全文获取类型
收费全文 | 2810篇 |
免费 | 74篇 |
国内免费 | 19篇 |
专业分类
化学 | 1517篇 |
晶体学 | 43篇 |
力学 | 94篇 |
数学 | 680篇 |
物理学 | 569篇 |
出版年
2023年 | 16篇 |
2022年 | 24篇 |
2021年 | 39篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 114篇 |
2017年 | 147篇 |
2016年 | 116篇 |
2015年 | 85篇 |
2014年 | 121篇 |
2013年 | 341篇 |
2012年 | 152篇 |
2011年 | 171篇 |
2010年 | 156篇 |
2009年 | 109篇 |
2008年 | 146篇 |
2007年 | 121篇 |
2006年 | 100篇 |
2005年 | 148篇 |
2004年 | 136篇 |
2003年 | 85篇 |
2002年 | 40篇 |
2001年 | 34篇 |
2000年 | 28篇 |
1999年 | 22篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1968年 | 12篇 |
排序方式: 共有2903条查询结果,搜索用时 15 毫秒
31.
Rozhon W Petutschnig E Wrzaczek M Jonak C 《Analytical and bioanalytical chemistry》2005,382(7):1620-1627
Salicylic acid (SA) is an important signaling compound in plants and is involved in various defense responses. Here we report a new method for quantification of free and total soluble SA in Arabidopsis thaliana with 5-fluorosalicylic acid (5-FSA) as internal standard. The SA was isolated from leaf extracts by solid-phase extraction with phenyl-phase cartridges and selectively eluted as the cationic iron(III)-complex. Recoveries of SA and 5-FSA were equal and exceeded 90%. Free SA was subsequently released from the iron(III)-complex by addition of 2,2-bipyridyl and high-performance anion-exchange chromatography was performed on an NH2 column. The SA appeared as last peak with a retention time of 15 min, baseline-separated from other substances. On-line detection was performed fluorimetrically for both SA and 5-FSA at an excitation wavelength of 300 nm and an emission wavelength of 410 nm, because both substances give similar fluorescence spectra. The detection limit for SA was 5 ng g–1 FW for a sample size of 100 mg. Thus the main advantages of the method are highly selective sample preparation, increased sensitivity, reduced analysis time compared with reversed-phase HPLC, and use of a novel internal standard detectable under the same conditions as SA. The techniques described are applicable to other plant materials. 相似文献
32.
Mustafa Şenyel T. Raci Sertbakan Güneş Kürkçüoğ Ergün Kasap Ziya Kantarci 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(1-2):175-180
Three Hofmann-diaminododecane-type clathrates of the form M(1,12-diaminododecane) Ni(CN)4G (M = Co, Ni or Cd; G = benzene, naphthalene, anthracene, phenanthrene or biphenyl) have been prepared in powder form. The 1,12-diaminododecane molecules in the host lattice permit the inclusion of bulky guest molecules. The spectral features suggest that these compounds are similar in structure to the other Hofmann-diam-type clathrates. 相似文献
33.
34.
N. Ibriş J. Mirza-Rosca A. Santana T. Vişan 《Journal of Solid State Electrochemistry》2002,6(2):119-125
The corrosion and passivation of Zn powder particles dispersed in a paste electrode immersed in 0.5 M Na2SO4 and 5×10–3 M Na2HPO4 solutions were studied mainly by electrochemical impedance spectroscopy. The role played by diffusion in the mechanism of
anodic oxidation of zinc powder particles has been shown. It was demonstrated that the anodic reactionof Zn powder in neutral
or near neutral media involves at least two adsorbed intermediates. By simulating the porous structure of the electrode, some
information about porous nature of zinc electrode could be extracted.
Electronic Publication 相似文献
35.
Manganese in vitamin-minerals tablets was determined by solid sampling electrothermal atomic absorption spectrometry (SS-ETAAS) using three different calibration methods, namely calibration against aqueous standards, standard addition with aqueous standards on solid samples and calibration against solid certified standards. Samples were only finely ground and introduced directly into the furnace by means of solid autosampler system without any dissolving process. Effects of different calibration techniques, temperatures and heating rates of atomization and pyrolysis steps on the accuracy and precision of the analyte elements were investigated. After optimization of the experimental parameters, there is good agreement (at 95% confidence level) between the results obtained by solid sampling and those obtained by acid digestion of samples. 相似文献
36.
Annals of Global Analysis and Geometry - We give an elementary and self-contained proof of the uniformization theorem for noncompact simply connected Riemann surfaces. 相似文献
37.
Metin Başarir 《Periodica Mathematica Hungarica》1995,30(3):177-181
In this paper, necessary and sufficient conditions that the real doubly infinite matrixA sums every strongly almost convergent double sequence, leaving the limit invariant, have been determined. 相似文献
38.
C. T. Zhang M. Sferrazza R. H. Mayer Z. W. Grabowski P. Bhattacharyya P. J. Daly R. Broda B. Fornal W. Królas T. Pawłat G. de Angelis D. Bazzacco S. Lunardi C. Rossi-Alvarez 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(1):11-12
Using an 11.4MeV/u136Xe beam of the UNILAC accelerator of GSI and anatW target, A=184 isobars were produced and separated by using an on-line mass separator. A new isomeric state was found in184Hf. This state decays with a half-life of 48(10) s and emits three -rays of 73, 482, and 555 keV as well as lower-lying cascade transitions. The hindrance of the 73 keV-E1 transition with K=8 is compared with those of other even-even hafnium isotopes. The half-life of184Lu was estimated to be between 15 and 25s. 相似文献
39.
A. Baştuğ Ö. Söğüt Y. Şahin M. Ertuğrul 《Journal of Radioanalytical and Nuclear Chemistry》2002,251(2):323-327
La and Lb X-ray fluorescence cross sections in Er, Ta, W and Au at excitation energies of 16.896, 22.581, 25.770, 32.890, 38.184, 43.949, 50.214 and 59.5 keV were investigated. Measurements were made using a low energy Si(Li) detector coupled to a model 4096 computerized multi-channel analyser. The experimental results were compared with the theoretically calculated values of L X-rays fluorescence cross sections and other experimental results. Good agreement was observed between experimental and theoretical values. 相似文献
40.
A stereoselective approach to the 9α-fluorinated analogue of the natural drimane sesquiterpene drimenin starting from β-ionone is described. β-Ionone is transformed into a bicyclic β-cetoester from which 9αF-drimenin is prepared through stereoselective electrophilic fluorination at the C-9 with N-fluorobenzenesulfonimide followed by Wittig methylenation, allylic bromination, bromine-hydroxyl exchange and γ-lactonization. 相似文献