全文获取类型
收费全文 | 6816篇 |
免费 | 235篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 107篇 |
综合类 | 11篇 |
化学工业 | 963篇 |
金属工艺 | 80篇 |
机械仪表 | 109篇 |
建筑科学 | 226篇 |
矿业工程 | 29篇 |
能源动力 | 176篇 |
轻工业 | 424篇 |
水利工程 | 30篇 |
石油天然气 | 12篇 |
武器工业 | 1篇 |
无线电 | 1409篇 |
一般工业技术 | 951篇 |
冶金工业 | 1460篇 |
原子能技术 | 75篇 |
自动化技术 | 1017篇 |
出版年
2022年 | 53篇 |
2021年 | 85篇 |
2020年 | 72篇 |
2019年 | 67篇 |
2018年 | 105篇 |
2017年 | 80篇 |
2016年 | 100篇 |
2015年 | 79篇 |
2014年 | 133篇 |
2013年 | 389篇 |
2012年 | 193篇 |
2011年 | 268篇 |
2010年 | 181篇 |
2009年 | 253篇 |
2008年 | 287篇 |
2007年 | 293篇 |
2006年 | 255篇 |
2005年 | 214篇 |
2004年 | 212篇 |
2003年 | 228篇 |
2002年 | 168篇 |
2001年 | 161篇 |
2000年 | 144篇 |
1999年 | 191篇 |
1998年 | 441篇 |
1997年 | 340篇 |
1996年 | 215篇 |
1995年 | 176篇 |
1994年 | 143篇 |
1993年 | 140篇 |
1992年 | 89篇 |
1991年 | 109篇 |
1990年 | 92篇 |
1989年 | 83篇 |
1988年 | 89篇 |
1987年 | 43篇 |
1986年 | 48篇 |
1985年 | 50篇 |
1984年 | 53篇 |
1983年 | 55篇 |
1982年 | 58篇 |
1981年 | 55篇 |
1980年 | 46篇 |
1979年 | 47篇 |
1978年 | 35篇 |
1977年 | 66篇 |
1976年 | 62篇 |
1975年 | 42篇 |
1973年 | 29篇 |
1972年 | 31篇 |
排序方式: 共有7080条查询结果,搜索用时 15 毫秒
41.
The behavioral disturbances of 16 nursing home patients with a history of sundowning behaviour and dementia were treated with light therapy instead of psychopharmacological medication. After the withdrawal of the before established medication a very individual, heterogenous deterioration of the symptoms was noted. A significant improvement of the behaviour was not found by light therapy in any patient. The problems in practical handling and possible consequences of further investigation are discussed. 相似文献
42.
A study is made of the electric fields and currents induced in the organs of the human body when exposed to high-voltage 50-60-Hz transmission lines and 10-30-kHz high-power transmitters. Relevant analyses previously carried out are summarized and supplemented with detailed investigations that complete the picture. Incomplete, misleading, and incorrect statements and methods in the related literature are pointed out, completed, and corrected. The major contribution is to provide quantitatively accurate, relatively simple analytic formulas that relate the incident electric field to the induced field in the organs of the body. The formulation and solution of the underlying integral equation are carried out in an Appendix 相似文献
43.
44.
Transformations for nonideal uniform circular arrays operating in correlated signal environments 总被引:2,自引:0,他引:2
Buon Kiong Lau Yee Hong Leung Yanqun Liu Kok Lay Teo 《Signal Processing, IEEE Transactions on》2006,54(1):34-48
The Davies transformation is a method to transform the steering vector of a uniform circular array (UCA) to one with Vandermonde form. As such, it allows techniques such as spatial smoothing for direction-of-arrival (DOA) estimation in a correlated signal environment, developed originally for uniform linear arrays, to be applied to UCAs. However, the Davies transformation can be highly sensitive to perturbations of the underlying array model. This paper presents a method for deriving a more robust transformation using optimization techniques. The effectiveness of the method is illustrated through a number of DOA estimation examples. 相似文献
45.
In unit selection-based concatenative speech synthesis, join cost (also known as concatenation cost), which measures how well two units can be joined together, is one of the main criteria for selecting appropriate units from the inventory. Usually, some form of local parameter smoothing is also needed to disguise the remaining discontinuities. This paper presents a subjective evaluation of three join cost functions and three smoothing methods. We also describe the design and performance of a listening test. The three join cost functions were taken from our previous study, where we proposed join cost functions derived from spectral distances, which have good correlations with perceptual scores obtained for a range of concatenation discontinuities. This evaluation allows us to further validate their ability to predict concatenation discontinuities. The units for synthesis stimuli are obtained from a state-of-the-art unit selection text-to-speech system: rVoice from Rhetorical Systems Ltd. In this paper, we report listeners' preferences for each join cost in combination with each smoothing method. 相似文献
46.
47.
48.
W. Chen S. -H. Wang R. Chu F. King T. R. Jack R. R. Fessler 《Metallurgical and Materials Transactions A》2003,34(11):2601-2608
A study was carried out to understand the effect of precyclic loading on stress-corrosion-crack initiation in an X-65 pipeline
steel exposed to a near-neutral-pH soil environment. The test specimens were precyclically loaded before corrosion exposure
to represent a service history of up to about 20 years, depending on the severity of pressure fluctuation. Microcracks had
initiated on the polished surface of the X-65 pipeline steel after long-time exposure at open-circuit potential (OCP) in a
near-neutral-pH synthetic soil solution. These microcracks were mostly initiated from pits at metallurgical discontinuities
such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed
along planes of the banded structures in the steel. The selective corrosion attack at these metallurgical discontinuities
is attributed to the galvanic nature of those areas to their neighbors. Cyclic loading prior to corrosion exposure had significant
effects on microcrack initiation and propagation during subsequent corrosion exposure. Cyclic loading prior to corrosion exposure
either reduced or increased the probability of crack initiation and the rate of crack propagation, depending upon the magnitude
of the stress cycles. The largest reduction was seen at a peak cyclic stress of about 0.8 of the yield strength. This cyclic-loading-dependent
cracking behavior might be related to the alteration of the substructures and the residual stress in the steel as a result
of precyclic loading. 相似文献
49.
The change of foot length and width with age has been reported in a few anthropometric studies in the literature. However, the relationship with body height rarely is reported, and the dynamic effect of weightbearing on foot size has not been documented. In this series, 2829 children 3 to 18 years of age of equal gender distribution were included in the study. The foot length and width on weightbearing and nonweightbearing were measured with a special precision electronic caliper. The foot length and width were found to increase linearly from the age of 3 years until 12 years in girls and 15 years in boys. This was followed by a phase during which the increase plateaued. The foot length and width increased significantly on weightbearing at all ages in both genders with a mean of 2.1 to 4.4 mm or 3.1% to 4.8%, respectively. The foot length and width also were found to correlate significantly with the body height in both genders, with a correlation coefficient of 0.96 to 0.98. No significant differences were found between the sizes of the dominant and nondominant foot in either gender. 相似文献
50.
OFDM/FM frame synchronization for mobile radio data communication 总被引:13,自引:0,他引:13
A synchronization scheme enabling the use of orthogonal frequency division multiplexing (OFDM)/FM over a mobile radio channel in a pure ALOHA environment is proposed. The scheme encodes synchronization information in parallel with data in the same manner in which data is encoded in the OFDM/FM frame. The synchronization information is in the form of tones, centered in certain reserved frequency subchannels of the OFDM signal. The receiver uses a correlation detector, implemented in the frequency domain, to acquire synchronization accurately on a packet-by-packet basis. Experimental results indicate that the bit-error-rate performance achievable with the proposed scheme is within 1.5 dB of the performance obtained with ideal synchronization 相似文献