全文获取类型
收费全文 | 198281篇 |
免费 | 2127篇 |
国内免费 | 633篇 |
专业分类
电工技术 | 4074篇 |
综合类 | 124篇 |
化学工业 | 26854篇 |
金属工艺 | 7512篇 |
机械仪表 | 5471篇 |
建筑科学 | 4053篇 |
矿业工程 | 752篇 |
能源动力 | 4673篇 |
轻工业 | 14402篇 |
水利工程 | 1695篇 |
石油天然气 | 2843篇 |
武器工业 | 7篇 |
无线电 | 27327篇 |
一般工业技术 | 37432篇 |
冶金工业 | 45494篇 |
原子能技术 | 3562篇 |
自动化技术 | 14766篇 |
出版年
2021年 | 1250篇 |
2019年 | 1283篇 |
2018年 | 2130篇 |
2017年 | 2113篇 |
2016年 | 2177篇 |
2015年 | 1500篇 |
2014年 | 2625篇 |
2013年 | 7970篇 |
2012年 | 4474篇 |
2011年 | 6127篇 |
2010年 | 4950篇 |
2009年 | 5791篇 |
2008年 | 6163篇 |
2007年 | 6209篇 |
2006年 | 5651篇 |
2005年 | 5315篇 |
2004年 | 5259篇 |
2003年 | 5099篇 |
2002年 | 4911篇 |
2001年 | 5316篇 |
2000年 | 4929篇 |
1999年 | 5445篇 |
1998年 | 15644篇 |
1997年 | 10337篇 |
1996年 | 7947篇 |
1995年 | 5795篇 |
1994年 | 5022篇 |
1993年 | 5036篇 |
1992年 | 3388篇 |
1991年 | 3264篇 |
1990年 | 3224篇 |
1989年 | 3041篇 |
1988年 | 2790篇 |
1987年 | 2240篇 |
1986年 | 2302篇 |
1985年 | 2611篇 |
1984年 | 2317篇 |
1983年 | 2066篇 |
1982年 | 1906篇 |
1981年 | 2048篇 |
1980年 | 1794篇 |
1979年 | 1663篇 |
1978年 | 1659篇 |
1977年 | 2026篇 |
1976年 | 2716篇 |
1975年 | 1424篇 |
1974年 | 1374篇 |
1973年 | 1318篇 |
1972年 | 1125篇 |
1971年 | 957篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Kringlebotn J.T. Morkel P.R. Reekie L. Archambault J.-L. Payne D.N. 《Photonics Technology Letters, IEEE》1993,5(10):1162-1164
We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er3+:Yb3+ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz 相似文献
62.
Variable rate speech coding is now recognized as an important system component for high-capacity cellular networks because it exploits speech statistics to reduce the average bit rate, which results in reduced interference and increased capacity. Once a variable rate capability is available, an additional capacity enhancement can be achieved by introducing network control of the user bit rate in response to changing traffic levels. We introduce the concept of network control of rate and propose a particular network-control method for code-division multiple access (CDMA) systems. Based on an M/M/∞//M queueing model applied to a cell under heavy traffic conditions and a new performance measure called averaged speech quality, we obtain simulation results to demonstrate how network control of rate can achieve improved speech quality or increased capacity for a given quality objective 相似文献
63.
64.
O. A. Ustrekhova T. G. Ezhikova-Babakhanova G. B. Basov 《Chemistry and Technology of Fuels and Oils》1993,29(11):544-548
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 11, pp. 17–18, 23, November, 1993. 相似文献
65.
N Usui S Kamata S Ishikawa T Sawai H Okuyama K Imura A Okada 《Canadian Metallurgical Quarterly》1996,31(2):258-262
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis. 相似文献
66.
67.
68.
The paper covers a simple idea. If we sample an aperture, we can obtain valid patterns over a limited angular region about the normal to the aperture. The same expression can be used with near-field measurements. I reduced the expression to a nomograph. A nomograph allows one to rapidly test various choices. In the second half of the paper, I answer questions caused by the February column which discussed polarization (Milligan, IEEE Antennas. Propag. Mag., vol.38, no.1, p.56-8, 1996) 相似文献
69.
Kasukawa A. Namegaya T. Fukushima T. Iwai N. Kikuta T. 《Quantum Electronics, IEEE Journal of》1993,29(6):1528-1535
The authors have fabricated 1.3-μm InAsP-InP separate-confinement-heterostructure (SCH) strained-layer double-quantum-well (SL-DQW) laser diodes (LDs) by metalorganic chemical vapor deposition (MOCVD). A low threshold current density of 410 A/cm 2 was obtained. The CW threshold current was as low as 1.8 mA at 20°C, and maximum CW operating temperature of 120°C was obtained. These characteristics are almost the same as those of well-designed GaInAsP-InP SL-QW LDs. Further improvement of the characteristics of InAsP-InP LDs is expected by optimizing the device structure 相似文献
70.