全文获取类型
收费全文 | 138339篇 |
免费 | 13530篇 |
国内免费 | 8376篇 |
专业分类
电工技术 | 10945篇 |
技术理论 | 2篇 |
综合类 | 10383篇 |
化学工业 | 19297篇 |
金属工艺 | 8399篇 |
机械仪表 | 8493篇 |
建筑科学 | 10425篇 |
矿业工程 | 3310篇 |
能源动力 | 3763篇 |
轻工业 | 13708篇 |
水利工程 | 3427篇 |
石油天然气 | 5311篇 |
武器工业 | 1139篇 |
无线电 | 17376篇 |
一般工业技术 | 15678篇 |
冶金工业 | 6426篇 |
原子能技术 | 1888篇 |
自动化技术 | 20275篇 |
出版年
2024年 | 697篇 |
2023年 | 2233篇 |
2022年 | 4495篇 |
2021年 | 5981篇 |
2020年 | 4251篇 |
2019年 | 3254篇 |
2018年 | 3537篇 |
2017年 | 4232篇 |
2016年 | 3825篇 |
2015年 | 5437篇 |
2014年 | 6978篇 |
2013年 | 8810篇 |
2012年 | 9904篇 |
2011年 | 10764篇 |
2010年 | 9637篇 |
2009年 | 9440篇 |
2008年 | 9569篇 |
2007年 | 9252篇 |
2006年 | 8507篇 |
2005年 | 6882篇 |
2004年 | 4886篇 |
2003年 | 3713篇 |
2002年 | 3689篇 |
2001年 | 3319篇 |
2000年 | 2921篇 |
1999年 | 2306篇 |
1998年 | 1943篇 |
1997年 | 1711篇 |
1996年 | 1490篇 |
1995年 | 1254篇 |
1994年 | 987篇 |
1993年 | 821篇 |
1992年 | 650篇 |
1991年 | 504篇 |
1990年 | 440篇 |
1989年 | 324篇 |
1988年 | 286篇 |
1987年 | 233篇 |
1986年 | 179篇 |
1985年 | 155篇 |
1984年 | 110篇 |
1983年 | 85篇 |
1982年 | 73篇 |
1981年 | 73篇 |
1980年 | 69篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1977年 | 36篇 |
1976年 | 57篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
The PTC-type BaTiO3 ceramics of similar microstructure are obtained by careful control of a sintering scheme. The defect chemistry of them is modified by varying the cooling rate and annealing conditons. In addition to applying Heywang and Jonker models for explaining the resistivity anomaly of these samples, the outward diffusion of oxygen vacancies (VO), which left excess barium vacancies (VBa) behind, is proposed to be the formation mechanism of surface states. The formation of defect complex consisting of a V
O
..
-
Ba
pair is assumed to be the cause of small diffusivity of VO in these materials. The phenomena, in which the slower cooling rate raises the resistivity of samples, is ascribed to the higher concentration of excess barium vacancies (VBa) contained in these samples. However, the maximum potential barrier height (max) of the samples is the same, irrespective of the amount of surface state concentration (N
s) and is estimated to be max = 0.66eV, from the In (max)-1/T
max plot. 相似文献
133.
本文着重于辐射作用于物质最初生成的产物,包括激发态的离子与分子,能量超过热能的次级电子等的反应以及电荷和激发能的转移,并试图论述它们的最新发展。 相似文献
134.
Morphology and geometry of melted zones, cooling rates, microstructure and microhardness in the laser-glazed Fe-4%C-10%Sn alloy have been investigated. The computer simulation on the basis of the moving gaussian source model was used successfully to predict the maximum width and depth of the melted zone and the cooling rate. The microstructure from the surface to the bottom of the laser-melted zone is a non-crystalline phase, dendritic grains and a microcrystalline zone successively. Values of the averaged-spacing of the non-crystalline phase are 0.2056 and 0.1219nm, respectively; twinned martensites, having an axial ratioc/a of 1.128, existed in dendritic grains, and carbides of Fe3 C at the interdendritic regions; the microcrystalline zone was composed of -Fe and a new bet (a=0.415 nm,c=0.955 nm) phase. The different microstructure in the melted zone can be explained by the results of the heat flow calculation. A fine eutectic structure (-Fe + Fe3C) was observed in heat-affected zones. Microhardness of the eutectic structure can be predicted by the empirical relation of fracture stress to the interlamellar spacing of pearlite. 相似文献
135.
Experiments were performed on the superplastic Zn-22% Al eutectoid alloy to determine the contribution of grain boundary sliding at both low (35%) and high (235%) elongations. The tests were conducted at two different strain rates in the superplastic Region II, and the results show that, within the accuracy of the measurements, there is a large sliding contribution at both elongations. By taking detailed measurements of both the magnitude of the sliding offset and the type of interface, it is shown that the average offsets are generally a maximum at the Zn-Zn boundaries, there is less sliding at the Zn-Al interfaces, and the offsets are a minimum at the Al-Al boundaries. In addition, the distributions of the magnitudes of the sliding offsets are similar at both the low and high elongations. It is concluded that grain boundary sliding is an important deformation process in the superplastic Region II and that it remains important even when the elongation is very high. The nature of the results indicates also that experimental observations of the deformation behaviour in superplastic materials at low elongations (up to 50%) provide meaningful information on the behaviour at much higher (superplastic) elongations.On leave from Mechanical Engineering Department, Nanjing Aeronautical Institute, Nanjing, Jiang-su 210002, People's Republic of China. 相似文献
136.
A new bioglass ceramic with composition of Na2O 12%, CaO 28%, P2O5 10% and SiO2 50% with a high bending strength (120–140 MPa) and compressive strength (600–750 MPa) was studied. The crystallized phases of-Ca2P2P7 and Na2Ca3Si6O16 were determined by X-ray diffraction. Optical microscopy of the material revealed that a very uniform crystal size of about 30 m was obtained with high nucleation frequency. The nucleation and crystallization processes were also investigated. The rat shoulder test showed that the material formed a tight chemical bond with biological texture and had good biocompatibility. 相似文献
137.
138.
Catalysis Letters - Pd-based heterogeneous nanocatalysts have wide application in chemical industry. However, the traditional synthesis process contains multi-steps such as impregnation, dry,... 相似文献
139.
Journal of Porous Materials - Aiming at the poor heat conduction performance of porous MIL-101 applied in adsorption cooling process, few layer graphene (FLG) was selected as a promising thermal... 相似文献
140.