全文获取类型
收费全文 | 99479篇 |
免费 | 3953篇 |
国内免费 | 3075篇 |
专业分类
化学 | 39869篇 |
晶体学 | 1054篇 |
力学 | 7943篇 |
综合类 | 187篇 |
数学 | 34019篇 |
物理学 | 23435篇 |
出版年
2024年 | 43篇 |
2023年 | 415篇 |
2022年 | 638篇 |
2021年 | 795篇 |
2020年 | 854篇 |
2019年 | 834篇 |
2018年 | 10964篇 |
2017年 | 10802篇 |
2016年 | 6973篇 |
2015年 | 1852篇 |
2014年 | 1446篇 |
2013年 | 1928篇 |
2012年 | 5640篇 |
2011年 | 12428篇 |
2010年 | 6910篇 |
2009年 | 7311篇 |
2008年 | 8036篇 |
2007年 | 10071篇 |
2006年 | 1464篇 |
2005年 | 2267篇 |
2004年 | 2297篇 |
2003年 | 2618篇 |
2002年 | 1626篇 |
2001年 | 710篇 |
2000年 | 745篇 |
1999年 | 633篇 |
1998年 | 612篇 |
1997年 | 568篇 |
1996年 | 659篇 |
1995年 | 479篇 |
1994年 | 458篇 |
1993年 | 367篇 |
1992年 | 308篇 |
1991年 | 296篇 |
1990年 | 214篇 |
1989年 | 189篇 |
1988年 | 176篇 |
1987年 | 154篇 |
1986年 | 152篇 |
1985年 | 131篇 |
1984年 | 101篇 |
1983年 | 85篇 |
1982年 | 79篇 |
1981年 | 66篇 |
1980年 | 77篇 |
1979年 | 61篇 |
1978年 | 44篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
Simple and sensitive electrochemical method for the determination of metronidazole, based on a nanostructured film coated glassy carbon electrode (GCE), is described. Multi-walled carbon nanotubes (MWNT) was dispersed into water in the presence of a hydrophobic surfactant to give very stable and homogeneous MWNT suspension, and a MWNT-film coated GCE was achieved via evaporating solvent. Metronidazole yields a well-defined reduction peak whose potential is −0.71 V at the MWNT-film coated GCE in pH 9.0 Britton-Robinson buffer. Compared with bare GCE, the MWNT-film modified GCE significantly enhances the reduction peak current of metronidazole. All the experimental parameters were optimized for the determination of metronidazole. The detection limit is 6×10−9 mol/l at 2 min accumulation. This method has been successfully used to determine metronidazole in the drugs. Furthermore, results obtained by the proposed method have been compared with spectrophotometric method. 相似文献
992.
Jocelyn Jalbert Roland Gilbert Pierre Tétreault Brigitte Morin Denise Lessard-Déziel 《Cellulose (London, England)》2007,14(4):295-309
In this study, headspace gas chromatography/mass spectrometry has been used to assess the volatile by-products generated by
the ageing of oil-impregnated paper insulation of power transformers. Sealed-glass ampoules were used to age under oxidative
conditions 0.5-g specimens of insulating paper in 9 mL of inhibited mineral oil in a temperature range of 60–120 °C and moisture
of 0.5, 1 and 2% (w/w). A linear relationship between one of the oil-soluble degradation by-products, i.e. methanol, and the
number of ruptured 1,4-β-glycosidic bonds of cellulose, regardless of the type of paper (ordinary Kraft or thermally-upgraded
(TU) Kraft paper), was established for the first time in this field. Ageing at 130 °C of model compounds of the Kraft paper
constituents (α-cellulose, hemicellulose and lignin) and two cellulosic breakdown by-products (D-(+)-glucose and 1,6-anhydro-β-d-glucopyranose) confirmed that the α-cellulose degradation was mostly responsible for the presence of this molecule in the
system. Furthermore, additional 130 °C-tests with six different papers and pressboard samples under a tight control of initial
moisture indicated that at least one molecule of methanol is formed for each rupture of 1,4-β-glucosidic bond of the molecular
chains. Stability tests showed that the ageing indicator is stable under the oxygen and temperature conditions of open-breathing
transformers. The presence of methanol was detected in 94% of oil samples collected from over than 900 in-service pieces of
equipment, confirming the potential for this application. Lastly, the tests have shown that oil-oxidation by-products and
TU-nitrogenous agents modify the methanol partitioning coefficients in the paper/oil/air system, which makes their study essential
over a range of field conditions encountered by power transformers. Results are presented and discussed in comparison with
2-furfuraldehyde, which is the current reference in the domain. 相似文献
993.
Muhammad Ilyas Sarwar Sonia Zulfiqar Zahoor Ahmad 《Colloid and polymer science》2007,285(15):1733-1739
Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline
and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce
amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop
bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were
carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide.
The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with
higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration.
The maximum increase in the T
g value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica
in the matrix with an average particle size ranging from 8 to 50 nm. 相似文献
994.
995.
996.
997.
TheA
1
–X
1
+ system of SnO is studied by laser- induced fluorescence excitation spectroscopy using isotopically enriched tin Sn116. The rotational structure analysis has been carried out for 6-0, 5-0, 2-0 bands. All these spectra were well resolved only with few perturbed lines in 2-0 band. Rotational constantsB
2,B
5,B
6 and henceB
e
,
e
e
have been obtained for the Sn116O molecule. An extension of perturbation study on 4-0 band has been made showing the maximum perturbation occurs at different J values for different isotopes. 相似文献
998.
G. H. Wang X. Y. Li Y. Y. Lu Y. Z. Zhu H. W. Wang L. Dou R. X. Yu 《Zeitschrift für Physik B Condensed Matter》1987,65(3):347-351
12 MeV electron beams with different doses of 4, 8, 16 and 32 Mrad from LINAC designed by Nanjing University have been used to irradiate polypropylene films and their structures studied by X-ray diffraction afterwards. We have found that the electron irradiation does not change the total crystallinity of polypropylene but greatly inflences its crystal structure with increase of phase and decrease of phase as irradiation dose increases (within 16 Mrad). However, it is unexpected that the structure of irradiated sample with 32 Mrad are similar to that of the control sample. This behavior has also been observed in positron annihilation lifetime measurements. 相似文献
999.
Aihara H Alston-Garnjost M Avery RE Barbaro-Galtieri A Barker AR Barnes AV Barnett BA Bauer DA Bengtsson H Bintinger DL Bobbink GJ Bolognese TS Bross AD Buchanan CD Buijs A Cain MP Caldwell DO Clark AR Cowan GD Crane DA Dahl OI Derby KA Eastman JJ Eberhard PH Eisner AM Enomoto R Erné FC Fujii T Gary JW Gorn W Hauptman JM Hofmann W Huth JE Hylen J Kamae T Kaye HS Kees KH Kenney RW Kerth LT Ko W Koda RI Kofler RR Kwong KK Lander RL Langeveld WG Layter JG Linde FL Lindsey CS Loken SC Lu A Lu X 《Physical review letters》1986,57(8):945-948
1000.
Two-dimensional protein database of human pancreas 总被引:7,自引:0,他引:7
We report here the two-dimensional protein database of human pancreas. The proteins were analyzed by two-dimensional electrophoresis followed by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Totally, 302 proteins were identified, of which about 27% were enzymes with a broad range of catalytic activities. Several of these are specifically expressed in pancreas, such as pancreatic amylase, pancreatic stone protein, pancreatitis-associated protein, pancreatic lipase, pancreatic elastase, etc. Structural and cytoskeletal proteins are also strongly represented on the gels. Thus, the pancreatic proteome reflects the organ's function. This work paves the way for further studies on pancreatic protein expression in health and disease, such as diabetes and pancreatic cancer. 相似文献