4′‐diphenylmethane diisocyanate, which was extended with a series of chain extenders (CEs) having 2–10 methylene units in their structure. The completion of the reaction was confirmed by Fourier transform infrared spectroscopy. The chemical structures of the synthesized PU samples were characterized with Fourier transform infrared, 1H‐NMR, and 13C‐NMR spectroscopy, and the thermal properties were determined by thermogravimetric analysis, DSC, and dynamic mechanical thermal analysis techniques. The mechanical properties were also studied and are discussed. The thermogravimetric analysis and DSC analysis showed that CE length had a considerable effect on the thermal properties of the prepared samples. The dynamic mechanical thermal analysis and damping peaks were also affected by the number of methylene units in the CE length. The elastomer extended with 1,2‐ethane diol exhibited optimum thermal properties, whereas the elastomer based on 1,10‐decane diol displayed the worst thermal properties. Tensile strength and elongation at break decreased with increasing CE length, whereas hardness showed the opposite trend. The glass‐transition temperature moved toward lower temperatures with increasing CE length. The decrease in the glass‐transition temperature and tensile properties were interpreted in terms of decreasing hard segments and increasing chain flexibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献