全文获取类型
收费全文 | 5921篇 |
免费 | 251篇 |
国内免费 | 73篇 |
专业分类
电工技术 | 170篇 |
综合类 | 57篇 |
化学工业 | 849篇 |
金属工艺 | 113篇 |
机械仪表 | 155篇 |
建筑科学 | 99篇 |
矿业工程 | 20篇 |
能源动力 | 144篇 |
轻工业 | 209篇 |
水利工程 | 44篇 |
石油天然气 | 37篇 |
武器工业 | 8篇 |
无线电 | 817篇 |
一般工业技术 | 685篇 |
冶金工业 | 2255篇 |
原子能技术 | 29篇 |
自动化技术 | 554篇 |
出版年
2024年 | 11篇 |
2023年 | 36篇 |
2022年 | 104篇 |
2021年 | 129篇 |
2020年 | 80篇 |
2019年 | 66篇 |
2018年 | 89篇 |
2017年 | 93篇 |
2016年 | 102篇 |
2015年 | 120篇 |
2014年 | 181篇 |
2013年 | 328篇 |
2012年 | 264篇 |
2011年 | 268篇 |
2010年 | 219篇 |
2009年 | 205篇 |
2008年 | 208篇 |
2007年 | 198篇 |
2006年 | 187篇 |
2005年 | 112篇 |
2004年 | 111篇 |
2003年 | 111篇 |
2002年 | 84篇 |
2001年 | 64篇 |
2000年 | 66篇 |
1999年 | 123篇 |
1998年 | 809篇 |
1997年 | 404篇 |
1996年 | 305篇 |
1995年 | 163篇 |
1994年 | 162篇 |
1993年 | 173篇 |
1992年 | 59篇 |
1991年 | 54篇 |
1990年 | 64篇 |
1989年 | 67篇 |
1988年 | 54篇 |
1987年 | 46篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1978年 | 9篇 |
1977年 | 31篇 |
1976年 | 112篇 |
1975年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有6245条查询结果,搜索用时 15 毫秒
31.
The incidence of stress fractures is increasing among competitive and recreational athletes as well as among children and the elderly. By understanding the continuum of bone's response to stress and maintaining an appropriate index of suspicion, the health care provider can diagnose these injuries appropriately. An accurate history and examination is essential and will differentiate stress fractures from other stress reactions. The more common stress fractures are discussed. 相似文献
32.
33.
34.
SH Braat B Leclercq R Itti A Lahiri B Sridhara P Rigo 《Canadian Metallurgical Quarterly》1994,35(10):1581-1585
There is no evidence of myocardial redistribution after tetrofosmin injection, therefore, two separate injections are needed to differentiate scar from ischemia with this tracer. The injections can be given on the same day (one-day protocol) or on separate days (two-day protocol). As part of a Phase II clinical study, a one-day protocol was compared with a two-day protocol. METHODS: Fifty-five patients with suspected coronary artery disease were studied according to the following protocol: on the first day at rest, anterior, left lateral, left anterior oblique 40 degrees and 70 degrees images were acquired 30 min after injection of 8 mCi of tetrofosmin for 5 min each. Two days later, exercise and rest images were acquired on the same day. At peak exercise, 8 mCi of tetrofosmin were injected and 30 min later the same four standard planar images were recorded as on Day one. Four hours after the exercise injection, 24 mCi of tetrofosmin were injected at rest and imaging was repeated 30 min later. Qualitative comparisons between the one- and two-day protocols were performed in 50 patients in whom all data were available following blinded evaluation of images by three readers. RESULTS: All three readers reported identical results for the 26 patients. A difference in extent or location between the observers was found in seven patients, differences between normal and abnormal in eight patients, while discrepancies between ischemia and necrosis were noted in four patients. In five patients, an ischemic area was found according to the one-day protocol, but according to the data of the two-day protocol, this area was judged to be necrotic. One observer reported the opposite in one patient. These discrepancies between the reversibility of defects were restricted to the inferior wall. Comparison with 201Tl data showed no systematic pattern of variation. CONCLUSION: Tetrofosmin can be used in a one-day protocol. However, in planar imaging, the inferior wall should be reported with caution. 相似文献
35.
Through rigorous full-wave analysis, the effective dielectric constant, normalized attenuation constant, characteristic impedance, and radiation pattern of two types of conductor-backed coplanar waveguides are obtained. The analytic results show that the leakage effect is not only controlled by the thickness and dielectric constant of the substrate but also by the slot width. The leakage power transforms to a radiation space wave and a surface wave, the transverse electric field diagrams in the substrate and the far-zone radiation pattern verify the leakage phenomenon. The first structure has the maximum radiation intensity in the endfire direction, while the second one which has more leaky waves radiates into the air, is better served as a radiating device. For both structures under the nonleakage condition, the characteristic impedance is sensitive to the change of the strip width but not the slot width. Using these properties, the nonleaky and leaky circuits can exist on the same circuit board by choosing appropriate circuit dimensions 相似文献
36.
W.R. Jong T.H. Kuo S.W. Ho H.H. Chiu S.H. Peng 《International Communications in Heat and Mass Transfer》2007
Capillary phenomena was studied and discussed by the scholars about 200 years ago, but the progress was slow due to the limited equipment and manufacture precision of the microchannel. In recent years, because of the rapid development of MEMS and micromachining, many applications of the capillary flow is widely developing in some modern processes, such as underfilling of flip chip, flow in microfluidic chip or biochip, and a variety of other fields. 相似文献
37.
38.
39.
Tsung-Nan Kuo Yo-Shen Lin Chi-Hsueh Wang Chun Hsiung Chen 《Microwave and Wireless Components Letters, IEEE》2006,16(2):90-92
In this letter, a compact branch-line coupler is proposed by making good use of the three-dimensional layout capability of the low-temperature co-fired ceramic (LTCC) substrate. This branch-line coupler is accomplished by using lumped-inductors and lumped-capacitors to realize the modified-T equivalent-circuit model for the transmission line so that the circuit size may drastically be reduced. Specifically, a very compact LTCC branch-line coupler with a size of 0.079/spl lambda//spl times/0.0717/spl lambda/ is implemented and carefully examined, where /spl lambda/ is the wavelength of the multilayer structure at the operating frequency f/sub 0/. 相似文献
40.
Dynamic RSVP protocol 总被引:5,自引:0,他引:5
Geng-Sheng Kuo Po-Chang Ko 《Communications Magazine, IEEE》2003,41(5):130-135
RSVP is a resource reservation setup protocol that can be used by a host to request specific QoS for multicast multimedia flows on the Internet. Multiprotocol label switching (MPLS) architecture also needs RSVP. The fact that the resolutions of the display system used in different receiver nodes might have different, multi-resolution characteristics is supported in the MPEG-4 standard, and the EZW compression algorithm can cease decoding at any point in the bitstream. However, RSVP does not provide a more flexible mechanism. In this article we propose an extension of RSVP to provide the needed mechanism, coined dynamic RSVP (DRSVP), to dynamically adjust reserved resources on nodes without much effort. It provides different video resolutions to different receiver nodes with different needed reserved resources. Therefore, it does not waste precious Internet resources to transmit unnecessary multimedia packets. 相似文献