全文获取类型
收费全文 | 32680篇 |
免费 | 4144篇 |
国内免费 | 1440篇 |
专业分类
电工技术 | 1331篇 |
技术理论 | 1篇 |
综合类 | 2160篇 |
化学工业 | 5797篇 |
金属工艺 | 4872篇 |
机械仪表 | 2107篇 |
建筑科学 | 4220篇 |
矿业工程 | 1367篇 |
能源动力 | 1082篇 |
轻工业 | 1325篇 |
水利工程 | 384篇 |
石油天然气 | 1236篇 |
武器工业 | 212篇 |
无线电 | 2790篇 |
一般工业技术 | 5161篇 |
冶金工业 | 2928篇 |
原子能技术 | 327篇 |
自动化技术 | 964篇 |
出版年
2024年 | 160篇 |
2023年 | 891篇 |
2022年 | 903篇 |
2021年 | 1265篇 |
2020年 | 1435篇 |
2019年 | 1373篇 |
2018年 | 1092篇 |
2017年 | 1256篇 |
2016年 | 1218篇 |
2015年 | 1218篇 |
2014年 | 2015篇 |
2013年 | 2079篇 |
2012年 | 2152篇 |
2011年 | 2216篇 |
2010年 | 1563篇 |
2009年 | 1624篇 |
2008年 | 1550篇 |
2007年 | 1867篇 |
2006年 | 1833篇 |
2005年 | 1662篇 |
2004年 | 1365篇 |
2003年 | 1378篇 |
2002年 | 1101篇 |
2001年 | 936篇 |
2000年 | 870篇 |
1999年 | 624篇 |
1998年 | 540篇 |
1997年 | 393篇 |
1996年 | 365篇 |
1995年 | 267篇 |
1994年 | 237篇 |
1993年 | 178篇 |
1992年 | 143篇 |
1991年 | 106篇 |
1990年 | 98篇 |
1989年 | 85篇 |
1988年 | 47篇 |
1987年 | 33篇 |
1986年 | 21篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
A number of copolymers were synthesised by condensing the 2,4-dinitrophenylhydrazone of resacetophenone with substituted benzoic acids/ phenols and formaldehyde in the presence of sodium hydroxide or hydrochloric acid. The decomposition temperature, solubility and viscosity of the polymers have been determined. The ion-exchange properties have been studied by using a batch equilibrium method. The distribution of a number of metal ions between an aqueous solution and the resin have been measured. A wide range of pH and variable ionic strengths have been investigated. 相似文献
72.
Although the gas metal arc welding (GMAW) process is widely used for joining metals, its planning is still a cumbersome task. The planning procedure involves many complex interrelationships among the process variables and depends heavily on empirical knowledge. Therefore, a solution method that allows a convenient way to represent the domain knowledge and evaluate the process variable relationships is needed. Further, the lack of a strong domain theory to quantify these interrelationships is a deficiency in the planning of the GMAW process. This paper presents a solution method that overcomes this deficiency and introduces a convenient knowledge representation scheme. The solution method considers the planning procedure to be a constraint satisfaction problem (CSP). The AC-4 algorithm is used to obtain arc consistency among nodes in the constraint network and the PC-4 algorithm is applied to obtain path consistency in the network. A modified version of the AC-4 algorithm is developed to reduce the search space and correspondingly reduce the computation time. An example is presented to demonstrate the capability of the method and its potential to reduce lead time. 相似文献
73.
Using the batch method, the retention of Ga(III) from HCl solutions by two gel‐type pyridine strong‐base anion exchangers containing 1‐methyl‐ or 1‐butyl‐4‐vinylpyridinium chloride structural units, called S1 and S2 resins, respectively, was studied. The influence of the HCl and Ga(III) concentrations as well as of the contact time between the resin and the liquid phase was investigated. The parameters, which characterize the retention process, were estimated using Langmuir and Freundlich isotherms. Both resins exhibited a higher affinity for gallium ions from a 6M HCl solution. According to Langmuir isotherms, maximum retention capacities of 44.44 and 60 mg Ga(III)/g dry resin for the S1 and S2 resins, respectively, were obtained. Freundlich isotherms provide additional proof for a higher affinity of the S2 resin for Ga(III) from HCl solutions. It is clear that the substituent length increase on N+ atoms led to an increasing affinity of the pyridine strong base anion exchangers toward Ga(III). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3440–3444, 2002 相似文献
74.
75.
介绍了鄂钢电炉厂70t consteel 电炉使用炉壁集束碳氧枪后对经济指标的改善,以及在生产实践中的冶金效果. 相似文献
76.
新一代高活性,高水热稳定性3961(PS-Ⅳ)型连续重整催化剂于1996年在上海石化芳烃厂400kt/a连续重整装置上首次进行工业应用试验。开工5a,催化剂跟踪分析结果表明,该剂保持了良好的物化性质和反应性能,表现为良好的比表面积稳定性和持氯能力,经过200个以上再生周期的催化剂未发现有明显的相变和金属分散度的变化。 相似文献
77.
The interaction of alkali metal with surfaces has been of great interest to the community of catalysis since alkali metal can play an important role as a promoter. On alkali-doped MoS2, such a promotion effect of alkali metal has been exemplified in the direct synthesis of linear alcohols from CO and H2, where the alkali-doping switches the catalyst selectivity from methanation to alcohol synthesis. This paper reviews recent high-resolution X-ray photoelectron spectroscopy experiments that have provided direct
observation of electron transfer from alkali metals to a model single crystal MoS2 and the capture of the supra-valence electrons in the subsequent oxidation reactions. 相似文献
78.
David Nistr Karin Keis Sten-Eric Lindquist Anders Hagfeldt 《Solar Energy Materials & Solar Cells》2002,73(4)
In this paper a transport equation is derived which describes the behaviour of the nanostructured metal oxide films in a photoelectrochemical cell. It is shown that a detailed analysis of the charge compensation mechanism necessarily leads to a transport equation with characteristics similar to but logically distinct from the pure diffusion equation. The studied phenomenon was named ambipolar diffusion in the early 1950s. It takes into account the fact that the diffusion processes of ions and electrons occur at different speeds. A weak electric field therefore couples the processes together to preserve charge neutrality. The electric field in turn affects the transport resulting in a deviation from purely diffusive behaviour. However, this has not been widely recognised in the literature for nanostructured semiconductor films until very recently. In this paper a detailed analysis is presented. It is based on the assumption that the current density is solenoidal. It is shown that application of the ambipolar diffusion model to a photoelectrochemical cell based on a nanostructured metal oxide film leads to an additional term in the transport equation, rather than only a new diffusion coefficient as in earlier work. It is also shown that the boundary conditions interact closely with the equation to form a transport model. 相似文献
79.
80.