全文获取类型
收费全文 | 2032篇 |
免费 | 77篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 36篇 |
综合类 | 6篇 |
化学工业 | 626篇 |
金属工艺 | 54篇 |
机械仪表 | 45篇 |
建筑科学 | 125篇 |
矿业工程 | 9篇 |
能源动力 | 46篇 |
轻工业 | 133篇 |
水利工程 | 5篇 |
无线电 | 133篇 |
一般工业技术 | 363篇 |
冶金工业 | 119篇 |
原子能技术 | 28篇 |
自动化技术 | 386篇 |
出版年
2023年 | 20篇 |
2022年 | 35篇 |
2021年 | 66篇 |
2020年 | 34篇 |
2019年 | 35篇 |
2018年 | 38篇 |
2017年 | 38篇 |
2016年 | 72篇 |
2015年 | 54篇 |
2014年 | 63篇 |
2013年 | 94篇 |
2012年 | 112篇 |
2011年 | 144篇 |
2010年 | 113篇 |
2009年 | 95篇 |
2008年 | 111篇 |
2007年 | 94篇 |
2006年 | 109篇 |
2005年 | 75篇 |
2004年 | 76篇 |
2003年 | 49篇 |
2002年 | 42篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 37篇 |
1998年 | 39篇 |
1997年 | 34篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 16篇 |
1973年 | 7篇 |
排序方式: 共有2114条查询结果,搜索用时 15 毫秒
1.
Claudia Popien Axel Kuepper Bernd Meyer 《Journal of Network and Systems Management》1994,2(4):383-400
New requirements of growing computer networks and information systems have an influence on extended client/server models with increased functionality. This forms the basis for service management in distributed systems which is realized by a service trading concept. This paper studies the requirements derived from the Open Distributed Processing (ODP) Reference Model in order to consider an open service market. Furthermore, it examines management possibilities for describing the service trading scenario. Because of similar architectures and properties ODP services, service offers, types, exporters and traders are mapped onto management components and modeled as managed objects. Therefore, the Guidelines for the Definition of Managed Objects (GDMO) are used. The final concept allows a precise and unambiguous study of the service trading scenario and provides means for exporting and importing of service offers in a distributed environment. 相似文献
2.
Ochratoxin A is a mycotoxin that may cause damage to the kidneys and the immune system in man. Foods are examined for this contaminant by the laboratories responsible for official food control. At present, there are no specific provisions for the sampling and examination of ochratoxin A in foods. Therefore, recourse is made to the provisions for aflatoxins. They prescribe the processing of samples with a weight of up to 30 kg. The examination of raw coffee for ochratoxin A in conjunction with the German Food Monitoring Programme of 2000 was undertaken with various sample weights (5, 10 and 30 kg) in order to identify the influence of the sample weight on the result. Overall, the sample weight did not have an effect on the detection and level of the ochratoxin A content in the samples of raw coffee examined. 相似文献
3.
4.
Is there a direct relationship between oral astringency and human salivary protein binding? 总被引:1,自引:0,他引:1
For decades, it is believed that astringency is due to the polyphenol-induced complexation of proline-rich salivary proteins
in the oral cavity. In order to compare for the first time the human sensory threshold concentrations and the salivary protein
binding activity of a series of astringent stimuli, human saliva protein was incubated for 5 min at 37 °C in the presence
of astringent food-derived compounds and, after micro-centrifugation, the amount of the target molecules in the supernatant
was quantitatively determined by HPLC-UV/Vis. Significant protein binding was observed for (−)-epigallocatechin-3-gallate,
(−)-gallocatechin-3-gallate, (+)-gallocatechin, and (−)-catechin-3-gallate, all of which containing at least one galloyl moiety
in the molecule and exhibiting rather high sensory thresholds of more than 200 μmol/L. In comparison, (+)-catechin and procyanidin
B2, both lacking in any galloyl function, showed only comparatively low binding activity and, most interestingly, quercetin-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside and 3-carboxymethyl-indole-1-N-β-d-glucopyranoside did not show any protein binding at all, although the later N- and O-glycosides exhibited extraordinarily low sensory threshold concentrations of less than 0.001 and 0.0003 μmol/L, respectively.
The data give some first evidence that the quantity of the non-bound, “free” astringent stimulus in the saliva liquid might
be more closely related to the sensory perception of astringency than the amount complexed or precipitated by proteins. It
is therefore questionable as to whether oral perception of astringency is related to the complexation and/or precipitation
of salivary proteins. 相似文献
5.
Process-based models have been extensively applied to assess the impact of landuse change on water quantity and quality at landscape scales. However, the routine application of those models suffers from large computational efforts, lack of transparency and the requirement of many input parameters. Data-based models such as Feed-Forward Multilayer Perceptrons (MLP) and Classification and Regression Trees (CART) may be used as effective models, i.e. simple approximations of complex process-based models. These data-based approaches can subsequently be applied for scenario analysis and as a transparent management tool provided climatic boundary conditions and the basic model assumptions of the process-based models do not change dramatically. In this study, we apply MLP, CART and Multiple Linear Regression (LR) to model the spatially distributed and spatially aggregated percolation in soils using weather, groundwater and soil data. The percolation data is obtained via numerical experiments with Hydrus1D. Thus, the complex process-based model is approximated using simpler data-based approaches. The MLP model explains most of the percolation variance in time and space without using any soil information. This reflects the effective dimensionality of the process-based model and suggests that percolation in the study area may be modelled much simpler than using Hydrus1D. The CART model shows that soil properties play a negligible role for percolation under wet climatic conditions. However, they become more important if the conditions turn drier. The LR method does not yield satisfactory predictions for the spatially distributed percolation however the spatially aggregated percolation is well approximated. This may indicate that the soils behave simpler (i.e. more linear) when percolation dynamics are upscaled. 相似文献
6.
7.
8.
Bernd Stöckel 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(10):2131-2148
A two beam interferometer in the Martin-Puplett configuration is used to determine the complex dielectric constant at 300 GHz of teflon, TPX-plastics, SPECTRALON and paraffin waxes with melting temperatures of 48° C and 72° C, respectively. The design of the quasi-optical system leads to a constant beam diameter at the power detector independent of path delay and frequency. The power detector signal is recorded not only along one period but over about 50 periods. A spectrum estimation routine allows to determine more exactly amplitude and phase angle of the signal. A basic problem is noticed: imperfect detector and source match cause harmonic distortion of the power detector signal. The effects on processing the loss tangent and the invalidation are shown. Finally loss tangent and dielectric constant are determined indirectly by optimizing an equivalent microwave circuit using a commercial available microwave design system to take multiple reflections and losses in consideration. 相似文献
9.
Vitrification of TRISO-coated gas reactor fuel particles was achieved via two methods: glass melting and sintering. Inert TRISO-coated fuel particles and a borosilicate glass were used. With glass melting at 1200-1300 °C floatation and decomposition of carbon and silicon carbide occurred. Thermal pre-treatment of the particles for oxidation of pyrocarbon did not improve the coating properties of the glass. During cooling most of the particles floated and sorbed on the crucible or mold walls. The sintered glass at 700 °C showed better coating properties of the TRISO-coated fuel particles despite higher porosity compared to glass made by melting. Aqueous leaching properties of glass with particles are similar regardless the mode of fabrication, indicating the good chemical durability of the sintered glass. Sintered glasses may constitute a good technique for TRISO-coated fuel particles immobilization for an eventual deep geological disposal. 相似文献
10.