全文获取类型
收费全文 | 297篇 |
免费 | 4篇 |
专业分类
化学 | 204篇 |
晶体学 | 2篇 |
力学 | 9篇 |
数学 | 30篇 |
物理学 | 56篇 |
出版年
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 23篇 |
2012年 | 13篇 |
2011年 | 18篇 |
2010年 | 8篇 |
2009年 | 13篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1995年 | 5篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1911年 | 2篇 |
排序方式: 共有301条查询结果,搜索用时 15 毫秒
61.
Dinabandhu Pramanick Santi R. Palit 《Journal of polymer science. Part A, Polymer chemistry》1968,6(8):2179-2185
The ammonia–halogen redox system has proved a promising initiator for polymerizing a number of vinyl monomers in aqueous media. Chlorine and bromine are most efficient, whereas iodine fails to initiate polymerization, probably due to its inhibitive tendency. Endgroups are halogen and amine and total about 0.5 per chain. On the basis of results of endgroup analysis, a mechanism of initiation through halogen and amine radicals, mainly through hydrogen atoms, is suggested. Consistent with the proposed mechanism the endgroup profile changes significantly with changes in pH. 相似文献
62.
Popovici M Gich M Roig A Casas L Molins E Savii C Becherescu D Sort J Suriñach S Muñoz JS Baró MD Nogués J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1425-1429
Monoliths of iron oxide-silica aerogel nanocomposites have been synthesized using a novel synthesis route which consists of impregnating silica wet gels with anhydrous iron(II) precursors followed by ethanol supercritical drying of the gels. The process yields aerogels exhibiting high porosity, large surface areas (approximately 900 m2/g), rather low densities (approximately 0.6 g/cm3), and a homogeneous distribution of single-phase maghemite, gamma-Fe2O3, nanoparticles with average sizes in the 7-8 nm range. Remarkably, the gamma-Fe2O3 nanoparticles are obtained in the as-dried state without the need of postannealing. The nanoparticles are mostly superparamagnetic at room temperature but become blocked in a ferrimagnetic state at lower temperatures. 相似文献
63.
S. Cesca P. V. Duranti A. Roggero G. Santi M. Bruzzone 《Journal of polymer science. Part A, Polymer chemistry》1974,12(6):1209-1232
The terpolymerization of ethylene, propylene, and methylcyclopentadienyl-5-endonorborn-2-enylmethane (III) by means of different vanadium-based coordination catalysts was investigated. The structure of III and its isomeric composition was studied by using vapor-phase chromatography, mass spectrometry, and NMR, infrared, and ultraviolet spectroscopy. The catalyst system V Acac3–Et2AlCl was used under different conditions, and the influence of several variables regulating the terpolymerization process were related to the properties of the resulting terpolymers (EPTM). The insertion of III into EPTM chains takes place randomly and does not influence the random distribution of comonomers. The selective opening of the norbornene double bond of III has been demonstrated by use of 2,3-dihydro-III as model compound. Tritiated III gave a radiochemical titer of unsaturation in excellent agreement with the value deduced from ultraviolet measurements. The influence of Lewis bases added to VAcac3–Et2AlCl catalyst is discussed. 相似文献
64.
S. Croft L.G. Evans A. Favalli D.K. Hauck D. Henzlova P. Santi 《Radiation measurements》2012,47(7):467-474
A standard nondestructive assay technique for determining the mass of plutonium in an item is passive neutron coincidence counting. In passive neutron coincidence counting, the dead time or rate loss corrections for the singles and doubles neutron counting rates are routinely made using empirical relationships that are based on the design and performance of the individual counter used to make the measurements. The empirical methods were developed ahead of any supporting theory for dead time losses and have worked well to date for the majority of safeguards measurement scenarios. Modern applications using highly efficient systems with short neutron lifetimes together with the challenges posed by highly multiplying items mean dead time corrections of higher fidelity are needed. While many attempts have been made to develop dead time corrections that are based on the physical principles of the measurements being performed, these corrections have often been found to be difficult to implement in a real system. For instance, Matthes and Haas developed an approach in 1985 which did not gain favor largely because the form of the doubles correction apparently required numerical integration which was difficult to implement with the computer technology of that time. A recent review into the approach that was developed by Matthes and Haas has determined that a straightforward analytical expression can be derived for the doubles correction that is similar to the singles rate correction that was developed in their original work. An analysis of the expressions is presented here to show how they relate to the traditional empirical methods. Further, we illustrate their implications and limitations. For instance the empirical methods do not address within burst losses i.e. rate related losses due to the correlated neutron bursts from fission, whereas the Matthes and Hass expression for singles counting does exhibit such an effect. 相似文献
65.
Marcello Tiecco Lorenzo Testaferri Andrea Temperini Luana Bagnoli Francesca Marini Claudio Santi 《合成通讯》2013,43(12):2167-2179
Simple alkenes react with PhSeOTf and NaN3 in MeCN to afford β-phenylseleno azides as the result of a stereospecific trans addition. The regioselectivity of the process is determined by the structure of the alkene. 相似文献
66.
67.
Dr. Haibo Mei Dr. Jianlin Han Dr. Santos Fustero Mercedes Medio-Simon Daniel M. Sedgwick Dr. Claudio Santi Dr. Renzo Ruzziconi Dr. Vadim A. Soloshonok 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(51):11797-11819
Over the last two decades, fluorine substitution has become one of the essential structural traits in modern pharmaceuticals. Thus, about half of the most successful drugs (blockbuster drugs) contain fluorine atoms. In this review, we profile 17 fluorine-containing drugs approved by the food and drug administration (FDA) in 2018. The newly approved pharmaceuticals feature several types of aromatic F and CF3, as well as aliphatic (CF2) substitution, offering advances in the treatment of various diseases, including cancer, HIV, malarial and smallpox infections. 相似文献
68.
Anna Demurtas Silvia Pescina Sara Nicoli Patrizia Santi Cristina Padula 《Biomedical chromatography : BMC》2019,33(11)
Crisaborole is a boron compound recently approved by the US Food and Drug Administration as a 2% ointment for the treatment of mild to moderate atopic dermatitis. This work describes a simple method for the quantification of the drug in the skin layers at the end of in‐vitro permeation experiments. Chromatographic separation was carried out on a reverse‐phase C18 column using a mixture of trifluoroacetic acid 0.05%–acetonitrile (55:45, v/v) as mobile phase, pumped at 1 ml/min. Column temperature was 35°C and UV detection was performed at 250 nm. The method was linear in the range of concentration from 0.06 to 6 μg/ml (R2 = 1) and was selective, precise and accurate. Depending on the solvent used, the LOQ ranged from 0.014 to 0.030 μg/ml and the LOD from 0.005 to 0.010 μg/ml. The extraction from all the skin layers was quantitative. The developed method was successfully tested in an in‐vitro permeation study, proving to be an effective tool in the development of new formulations containing crisaborole. 相似文献
69.
Our aim is to investigate spaces with σ-discrete and meager dense sets, as well as selective versions of these properties. We construct numerous examples to point out the differences between these classes while answering questions of Tkachuk [22], Hutchison [13] and the authors of [7]. 相似文献
70.
Yindee Suttisawat Pramoch Rangsunvigit Boonyarach Kitiyanan Santi Kulprathipanja 《Journal of Solid State Electrochemistry》2010,14(10):1813-1819
Sodium aluminum hydride or sodium alanate (NaAlH4) has been considered as a potential material for hydrogen storage. Although its theoretical hydrogen storage capacity is
5.5 wt.% at 250 °C, the material still has its drawback in the regeneration issue. With the use of certain catalysts, the
regeneration problem can somewhat be alleviated with added benefits in the decrease in the hydrogen decomposition temperature
and the increase in the decomposition rate. This work summarizes what we have learned from the decomposition of NaAlH4 with/without catalysts and co-dopants. The decomposition was carried out using a thermovolumetric apparatus. For the tested
catalysts—HfCl4, VCl3, TiO2, TiCl3, and Ti—the decomposition temperature of the hydride decreases; however, they affect the temperature in the subsequent cycles
differently and TiO2 appears to have the most positive effect on the temperature. Sample segregation and the morphological change are postulated
to hinder the reversibility of the hydride. To prevent the problems, co-dopants—activated carbon, graphite, and MCM-41—were
loaded. Results show that the hydrogen reabsorption capacity of HfCl4- and TiO2-doped NaAlH4 added with the co-dopants increases 10–50% compared with that without a co-dopant, and graphite is the best co-dopant in
terms of reabsorption capacity. In addition, the decomposition temperature in the subsequent cycles of the co-dopant doped
samples decreases about 10–15 °C as compared to the sample without a co-dopant. Porosity and large surface area of the co-dopant
may decrease the segregation of bulk aluminum after the desorption and improve hydrogen diffusion in/out bulk of desorbed/reabsorbed
samples. 相似文献