全文获取类型
收费全文 | 79680篇 |
免费 | 9276篇 |
国内免费 | 4765篇 |
专业分类
电工技术 | 12720篇 |
技术理论 | 1篇 |
综合类 | 7026篇 |
化学工业 | 13969篇 |
金属工艺 | 7899篇 |
机械仪表 | 3551篇 |
建筑科学 | 7507篇 |
矿业工程 | 2518篇 |
能源动力 | 3117篇 |
轻工业 | 3847篇 |
水利工程 | 2451篇 |
石油天然气 | 3985篇 |
武器工业 | 744篇 |
无线电 | 5898篇 |
一般工业技术 | 7891篇 |
冶金工业 | 3464篇 |
原子能技术 | 1161篇 |
自动化技术 | 5972篇 |
出版年
2024年 | 232篇 |
2023年 | 1357篇 |
2022年 | 2409篇 |
2021年 | 3196篇 |
2020年 | 3100篇 |
2019年 | 2595篇 |
2018年 | 2476篇 |
2017年 | 3233篇 |
2016年 | 3170篇 |
2015年 | 3303篇 |
2014年 | 4759篇 |
2013年 | 5075篇 |
2012年 | 5639篇 |
2011年 | 6112篇 |
2010年 | 4326篇 |
2009年 | 4775篇 |
2008年 | 4248篇 |
2007年 | 4902篇 |
2006年 | 4672篇 |
2005年 | 3827篇 |
2004年 | 3308篇 |
2003年 | 2855篇 |
2002年 | 2364篇 |
2001年 | 1976篇 |
2000年 | 1679篇 |
1999年 | 1489篇 |
1998年 | 1209篇 |
1997年 | 972篇 |
1996年 | 763篇 |
1995年 | 747篇 |
1994年 | 681篇 |
1993年 | 464篇 |
1992年 | 372篇 |
1991年 | 313篇 |
1990年 | 247篇 |
1989年 | 217篇 |
1988年 | 151篇 |
1987年 | 114篇 |
1986年 | 73篇 |
1985年 | 61篇 |
1984年 | 49篇 |
1983年 | 34篇 |
1982年 | 45篇 |
1981年 | 14篇 |
1980年 | 27篇 |
1979年 | 12篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1959年 | 14篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
951.
The first use of nickel foam (NF) as electrocatalytic negative electrode in a polysulfide/bromine battery (PSB) is described. The performance of a PSB employing NF and polyacrylonitrile (PAN)-based carbon felt (CF) as negative and positive electrode materials, respectively, was evaluated by constant current charge-discharge tests in a single cell. Charge/discharge curves of the cell, positive and negative electrodes show that the rapid fall in cell voltage is due to the drop of positive potential caused by depletion of Br2 dissolved in the catholyte at the end of discharge. Cell voltage efficiency was limited by the relatively high internal ohmic resistance drop (iR drop). Polarization curves indicated that both NF and CF have excellent catalytic activity for the positive and negative redox reactions of PSB. The average energy efficiency of the single cell designed in this work could be as high as 77.2% at 40 mA cm−2 during 48 charge-discharge cycles. 相似文献
952.
Michael J. Banach Stephen J. Clarson Gregory Beaucage Jason Benkoski Tom Mates Edward J. Kramer Richard A. Vaia 《应用聚合物科学杂志》2002,86(8):2021-2024
For many microelectronic and optoelectronic applications, polymer thin films require the addition of small molecules. However, the thin‐film geometry and associated processing techniques will influence the final morphology and compositional distribution of the constituents. It is therefore important that these be examined directly rather than inferred from bulk measurements. As an example system, the concentration and distribution of Disperse Red 1 (DR1) molecules in poly(methyl methacrylate) thin films were examined. Ultraviolet visibility spectroscopy and dynamic secondary ion mass spectrometry indicate that the composition of the molecules decreased dramatically with thermal treatment of the film. The sublimation of the chromophore was observed to occur at temperatures well below the melting point of the small molecule and the glass transition of the pure polymer; this solute loss manifested itself in changes in the glass transition temperature of the film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2021–2024, 2002 相似文献
953.
A model is developed to address the uniformity of displacement deposition of nickel inside porous silicon with an ultrahigh aspect ratio as high as 200. The nickel distribution is treated as a current distribution issue as in electrodeposition. It is shown that the deposition distribution along the pore depth exhibits a strong dependence on a polarization parameter ξ. High values of ξ correspond to mass transport limitations and lead to non-uniform distributions, whereas small ξ values, representing interfacial reaction control, produce uniform distributions. Non-uniform deposition primarily occurs at an initial stage in which the reaction is dominated by mass transfer. As the deposition process continues, the deposition rate drops to a low value, and the deposition uniformity shifts from Ni2+ mass transport limitations to its interfacial reaction control, leading to uniform Ni2+ concentration and deposition rate distributions. It is predicted that the non-uniformity at the initial stage could be remedied by increasing the bulk concentration of the nickel ions and decreasing the plating bath pH. In addition, the uniformity of the deposition distribution can be significantly improved by introducing inhibiting additive coumarin to the plating solution. 相似文献
954.
The behavior of sulfur transformation during rapid hydropyrolysis of coal was investigated using a pressurized, continuous free fall pyrolyzer under the conditions of temperature ranging from 923 to 1123 K and hydrogen pressure up to 5 MPa. The yields of sulfur converted to gas, tar and char were determined, together with the analyses of sulfur form distributions in coals and chars. The results showed that the decomposition of inorganic sulfur species was affected only by the temperature, while the increases in temperature and hydrogen pressure obviously enhanced the removal of organic sulfur from coal. The extent of organic sulfur removal was proportional to the coal conversion, depending on coal type. A significant retention of gaseous sulfur products by the organic matrix of the char was observed during hydropyrolysis of a Chinese coal above 1023 K, even under the pressurized hydrogen atmosphere. The kinetic analysis indicates that the rate of organic sulfur removal from coal was 0.2th-order with respect to the hydrogen pressure, and the activation energy for total sulfur removal and organic sulfur removal is 17-26 and 13-55 kJ/mol, respectively. The low activation energies suggest that the transformation and removal of sulfur from coal might be controlled by the diffusion and/or thermodynamic equilibrium during hydropyrolysis under the pressurized conditions. 相似文献
955.
Xiufeng Hao Xiaofeng Lu Zhenyu Li Yiyang Zhao Tiecun Shang Qingbiao Yang Ce Wang Lijuan Li 《应用聚合物科学杂志》2006,102(3):2889-2893
Polyacrylonitrile colloidal microspheres have been successfully prepared with different concentrations of electrospraying polyacrylonitrile solutions. The morphology of the colloidal spheres has two kinds of structures and is strongly affected by electrospray‐ionization parameters, such as the polymer concentration, applied voltage, and distance between the electrodes. The solvent can also affect the morphology of polyacrylonitrile. The optimum conditions for preparing colloidal spheres have been found, and differential scanning calorimetry results indicate that polyacrylonitrile colloid spheres are amorphous. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2889–2893, 2006 相似文献
956.
957.
958.
959.
Further experimental investigation based on a microscopic, or single granule, scale has been conducted to investigate the uniformity of binder composition within a given size class for high shear melt granulation. This work assesses whether there is significant non-uniformity of binder composition within size classes to warrant considering this level of detail to improving population balance modelling of high shear granulation. It is concluded that at early times in a batch granulation process there is a broad variation in binder content between individual granules and that this variation persists in granules of small size. 相似文献
960.
Marco Lattuada 《Chemical engineering science》2004,59(21):4401-4413
The radial density distributions of fractal clusters generated in both DLCA and RLCA conditions by Monte-Carlo off-lattice cluster-cluster aggregation have been investigated. It has been computed by averaging a large number of clusters of same mass to form an average cluster, which is then considered as spherically symmetric. It is found that the radial density distribution, calculated using the mass center of the cluster as the center point, does not follow the fractal scaling, as sometimes assumed in the literature. An empirical model has been proposed to describe the dependence of the radial density distribution on the number of particles in the cluster. The obtained radial density distribution is used to compute permeability profile of the fractal cluster using several literature models, which is then applied to estimate the cluster hydrodynamic radius, Rh, by considering the cluster as a porous permeable object and using the solution of Brinkman equations for the fluid flow inside the cluster. The so obtained Rh values are compared to those in the literature, computed using the Kirkwood-Riseman (KR) theory. It has been found that, among the five permeability models examined, only the model proposed by Davis (Proceedings of the Institution of Mechanical Engineers Part B 1, 185) provides results in good agreement with those obtained using the KR model. Furthermore, it has been verified that the Rh values are insensitive to the model used for the density distribution. 相似文献