全文获取类型
收费全文 | 127265篇 |
免费 | 5400篇 |
国内免费 | 2406篇 |
专业分类
电工技术 | 3390篇 |
技术理论 | 5篇 |
综合类 | 5326篇 |
化学工业 | 18662篇 |
金属工艺 | 7270篇 |
机械仪表 | 5614篇 |
建筑科学 | 5437篇 |
矿业工程 | 1683篇 |
能源动力 | 2302篇 |
轻工业 | 8014篇 |
水利工程 | 2155篇 |
石油天然气 | 2602篇 |
武器工业 | 293篇 |
无线电 | 13895篇 |
一般工业技术 | 21302篇 |
冶金工业 | 4742篇 |
原子能技术 | 788篇 |
自动化技术 | 31591篇 |
出版年
2024年 | 414篇 |
2023年 | 953篇 |
2022年 | 1604篇 |
2021年 | 2031篇 |
2020年 | 1664篇 |
2019年 | 1414篇 |
2018年 | 15773篇 |
2017年 | 14925篇 |
2016年 | 11343篇 |
2015年 | 2667篇 |
2014年 | 2664篇 |
2013年 | 3273篇 |
2012年 | 6274篇 |
2011年 | 12570篇 |
2010年 | 11079篇 |
2009年 | 8189篇 |
2008年 | 9339篇 |
2007年 | 10138篇 |
2006年 | 2493篇 |
2005年 | 3185篇 |
2004年 | 2359篇 |
2003年 | 2188篇 |
2002年 | 1424篇 |
2001年 | 844篇 |
2000年 | 946篇 |
1999年 | 878篇 |
1998年 | 721篇 |
1997年 | 523篇 |
1996年 | 521篇 |
1995年 | 403篇 |
1994年 | 330篇 |
1993年 | 241篇 |
1992年 | 214篇 |
1991年 | 149篇 |
1990年 | 120篇 |
1989年 | 68篇 |
1988年 | 94篇 |
1987年 | 60篇 |
1986年 | 52篇 |
1985年 | 46篇 |
1984年 | 50篇 |
1980年 | 35篇 |
1968年 | 47篇 |
1966年 | 43篇 |
1965年 | 47篇 |
1959年 | 41篇 |
1958年 | 39篇 |
1957年 | 37篇 |
1955年 | 66篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
51.
Many video service sites headed by YouTube know what content requires copyright protection. However, they lack a copyright
protection system that automatically distinguishes whether uploaded videos contain legal or illegal content. Existing protection
techniques use content-based retrieval methods that compare the features of video. However, if the video encoding has changed
in resolution, bit-rate or codec, these techniques do not perform well. Thus, this paper proposes a novel video matching algorithm
even if the type of encoding has changed. We also suggest an intelligent copyright protection system using the proposed algorithm.
This can serve to automatically prevent the uploading of illegal content. The proposed method has represented the accuracy
of 97% with searching algorithm in video-matching experiments and 98.62% with automation algorithm in copyright-protection
experiments. Therefore, this system could form a core technology that identifies illegal content and automatically excludes
access to illegal content by many video service sites. 相似文献
52.
In this paper we have proposed a dynamic pricing scheme for the contributing peers in the Video on Demand (VoD) system. The
scheme provides an effective mechanism to maximize the profit through the residual resources of the contributing peers. A
utilization function is executed for each contributing peer to estimate the utility factor based on the parameters such as
initial setup cost, holding cost, chaining cost and salvage cost. In this paper, we urge an effective dynamic pricing algorithm
that efficiently utilizes a range of parameters with a varying degree of complexity. The key findings of the algorithm are
(i) each contributing peers are benefitted by the monetary based on its resource contributions to the VoD system and (ii)
a high degree of social optimum is established by proficiently aggregating the contributing peer’s resources with the overall
resources of the VoD system. We validate our claim by simulating the proposed dynamic pricing scheme with other standard pricing
schemes such as altruism, cost model and game theory perspective. The result of our dynamic pricing scheme shows the best
utility factor than other standard pricing schemes. 相似文献
53.
Distortion as a result of the quenching process is predominantly due to the thermal gradient and phase transformations within
the component. Compared with traditional liquid quenching, the thermal boundary conditions during gas quenching are relatively
simple to control. By adjusting the gas-quenching furnace pressure, the flow speed, or the spray nozzle configuration, the
heat-transfer coefficients can be designed in terms of both the component geometry and the quenching time. The purpose of
this research is to apply the optimization methodology to design the gas-quenching process. The design objective is to minimize
the distortion caused by quenching. Constraints on the average surface hardness, and its distribution and residual stress
are imposed. The heat-transfer coefficients are used as design variables. DEFORM-HT is used to predict material response during
quenching. The response surface method is used to obtain the analytical models of the objective function and constraints in
terms of the design variables. Once the response surfaces of the objective and constraints are obtained, they are used to
search for the optimum heat-transfer coefficients. This process is then used instead of the finite-element analysis. A one-gear
blank case study is used to demonstrate the optimization scheme. 相似文献
54.
Jaspreet S. Gandhi William J. van Ooij 《Journal of Materials Engineering and Performance》2004,13(4):475-480
Organofunctional silanes recently have emerged as outstanding, environmentally friendly corrosion protectors for metal substrates,
compared with conventional chromate treatments. A simple immersion technique is typically used to coat the metal surface with
silane films. However, the thickness and uniformity of the films are uncontrolled in this process. This paper proposes a new
deposition technique for the silane films on the metal surface, i.e., by electrodeposition. Hydrolyzed silanes are water-soluble,
ionized molecules, so they can be deposited on metals by electrodeposition. Various combinations of silane mixtures were tested
at different voltages, pH values, bath concentrations, and exposure times on panels of alloy aluminum and mirror-polished
ferro-plate. The surface structure was characterized by scanning electron microscopy (SEM) and ellipsometry. The resistance
of the film to corrosion was investigated by direct current (DC) polarization and electrochemical impedance spectroscopy (EIS)
techniques. Electrodeposition results in a more organized and uniform film with fewer pores, compared with immersed or dipped
films.
This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September
15–17, 2003, in Indianapolis, Indiana, and appears on pp. 320–26 of the Proceedings. 相似文献
55.
During the last ten years, techniques have been developed to measure the distribution of grain boundaries in polycrystals
as a function of both lattice misorientation and grain boundary plane orientation. This paper presents a brief overview of
the techniques used for these measurements and the principle findings of studies implementing these techniques. The most significant
findings are that grain boundary plane distributions are anisotropic, that they are scale invariant during normal grain growth,
that the most common grain boundary planes are those with low surface energies, that the grain boundary populations are inversely
correlated with the grain boundary energy, and that the coincident site lattice number is a poor predictor of the grain boundary
energy and population. 相似文献
56.
Boon-Seang Chu Sosaku Ichikawa Sumiyo Kanafusa Mitsutoshi Nakajima 《Journal of the American Oil Chemists' Society》2007,84(11):1053-1062
This work was initiated to prepare protein-stabilized β-carotene nanodispersions using emulsification–evaporation. A pre-mix
of the aqueous phase composed of a protein and hexane containing β-carotene was subjected to high-pressure homogenization
using a microfluidizer. Hexane in the resulting emulsion was evaporated under reduced pressures, causing crystallization and
precipitation of β-carotene inside the droplets and formation of β-carotene nanoparticles. Sodium caseinate (SC) was the most
effective emulsifier among selected proteins in preparing the nanodispersion, with a monomodal β-carotene particle-size distribution
and a 17-nm mean particle size. The results were confirmed by transmission-electron microscopy analysis. SC-stabilized nanodispersion
also had considerably high ζ-potential (−27 mV at pH 7), suggesting that the nanodispersion was stable against particle aggregation.
Increasing the SC concentration decreased the mean particle size and improved the polydispersity of the nanodispersions. Nanodispersions
prepared with higher β-carotene concentrations and higher organic-phase ratios resulted in larger β-carotene particles. Although
increased microfluidization pressure did not decrease particle size, it did improve the polydispersity of the nanodispersions.
Repeating the microfluidization process at 140 MPa caused the nanodispersions to become polydisperse, indicating the loss
of emulsifying capacity of SC due to protein denaturation. 相似文献
57.
Informational Entropy: a Failure Tolerance and Reliability Surrogate for Water Distribution Networks
Tiku T. Tanyimboh 《Water Resources Management》2017,31(10):3189-3204
Evolutionary algorithms are used widely in optimization studies on water distribution networks. The optimization algorithms use simulation models that analyse the networks under various operating conditions. The solution process typically involves cost minimization along with reliability constraints that ensure reasonably satisfactory performance under abnormal operating conditions also. Flow entropy has been employed previously as a surrogate reliability measure. While a body of work exists for a single operating condition under steady state conditions, the effectiveness of flow entropy for systems with multiple operating conditions has received very little attention. This paper describes a multi-objective genetic algorithm that maximizes the flow entropy under multiple operating conditions for any given network. The new methodology proposed is consistent with the maximum entropy formalism that requires active consideration of all the relevant information. Furthermore, an alternative but equivalent flow entropy model that emphasizes the relative uniformity of the nodal demands is described. The flow entropy of water distribution networks under multiple operating conditions is discussed with reference to the joint entropy of multiple probability spaces, which provides the theoretical foundation for the optimization methodology proposed. Besides the rationale, results are included that show that the most robust or failure-tolerant solutions are achieved by maximizing the sum of the entropies. 相似文献
58.
Optimization of reduction potential for electroseparation was studied for the recovery of gold, copper, and lead from acidic
solution. A linear sweep voltammetric method enabled us to determine characteristic reduction potentials for each metal and
the kinetics of the metal deposition indicated by current-voltage curves. In order to precipitate the metal species sequentially,
reduction potentials were examined for the individual and mixed solutions of Au(III), Cu(II), and Pb(II). The three metals
were reasonably well isolated from the mixed solutions such as Cu(II)/ Pb(II) and Au(III)/Cu(II)/Pb(II) in the order of the
corresponding reduction potentials, in particular, the mass transfer controlled reduction potentials, obtained from linear
sweep voltammetry (LSV) measurement. 相似文献
59.
The hydrodynamic and gas mixing characteristics have been determined in a FCC regenerator (0.48 m I.D.x3.4 m high) with FCC
particles. Solids holdup in the dense bed decreases with increasing gas velocity, but it increases in the freeboard region.
The bubble/void fraction increases with an increase along the bed height at a given gas velocity and increases with increasing
gas velocity at a constant bed height. Backmixed tracer gas at the wall region is higher than that at the center region of
the bed. The gas backmixing coefficient decreases with increasing gas velocity. 相似文献
60.
为提高重点建设项目的管理水平和工作效率,在详细分析重点建设项目的业务流程和用户需求的基础上,提出基于Web的重点建设项目信息管理系统。该系统采用典型的三层体系架构,具有较强的可扩展性和灵活性。通过该系统对重点建设项目信息科学管理,可以有效克服传统管理方式的弊端,极大地提高重点建设项目信息管理工作的效率。 相似文献