全文获取类型
收费全文 | 1685篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 23篇 |
综合类 | 2篇 |
化学工业 | 306篇 |
金属工艺 | 29篇 |
机械仪表 | 28篇 |
建筑科学 | 86篇 |
矿业工程 | 2篇 |
能源动力 | 48篇 |
轻工业 | 138篇 |
水利工程 | 18篇 |
石油天然气 | 4篇 |
无线电 | 93篇 |
一般工业技术 | 442篇 |
冶金工业 | 216篇 |
原子能技术 | 12篇 |
自动化技术 | 267篇 |
出版年
2024年 | 13篇 |
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 45篇 |
2020年 | 35篇 |
2019年 | 39篇 |
2018年 | 38篇 |
2017年 | 34篇 |
2016年 | 42篇 |
2015年 | 50篇 |
2014年 | 71篇 |
2013年 | 96篇 |
2012年 | 94篇 |
2011年 | 136篇 |
2010年 | 91篇 |
2009年 | 82篇 |
2008年 | 103篇 |
2007年 | 117篇 |
2006年 | 91篇 |
2005年 | 87篇 |
2004年 | 55篇 |
2003年 | 48篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1967年 | 2篇 |
1960年 | 7篇 |
排序方式: 共有1714条查询结果,搜索用时 15 毫秒
871.
Huseyin Ayvaz Sarah Schirmer Yash Parulekar V.M. Balasubramaniam Jeremy A. Somerville Hossein Daryaei 《LWT》2012,46(2):437-447
Role of packaging barrier properties and storage conditions on pressure-assisted thermally processed (PATP) carrot quality were investigated. Samples were packaged in pouches fabricated using three packaging materials (Nylon/EVOH/EVA, Nylon/EVA and MetPET/PE) and processed at 600 MPa and 110 °C for 10 minutes. Processed pouches were stored at 25 and 37 °C, and withdrawn over 12 weeks. Samples were analyzed for color, β-carotene and total plate count. Oxygen and water vapor transmission rates (OTR, WVTR), melting point and enthalpy of fusion of the packages were evaluated. PATP treatment resulted in product shelf-stability during storage. Packaging type and storage conditions significantly influenced the product color and β-carotene content. Nylon/EVOH/EVA package best preserved carrot quality. PATP increased OTR of the MetPET/PE and degraded carrot color and β-carotene during storage. Raw carrots had 11.13 mg/100g β-carotene content. PATP treatment followed by 12 weeks storage at 37 °C reduced the β-carotene content of carrots packaged in Nylon/EVOH/EVA, Nylon/EVA and MetPET/PE to 7.19, 0.04 and 0.06 mg/100g, respectively. Similarly, the red color of carrot samples (25.51 for raw carrots) decreased to 19.85, 3.44 and 7.20 for Nylon/EVOH/EVA, Nylon/EVA and MetPET/PE, respectively. The study demonstrated the importance of high barrier packaging materials in preserving PATP-treated carrot quality. 相似文献
872.
Subsidies for electricity-generating technologies: A review 总被引:1,自引:0,他引:1
This paper presents estimates of the extent of subsidisation globally, via selected mechanisms, for a number of different electricity-generating technologies. The technologies covered are coal-fired, nuclear, wind, solar PV, concentrating solar, geothermal, biomass and hydroelectric power. To the knowledge of the authors, this study provides the most complete and comprehensive collation of energy subsidies so far at a global level. Our series of information allows a comparison of subsidies for electricity-generating technologies, based on the respective states of development and deployment during different time periods. To date, on average, hydropower receives the least subsidies per unit of electricity it generates and geothermal and nuclear power receive an equally low level of subsidies per kWh generated. Amongst renewables, wind power has registered a spectacular success story in reducing the need for subsidisation. The same cannot be said for the two solar technologies, and for biomass. Coal-fired power has the highest subsidisation level, despite its high level of global deployment, which is mainly because of external costs due to climate change impacts. Our study demonstrates that accounting for subsidies under an agreed framework can be important for informing future policy decisions on subsidisation. 相似文献
873.
von Schneidemesser E Zhou I Stone EA Schauer JI Shpund J Brenner S Qasrawi R Abdeen Z Sarnat JA 《Environmental science & technology》2010,44(6):1911-1917
Carbonaceous aerosol concentrations and sources were compared during a year long study at two sites in East and West Jerusalem that were separated by a distance of approximately 4 km. One in six day 24-h PM(2.5) elemental and organic carbon concentrations were measured, along with monthly average concentrations of particle-phase organic compound tracers for primary and secondary organic aerosol sources.Tracer compounds were used in a chemical mass balance ICMB) model to determine primary and secondary source contributions to organic carbon. The East Jerusalem sampling site at Al Quds University experienced higher concentrations of organic carbon (OC) and elemental carbon (EC) compared to the West Jerusalem site at Hebrew University. The annual average concentrations of OC and EC at the East Jerusalem site were 5.20 and 2.19 μg m(-3), respectively, and at the West Jerusalem site were 4.03 and 1.14 μg m(-3), respectively. Concentrations and trends of secondary organic aerosol and vegetative detritus were similar at both sites, but large differences were observed in the concentrations of organic aerosol from fossil fuel combustion and biomass burning, which was the cause of the large differences in OC and EC concentrations observed at the two sites. 相似文献
874.
High power density from a miniature microbial fuel cell using Shewanella oneidensis DSP10 总被引:1,自引:0,他引:1
Ringeisen BR Henderson E Wu PK Pietron J Ray R Little B Biffinger JC Jones-Meehan JM 《Environmental science & technology》2006,40(8):2629-2634
A miniature microbial fuel cell (mini-MFC) is described that demonstrates high output power per device cross-section (2.0 cm2) and volume (1.2 cm3). Shewanella oneidensis DSP10 in growth medium with lactate and buffered ferricyanide solutions were used as the anolyte and catholyte, respectively. Maximum power densities of 24 and 10 mW/m2 were measured using the true surface areas of reticulated vitreous carbon (RVC) and graphite felt (GF) electrodes without the addition of exogenous mediators in the anolyte. Current densities at maximum power were measured as 44 and 20 mA/m2 for RVC and GF, while short circuit current densities reached 32 mA/m2 for GF anodes and 100 mA/m2 for RVC. When the power density for GF was calculated using the cross sectional area of the device or the volume of the anode chamber, we found values (3 W/m2, 500 W/m3) similar to the maxima reported in the literature. The addition of electron mediators resulted in current and power increases of 30-100%. These power densities were surprisingly high considering a pure S. oneidensis culture was used. We found that the short diffusion lengths and high surface-area-to-chamber volume ratio utilized in the mini-MFC enhanced power density when compared to output from similar macroscopic MFCs. 相似文献
875.
Bacterial chemotaxis is of medical, biological, and geological significance. Despite its importance, current chemotaxis measurements fail to account for the speciation of the chemical effector and the protonation state of the bacterial surface. We hypothesize that adsorption of Ni2+ onto the surface of Escherichia coli can influence its effective concentration and therefore influence its ability to induce a repellent response. By measuring repellent response at different pH values, the influence of Ni2+ adsorption on chemotaxis was assessed. In addition, we tested the effect of different Ni2+ chelating agents. Our data indicate that adsorption reactions influence the chemotactic response to Ni2+. We use potentiometric titration and Ni2+ adsorption experiments to develop and constrain a thermodynamic model capable of quantifying the concentration of Ni2+ at the bacteria/solution interface. Results from this model predict that the concentration of adsorbed Ni2+ is linearly proportional to the magnitude of the chemotactic response in E. coli. If adsorption is linked to chemotaxis in other cases, then chemotactic responses in realistic settings depend on a number of environmental factors such as pH, competing binding agents (e.g., aqueous organic acids, natural organic matter, mineral surfaces, etc.), and ionic strength. Our modeling approach quantifies adsorbed species on bacterial surfaces and may be used to predict the responses of different species to a variety of chemoeffectors. Our data suggest that specified changes in environmental conditions can be used to tune chemotactic responses in natural biological and geological settings. 相似文献
876.
A Langner H Wolska J Kowalski H Duralska E Murawska 《Canadian Metallurgical Quarterly》1976,15(9):688-689
Twenty-eight psoriatic patients received PUVA treatment (psoralen and long ultraviolet irradiations. Two preparations were used; 8-methoxypsoralen and a mixture of 5-methoxypsoralen and 8-methoxypsoralen. Both gave considerable improvement, but in 6 cases the lesions reappeared after 2 to 8 weeks, in spite of maintenance treatment. In this report, photochemotherapy of psoriasis was compared, using a UVA emitting lamp, 8-MOP, and a mixture of 8-MOP and 5-methoxypsoralen (5-MOP). 相似文献
877.
McFall Sametria R.; Jamieson Jeremy P.; Harkins Stephen G. 《Canadian Metallurgical Quarterly》2009,96(1):135
Research traditions in psychology in which the evaluation-performance relationship was examined do not show agreement on the mediating process, nor is there any compelling evidence that favors one account over the others. On the basis of a molecular analysis of performance on the Remote Associates Test (RAT), Harkins (2006) argued that the potential for evaluation motivates participants to perform well, which potentiates prepotent responses. If the prepotent response is correct, performance is facilitated. If the prepotent response is incorrect, and participants do not know, or if they lack the knowledge or time required for correction, performance is debilitated. The present research pits this mere effort account against 4 other potential explanations (withdrawal of effort, processing interference, focus of attention, and drive) on 3 tasks that were specifically selected for this purpose (anagram solution, the Stroop Color-Word task, and the antisaccade task). In each case, the results are consistent with the mere effort account. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
878.
Walker H. Jack; Feild Hubert S.; Giles William F.; Armenakis Achilles A.; Bernerth Jeremy B. 《Canadian Metallurgical Quarterly》2009,94(5):1354
This study investigated participants’ reactions to employee testimonials presented on recruitment Web sites. The authors manipulated the presence of employee testimonials, richness of media communicating testimonials (video with audio vs. picture with text), and representation of racial minorities in employee testimonials. Participants were more attracted to organizations and perceived information as more credible when testimonials were included on recruitment Web sites. Testimonials delivered via video with audio had higher attractiveness and information credibility ratings than those given via picture with text. Results also showed that Blacks responded more favorably, whereas Whites responded more negatively, to the recruiting organization as the proportion of minorities shown giving testimonials on the recruitment Web site increased. However, post hoc analyses revealed that use of a richer medium (video with audio vs. picture with text) to communicate employee testimonials tended to attenuate these racial effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
879.
Yuichiro Tameda Akimichi Taketa Jeremy D. Smith Manobu Tanaka Masaki Fukushima Charles C.H. Jui Kenichi Kadota Fumio Kakimoto Takeshi Matsuda John N. Matthews Shoichi Ogio Hiroyuki Sagawa Nobuyuki Sakurai Tatsunobu Shibata Masahiro Takeda Stanton B. Thomas Hisao Tokuno Yoshiki Tsunesada Shigeharu Udo 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2009,609(2-3):227-234
The Telescope Array Project is an experiment designed to observe Ultra High Energy Cosmic Rays via a “hybrid” detection technique utilizing both fluorescence light detectors (FDs) and scintillator surface particle detectors (SDs). We have installed three FD stations and 507 SDs in the Utah desert, and initiated observations from March 2008. The northern FD station reuses 14 telescopes from the High Resolution Fly's Eye, HiRes-I station. Each of the two southern FD stations contains 12 new telescopes utilizing new FADC electronics. Each telescope is instrumented with a camera composed of 256 PMTs. Since the detectors are composed of many PMTs and each PMT detects fluorescence photons together with the vast amount of night sky background, a sophisticated triggering system is required. In this paper, we describe the trigger electronics of these new FD stations. We also discuss performance of the FDs with this triggering system, in terms of efficiencies and apertures for various detector configurations. 相似文献
880.
Holt SA Le Brun AP Majkrzak CF McGillivray DJ Heinrich F Lösche M Lakey JH 《Soft matter》2009,5(13):2576-2586
To many biophysical characterisation techniques, biological membranes appear as two-dimensional structures with details of their third dimension hidden within a 5 nm profile. Probing this structure requires methods able to discriminate multiple layers a few ?ngstr?ms thick. Given sufficient resolution, neutron methods can provide the required discrimination between different biochemical components, especially when selective deuteration is employed. We have used state-of-the-art neutron reflection methods, with resolution enhancement via magnetic contrast variation to study an oriented model membrane system. The model is based on the Escherichia coli outer membrane protein OmpF fixed to a gold surface via an engineered cysteine residue. Below the gold is buried a magnetic metal layer which, in a magnetic field, displays different scattering strengths to spin-up and spin-down neutrons. This provides two independent datasets from a single biological sample. Simultaneous fitting of the two datasets significantly refines the resulting model. A β-mercaptoethanol (βME) passivating surface, applied to the gold to prevent protein denaturation, is resolved for the first time as an 8.2 ± 0.6 ? thick layer, demonstrating the improved resolution and confirming that this layer remains after OmpF assembly. The thiolipid monolayer (35.3 ± 0.5 ?), assembled around the OmpF is determined and finally a fluid DMPC layer is added (total lipid thickness 58.7 ± 0.9 ?). The dimensions of trimeric OmpF in isolation (53.6 ± 2.5 ?), after assembly of lipid monolayer (57.5 ± 0.9 ?) and lipid bilayer (58.7 ± 0.9 ?), are precisely determined and show little variation. 相似文献