全文获取类型
收费全文 | 1487篇 |
免费 | 66篇 |
国内免费 | 4篇 |
专业分类
化学 | 1308篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 106篇 |
物理学 | 130篇 |
出版年
2024年 | 1篇 |
2023年 | 20篇 |
2022年 | 29篇 |
2021年 | 40篇 |
2020年 | 39篇 |
2019年 | 26篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 60篇 |
2014年 | 71篇 |
2013年 | 90篇 |
2012年 | 107篇 |
2011年 | 105篇 |
2010年 | 61篇 |
2009年 | 56篇 |
2008年 | 95篇 |
2007年 | 99篇 |
2006年 | 87篇 |
2005年 | 80篇 |
2004年 | 58篇 |
2003年 | 44篇 |
2002年 | 56篇 |
2001年 | 12篇 |
2000年 | 27篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 18篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有1557条查询结果,搜索用时 654 毫秒
941.
942.
943.
Steinhart M Göring P Dernaika H Prabhukaran M Gösele U Hempel E Thurn-Albrecht T 《Physical review letters》2006,97(2):027801
We show that the crystal orientation in polymer nanotubes and nanorods inside porous templates is controlled by the kinetics of nucleation and growth under 2D confinement. Two clear limiting cases are identified: In separated nanostructures, any crystal orientation allowing the growth of lamellar crystals along the pores appears statistically. If a bulklike surface film connects the nanostructures, macroscopic arrays with uniform crystal orientation are obtained, in which the dominant growth direction of the crystals is aligned with the long axes of the pores of the template. 相似文献
944.
945.
Filip Kužel Petra Staffová Irena Špendlíková Jan John Ferdinand Šebesta 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):729-734
Solid extractants containing di-(2-ethylhexyl)phosphoric acid (HDEHP) in the support based on modified polyacrylonitrile (PAN)
were studied for the determination of 90Sr by means of measuring the activity of its separated 90Y daughter. In this paper, 152Eu and 133Ba were used as chemical homologues of 90Y and 90Sr. For these radionuclides, dependences of mass distribution coefficients (D
g) on the nitric acid concentration were measured for several types of HDEHP-PAN solid extractants. The mechanism of the Eu3+ and Ba2+ ions extraction was confirmed to follow the theoretical two-phase equation for the chelating extractants. Further, the influences
of the presence of nitrates, calcium and iron ions on the values of D
g(Ba, Eu) were determined concentrating on the possibility of masking the iron ions by the addition of the ascorbic acid. This method
was tested on the solution simulating the leachate of ashed green plant sample. The results obtained make the application
of solid extractants containing HDEHP in PAN support prospective for 90Sr determination. 相似文献
946.
Li WW Hellwig P Ritter M Haehnel W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(27):7236-7245
Quinones and quinoproteins are essential redox components and enzymes in biological systems. Here, we report the de novo design, synthesis, and properties of model four-alpha-helix bundle quinoproteins. The proteins were designed and constructed from three different helices with 21 or 22 amino acid residues by chemoselective ligation to a cyclic decapeptide template. A free cysteine unit is placed at the hydrophobic core of the protein for binding of ubiquinone-0 and menaquinone-0 through a thioether bond. The quinoproteins with molecular weights of 11-12 kDa were characterized by electrospray ionization mass spectrometry, UV/Vis spectroscopy, size-exclusion chromatography, circular dichroism measurements, (1)H NMR spectroscopy, cyclic voltammetry, and redox-induced FTIR difference spectroscopy. The midpoint redox potentials at pH 8 in aqueous solution E(m,8) of thioether conjugates with N-acetyl cysteine methyl ester were 89 mV and -63 mV and with a synthetic protein 229 mV and 249 mV versus standard hydrogen electrode (SHE) for ubiquinone-0 and menaquinone-0, respectively. Detailed redox-induced FTIR difference spectroscopic studies of the model compounds and quinoproteins show the special resonance features for C=O bands at 1656-1660 and 1655-1665 cm(-1) due to the sulfur substitution to ubiquinone-0 and menaquinone-0, respectively. The construction of model quinoproteins represents a significant step toward more complex artificial redox systems. 相似文献
947.
Lebdusková P Sour A Helm L Tóth E Kotek J Lukes I Merbach AE 《Dalton transactions (Cambridge, England : 2003)》2006,(28):3399-3406
A DTPA-based chelate containing one phosphinate group was conjugated to a generation 5 polyamidoamine (PAMAM) dendrimer via a benzylthiourea linkage. The Gd(III) complex of this novel conjugate has potential as a contrast agent for magnetic resonance imaging (MRI). The chelates bind Gd3+via three nitrogen atoms, four carboxylates and one phosphinate oxygen, and one water molecule completes the inner coordination sphere. The monomer Gd(III) chelates bearing nitrobenzyl and aminobenzyl groups ([Gd(DTTAP-bz-NO2)(H2O)]2- and [Gd(DTTAP-bz-NH2)(H2O)]2-) as well as the dendrimeric Gd(III) complex G5-(Gd(DTTAP))63) were studied by multiple-field, variable temperature 17O and 1H NMR. The rate of water exchange is faster than that of [Gd(DTPA)(H2O)]2- and very similar on the two monomeric complexes (8.9 and 8.3 x 10(6) s-1 for [Gd(DTTAP-bz-NO2)(H2O)]2- and [Gd(DTTAP-bz-NH2)(H2O)]2-, respectively), while it is decreased on the dendrimeric conjugate (5.0 x 10(6) s-1). The Gd(III) complex of the dendrimer conjugate has a relaxivity of 26.8 mM-1 s-1 at 37 degrees C and 0.47 T (corresponding to 1H Larmor frequency of 20 MHz). Given the contribution of the second sphere water molecules to the overall relaxivity, this value is slightly higher than those reported for similar size dendrimers. The experimental 17O and 1H NMR data were fitted to the Solomon-Bloembergen-Morgan equations extended with a contribution from second coordination sphere water molecules. The rotational dynamics of the dendrimeric conjugate was described in terms of global and local motions with the Lipari-Szabo approach. 相似文献
948.
949.
Hentschel P Grynbaum MD Molnár P Putzbach K Rehbein J Deli J Albert K 《Journal of chromatography. A》2006,1112(1-2):285-292
Thermal and iodine-catalyzed photochemical (Z/E)-isomerization of deoxylutein II [(3R,6'R)-3-hydroxy-3',4'-didehydro-beta,gamma-carotene, anhydrolutein I] (2), the dehydration product of lutein [(3R,3'R,6'R)-beta,varepsilon-carotene-3,3'-diol] (4), yielded multi-component mixtures of (Z)-isomers. By I(2)-catalyzed photoisomerization, (9Z)-2, (9'Z)-2, (13Z)-2, (13'Z)-2 and (15Z)-2 are generated as main products. In addition, this thermodynamic-equilibrium mixture contains traces of (9Z,9'Z)-2 and other (di-Z)-isomers in minor concentrations. Thirteen isomers are chromatographically separated and detected on-line by UV-vis and mass spectrometry. (all-E)-Deoxylutein II (2) and six of its (Z)-configured isomers are separated by capillary HPLC (acetone-d(6)/D(2)O = 85:15) and detected on-line by (1)H NMR spectroscopy in a microprobe. With the microprobe and the active detection volume of 1.5 microl, it is possible to perform structure elucidation with very small amounts available for various (Z)-isomers of deoxylutein II (2) in the isomerization mixture. 相似文献
950.
Effects of static and radiofrequency magnetic field inhomogeneity in ultra-high field magnetic resonance imaging 总被引:2,自引:0,他引:2
Truong TK Chakeres DW Beversdorf DQ Scharre DW Schmalbrock P 《Magnetic resonance imaging》2006,24(2):103-112
To characterize the severe static (B(0)) and radiofrequency (B(1)) magnetic field inhomogeneity in ultra-high field (> or =7 T) magnetic resonance imaging, gradient echo (GE) and spin echo (SE) images of in vivo and postmortem human brains were acquired. The B(0) and B(1) inhomogeneity were experimentally mapped and/or numerically simulated, and correlated with the image artifacts. Whereas B(0) inhomogeneity affects predominantly GE images near air/tissue interfaces, B(1) inhomogeneity affects SE images more severely and shows non-intuitive patterns. Mapping of the B(0) and B(1) inhomogeneity is important in characterizing image artifacts. This will help develop better B(0) and B(1) inhomogeneity correction methods. 相似文献