全文获取类型
收费全文 | 397191篇 |
免费 | 40697篇 |
国内免费 | 14609篇 |
专业分类
电工技术 | 20704篇 |
技术理论 | 56篇 |
综合类 | 22822篇 |
化学工业 | 75991篇 |
金属工艺 | 20695篇 |
机械仪表 | 23886篇 |
建筑科学 | 30590篇 |
矿业工程 | 11933篇 |
能源动力 | 11651篇 |
轻工业 | 27101篇 |
水利工程 | 6200篇 |
石油天然气 | 24526篇 |
武器工业 | 2858篇 |
无线电 | 46355篇 |
一般工业技术 | 52636篇 |
冶金工业 | 20247篇 |
原子能技术 | 3751篇 |
自动化技术 | 50495篇 |
出版年
2024年 | 1419篇 |
2023年 | 5608篇 |
2022年 | 9646篇 |
2021年 | 13830篇 |
2020年 | 11861篇 |
2019年 | 11266篇 |
2018年 | 12515篇 |
2017年 | 14154篇 |
2016年 | 13330篇 |
2015年 | 16807篇 |
2014年 | 20739篇 |
2013年 | 25331篇 |
2012年 | 24485篇 |
2011年 | 26601篇 |
2010年 | 23617篇 |
2009年 | 22406篇 |
2008年 | 21650篇 |
2007年 | 20853篇 |
2006年 | 21407篇 |
2005年 | 18819篇 |
2004年 | 13006篇 |
2003年 | 12196篇 |
2002年 | 11740篇 |
2001年 | 10605篇 |
2000年 | 10138篇 |
1999年 | 10848篇 |
1998年 | 8654篇 |
1997年 | 7164篇 |
1996年 | 6727篇 |
1995年 | 5641篇 |
1994年 | 4607篇 |
1993年 | 3249篇 |
1992年 | 2628篇 |
1991年 | 2091篇 |
1990年 | 1592篇 |
1989年 | 1299篇 |
1988年 | 1063篇 |
1987年 | 717篇 |
1986年 | 551篇 |
1985年 | 361篇 |
1984年 | 255篇 |
1983年 | 220篇 |
1982年 | 209篇 |
1981年 | 135篇 |
1980年 | 145篇 |
1979年 | 72篇 |
1978年 | 35篇 |
1977年 | 39篇 |
1976年 | 55篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Yun‐Hwei Shen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(5):581-586
A novel strategy of sweep coagulation to treat low turbidity water is presented herein. Study findings demonstrated that an Na+‐saturated bentonite with medium cation exchange capacity (CEC) resulted in significant turbidity removal at a bentonite dosage of 30 mg dm?3. Bentonite dispersion with fully delaminated platelets tended to undergo a more porous type of coagulation with intense face‐to‐face interactions of platelets and effectively entrapped TiO2 particles in band‐type structures. This type of coagulation usually results in a large volume of settled flocs with a fluffy structure and excellent turbidity removal efficiency for sweep coagulation. The sign and magnitude of electrical charge on TiO2 particles has a minor effect on the efficiency of sweep coagulation. Copyright © 2005 Society of Chemical Industry 相似文献
952.
Hung‐Yee Shu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(3):273-280
Liquid–liquid two‐phase epoxidation from cyclohexene and cyclooctene in aqueous potassium peroxymonosulfate (commercially available as Oxone®) solution was studied as an application in pollution prevention. To avoid potential emissions of volatile organic compounds an aqueous solution was employed to replace the usual chlorinated solvents used in epoxide production. A droplet column reactor and stirred tank reactor were used to investigate two‐phase synthesis of epoxide. An aqueous Oxone® solution was used to oxidize a dispersion of alkene droplets and form epoxide. The study of aqueous epoxidation in both reactors showed that the epoxidation of alkenes can be represented as a first order reaction with respect to alkene. The salting out effect of Oxone® concentration was studied in both reactors and found to be very similar at optimal conditions. In comparing the two reactors, it was found that the droplet column reactor produces larger quantities of product per unit reactor volume for the same reaction time. The objective of this study is to provide an alternative reactor design and synthesis route that can meet pollution prevention goals. Copyright © 2004 Society of Chemical Industry 相似文献
953.
In this paper we verified the submodeling technique applied in the thermomechanical reliability assessment of a flip-chip BGA under accelerated thermal cycling test conditions. Since the steady-state creep model was implemented for the solder bump to better represent its realistic mechanical behavior, submodeling procedures developed specifically for path-dependent thermomechanical problems were considered. A detailed global model for the flip-chip BGA was built up to verify submodeling solutions. This model also served as a benchmark to examine solution discrepancies caused by different simplifications of the global model. 相似文献
954.
955.
956.
核磁共振谱的岩石孔喉结构分析 总被引:20,自引:1,他引:19
刘堂宴 ,王绍民 ,傅容珊 ,周明顺 ,李艳华 ,罗曼 .核磁共振谱的岩石孔喉结构分析 .石油地球物理勘探 ,2 0 0 3,38(3) :32 8~ 333岩心核磁共振 T2 谱和压汞分析数据均在一定程度上反映了岩石的孔喉结构 ,理论分析表明 ,这两组数据具有相关性。应用岩心核磁共振 T2 谱研究岩石孔喉结构 ,关键是确定 T2 与 Pc的转换系数。但以前的方法在 T2与 Pc 的转换过程中 ,需要涉及某些岩石特性参数 ,实用中有一定困难。本文直接利用岩心核磁共振 T2 谱和压汞分析数据之间的相关性 ,客观地确定 T2 与 Pc之间的转换系数 ,避免了确定岩石特性参数的困难。应用本文方法 ,对 6块岩心的多种核磁共振分析数据进行了对比分析 ,做出了 NMR (Nuclear Magnetic Resonance,简称NMR) T2 毛管力曲线和孔喉半径分布 ,并将这些结果与压汞分析的结果进行了对比。结果表明 ,岩心 NMR T2谱在实用性和评价精度上均略显优势 ;至少是在饱含油的条件下 ,岩心的 NMR T2 谱可以用于研究孔喉结构分布 ,油气的弛豫特性作为影响背景值存在 ,对于评价结果没有明显的影响 ;在全部 6块岩心中 ,T2 与 Pc 的转换系数位于 2 5 0 0~ 4 0 0 0μs· MPa之间。 相似文献
957.
958.
Grain refinement of Al-7Si alloys and the efficiency assessment by recognition of cooling curves 总被引:5,自引:0,他引:5
Under sand cup solidification condition, the influence of Ti, B concentration, and holding time on the grain size of a high-purity
Al-7Si alloy has been systematically studied. It is found that the grain size decreases rapidly at lower Ti or B additions,
and is almost constant at the higher concentrations. For Al-3B refined Al-7Si alloys, the grain size increases at the initial
period of holding time, and then rapidly becomes independent of holding time; while for Al-7Si alloys refined with Al-5Ti-1B,
the grain size increases with holding time throughout. To evaluate the refinement efficiency, a new method named “intelligent
evaluating of melt quality by pattern recognition of thermal analysis cooling curves” has also been introduced in this article.
The results show that comparing the cooling curve of the evaluated melt with those in a database to find the most similar
one to it can precisely assess the grain refinement efficiency of the measured Al-7Si alloy. In addition, the influence of
Ti, B addition levels, and pouring temperatures on some characteristic parameters of cooling curve has also been discussed. 相似文献
959.
960.
本文综术了集成电路工艺的Cu布线中Cu薄膜化学气相沉积(CVD)的研究背景,详细介绍了CVD生长Cu金属薄膜的国内外研究进展及CVD对前趋物的要求,并对前趋物的一些物理、化学性质进行了总结,最后,对薄膜沉积的计算机摸拟作了简要介绍。 相似文献