全文获取类型
收费全文 | 3014篇 |
免费 | 98篇 |
国内免费 | 11篇 |
专业分类
化学 | 1978篇 |
晶体学 | 12篇 |
力学 | 89篇 |
数学 | 395篇 |
物理学 | 649篇 |
出版年
2024年 | 4篇 |
2023年 | 26篇 |
2022年 | 38篇 |
2021年 | 97篇 |
2020年 | 82篇 |
2019年 | 87篇 |
2018年 | 66篇 |
2017年 | 64篇 |
2016年 | 138篇 |
2015年 | 101篇 |
2014年 | 126篇 |
2013年 | 192篇 |
2012年 | 182篇 |
2011年 | 236篇 |
2010年 | 136篇 |
2009年 | 199篇 |
2008年 | 180篇 |
2007年 | 197篇 |
2006年 | 149篇 |
2005年 | 116篇 |
2004年 | 95篇 |
2003年 | 69篇 |
2002年 | 64篇 |
2001年 | 58篇 |
2000年 | 54篇 |
1999年 | 36篇 |
1998年 | 27篇 |
1997年 | 31篇 |
1996年 | 41篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1975年 | 9篇 |
1973年 | 4篇 |
1916年 | 3篇 |
排序方式: 共有3123条查询结果,搜索用时 250 毫秒
101.
Carla Marisa Brito Carvalho Marta Akemi FujitaTimothy John Brocksom Kleber Thiago de Oliveira 《Tetrahedron》2013
New β-fused uracil-porphyrin conjugates were synthesized by the tetramerization of uracil-pyrroles under acidic conditions. Two different synthetic approaches were systematically studied in order to evaluate their efficiency, as well as the possibility to obtain a single regioisomer. Metallation effects were studied for aggregation in solution, and preliminary photophysical experiments were also performed in order to evaluate the potential of these new compounds. 相似文献
102.
103.
104.
105.
106.
Elionai Cassiana de Lima Gomes Izabella Ercole de Carvalho Silvia Ligório Fialho Jamile Barbosa Maria Irene Yoshida Armando da Silva Cunha Júnior 《Journal of Thermal Analysis and Calorimetry》2018,131(3):2123-2128
Most of the pharmaceutical products are formulated as solid dosage form, which may present drug–excipient interactions that lead to changes in the chemical nature of the drug, such as solubility and bioavailability and may compromise its safety and effectiveness. Differential scanning calorimetry (DSC) is a widely used method for the rapid evaluation of the drug-excipient compatibility and the stability of the mixture formed; however, there is no consensus on the preparation methods of the drug–excipient mixtures. The aim of this study was to investigate the influence of the mixing method on the drug–excipient compatibility studies by means of DSC analysis, using tenofovir disoproxil fumarate as a drug model. Statistical analysis revealed significant differences in the heat of fusion of the drug in the mixtures prepared by several mixing methods. Vortex Mixer with a Pop-Off Cup used for 3 min proved to be very satisfactory for these studies. A polymorphic transition was observed in the mixture prepared with the mortar and pestle. Therefore, this method should be avoided since it may induce errors in the interpretation of DSC results. In this way, the mixing method used to prepare a mixture for studies of interactions between the API and the excipients in a pharmaceutical formulation has a great influence on the results and it must be chosen carefully. 相似文献
107.
Giovanni Amelino-Camelia Leonardo Barcaroli Niccoló Loret 《International Journal of Theoretical Physics》2012,51(11):3359-3375
We investigate some aspects of relativistic classical theories with “relative locality”, in which pairs of events established to be coincident by nearby observers may be described as non-coincident by distant observers. While previous studies focused mainly on the case of longitudinal relative locality, where the effect occurs along the direction connecting the distant observer to the events, we here focus on transverse relative locality, in which instead the effect is found in a direction orthogonal to the one connecting the distant observer to the events. Our findings suggest that, at least for theories of free particles, transverse relative locality is as significant as longitudinal relative locality both conceptually and quantitatively. And we observe that “dual gravity lensing” can be viewed as one of two components of transverse relative locality. We also speculate about a type of spacetime noncommutativity for which transverse relative locality could be particularly significant. 相似文献
108.
109.
110.
Pier G. Desideri Luciano Lepri Roberto Udisti Leonardo Checchini Massimo Del Bubba Renato Cini 《International journal of environmental analytical chemistry》2013,93(3-4):331-351
Abstract Organic compounds extractable with n-hexane were identified and quantitatively determined in pack, surface and deep snow samples taken at different depths and collected at several altitudes above sea level from Antarctica during the 1993/94 Italian expedition. The comparison between the composition of organic compounds in snow and the ones in pack and sea-water samples pointed out that the three matrices substantially contain the same biogenic and anthropogenic organic compounds. The contribution of marine aerosol to organic content in the snow is confirmed by the enrichment ratios calculated for the more representative classes of identified compounds (n-alkanes, phthalates and low molecular weight alkylbenzenes). The changes in the composition of organic compounds in snow as the altitude increases seem to depend on the dimensional spectrum of the aerosol. Thus, smallest particles, richest in surfactant material, reach the highest altitudes. 相似文献