全文获取类型
收费全文 | 1976篇 |
免费 | 23篇 |
专业分类
电工技术 | 83篇 |
化学工业 | 318篇 |
金属工艺 | 32篇 |
机械仪表 | 31篇 |
建筑科学 | 23篇 |
能源动力 | 46篇 |
轻工业 | 97篇 |
水利工程 | 5篇 |
无线电 | 439篇 |
一般工业技术 | 301篇 |
冶金工业 | 467篇 |
原子能技术 | 41篇 |
自动化技术 | 116篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 5篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 24篇 |
2015年 | 18篇 |
2014年 | 22篇 |
2013年 | 44篇 |
2012年 | 43篇 |
2011年 | 53篇 |
2010年 | 37篇 |
2009年 | 48篇 |
2008年 | 68篇 |
2007年 | 51篇 |
2006年 | 47篇 |
2005年 | 45篇 |
2004年 | 59篇 |
2003年 | 81篇 |
2002年 | 59篇 |
2001年 | 70篇 |
2000年 | 47篇 |
1999年 | 61篇 |
1998年 | 195篇 |
1997年 | 125篇 |
1996年 | 102篇 |
1995年 | 86篇 |
1994年 | 52篇 |
1993年 | 53篇 |
1992年 | 33篇 |
1991年 | 39篇 |
1990年 | 29篇 |
1989年 | 39篇 |
1988年 | 40篇 |
1987年 | 21篇 |
1986年 | 28篇 |
1985年 | 34篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 15篇 |
1974年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有1999条查询结果,搜索用时 17 毫秒
191.
S Narumi Y Tominaga M Tamaru S Shimai H Okumura K Nishioji Y Itoh T Okanoue 《Canadian Metallurgical Quarterly》1997,158(11):5536-5544
Chemokines such as IFN-inducible protein-10 (IP-10) and JE/monocyte chemotactic protein-1 (MCP-1) are induced in the murine liver in a tissue-specific manner. We examined whether IP-10 and MCP-1 are pathologically involved in chronic hepatitis. Whereas the serum levels of IP-10 and MCP-1 in patients with chronic persistent hepatitis C were elevated compared with those in normal volunteers, both chemokine levels were further significantly higher in patients with the active form (chronic active hepatitis (CAH)). The elevated IP-10 level was not a general phenomenon of inflammation, because it was not seen in patients with rheumatoid arthritis, whereas MCP-1 levels were elevated to the same extent in both patient groups. Better responsiveness to IFN therapy in CAH was related to lesser grades of necroinflammatory activity and was predicted by the lower IP-10 and higher MCP-1 levels. IP-10 levels in patients cured by IFN therapy decreased to the levels in normal volunteers, while the MCP-1 levels only slightly decreased. Serum levels of both chemokines in patients who were not cured remained unchanged after IFN therapy. In situ hybridization analysis of CAH revealed that IP-10 mRNA was expressed mainly in hepatocytes around intralobular focal and periportal piecemeal necrosis, while some MCP-1 mRNA was expressed in some sinusoidal cells. These results suggested that IP-10 plays a specific role in the intralobular accumulation of mononuclear cells and/or the death of hepatocytes in chronic hepatitis. 相似文献
192.
Uterine contractile activity in nonpregnant conscious dogs was investigated based on 2- to 6-mo-long continuous recording by means of a chronically implanted force transducer. We found that nonpregnant uterine contractile activity could be classified into six major patterns: sporadic contractions, weak and strong tonic contractions, weak and strong phasic contractions, and phasic contraction bursts. The contractile patterns during proestrus and estrus were the most active, with strong phasic and tonic contractions and phasic contraction bursts. The phasic and tonic contractions were inhibited dose-dependently by a beta 2 adrenergic agonist, ritodrine, and reproduced by an alpha 2 adrenergic agonist, clonidine. In contrast, the cholinergic inhibitors atropine and hexamethonium did not affect the spontaneous occurrence of these contractions, although bethanechol evoked uterine contractions. Oxytocin and prostaglandin F2 alpha-induced contractions were phasic during estrus, whereas they showed tonic increases with phasic contractions during proestrus, diestrus, and anestrus, and these contractions did not resemble the spontaneous contractions. In conclusion, the nonpregnant uterus contracts continuously in harmony with the estrous cycle phases, and its contractile activity is enhanced by alpha adrenergic receptors and inhibited by beta 2 adrenergic receptors. 相似文献
193.
194.
Itoh A. Takahashi W. Nagano H. Kurisaka M. Iwasaki S. 《Selected Areas in Communications, IEEE Journal on》1991,9(8):1280-1288
The practical implementation of a trial large-scale asynchronous transfer mode (ATM) switching system and its packaging technologies are described. The architecture of the ATM switching system is discussed with an emphasis on system scalability. A building block architecture in which switching capacity can be expanded in a modular fashion is introduced. The design of the ATM switching system, including the ATM switch element, is described. The implementation of the VLSIs for the ATM switch which realize a highly modular system is explained. Bit-slice techniques are effectively used to realize a high-speed switch element as a CMOS VLSI chipset. An edge-to-edge orthogonal packaging technique is also presented 相似文献
195.
Miyamoto R.Y. Leong K.M.K.H. Seong-Sik Jeon Yuanxun Wang Yongxi Qian Itoh T. 《Vehicular Technology, IEEE Transactions on》2003,52(5):1181-1188
A wireless sensor server is developed based on a reconfigurable active smart-antenna/retrodirective array. The system can serve as both a retrodirective array transponder and a smart-antenna receiver simply by changing the frequency of the local oscillator applied to the mixers, enabling it to utilize its hardware best to suit its communication environment. When operating as a direct-conversion receiver, the receiver array successfully demodulates a quaternary phase-shift keying (QPSK) modulated signal with circuit gain of 7 dB, and E/sub b//N/sub 0/ for BER=10/sup -4/ is approximately 12 dB without any error correction. In the retrodirective array mode, the system provides 20 dB circuit gain and 20 dB radio-frequency/intermediate-frequency isolation at the center frequency as well as phase conjugation, exhibiting excellent retrodirectivity. The mixers perform phase conjugation and modulation simultaneously, enabling the transmission of locally stored data. The local data is successfully extracted by an interrogator. 相似文献
196.
197.
A sampling theorem for shift-invariant subspace 总被引:2,自引:0,他引:2
A sampling theorem for regular sampling in shift-invariant subspaces is established. The sufficient-necessary condition for which it holds is found. Then, the theorem is modified to the shift sampling in shift-invariant subspaces by using the Zak transform. Finally, some examples are presented to show the generality of the theorem 相似文献
198.
199.
Single microtips, 2×2 and 10×10 arrays of microtips surrounded by an integrated focusing ring, were fabricated and their focusing characteristics experimentally investigated. Observation of the beam on a phosphor screen shows that the focusing is very effective for single microtips and 2×2 arrays; moreover, the reduction in emitted current is much smaller than for double-gate focusing. 10×10 arrays of microtips, however, do not generate very focused beams. These results agree well with simulations. The possibility of simultaneous focusing and deflecting is also discussed, and a new structure combining the advantages of double-gate and surrounding ring focusing is suggested 相似文献
200.
The phenomenological loss equivalence method (PEM), the enhanced two-fluid model for thin-film superconducting materials, and the dynamical calculation of radiation losses in planar structures are used-in the context of a linear filter approach-to model attenuation and dispersion of ultrafast pulses in coplanar striplines. The numerical simulation of this modeling shows excellent agreement with experimental results available in the literature. Simple relationships between the peak attenuation and delay time of the propagation pulse, and penetration depth at absolute zero and conductivity at critical temperature may open the possibility of using pulse distortion to characterize thin-film, high-temperature superconducting materials 相似文献