全文获取类型
收费全文 | 606篇 |
免费 | 27篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 112篇 |
金属工艺 | 6篇 |
机械仪表 | 10篇 |
建筑科学 | 18篇 |
能源动力 | 17篇 |
轻工业 | 72篇 |
水利工程 | 3篇 |
无线电 | 26篇 |
一般工业技术 | 108篇 |
冶金工业 | 161篇 |
原子能技术 | 4篇 |
自动化技术 | 89篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 14篇 |
2014年 | 9篇 |
2013年 | 40篇 |
2012年 | 32篇 |
2011年 | 41篇 |
2010年 | 28篇 |
2009年 | 17篇 |
2008年 | 25篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 50篇 |
1997年 | 33篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有633条查询结果,搜索用时 15 毫秒
101.
AM Nersissian C Immoos MG Hill PJ Hart G Williams RG Herrmann JS Valentine 《Canadian Metallurgical Quarterly》1998,7(9):1915-1929
The cDNAs encoding plantacyanin from spinach were isolated and characterized. In addition, four new cDNA sequences from Arabidopsis ESTs were identified that encode polypeptides resembling phytocyanins, plant-specific proteins constituting a distinct family of mononuclear blue copper proteins. One of them encodes plantacyanin from Arabidopsis, while three others, designated as uclacyanin 1, 2, and 3, encode protein precursors that are closely related to precursors of stellacyanins and a blue copper protein from pea pods. Comparative analyses with known phytocyanins allow further classification of these proteins into three distinct subfamilies designated as uclacyanins, stellacyanins, and plantacyanins. This specification is based on (1) their spectroscopic properties, (2) their glycosylation state, (3) the domain organization of their precursors, and (4) their copper-binding amino acids. The recombinant copper binding domain of Arabidopsis uclacyanin 1 was expressed, purified, and shown to bind a copper atom in a fashion known as "blue" or type 1. The mutant of cucumber stellacyanin in which the glutamine axial ligand was substituted by a methionine (Q99M) was purified and shown to possess spectroscopic properties similar to uclacyanin 1 rather than to plantacyanins. Its redox potential was determined by cyclic voltammetry to be +420 mV, a value that is significantly higher than that determined for the wild-type protein (+260 mV). The available structural data suggest that stellacyanins (and possibly other phytocyanins) might not be diffusible electron-transfer proteins participating in long-range electron-transfer processes. Conceivably, they are involved in redox reactions occurring during primary defense responses in plants and/or in lignin formation. 相似文献
102.
Particle Filters (PFs) have been successfully used in three‐dimensional (3D) model‐based pose estimation. Typically, these filters depend on the computation of importance weights that use similarity metrics as a proxy to approximate the likelihood function. In this paper, we explore the use of a two‐stage 3D model‐based approach based on a PF for single‐frame pose estimation. First, we use a classifier trained in a synthetic data set for Unmanned Aerial Vehicle (UAV) detection and a pretrained database indexed by bounding boxes properties to obtain an initial rough pose estimate. Second, we employ optimization algorithms to optimize the used similarity metrics and decrease the obtained error. We have tested four different algorithms: (a) Particle Filter Optimization (PFO), (b) Particle Swarm Optimization (PSO), (c) modified PSO, and (d) an approach based on the evolution strategies present in the genetic algorithms named Genetic Algorithm‐based Framework (GAbF). To check the quality of the estimate on each iteration, we have tested several similarity metrics (color, edge, and mask‐based) based on the UAV Computer‐Aided Design (CAD) model. The framework is applied to the outdoor pose estimation of a fixed‐wing UAV for autonomous landing in a Fast Patrol Boat (FPB). We extend our previous approach by adopting a better problem formulation, using Deep Neural Networks (DNNs) for UAV detection, making the comparison between the used similarity metrics, comparing pose optimization schemes, and showing new results. The future work will focus on the inclusion of this scheme in a tracking architecture to increase the accuracy of the result between observations. 相似文献
103.
Jiali Jiang Erik Valentine Bachtiar Jianxiong Lu Peter Niemz 《Holz als Roh- und Werkstoff》2018,76(3):953-964
Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. The purpose of this study was to analyze the orthotropic elastic properties of Chinese fir wood [Cunninghamia lanceolata (Lamb.) Hook] determined at different moisture conditions using an ultrasonic wave propagation method. The results were compared with those obtained by the traditional static compression or tension tests. The results confirm that the stiffness coefficients obtained by the ultrasound without considering the complete stiffness matrix show significantly higher values than the compression or tension Young’s moduli in all the three anatomical directions at each specific MC. The differences between stiffness coefficients and Young’s moduli were significantly reduced by corrections with Poisson ratio. Only in tangential direction, the Young’s moduli with Poisson ratio correction are statistically equivalent to the Young’s moduli obtained by compression and tension. 相似文献
104.
Gary C. Hart Sampson C. Huang Roy F. Lobo Joe Stewart 《The Structural Design of Tall and Special Buildings》1995,4(4):313-344
Two adjacent buildings near the epicenter of the January 17th Northridge earthquake, one with weld fractures and one without weld fractures, are considered in this research. Both buildings are six stories in height, and their primary lateral force resisting system comprises special moment resisting frames above grade. The buildings considered are referred to herein as the East Building and the West Building. Two basic types of computer studies were performed. One was an elastic 3-D analysis using SAP90, and the other an inelastic 2-D analysis using DRAIN-2DX. Three different models were, created for the elastic analysis. Two for the East Building, designated the ‘benchmark model’, and the ‘probable model’, and one for the West Building, designated the ‘West Building model’. Two different models were created for the inelastic analysis only for the East Building, also called the benchmark model and the probable model. The East Building was unoccupied at the time of the earthquake, hence two models were created for this building. The benchmark model is representative of the design state of the building, while the probable model is representative of the state of the building at the time of the earthquake. The West Building, which was fully occupied at the time of the earthquake, was modeled similarly to the benchmark. Elastic and inelastic studies were performed on these models to determine if a correlation exists between analysis and observed behavior. The findings from the analysis showed no damage to the West Building with possible damage to the East Building. This result is corroborated by the damage survey. 相似文献
105.
Electron beam induced etching (EBIE) and deposition (EBID) are promising fabrication techniques in which an electron beam is used to dissociate surface-adsorbed precursor molecules to achieve etching or deposition. Spatial resolution is normally limited by the electron flux distribution at the substrate surface. Here we present simultaneous EBIE and EBID (EBIED) as a method for surpassing this resolution limit by using adsorbate depletion to induce etching and deposition in adjacent regions within the electron flux profile. Our simulation results indicate the possibility of growth control of radially symmetric nanostructures at the sub-1 nm length scale on bulk substrates. The technique is well suited to the fabrication of ring-shaped nanostructures such as those employed in plasmonics, sensing devices, magneto-optics and magnetoelectronics. 相似文献
106.
Electron beam induced deposition (EBID) is a maskless nanofabrication technique capable of surpassing the resolution limits of resist-based lithography. However, EBID fabrication of functional nanostructures is limited by beam spread in bulk substrates, substrate charging, and delocalized film growth around deposits. Here, we overcome these problems by using environmental scanning electron microscopy (ESEM) to perform EBID and etching while eliminating charging artifacts at the nanoscale. Nanostructure morphology is tailored by slimming of deposits by ESEM imaging in the presence of a gaseous etch precursor and by pre-etching small features into a deposit (using a stationary or a scanned electron beam) prior to a final imaging process. The utility of this process is demonstrated by slimming of nanowires deposited by EBID, by the fabrication of gaps (between 4 and 7 nm wide) in the wires, and by the removal of thin films surrounding such nanowires. ESEM imaging provides a direct view of the slimming process, yielding process resolution that is limited by ESEM image resolution ( approximately 1 nm) and surface roughening occurring during etching. 相似文献
107.
Narashans Alok Sagar Sunil Pareek Sunil Sharma Elhadi M. Yahia Maria Gloria Lobo 《Comprehensive Reviews in Food Science and Food Safety》2018,17(3):512-531
Fruits and vegetables are the most utilized commodities among all horticultural crops. They are consumed raw, minimally processed, as well as processed, due to their nutrients and health‐promoting compounds. With the growing population and changing diet habits, the production and processing of horticultural crops, especially fruits and vegetables, have increased very significantly to fulfill the increasing demands. Significant losses and waste in the fresh and processing industries are becoming a serious nutritional, economical, and environmental problem. For example, the United Nations Food and Agriculture Organization (FAO) has estimated that losses and waste in fruits and vegetables are the highest among all types of foods, and may reach up to 60%. The processing operations of fruits and vegetables produce significant wastes of by‐products, which constitute about 25% to 30% of a whole commodity group. The waste is composed mainly of seed, skin, rind, and pomace, containing good sources of potentially valuable bioactive compounds, such as carotenoids, polyphenols, dietary fibers, vitamins, enzymes, and oils, among others. These phytochemicals can be utilized in different industries including the food industry, for the development of functional or enriched foods, the health industry for medicines and pharmaceuticals, and the textile industry, among others. The use of waste for the production of various crucial bioactive components is an important step toward sustainable development. This review describes the types and nature of the waste that originates from fruits and vegetables, the bioactive components in the waste, their extraction techniques, and the potential utilization of the obtained bioactive compounds. 相似文献
108.
Fbia D. Lobo de S Steffen Backert Praveen K. Nattramilarasu Soraya Mousavi Geoffrey I. Sandle Stefan Bereswill Markus M. Heimesaat Jrg-Dieter Schulzke Roland Bücker 《International journal of molecular sciences》2021,22(16)
Infections by the zoonotic foodborne bacterium Campylobacter jejuni (C. jejuni) are among the most frequent causes of bacterial gastroenteritis worldwide. The aim was to evaluate the relationship between epithelial barrier disruption, mucosal immune activation, and vitamin D (VD) treatment during C. jejuni infection, using intestinal epithelial cells and mouse models focused on the interaction of C. jejuni with the VD signaling pathway and VD treatment to improve C. jejuni-induced barrier dysfunction. Our RNA-Seq data from campylobacteriosis patients demonstrate inhibition of VD receptor (VDR) downstream targets, consistent with suppression of immune function. Barrier-preserving effects of VD addition were identified in C. jejuni-infected epithelial cells and IL-10−/− mice. Furthermore, interference of C. jejuni with the VDR pathway was shown via VDR/retinoid X receptor (RXR) interaction. Paracellular leakiness of infected epithelia correlated with tight junction (TJ) protein redistribution off the TJ domain and apoptosis induction. Supplementation with VD reversed barrier impairment and prevented inhibition of the VDR pathway, as shown by restoration of transepithelial electrical resistance and fluorescein (332 Da) permeability. We conclude that VD treatment restores gut epithelial barrier functionality and decreases bacterial transmigration and might, therefore, be a promising compound for C. jejuni treatment in humans and animals. 相似文献
109.
Lin J Zhong J Bao D Reiber-Kyle J Wang W Vullev V Ozkan M Ozkan CS 《Journal of nanoscience and nanotechnology》2012,12(3):1770-1775
We describe the fabrication of highly conductive and large-area three dimensional pillared graphene nanostructure (PGN) films from assembly of vertically aligned CNT pillars on flexible copper foils for applications in electric double layer capacitors (EDLC). The PGN films synthesized via a one-step chemical vapor deposition process on flexible copper foils exhibit high conductivity with sheet resistance as low as 1.6 ohms per square and possessing high mechanical flexibility. Raman spectroscopy indicates the presence of multi walled carbon nanotubes (MWCNT) and their morphology can be controlled by the growth conditions. It was discovered that nitric acid treatment can significantly increase the specific capacitance of the devices. EDLC devices based on PGN electrodes (surface area of 565 m2/g) demonstrate enhanced performance with specific capacitance value as high as 330 F/g extracted from the current density-voltage (CV) measurements and energy density value of 45.8 Wh/kg. The hybrid graphene-CNT nanostructures are attractive for applications including supercapacitors, fuel cells and batteries. 相似文献
110.
Improving the efficiency of IMS-IMS by a combing technique 总被引:1,自引:0,他引:1
Merenbloom SI Koeniger SL Bohrer BC Valentine SJ Clemmer DE 《Analytical chemistry》2008,80(6):1918-1927
A simple method for increasing the efficiency of multidimensional ion mobility spectrometry (IMS-IMS) measurements (as defined by the number of two-dimensional data sets necessary to sample all of the ions in a complex mixture) is illustrated. In this approach, components from a packet containing a mixture of ions are introduced into the first IMS drift region where they are separated based on differences in mobility. At the exit of this region, narrow distributions of ions having identical mobilities are selected, subjected to gentle activation conditions that are intended to induce conformational changes, and transmitted into a second IMS drift region where the new conformations are separated. Here, we describe a simple timing sequence associated with selection and activation of multiple distributions at the entrance of the second drift region in a systematic fashion that improves the efficiency of two-dimensional IMS-IMS by a factor of approximately 8. The method is illustrated by examination of a mixture of tryptic peptides from human hemoglobin. 相似文献