全文获取类型
收费全文 | 77762篇 |
免费 | 5692篇 |
国内免费 | 3343篇 |
专业分类
电工技术 | 3924篇 |
技术理论 | 8篇 |
综合类 | 3667篇 |
化学工业 | 11890篇 |
金属工艺 | 5090篇 |
机械仪表 | 4201篇 |
建筑科学 | 4383篇 |
矿业工程 | 1531篇 |
能源动力 | 2598篇 |
轻工业 | 4557篇 |
水利工程 | 1232篇 |
石油天然气 | 3139篇 |
武器工业 | 651篇 |
无线电 | 9569篇 |
一般工业技术 | 13209篇 |
冶金工业 | 6651篇 |
原子能技术 | 982篇 |
自动化技术 | 9515篇 |
出版年
2024年 | 215篇 |
2023年 | 897篇 |
2022年 | 1876篇 |
2021年 | 2601篇 |
2020年 | 1900篇 |
2019年 | 1728篇 |
2018年 | 2069篇 |
2017年 | 2149篇 |
2016年 | 2021篇 |
2015年 | 2590篇 |
2014年 | 3218篇 |
2013年 | 4905篇 |
2012年 | 4456篇 |
2011年 | 5144篇 |
2010年 | 4378篇 |
2009年 | 4462篇 |
2008年 | 4370篇 |
2007年 | 4195篇 |
2006年 | 4071篇 |
2005年 | 3478篇 |
2004年 | 2690篇 |
2003年 | 2393篇 |
2002年 | 2411篇 |
2001年 | 2246篇 |
2000年 | 1996篇 |
1999年 | 2046篇 |
1998年 | 2613篇 |
1997年 | 2018篇 |
1996年 | 1690篇 |
1995年 | 1225篇 |
1994年 | 944篇 |
1993年 | 799篇 |
1992年 | 560篇 |
1991年 | 505篇 |
1990年 | 336篇 |
1989年 | 346篇 |
1988年 | 259篇 |
1987年 | 169篇 |
1986年 | 143篇 |
1985年 | 130篇 |
1984年 | 69篇 |
1983年 | 55篇 |
1982年 | 62篇 |
1981年 | 63篇 |
1980年 | 39篇 |
1979年 | 29篇 |
1977年 | 24篇 |
1976年 | 38篇 |
1975年 | 24篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
951.
Systems of Pd supported on various La2O3-modified -Al2O3 and CeO2–Al2O3 catalysts were tested for catalytic methanol decomposition and characterized by means of XRD, BET, TPR, H2-chemisorption and CO–FTIR. The addition of lanthanum significantly improved the selectivity of CO and H2 for all the catalysts but showed a different influence on the catalytic activity in two systems. Methanol conversion decreased on La2O3-modified Pd/-Al2O3 catalysts, in line with the reduction of Pd dispersion, while the addition of La2O3 improved the dispersion of Pd and reinforced Pd–CeO2 interaction for La2O3-modified Pd/CeO2–Al2O3 catalysts, which resulted in a high production rate of CO and H2. Thus, a synergistic effect between CeO2 and La2O3 was observed on -Al2O3-supported Pd catalyst for methanol decomposition. 相似文献
952.
Ramie yarns were treated with various concentrations of NaOH at room temperature and subsequently crosslinked with 1,2,3,4‐butanetetracarboxylic acid (BTCA). The microstructure and tensile properties of the treated yarns were characterized. X‐ray diffraction (XRD) and FTIR were used to study the crystalline structure of the resultant ramie yarns. The results showed that the maximum change in the structure of the alkali‐modified ramie took place at 16% NaOH, which would completely transform cellulose I to cellulose II. At the same time, the crystallinity index and fiber orientation decreased to the minimum value while the absorption properties were enhanced. The average degree of polymerization (DP ) of the treated ramie yarns slightly decreased after NaOH treatment. Tensile properties including tenacity, breaking elongation, and modulus of the treated yarns were also investigated. Scanning electron microscopy (SEM) was used to investigate the breakage of the treated yarns. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1857–1864, 2004 相似文献
953.
The application of supercritical fluid chromatography (SFC) coupled with a UV variable-wavelength detector to isolate the
minor components (carotenes, vitamin E, sterols, and squalene) in crude palm oil (CPO) and the residual oil from palm-pressed
fiber is reported. SFC is a good technique for the isolation and analysis of these compounds from the sources mentioned. The
carotenes, vitamin E, sterols, and squalene were isolated in less than 20 min. The individual vitamin E isomers present in
palm oil were also isolated into their respective components, α-tocopherol, α-tocotrienol, γ-tocopherol, γ-tocotrienol, and
δ-tocotrienol. Calibration of all the minor components of palm as well as the individual components of palm vitamin E was
carried out and was found to be comparable to those analyzed by other established analytical methods. 相似文献
954.
Summary A water insoluble azo-containing polyelectrolyte (PEAPB6P-AC) was successfully fabricated into multilayer films based on the layer-by-layer adsorption technique by using N, N-dimethylformamide (DMF) as the assembling media. The multilayer growth and structure were studied with UV-vis spectroscopy, and the multilayer surface were imaged with Atomic Force Microscopy and compared with that fabricated in water. The results show that assembling PEAPB6P-AC in DMF can effectively eliminate the hydrophobic aggregation of the azo units and consequently results in a much smoother multilayer surface than that fabricated in water. This improvement to the layer-by-layer adsorption technique, which can avoid some major difficulties faced when assembling hydrophobic polyelectrolytes in aqueous solutions, seems to be a versatile way to fabricate high quality multilayer films when using the hydrophobic even water-insoluble polyelectrolytes as assembling units. 相似文献
955.
A new catalyst (Ni/Mo/MgO) is reported, with which one can synthesize multi-walled carbon nanotube (MWNT) bundles with a yield of more than 45 times the amount of the pristine catalyst, using a methane-hydrogen mixture as precursor. Powder X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis show that the purity of the as-prepared MWNTs is over 97%. The diameter of the carbon nanotubes is 9-20 nm, measured by high-resolution electron microscopy on 421 individual MWNTs. The high purity of the as-prepared MWNTs allows us to omit the usual complex purification process required for carbon nanotubes synthesized by chemical vapor deposition. Because of its durable high activity, the Ni/Mo/MgO catalyst in its pristine state is ideal for mass production of high-quality MWNTs. The synergism of nickel and molybdenum is considered the main reason for the high yield of carbon nanotubes. 相似文献
956.
957.
Carbon dioxide reforming of methane to synthesis gas has been investigated over supported Ni catalysts in the temperature range of 500–850°C. Addition of CaO (10mol%) promoter to the Ni/γ-Al2O3 resulted in an increase of reaction rate and an improvement of catalyst stability, which may be related to enhanced reducibility of the promoted catalyst. The kinetic studies show that the overall reaction can be described by a Langmuir-Hinshelwood mechanistic scheme, assuming that methane dissociation is the rate determining step. In addition to adsorbed CO and formate species, three types of carbonaceous species, C, Cβ and Cγ, were found to exist on the Ni catalyst. While the active C, species is suggested to be responsible for CO formation, the less active Cβ and Cγ species are attributed to causing catalyst deactivation. 相似文献
958.
L. Rodríguez-Liñares M.J. Lado X.A. Vila A.J. Méndez P. Cuesta 《Computer methods and programs in biomedicine》2014
In this paper, the gHRV software tool is presented. It is a simple, free and portable tool developed in python for analysing heart rate variability. It includes a graphical user interface and it can import files in multiple formats, analyse time intervals in the signal, test statistical significance and export the results. 相似文献
959.
Ping Shen Lifeng Zhang Jianxun Fu Hao Zhou Yi Wang Limei Cheng 《Ceramics International》2019,45(9):11287-11295
In the present study, the wettability between liquid iron with two different Al contents and MgOAl2O3 binary substrates was studied in reducing atmosphere. The contact angles between liquid iron with 18?ppm Al and MgO, MgO·Al2O3, Al2O3 were 133.5°, 113.7°, 126.9° respectively. With the variation of the substrate composition, the contact angles for the intermediate binary phases of the three components (MgO, MgO·Al2O3, Al2O3) obeyed the Cassie theory. In the experiment using iron with 370?ppm Al, all the contact angles were higher than that using low Al-containing iron. The surface of the iron drop was covered with an oxide layer, which mainly consisted of many small particles. With the variation of the substrate gradually from MgO to Al2O3, the composition of the oxide layer changed from MgO·Al2O3 to CaOAl2O3. The formation of the oxide layer prevented the spreading of liquid iron, leading to the increase of the contact angle. 相似文献
960.