全文获取类型
收费全文 | 103496篇 |
免费 | 9675篇 |
国内免费 | 7549篇 |
专业分类
电工技术 | 3943篇 |
技术理论 | 5篇 |
综合类 | 11767篇 |
化学工业 | 13804篇 |
金属工艺 | 6604篇 |
机械仪表 | 5445篇 |
建筑科学 | 27335篇 |
矿业工程 | 4398篇 |
能源动力 | 2549篇 |
轻工业 | 5401篇 |
水利工程 | 5344篇 |
石油天然气 | 4437篇 |
武器工业 | 895篇 |
无线电 | 5413篇 |
一般工业技术 | 10056篇 |
冶金工业 | 3795篇 |
原子能技术 | 661篇 |
自动化技术 | 8868篇 |
出版年
2024年 | 354篇 |
2023年 | 1374篇 |
2022年 | 2712篇 |
2021年 | 3185篇 |
2020年 | 3061篇 |
2019年 | 2568篇 |
2018年 | 2414篇 |
2017年 | 3028篇 |
2016年 | 3234篇 |
2015年 | 3495篇 |
2014年 | 6472篇 |
2013年 | 5360篇 |
2012年 | 7225篇 |
2011年 | 8006篇 |
2010年 | 6266篇 |
2009年 | 6718篇 |
2008年 | 6083篇 |
2007年 | 7313篇 |
2006年 | 6676篇 |
2005年 | 5949篇 |
2004年 | 4895篇 |
2003年 | 4284篇 |
2002年 | 3572篇 |
2001年 | 2948篇 |
2000年 | 2552篇 |
1999年 | 2113篇 |
1998年 | 1674篇 |
1997年 | 1392篇 |
1996年 | 1060篇 |
1995年 | 925篇 |
1994年 | 847篇 |
1993年 | 538篇 |
1992年 | 505篇 |
1991年 | 402篇 |
1990年 | 331篇 |
1989年 | 232篇 |
1988年 | 182篇 |
1987年 | 109篇 |
1986年 | 87篇 |
1985年 | 85篇 |
1984年 | 74篇 |
1983年 | 62篇 |
1982年 | 76篇 |
1981年 | 31篇 |
1980年 | 71篇 |
1979年 | 48篇 |
1978年 | 12篇 |
1975年 | 12篇 |
1959年 | 12篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
941.
942.
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
943.
针对熔融石英砂与混合油、溴化钙及蔗糖等孔隙液体制配成的3种透明土试样,开展渗流液体与孔隙液体一致或者不一致两种情况下的常水头渗透试验,测得透明土材料在不同孔隙液体、粒径及相对密实度等情况下的渗透率,以及水在3种透明土试样中的渗透过程;并与福建标准砂相关试验结果进行了对比分析。进而开展透明土试样电渗可视化模型试验,初步探讨孔隙液体、渗透率等因素对电渗过程与机理的影响规律。试验结果表明,透明土试样渗透特性不仅与粒径分布、相对密实度等因素相关,而且与孔隙液体种类相关;混合油、溴化钙溶液制配成的透明土渗透率与天然砂土渗透率最为相近。 相似文献
944.
E. A. Levashov A. S. Rogachev V. V. Kurbatkina Yu. K. Epishko N. A. Kochetov 《International Journal of Self-Propagating High-Temperature Synthesis》2007,16(4):218-224
Biocompatible composites (Ti, Ta)C
x
+ Ca3(PO4)2 for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca3(PO4)2 mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have
little or no influence on the burning velocity U and combustion temperature T
c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to
formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.
相似文献
945.
In this review, which consists of two parts, major interactions between nitrous oxide (N2>O) and soil solution are described. In the first part, as an introduction, concentrations of dissolved N2>O in different aqueous systems are summarized. An inventory of data on maximal N2>O concentrations in soil solution (up to 9984 g N2>O-N l–1>) and in soil air (up to 8300 ppm) from literature is presented. The peak N2>O concentrations represent a N2>O supersaturation in the soil solution up to 30000 times with respect to ambient air and a soil air N2>O concentration about 25000 times higher than in the atmosphere. The main physico–chemical parameters (solubility, diffusion) controlling N2>O distribution between soil solution and soil air are outlined. The influences of cultivation practice, nitrogen turnover, water content and temperature on N2>O a ccumulation in soil solution and soil air are reviewed. In the second part some models of N2>O dynamics in soils are discussed with emphasis on N2>O transport processes. A simple qualitative scheme is developed to categorize the effects of the soil solution on N2>O dynamics in soils. In this scheme the temporary, intensive N2>O oversaturation of the soil solution is interpreted as a result of gas diffusion inhibition by water (barrier function of soil solution) resulting in an accumulation of N2>O. In addition, N2>O supersaturation is an indication that transitory much N2>O can be stored in the soil solution (storage function of soil solution). Where the soil solution flows up-, down- or sidewards it can act as a relevant transport medium for dissolved N2>O (transport function of soil solution). This scheme is applied to examples from the literature. 相似文献
946.
947.
948.
949.
纤维素科学与技术研究进展 总被引:3,自引:0,他引:3
梁锋 《纤维素科学与技术》1993,1(3):1-14
本文综述纤维素科学与技术的研究进展。阐述了纤维素结构、纤维素的合成、纤维素液晶、功能纤维素、纤维素溶剂、纤维素裂解和纤维素的废物利用等的最新动态。 相似文献
950.
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