全文获取类型
收费全文 | 5113篇 |
免费 | 145篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 93篇 |
综合类 | 5篇 |
化学工业 | 992篇 |
金属工艺 | 122篇 |
机械仪表 | 199篇 |
建筑科学 | 97篇 |
能源动力 | 193篇 |
轻工业 | 231篇 |
水利工程 | 27篇 |
石油天然气 | 4篇 |
无线电 | 905篇 |
一般工业技术 | 913篇 |
冶金工业 | 564篇 |
原子能技术 | 25篇 |
自动化技术 | 927篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 111篇 |
2021年 | 108篇 |
2020年 | 35篇 |
2019年 | 56篇 |
2018年 | 66篇 |
2017年 | 76篇 |
2016年 | 101篇 |
2015年 | 102篇 |
2014年 | 177篇 |
2013年 | 374篇 |
2012年 | 269篇 |
2011年 | 323篇 |
2010年 | 232篇 |
2009年 | 266篇 |
2008年 | 271篇 |
2007年 | 241篇 |
2006年 | 229篇 |
2005年 | 197篇 |
2004年 | 162篇 |
2003年 | 157篇 |
2002年 | 126篇 |
2001年 | 116篇 |
2000年 | 86篇 |
1999年 | 99篇 |
1998年 | 250篇 |
1997年 | 150篇 |
1996年 | 114篇 |
1995年 | 72篇 |
1994年 | 96篇 |
1993年 | 61篇 |
1992年 | 45篇 |
1991年 | 54篇 |
1990年 | 36篇 |
1989年 | 45篇 |
1988年 | 53篇 |
1987年 | 39篇 |
1986年 | 32篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 24篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 18篇 |
1976年 | 34篇 |
1974年 | 7篇 |
排序方式: 共有5297条查询结果,搜索用时 15 毫秒
991.
Chiarenzelli J Pagano J Scrudato R Falanga L Migdal K Hartwell A Milligan M Battalagia T Holsen TM Hsu Y Hopke P 《Environmental science & technology》2001,35(16):3280-3286
Air samples were collected simultaneously at three sites downwind of Lake Ontario and at a control site near Lake Erie from March to July of 1999. The Lake Erie site (Stockton, NY) had PCB concentrations similar to rural Integrated Atmospheric Deposition Network (IADN) sampling sites across the Great Lakes, exhibited limited seasonal variation, and approximates regional background. Samples taken along Lake Ontario's southeastern shore (Rice Creek and Sterling, NY) had elevated PCB concentrations averaging approximately 1 ng/m3 and were more chlorinated than air collected at IADN sites and at Stockton. Air samples from Potsdam (approximately 75 km inland) had similar concentrations but were less chlorinated. Clausius-Clapeyron plots revealed a strong correlation between PCB fugacity and temperature near Lake Ontario; however, the extent of chlorination of the air samples rules out volatilization from the lake as a major source. It is hypothesized that volatilization from local surfaces, enriched in higher chlorinated congeners by meteorological or geographic factors, drives both the concentration and composition of airborne PCBs along Lake Ontario's southeastern shore. 相似文献
992.
Been‐Huang Chiang Su‐Tze Chou Cheng‐Kuang Hsu 《Journal of the science of food and agriculture》2005,85(14):2385-2390
The antioxidative activities and textural properties of pollock surimi gels containing four different yams were determined to evaluate the potential of using yam as a health ingredient and an alternative source for starch in surimi‐based seafoods. Surimi gels containing 20% fresh yam showed higher α,α‐diphenyl‐β‐pricryl‐hydrazyl (DPPH) radicals scavenging activities and total phenolic contents than the gels without yam. Two tested cultivars, 70W34 and 70W35, did not show significant reductions in antioxidative activities when used in surimi gel while three other cultivars revealed species‐dependant declines in both the DPPH scavenging activities and total phenolic contents. The surimi gel containing the cultivar 70R20 showed the highest breaking forces and deformations. In general, 20% fresh yam could be used to form a yam‐containing surimi gel having similar textural properties with a potato starch containing pollock surimi gel. The dried yam powders might be used at the amount of 30% fresh yam equivalent without causing significant losses of the textural properties of pollock surimi gels. Copyright © 2005 Society of Chemical Industry 相似文献
993.
Absorption and chemopreventive targets of sulforaphane in humans following consumption of broccoli sprouts or a myrosinase‐treated broccoli sprout extract
下载免费PDF全文
![点击此处可从《Molecular nutrition & food research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
994.
Bi-layer electrolyte films of Zr0.84Y0.16O1.92 (YSZ)- 0.79Bi2O3-0.21Nb2O5 (BNO) were deposited by RF magnetron sputtering on NiO-SDC anode substrates. The stoichiometry of the BNO electrolyte film was found strongly dependent on the ratio of Ar and O2 during sputtering, and the BNO film deposited at a mixture of 31 sccm Ar and 7 sccm O2 appeared to be the closest to the target composition. When deposited at 300 °C and subsequently annealed at 700 °C, the BNO electrolyte emerged to be crack free and dense with some scattering closed pores. The XRD patterns of the film are indexed to the cubic Fm m structure of Bi3NbO7. The as-deposited film was well-crystalline and consisted of fine grains and random orientation microstructures. For electrolyte thicknesses of approximately 4.0 μm YSZ and 1.5 μm BNO layers, the open circuit voltage (OCV) and the maximum power density of the single cell with Ag cathode read respectively 0.94 V and 10 mW/cm2 at 600 °C. These OCV values are lower than the expected theoretical value due to the high partial electronic conductivity. 相似文献
995.
Chi Wang Yong-Wen Cheng Chia-Hung Hsu Huan-Sheng Chien Shih-Yung Tsou 《Journal of Polymer Research》2011,18(1):111-123
Solutions of five different polymers, namely, polystyrene (PS), polyacrylonitrile (PAN), polyhydroxybutrate (PHB), poly(D-L-lactic
acid) (PLA), and Nylon6, were used to investigate their rheological properties on the electrospinnability. In order to effectively
reduce the diameter of electrospun fibers, polymers with higher molecular weights (MW) were needed to develop entangled solutions
at much lower concentrations and with viscosities as low as that of a pure solvent. A minimum polymer concentration 1.0–2.0
times larger than the entanglement concentration was required to prepare the bead-free fibers. Using this strategy, uniform
PS fibers with the lowest ever diameter of ∼15 nm were successfully obtained using an MW of 3 × 107 g/mol at a concentration of 0.1 vol.%. For a given electrospinning solution, processing variables of low flow-rate (Q) and high voltage (V) were desirable in obtaining fibers with small diameters. However, Q and V were correlated by a power law relation: V∼Q
a, wherein the exponent a had a value of 0.1–0.4, which was relevant with the solution types. Based on the finite element analysis (FEA), a significant
measure of electric field (E) occurred around the needle tip used in the experiment, and its magnitude decayed with increasing distance from the needle
end (z): E∼z
−n. The exponent n was 1.0–2.0, depending on the needle–plate geometry, i.e., needle length, needle diameter (D
o
), plate diameter, and tip-to-plate distance (H). According to FEA results, H exhibited negligible effects on the electric field in the region of interest, i.e., z/D
o
∼1 to 10. Due to the presence of high measures of E at the needle end, approaches to render a shorter and thinner straight jet issuing from the Taylor cone to yield thinner
fibers were sought because a more significant jet stretching in the “jet whipping region” can take place. A feasible route
to predict the as-spun fiber diameter produced by the manipulation of the electrified jet is provided by experimentally measuring
the jet diameter and numerically calculating the electric field for the jet whipping process. 相似文献
996.
Liao JH Wu TH Hsu FL Huang YS Chiang PH Huang ZY Huang CH Wu SH Lin MH 《International journal of molecular sciences》2011,12(10):7059-7076
Coumarin derivative 1, 5,7-dihydroxy-6-(3-methyl-1-butyryl)-4-phenyl-chromen- 2-one, has been reported to possess radical scavenging activity and DNA protection. We have synthesized a series of coumarins with structural modifications at positions C4, C5, C6 and C7 and evaluated them for their anti-UVC properties. Coumarin 7, 6-benzoyl-5,6-dihydroxy-4-phenyl-chromen-2-one, was found to have the most potent activity in protecting porcine γ-crystallin against UVC insults. Results of fluorescence assays indicated that compound 7 was capable of decreasing the loss of intensity while lens crystallins and DNA PUC19 were irradiated with UVC. Presence of compound 7 decreased hydroxyl radical levels determined by probe 1b and the free iron concentrations determined by Ferrozine reagent. The chelation assay showed that compound 7 was chelated to metal via 6-CO and 5-OH on the benzopyrone ring. The observed protective effects of compound 7 towards crystallins from insults of UVC and free radicals may be due to its iron-chelating activity and its peak absorption at 254 nm. 相似文献
997.
Cha-Jung Chen Chi-Hung LiaoKai-Chien Hsu Yi-Ting WuJeffrey C.S. Wu 《Catalysis communications》2011,12(14):1307-1310
The composite photocatalyst comprising p-type NiO and n-type TiO2 showed improved photoactivity due to the inhibition of electron–hole recombination. A series of P–N junction photocatalysts, NiO/TiO2, were prepared by incipient wetness impregnation. The photocatalysts were characterized by UV–vis spectroscopy, XRD and XPS. The photoactivity of photocatalysts was tested by the degradation of methylene blue. The results showed that 0.5 wt.% NiO/TiO2 had the highest activity as compared with TiO2. A P–N junction mechanism was proposed and verified that the photocurrent could be enhanced under forward bias in the NiO/TiO2 film. The photoactivity enhancement is attributed to P–N junction and co-catalyst effects. 相似文献
998.
Hsin-Wei Chen Kuan-Chieh Huang Chih-Yu Hsu Chia-Yu Lin Jian-Ging Chen Chuan-Pei Lee Lu-Yin Lin R. Vittal Kuo-Chuan Ho 《Electrochimica acta》2011,(23):621
Electrophoretic deposition (EPD) method is employed to obtain mesoporous TiO2 film on a titanium (Ti) foil; the film is then mechanically compressed and sintered at 350 °C before being subjected to dyeing. A comprehensive study was made on the mechanistic aspects of the EPD process. The dye-sensitized solar cell (DSSC) using the thus formed TiO2 film rendered a power conversion efficiency (Eff.) of 6.5%. Effects of various compression pressures on the photovoltaic parameters and on other characteristic parameters of the pertinent DSSCs are studied. Electrochemical impedance spectroscopy (EIS) is applied for the first time, using a novel equivalent model, to study the impedance behavior of the DSSC with this type of TiO2 film. We also obtain characteristic parameters of the TiO2 photoanode by using EIS. The coordination number of the TiO2 film, and the ratio of charge transfer resistances of electron recombination and electron transport are also obtained and analyzed. Moreover, we employ a multilayer approach and increase the film thickness to prepare TiO2 films with the same coordination number and porosity; DSSCs using such TiO2 films obtained from P90 and P25 rendered efficiencies of 6.5% and 5.24%, respectively. Scanning electron microscopy (SEM) micrographs are obtained to characterize the TiO2 films formed by the EPD technique and laser-induced transient technique is used to estimate the electron lifetime in the TiO2 films. 相似文献
999.
Polybenzimidazole (PBI)/ionic liquid (IL) composite membranes were prepared from an organosoluble, fluorine-containing PBI with ionic liquid, 1-hexyl-3-methylimidazolium tri?uoromethanesulfonate (HMI-Tf). PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The composite membranes achieve high ionic conductivity (1.6 × 10−2 S/cm) at 250 °C under anhydrous conditions. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes, the PBI/HMI-Tf composite membranes have demonstrated high thermal stability up to 300 °C, which is attractive for high-temperature (>200 °C) polymer electrolyte membrane fuel cells. 相似文献
1000.
Chiou‐Juy Chen Hsu‐Tung Lu Wen‐Yen Tseng I‐Hsiang Tseng Shih‐Liang Huang Mei‐Hui Tsai 《应用聚合物科学杂志》2011,122(1):648-656
Polyimide (PI)/silica hybrid membranes with high contact angles were prepared through the in situ sol–gel process. The precursor, poly(amic acid) with controlled block chain length, was synthesized using 4,4′‐diaminodiphenyl ether (ODA), 3,3′,4,4′‐benzophenone‐tetracarboxylic dianhydride (BTDA) and 3‐aminopropyl‐trimethoxysilane (APrTMOS) or 3‐aminopropyldimethylethoxysilane (APDiMOS). And then, phenyltrimethoxysilane (PTS) or tetramethoxysilane (TMOS) or methyltrimethoxysilane (MTrMOS) was respectively, added to the above polyamic acid and mixed thoroughly. Following curing reaction, the PI/silica hybrid membranes with different cross‐linkages, silica content, and hydrophobic properties were prepared. The effect on the formation of PI imide ring during imidization reaction is increased as the increase of silanes content and characterized by frequency shiftment and absorbance ratio of Fourier transform infrared (FTIR) measurements. All the hybrid membranes show high transparency though with high silica contents. The storage modulus, tan δ, and damping intensity by DMA measurements are all correlated with silane content or block chain length. And all these membranes with silane content possess high contact angle as compared to pure PI without any silanes added and the contact angles increase with increasing the silane content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献