全文获取类型
收费全文 | 5016篇 |
免费 | 178篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 58篇 |
综合类 | 5篇 |
化学工业 | 1144篇 |
金属工艺 | 92篇 |
机械仪表 | 100篇 |
建筑科学 | 347篇 |
矿业工程 | 8篇 |
能源动力 | 121篇 |
轻工业 | 458篇 |
水利工程 | 39篇 |
石油天然气 | 22篇 |
无线电 | 320篇 |
一般工业技术 | 753篇 |
冶金工业 | 1070篇 |
原子能技术 | 64篇 |
自动化技术 | 603篇 |
出版年
2022年 | 48篇 |
2021年 | 50篇 |
2020年 | 46篇 |
2019年 | 57篇 |
2018年 | 62篇 |
2017年 | 83篇 |
2016年 | 87篇 |
2015年 | 66篇 |
2014年 | 115篇 |
2013年 | 311篇 |
2012年 | 156篇 |
2011年 | 233篇 |
2010年 | 205篇 |
2009年 | 182篇 |
2008年 | 205篇 |
2007年 | 208篇 |
2006年 | 191篇 |
2005年 | 163篇 |
2004年 | 148篇 |
2003年 | 139篇 |
2002年 | 125篇 |
2001年 | 103篇 |
2000年 | 85篇 |
1999年 | 86篇 |
1998年 | 173篇 |
1997年 | 132篇 |
1996年 | 88篇 |
1995年 | 84篇 |
1994年 | 89篇 |
1993年 | 85篇 |
1992年 | 62篇 |
1991年 | 62篇 |
1990年 | 69篇 |
1989年 | 75篇 |
1988年 | 78篇 |
1987年 | 47篇 |
1986年 | 61篇 |
1985年 | 69篇 |
1984年 | 72篇 |
1983年 | 57篇 |
1982年 | 56篇 |
1981年 | 64篇 |
1980年 | 58篇 |
1979年 | 70篇 |
1978年 | 65篇 |
1977年 | 57篇 |
1976年 | 59篇 |
1975年 | 35篇 |
1974年 | 41篇 |
1973年 | 40篇 |
排序方式: 共有5204条查询结果,搜索用时 15 毫秒
1.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry 相似文献
2.
3.
Maimaitiaili Tayier Yunfeng Zhao Dengle Duan Rongge Zou Yunpu Wang Roger Ruan 《木材化学与工艺学杂志》2020,40(3):190-199
AbstractLignin biochar-catalytic depolymerization using biochar Fe-600, Fe-800, Ni-600, Ni-800 catalysts under microwave-heating (180?°C for 30?min) was explored in an ethanol/formic acid (1:1) media. Non-catalyst depolymerization was also studied and compared with the biochar-catalysts results. Characteristics of the bio-char catalysts were analyze by BET, XRD, and FT-IR. GPC, FT-IR, and MALDI-TOF MS spectrometry were also used to characterize the depolymerization products. The experimental results showed that the SBET, Vt, and Vmec and average pore diameter of the biochars are considerably dependent on the preparation temperature and type of cation (Ni2+ or Fe3+). The maximum yield of bio-oil product was obtained as 85?wt% with the addition of biochar Ni-600 and the total amount of oligomers or monomers with a molecular weight of 164 to 446 reaches 80.4%. 相似文献
4.
5.
This work examines the correlation between the 1H‐NMR T2 relaxation constant and the mechanical properties of aged crosslinked polyolefin cable insulation. T2 experiments on unswollen samples could not differentiate between unaged and highly aged materials; all exhibited 1H T2 constants of approximately 0.5 ms. To accentuate the effects of aging, samples were swollen in various solvents. Unaged samples had T2 values of approximately 15 ms in good solvents. With thermal aging, T2 values decreased as the ultimate tensile elongation decreased. However, the correlation between T2 and elongation differed for samples irradiated with high‐energy radiation and for materials aged above versus below the crystalline melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2578–2582, 2003 相似文献
6.
Models that link ecological responses to hydrologic changes are important for assessing the effects of flow regulation on aquatic and riparian ecosystems. Based on the Recruitment Box Model, a graphical model used to prescribe environmental flows for cottonwood (Populus spp.) recruitment, we designed a simulation model to represent the influence of river flow dynamics on seedling recruitment of riparian pioneer woody plants. The model simulates the influence of temporal patterns of river stage on dispersal, germination, initial recruitment and over‐winter survival of first‐year seedlings of riparian pioneer shrubs and trees. We used the model to simulate seedling recruitment patterns for five species (Acer saccharinum, Betula nigra, Populus deltoides, Salix nigra and Salix exigua) on the Wisconsin River (Wisconsin, USA) under three flow scenarios: historic (1935–2002), simulated natural (1915–1975) and simulated regulated flows (1915–1975). Simulation results agreed well with field‐observed relative differences among years (1997–2000) in seedling densities for the five focal species. Simulated successful recruitment years were highly synchronous among species, but species differed in their sensitivity to flows at different times during the growing season, consistent with among‐species differences in seed dispersal timing. Comparison of simulated natural and regulated flows for 1915–1975 showed that flow regulation decreased monthly flow variability, increased late summer to winter baseflow and reduced the magnitude of spring peaks. Simulated recruitment and over‐winter survival of tree seedlings of all species was enhanced under the regulated flow scenario, likely due to increased summer baseflow and reductions in peak flood magnitude. Our analyses show the utility of extending the Recruitment Box Model to include multiple species of riparian shrubs and trees, and the effects of post‐colonization flows on their recruitment success. However, some key functional relationships between flow patterns and woody seedling demography (e.g. shear stress thresholds for seedling mortality) have not been adequately quantified and merit further study. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
7.
8.
Marginal costs of electricity vary by time and location. In the past, researchers attributed the variations to factors related to electricity generation and transmission. These authors, however, have not analyzed possible variations in marginal distribution capacity costs (MDCC). The objectives of this paper are:
- 1. (i) to show that large MDCC variations are due to the dispersion in distribution capital expenditures by time and space,
- 2. (ii) to propose a method for quantifying the area- and time-specific MDCC in the presence of lumpy investments, and
- 3. (iii) to compare our MDCC estimates to those commonly used in the electric utility industry.
9.
10.
O Bernard B Chachuat A Hélias B Le Dantec B Sialve J-P Steyer L Lardon P Neveu S Lambert J Gallop M Dixon P Ratini A Quintabà S Frattesi J M Lema E Roca G Ruiz J Rodriguez A Franco P Vanrolleghem U Zaher D J W De Pauw K De Neve K Lievens D Dochaine O Schoefs H Fibrianto R Farina V Alcaraz Gonzalez V Gonzalez Alvarez P Lemaire J A Martinez F Esandi O Duclaud J F Lavigne 《Water science and technology》2005,52(1-2):457-464
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem. 相似文献