首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   946篇
  免费   62篇
  国内免费   1篇
电工技术   12篇
化学工业   191篇
金属工艺   8篇
机械仪表   17篇
建筑科学   26篇
能源动力   67篇
轻工业   109篇
水利工程   5篇
石油天然气   2篇
无线电   113篇
一般工业技术   167篇
冶金工业   58篇
原子能技术   11篇
自动化技术   223篇
  2024年   2篇
  2023年   11篇
  2022年   8篇
  2021年   56篇
  2020年   28篇
  2019年   24篇
  2018年   33篇
  2017年   23篇
  2016年   54篇
  2015年   32篇
  2014年   51篇
  2013年   77篇
  2012年   61篇
  2011年   82篇
  2010年   42篇
  2009年   50篇
  2008年   30篇
  2007年   46篇
  2006年   39篇
  2005年   28篇
  2004年   25篇
  2003年   21篇
  2002年   23篇
  2001年   15篇
  2000年   10篇
  1999年   6篇
  1998年   22篇
  1997年   8篇
  1996年   12篇
  1995年   10篇
  1994年   10篇
  1993年   9篇
  1992年   4篇
  1991年   3篇
  1990年   3篇
  1989年   4篇
  1988年   2篇
  1987年   4篇
  1985年   3篇
  1984年   4篇
  1983年   3篇
  1982年   4篇
  1981年   2篇
  1980年   5篇
  1979年   2篇
  1978年   5篇
  1977年   2篇
  1976年   2篇
  1965年   1篇
  1954年   1篇
排序方式: 共有1009条查询结果,搜索用时 78 毫秒
71.
A Geographical Information System (GIS) supported methodology has been developed in order to assess the technical and economic potential of biomass exploitation for energy production in Sicily. The methodology was based on the use of agricultural, economic, climatic, and infrastructural data in a GIS. Data about land use, transportation facilities, urban cartography, regional territorial planning, terrain digital model, lithology, climatic types, and civil and industrial users have been stored in the GIS to define potential areas for gathering the residues coming from the pruning of olive groves, vineyards, and other agricultural crops, and to assess biomass available for energy cultivation. Further, it was possible to assess the potential of biodiesel production, supposing the cultivation of rapeseed in arable crop areas. For the biomass used for direct combustion purposes, the economic availability has been assessed assuming a price of the biomass and comparing it with other fuels. This assessment has shown the strong competitiveness of firewood in comparison with traditional fossil fuels when the collection system is implemented in an efficient way. Moreover, the economic potential of biodiesel was assessed considering the on-going financial regime for fuel. At the same time, the study has shown a significant competitiveness of the finished biomass (pellets), and good potential for a long-term development of this market. An important result was the determination of biofuel production potential in Sicily. An outcome of the study was to show the opportunities stemming from the harmonisation of Energy Policy with the Waste Management System and Rural Development Plan.  相似文献   
72.
An analysis of high viscosity oil/water flow in horizontal and slightly inclined pipe is presented. We propose experimental flow maps – in particular we focus on the core-annular flow pattern boundary – pressure drops, and oil hold-up measurements. Experimental data are used to validate some models present in literature. Since hold-up measurement in liquid–liquid systems is particularly challenging and, therefore, only few data are available in literature, they are analyzed and commented in detail. The slip ratio computed by hold-up data is also provided and analyzed.  相似文献   
73.
Iron oxide nanoparticles are formidable multifunctional systems capable of contrast enhancement in magnetic resonance imaging, guidance under remote fields, heat generation, and biodegradation. Yet, this potential is underutilized in that each function manifests at different nanoparticle sizes. Here, sub‐micrometer discoidal magnetic nanoconstructs are realized by confining 5 nm ultra‐small super‐paramagnetic iron oxide nanoparticles (USPIOs) within two different mesoporous structures, made out of silicon and polymers. These nanoconstructs exhibit transversal relaxivities up to ≈10 times (r 2 ≈ 835 mm ?1 s?1) higher than conventional USPIOs and, under external magnetic fields, collectively cooperate to amplify tumor accumulation. The boost in r 2 relaxivity arises from the formation of mesoscopic USPIO clusters within the porous matrix, inducing a local reduction in water molecule mobility as demonstrated via molecular dynamics simulations. The cooperative accumulation under static magnetic field derives from the large amount of iron that can be loaded per nanoconstuct (up to ≈65 fg) and the consequential generation of significant inter‐particle magnetic dipole interactions. In tumor bearing mice, the silicon‐based nanoconstructs provide MRI contrast enhancement at much smaller doses of iron (≈0.5 mg of Fe kg?1 animal) as compared to current practice.  相似文献   
74.
We present a 2nd-order 4-bit continuous-time (CT) delta-sigma modulator (DSM) employing a 2nd-order loop filter with a single operational amplifier. This choice strongly reduces the power consumption, since operational amplifiers are the most power hungry blocks in the DSM. The DSM has been implemented in a 65 nm CMOS process, where it occupies an area of \(0.08\,\hbox {mm}^2\) . It achieves an SNDR of 64 dB over a 500 kHz signal bandwidth with an oversampling ratio of 16. The power consumption is \(76\,\upmu \hbox {W}\) from a 800 mV power supply. The DSM figure-of-merit is 59 fJ/conversion. The CT DSM is well suited for the receiver of an ultra-low-power radio.  相似文献   
75.
In this study, a sterile and biocompatible chitosan (CHI) gel for wound healing applications was formulated. CHI powder was treated in autoclave (ttCHI) to prepare sterile formulations. The heat treatment modified the CHI molecular weight, as evidenced by GPC analysis, and its physical–chemical features. Differential scanning calorimetry studies indicated that the macromolecules, before and after thermal treatment, differ in the strength of water-polymer interaction leading to different viscoelastic and flow properties. Thermally treated CHI exhibited the following effects: (i) increased the proliferation and migration of human foreskin foetal fibroblasts at 24 h; (ii) accelerated wound healing (measured as area of lesion) at 3 and 10 days in an in vivo model of pressure ulcers. These effects were linked to the increase of the hydroxyproline and haemoglobin content as well as Wnt protein expression. Moreover, we found a reduction of myeloperoxidase activity and TNF-α mRNA expression. These observations suggest the potential of this novel CHI gel in wound healing and other therapeutic applications.  相似文献   
76.
The purpose of this article is to present a methodology to identify the sources of activity in brain networks from functional magnetic resonance imaging (fMRI) data using the multiset canonical correlation analysis algorithm. The aim is to lay the foundations for a screening marker to be used as indicator of mental diseases. Group analysis blind source separation methods have proved reliable to extract the latent sources underlying the brain activities but currently there is no recognized biomarker for mental disorders. Recent studies have identified alterations in the so called default mode network (DMN) that are common to several neuropsychiatric disorders, including schizophrenia. In particular, here we account for the hypothesis that the alterations in the DMN activity can be effectively highlighted by analyzing the transient states between two different tasks. A set of fMRI data acquired from 18 subjects performing working memory tasks is investigated for such purpose. Subjects are patients affected by schizophrenia for one half and healthy control subjects for the other. Under these conditions, the proposed methodology provides high discrimination performances in terms of classification error, thereby providing promising results for a preliminary tool able to monitor the disease state or to perform a prescreening for patients at risk for schizophrenia. © 2014 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 24, 239–248, 2014  相似文献   
77.
Inherited retinal diseases (IRDs) are a heterogeneous group of conditions that include retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) and early-onset severe retinal dystrophy (EO[S]RD), which differ in severity and age of onset. IRDs are caused by mutations in >250 genes. Variants in the RPE65 gene account for 0.6–6% of RP and 3–16% of LCA/EORD cases. Voretigene neparvovec is a gene therapy approved for the treatment of patients with an autosomal recessive retinal dystrophy due to confirmed biallelic RPE65 variants (RPE65-IRDs). Therefore, the accurate molecular diagnosis of RPE65-IRDs is crucial to identify ‘actionable’ genotypes—i.e., genotypes that may benefit from the treatment—and is an integral part of patient management. To date, hundreds of RPE65 variants have been identified, some of which are classified as pathogenic or likely pathogenic, while the significance of others is yet to be established. In this review, we provide an overview of the genetic diagnostic workup needed to select patients that could be eligible for voretigene neparvovec treatment. Careful clinical characterization of patients by multidisciplinary teams of experts, combined with the availability of next-generation sequencing approaches, can accelerate patients’ access to available therapeutic options.  相似文献   
78.
79.
A new approach to take into account the effects of variable physical properties on turbulence is suggested. It allows to choose freely the turbulent closure model for conventional terms due to velocity fluctuations and to describe coherently the additional terms due to density fluctuations. Numerical calculations based on the suggested approach have been performed for carbon dioxide flowing within mini/micro channels under cooling conditions. The numerical predictions show that the effects due to density fluctuations are smaller than it could have been initially supposed and that the heat transfer impairment for mini/micro channels, which some experiments seem to highlight, is not completely explained by the considered model.  相似文献   
80.
Generalizations and unification of the celebrated Paris’ and Wöhler’s laws for fatigue crack propagation are derived by applying the recently developed quantized (or finite) fracture mechanics. In particular, three generalized Paris’, Wöhler’s or unified laws are proposed and compared, demonstrating their applicability for predicting the life time of structures containing from small (the Wöhler’s regime) to large (the Paris’ regime) propagating fatigue cracks.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号