全文获取类型
收费全文 | 84547篇 |
免费 | 8004篇 |
国内免费 | 5040篇 |
专业分类
电工技术 | 5394篇 |
技术理论 | 1篇 |
综合类 | 8493篇 |
化学工业 | 12761篇 |
金属工艺 | 4703篇 |
机械仪表 | 5535篇 |
建筑科学 | 5945篇 |
矿业工程 | 2115篇 |
能源动力 | 2254篇 |
轻工业 | 7916篇 |
水利工程 | 1888篇 |
石油天然气 | 3251篇 |
武器工业 | 808篇 |
无线电 | 10116篇 |
一般工业技术 | 8677篇 |
冶金工业 | 3556篇 |
原子能技术 | 1136篇 |
自动化技术 | 13042篇 |
出版年
2024年 | 286篇 |
2023年 | 998篇 |
2022年 | 2016篇 |
2021年 | 2709篇 |
2020年 | 2131篇 |
2019年 | 1757篇 |
2018年 | 1896篇 |
2017年 | 2239篇 |
2016年 | 2180篇 |
2015年 | 3111篇 |
2014年 | 4163篇 |
2013年 | 4962篇 |
2012年 | 5977篇 |
2011年 | 6393篇 |
2010年 | 6068篇 |
2009年 | 5988篇 |
2008年 | 5959篇 |
2007年 | 5873篇 |
2006年 | 5466篇 |
2005年 | 4585篇 |
2004年 | 3708篇 |
2003年 | 3178篇 |
2002年 | 3698篇 |
2001年 | 3250篇 |
2000年 | 2242篇 |
1999年 | 1537篇 |
1998年 | 954篇 |
1997年 | 805篇 |
1996年 | 723篇 |
1995年 | 630篇 |
1994年 | 460篇 |
1993年 | 343篇 |
1992年 | 275篇 |
1991年 | 210篇 |
1990年 | 176篇 |
1989年 | 115篇 |
1988年 | 111篇 |
1987年 | 82篇 |
1986年 | 38篇 |
1985年 | 55篇 |
1984年 | 42篇 |
1983年 | 33篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 23篇 |
1979年 | 17篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1959年 | 8篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
制作压力传感器时,在二氧化硅层上淀积多晶硅膜,既可利用优良的机械特性,又可保证压敏电阻与衬底间具有良好的绝缘性,由此可大大提高器件的温度特性。介绍了一种多晶硅压力传感器的原理和设计。实验结果表明,这类传感器具有灵敏度好,精度高等特点,电路工作范围为0-250℃,且具有良好的温度稳定性。 相似文献
92.
本文提出一个同温冶炼过程中预测非金属夹杂物沉淀的计算机程序。本研究中,多元硅酸盐溶体的Gibbs自由能由基于统计热力学的晶胞模型来计算,该晶胞模型按照氧与周围的阳离子构成的对称和非对称晶胞来描述硅酸盐熔体结构,假定高温冶炼时认与非金属夹杂物平衡,钢液中氧化物元素的活度由Wagner交互作用系数来计算,利用本程序可以估计炼钢时沉淀的非金属氧化物的成分,为调整冶炼工艺和提高产品质量提供指导,进一步可计 相似文献
93.
Tzung-Pei Hong Shian-Shyong Tseng 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(6):857-867
Applies the technique of parallel processing to concept learning. A parallel version-space learning algorithm based upon the principle of divide-and-conquer is proposed. Its time complexity is analyzed to be O(k log2n) with n processors, where n is the number of given training instances and k is a coefficient depending on the application domains. For a bounded number of processors in real situations, a modified parallel learning algorithm is then proposed. Experimental results are then performed on a real learning problem, showing that our parallel learning algorithm works, and being quite consistent with the results of theoretical analysis. We conclude that when the number of training instances is large, it is worth learning in parallel because of its faster execution 相似文献
94.
Min Jeong Noh Tae Gyun Kim In Kwon Hong Ki-Pung Yoo 《Korean Journal of Chemical Engineering》1995,12(1):48-55
A new transparent microscale circulation-type high pressure equilibrium cell with on-line sampling was devised. With this
apparatus, experimental solubility of molecularly complex species such as steroids (cholesterol, stigmasterol and ergosterol)
and fatty acids (palmitic acid and stearic acid) in supercritical carbon dioxide(sc-C02) were measured. Also, to find an appropriate substance for enhancing both the polarity and the solubility power of the SC-CO2 solvent, we arbitrarily selected three polar substances such as acetone, methanol and water and the effect of these cosolvents
on the solubility of solutes in SC-CO2 are examined. The supercritical phase equilibrium data of solute-cosolvent-sc-CO2 systems were quantitatively correlated using a new equation of state based on the lattice fluid theory incorporated with
the concept of multibody interaction. We found that the addition of tracer amount of acetone or methanol to SC-CO2 enhances the solubility of all solutes about thirty to sixty times when compared with the case of pure sc-CO2 However, for the case of cosolvent water, no further enhancement of the solubility of solutes was realized. Also, the versatile
fittability of the equation of state proposed in this work was demonstrated with the newly measured ternary supercritical
equilibrium data. 相似文献
95.
96.
Certain new sulfide-smelting processes and coal-gasification processes generate high-strength sulfur dioxide streams, for
which a new process for converting sulfur dioxide to elemental sulfur needs to be developed because no process exists that
is generally and economically applicable to the treatment of such streams. A thermodynamic and experimental investigation
to develop a new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and
calcium sulfate without generating secondary pollutants was carried out. In this process, the starting raw material, calcium
sulfate, is reduced by a suitable reducing agent, such as hydrogen, to produce calcium sulfide, which is used to reduce sulfur
dioxide to elemental sulfur vapor and calcium sulfate. The latter is, in turn, reduced to regenerate calcium sulfide. In this
Part I, detailed experimental results are presented on the kinetics of the reaction between sulfur dioxide and calcium-sulfide
pellets, which produces elemental sulfur and calcium sulfate. The experiments were carried out at temperatures between 1023
and 1088 K and sulfur-dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis (TGA) technique.
The rate of this reaction was demonstrated by the conversion of 40 pct calcium-sulfide pellets obtained from the hydrogen
reduction of fresh calcium sulfate in 10 minutes at 1073 K under a sulfur-dioxide partial pressure of 43 kPa. The reactivity
decreased somewhat during the first three cycles but remained largely unchanged thereafter up to the tenth cycle. This characteristic
of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants.
A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur-dioxide partial
pressure and has an activation energy of 101 to 134 kJ/mol (24 to 32 kcal/mol) for calcium-sulfide pellets reacted and regenerated
several different times. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated-gasification,
combined-cycle, desulfurization unit and new sulfide-smelting plants, contain much higher partial pressures of SO2. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported
in this article. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part
II. 相似文献
97.
98.
99.
当成千上万的农民远离穷困的村落,视而不见地掠过小城镇,径奔大城市寻梦或淘金,一个显见的事实是,大城市里有更多的就业机会,有更多的钱赚——从生存的角度看,只要条件具备,没有谁不愿意趋利避害。 站在政府的角度,秩序则是重要的。任何政府都担心刑事案件随着它的城市人口的暴涨而剧增,而且,这还不是惟一的,因为与“月黑风高夜,杀人放火天”的刑事案件相伴的至少还有贫民窟。杀人、放火、贫民窟等等一系列大城市综合症,恰恰是西方国家城市化道路的“遗产”,是发展中国家快速城市化的特产。 相似文献
100.