全文获取类型
收费全文 | 949篇 |
免费 | 45篇 |
国内免费 | 2篇 |
专业分类
化学 | 650篇 |
晶体学 | 9篇 |
力学 | 15篇 |
数学 | 164篇 |
物理学 | 158篇 |
出版年
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 21篇 |
2016年 | 40篇 |
2015年 | 32篇 |
2014年 | 30篇 |
2013年 | 51篇 |
2012年 | 67篇 |
2011年 | 65篇 |
2010年 | 47篇 |
2009年 | 30篇 |
2008年 | 55篇 |
2007年 | 54篇 |
2006年 | 65篇 |
2005年 | 50篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有996条查询结果,搜索用时 31 毫秒
31.
Chlorosomes isolated from Chloroflexus aurantiacus were extracted with chloroform/methanol. The extract contained bacteriochlorophylls c and a and lipids, but was devoid of proteins. This crude extract spontaneously formed aggregates when a methanol solution was dispersed in aqueous buffer. The aggregates could be sedimented by ultracentrifugation and appeared in electron micrographs as stain-excluding bodies with diameters between 70 and 170 nm. The absorption spectrum is remarkably similar to that of intact chlorosomes with an absorption maximum of bacteriochlorophyll c at around 740 nm. The circular dichroism spectrum of the aggregate is also very similar to that of intact chlorosomes. A conservative (±) band centered at 740 nm confirms the highly aggregated state of bacteriochlorophyll c in both systems. Steady-state fluorescence studies showed that in the aggregate energy-transfer from bacteriochlorophyll c to a component emitting at 830 nm took place. When the aggregate was suspended in buffer saturated with 1-hexanol the 740 nm form of bacteriochlorophyll c was reversibly converted to a form with spectral properties resembling the monomer absorbing at 670 nm but still in an aggregated state. This form of bacteriochlorophyll c showed no circular dichroism signal. 相似文献
32.
33.
34.
Regioselective hydrolysis of cocaine led, according to the reaction conditions, either to benzoylecgonine or to ecgonine methyl ester. Acylation with benzoylecgonine was readily achieved when benzotriazolyloxytrisdimethylamino-phosphonium (BOP) was used as a coupling agent. 相似文献
35.
36.
Tomas Grinys Mantas Dmukauskas Mindaugas Ščiuka Saulius Nargelas Andrius Melninkaitis 《Applied Physics A: Materials Science & Processing》2014,114(2):381-385
Mg- and Si-doped GaN layers deposited by metalorganic chemical vapor deposition method were irradiated with femtosecond pulse duration laser of three different wavelengths 1,030, 515 and 343 nm. Both single and multiple shot laser induced damage thresholds of doped GaN layers were evaluated and discussed. The scanning electron microscopy employed with electron beam induced current and energy dispersive X-ray techniques were used to study laser damage morphology. It was observed that ablated area and laser-induced damage increased with irradiation fluence. The mechanism of damage generation by Gaussian beam profile laser was considered. 相似文献
37.
Roman Tkachov Lukas Stepien Aljoscha Roch Hartmut Komber Felix Hennersdorf Jan J. Weigand Ingmar Bauer Anton Kiriy Christoph Leyens 《Tetrahedron》2017,73(16):2250-2254
Herein, aiming at optimization of the polymerization process leading to a family of hole- and electron-conducting 1,1,2,2-ethenetetrathiolate-based polymers, such as poly(nickel-1,1,2,2-ethenetetrathiolate), poly[Kx(Ni-ett)], we investigated transformations of the monomer precursor 1,3,4,6-tetrathiapentalene-2,5-dione (TPD) occurring under polymerization conditions. We found that only one ring of TPD opens upon its reaction with potassium methoxide under inert conditions at room temperature which leads to the formation of potassium 2-oxo-1,3-dithiol-4,5-dithiolate (K2[3]). Heating of K2[3] under reflux in methanol solution under inert conditions opens the second ring, however the resulting product is not potassium ethenetetrathiolate (K4[2]), the product of an exhaustive methanolysis of TPD, but potassium tetrathiooxalate (K2[4]), the product of the decarbonylation of K2[3]. Preliminary experiments reveal that the involvement of K2[4] in the polymerization process is beneficial for reproducible formation of high quality 1,1,2,2-ethenetetrathiolate-based polymers suitable for thermoelectric applications. 相似文献
38.
39.
Kamila Kalachova Jana Pulkrabova Tomas Cajka Lucie Drabova Michal Stupak Jana Hajslova 《Analytical and bioanalytical chemistry》2013,405(24):7803-7815
A new method for rapid determination of 73 target organic environmental contaminants including 18 polychlorinated biphenyls, 16 organochlorinated pesticides, 14 brominated flame retardants and 25 polycyclic aromatic hydrocarbons in fish and fish feed using gas chromatography coupled with triple quadrupole tandem mass spectrometry (GC–MS/MS) was developed and validated. GC–MS/MS in electron ionization mode was shown to be a powerful tool for the (ultra)trace analysis of multiclass environmental contaminants in complex matrices, providing measurements with high selectivity and sensitivity. Another positive aspect characterizing the newly developed method is a substantial simplification of the sample preparation, which was achieved by an ethyl acetate QuEChERS (quick, easy, cheap, effective, rugged and safe) based extraction followed by silica minicolumn clean-up. With use of this sample preparation approach the sample laboratory throughput was increased not only because six samples may be prepared in approximately 1 h, but also because all the above-mentioned groups of contaminants can be determined in a single GC–MS/MS run. Under the optimized conditions, the recoveries of all target analytes in both matrices were within the range from 70 to 120 % and the repeatabilities were 20 % or less. The method quantification limits were in the range from 0.005 to 1 μg kg–1 and from 0.05 to 10 μg kg–1 for fish muscle tissue and fish feed, respectively. The developed method was successfully applied to the determination of halogenated persistent organic pollutants and polycyclic aromatic hydrocarbons in fish and fish feed samples. 相似文献
40.
Tomas Bertok Pavol Gemeiner Milan Mikula Peter Gemeiner Jan Tkac 《Mikrochimica acta》2013,180(1-2):151-159
We report on an ultrasensitive label-free lectin-based impedimetric biosensor for the determination of the sialylated glycoproteins fetuin and asialofetuin. A sialic acid binding agglutinin from Sambucus nigra I was covalently immobilised on a mixed self-assembled monolayer (SAM) consisting of 11-mercaptoundecanoic acid and 6-mercaptohexanol. Poly(vinyl alcohol) was used as a blocking agent. The sensor layer was characterised by atomic force microscopy, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The biosensor exhibits a linear range that spans 7 orders of magnitude for both glycoproteins, with a detection limit as low as 0.33 fM for fetuin and 0.54 fM for asialofetuin. We also show, by making control experiments with oxidised asialofetuin, that the biosensor is capable of quantitatively detecting changes in the fraction of sialic acid on glycoproteins. We conclude that this work lays a solid foundation for future applications of such a biosensor in terms of the diagnosis of diseases such as chronic inflammatory rheumatoid arthritis, genetic disorders and cancer, all of which are associated with aberrant glycosylation of protein biomarkers. Figure
Key aspects of the biosensor: 1) mixed SAM formation, 2) immobilisation of lectin & blocking and 3) a glycoprotein recognition. 相似文献