全文获取类型
收费全文 | 1156篇 |
免费 | 66篇 |
国内免费 | 15篇 |
专业分类
化学 | 646篇 |
晶体学 | 2篇 |
力学 | 56篇 |
数学 | 158篇 |
物理学 | 175篇 |
无线电 | 200篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 29篇 |
2021年 | 60篇 |
2020年 | 44篇 |
2019年 | 71篇 |
2018年 | 61篇 |
2017年 | 71篇 |
2016年 | 100篇 |
2015年 | 53篇 |
2014年 | 80篇 |
2013年 | 134篇 |
2012年 | 70篇 |
2011年 | 76篇 |
2010年 | 53篇 |
2009年 | 50篇 |
2008年 | 38篇 |
2007年 | 31篇 |
2006年 | 25篇 |
2005年 | 10篇 |
2004年 | 23篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 3篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1992年 | 2篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有1237条查询结果,搜索用时 15 毫秒
51.
Jaber Javidi Mohsen Esmaeilpour Zahra Rahiminezhad Fatemeh Nowroozi Dodeji 《Journal of Cluster Science》2014,25(6):1511-1524
In this study H3PW12O40·9H2O and H3PMo12O40·6H2O (HPA) particles were changed into nano forms by heat-treatment in an autoclave as a simple, repaid, inexpensive and one step method. The particle size of these nanoparticles was around 25 nm. The as-synthesized nanostructures were characterized by dynamic light scattering, X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and inductively coupled plasma analyzer. Thermal stability of nanoparticles was surveyed by thermal gravimeter analyse. Acidity of prepared nanoparticles was investigated by pyridine adsorption method. Results showed rising acidity by declining particle size of HPA. 相似文献
52.
Vahideh Masoumi Ali Mohammadi Mohsen Amini Mohammad Reza Khoshayand Rasoul Dinarvand 《Journal of Solid State Electrochemistry》2014,18(6):1763-1771
In this work, polyaniline, polypyrrole, and polyaniline/polypyrrole composite fibers were synthesized in the absence and presence of oxidized multiwalled carbon nanotubes using electrochemical cyclic voltammetry with CF3COOH as dopant. Thermal stability of these fibers was studied by differential scanning calorimetry. Then, headspace solid-phase microextraction process coupled with gas chromatography and flame ionization detector was used for comparing extraction capability of benzaldehyde from aqueous solution. Since polyaniline fiber showed better extraction efficiency than the other fibers, its preparation conditions including acid concentration, aniline concentration, scan rate, and amount of multiwalled carbon nanotubes were studied by means of the “one-factor-at-a-time method”. The analytical performance of polyaniline fibers were investigated to determine benzaldehyde from the aqueous solution. The morphology and texture of polyaniline fibers were examined by field emission scanning electron microscopy and Fourier transform infrared spectroscopy analyses. The attained results revealed that the perfect conditions for acid concentration, aniline concentration, scan rate, and multiwalled carbon nanotubes content were 0.5 M, 0.2 M, 25 mV s?1, and 0.02 wt%, respectively. The limit of detection for the proposed polyaniline fiber was 15 ng ml?1. 相似文献
53.
Prof. Daniel W. Armstrong Dr. Mohsen Talebi Nimisha Thakur Dr. M. Farooq Wahab Dr. Alexander V. Mikhonin Matt T. Muckle Dr. Justin L. Neill 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):198-202
We designed and demonstrated the unique abilities of the first gas chromatography–molecular rotational resonance spectrometer (GC-MRR). While broadly and routinely applicable, its capabilities can exceed those of high-resolution MS and NMR spectroscopy in terms of selectivity, resolution, and compound identification. A series of 24 isotopologues and isotopomers of five organic compounds are separated, identified, and quantified in a single run. Natural isotopic abundances of mixtures of compounds containing chlorine, bromine, and sulfur heteroatoms are easily determined. MRR detection provides the added high specificity for these selective gas-phase separations. GC-MRR is shown to be ideal for compound-specific isotope analysis (CSIA). Different bacterial cultures and groundwater were shown to have contrasting isotopic selectivities for common organic compounds. The ease of such GC-MRR measurements may initiate a new era in biosynthetic/degradation and geochemical isotopic compound studies. 相似文献
54.
In this work, a novel electrochemiluminescent (ECL) pesticide sensor based on zinc oxide nanocrystals decorated nickel foam is proposed for determination of imidacloprid for the first time. The silica film was used as a morphology‐controlling factor for modification of the electrode with zinc oxide nanocrystals. Zinc oxide was selected as luminescent material due to its cheapness, non‐toxicity, high thermal stability and excellent luminescence properties which truly adhered on the surface of nickel foam. The K2S2O8 was used as strong co‐reactant for this purpose. The silica template plays an important role in controlling the size of ZnO nanocrystals. The Physical morphology of the ZnO/Ni‐foam electrode was performed by electrochemical impedance spectroscopy, Brunauer‐Emmett‐Teller (BET), X‐Ray diffraction analysis, field emission scanning electron microscopy, and energy‐dispersive X‐ray analysis. The ultra‐sensitive electrochemiluminescence method was successfully used for ultra‐trace determination of imidacloprid. The linear dynamic range and low detection limit were obtained 3×10?14 ?8×10?8 M and 4.4×10?15 M, respectively. Also, the relative standard deviation for 15 repetitive optical signals was calculated 1.09 %.The present ECL sensor exhibited superior performance toward the accurate determination of imidacloprid with good reproducibility and stability. 相似文献
55.
Nonlinear Dynamics - Gears are important mechanical parts with various industrial applications. Many researchers have investigated the complex nonlinear behavior of geared systems by studying the... 相似文献
56.
Hydroxyapatite Wrapped Multiwalled Carbon Nanotubes/Ionic Liquid Composite Electrode: A High Performance Sensor for Trace Determination of Lead Ions 下载免费PDF全文
A nanocomposite consisting of multiwalled carbon nanotubes wrapped with hydroxyapatite (HA/MWCNTs) was used in the construction of a new composite paste electrode using an ionic liquid as the binder. The stable surface in aqueous solutions as well as the high sorptive behaviors towards heavy metal ions and the favorable charge transfer make the electrode highly efficient especially for stripping or adsorptive analysis. The analysis of Pb2+ as a model of heavy metal ions has been performed. Good sensitivity, detection limit, selectivity and reproducibility were obtained for the suggested sensor. The linear range of the electrode response covered four orders of magnitude (1 nM–10 µM), in two linear ranges. The obtained detection limit for Pb2+ was 2×10?11 M. 相似文献
57.
58.
Hamid Reza Safaei Mohsen Shekouhy Athar Shirinfeshan Sudabeh Rahmanpur 《Molecular diversity》2012,16(4):669-683
CaCl2 is applied as an efficient reusable and eco-friendly bifunctional catalyst for the one-pot three-component synthesis of 4H-pyrans under ultrasonic irradiation. A broad range of substrates including the aromatic and heteroaromatic aldehydes, indoline-2,3-dione (isatin) derivatives, acenaphthylene-1,2-dione (acenaphthenequinone) and 2, 2-dihydroxy-2H-indene-1,3-dione (ninhydrin) were condensed with carbonyl compounds possessing a reactive ??-methylene group and alkylmalonates. All reactions are completed in short times, and the products are obtained in good to excellent yields. The catalyst could be recycled and reused several times without any loss of efficiency. 相似文献
59.
Nabil Abdo Ahmed Al-Shwafi Abdulhakim Mohsen Ahmed 《Russian Journal of General Chemistry》2011,81(13):2717-2723
Distribution of litter: ropes, netting, lamb bulbs, foot wear, plastic bags, bottles, aluminum cans, cardboard, wood loges,
rubber, polystyrene blocks and plastic sheets accumulating on Red Sea beaches of Yemen were examined. The results of the study
reflected these wastes to be varied from a region to region but they were similar in almost all-coastal areas. Most of the
litter were plastics including food bags, oil and water bottles, bait bags, and also vehicles tires. Most of pollution occurred
from the sea, due to the heavy traffic and to the fishing vessels, which fish in the area. 相似文献
60.
Seyed Hamed Aboutalebi Mohsen Moazzami Gudarzi Qing Bin Zheng Jang‐Kyo Kim 《Advanced functional materials》2011,21(15):2978-2988
A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution‐phase method involving pre‐exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self‐assembled brick‐like graphene oxide nanostructure can be applied in many areas, such as energy‐storage devices and nanocomposites with a high degree of orientation. 相似文献