全文获取类型
收费全文 | 912篇 |
免费 | 8篇 |
国内免费 | 5篇 |
专业分类
化学 | 760篇 |
力学 | 16篇 |
数学 | 87篇 |
物理学 | 62篇 |
出版年
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 7篇 |
2013年 | 23篇 |
2012年 | 38篇 |
2011年 | 54篇 |
2010年 | 33篇 |
2009年 | 16篇 |
2008年 | 45篇 |
2007年 | 50篇 |
2006年 | 55篇 |
2005年 | 49篇 |
2004年 | 48篇 |
2003年 | 40篇 |
2002年 | 32篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 14篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有925条查询结果,搜索用时 0 毫秒
891.
Boudinet D Benwadih M Altazin S Verilhac JM De Vito E Serbutoviez C Horowitz G Facchetti A 《Journal of the American Chemical Society》2011,133(26):9968-9971
Organic thin-film transistor (OTFT) performance depends on the chemical characteristics of the interface between functional semiconductor/dielectric/conductor materials. Here we report for the first time that OTFT response in top-gate architectures strongly depends on the substrate chemical functionalization. Depending on the nature of the substrate surface, dramatic variations and opposite trends of the TFT threshold voltage (~±50 V) and OFF current (10(5)×!) are observed for both p- and n-channel semiconductors. However, the field-effect mobility varies only marginally (~2×). Our results demonstrate that the substrate is not a mere passive mechanical support. 相似文献
892.
Claire Le ManachAurélie Baron Régis GuillotBoris Vauzeilles Jean-Marie Beau 《Tetrahedron letters》2011,52(13):1462-1465
A library of paclitaxel (taxol) mimics was obtained by a straightforward strategy involving rational design and an efficient synthesis of a simplified taxane core substitute, together with a click-chemistry combinatorial search for phenylisoserine side-chain surrogates. 相似文献
893.
Nikonova OA Nedelec JM Kessler VG Seisenbaeva GA 《Langmuir : the ACS journal of surfaces and colloids》2011,27(18):11622-11628
The use of an inorganic perrhenate ligand in the structure of early-transition-metal alkoxide precursors permits to achieve uniform self-assembly of the primary nanoparticles produced by their hydrolysis. The latter has been carried out in a hydrocarbon reaction medium by the addition of water with vigorous stirring, either in the pure form or in solutions in parent alcohols. The self-assembly is guided by the surface charge enhanced by the presence of strongly coordinated anions as determined by zeta potential measurements. The aggregation process has been followed in real time by nanoparticle tracking analysis (NanoSight technique). The reaction products are spherical aggregates with a size that can be efficiently controlled through the polarity of the reaction medium. The produced nanobeads have been characterized by TEM, SEM-EDS, DLS, nitrogen adsorption, and FTIR. The coordination of metal centers has been investigated using EXAFS spectroscopy. The aggregates remain amorphous on thermal treatment of up to 700 °C (24 h treatment) but crystallize when treated at 1000 °C. This latter process is associated with the total loss of rhenium content and offers early-transition-metal oxides as products. 相似文献
894.
Aurore Olivier Jean-Marie Raquez Philippe Dubois Pascal Damman 《European Polymer Journal》2011,(1):31-39
This paper is the first report about the morphology of semi-crystalline poly(ε-caprolactone) (PCL) brushes studied by Atomic Force Microscopy (AFM) in tapping mode. This represents a convenient way to observe how the growth of a polymer proceeds from a thiol monolayer on gold substrate in terms of grafting density and thiol monolayer stability. The synthesis of semi-crystalline PCL brushes was carried out by Ring-Opening Polymerization (ROP) of ε-caprolactone (ε-CL) from hydroxyl end-group of thiol monolayer on gold surface as catalyzed with tin octoate (Sn(Oct)2) at 50 °C. Addition of a sacrificial initiator was also attempted in order to get a finer control over PCL crystals. For a sake of comparison, triazabicyclo[4.4.0]dec-5-ene (TBD) was also investigated as another ROP catalyst active at ambient temperature. The composition and the morphology of resulting semi-crystalline PCL brushes were characterized using X-ray Photoelectron Spectroscopy (XPS) and AFM. In the case of Sn(Oct)2-promoted ROP of CL with or without free (sacrificial) initiator (i.e., benzyl alcohol), different types of morphologies were observed on the gold substrate, due to the thermal instability of thiol-gold bond under the experimental conditions. When TBD was used at ambient temperature, a regular and homogeneous crystalline morphology, i.e., compact PCL crystals, could be observed. 相似文献
895.
Pelletier J Espinas J Vu N Norsic S Baudouin A Delevoye L Trébosc J Le Roux E Santini C Basset JM Gauvin RM Taoufik M 《Chemical communications (Cambridge, England)》2011,47(10):2979-2981
Impregnation of [(AliBu(3))(Et(2)O)] on partially dehydroxylated SBA-15 affords a mesoporous material bearing the well-defined single site surface aluminium species [(≡SiO)(2)Al(iBu)(Et(2)O)]. 相似文献
896.
Schinzel S Chermette H Copéret C Basset JM 《Journal of the American Chemical Society》2008,130(25):7984-7987
Olefin metathesis on a silica supported tantalumhydridocarbene complex, the key carbon-carbon making process in alkane metathesis, requires a large number of elementary steps in contrast to the known olefin metathesis pathway, which corresponds to successive [2 + 2]-cycloaddition and cycloreversion steps. The direct pathway is forbidden because it requires the formation of a high energy reaction intermediates, an olefin adduct of trigonal bipyramid (TBP) geometry, where the carbene is trans to an hydride ligand. Extra low-energy steps are therefore necessary to connect the reactants to products, the key being a turnstile interconversion at the metallacyclobutane intermediates. 相似文献
897.
Blanc F Basset JM Copéret C Sinha A Tonzetich ZJ Schrock RR Solans-Monfort X Clot E Eisenstein O Lesage A Emsley L 《Journal of the American Chemical Society》2008,130(18):5886-5900
The molecular dynamics of a series of organometallic complexes covalently bound to amorphous silica surfaces is determined experimentally using solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory calculations (DFT). The determination is carried out for a series of alkylidene-based catalysts having the general formula [([triple bond]SiO)M(ER)(=CH(t)Bu)(R')] (M = Re, Ta, Mo or W; ER = C(t)Bu, NAr or CH2(t)Bu; R' = CH2(t)Bu, NPh2, NC4H4). Proton-carbon dipolar coupling constants and carbon chemical shift anisotropies (CSA) are determined experimentally by solid-state NMR. Room-temperature molecular dynamics is quantified through order parameters determined from the experimental data. For the chemical shift anisotropy data, we validate and use a method that integrates static values for the CSA obtained computationally by DFT, obviating the need for low-temperature measurements. Comparison of the room-temperature data with the calculations shows that the widths of the calculated static limit dipolar couplings and CSAs are always greater than the experimentally determined values, providing a clear indication of motional averaging on the NMR time scale. Moreover, the dynamics are found to be significantly different within the series of molecular complexes, with order parameters ranging from = 0.5 for [([triple bond]SiO)Ta(=CH(t)Bu)(CH2(t)Bu)2] and [([triple bond]SiO)Re([triple bond]C(t)Bu)(=CH(t)Bu)(CH2(t)Bu)] to = 0.9 for [([triple bond]SiO)Mo([triple bond]NAr)(=CH(t)Bu)(R') with R' = CH2(t)Bu, NPh2, NC4H4. The data also show that the motion is not isotropic and could be either a jump between two sites or more likely restricted librational motion. The dynamics are discussed in terms of the molecular structure of the surface organometallic complexes, and the orientation of the CSAs tensor at the alkylidene carbon is shown to be directly related to the magnitude of the alpha-alkylidene CH agostic interation. 相似文献
898.
Soulivong D Norsic S Taoufik M Copéret C Thivolle-Cazat J Chakka S Basset JM 《Journal of the American Chemical Society》2008,130(15):5044-5045
Silica-supported tantalum hydride, (SiO)2Ta-H (1), proves to be the first single-site catalyst for the direct non-oxidative coupling transformation of methane into ethane and hydrogen at moderate temperatures, with a high selectivity (>98%). The reaction likely involves the tantalum-methyl-methylidene species as a key intermediate, where the methyl ligand can migrate onto the tantalum-methylidene affording the tantalum-ethyl. 相似文献
899.
Basset C Dedieu A Guérin P Quéméneur E Meyer D Vidaud C 《Journal of chromatography. A》2008,1185(2):233-240
To improve general understanding of biochemical mechanisms in the field of uranium toxicology, the identification of protein targets needs to be intensified. Immobilized metal affinity chromatography (IMAC) has been widely developed as a powerful tool for capturing metal binding proteins from biological extracts. However uranyl cations (UO2(2+)) have particular physico-chemical characteristics which prevent them from being immobilized on classical metal chelating supports. We report here on the first development of an immobilized uranyl affinity chromatography method, based on the cation-exchange properties of aminophosphonate groups for uranyl binding. The cation distribution coefficient and loading capacity on the support were determined. Then the stability of the uranyl-bonded phase under our chromatographic conditions was optimized to promote affinity mechanisms. The successful enrichment of uranyl binding proteins from human serum was then proven using proteomic and mass spectral analysis. 相似文献
900.
The interaction of beta-cyclodextrin (beta-CD) with different lipids has been studied, using Langmuir monolayers kept at constant surface pressure or constant spreading surface. Results show that beta-CD, injected beneath the monolayer, is able to desorb unsaturated palmitoyloleoylphosphatidylcholine (POPC) and sphingomyelin (SM) under specific experimental conditions. In this last case, SM monolayers, labeled with the fluorescent NBD-PC probe, were also observed by fluorescence microscopy, before and after beta-CD injection. Images show that SM monolayers are more homogeneous after beta-CD injection, because of the lipid desorption. At last, it seems that lipid desorption occurs only in a restricted surface pressure range, depending on the lipid. 相似文献