全文获取类型
收费全文 | 3674篇 |
免费 | 87篇 |
国内免费 | 15篇 |
专业分类
化学 | 2266篇 |
晶体学 | 18篇 |
力学 | 195篇 |
数学 | 750篇 |
物理学 | 547篇 |
出版年
2023年 | 19篇 |
2022年 | 52篇 |
2021年 | 103篇 |
2020年 | 75篇 |
2019年 | 55篇 |
2018年 | 65篇 |
2017年 | 57篇 |
2016年 | 112篇 |
2015年 | 107篇 |
2014年 | 84篇 |
2013年 | 188篇 |
2012年 | 212篇 |
2011年 | 252篇 |
2010年 | 149篇 |
2009年 | 125篇 |
2008年 | 208篇 |
2007年 | 230篇 |
2006年 | 167篇 |
2005年 | 159篇 |
2004年 | 154篇 |
2003年 | 121篇 |
2002年 | 103篇 |
2001年 | 45篇 |
2000年 | 26篇 |
1999年 | 38篇 |
1998年 | 34篇 |
1997年 | 36篇 |
1996年 | 39篇 |
1995年 | 26篇 |
1994年 | 35篇 |
1993年 | 50篇 |
1992年 | 20篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 19篇 |
1988年 | 31篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 49篇 |
1984年 | 45篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 28篇 |
1979年 | 25篇 |
1978年 | 27篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1975年 | 13篇 |
1974年 | 21篇 |
排序方式: 共有3776条查询结果,搜索用时 15 毫秒
141.
Destri GL Keller TF Catellani M Punzo F Jandt KD Marletta G 《Langmuir : the ACS journal of surfaces and colloids》2012,28(11):5257-5266
The nanostructure of thermally annealed thin films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends on hydrophobic and hydrophilic substrates was studied to unravel the relationship between the substrate properties and the phase structure of polymer blends in confined geometry. Indeed, the nature of the employed substrates was found to affect the extent of phase separation, the PCBM aggregation state and the texture of the whole system. In particular, annealing below the melting temperature of the polymer yielded the formation of PCBM nanometric crystallites on the hydrophobic substrates, while mostly amorphous microscopic aggregates were formed on the hydrophilic ones. Moreover, while an enhanced in-plane orientation of P3HT lamellae was promoted on hydrophobic substrates, a markedly tilted geometry was produced on the hydrophilic ones. The observed effects were interpreted in terms of a simple model connecting the interface free energy for the blend films to the different polymer chain mobility and diffusion velocity of PCBM molecules on the different substrates. 相似文献
142.
Valenti G Rampazzo E Bonacchi S Khajvand T Juris R Montalti M Marcaccio M Paolucci F Prodi L 《Chemical communications (Cambridge, England)》2012,48(35):4187-4189
Colour emission of core-shell silica-PEG nanoparticles in water is tuned with an electrochemically induced energy transfer approach. The lack of solubility problems, side electrochemical reactions involving donors and acceptors within the nanoparticle, and the possibility of using many classes of dyes in ECL applications confirm the validity of this strategy. 相似文献
143.
A Practical Synthesis of 1,4,7,10-Tetraaza-Cyclododecane,A Pivotal Precursor for MRI Contrast Agents
A practical preparation of the versatile macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) was developed starting from cheap and easily available starting materials as ethylenediamine and glyoxal. 相似文献
144.
The synthesis of the methyl esters of optically pure trans and cis 4-guanidinocyclohexylglycine as rigid analogues of D-arginine methyl ester are described. 相似文献
145.
The synthesis of the title compound is described. The key-step is the photochemical coupling between 5-iodo-2-thienylcarbaldehyde and 2-bromothio-phene to give 5-bromo-2,2′-bithienyl-5′-carbaldehyde. 相似文献
146.
S-methyl dinucleoside phosphorothioates are prepared from 0-2,4-dichlorophenyl S-methyl nucleoside phosphorothioates by selective removal of the transient 0-2,4-dichlorophenyl protecting group followed by condensation with appropriate nucleosides in the presence of MSNT activating reagent. 相似文献
147.
Dr. Yuexia Wang Dr. Giovanni Barcaro Dr. Fabio R. Negreiros Dr. Thierry Visart de Bocarmé Dr. Mathieu Moors Dr. Norbert Kruse Dr. Marc Hou Dr. Alessandro Fortunelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):406-413
Carbon adsorption on various Ni surfaces is investigated as a function of coverage via a combination of first‐principles simulations and field emission microscope experiments. It is found that carbon can be efficiently stored as subsurface carbides, but with different energetics on differently oriented surfaces depending on their compactness and density of adsorption sites. In the resulting morphological reshaping, {113} facets are predicted to grow at the expense of {111} and {100} facets, in excellent agreement with experimental observations. Moreover, at high coverage on the {113} surface the carbon adsorption energy passes through a maximum after which a structural crossover is realized such that carbon atoms tend to ascend to the surface to form one‐dimensional chains (which are the precursors of graphitic nanostructures). This rationalizes the experimental observation of an incubation time between carbon storage and the beginning of catalytic growth, and provides insight into the early stages (nucleation mechanism) of carbon nanotubes on Ni nanoparticles. 相似文献
148.
Marco Cespi Luca Casettari Giulia Bonacucina Gianfabio Giorgioni Diego R Perinelli Giovanni Filippo Palmieri 《先进技术聚合物》2013,24(11):1018-1024
This paper deals with a new application of diblock methoxy polyethylene glycol‐polylactide block copolymers, a class of synthetic biomaterials largely studied in the pharmaceutical and biomedical fields owing to their favorable properties such as biocompatibility, biodegradability, low immunogenicity, and good mechanical properties. In this work, these materials were evaluated as additives for gastro‐soluble pharmaceutical coating aimed to reduce film stiffness and water permeability. Two copolymers with different polylactide chain lengths were synthesized and characterized in term of molecular weight and solid‐state properties. A series of free films with different hypromellose/copolymers ratio were prepared and characterized in terms of appearance, components miscibility, plasticity, and water vapor permeability. The obtained results demonstrate that copolymers effectively influence hypromellose film properties according to their concentration and molecular weight. Specifically, the addition of the copolymer with a molecular weight of 6.5 kDa in a ratio hypromellose:polymer 5:1, allowed to obtain films with good appearance, improved plasticization, and water permeability properties. For higher molecular weight, copolymer or different ratios was not possible to observe the improvement of all the properties at the same time. The results also make possible to define the critical features to improve in order to use block copolymers as additive in hypromellose film coating. The availability of new water‐soluble additives able to work as plasticizer and moisture sealer in polymeric films represents an important progress not only in the field of pharmaceutical coating but also in that of food coatings, as for example in the formulation of edible films. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
149.
Giuseppe Leone Antonella Caterina Boccia Giovanni Ricci Antonino Giarrusso Lido Porri 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3227-3232
(E)‐1,3‐Pentadiene (EP) and (E)‐2‐methyl‐1,3‐pentadiene (2MP) were polymerized to cis‐1,4 polymers with homogeneous and heterogeneous neodymium catalysts to examine the influence of the physical state of the catalyst on the polymerization stereoselectivity. Data on the polymerization of (E)‐1,3‐hexadiene (EH) are also reported. EP and EH gave cis‐1,4 isotactic polymers both with the homogeneous and with the heterogeneous system, whereas 2MP gave an isotactic cis‐1,4 polymer with the heterogeneous catalyst and a syndiotactic cis‐1,4 polymer, never reported earlier, with the homogeneous one. For comparison, the results obtained with the soluble CpTiCl3‐based catalyst (Cp = cyclopentadienyl), which gives cis‐1,4 isotactic poly(2MP), are examined. A tentative interpretation is given for the mechanism of the formation of the stereoregular polymers obtained and a complete NMR characterization of the cis‐1,4‐syndiotactic poly(2MP) is reported. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3227–3232 相似文献
150.
Julia Vallejo Alejandro Pascual‐Álvarez Dr. Joan Cano Dr. Isabel Castro Prof. Dr. Miguel Julve Prof. Dr. Francesc Lloret Dr. J. Krzystek Prof. Dr. Giovanni De Munno Dr. Donatella Armentano Prof. Dr. Wolfgang Wernsdorfer Dr. Rafael Ruiz‐García Dr. Emilio Pardo 《Angewandte Chemie (International ed. in English)》2013,52(52):14075-14079