全文获取类型
收费全文 | 88263篇 |
免费 | 7320篇 |
国内免费 | 3707篇 |
专业分类
电工技术 | 3812篇 |
技术理论 | 8篇 |
综合类 | 8028篇 |
化学工业 | 16057篇 |
金属工艺 | 1616篇 |
机械仪表 | 2031篇 |
建筑科学 | 13688篇 |
矿业工程 | 5006篇 |
能源动力 | 5228篇 |
轻工业 | 5186篇 |
水利工程 | 18806篇 |
石油天然气 | 7748篇 |
武器工业 | 206篇 |
无线电 | 1259篇 |
一般工业技术 | 3974篇 |
冶金工业 | 3345篇 |
原子能技术 | 1132篇 |
自动化技术 | 2160篇 |
出版年
2024年 | 230篇 |
2023年 | 930篇 |
2022年 | 1894篇 |
2021年 | 2354篇 |
2020年 | 2505篇 |
2019年 | 2117篇 |
2018年 | 2035篇 |
2017年 | 2501篇 |
2016年 | 2847篇 |
2015年 | 2830篇 |
2014年 | 5397篇 |
2013年 | 5409篇 |
2012年 | 6692篇 |
2011年 | 6667篇 |
2010年 | 4948篇 |
2009年 | 5164篇 |
2008年 | 4531篇 |
2007年 | 6025篇 |
2006年 | 5622篇 |
2005年 | 5149篇 |
2004年 | 4029篇 |
2003年 | 3702篇 |
2002年 | 3188篇 |
2001年 | 2590篇 |
2000年 | 2154篇 |
1999年 | 1657篇 |
1998年 | 1196篇 |
1997年 | 992篇 |
1996年 | 761篇 |
1995年 | 688篇 |
1994年 | 502篇 |
1993年 | 384篇 |
1992年 | 307篇 |
1991年 | 239篇 |
1990年 | 177篇 |
1989年 | 189篇 |
1988年 | 114篇 |
1987年 | 130篇 |
1986年 | 96篇 |
1985年 | 96篇 |
1984年 | 91篇 |
1983年 | 55篇 |
1982年 | 30篇 |
1981年 | 9篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1959年 | 3篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 251 毫秒
931.
Climatic variation and intersectoral water competition increasingly challenge the effective provision of irrigation services. This article explores their combined effects on irrigation allocation from the Angat Reservoir (Philippines), where domestic water use in Metro Manila has overtaken regional irrigation as the dominant right-holder. Rules protecting Metro Manila’s large right to water ‘interact’ with dry spells to affect irrigation security in wet and dry seasons. Historically, irrigators were uncompensated because re-allocation’s cause was contested as (1) an unforeseeable climatic event (releasing domestic utilities of liability), or (2) produced by urban demand (requiring compensation). Trade-off rules must be prepared to navigate combinatory effects. 相似文献
932.
933.
以北京大兴区农村生活污水为处理对象,设计了4个反应柱,研究了3种填料结构、2种气水比条件下曝气生物滤池(BAF)对农村生活污水处理效率及微生物群落的影响。结果表明:(1)1~#、2~#、3~#柱气水比相同、填料结构不同,BOD5、CODCr和氨氮的去除率达到84.51%~96.49%;4~#柱与2~#柱填料结构相同,但气水比小,BOD5和CODcr处理效果差;4个柱TP的去除率低,需要强化除磷。(2)1~#、2~#、3~#柱OTU数量差异很小,说明微生物种类数量基本相同;2~#柱特有OTU数远大于4~#柱,说明填料结构相同条件下较大气水比有利于增加微生物种类。(3)1~#、2~#、3~#柱优势菌群主要有6种,在不同高度的优势菌群种类基本相同,但数量上有所差异;仅变形菌门中可能含有聚磷菌,这也是除磷效果差的原因之一。 相似文献
934.
本文文综述了中老油田采出液性质的变化和高含水采出液的油水分离特性,探讨了聚醚型破乳剂和高分子破乳剂在高含水采出液状况下的适应性。通过理论分析和大庆两个联合站的现场实验证明,高分子破乳剂特别适用于高含水采出液的事实,并指出了其适应性和提出了其质量与适应性的评价方法。 相似文献
935.
Chlorinated poly(vinyl chloride) (CPVC)/poly(vinyl pyrrolidone) (PVP) membranes were prepared by using the solvent system tetrahydrofuran (THF)/n‐butyl alcohol (n‐BA) to investigate the possibility of pore size and pore‐size distribution control. The coagulation of CPVC/PVP solution was induced by the exposure to water vapor at 25 (±0.5)°C. The average pore diameter, dp, and the size distribution of pores on the surface of the membrane were quantified through the image analyzer from the images visualized by field emission scanning electron microscope (FE‐SEM). Surface pore size and distribution of the prepared CPVC/PVP membrane were strongly affected by the relative humidity (RH) in the environment and the content of PVP used as an additive. Particularly, in the case of CPVC membrane without PVP, the mean pore size was 0.15–0.2 μm, depending on the RH. The pore distribution became broad with the increase of the RH. The membranes had open pores as confirmed by the hydraulic permeation experiment. In addition, the water flux and membrane resistance (Rm) were greatly affected by the composition of polymer solution and the RH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1195–1202, 2002 相似文献
936.
为提高合成氨的产量,对空压机作节能增产改造。介绍空压机国产节能增产件的特点、安装和大修情况,并通过机械性能和热力性能考核结果,说明国产件已基本达到预期目的 相似文献
937.
电石渣浆的综合治理与利用 总被引:5,自引:0,他引:5
介绍了综合治理电石乙炔法生产 PV C 时产生电石渣浆的工艺技术。采用电石渣浆废水全部 闭路循环回用工 艺,实现电石 渣浆上清液 的回收利用;同时以电石渣 代替熟石灰用 于环氧丙烷的生产。取得了显著的经济效益和社会环境效益。 相似文献
938.
The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH4 traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H2S (100 vol.ppm). Their catalytic properties were compared to those of Pd/Al2O3 and Pt/Al2O3. In the absence of H2S in the feed, Pt/SnO2appears as a very promising catalyst for CH4 oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al2O3. Catalysts steamed-aged at 873 K were also studied in order to simulate long term ageing in real lean-burn NGV exhaust conditions. To this respect, Pt/SnO2 is slightly less resistant than Pd/Al2O3. In the presence of H2S, Pt/SnO2catalysts are rapidly and almost completely poisoned, comparably to Pd/Al2O3and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO2sites active in CH4oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO2. 相似文献
939.
基于集流型涡轮流量计与放射性低能源密度—持水率计在大庆生产测井研究所油、气、水三相流动环路中的实验响应结果,首先考察了用于气液两相流中涡轮流量计的Aya物理模型,进而提出了经过校正后用于确定油、气、水三相流总流量的测量模型,用此模型预测三相流总流量与流动环标定数据对比后其误差小于5%,满足了石油工业应用要求 相似文献
940.
Highly Efficient Overall Water Splitting Through Optimization of Preparation and Operation Conditions of Layered Perovskite Photocatalysts 总被引:1,自引:0,他引:1
Jindo Kim Dong Won Hwang Hyun Gyu Kim Sang Won Bae Jae Sung Lee Wei Li Se Hyuk Oh 《Topics in Catalysis》2005,35(3-4):295-303
The layered perovskite materials were found to give the high photocatalytic activity in water splitting reaction under UV
irradiation, where the electronic structure of perovskite slab constructing the layered structure (the total cation valency)
was the most crucial factor to the high photocatalytic activity. Both the excessive cation valency and the layered structure
were required for active photocatalysts, while the slab thickness of layered perovskites had an insignificant effect on water-splitting
activity. In order to identify key variables that affected photocatalytic activity and to optimize the performance of (110)
layered perovskite, La2Ti2O7 was modified by various methods. The optimum amount of loaded nickel had a great effect and the amount depended on the surface
area of the perovskite phase. When an alkaline-earth element such as Ba, Sr, and Ca was doped on La2Ti2O7, the photocatalytic activity was enhanced markedly. Introduction of an alkaline hydroxide into the reaction system as an
external additive enhanced the activity further showing extremely high quantum yields close to 50%. 相似文献