全文获取类型
收费全文 | 27742篇 |
免费 | 2908篇 |
国内免费 | 1240篇 |
专业分类
电工技术 | 842篇 |
综合类 | 1330篇 |
化学工业 | 8869篇 |
金属工艺 | 1716篇 |
机械仪表 | 1294篇 |
建筑科学 | 463篇 |
矿业工程 | 3127篇 |
能源动力 | 884篇 |
轻工业 | 1730篇 |
水利工程 | 201篇 |
石油天然气 | 1334篇 |
武器工业 | 175篇 |
无线电 | 1405篇 |
一般工业技术 | 4584篇 |
冶金工业 | 1689篇 |
原子能技术 | 746篇 |
自动化技术 | 1501篇 |
出版年
2024年 | 88篇 |
2023年 | 471篇 |
2022年 | 781篇 |
2021年 | 1024篇 |
2020年 | 980篇 |
2019年 | 854篇 |
2018年 | 835篇 |
2017年 | 986篇 |
2016年 | 1092篇 |
2015年 | 1051篇 |
2014年 | 1657篇 |
2013年 | 1830篇 |
2012年 | 2061篇 |
2011年 | 2144篇 |
2010年 | 1528篇 |
2009年 | 1614篇 |
2008年 | 1406篇 |
2007年 | 1558篇 |
2006年 | 1474篇 |
2005年 | 1345篇 |
2004年 | 1063篇 |
2003年 | 1046篇 |
2002年 | 861篇 |
2001年 | 660篇 |
2000年 | 599篇 |
1999年 | 505篇 |
1998年 | 452篇 |
1997年 | 361篇 |
1996年 | 301篇 |
1995年 | 265篇 |
1994年 | 226篇 |
1993年 | 158篇 |
1992年 | 122篇 |
1991年 | 100篇 |
1990年 | 78篇 |
1989年 | 51篇 |
1988年 | 67篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1974年 | 3篇 |
1959年 | 3篇 |
1955年 | 1篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
There are a few bimodal molecular imaging probes constructed by gadolinium (3+) ions in combination with carbon quantum dots (CQDs), and the reported ones show such obvious drawbacks as low luminous efficiency and weak MRI contrast. In the paper, a kind of CQDs photoluminescence materials with magnetic resonance response was prepared by hydrothermal method and employing gadopentetate monomeglumine (GdPM) as a precusor. Here, the GdPM plays a role of not only carbon source, but also gadolinium (3+) sources. When the GdPM aqueous solution with a concentration of 4 mg mL−1 was pyrolyzed under 220 °C and 2.0 MPa for 8 h, an optimal CQDs was obtained which are doped with gadolinium (3+) ions in both chelates and Gd2O3 (named as Gd3+-CQDs). The average diameter of the Gd3+-CQDs is about 1.6 nm, which show a high photoluminescence quantum yield of 7.1%, as well as high longitudinal relaxivity (r1) of 9.87 mM−1 s−1. And owing to the unconspicuous cell toxicity, the Gd3+-CQDs show big possibility for clinical application in magnetic resonance/fluorescence bimodal molecular imaging. 相似文献
952.
953.
ABSTRACT An integrated technique has been developed for the study of the thermal chemistry of petroleum fractions—particularly the asphaltenes. The procedure involves the integrated use of a pyroprobe/gas chroma-tographic/mass spectrometric technique which offers information about the structuraI-types and distribution within the volatile products from the thermal decomposition of asphaltenes. The technique offers itself as an attractive on-line analytical method for the study of structural types that occur in asphaltenes as well as a technique for studying the parameters that can influence asphaltene decomposition. The concept of deducing “average” structures of asphaltenes is briefly discussed in terms of the observance of the lower molecular weight species in the volatile products of the thermal decomposition. 相似文献
954.
955.
This work reports two preparation methods of Ni-Al2O3 composite to be used as a hydrogen separation membrane. The first method was powder impregnation while the second method was soaking-drying-firing or bulk impregnation. In the first method, the 10 wt pct Nickel (II) nitrate hexahydrate solution was mixed with Al2O3 powder. The mixed powders were dried at 100℃ and uniaxially pressed into a disk shape at 7 MPa. The densification of composite membranes was accomplished by pressureless sintered at 900–1300℃.... 相似文献
956.
Won-Seok Ko Ju-Young Oh Jae-Hyeok Shim Jin-Yoo Suh Woo Young Yoon Byeong-Joo Lee 《International Journal of Hydrogen Energy》2014
Inter-diffusion between vanadium and palladium coating layers in vanadium-based hydrogen separation membranes is investigated by using a computational approach based on first-principles calculations and semi-empirical atomistic simulations, paying attention to the surface stability and the prevention of the degradation of hydrogen permeability. It is found that the governing mechanism of the inter-diffusion is the grain boundary diffusion, and therefore a diffusion barrier based on the grain boundary segregation of impurities can be an efficient way to inhibit the inter-diffusion that causes the degradation. An interesting aspect in previous experimental works that showed a good resistance to the inter-diffusion by an addition of a trace amount of yttrium is discussed from the view point of the grain boundary segregation. An experiment that proves the validity of the present alloy design scheme (inhibition of inter-diffusion using grain boundary segregation) is carried out, and a process to maximize the sustainability of the membrane is also proposed. 相似文献
957.
《Food Control》2017
To quantify trace pesticide residue in vegetable oil rapidly, low temperature cleanup combined with magnetic nanoparticle based solid phase extraction was developed to determine eight pyrethroids in vegetable oils, including tetramethrin, fenpropathrin, cypermethrin, decamethrin, fenvalerate, acrinathrin, permethrin and bifenthrin. Polystyrene coated magnetic nanoparticles were synthesised by a modified chemical coprecipitation combined with emulsion polymerisation method. The nanoparticles were afterwards characterised by Fourier transform-infrared spectroscopy, X-ray diffraction, transmission electron microscopy as well as vibrating sample magnetometer, and successfully employed as adsorbents for the magnetic solid phase extraction of pyrethroids which were cleaned up using low temperature approach in advance. Critical impact factors on the efficiency of the extraction method such as the mass of adsorbents used, volume and type of eluent solvent, extraction time as well as elution time were optimised subsequently. Regression analysis of the calibration curves of the eight pyrethroids yielded satisfactory correlation coefficients within the range of 0.980–0.998. Limit of detection and limit of quantification were calculated to be between 0.0290-0.0658 and 0.0890–0.1994 ng g−1, respectively. Intra-day and inter-day reproducibility at different concentration levels also produced satisfactory recovery rates of 83.18–112.79% with relative standard deviations not exceeding 10.84% and 12.01%, respectively, suggesting desirable stability of the proposed method. 相似文献
958.
《Journal of Industrial and Engineering Chemistry》2014,20(5):2830-2839
β-Cyclodextrin (CD) was grafted onto montmorillonite/iron oxides to prepare a novel magnetic CD/MMT/iron oxide composite by low-temperature plasma technology, and applied to remove U(VI) from aqueous solutions. The sorption irreversibility was attributed to inner-sphere binding of U(VI) on CD/MMT/iron oxide surface sites. The thermodynamic parameters indicated that the sorption of U(VI) on CD/MMT/iron oxide was an endothermic and spontaneous process. The maximum sorption capacity of U(VI) on CD/MMT/iron oxide was considerably higher than that of U(VI) on other reported materials. The CD/MMT/iron oxide can be potentially used as a cost-effective material for the purification of actual U(VI)-bearing effluents. 相似文献
959.
The selective separation of carbon dioxide (CO2) from a wet gaseous mixture of CO2/H2 through facilitated transport membranes containing immobilized aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), ethylenediamine (EDA) and monoprotonated ethylenediamine (EDAH+) and their blends was experimentally investigated. The effect of CO2 partial pressure, amine concentration, feed side pressure and amine species on the CO2 and H2 permeances were studied. The CO2 permeability through amine solution membranes decreased with increasing CO2 feed partial pressure but the H2 permeance was almost independent of the H2 partial pressure. A comparison of experimental results showed that single or blended amines with low viscosity and a moderate equilibrium constant, i.e., large forward and reverse reaction rate of CO2‐amine, are suitable for effective separation of CO2. The permeability of CO2 generally increased with an increase in amine concentration, although this increase may be compromised by the salting out effect and decrease in diffusivities of species. The results obtained indicated that CO2 permeance across a variety of amines are in the order of DEA (2 M) > MD (2 M) > MD (1 M) > MEA (2 M) > MEA (4 M) > MD (4 M) > DEA (1 M) > DEA (4 M) > MEA (1 M) for various concentrations of MEA + DEA blend and are in the order of EDAH+ (2 M) > DEA (2 M) > MH (2 M) > DH (2 M) > ED (2 M) > EDA (2 M) > MEA (2 M) for various blends of amine. 相似文献
960.
A. J. Redd D. J. Battaglia M. W. Bongard R. J. Fonck E. T. Hinson B. A. Kujak-Ford B. T. Lewicki A. C. Sontag G. R. Winz 《Journal of Fusion Energy》2009,28(2):203-207
Recent Pegasus experiments are developing solenoid-free startup techniques using point-source magnetic helicity injection.
These plasma sources, called “plasma guns”, ionize a stream of gas in a discharge channel, and bias this channel with respect
to an external electrode, driving current along the plasma stream, which relaxes into a tokamak-like equilibrium. The relaxed
discharges formed by these injectors exhibit high current amplification, which is the ratio of total toroidal current to the
gun-driven current. The development and present design of these injectors are described, and time traces from a typical discharge
are presented. 相似文献