全文获取类型
收费全文 | 1158篇 |
免费 | 22篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 105篇 |
综合类 | 4篇 |
化学工业 | 399篇 |
金属工艺 | 30篇 |
机械仪表 | 28篇 |
建筑科学 | 30篇 |
能源动力 | 63篇 |
轻工业 | 116篇 |
水利工程 | 1篇 |
无线电 | 55篇 |
一般工业技术 | 228篇 |
冶金工业 | 22篇 |
原子能技术 | 30篇 |
自动化技术 | 81篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 19篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 60篇 |
2012年 | 35篇 |
2011年 | 47篇 |
2010年 | 42篇 |
2009年 | 73篇 |
2008年 | 50篇 |
2007年 | 68篇 |
2006年 | 53篇 |
2005年 | 53篇 |
2004年 | 57篇 |
2003年 | 46篇 |
2002年 | 38篇 |
2001年 | 36篇 |
2000年 | 41篇 |
1999年 | 23篇 |
1998年 | 23篇 |
1997年 | 23篇 |
1996年 | 26篇 |
1995年 | 23篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 14篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有1192条查询结果,搜索用时 15 毫秒
941.
Yuka Ezoe Sumio Goto Kiyoshi Tanabe Osamu Endo Michiko Koyano Ikuo Watanabe 《Polycyclic Aromatic Compounds》2013,33(4-5):635-646
To estimate human exposure to hazardous chemicals, it is important to measure the annual trends regarding the concentrations of these compounds in the environment. Airborne particulate samples were collected over the past 20 years (1980–2001) from ambient air using a quartz fiber filter with the help of a high-volume air sampler placed on the top of the National Institute of the Public Health building, Minato-ku, Tokyo, Japan. In the present study, portions of these filter samples were analyzed to investigate the trends regarding the concentration of PAHs in urban air over the sampling period. The concentrations of various PAHs per unit air volume were determined. The concentrations of seven PAHs decreased within the sampling periods, especially in the late 1980s, and slowly decreased from the middle 1990s. The concentrations of seven PAHs were higher in autumn and winter than in the spring and summer. 相似文献
942.
943.
A liquid-liquid extraction of chromium(III) ion was achieved by a cooperative action of light (photoreduction) and conventional extractants on chromium(VI) species. The extraction of chromium spcies was studied by both molecular and atomic absorption spectrophotometry measurements. Trioctylphosphine oxide (TOPO) was the most effective among the extractants studied (TOPO, dibutylsulfoxide, tributyl phosphate, 2-ethyhexyl hydrogen 2-ethylhexylphosphonate, di (2,4,4-trimethylpentyl)-phosphinic acid). A back-extraction of chromium(III) species to aqueous solution was also promoted by photo-irradiation. The nature of the extraction system was studied under various operational conditions such as wavelength of illuminating light, coordinating ah ionic species in aqueous solution, and coexisting metal ions. A liquid- liquid (back-) extraction of some 相似文献
944.
945.
Soichiro Kudo Akira Kishioka Hideki Kuwahara Haruhiko Kuroe Hubertus T. Hintzen Kiyoshi Itatani 《Journal of the American Ceramic Society》2019,102(3):1259-1268
The encapsulation conditions of Eu2+-doped calcium silicon nitride ((Ca0.90Eu0.10)2Si5N8) and strontium silicon nitride ((Sr0.98Eu0.02)2Si5N8) phosphors into phosphate glass ((50-x)Na2O–xZnO–5B2O3–45P2O5; x = 10-40) were examined by pressureless sintering (normal or infrared firing) and subsequent oxygen-assisted hot isostatic pressing. The evaluation of water resistivity, as well as glass transition temperature (Tg), indicated that the excellent water resistivity and low Tg (313°C) could be achieved at x = 30. The colorless and clear glass body could be fabricated by infrared firing at 370°C for 20 minutes in air, followed by the hot isostatic pressing at 370°C for 24 hours (80%Ar + 20%O2, pressure: 130 MPa). The encapsulations of 3.0 mass% (Ca0.90Eu0.10)2Si5N8 and (Sr0.98Eu0.02)2Si5N8 into the glass body produced reddish orange light emission (peak wavelength: 604 nm under excitation wavelength of 423 nm) and red-light emission (617 nm under 383 nm), respectively, showing higher chemical and thermal stability of nitride phosphors in the glass matrix. 相似文献
946.
You Zhou Hideki Hyuga Dai Kusano Chika Matsunaga Kiyoshi Hirao 《Journal of the American Ceramic Society》2019,102(4):1579-1588
A variety of combinations of Y2O3 and MgO were used as additives in preparing Si3N4 ceramics by the sintering of reaction-bonded silicon nitride (SRBSN) method. By varying the amount of Y2O3 in the range of 0-5 mol% and that of MgO in the range of 0-8 mol%, the effects of Y2O3 and MgO additives on nitridation and sintering behaviors as well as thermal conductivity were studied. It was found that appropriate amount and combination of Y2O3 and MgO additives were essential for attaining full densification and achieving high thermal conductivity. The sample doped with 2.5 mol% of Y2O3 and 5 mol% of MgO attained a thermal conductivity of 128 Wm−1K−1 when sintered at 1900°C for 6 hours, and the sample doped with 2 mol% of Y2O3 and 4 mol% of MgO achieved a thermal conductivity of 156 Wm−1K−1 when sintered for 24 hours. 相似文献
947.
Catalin Popa Ken-ichi Katsumata Toshihiro Isobe Nobuhiro Matsushita Akira Nakajima Taisuke Kurata Kiyoshi Okada 《Ceramics International》2013,39(2):1443-1449
Four kinds of porous mullite ceramics, named lotus ceramics because of the similarity of their microstructure with lotus roots, were prepared by an extrusion method using rayon fibers of four different diameters (8.1, 9.6, 16.8 and 37.6 μm) as the pore formers. The physicochemical properties of these samples were characterized to test their applicability for the generation of microbubbles. The lotus ceramic samples contained pores of 9.4, 10, 15.6 and 30 μm size and porosities of 45–48%. SEM micrographs confirmed that the cylindrical pores were oriented unidirectionally along the extrusion direction and the degree of alignment was greater with larger fiber diameter. The permeability for gaseous CO2 increased with increasing pore size from 3×10?13 to 8×10?13 m2. The four lotus ceramic samples, a commercial air stone (72 μm) and two simple tubes (1000 and 3500 μm) were used to generate microbubbles in water under ambient conditions from a gas mixture of CO2 and air. It was found that the bubble size could be decreased with bubblers of smaller pore size. In the bubble size measurements for pure CO2 and air, the air bubbles were larger than the CO2 bubbles due to partial dissolution of CO2 into the water during bubbling. In order to generate smaller size bubbles using porous ceramic bubblers, the liquid must penetrate through the pores of the lotus ceramics before the gas is introduced into the system. 相似文献
948.
Yoshitoshi Saito Takahiro Takei Shigeo Hayashi Atsuo Yasumori Kiyoshi Okada 《Journal of the American Ceramic Society》1998,81(8):2197-2200
This paper focused on the effects of various phases of SiO2 additives on the γ-Al2 O3 -to-α-Al2 O3 phase transition. In the differential thermal analysis, the exothermic peak temperature that corresponded to the theta-to-α phase transition was elevated by adding amorphous SiO2 , such as fumed silica and silica gel obtained from the hydrolysis of tetraethyl orthosilicate. In contrast, the peak temperature was reduced by adding crystalline SiO2 , such as quartz and cristobalite. Amorphous SiO2 was considered to retard the γ-to-α phase transition by preventing γ-Al2 O3 particles from coming into contact and suppressing heterogeneous nucleation on the γ-Al2 O3 surface. On the other hand, crystalline SiO2 accelerated the α-Al2 O3 transition; thus, this SiO2 may be considered to act as heterogeneous nucleation sites. The structural difference among the various SiO2 additives, especially amorphous and crystalline phases, largely influenced the temperature of γ-Al2 O3 -to-α-Al2 O3 phase transition. 相似文献
949.
Very Rapid Densification of Nanometer Silicon Carbide Powder by Pulse Electric Current Sintering 总被引:1,自引:0,他引:1
You Zhou Kiyoshi Hirao Motohiro Toriyama Hidehiko Tanaka 《Journal of the American Ceramic Society》2000,83(3):654-656
Rapid densification of a nanometer SiC powder doped with 2.04 wt% Al4 C3 and 0.4 wt% B4 C was conducted by using a nonconventional sintering technique called pulse electric current sintering (PECS). In all experiments, the sintering temperature and applied pressure were kept to be 1600o C and 47 MPa, respectively, while heating rates varied between 100o C/min and 400o C/min and the holding time was either 2 or 5 min. All of the specimens which were PECS-sintered under various conditions reached near-theoretical density. The microstructures of the rapidly densified SiC ceramics consisted of large elongated grains, and the grain size increased with the increase of heating rate. Polytype transformation of SiC occurred during the PECS process, where faster heating favored the formation of 6H polytype while slower heating favored 4H polytype. 相似文献
950.