全文获取类型
收费全文 | 54275篇 |
免费 | 5388篇 |
国内免费 | 3236篇 |
专业分类
电工技术 | 4132篇 |
综合类 | 5021篇 |
化学工业 | 2167篇 |
金属工艺 | 1550篇 |
机械仪表 | 8180篇 |
建筑科学 | 2770篇 |
矿业工程 | 1755篇 |
能源动力 | 1353篇 |
轻工业 | 989篇 |
水利工程 | 859篇 |
石油天然气 | 829篇 |
武器工业 | 769篇 |
无线电 | 8083篇 |
一般工业技术 | 8291篇 |
冶金工业 | 758篇 |
原子能技术 | 208篇 |
自动化技术 | 15185篇 |
出版年
2024年 | 241篇 |
2023年 | 687篇 |
2022年 | 1322篇 |
2021年 | 1421篇 |
2020年 | 1564篇 |
2019年 | 1230篇 |
2018年 | 1243篇 |
2017年 | 2024篇 |
2016年 | 2222篇 |
2015年 | 2673篇 |
2014年 | 3824篇 |
2013年 | 3266篇 |
2012年 | 4624篇 |
2011年 | 4864篇 |
2010年 | 3392篇 |
2009年 | 3589篇 |
2008年 | 3310篇 |
2007年 | 3947篇 |
2006年 | 3244篇 |
2005年 | 2416篇 |
2004年 | 1916篇 |
2003年 | 1793篇 |
2002年 | 1307篇 |
2001年 | 1218篇 |
2000年 | 1061篇 |
1999年 | 831篇 |
1998年 | 662篇 |
1997年 | 755篇 |
1996年 | 482篇 |
1995年 | 407篇 |
1994年 | 348篇 |
1993年 | 231篇 |
1992年 | 191篇 |
1991年 | 172篇 |
1990年 | 116篇 |
1989年 | 116篇 |
1988年 | 79篇 |
1987年 | 33篇 |
1986年 | 14篇 |
1985年 | 6篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1974年 | 2篇 |
1965年 | 2篇 |
1959年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
空调器中多翼离心风机的噪声研究及结构优化 总被引:1,自引:1,他引:0
采用逐步回归法对大量的多翼离心风机实验数据进行拟合,针对家用空调行业中以噪声为其最重要 的考核标准,得出了噪声与叶轮结构参数及风机性能参数间的近似关系式,并以噪声为目标函数进行了优化计算。 相似文献
32.
Abstract: This paper presents a novelty detection-based technique to identify core material properties of honeycombs and cellular structures. A numerical model (finite element) representing full scale and/or reduced size of the cellular solid is used to generate transmissibilities between topological homologous points at cells in different locations. In order to make the procedure robust against noise, these transmissibilities are artificially corrupted. This step is representative of a series of experimentally obtained measurements which automatically return information relating to the size and shape of data noise along with the mean measurement. The next stage, both in this paper and in the proposal for the experimental approach, is to generate several further sets of transmissibilities from the finite element model; the only difference being that the core material properties are altered from the original values. A novelty detection framework is then adopted to find a similarity measure between each of these 'test' transmissibilities and the original set thereby identifying the material properties. Although this work is concerned with identifying only one material property, the methodology extends to identifying several properties. 相似文献
33.
KMLS型立式砂泵的振动噪声产生原因及解决措施 总被引:1,自引:1,他引:0
针对KMLS型立式砂泵振动、噪声产生原因及其表现特征,提出了解决措施。通过对这些原因的分析研究,可以提供泵设计者和生产者在减少砂泵振动方面采取相应的措施,使KMLS型立式砂泵能更好的服务于用户。 相似文献
34.
Termites live in a material world: exploration of their ability to differentiate between food sources. 下载免费PDF全文
Ra Inta Joseph C S Lai Eugene W Fu Theodore A Evans 《Journal of the Royal Society Interface》2007,4(15):735-744
Drywood termites are able to assess wood size using vibratory signals, although the exact mechanism behind this assessment ability is not known. Important vibratory characteristics such as the modal frequencies of a wooden block depend on its geometry and boundary conditions; however, they are also dependent on the material characteristics of the block, such as mass, density and internal damping. We report here on choice experiments that tested the ability of the drywood termite Cryptotermes secundus to assess wooden block size using a solid wooden block paired with a composite block, the latter made of either wood and aluminium or wood and rubber. Each composite block was constructed to match mass or low-frequency vibratory modes (i.e. fundamental frequency) of the solid wooden block. The termites always chose the blocks with more wood; they moved to the solid wooden blocks usually within a day and then tunnelled further into the solid wooden block by the end of the experiment. Termites offered composite blocks of wood and rubber matched for mass were the slowest to show a preference for the solid wooden block and this preference was the least definitive of any treatment, which indicated that mass and/or damping may play a role in food assessment. This result clearly shows that the termites were not fooled by composite blocks matched for mass or frequency, which implies that they probably employ more than a single simple measure in their food assessment strategy. This implies a degree of sophistication in their ability to assess their environment hitherto unknown. The potential importance of alternative features in the vibrational signals is discussed. 相似文献
35.
Gert van der Horn Johan H. Huijsing 《Analog Integrated Circuits and Signal Processing》1997,14(3):207-222
In many applications electronic sensors are used toimprove performance and reliability of measurement systems. Suchsensors should provide a correct transfer from the physical signalto be measured to the electrical output signal. One importantstep to achieve this, is to calibrate each sensor by applyingdifferent reference input signals and adjusting the sensor transferaccordingly. Besides expensive reference equipment the calibrationprocess takes much time and attention per individual sensor,which means a considerable increase in sensor production costs.By including at the sensor or sensor interface chip a programmablecalibration facility the calibration of such smart sensors caneasily be automated and can be executed for a batch of sensorsat a time, thus minimizing the calibration time and costs. Thispaper presents a calibration method and options for integrationin the smart sensor concept, in hardware as well as in software.An advantage of the proposed method is that it does not needa large matrix of calibration data, which needs to be storedin a look-up table or converted into a correction formula, butinstead it uses a step-by-step approach to correct the sensortransfer at each calibration measurement until the error is sufficientlysmall. 相似文献
36.
往复式压缩机管道的防振设计 总被引:1,自引:0,他引:1
分析了往复式压缩机管道产生振动的原因及影响因素,提出解决管道振动的方法及对策。 相似文献
37.
1IntrodctionThesdV8fltsg6Sofffi1CY0bCfldf山CY0ptlCS6fiS0f8f6lflt6llSltyffiDdU18tlflgsliddCtCCtlflg,simpletechnique,highrellabllltyandlowprice,thereformlcrobendfiberoptlcsensorIswidelyusedtomeasurementofstrain,stressandv比rationetc.Inpractice,thesensltlvltyofsensorIsaveryimportantparameter,andthesensltlvltyofmlcrobendf山eroptlcsensorIsmainlyrelat-6dtofoil0WlflgthY66f8CtofS[‘-:ffilCfob6fldsffiplltlld6:fillffib6yofthlCY0b6fldS6Ct10llSsfldffil-crobendperiod,andmlcrobendperio… 相似文献
38.
39.
40.
The problem of determining the maximum mean response level crossing rate of a linear system driven by a partially specified Gaussian load process has been considered. The partial specification of the load is given only in terms of its total average energy. The critical input power spectral (PSD) function, which maximizes the mean response level crossing rate, is obtained. The critical input PSD turns out to be highly narrow-banded which fails to capture the erratic nature of the excitation. Consequently, the trade-off curve between the maximum mean response level crossing rate and the maximum disorder in the input process, quantified in terms of its entropy rate, has been generated. The method of Pareto optimization is used to tackle the conflicting objectives of the simultaneous maximization of the mean response level crossing rate and the input entropy rate. The non-linear multi-objective optimization has been carried out using a recently developed multi-criteria genetic algorithm scheme. Illustrative example of determining the critical input of an axially vibrating rod, excited by a partially specified stationary Gaussian load process, has been considered. 相似文献