全文获取类型
收费全文 | 815365篇 |
免费 | 97030篇 |
国内免费 | 63371篇 |
学科分类
工业技术 | 975766篇 |
出版年
2024年 | 2268篇 |
2023年 | 12212篇 |
2022年 | 29960篇 |
2021年 | 39004篇 |
2020年 | 28435篇 |
2019年 | 19882篇 |
2018年 | 21343篇 |
2017年 | 24568篇 |
2016年 | 21912篇 |
2015年 | 35905篇 |
2014年 | 46155篇 |
2013年 | 54349篇 |
2012年 | 68378篇 |
2011年 | 71808篇 |
2010年 | 68441篇 |
2009年 | 65127篇 |
2008年 | 67322篇 |
2007年 | 65599篇 |
2006年 | 56536篇 |
2005年 | 45827篇 |
2004年 | 32669篇 |
2003年 | 22287篇 |
2002年 | 20713篇 |
2001年 | 18770篇 |
2000年 | 14918篇 |
1999年 | 6576篇 |
1998年 | 2631篇 |
1997年 | 2018篇 |
1996年 | 1808篇 |
1995年 | 1574篇 |
1994年 | 1212篇 |
1993年 | 940篇 |
1992年 | 805篇 |
1991年 | 537篇 |
1990年 | 491篇 |
1989年 | 514篇 |
1988年 | 330篇 |
1987年 | 231篇 |
1986年 | 223篇 |
1985年 | 106篇 |
1984年 | 127篇 |
1983年 | 104篇 |
1982年 | 97篇 |
1981年 | 139篇 |
1980年 | 239篇 |
1979年 | 157篇 |
1975年 | 17篇 |
1965年 | 24篇 |
1959年 | 141篇 |
1951年 | 157篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Yong Jiang Zhenbang Wei Wenzhou Sun Limeng Liu Zhenkun Huang 《Ceramics International》2021,47(6):7588-7592
Samples in Si–Al-R-O-N (R = Y, Gd, Yb) systems were prepared by solid-state reactions using R2O3, Al2O3, SiO2 and Si3N4 powders as starting materials. X-ray diffraction was done to investigate RAM-J(R) solid solutions [RAM = R4Al2O9, J(R) = R4Si2N2O7] formation and their equilibrium with RSO (R4Si2O10). Phase relations between RAM, J(R) and RSO at 1700 °C were summarized in a phase diagram. It was determined that a limited solid solution of RAM and RSO could be formed along RAM-RSO tie-line, while RAM and J(R) form a continuous solid solution along RAM-J(R) tie-line. In RAM-J(R)-RSO ternary systems, the RAM-J(R) tie-lines were extended towards the RSO corner to form a continuous solid solution area of JRAMss (R = Y, Gd, Yb). The established phase relations in the Si–Al-R-O-N (R = Y, Gd, Yb) systems may facilitate compositional selections for developing JRAMss as monolithic ceramics or for SiC/Si3N4 based composites using the solid-solutions as a second refractory phase. 相似文献
2.
Because of its ability to change optical absorption dynamically by applied electric field, nickel oxide (NiO) is a promising anodic material in smart windows, which can improve energy conversion efficiency in construction buildings. Although many works have achieved high electrochromic performance with different method. The underlying mechanism is still not fully investigated. In this article, we prepared the NiO films with large specific surface area and high stability by electron beam evaporation. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to figure out the surface morphology and composition of as-deposited films. Afterwards, the electrochemical properties and optical performance of the prepared NiO films were investigated. On this basis, the origin of surface charge was fully analyzed by cyclic voltammetry and diffusion coefficient test. These experimental and theoretical results firmly confirm that both the surface reaction and capacitive effect bring about the excellent EC performance in NiO films. These results not only provide clear evidence about electrochemical kinetics in NiO films, but also offer some useful guidelines for the design of EC materials with higher performance and longer stability. 相似文献
3.
4.
The exosome-mediated response can promote or restrain the diseases by regulating the intracellular pathways, making the exosome become an effective marker for diagnosis and therapeutic control at the single-cell level. However, real-time analysis is hard to be achieved with traditional approaches because the exosomes usually need to be enriched by ultracentrifugation for a measurable signal-to-noise ratio. Recently developed label-free single-molecule imaging approaches may become an real-time quantitative tool for the analysis of single exosomes and related secretion behaviors of single living cells owing to their extreme sensitivity. 相似文献
5.
6.
7.
8.
Haiyue Xu Ji Zou Weimin Wang Hao Wang Wei Ji Zhengyi Fu 《Journal of the European Ceramic Society》2021,41(1):635-645
Fully dense ceramics with retarded grain growth can be attained effectively at relatively low temperatures using a high-pressure sintering method. However, there is a paucity of in-depth research on the densification mechanism, grain growth process, grain boundary characterization, and residual stress. Using a strong, reliable die made from a carbon-fiber-reinforced carbon (Cf/C) composite for spark plasma sintering, two kinds of commercially pure α-Al2O3 powders, with average particle sizes of 220 nm and 3 μm, were sintered at relatively low temperatures and under high pressures of up to 200 MPa. The sintering densification temperature and the starting threshold temperature of grain growth (Tsg) were determined by the applied pressure and the surface energy relative to grain size, as they were both observed to increase with grain size and to decrease with applied pressure. Densification with limited grain coarsening occurred under an applied pressure of 200 MPa at 1050 °C for the 220 nm Al2O3 powder and 1400 °C for the 3 μm Al2O3 powder. The grain boundary energy, residual stress, and dislocation density of the ceramics sintered under high pressure and low temperature were higher than those of the samples sintered without additional pressure. Plastic deformation occurring at the contact area of the adjacent particles was proved to be the dominant mechanism for sintering under high pressure, and a mathematical model based on the plasticity mechanics and close packing of equal spheres was established. Based on the mathematical model, the predicted relative density of an Al2O3 compact can reach ~80 % via the plastic deformation mechanism, which fits well with experimental observations. The densification kinetics were investigated from the sintering parameters, i.e., the holding temperature, dwell time, and applied pressure. Diffusion, grain boundary sliding, and dislocation motion were assistant mechanisms in the final stage of sintering, as indicated by the stress exponent and the microstructural evolution. During the sintering of the 220 nm alumina at 1125 °C and 100 MPa, the deformation tends to increase defects and vacancies generation, both of which accelerate lattice diffusion and thus enhance grain growth. 相似文献
9.
10.