全文获取类型
收费全文 | 672篇 |
免费 | 10篇 |
国内免费 | 5篇 |
专业分类
化学 | 514篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 69篇 |
物理学 | 94篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 30篇 |
2012年 | 34篇 |
2011年 | 47篇 |
2010年 | 20篇 |
2009年 | 28篇 |
2008年 | 48篇 |
2007年 | 52篇 |
2006年 | 49篇 |
2005年 | 44篇 |
2004年 | 36篇 |
2003年 | 31篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1969年 | 4篇 |
1925年 | 2篇 |
排序方式: 共有687条查询结果,搜索用时 171 毫秒
681.
Shillito LM Almond MJ Wicks K Marshall LJ Matthews W 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,72(1):120-125
A range of archaeological samples have been examined using FT-IR spectroscopy. These include suspected coprolite samples from the Neolithic site of Catalh?yük in Turkey, pottery samples from the Roman site of Silchester, UK and the Bronze Age site of Gatas, Spain and unidentified black residues on pottery sherds from the Roman sites of Springhead and Cambourne, UK. For coprolite samples the aim of FT-IR analysis is identification. Identification of coprolites in the field is based on their distinct orange colour; however, such visual identifications can often be misleading due to their similarity with deposits such as ochre and clay. For pottery the aim is to screen those samples that might contain high levels of organic residues which would be suitable for GC-MS analysis. The experiments have shown coprolites to have distinctive spectra, containing strong peaks from calcite, phosphate and quartz; the presence of phosphorus may be confirmed by SEM-EDX analysis. Pottery containing organic residues of plant and animal origin has also been shown to generally display strong phosphate peaks. FT-IR has distinguished between organic resin and non-organic compositions for the black residues, with differences also being seen between organic samples that have the same physical appearance. Further analysis by GC-MS has confirmed the identification of the coprolites through the presence of coprostanol and bile acids, and shows that the majority of organic pottery residues are either fatty acids or mono- or di-acylglycerols from foodstuffs, or triterpenoid resin compounds exposed to high temperatures. One suspected resin sample was shown to contain no organic residues, and it is seen that resin samples with similar physical appearances have different chemical compositions. FT-IR is proposed as a quick and cheap method of screening archaeological samples before subjecting them to the more expensive and time-consuming method of GC-MS. This will eliminate inorganic samples such as clays and ochre from GC-MS analysis, and will screen those samples which are most likely to have a high concentration of preserved organic residues. 相似文献
682.
Wu Ma Silvia Chen Wendy Fitzgerald Dragan Maric Hsingch J. Lin Thomas J. O'Shaughnessy Jeremy Kelly Xiu-Huai Liu Jeffery L. Barker 《Macromolecular Symposia》2005,227(1):327-334
Stem and progenitor cells isolated from the embryonic rat cerebral cortex were immobilized by matrix entrapment in three-dimensional (3D) Type I collagen gels, and cultured in serum-free medium containing basic fibroblast growth factor. The cells trapped within the collagen networks actively proliferated and formed clone-like aggregates. Neurons were the first differentiated cells to appear within the aggregates, followed by generation of astrocytes and oligodendrocytes. In addition, necrotic cores were developed as the aggregate diameter increased and cell viability declined significantly after 3 weeks in culture. To overcome these problems, the cell-collagen constructs were transferred to Rotary Wall Vessel bioreactors for up to 10 weeks. In the rotary culture, the collagen gels compacted 3-4 folds and a long-term growth and differentiation of neural stem and progenitor cells was dynamically maintained. Remarkably, the cell-collagen constructs formed a complex two-layered structure that superficially emulated to a certain extent the cerebral cortex of the embryonic brain in architecture and functionality. The engineered 3D tissue-like constructs displaying characteristic properties of neuronal circuits may have potential use in tissue replacement therapy for injured brain and spinal cord. 相似文献
683.
684.
Wendy M. Simon Hernando A. Trujillo Erin T. Pelkey Gordon W. Gribble Jerry P. Jasinski 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):461-462
Crystal structure determination of the title molecule, C30H24N2O2S, reveals that the pyrrole ring in this fused heterocycle, although presumably strained and reactive in cycloaddition reactions, does not differ appreciably from N‐methylpyrrole except for a shorter C—C single bond [1.409 (4) Å] in the pyrrole ring. 相似文献
685.
686.
Single crystals of (Me4N)4 [UO2(CO3)3]·8H2O are grown by slow evaporation (25 °C, 6 weeks) of an aqueous solution of uranyl 1‐hydroxyethane‐1,1‐diphosphonate and Me4NOH. 相似文献
687.