全文获取类型
收费全文 | 387篇 |
免费 | 22篇 |
专业分类
化学 | 342篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 40篇 |
物理学 | 23篇 |
出版年
2023年 | 4篇 |
2021年 | 8篇 |
2020年 | 22篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 2篇 |
2016年 | 10篇 |
2015年 | 17篇 |
2014年 | 18篇 |
2013年 | 24篇 |
2012年 | 21篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 22篇 |
2008年 | 20篇 |
2007年 | 22篇 |
2006年 | 32篇 |
2005年 | 20篇 |
2004年 | 16篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1966年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有409条查询结果,搜索用时 218 毫秒
71.
Rheological measurements were performed on aqueous dispersions of two commercial crosslinked polymer microgels, Carbopol Ultrez
10 and Carbopol ETD 2050, prepared over a wide range of concentration and pH. For all concentrations studied, both the yield
stress and the elastic modulus initially increased dramatically with pH and displayed broad peaks at intermediate pH. This
is consistent with the onset of jamming of the Carbopol particles due to a rapid increase in particle size caused by osmotic
swelling in the presence of NaOH. Scaling of both yield stress and elasticity with concentration was observed only at higher
concentrations, which we believe indicates a change from a percolated structure at low volume fractions to a space filling
network of compressed particles at high volume fractions. This model is supported by confocal microscopy of fluorescently
dyed Carbopol dispersions. 相似文献
72.
A. Chaudhuri C. Andreoiu M. Brodeur T. Brunner U. Chowdhury S. Ettenauer A. T. Gallant A. Grossheim G. Gwinner R. Klawitter A. A. Kwiatkowski K. G. Leach A. Lennarz D. Lunney T. D. Macdonald R. Ringle B. E. Schultz V. V. Simon M. C. Simon J. Dilling 《Applied physics. B, Lasers and optics》2014,114(1-2):99-105
The introduction of Paul traps, in particular linear radio-frequency quadrupoles in the early 2000s, has revolutionized the use of ion traps for probing the properties of radioactive nuclides. It opened the path to trapping all available nuclides, independent of their chemical properties. We present an overview of direct mass measurements of short-lived nuclides using TITAN, a Penning trap mass spectrometer facility particularly suitable for precision measurements of ms-half-life nuclides. 相似文献
73.
74.
D Jiang I Rauda S Han S Chen F Zhou 《Langmuir : the ACS journal of surfaces and colloids》2012,28(35):12711-12721
Amyloid β (Aβ) fibrils are present as a major component in senile plaques, the hallmark of Alzheimer's disease (AD). Diffuse plaques (nonfibrous, loosely packed Aβ aggregates) containing amorphous Aβ aggregates are also formed in brain. This work examines the influence of Cu(2+) complexation by Aβ on the aggregation process in the context of charge and structural variations. Changes in the surface charges of Aβ molecules due to Cu(2+) binding, measured with a ζ-potential measurement device, were correlated with the aggregate morphologies examined by atomic force microscopy. As a result of the charge variation, the "colloid-like" stability of the aggregation intermediates, which is essential to the fibrillation process, is affected. Consequently, Cu(2+) enhances the amorphous aggregate formation. By monitoring variations in the secondary structures with circular dichroism spectroscopy, a direct transformation from the unstructured conformation to the β-sheet structure was observed for all types of aggregates observed (oligomers, fibrils, and/or amorphous aggregates). Compared to the Aβ aggregation pathway in the absence of Cu(2+) and taking other factors affecting Aβ aggregation (i.e., pH and temperature) into account, our investigation indicates that formations of amorphous and fibrous aggregates diverge from the same β-sheet-containing partially folded intermediate. This study suggests that the hydrophilic domain of Aβ also plays a role in the Aβ aggregation process. A kinetic model was proposed to account for the effects of the Cu(2+) binding on these two aggregation pathways in terms of charge and structural variations. 相似文献
75.
DA Rusling IS Nandhakumar T Brown KR Fox 《Chemical communications (Cambridge, England)》2012,48(77):9592-9594
The triplex approach to DNA recognition is exploited to direct covalent inter-strand cross-links to unique locations within a pre-assembled DNA nanostructure. This approach can be used to improve the stability of DNA nanostructures and demonstrates the feasibility of directing other reactive groups to unique locations within these complexes. 相似文献
76.
Norbert Moszner Juraj Pavlinec Iris Lamparth Frank Zeuner Jrg Angermann 《Macromolecular rapid communications》2006,27(14):1115-1120
Summary: 1,3‐Bis(methacrylamido)propane‐2‐yl dihydrogen phosphate ( 1 ) was synthesised by phosphorylation of 1,3‐bis(methacrylamido)‐2‐hydroxypropane ( 2 ) with phosphorus oxychloride in tetrahydrofuran (THF) in the presence of triethylamine (TEA). The structure of the new monomer 1 was characterised by IR, 1H NMR, 13C NMR and 31P NMR spectroscopies, elemental analysis and mass spectrometry. The monomer dissolves well in water, ethanol or aqueous THF and shows an improved hydrolytic stability compared to the corresponding methacrylate‐based dihydrogen phosphates. 1 was homopolymerised in ethanol with 2,2′‐azoisobutyronitrile (AIBN) as the initiator at 55–75 °C under the formation of an insoluble, cross‐linked product. Aqueous solutions of 1 are strongly acidic and enable to etch enamel and dentin. Nevertheless, 1 did not show any cytotoxic effect. Furthermore, the adhesive properties of 1 were measured.
77.
78.
Cyprian M. Chunkang Iris E. Ikome Emmanuel N. Nfor Yuta Mitani Natsuki Katsuumi Tomoyuki Haraguchi Takashiro Akitsu 《Molecules (Basel, Switzerland)》2020,25(23)
Single crystals of two achiral and planar heterocyclic compounds, C9H8H3O(CA1) and C8H5NO2 (CA4), recrystallized from ethanol, were characterized by single crystal X-ray analysis, respectively, and chiral crystallization was observed only for CA1 as P212121 (# 19), whereas it was not observed for CA4 P21/c (# 14). In CA1, as a monohydrate, the hydrogen bonds were pronounced around the water of crystallization (O4), and the planar cyclic sites were arranged in parallel to slightly tilted positions. On the other hand, an anhydride CA4 formed a dimer by hydrogen bonds between adjacent molecules in the crystal, which were aggregated by van der Waals forces and placed in parallel planar cyclic sites. 相似文献
79.
A. Carel N. Kwamen Marcel Schlottmann Dr. David Van Craen Dr. Elisabeth Isaak Julia Baums Li Shen Ali Massomi Dr. Christoph Räuber Benjamin P. Joseph Prof. Dr. Gerhard Raabe Dr. Christian Göb Prof. Dr. Iris M. Oppel Dr. Rakesh Puttreddy Dr. Jas S. Ward Prof. Dr. Kari Rissanen Dr. Roland Fröhlich Prof. Dr. Markus Albrecht 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1396-1405
The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The 1H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n-alkyls, n-Ω-alkenyls or n-Ω-alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation. 相似文献
80.