全文获取类型
收费全文 | 1064篇 |
免费 | 68篇 |
专业分类
电工技术 | 18篇 |
综合类 | 2篇 |
化学工业 | 245篇 |
金属工艺 | 13篇 |
机械仪表 | 28篇 |
建筑科学 | 54篇 |
矿业工程 | 11篇 |
能源动力 | 67篇 |
轻工业 | 132篇 |
水利工程 | 6篇 |
石油天然气 | 3篇 |
无线电 | 89篇 |
一般工业技术 | 168篇 |
冶金工业 | 53篇 |
原子能技术 | 7篇 |
自动化技术 | 236篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 48篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 17篇 |
2017年 | 30篇 |
2016年 | 48篇 |
2015年 | 49篇 |
2014年 | 61篇 |
2013年 | 79篇 |
2012年 | 73篇 |
2011年 | 88篇 |
2010年 | 57篇 |
2009年 | 65篇 |
2008年 | 72篇 |
2007年 | 47篇 |
2006年 | 49篇 |
2005年 | 44篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有1132条查询结果,搜索用时 656 毫秒
81.
82.
83.
Paulo H. G. Zarbin Marcy G. Fonseca Daiane Szczerbowski Alfredo R. M. Oliveira 《Journal of chemical ecology》2013,39(3):358-363
We determined the site of pheromone production tissues and a partial route for the biosynthesis of the sex pheromone in Hedypathes betulinus (Coleoptera: Cerambycidae: Lamiinae), Brazil’s main green maté pest. Pheromone was found predominantly in the prothorax of males, suggesting that this is the region of production of pheromones in this insect. Scanning electron microscopy revealed small pores that may be associated with pheromone release in males; these pores also were observed in females. A deuterium-labeled putative precursor (geranyl acetone-D5) of the sex pheromone of H. betulinus was synthesized. When applied to the prothorax of males, label from the precursor was incorporated into the pheromone components, confirming that pheromone production occurs in the prothorax and that the pheromone components are biosynthesized from geranyl acetone. 相似文献
84.
Michele Casini Simonetta Ciuffi Adolfo Fiordelisi Alfredo Mazzotti Eusebio Stucchi 《Geothermics》2010
In the last 15 years geothermal exploration in Tuscany, Italy, has addressed deep reservoirs (depth ≥ 3000 m), hosted within complex geological systems, such as metamorphic formations and/or intrusive bodies. Reservoir productivity is linked to fractured and permeable zones that are rather confined and not uniformly distributed. In this context, the seismic methods represent one of the most reliable geophysical techniques for locating potential drilling targets. A 3D seismic survey has been acquired at the Travale test site, and its results have been used to develop a geological and structural model of the site, and to identify and characterize fractured zones inside the deep geothermal reservoir. A correlation between a high-amplitude reflector (H marker) and fractured contact-metamorphic rocks has been highlighted. More than 70% of the total geothermal fluid production at the Travale area comes from this seismic marker. 相似文献
85.
We measured turn-taking in terms of hand and head movements and asked if the global rhythm of the participants' body activity relates to word learning. Six dyads composed of parents and toddlers (M = 18 months) interacted in a tabletop task wearing motion-tracking sensors on their hands and head. Parents were instructed to teach the labels of 10 novel objects and the child was later tested on a name-comprehension task. Using dynamic time warping, we compared the motion data of all body-part pairs, within and between partners. For every dyad, we also computed an overall measure of the quality of the interaction, that takes into consideration the state of interaction when the parent uttered an object label and the overall smoothness of the turn-taking. The overall interaction quality measure was correlated with the total number of words learned.In particular, head movements were inversely related to other partner's hand movements, and the degree of bodily coupling of parent and toddler predicted the words that children learned during the interaction. The implications of joint body dynamics to understanding joint coordination of activity in a social interaction, its scaffolding effect on the child's learning and its use in the development of artificial systems are discussed. 相似文献
86.
Alfredo B. J. C. Nhantumbo Thomas Kätterer Stig Ledin Christiaan C. Du Preez 《Nutrient Cycling in Agroecosystems》2009,83(1):13-26
Leaves of Brachystegia spiciformis represent a substantial fraction of the total aboveground litter in bush fallow fields with sandy soils in southern Mozambique,
where annual rainfall exceeds 600 mm. This species is one of the most important in the miombo woodland that is the natural
vegetation of the region. Proper knowledge of the decomposition of its litter is therefore crucial for understanding processes
responsible for natural build-up of fertility in agricultural soils abandoned to bush fallow during shifting cultivation.
This study investigated the effects of soil water content and soil temperature on loss of organic carbon (C) from decomposing
leaves in litterbags with 1 mm mesh size. The litterbags were buried 50 mm deep in recently abandoned agricultural fields
cleared of any vegetation (Bare) and in more than 15-year-old bush fallow fields (Fallow) of sites covering a climatic transect
with annual rainfall from <400 mm to >1,000 mm. Two patterns of C loss were observed, one in coastal and wetter agroecosystems
(rainfall >600 mm) and the other in inland and drier agroecosystems (rainfall <600 mm). In the wetter agroecosystems C loss
was faster, whereas in drier agroecosystems it was more sensitive to rainfall pulses. Similarly, C loss was faster in fallow
fields than in bare fields. During summer, bare fields reached soil temperatures higher than the estimated upper boundary
favourable for C loss from decomposing leaf litter at all sites. A simple dynamic decomposition model describing the C fraction
remaining in the litterbags was developed. Coefficients of determination (R
2) for the individual experimental units varied between 0.79 and 0.97. The general model for all sites and fields improved
explanation of total variation from 81% to 86% when measured soil temperature and soil water content were used as modifiers
of decomposition rate, compared with the standard negative exponential model. Root-mean-square error and systematic bias were
9.7% and 0.5% of initial C, respectively. Decomposition was more strongly affected by soil water content than by soil temperature
and explained 75% of total variation. Thus, rainfall is the main driver of C loss from leaf litter in these agroecosystems. 相似文献
87.
Summary The objective of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms
in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept
heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting,
suitably-chosen, discrete micro- and nano-particles. We ran direct numerical simulations for hydrodynamically fully developed,
thermally developing turbulent channel flow at shear Reynolds number Re
τ
= 150 and Prandtl number Pr = 3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results
on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes
at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability
against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is
observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings
and are discussed in the frame of the current research activities in the field. Future developments are also outlined.
Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday
It is our great pleasure to take part in this Festschrift Issue dedicated to the celebration of the 70th birthday of Professor
Franz Ziegler. To honour his activity and his scientific achievements, we prepared this paper, crafted with friendship and
respect. We wish Franz many more productive, enjoyable and happy years and a solid and long collaboration as Editors of Acta
Mechanica. 相似文献
88.
On the Contrast in Visual Cryptography Schemes 总被引:16,自引:0,他引:16
A visual cryptography scheme is a method to encode a secret image SI into shadow images called shares such that certain qualified subsets of shares enable the ``visual' recovery of the secret
image. The ``visual' recovery consists of xeroxing the shares onto transparencies, and then stacking them. The shares of
a qualified set will reveal the secret image without any cryptographic computation.
In this paper we analyze the contrast of the reconstructed image in k out of n visual cryptography schemes. (In such a scheme any k shares will reveal the image, but no set of k-1 shares gives any information about the image.) In the case of 2 out of n threshold schemes we give a complete characterization of schemes having optimal contrast and minimum pixel expansion in
terms of certain balanced incomplete block designs. In the case of k out of n threshold schemes with we obtain upper and lower bounds on the optimal contrast.
Received 27 September 1996 and revised 13 February 1998 相似文献
89.
A widely used procedure for solving the problem of vertical consolidation of layers with different properties is to transform the thicknesses of the layers in proportion to the square root of their coefficients of consolidation. However, the Gray–Barber closed-form solution shows that this procedure is not correct except under a restrictive set of conditions. The transformation method should not be used. When solutions are needed for layered systems, the Gary–Barber solution or numerical methods should be employed. 相似文献
90.
This article presents a generic project risk management process that has been particularized for construction projects from the point of view of the owner and the consultant who may be assisting the owner. The process could also be adapted to the needs of other project participants, and many points referred to in the article can be directly applied to them. Any project risk management process must be tailored to the particular circumstances of the project and of the organization undertaking it. First, the article explains a complete or generic project risk management process to be undertaken by organizations with the highest level of risk management maturity in the largest and most complex construction projects. After that, factors influencing possible simplifications of the generic process are identified, and simplifications are proposed for some cases. Then the application to a real project is summarized. As a final validation, a Delphi analysis has been developed to assess the project risk management methodology explained here, and the results are presented. 相似文献