全文获取类型
收费全文 | 3885篇 |
免费 | 170篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 58篇 |
综合类 | 9篇 |
化学工业 | 541篇 |
金属工艺 | 98篇 |
机械仪表 | 77篇 |
建筑科学 | 289篇 |
矿业工程 | 14篇 |
能源动力 | 139篇 |
轻工业 | 367篇 |
水利工程 | 45篇 |
石油天然气 | 16篇 |
无线电 | 303篇 |
一般工业技术 | 691篇 |
冶金工业 | 415篇 |
原子能技术 | 20篇 |
自动化技术 | 980篇 |
出版年
2024年 | 6篇 |
2023年 | 20篇 |
2022年 | 33篇 |
2021年 | 71篇 |
2020年 | 54篇 |
2019年 | 71篇 |
2018年 | 104篇 |
2017年 | 124篇 |
2016年 | 113篇 |
2015年 | 98篇 |
2014年 | 116篇 |
2013年 | 289篇 |
2012年 | 233篇 |
2011年 | 297篇 |
2010年 | 227篇 |
2009年 | 206篇 |
2008年 | 268篇 |
2007年 | 229篇 |
2006年 | 218篇 |
2005年 | 170篇 |
2004年 | 125篇 |
2003年 | 122篇 |
2002年 | 129篇 |
2001年 | 83篇 |
2000年 | 78篇 |
1999年 | 69篇 |
1998年 | 60篇 |
1997年 | 53篇 |
1996年 | 48篇 |
1995年 | 46篇 |
1994年 | 33篇 |
1993年 | 24篇 |
1992年 | 30篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 5篇 |
排序方式: 共有4062条查询结果,搜索用时 15 毫秒
61.
Chris I. Chiwetelu Graham H. Neale Vladimir Hornof 《Chemical Engineering Communications》1989,84(1):13-20
In reacting systems, dynamic interfacial tension (IFT) values above 10-20 mN/m are often encountered. For such high tension values, infinitely long oil droplets will not be realised in spinning drop tensiometry. Hence, Vonnegut's solution will not be strictly valid. The experimentalist is then compelled to use one of the several alternative solution schemes proposed in the literature. We have obtained dynamic IFT data for 0.3125 mM oleic acid in hexadecane contacted with various NaOH solutions by the use of a novel experimental scheme called photo-micropendography. These tension values were then compared with spinning drop tensiometer data calculated by using three alternative solution schemes, namely, Vonnegut's method, the formula of Slattery and Chen and the analysis of Princen el al. The comparison showed that when the droplet's length/width ratio was below 2.5, Vonnegut's formula was severely in error. The solution scheme proposed by Slattery and Chen gave tension values close to those found by photo-micropendography over the entire range of IFT values exhibited by the oleic acid/caustic systems. However, the most consistent and reasonably accurate tension values resulted from the use of Table I in the paper by Princen, Zia and Mason. A simplified computer algorithm has been proposed for calculating dynamic interfacial tensions using the formulas and tables proposed by the latter authors. However, at length/width ratios above 2.5, the agreement between interfacial tensions determined by micropendography and spinning drop data calculated by the use of Vonnegut's solution was quite good. 相似文献
62.
63.
Jan Willem?van?GroenigenEmail author Pieter Jan?Georgius Chris?van?Kessel Eduard W.J.?Hummelink Gerard L.?Velthof Kor B.?Zwart 《Nutrient Cycling in Agroecosystems》2005,72(1):13-25
Studies on emissions of nitrous oxide (N2O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in
the topsoil. However, in soils with shallow water tables, significant N2O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N2O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N2O to the overall losses of N2O to the environment. We applied 15N labeled fertilizer at a rate of 5.22 kg 15N ha−1; 50% as Ca(NO3)2 and 50% as NH4Cl, on a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.), and traced soil N2O concentrations and fluxes over a one-year period. Throughout the year, total N2O and the amount of 15N recovered in soil N2O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m−3 and 24 μg 15N m−3, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of
N2O was 446 g N2O-N ha−1, the recovery of 15N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N2O concentrations. During winter, no such relation was found. We concluded that the formation of N2O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO3− concentration or temperature. Although high subsoil N2O concentrations did not lead to high surface fluxes of N2O in the winter, artificial draining may lead to high indirect N2O emissions through supersaturated drainage water. 相似文献
64.
Methods for the analysis of reliability of ordered categorical scales are discussed, focussing on the limitation of the single summary-weighted kappa coefficients. A symmetric matrix of kappa-type coefficients is suggested as an alternative. The method is proposed as being suitable for ordinal scale where there is no underlying continuum. Their application is illustrated using two data sets from reliability studies. If, instead, distances between categories can be specified, a weighted mean of the matrix terms can be used as a summary measure. This is equal to a weighted kappa coefficient with squared weights, provided distances between adjacent categories are equal. When a study design corresponds to a one-way random effects model, estimates of precision of kappa-type coefficient, including the coefficients described here, can be obtained using the delta-method, bootstrap resampling by subjects or jack-knifing by subjects. In the case of interobserver reliability studies, where there may be systematic differences between observers, the investigator may wish to generalise to a population of observers and subjects. In this case, jack-knifing by observer and subject is suggested. Empirical comparisons are made between standard error estimates based on the delta-method, on jack-knifing by subjects and a two-way jack-knife by subjects and observers. The results suggest that standard errors based on the delta-method or jack-knifing by subject alone may be overly precise. 相似文献
65.
Maintaining or restoring physical habitat diversity is a central tenet of sustainable river management, yet a link between habitat and ecological diversity in fluvial systems has long remained equivocal. The lack of consistent evidence partly reflects the problems of characterizing habitat in ways that are ecologically meaningful. This paper assesses the influence of habitat heterogeneity and complexity on macroinvertebrate assemblages in a mountain gravel‐bed river. With the use of 0.1‐m resolution data obtained from an acoustic Doppler current profiler, heterogeneity and complexity in hydraulic conditions and bed topography were characterized using 13 metrics applied to 30 areas, each 1 m2, with an invertebrate sample collected from each area. Turnover of invertebrate taxa (i.e., β‐diversity) between sampled areas was rather limited, but observed differences in diversity were related significantly to several metrics of habitat heterogeneity. Invertebrate abundance was related to habitat diversity, patch size coefficient of variation, and patch size, whereas the Shannon diversity was related to the number of patches and patch size. None of the habitat complexity metrics accounted for a significant amount of observed variation in invertebrate communities between sampled areas. The paper demonstrates that high‐resolution data can help reveal relationships between habitat and benthic invertebrate diversity. 相似文献
66.
8月中旬当美国大型投资机构Sentinel停止投资者抽离资金时,它的理由是市场出现了“恐慌”。毫无疑问:近日全球市场剧烈震荡,导致金融界某些领域的危机感日益加剧。[第一段] 相似文献
67.
Arvind Agarwal Tim McKechnie Sudipta Seal 《JOM Journal of the Minerals, Metals and Materials Society》2002,54(9):42-44
Research Summary Nanostructured ceramics and their composites possess improved properties such as tensile strength, fatigue
strength, hardness, and wear resistance. Freestanding, near-net shape, nanostructured Al2O3 components can be synthesized via plasma-spray forming. In this study, plasma-spray parameters were optimized and an innovative
substrate cooling technique was developed to retain nanosize Al2O3 in the spray deposit. Nanosize Al2O3 particles were partially melted and trapped between the fully melted coarser, micrometersize Al2O3grains. Densification of the spray-deposited Al2O3occurred via solidification and sintering. A similar processing approach can be adopted for fabrication of near-net shapes
of a variety of nanostructured materials (metals, ceramics, and intermetallics) and their combinations by selecting suitable
powder-treatment and plasmaspray parameters. 相似文献
68.
Competence management in knowledge intensive organizations using consensual knowledge and ontologies
Chris Kimble José Braga de Vasconcelos Álvaro Rocha 《Information Systems Frontiers》2016,18(6):1119-1130
This article describes an architecture suitable for use in a competence management system for knowledge intensive organizations (KIOs). The underlying motivation for this work is to explore the practical problems of the use of codified knowledge in knowledge management systems (KMS) in KIOs. We explore some of the key issues associated with the use of tacit and codified knowledge in KMS, and describe an architecture based on an ontology-driven framework derived from collective and consensual knowledge that acts as a structure for a formal knowledge base. We describe, in outline, a prototype competence management system based on this architecture designed to support the management of competencies in a structured way. We conclude with some observations about our approach to the representation of knowledge in a KMS and its potential value to KIOs. 相似文献
69.
Xin Lin Chris M. J. Tampère Francesco Viti Ben Immers 《Networks and Spatial Economics》2016,16(1):349-369
Increasing numbers of hard environmental constraints are being imposed in urban traffic networks by authorities in an attempt to mitigate pollution caused by traffic. However, it is not trivial for authorities to assess the cost of imposing such hard environmental constraints. This leads to difficulties when setting the constraining values as well as implementing effective control measures. For that reason, quantifying the cost of imposing hard environmental constraints for a certain network becomes crucial. This paper first indicates that for a given network, such cost is not only related to the attribution of environmental constraints but also related to the considered control measures. Next, we present an assessment criterion that quantifies the loss of optimality under the control measures considered by introducing the environmental constraints. The criterion can be acquired by solving a bi-level programming problem with/without environmental constraints. A simple case study shows its practicability as well as the differences between this framework and other frameworks integrating the environmental aspects. This proposed framework is widely applicable when assessing the interaction of traffic and its environmental aspects. 相似文献
70.
Bob?Coecke Chris?HeunenEmail author Aleks?Kissinger 《Quantum Information Processing》2016,15(12):5179-5209
We introduce a construction that turns a category of pure state spaces and operators into a category of observable algebras and superoperators. For example, it turns the category of finite-dimensional Hilbert spaces into the category of finite-dimensional C*-algebras and completely positive maps. In particular, the new category contains both quantum and classical channels, providing elegant abstract notions of preparation and measurement. We also consider nonstandard models that can be used to investigate which notions from algebraic quantum information theory are operationally justifiable. 相似文献