全文获取类型
收费全文 | 6112篇 |
免费 | 128篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 57篇 |
综合类 | 3篇 |
化学工业 | 1092篇 |
金属工艺 | 156篇 |
机械仪表 | 97篇 |
建筑科学 | 214篇 |
矿业工程 | 26篇 |
能源动力 | 105篇 |
轻工业 | 1030篇 |
水利工程 | 28篇 |
石油天然气 | 24篇 |
无线电 | 315篇 |
一般工业技术 | 816篇 |
冶金工业 | 1405篇 |
原子能技术 | 68篇 |
自动化技术 | 809篇 |
出版年
2021年 | 59篇 |
2019年 | 53篇 |
2018年 | 55篇 |
2017年 | 50篇 |
2016年 | 73篇 |
2015年 | 62篇 |
2014年 | 91篇 |
2013年 | 294篇 |
2012年 | 163篇 |
2011年 | 211篇 |
2010年 | 181篇 |
2009年 | 206篇 |
2008年 | 237篇 |
2007年 | 219篇 |
2006年 | 198篇 |
2005年 | 158篇 |
2004年 | 154篇 |
2003年 | 144篇 |
2002年 | 155篇 |
2001年 | 112篇 |
2000年 | 107篇 |
1999年 | 109篇 |
1998年 | 165篇 |
1997年 | 139篇 |
1996年 | 114篇 |
1995年 | 113篇 |
1994年 | 91篇 |
1993年 | 98篇 |
1992年 | 104篇 |
1991年 | 48篇 |
1990年 | 87篇 |
1989年 | 76篇 |
1988年 | 74篇 |
1987年 | 86篇 |
1986年 | 80篇 |
1985年 | 116篇 |
1984年 | 101篇 |
1983年 | 93篇 |
1982年 | 92篇 |
1981年 | 85篇 |
1980年 | 57篇 |
1979年 | 67篇 |
1978年 | 72篇 |
1977年 | 70篇 |
1976年 | 71篇 |
1975年 | 69篇 |
1973年 | 47篇 |
1917年 | 84篇 |
1913年 | 68篇 |
1912年 | 115篇 |
排序方式: 共有6245条查询结果,搜索用时 187 毫秒
81.
Responses ofRhagoletis pomonella (Walsh) (Diptera: Tephritidae) flies to host fruit visual stimuli (apples or models of apples) and chemical stimuli (synthetic apple volatile blend) were studied in semidwarf field-caged apple trees. Three different fruit or model densities (1, 4, or 16 fruit or models/ tree) and two odor release rates [ca. 0.7g/hr (close to the natural release rate of a ripe apple) and ca. 500g/hr (amount of odor released by commercially sold apple maggot traps)] were tested. Individually released flies were followed as they moved within a tree for a maximum of 20 min. We recorded three-dimensional search paths followed by foraging flies and computed such variables as total relative distance traveled before alighting on a fruit or model, track length between individual alightment sites, and directness of flight to fruits or models. Effect of odor on propensity to alight on fruit or models and host-searching behavior prior to alighting on fruit or on models varied according to fruit or model color and density. If the fruit visual stimulus was strong (e.g., red color), odor did not increase the probability of finding fruit or fruit models. As the visual stimulus became progressively weaker (red to green to clear), odor (irrespective of concentration) appeared to aid flies during the fruit-finding process. As density of fruit or models increased, the probability of flies finding a fruit or model also increased (e.g., 50% of flies found a red fruit model at 1 model/tree while 90% found a red model at 16 models/tree; 4% of flies found a clear model with odor at 1 model/tree while 35% found a clear model with odor at 16 models/tree). Findings reported elsewhere indicate thatR. pomonella flies are able to discover a point source of odor (an odor-bearing tree in a patch of trees) by flying upwind (in the tree patch) in response to intermittent exposure to odor. Findings here indicate that after arrival on a host tree (point source), flies discover individual apparent and abundant host fruit on the basis of vision. If fruit are less apparent or scarce, odor appears to interact with vision during the fruit-finding process. 相似文献
82.
83.
In order to explore the effects of chemical composition on the rheological behavior o filled polymeric systems, we prepared polystyrene (9PS) and poly(methyl methacrylate) (PMMA) particles crosslinked with either ethylene glycol dimethacrylate (EGDMA) or divinyl benzene (DVB), and mixed these particles in a PMMA matrix. PS particles crosslinked with 10% EGDMA are better dispersed in a PMMA matrix, compared to PS particles, crosslinked with 10% DVB, due to the compatibilizing effect of EGDMA. For PMMA particles crosslinked with DVB, particle-matrix interactions in a PMMA matrix are smaller than in EGDMA-PMMA filled PMMA. Therefore, particles tend to agglomerate in PMMA composites filled with DVB-PMMA particles, especially in a low molecular weight matrix. We compared PMMA matrices of molecular weights 35,000 and 75,000. Higher particle-matrix interaction in the higher molecular weight matrix resulted in lower relative viscosities for DVB-PS filled systems, due to better dispersion of the particles. Composites filled with EGDMA-PS particles behave similarly to those filled with DVB-PS particles. PMMA composites filled with DVB-PMMA particles have a lower relative viscosity in the higher molecular weight PMMA matrix at low shear rates, due to better dispersion in the higher molecular weight matrix. However at high shear rates, particles are well dispersed in both PMMA matrices and, then, the relative viscosity is higher due to better bonding in the higher molecular weight matrix. 相似文献
84.
Ronald R. Yager 《国际智能系统杂志》2014,29(10):881-905
Our interest is in the problem of comparing alternatives with uncertain payoffs when the uncertainty is represented using a measure. We first describe various aspects of the use of a measure to represent uncertainty. We recall that probability is a special well‐understood example of measure‐based uncertainty. We note that stochastic dominance provides a well‐established method for comparing alternatives in the case of probabilistic uncertainty. Inspired by this we develop an extension of the use of stochastic dominance for comparing uncertainty profiles to the case where the uncertainty is represented by a measure. We refer to this as measure based stochastic dominance. Do to the fact that in most cases a stochastic dominance relationship does not exist between alternatives this requires us to consider the use of surrogates for measure based stochastic dominance to compare alternatives. Here we investigate a class of surrogates for measure based stochastic dominance that we call Measure Weighted Means (MWM). As we see these MWM are numeric values consistent with measure based stochastic dominance. 相似文献
85.
The processing–property relationship of a model cryogenically mechanically alloyed polymer–polymer system [polycarbonate (PC) and poly(aryl ether ether ketone) (PEEK)] was investigated. PC and PEEK powders were cryogenically mechanically alloyed for 10 h, and the resulting two‐phase powder particles were processed into testable coupons with a miniature ram‐injection molder. The bulk mechanical properties of the coupons made from the mechanically alloyed powders and nonmechanically alloyed powders were investigated as a function of mechanical alloying and injection‐molding parameters. The injection‐molded coupons were mechanically tested in the three‐point‐bending mode. The results demonstrated that no measurable improvement was achieved in the energy to break, strain at failure, or failure strength in the coupons made from the mechanically alloyed materials in comparison with those of the coupons made from the nonmechanically alloyed powders. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1196–1202, 2003 相似文献
86.
G. William Chase Jr. Casimir C. Akoh Ronald R. Eitenmiller 《Journal of the American Oil Chemists' Society》1994,71(11):1273-1276
A high-performance liquid chromatographic method is described to determine the sucrose polyester (SPE) content in seven blends
of cooking oils. Four gel-permeation chromatography (GPC) columns were used in series with an evaporative light scattering
mass detector to separate the SPE from the acylglycerols in the final chromatogram. The SPE fraction was collected off the
GPC column and injected onto a reverse-phase C-18 column for quantitation with sucrose octaacetate as an internal standard
and a gradient of nonaqueous solvents as mobile phase. The chromatograms were interference-free, with only two sharp peaks
appearing. The standards were linear from 500 to 5000 μg/mL with a correlation coefficient of r=0.999. The mean percent recovery
(n=9) and standard deviation were 102±6.7. The detector could detect amounts as low as 5 μg SPE. 相似文献
87.
Dr. Christoph Goebel Prof.?Dr. Hans-Arno Jacobsen Victor del Razo Mag.? Christoph Doblander Dipl.-Ing. Jose Rivera Dipl-Inform.?Wirt Jens Ilg Dr. Christoph Flath Prof.?Dr. Hartmut Schmeck Prof.?Dr. Christof Weinhardt Dipl-Inform. Daniel Pathmaperuma Prof.?Dr. Dr.?h.?c. Hans-Jürgen Appelrath Prof.?Dr. Michael Sonnenschein Prof.?Dr. Sebastian Lehnhoff Prof.?Dr. Oliver Kramer Prof.?Dr. Thorsten Staake Prof.?Dr. Elgar Fleisch Prof.?Dr. Dirk Neumann Prof.?Dr. Jens Strüker Dr. Koray Erek Prof.?Dr. Rüdiger Zarnekow Dr. Holger Ziekow Prof.?Dr. J?rg L?ssig 《WIRTSCHAFTSINFORMATIK》2014,56(1):31-39
Due to the increasing importance of producing and consuming energy more sustainably, Energy Informatics (EI) has evolved into a thriving research area within the CS/IS community. The article attempts to characterize this young and highly dynamic field of research by describing current EI research topics and methods and provides an outlook of how the field might evolve in the future. It is shown that two general research questions have received the most attention so far and are likely to dominate the EI research agenda in the coming years: How to leverage information and communication technology (ICT) to (1) improve energy efficiency, and (2) to integrate decentralized renewable energy sources into the power grid. Selected EI streams are reviewed, highlighting how the respective research questions are broken down into specific research projects and how EI researchers have made contributions based on their individual academic background. 相似文献
88.
Transient and steady-state deformations and breakup of viscoelastic polystyrene droplets dispersed in viscoelastic high-density polyethylene matrices were observed in a simple steady shear flow between two transparent parallel disks. By separately varying the elasticities of the individual blend components, the matrix shear viscosity, and the viscosity ratio, their effects on the transient deformation, steady-state droplet size, and the breakup sequence were determined. After the startup of a steady shear flow, the viscoelastic droplet initially exhibits oscillations of its length in the flow direction, but eventually stretches preferentially in the vorticity direction. We find that at fixed capillary number, the oscillation amplitude decreases with increasing droplet elasticity, while the oscillation period depends primarily on, and increases with, the viscosity ratio. At steady-state, the droplet length along the vorticity direction increases with increasing capillary number, viscosity ratio, and droplet elasticity. Remarkably, at a viscosity ratio of unity, the droplets remain in a nearly undeformed state as the capillary number is varied between 2 and 8, apparently because under these conditions a tendency for the droplets to widen in the vorticity direction counteracts their tendency to stretch in the flow direction. When a critical capillary number, Cac, is exceeded, the droplet finally stretches in the vorticity direction and forms a string which becomes thinner and finally breaks up, provided that the droplet elasticity is sufficiently high. For a fixed matrix shear stress and droplet elasticity, the steady-state deformation along the vorticity direction and the critical capillary number for breakup both increase with increasing viscosity ratio. 相似文献
89.
The purpose of this work was to study how mineral fillers would behave in a polypropylene (PP) matrix when PP modified with maleic anhydride (MA) and/or itaconic acid (IA) was used as a coupling agent in the preparation of mineral‐filled PP composites. The composites were characterized with tensile mechanical measurements and morphological analysis. The optimum amount of the coupling agent to be used to obtain composites with improved mechanical properties was established. The results indicated that these coupling agents enhanced the tensile strength of the composites significantly, and the extent of the coupling effect depended on the nature of the interface that formed. The incorporation of coupling agents enhanced the resistance to deformation of the composite. The behavior of IA‐modified PP as a coupling agent was similar to that of a commercial MA‐modified PP for the filled PP composites. Evidence of improved interfacial bonding was revealed by scanning electron microscopy studies, which examined the surfaces of fractured tensile test specimens; their microstructures confirmed the mechanical results with respect to the observed homogeneous or optimized dispersion of the mineral‐filler phase in these composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2343–2350, 2007 相似文献
90.
A detailed investigation of the seed oil ofByrsocarpus coccineus Schum. and Thonn. has disclosedcis-11,12-methyleneoctadecanoic (lactobacillic) (13%) and two branched octadecenoic acids (0.1%). Other fatty acids in the oil
are those normally associated with seed lipids except for an unusually high proportion (12%) ofcis-11-octadecenoic acid. Lactobacillic acid has long been known as a constituent of certain bacterial lipids, but this is the
first report of its presence in a seed oil. The branched olefinic acids have not heretofore been found to occur in plants.
Mention of firm names or trade products does not imply endorsement or recommendation by the Department of Agriculture over
other firms or similar products not mentioned. 相似文献