全文获取类型
收费全文 | 2144篇 |
免费 | 85篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 24篇 |
综合类 | 9篇 |
化学工业 | 460篇 |
金属工艺 | 88篇 |
机械仪表 | 82篇 |
建筑科学 | 41篇 |
矿业工程 | 8篇 |
能源动力 | 154篇 |
轻工业 | 247篇 |
水利工程 | 12篇 |
石油天然气 | 2篇 |
无线电 | 151篇 |
一般工业技术 | 466篇 |
冶金工业 | 187篇 |
原子能技术 | 12篇 |
自动化技术 | 293篇 |
出版年
2024年 | 7篇 |
2023年 | 31篇 |
2022年 | 93篇 |
2021年 | 92篇 |
2020年 | 70篇 |
2019年 | 86篇 |
2018年 | 94篇 |
2017年 | 100篇 |
2016年 | 92篇 |
2015年 | 40篇 |
2014年 | 97篇 |
2013年 | 174篇 |
2012年 | 101篇 |
2011年 | 135篇 |
2010年 | 104篇 |
2009年 | 88篇 |
2008年 | 82篇 |
2007年 | 82篇 |
2006年 | 45篇 |
2005年 | 51篇 |
2004年 | 32篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 26篇 |
1998年 | 37篇 |
1997年 | 34篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1976年 | 14篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2236条查询结果,搜索用时 15 毫秒
131.
Helianthinin (11S), a multisubunit protein from Sunflower Seeds (Helianthus annuus L.) dissociates to its monomer (2S) through a trimeric (7S) intermediate as a function of guanidine hydrochloride (GuHCl) and guanidine thiocyanate (GuHSCN) concentration. Measurements of viscosity, velocity sedimentation patterns and spectroscopic parameters of the protein in presence of these denaturants both at equilibrium and as a function of time clearly suggest that the dissociation, unfolding and aggregation of this multimeric protein occur sequentially. The unfolding of the protein in guanidinium salts has two transitions with the first transition occurring between native to intermediate and the second transition occurring between intermediate state and unfolded state. The midpoint concentration for the major transition is 1.75 M for GuHCl and 0.8 M for GuHSCN. Evaluation of this data suggests that during the process of denaturation the simultaneous unfolding of acidic and basic subunits of the protein takes place. At intermediate concentrations of denaturant namely 1.6 M of GuHCl or 1.1 M of GuHSCN the aggregation of the protein was found to be maximum. The results suggests the possibility of a mechanism for the dissociation, denaturation and unfolding of multimeric proteins in presence of the chemical denaturants. 相似文献
132.
Zhang D. Rahmat-Samii Y. Fetterman H.R. Prakash S. Bunshah F.R. Eddy M. Nilsson J.L. 《Microwave Theory and Techniques》1993,41(6):1032-1036
The use of YBa2Cu3O7-x and Tl2CaBa2Cu2O8 high-temperature superconducting thin films to fabricate frequency selective surfaces (FSS) at millimeter-wave frequencies (75-110 GHz) is discussed. An analytical/numerical model was applied, using a Floquet expansion and the method of moments, to analyze bandstop superconducting frequency selective surfaces. Experimental results were compared with the model, and showed agreement with resonant frequency prediction with an accuracy of better than 1%. The use of the superconducting frequency selective surfaces as quasi-optical millimeter-wave bandpass filters was also demonstrated 相似文献
133.
In this paper we discuss an inexpensive solar collector in which the heat storage material is sand or sand mixed with iron filings. The heat is absorbed by the blackened portion of the heat storage material. The heat is withdrawn from the system by water flowing through a network of plastic pipes buried in the heat storage material at an appropriate depth. The large efficiency is obtained when the material is sand mixed with iron filings. It is shown that the efficiency of the system can be judged from the glass cover temperature. As the glass cover temperature decreases, the efficiency of the system increases. 相似文献
134.
Significant improvements in the performance of a capillary electrophoresis (CE) microchip with an electrochemical detector are observed using a carbon nanotube (CNT)-modified working electrode. The CNT-modified electrode allows CE amperometric detection at significantly lower operating potentials and yields substantially enhanced signal-to-noise characteristics. The electrocatalytic detection is coupled to resistance to surface fouling and hence enhanced stability. Such advantages are illustrated in connection with several classes of hydrazine, phenol, purine, and amino acid compounds. Substantial minimization of surface fouling effects has been demonstrated in connection with the monitoring of phenol and tyrosine. Factors affecting the performance of the new CNT detector were assessed and optimized. CNTs from different sources are evaluated, and the effect of an anodic pretreatment is explored. The broad and significant catalytic activity exhibited by CNT-based CE detectors indicates great promise for a wide range of bioanalytical and environmental applications. 相似文献
135.
Mobile ad hoc networks (MANETs) are infrastructure-less, multi-hop wireless networks, which can be deployed without any pre-existing setup. MANETs are mobile in nature and any node can join and leave the network at any time. Due to mobility, MANETs must be able to configure themselves without human intervention. Configuration (such as address assignment) of a node in such a network is an important issue. In this paper, we present a solution for address assignment, which is distributed in nature and can be used for IP address configuration in MANETs. Each node can allocate the address independent of others. Although our solution uses broadcast messages, results show that by fixing a few parameter values we can reduce the number of broadcast messages. We simulate the protocol and results show that our solution yields better performance those of the earlier algorithms.
相似文献
Abhishek Prakash TayalEmail: |
136.
A relatively simple and more economical process of open die hot pressing has been employed in preparing high density yttrium iron garnet samples of fine grain size (~ 1–2 μM). The samples have been investigated for the microstructure dependent spinwave line-width (ΔHk) and FMR line-width (ΔH). The values of ΔHk and ΔH are in fair agreement with the samples having the same grain size but prepared by the conventional hot pressing using refractory dies. 相似文献
137.
Clinical diagnostics and genomic research often require performing numerous genetic tests. While microfluidic devices provide
a low-cost alternative to such demands, integrated microfluidic devices are fabricated using expensive technology not always
affordable for single use. However, carryover cross-contamination (CXC) concerns (i.e. either false positive or false negative
PCR data) in PCR chips prevent reuse, defying much of the advantages of miniaturized systems developed using expensive MEMS
processing. In this work, we present an integrated and reusable PCR–CE glass microfluidic chip capable of multi-chamber PCR
and sequential CE, with emphasis on a unique chip reusability approach to avoid CXC. For reliable PCR, the surface of the
chamber is re-configured from its virgin hydrophilic (CA < 20°) to hydrophobic (CA > 110°) by silanization. To then extend
this silanization method as a chip reusability technique, the silanization coating is ‘stripped and re-silanized’ (SRS) to
create a fresh coating prior to each successive PCR run. Experimental confirmation of the effectiveness of SRS method in avoiding
the CXC is demonstrated using plasmid DNA and HIV-1 infected DNA samples. We also present passive plug microvalves incorporated
in the chip to enable fluid/vapor retention during the PCR and controlled fluid flow from the PCR chamber to the CE section
for further analysis. 相似文献
138.
Absract Samples of Cr3C2-NiCr cermet and NiCrBSi coatings formed by the high velocity oxy-fuel (HVOF) process on Superni 718 superalloy have been
corroded in the Na2SO4-V2O5 molten salt environment at 900 °C under cyclic conditions. The hot corrosion behavior of the coatings has been investigated
by means of thermogravimetric analysis, X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy, and
electron probe microanalyzer techniques. Efforts have been made to formulate the mode of corrosion attack. Both the coatings
protected the substrate superalloy Superni 718 completely. While protecting the superalloy, the Cr3C2-NiCr cermet coating partially oxidized along the splat boundaries up to the coating substrate interface, whereas only the
upper part of the coating, to about 100 μm from the surface, oxidized in the case of the NiCrBSi coating. The hot corrosion
resistance of both the coatings has been attributed to the formation of protective oxides of chromium/silicon at the surface
and at the splat boundaries of the coatings. 相似文献
139.
Metalloids normally get transferred at the interface of metal droplets passing through the slag system in the dropping zone and at the slag‐metal interface in the hearth zone in the lower region of a blast furnace. In these high temperature processes, the mass transport being the rate‐controlling factor, the viscosity of the slag system determines the kinetics of the refining reactions accompanied by mass and heat transfer at the metal droplets and slag interface. Slag systems generally possess random network structures comprising internal regions of weak ordering. The presence of these regions may result in non‐Newtonian behaviour of the slag. The rheological characteristics of a fluid relating to its network structure is expressed in terms of the indices consistency (k') and flow behaviour (n'). The extent of metalloids presence in hot metal is subjected to their residence time at the slag‐metal interface. The metal droplet descent through a surrounding fluid system has been studied and a co‐relation between drag Reynolds number and modified Reynolds number has been obtained. This correlation has been used to determine the drag velocity of a metal droplet falling through a slag system and the residence time distribution (RTD) of the metalloids at the slag‐metal interface in the lower region of the blast furnace. 相似文献
140.
A. Prakash E. J. Fielding R. Gens J. L. Van Genderen D. L. Evans 《International journal of remote sensing》2013,34(6):921-932
Coal mining areas all over the world are often threatened by serious environmental hazards such as the occurrence of coal fires, land subsidence, etc. Coal fires burn away the natural non-renewable coal resources, locally raise the temperature of the area, emit polluting gases such as oxides of carbon, sulphur and nitrogen, and when present underground are even the cause of land subsidence. Mining-induced subsidences, on the other hand, cause horizontal and vertical movements in the land surface, and open cracks and fissures that serve as inlets for oxygen, which in turn aggravate the problem of coal fires. These inter-related phenomena often render the mining areas unfit for human inhabitation and the commercial exploitation of coal nearly impossible in some parts. In this study, satellite data acquired in three regions of the electromagnetic spectrum, namely optical, thermal and microwave, along with field data, are used to identify the areas affected by coal fires and land subsidence in a coalfield in north-west China. Data fusion techniques are used for an integrated analysis of this complex problem. 相似文献