全文获取类型
收费全文 | 643970篇 |
免费 | 8487篇 |
国内免费 | 1971篇 |
专业分类
电工技术 | 11749篇 |
综合类 | 597篇 |
化学工业 | 97551篇 |
金属工艺 | 25243篇 |
机械仪表 | 18559篇 |
建筑科学 | 15878篇 |
矿业工程 | 2957篇 |
能源动力 | 17584篇 |
轻工业 | 57229篇 |
水利工程 | 6294篇 |
石油天然气 | 11305篇 |
武器工业 | 39篇 |
无线电 | 72793篇 |
一般工业技术 | 123414篇 |
冶金工业 | 126683篇 |
原子能技术 | 13200篇 |
自动化技术 | 53353篇 |
出版年
2021年 | 5690篇 |
2020年 | 4063篇 |
2019年 | 5245篇 |
2018年 | 9008篇 |
2017年 | 8832篇 |
2016年 | 9282篇 |
2015年 | 6532篇 |
2014年 | 10814篇 |
2013年 | 29292篇 |
2012年 | 17362篇 |
2011年 | 23989篇 |
2010年 | 18971篇 |
2009年 | 21344篇 |
2008年 | 21704篇 |
2007年 | 21433篇 |
2006年 | 18720篇 |
2005年 | 17194篇 |
2004年 | 16461篇 |
2003年 | 16076篇 |
2002年 | 15345篇 |
2001年 | 15451篇 |
2000年 | 14417篇 |
1999年 | 15251篇 |
1998年 | 39510篇 |
1997年 | 27702篇 |
1996年 | 21162篇 |
1995年 | 15938篇 |
1994年 | 13755篇 |
1993年 | 13458篇 |
1992年 | 9728篇 |
1991年 | 9167篇 |
1990年 | 8955篇 |
1989年 | 8737篇 |
1988年 | 8186篇 |
1987年 | 7310篇 |
1986年 | 7150篇 |
1985年 | 8014篇 |
1984年 | 7484篇 |
1983年 | 6701篇 |
1982年 | 6314篇 |
1981年 | 6425篇 |
1980年 | 6056篇 |
1979年 | 5976篇 |
1978年 | 5723篇 |
1977年 | 6927篇 |
1976年 | 9062篇 |
1975年 | 4975篇 |
1974年 | 4734篇 |
1973年 | 4866篇 |
1972年 | 4002篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A melt-extraction technique, using a sharpened molybdenum wheel, has been used to produce fine oxide ceramic fibres. Wetting of the molybdenum wheel by molten ceramic is a key parameter in the melt-extraction process. Two types of fibre are generally obtained, depending on the extraction speed. At very low wheel speed, fine and uniform fibres of high quality are produced. However, when the wheel speed exceeds a critical velocity, Rayleigh waves are formed on the free surface of the fibres. Moreover, the average fibre thickness first increases with the wheel velocity, then passes through a maximum, decreasing at high velocity. This thickness variation is discussed in terms of both surface tension and viscosity of the liquid ceramics. 相似文献
992.
993.
Fractal geometry is finding its application in the nondestructive evaluation (NDE) of corrosion by characterizing the corrosion surface with fractal dimensions. It was found that corrosion surfaces can be well described by multifractals. Two algorithms were used to obtain the fractal dimensions of a corroded aluminum alloy surface, one being box-counting and another being coherent light scattering. Fractal dimensions were related with the damage caused by corrosion and fatigue. 相似文献
994.
R. Knockaert I. Doghri Y. Marchal T. Pardoen F. Delannay 《International Journal of Fracture》1996,81(4):383-399
Double-edge notched (DENT) steel plates were pulled until complete fracture and several experimental observations were made (using profilometry and scanning electron microscopy). The essential work of fracture (EWF) model was found to be well verified. Numerical simulations—up to the maximum load only—of some experiments were performed using the finite element method (FEM), and incorporating geometric and material non-linearities (large deformation elasto-plasticity). Some experimental measurements were compared with the corresponding numerical computations and excellent agreement was found. 相似文献
995.
In this study, an aluminum based metallic matrix (Al-2wt.% Cu) was reinforced with SiC particulates using a conventional casting technique and a new disintegrated melt deposition technique. Microstructural characterization studies conducted on the samples taken from disintegrated melt deposition technique revealed a more uniform distribution of SiC particulates and good interfacial integrity between SiC particulates and metallic matrix when compared to the conventionally cast composite samples. Results of ambient temperature mechanical tests demonstrate an increase in 0.2% YS and ultimate tensile strength of samples taken from disintegrated melt deposition technique when compared with the unreinforced and conventionally cast composite samples. The results of microstructural characterization and mechanical testing were finally rationalized in terms of the nature of processing technique employed to reinforce Al-2wt.% Cu metallic matrix with SiC particulates. 相似文献
996.
The anisotropic nature of fibre reinforced composites leads to large stress concentrations around pin-loaded holes through standard weave cloths. Proper understanding of how this anisotropic nature affects the load distribution around holes can be utilised to reduce these concentrations if sufficient thought is given to the internal fibre geometry near to the hole. Such local reinforcements need not be highly complex and can be readily produced without excessive effort, producing significant improvements in performance. 相似文献
997.
998.
999.
The release of ibuprofen from mixtures of polyethylene glycol (PEG) with polyvinyl acetate (PVAc) has been studied in vitro and complemented by x-ray diffraction measurements, differential scanning calorimetry (DSC), and melting point determinations via hot-stage microscopy (HSM). Results indicate that ibuprofen release can be affected markedly by alteration of the PVAc concentration. The molecular weight of the PEG and the pH of the dissolution medium are also shown to affect the release profile. Visual observation during the drug release process revealed a complex behavior which included emission of liquidlike droplets, formation of a crust around the releasing mass, and/or production of flakes of solid material. This behavior appeared to have a disadvantageous effect on the reproducibility of drug release. Construction of a phase diagram from results of thermal analysis using DSC and HSM indicated the formation of an eutectic mixture with a composition of 35% ibuprofen and 65% PEG 1500 and a melting point of 36°C. The complex behavior of the drug-releasing mass is discussed in terms of this phase diagram. Only the release data for systems containing 4% w/w or more of PVAc could be linearized by plotting against the square root of time whereas data for all of the systems studied could be linearized by first-order plots. 相似文献
1000.
N. Satou A. Morikawa K. Ohmoto H. Urabe H. Shintani K. Wakasa M. Yamaki 《Journal of materials science. Materials in medicine》1996,7(12):749-752
This study was designed to evaluate the bacterial adhesion to five types of experimental composite-based resins and a commercial composite resin used as a control. Physicochemical surface characteristics of composite resins with and without an artificial saliva coating were measured. The relationship between the numbers of adhering cells (Streptococcus sanguis, S. mutans and S. sobrinus) and surface characteristics was analysed. The values of contact angles and the number of adhering cells were small with saliva coating. S. sanguis ATCC 10557 showed a positive correlation (r=0.835, p<0.05) with the contact angles of uncoated resins, whereas no relationship was observed for saliva-coated resins. With S. mutans Ingbritt the cell numbers adhering to resins correlated strongly (p<0.01) with the values of zeta potential of resins for either saliva coated or uncoated. Electrical repulsion forces had a strong contribution to adherence of cells such as S. mutans and S. sobrinus which show a high absolute zeta potential. 相似文献