全文获取类型
收费全文 | 562篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 440篇 |
晶体学 | 6篇 |
力学 | 8篇 |
数学 | 57篇 |
物理学 | 75篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 48篇 |
2012年 | 37篇 |
2011年 | 49篇 |
2010年 | 26篇 |
2009年 | 16篇 |
2008年 | 27篇 |
2007年 | 28篇 |
2006年 | 31篇 |
2005年 | 31篇 |
2004年 | 25篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1932年 | 2篇 |
1915年 | 2篇 |
1903年 | 2篇 |
1902年 | 2篇 |
排序方式: 共有586条查询结果,搜索用时 15 毫秒
71.
Ma CQ Pisula W Weber C Feng XL Müllen K Bäuerle P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(5):1507-1518
Three-dimensional (3D) π-conjugated dendritic oligothiophenes up to a third generation have been functionalized with tris(decyloxy)phenylethynyl tails at the periphery. The first-generation compounds (3 T-p-Ph-C10 and 6 T-p-Ph-C10) were synthesized by palladium-catalyzed Sonogashira coupling reactions, whereas the higher generation products were synthesized by palladium-catalyzed Suzuki coupling reactions in a divergent approach. The optical and electrochemical properties were investigated by UV/Vis absorption, fluorescence spectroscopy, and cyclic voltammetry. The results revealed that the terminal tris(alkyloxy)phenylethynyl groups are conjugated to the branched oligothiophene core, yielding redshifted absorption and fluorescence spectra and reduced optical band gaps relative to the dendritic oligothiophene core. A structural study revealed a close relationship between the type of supramolecular organization and the size of the oligothiophene core. The first-generation compounds 3 T-p-Ph-C10 and 6 T-p-Ph-C10 displayed columnar phases in the bulk state, which was confirmed by two-dimensional wide-angle X-ray scattering (2D WAXS) measurements. The self-assembly into columnar stacks has mainly been attributed to phase separation between the rigid thiophene cores and the flexible side-chains assisted by minor π-stacking interactions between the conjugated dendritic oligothiophene units. The high-generation compounds, however, showed less ordered structures in the solid state. 相似文献
72.
Egli S Nussbaumer MG Balasubramanian V Chami M Bruns N Palivan C Meier W 《Journal of the American Chemical Society》2011,133(12):4476-4483
Vesicles assembled from amphiphilic block copolymers represent promising nanomaterials for applications that include drug delivery and surface functionalization. One essential requirement to guide such polymersomes to a desired site in vivo is conjugation of active, targeting ligands to the surface of preformed self-assemblies. Such conjugation chemistry must fulfill criteria of efficiency and selectivity, stability of the resulting bond, and biocompatibility. We have here developed a new system that achieves these criteria by simple conjugation of 4-formylbenzoate (4FB) functionalized polymersomes with 6-hydrazinonicotinate acetone hydrazone (HyNic) functionalized antibodies in aqueous buffer. The number of available amino groups on the surface of polymersomes composed of poly(dimethylsiloxane)-block-poly(2-methyloxazoline) diblock copolymers was investigated by reacting hydrophilic succinimidyl-activated fluorescent dye with polymersomes and evaluating the resulting emission intensity. To prove attachment of biomolecules to polymersomes, HyNic functionalized enhanced yellow fluorescent protein (eYFP) was attached to 4FB functionalized polymersomes, resulting in an average number of 5 eYFP molecules per polymersome. Two different polymersome-antibody conjugates were produced using either antibiotin IgG or trastuzumab. They showed specific targeting toward biotin-patterned surfaces and breast cancer cells. Overall, the polymersome-ligand platform appears promising for therapeutic and diagnostic use. 相似文献
73.
Do C Hatfield J Patel S Vasudevan D Tirla C Mills NS 《The Journal of organic chemistry》2011,76(1):181-187
Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and unsubstituted phenyl rings in the 3-position; attempts to oxidize the m-substituted derivatives via electrochemistry were unsuccessful. Chemical oxidation with SbF(5)/SO(2)ClF gave the dication of 9-[(4-methoxyphenyl)methylene]-9H-fluorene cleanly; oxidation of all other substituted benzylidene fluorenes resulted in mixtures of products. The excellent linear relationship between the chemical shifts calculated by the GIAO method and the experimental shifts for the p-methoxy-substituted benzylidene fluorene dication suggests that the calculations satisfactorily reflect the magnetic properties of this dication and potentially those of the other dications studied. The redox potentials from electrochemical oxidation, a measure of the stability of the dications, showed a good linear relationship with another measure of stability, the calculated difference in energy between each dication and its neutral precursor. The dications of benzylidene fluorenes were less stable than the dications of diphenylmethylidene fluorenes; within each type of compound, dications with p-substituted phenyl rings were more stable than dications with m-substituted phenyl rings and dications with phenyl rings substituted with electron-donating groups were more stable than dications with phenyl rings substituted with electron-withdrawing groups. The antiaromaticity of the fluorenyl system was assessed through the nucleus-independent chemical shift (NICS) that was also calculated by the GIAO method. The plot of the NICS values per square area versus the calculated energy difference for the dications showed a moderate degree of linearity; the plot of NICS values per square area versus the oxidation potentials was less linear. Thus, a suggestive, but not conclusive, relationship between magnetic and energetic measures of antiaromaticity was observed. 相似文献
74.
Rohr C Balbás Gambra M Gruber K Höhl C Malarek MS Scherer LJ Constable EC Franosch T Hermann BA 《Chemical communications (Cambridge, England)》2011,47(6):1800-1802
An interaction-site model can a priori predict molecular self-organisation on a new substrate in Monte Carlo simulations. This is experimentally confirmed with scanning tunnelling microscopy on Fréchet dendrons of a pentacontane template. Local and global ordering motifs, inclusion molecules and a rotated unit cell are correctly predicted. 相似文献
75.
Thorwirth R Stolle A Ondruschka B Wild A Schubert US 《Chemical communications (Cambridge, England)》2011,47(15):4370-4372
A new, ligand- and solvent-free method for the Huisgen 1,3-dipolar cycloaddition (click reaction) was developed using a planetary ball mill. Besides various alkynes and azides, a propargyl functionalized polymer was converted by mill clicking. Moreover, it was possible to carry out a click polymerization in a ball mill. 相似文献
76.
Dr. Gaël Rouillé Mathias Steglich Dr. Cornelia Jäger Prof. Dr. Friedrich Huisken Prof. Dr. Thomas Henning Gabriele Theumer Dr. Ingmar Bauer Prof. Dr. Hans‐Joachim Knölker 《Chemphyschem》2011,12(11):2131-2137
We report on the characterization of dibenzo[cde,opq]rubicene (C30H14). The molecule was studied in solution at room temperature with absorption spectroscopy in the visible (vis) and ultraviolet (UV) wavelength ranges, and with emission spectroscopy. The infrared (IR), visible, ultraviolet, and vacuum ultraviolet (VUV) absorption spectra of a thin film were measured also at room temperature. In addition, the UV/vis absorption spectrum was measured at cryogenic temperatures using the matrix isolation spectroscopy technique. The interpretation of spectra was supported by theoretical calculations based on semiempirical and ab initio models, as well as on density functional theory. Finally, the results of the laboratory study were compared with interstellar spectra. 相似文献
77.
Martin Gericke Katja Geitel Cornelia Jrke Joachim H. Clement Thomas Heinze 《Molecules (Basel, Switzerland)》2021,26(13)
Polysaccharide (PS) based nanoparticles (NP) are of great interest for biomedical applications. A key challenge in this regard is the functionalization of these nanomaterials. The aim of the present work was the development of reactive PS-NP that can be coupled with an amino group containing compounds under mild aqueous conditions. A series of cellulose phenyl carbonates (CPC) and xylan phenyl carbonates (XPC) with variable degrees of substitution (DS) was obtained by homogeneous synthesis. The preparation of PS-NP by self-assembling of these hydrophobic derivatives was studied comprehensively. While CPC mostly formed macroscopic aggregates, XPC formed well-defined spherical NP with diameters around 100 to 200 nm that showed a pronounced long-term stability in water against both particle aggregation as well as cleavage of phenyl carbonate moieties. Using an amino group functionalized dye it was demonstrated that the novel XPC-NP are reactive towards amines. A simple coupling procedure was established that enables direct functionalization of the reactive NP in an aqueous dispersion. Finally, it was demonstrated that dye functionalized XPC-NP are non-cytotoxic and can be employed in advanced biomedical applications. 相似文献
78.
79.
Let BG be the classifying space for stable spherical fibrations, and let V be a finite dimensional vector subspace of the cohomology algebra H1(BG; 2). We prove that V may be realized by a Poincaré duality space P, which means that if v:P→BG is the Spivak fibration, then v1 maps V isomorphically onto its image in H1(P;2). By construction, P is the product of a certain Grassman manifold and a spherical fiber space over a closed smooth manifold. 相似文献
80.
Cornelia Niederdrenk 《Geometriae Dedicata》1982,12(1):25-33
Ohne Zusammenfassung 相似文献