全文获取类型
收费全文 | 30772篇 |
免费 | 599篇 |
国内免费 | 913篇 |
专业分类
电工技术 | 596篇 |
技术理论 | 2篇 |
综合类 | 805篇 |
化学工业 | 5058篇 |
金属工艺 | 3102篇 |
机械仪表 | 3324篇 |
建筑科学 | 4451篇 |
矿业工程 | 540篇 |
能源动力 | 964篇 |
轻工业 | 1122篇 |
水利工程 | 272篇 |
石油天然气 | 483篇 |
武器工业 | 124篇 |
无线电 | 1121篇 |
一般工业技术 | 5492篇 |
冶金工业 | 1041篇 |
原子能技术 | 229篇 |
自动化技术 | 3558篇 |
出版年
2024年 | 34篇 |
2023年 | 342篇 |
2022年 | 561篇 |
2021年 | 731篇 |
2020年 | 671篇 |
2019年 | 500篇 |
2018年 | 592篇 |
2017年 | 602篇 |
2016年 | 804篇 |
2015年 | 1161篇 |
2014年 | 1818篇 |
2013年 | 2052篇 |
2012年 | 1808篇 |
2011年 | 2570篇 |
2010年 | 1628篇 |
2009年 | 1713篇 |
2008年 | 1398篇 |
2007年 | 1696篇 |
2006年 | 1670篇 |
2005年 | 1487篇 |
2004年 | 1290篇 |
2003年 | 1346篇 |
2002年 | 1093篇 |
2001年 | 775篇 |
2000年 | 751篇 |
1999年 | 658篇 |
1998年 | 510篇 |
1997年 | 437篇 |
1996年 | 370篇 |
1995年 | 302篇 |
1994年 | 221篇 |
1993年 | 159篇 |
1992年 | 119篇 |
1991年 | 104篇 |
1990年 | 64篇 |
1989年 | 46篇 |
1988年 | 46篇 |
1987年 | 28篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1971年 | 2篇 |
1958年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
201.
J. R. He G. C. I. Lin 《The International Journal of Advanced Manufacturing Technology》1992,7(4):210-217
A computerised trace method has been developed for determining the relationships of assembly requirements with design dimensions
and tolerances of the components in an assembly, and the relationships of design specifications and machining allowance requirements
with manufactured dimensions and tolerances of the component in a process plan. This method traces from the proposed components
or planned operations only the dimensions and tolerances that affect the given requirement, and therefore the equations for
design or for manufacture can be established simultaneously and accurately. Hence it is possible to establish constraints
for the optimisation of dimensions and tolerances for design or for manufacture. 相似文献
202.
Unidirectional (UD) and multidirectional (MD) flax/polypropylene composites were studied. Flax with varying retting degree and boiled flax was used as reinforcement for the UD composites and unmodified and maleic acid anhydride modified polypropylene (MAA-PP) was used as matrix. Multidirectional flax/polypropylene composites were manufactured on laboratory scale and on pilot scale. They were made from needle-punched hybrid flax/PP non-wovens. Normally retted flax as well as boiled flax was used. For the specimens made on pilot scale, a third kind of flax, namely bleached flax was also studied. The influence of different process times and temperatures on the mechanical properties of the composites was analysed. Generally, the composites have adequate good mechanical properties. The unidirectional composites of boiled flax combined with MAA-PP show the best mechanical properties. Contrary to the UD composites, flax treatment did not lead to the expected property improvements for MD composites. 相似文献
203.
Nirmal Kumar Acharya Young-Dai Lee Jong-Soon Kim 《Canadian Metallurgical Quarterly》2006,20(2):192-195
Design defects are experienced in many projects; the difference is only in the extent of occurrence. This technical note discusses a design error case in a building project in Nepal, where the designer made the wrong assumptions in roof treatment work for waterproofing as well as for heat insulation purposes. From the investigation of the problem, it was found that the waterproofing polymer was not applied directly over concrete slab top. Use of heavy concrete block as a heat insulation material also helped to increase the leakage problem. The problem evoked loss of prestige for project officials, the design consortium, and the contractor. 相似文献
204.
MEMORY·童年·印象--合肥市政务文化新区儿童公园概念性方案 总被引:1,自引:0,他引:1
合肥市政务文化新区儿童乐园的概念性方案,充分考虑了儿童的心理和成长交流需要,以儿童的自发活动为特色,兼顾各类活动设施,创造丰富活动空间,构筑了一个富有感染力、空间变幻多彩的都市儿童乐园. 相似文献
205.
Z.M. Zhong J. Chen P. Zhong J.B. Wu 《The International Journal of Advanced Manufacturing Technology》2006,28(9):855-862
As the result of vibration emission in air, a machine sound signal carries important information about the working condition
of machinery. But in practice, the sound signal is typically received with a very low signal-to-noise ratio. To obtain features
of the original sound signal, uncorrelated sound signals must be removed and the wavelet coefficients related to fault condition
must be retrieved. In this paper, the blind source separation technique is used to recover the wavelet coefficients of a monitored
source from complex observed signals. Since in the proposed blind source separation (BSS) algorithms it is generally assumed
that the number of sources is known, the Gerschgorin disk estimator method is introduced to determine the number of sound
sources before applying the BSS method. This method can estimate the number of sound sources under non-Gaussian and non-white
noise conditions. Then, the partial singular value analysis method is used to select these significant observations for BSS
analysis. This method ensures that signals are separated with the smallest distortion. Afterwards, the time-frequency separation
algorithm, converted to a suitable BSS algorithm for the separation of a non-stationary signal, is introduced. The transfer
channel between observations and sources and the wavelet coefficients of the source signals can be blindly identified via
this algorithm. The reconstructed wavelet coefficients can be used for diagnosis. Finally, the separation results obtained
from the observed signals recorded in a semi-anechoic chamber demonstrate the effectiveness of the presented methods . 相似文献
206.
Design optimization of 3D steel structures: Genetic algorithms vs. classical techniques 总被引:1,自引:0,他引:1
María Belén Prendes Gero Antonio Bello García 《Journal of Constructional Steel Research》2006,62(12):1303-1309
In this paper an elitist genetic algorithm (GA) developed by the authors is compared with common commercial solutions for complex structural optimization. After its prior validation on two-dimensional (2D) structures, the GA was tuned and improved in order to obtain structural elements with minimum weights that satisfy the ultimate limit states of the applicable building code. Subsequently, the same spatial structures were optimized using a commercial structural analysis program. Finally, the cost and weight improvements obtained using the GA, although at a higher computational cost, are discussed. 相似文献
207.
Ren-Jye Dzeng 《Canadian Metallurgical Quarterly》2006,132(6):606-614
Concurrent design is commonly used in building a semiconductor wafer fabrication facilities to shorten projects. Current practice in managing a design schedule involves preset milestones that represent percentages of completion. Such a simple control scheme does not provide sufficient information to support concurrent design. This study presents an analytical model that applies a cluster identification algorithm to separate the work of designing a multisystem project into management packages that support concurrent design. Tasks within a package have strong informational dependency relationships on each other, and are not suited for concurrent design. Tasks of different packages have weak dependency relationships on each other, and are suited for concurrent design. Tendering design work based on these packages may reduce the number of design interfaces between participating design firms. Possible application of the model includes the management of design schedule, design contract tendering, and design information flow. 相似文献
208.
209.
A monolayer and a few layers of carbon sp2-bonded networks were torn and folded by the tip of an atomic force microscope at the steps on newly cleaved highly oriented pyrolytic graphite. It was found that the preferential breaking directions and folding axes are along the symmetry directions of the graphite hexagonal structure. Depending on the force exerted by the tip, breaking may occur along other directions. The torn part of the graphene sheet can even be stretched and deformed, and does not resume its original shape after release from the tip. 相似文献
210.
Different fluorination methods were applied to modify the surface properties of carbon fibers. The relationship between the degree of fluorination and the physicochemical properties of carbon fibers was studied using a combination of mechanical tests, elemental analysis (EA), X-ray photoelectron spectrometry (XPS), and X-ray diffraction (XRD). EA and XPS analyses of fluorinated carbon fibers showed that treatment with mixtures of F2/O2 introduced a much higher fluorine concentration than that with F2 only. However, XRD analysis showed that there was no increase in the interlayer distance, due to the mild fluorination condition applied. Consequently, the oxyfluorination was one of the more effective methods to increase surface polarity of carbon fibers, which probably played an important role in improving the tensile properties of the fibers in the epoxy resin system. 相似文献