全文获取类型
收费全文 | 40666篇 |
免费 | 3591篇 |
国内免费 | 1908篇 |
专业分类
电工技术 | 2333篇 |
技术理论 | 2篇 |
综合类 | 3207篇 |
化学工业 | 6879篇 |
金属工艺 | 2346篇 |
机械仪表 | 2534篇 |
建筑科学 | 3362篇 |
矿业工程 | 1135篇 |
能源动力 | 1254篇 |
轻工业 | 2719篇 |
水利工程 | 816篇 |
石油天然气 | 2011篇 |
武器工业 | 368篇 |
无线电 | 4517篇 |
一般工业技术 | 4843篇 |
冶金工业 | 1804篇 |
原子能技术 | 385篇 |
自动化技术 | 5650篇 |
出版年
2024年 | 153篇 |
2023年 | 599篇 |
2022年 | 935篇 |
2021年 | 1405篇 |
2020年 | 1108篇 |
2019年 | 1003篇 |
2018年 | 1086篇 |
2017年 | 1126篇 |
2016年 | 1079篇 |
2015年 | 1516篇 |
2014年 | 1786篇 |
2013年 | 2112篇 |
2012年 | 2410篇 |
2011年 | 2561篇 |
2010年 | 2362篇 |
2009年 | 2416篇 |
2008年 | 2240篇 |
2007年 | 2145篇 |
2006年 | 2313篇 |
2005年 | 1922篇 |
2004年 | 1496篇 |
2003年 | 1683篇 |
2002年 | 2047篇 |
2001年 | 1749篇 |
2000年 | 1198篇 |
1999年 | 1144篇 |
1998年 | 837篇 |
1997年 | 704篇 |
1996年 | 671篇 |
1995年 | 559篇 |
1994年 | 418篇 |
1993年 | 342篇 |
1992年 | 259篇 |
1991年 | 179篇 |
1990年 | 147篇 |
1989年 | 110篇 |
1988年 | 107篇 |
1987年 | 61篇 |
1986年 | 34篇 |
1985年 | 38篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 10篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1961年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
本文提出了用有限元法验证变幅杆解析法设计的可靠性,对三种类型的变幅杆先作解析法设计;然后利用有限元分析软件ANSYS进行模态分析,确定了变幅杆的固有频率,计算了固有频率与工作频率之间的相对误差,以此来评价解析法设计的可靠性;并分析了影响解析法设计可靠性的两个基本因素。 相似文献
42.
43.
本文通过两栋不同加固方案的二层农村楼房抗采动现场试验结果的分析,对不同加固措施的作用机理、效果及其设置条件进行了研究探讨,并提出,在农村采动区兴建抗采动变形楼房,是解放村庄下压煤、节约耕地和降低加固费用的途径。 相似文献
44.
45.
The network model is given and used to calculate the oscillating frequency of thermoacoustic prime mover. Theoretically calculated frequency by the model is plural, whose real part denotes actual frequency of the system, and imaginary part means attenuation coefficient of acoustic pressure. Numerical calculation is made under different conditions including different acoustic cavities, spacing between each parallel plate, gas pressures and system lengths. Theoretically calculated frequency and experimentally measured frequency are in quite good agreement. 相似文献
46.
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
47.
The stability of five major phenolics, namely (−)-epicatechin (EC), procyanidin B2 (PC-B2), chlorogenic acid (ChA), hyperoside (HP) and isoquercitrin (IQ), in hawthorn fruits and a canned hawthorn drink were evaluated during 6 months of storage in the dark at three different temperatures (4, 23 and 40 °C). HPLC with a diode-array detector was used to determine the contents of the individual compounds. The results showed that the studied phenolics in the hawthorn fruits and the drink were both stable at 4 °C and relatively unstable at 23 and 40 °C with varied extents of degradation. At room temperature (23 °C), marked degradations of EC and PC-B2 were observed in both the fruits and the drink with around 50% and 30% decrease after a 6-month storage, respectively. A more significant decrease of the phenolics was observed at 40 °C, especially for EC and PC-B2, which were almost completely degraded after a 6-month storage. HP, IQ and ChA were relatively stable at 23 °C, but unstable at 40 °C. Therefore, low-temperature storage is recommended for maintaining the quality and efficacy of hawthorn fruits and its preparations. 相似文献
48.
PURPOSE: To evaluate the accuracy of measuring intraocular pressure by handheld non-contact applanation tonometer. METHOD: 58 patients' (113 eyes) intraocular pressure were measured by Keeler, non-contact tonometer and R 900 Goldmann applanation tonometer and the results of measurement of intraocular pressure by the two kinds of tonometers were compared. RESULT: The mean intraocular pressure measured by non-contact is 16.31 +/- 5.59 mmHg and 17.49 +/- 6.13 mmHg (1 mmHg = 0.1333 kPa) by Goldmann applanation tonometer, respectively. There was no statistical significance to be found (P > 0.05) between the two methods. By linear correlation and regression analysis, a positive correlation was found between the two methods (r = 0.8942, b = 0.8154). CONCLUSION: The handheld non-contact tonometer has the same accuracy and reliability of measurement of intraocular pressure comparing with Goldmann applanation tonometer, and it can be used in glaucoma clinic and screening. 相似文献
49.
Four monoalkyl esters of isoalkylphosphonic acids have been studied for the chromatographic separation ofrare earths (RE).The relationship between distribution ratios and acid concentration of the eluants forsamarium and ytterbium has been explored.The characteristics of these extractants loaded onto macroreticularpoly (methyl methacrylate) resin beads for the separation of lanthanum,cerium,praseodymium and neodymiumhave been compared.Among the extractants studied,mono(1-methylheptyl) ester of isooctylphosphonic acidwas found to be the best for RE separation.The acidity for separation is lower than any known P-containingextractants for the same purpose.For instance,with 1.73 mol·L~(-1) nitric acid as eluent,thulium,ytterbium andlutetium can be separated quantitatively.The extractant-loaded resins possess high column efficiency with goodkinetic characteristics.The extraction mechanism was also explored. 相似文献
50.