全文获取类型
收费全文 | 424669篇 |
免费 | 4752篇 |
国内免费 | 1356篇 |
专业分类
电工技术 | 7778篇 |
综合类 | 323篇 |
化学工业 | 63034篇 |
金属工艺 | 18261篇 |
机械仪表 | 13392篇 |
建筑科学 | 9535篇 |
矿业工程 | 2803篇 |
能源动力 | 10884篇 |
轻工业 | 31712篇 |
水利工程 | 4785篇 |
石油天然气 | 9932篇 |
武器工业 | 35篇 |
无线电 | 51376篇 |
一般工业技术 | 87654篇 |
冶金工业 | 76563篇 |
原子能技术 | 10560篇 |
自动化技术 | 32150篇 |
出版年
2021年 | 3895篇 |
2020年 | 2911篇 |
2019年 | 3639篇 |
2018年 | 6364篇 |
2017年 | 6426篇 |
2016年 | 6807篇 |
2015年 | 4100篇 |
2014年 | 7086篇 |
2013年 | 18725篇 |
2012年 | 10927篇 |
2011年 | 14644篇 |
2010年 | 11803篇 |
2009年 | 13334篇 |
2008年 | 13920篇 |
2007年 | 13674篇 |
2006年 | 11911篇 |
2005年 | 10685篇 |
2004年 | 10109篇 |
2003年 | 10246篇 |
2002年 | 9652篇 |
2001年 | 10155篇 |
2000年 | 9426篇 |
1999年 | 9794篇 |
1998年 | 24391篇 |
1997年 | 17080篇 |
1996年 | 13217篇 |
1995年 | 9975篇 |
1994年 | 8832篇 |
1993年 | 8928篇 |
1992年 | 6590篇 |
1991年 | 6458篇 |
1990年 | 6247篇 |
1989年 | 6010篇 |
1988年 | 5953篇 |
1987年 | 5137篇 |
1986年 | 5130篇 |
1985年 | 5608篇 |
1984年 | 5235篇 |
1983年 | 5011篇 |
1982年 | 4581篇 |
1981年 | 4501篇 |
1980年 | 4472篇 |
1979年 | 4346篇 |
1978年 | 4148篇 |
1977年 | 4750篇 |
1976年 | 6053篇 |
1975年 | 3681篇 |
1974年 | 3520篇 |
1973年 | 3581篇 |
1972年 | 3190篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling
theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a–b) layers in a unit cell. The interaction potential properly takes care of electron-electron, electron-phonon and electron-plasmon
interactions. Furthermore, the electron-phonon coupling parameter (λ), the modified Coulomb repulsive parameter (μ*) and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting
transition temperature (T
c) is then evaluated by using these coupling parameters and obtainedT
c = 95(92)K for Y(Yb)Ba2Cu3O7−δ
superconductors withδ = 0·0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory.
The result deduced on the variation ofT
c withδ are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed. 相似文献
102.
A general (possibly asymmetric noncausal and/or nonminimum phase) 2D autoregressive moving average random field model driven by an independent and identically distributed 2D nonGaussian sequence is considered. The model is restricted to be invertible, i.e., system zeros are not allowed to lie on the unit bicircle. Three performance criteria are investigated for parameter estimation of the system parameters given only the output measurements (image pixels). The proposed criteria are functions of the higher order cumulant statistics of an inverse filter output. One of these criteria is novel and the others have been considered in past only for moving average inverses and without any analysis of their consistency. In the paper strong consistency of the proposed methods under the assumption that the system order is known is proved. The convergence of the proposed parameter estimators under overparametrization is also analyzed. Experimental results involving synthesized as well as real life textures are presented to illustrate the performance of two of the considered approaches. Experimental results of synthesis of 128x128 textures visually resembling several real life textures in the Brodatz album (and other sources) are presented. 相似文献
103.
104.
105.
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
106.
One month following the Great Hanshin Earthquake of January 17, 1995, we conducted a survey of 173 hospitals in Aichi Prefecture to pinpoint problems related to their actual disaster-readiness and the medical backup systems in place to deal with such disasters. This study revealed that staff at 50% of the surveyed hospitals could reach the hospital within an hour, but that communication is almost entirely dependent on phone lines, suggesting that cordless/portable/mobile phones, radio systems, Internet, communications satellites and the like should be studied in the days to come for possible use as effective communication alternatives in times of disaster. Whereas 92% of the surveyed hospitals had manuals dealing with fire outbreaks, other areas were less well represented. For example, only 36.9% of surveyed hospitals had manuals for earthquakes, 31.7% had manuals for power outages and 14.2% had manuals to deal with flooding and water disasters. New manuals must be developed incorporating the key points garnered from experience (especially Hanshin) and be ready for use immediately. It is the time for each hospital to seriously rethink the measures it should take to deal with disasters. 相似文献
107.
An analytic expression of fmax is derived based on a practical HBT circuit model where collector junction capacitance is split up into internal and external parts. It shows that for advanced HBTs, fmax is well characterized by the product of the base resistance and internal collector capacitance. In other words, the external collector capacitance has only a small impact on the determination of fmax. Good agreement between experimental results and numerical circuit simulation confirms the validity of the HBT circuit model. The influence of the external collector capacitance on maximum available gain is also described 相似文献
108.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well 相似文献
109.
K Alanko L Kanerva B Mohell-Talolahti R Jolanki T Estlander 《Canadian Metallurgical Quarterly》1996,35(4):647-648
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data. 相似文献
110.