全文获取类型
收费全文 | 33075篇 |
免费 | 866篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 366篇 |
综合类 | 35篇 |
化学工业 | 6788篇 |
金属工艺 | 859篇 |
机械仪表 | 622篇 |
建筑科学 | 1842篇 |
矿业工程 | 247篇 |
能源动力 | 1016篇 |
轻工业 | 2762篇 |
水利工程 | 335篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2149篇 |
一般工业技术 | 5196篇 |
冶金工业 | 6641篇 |
原子能技术 | 322篇 |
自动化技术 | 4618篇 |
出版年
2022年 | 196篇 |
2021年 | 386篇 |
2020年 | 332篇 |
2019年 | 399篇 |
2018年 | 488篇 |
2017年 | 510篇 |
2016年 | 520篇 |
2015年 | 463篇 |
2014年 | 736篇 |
2013年 | 2133篇 |
2012年 | 1241篇 |
2011年 | 1590篇 |
2010年 | 1169篇 |
2009年 | 1258篇 |
2008年 | 1436篇 |
2007年 | 1467篇 |
2006年 | 1256篇 |
2005年 | 1172篇 |
2004年 | 1052篇 |
2003年 | 1023篇 |
2002年 | 1031篇 |
2001年 | 634篇 |
2000年 | 615篇 |
1999年 | 575篇 |
1998年 | 599篇 |
1997年 | 499篇 |
1996年 | 604篇 |
1995年 | 546篇 |
1994年 | 532篇 |
1993年 | 534篇 |
1992年 | 486篇 |
1991年 | 321篇 |
1990年 | 438篇 |
1989年 | 424篇 |
1988年 | 379篇 |
1987年 | 425篇 |
1986年 | 382篇 |
1985年 | 515篇 |
1984年 | 491篇 |
1983年 | 443篇 |
1982年 | 464篇 |
1981年 | 445篇 |
1980年 | 353篇 |
1979年 | 365篇 |
1978年 | 329篇 |
1977年 | 307篇 |
1976年 | 268篇 |
1975年 | 318篇 |
1974年 | 243篇 |
1973年 | 279篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
P.C. Rajath Varma John Colreavy John Cassidy Mohamed Oubaha Brendan Duffy Colette McDonagh 《Progress in Organic Coatings》2009,66(4):406-411
Sol–gels are organic–inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, primarily silanes, which have found applications as electronic, optical and protective coatings. These coatings possess important characteristics such as chemical stability, physical strength and scratch resistance. Further performance improvement is achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through the sol–gel process. However due to the inherent difference in the reactivity of the precursors, the hydrolysis of each precursor must be carried out separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acids, prior to hydrolysis, to lower the hydrolysis rate.In this body of work various ligands such as organic acids, acetyl acetone (AcAc) and 2,2′-bipyridine (Bipy) were used to control the zirconium hydrolysis reaction and form nanoparticles within the silane sol matrix.Nanoparticle modified coatings formed from the silane sol on AA 2024-T3 aluminium were characterised spectroscopically, electrochemically and calorimetrically to evaluate the potential effect of the different chelates on the final film properties while neutral salt spray tests were performed to study their anti-corrosion performance. Results indicate that the acid ligand modified coatings provided the best performance followed by AcAc, while Bipy was the poorest. In all cases the zirconium nanoparticle improved the protective properties of the sol–gel coating. 相似文献
992.
Francesca Frati Keith Chamberlain Michael Birkett Samuel Dufour Patrick Mayon Christine Woodcock Lester Wadhams John Pickett Gianandrea Salerno Eric Conti Ferdinando Bin 《Journal of chemical ecology》2009,35(2):201-208
The profiles of volatile chemicals emitted by Vicia faba plants damaged by Lygus rugulipennis feeding, and by feeding plus oviposition, were shown to be quantitatively different from those released by undamaged plants.
Samples of volatile chemicals collected from healthy plants, plants damaged by males as a consequence of feeding, plants damaged
by females as a consequence of feeding and oviposition, plants damaged by feeding with mated males still present, and plants
damaged by feeding and oviposition with gravid females still present, showed significant differences in the emission of hexyl
acetate, (Z)-β-ocimene, (E)-β-ocimene, (E)-β-caryophyllene, and methyl salicylate. In particular, treatments with mated females present on plants had a significant
increase in emission levels of the above compounds, possibly due to eggs laid within plant tissues or active feeding, compared
with undamaged plants and plants damaged by males feeding, with or without insects still present. Furthermore, the pheromonal
blend released by mated L. rugulipennis females, mainly comprising hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal, was enhanced when females were active on broad bean plants, whereas such an increase was not observed in
males. Both sexes gave electroantennogram responses to green leaf volatiles from undamaged plants and to methyl salicylate
and (E)-β-caryophyllene emitted by Lygus-damaged plants, suggesting that these compounds may be involved in colonization of host plants by L. rugulipennis. In addition, mated males and females were responsive to hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal released by mated females on V. faba, indicating that these substances could have a dual function as a possible aggregation pheromone in female–female communication,
and as a sex pheromone in female–male communication.
An erratum to this article can be found at 相似文献
993.
Jie Fu Masaaki Kobayashi Shojiro Sugimoto John M. Parker 《Journal of the American Ceramic Society》2009,92(9):2119-2121
A Eu2+ -doped SiO2 –Al2 O3 –CaO–CaF2 glass was prepared and converted into a transparent glass ceramic by heat treatment. The crystalline phase and its size were determined by X-ray diffraction and a transmission electron microscopy. The scintillation of Eu2+ ions in both glass and ceramic under X-ray excitation was investigated and compared with that in a single-crystal scintillator. 相似文献
994.
The relationship between lecithin:cholesterol acyltransferase (LCAT) activity and weight loss in dogs was investigated. Four
experimental weight-loss diets were fed to 12 obese female beagles for 56 days in a partial crossover design (n = 6). High- (HGI) or low- (LGI) glycemic index starch and diacylglycerol or triacylglycerol oils were combined to compose
experimental diets with similar fatty acid profiles. Food intake and body weights were measured daily and weekly, respectively.
Fasted blood samples were drawn at day 0, day 28, and day 56 to measure plasma LCAT activity and total (TC), unesterified
(UC), and esterified (EC) cholesterol concentrations, and for fatty acid analysis of the phospholipid (PL) and EC fractions.
The LGI groups lost more weight than the HGI groups due to starch digestibility differences. An HGI starch effect on TC and
UC concentrations was observed but was unrelated to weight loss. LCAT activities increased over time but were not different
after controlling for percentage weight loss. However, a positive linear correlation was found between LCAT and UC concentrations
in all groups. Plasma PL fatty acid profiles reflected the diets fed, but increases in 16 and 18 carbon saturated and monounsaturated
fatty acids in all groups appeared to be an effect of fatty acid mobilization from storage sites. Both plasma PL and EC fatty
acid profiles were similar with both acylglycerol types and EC fatty acids reflected linoleic acid specificity with minimal
diet or time effects. 相似文献
995.
John Wawrowski 《化工设备与管道》2005,42(6):I0001-I0002
阀门选用不当,给工业界每年都造成了数百万美元的损失。不合适的阀门会导致阀门失灵,从而造成系统流体泄漏、产品偏离规格、停工检修费用、工作场所不安全以及对环境的危害。 相似文献
996.
The sex pheromone released by the adult female Tenebrio molitor, 4-methyl-1-nonanol, is well known. In addition, there is evidence that adult males release a pheromone that attracts females.
The purpose of the present study was to isolate and identify male-released pheromone(s). Emissions from virgin adult males
and females were collected on filter paper and extracted with pentane. Extracts were analyzed by gas chromatography-mass spectrometry.
One male-specific compound was detected and identified as (Z)-3-dodecenyl acetate (Z3-12:Ac). In arena bioassays, E3-12:Ac was attractive to females only, at 1 and 10 μg doses. E3-12:Ac
was also attractive to females at a 10-μg dose. The presence of both male and female pheromones, each attracting the opposite
sex, may contribute to maintaining a high-density population of both sexes. 相似文献
997.
Bozena Silberova Hilde J. Venvik John C. Walmsley Anders Holmen 《Catalysis Today》2005,100(3-4):457-462
Partial oxidation and oxidative steam reforming of propane were investigated over 0.01 wt.% Rh/Al2O3 foam catalysts. High selectivity to hydrogen was obtained for both reactions, but addition of steam to the reactant mixture gave higher selectivity to hydrogen. Stability tests over 7 h revealed that the catalytic activity of Rh was quite stable under partial oxidation conditions. Higher loss in Rh activity was observed when steam was present in the reactant mixture. FE-SEM images showed that Rh particle size and distribution are modified under partial oxidation and oxidative steam reforming conditions. However, these changes were more distinct on the catalyst used for oxidative steam reforming. 相似文献
998.
The aerodynamic particle sizer (APS) measures the size distributions of particles with aerodynamic diameter between 0.5 and in real time. To provide accurate size distributions, the APS must measure both particle size and concentration correctly. The objective of this study was to characterize the counting efficiency of the APS as a function of particle size (0.8–), particle type (liquid or solid), and APS model number (3310 vs. 3321). For solid particles, counting efficiencies ranged between 85% and 99%. For liquid droplets, counting efficiencies progressively declined from 75% at 0.8-μm drops to 25% for 10-μm drops. Fluorometric wash tests indicated that transmission losses occur when larger droplets impact on the instrument's inner nozzle. However, transmission losses did not account entirely for the reduced droplet counting efficiencies, indicating that additional losses may have occurred downstream of the inner nozzle. Between instrument comparisons revealed that although multiple APSs report similar number concentrations, small deviations in particle sizing can produce substantial errors when number concentrations are converted to mass concentrations. 相似文献
999.
This paper deals with an experimental investigation concerning steam reforming of methanol at 280, 340 and 380 °C over NiAl
and Ni (Au, Rh or Ir)Al layered double hydroxides (LDHs) derived catalysts. Incorporation of noble metal ions into the NiAl-LDH
framework was evidenced by XRD, TGA and TEM techniques. High selectivity to H2 and CO2 with less than 5% (volume) CO and trace CH4 was observed over the NiAl-LDH catalyst. Whereas CO and H2 are major products at lower temperatures after addition of Au, Rh and Ir to the NiAl-LDH system. They are significantly reduced
with the concomitant increase in CH4 and CO2 as the temperature increased. 相似文献
1000.
Gries R Khaskin G Clearwater J Hasman D Schaefer PW Khaskin E Miroshnychenko O Hosking G Gries G 《Journal of chemical ecology》2005,31(3):603-620
(Z, Z)-6,9-Heneicosadien-11-one (Z6Z9-11-one-21Hy) was identified as the major sex pheromone component of the painted apple moth (PAM), Teia anartoides (Lepidoptera: Lymantriidae), on the basis of (1) comparative gas chromatographic-electroantennographic detection (GC-EAD) analyses, GC-mass spectrometry (MS), high-performance liquid chromatography (HPLC)-MS, and HPLC-UV/visible spectroscopy of pheromone gland extracts and authentic standards; (2) GC-EAD analyses of effluvia of calling females; and (3) wind tunnel and field trapping experiments with a synthetic standard. In field experiments in Australia, synthetic Z6Z9-11-one-21Hy as a single component attracted male moths. Wind tunnel experiments suggested that a 4-component blend consisting of Z6Z9-11-one-21Hy, (6Z,9R,10S)-cis-9,10-epoxy-heneicosene (Z6-9R10S-epo-21Hy), (E, E)-7,9-heneicosadien-6,11-dione (E7E9-6,11-dione-21Hy), and 6-hydroxy-(E, E)-7,9-heneicosadien-11-one (E7E9-6-ol-11-one-21Hy) (all present in pheromone gland extracts) might induce more males to orient toward, approach, and contact the source than did Z6Z9-11-one-21Hy as a single component. Additional experiments are needed to determine conclusively whether or not Z6-9R10S-epo-21Hy, E7E9-6,11-dione-21Hy, and E7E9-6-ol-11-one-21Hy might be minor sex pheromone components of PAM. Moreover, attractiveness of synthetic pheromone and virgin PAM females needs to be compared to determine whether synthetic pheromone could replace PAM females as trap baits in the program to monitor eradication of exotic PAM in New Zealand. 相似文献