全文获取类型
收费全文 | 370篇 |
免费 | 13篇 |
专业分类
化学 | 253篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 58篇 |
物理学 | 60篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 27篇 |
2012年 | 12篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 24篇 |
2007年 | 33篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 25篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
1963年 | 2篇 |
1960年 | 2篇 |
1936年 | 2篇 |
1929年 | 1篇 |
1920年 | 1篇 |
1897年 | 1篇 |
排序方式: 共有383条查询结果,搜索用时 15 毫秒
121.
A recent paper described the overall 5-endo cyclisation of homoallylic sulfonamides to give pyrrolidines. This reaction was also used to prepare polycyclic systems. Mass spectrometric analysis using classical electron ionisation spectra and accurate mass measurement played a vital role in confirming the proposed structures for the products. These materials were not amenable to newer mass spectrometric methods and this study shows the continuing importance of older techniques. 相似文献
122.
123.
124.
Shi Z Olson CA Kallenbach NR Sosnick TR 《Journal of the American Chemical Society》2002,124(47):13994-13995
The contribution of amide related hydrogen bonds to protein stability has recently been evaluated using the "Cm experiment", which measures the D/H amide isotope effect in proteins. We show here using isolated alpha-helical peptides that there is a significant effect of denaturant concentration on the measured D/H isotope effect, and that valid comparison of different proteins requires correcting for differences in denaturant (GdmHCl) concentration. Finally our results suggest that H-bonds in an isolated alpha-helix may contribute more to helix stability because of less strain compared to those in helical proteins and that the buried helical H-bonds in helical proteins are not necessarily energetically more favorable than solvent exposed H-bonds in isolated helices. 相似文献
125.
Detailed studies of the structures formed by the electrodeposition of atomic layers of Te on Au(1 1 1) surfaces from aqueous solutions were performed using in situ scanning tunneling microscopy (STM), as well as by UHV-EC techniques such as low energy electron diffraction and Auger electron spectroscopy. There are two features in the voltammetry that may be considered underpotential deposition (UPD). However, from the voltammetry, it is clear that the deposition process is kinetically slow, and from this study it appears that several atomic layer structures are actually formed at overpotentials. Prior to deposition, a surface excess of a tellurium oxide species coats the surface. This layer is then converted to a Au(1 1 1)(√3×√3)R30°–Te structure with an array of domain walls, at 1/3 ML. The initial structure appears to have a symmetric array of walls, resulting in a (13×13) periodicity, which then converts to a less symmetric structure where the domain walls form rhombi, with a larger periodicity. During the second UPD feature, the coverage increases, forming a (√7×√13) unit cell at 0.36 ML and then a (3×3) at 0.44 ML. Commensurate with the formation of these higher coverage structures, a roughening transition takes place, where the surface becomes pitted, resulting in about 40% of the surface being covered with single atom deep pits. This process appears to be related to the pits formed in the surfaces of self-assembled monolayers (SAM) of thiols on Au surfaces, and layers of Se and S on Au surfaces. Several theories have been suggested to account for these pits. The model that appears to best explain the pits is based on shrinking of the size of the underlying Au atoms, reconstructing the underlying Au. There also appears to be a high coverage structure, near 0.9 ML, that forms at potentials near where the (3×3) forms, but only by holding the potential for an extended period of time. Subsequent dissolution of this high coverage structure produces domains of disordered Te atoms, which gradually decrease in coverage until the (3×3) is again formed at 0.44 ML. 相似文献
126.
Joke De Gelder Kris De Gussem Peter Vandenabeele Luc Moens 《Journal of Raman spectroscopy : JRS》2007,38(9):1133-1147
Raman spectra of biological materials are very complex, because they consist of signals from all molecules present in cells. In order to obtain chemical information from these spectra, it is necessary to know the Raman patterns of the possible components of a cell. In this paper, we present a collection of Raman spectra of biomolecules that can serve as references for the interpretation of Raman spectra of biological materials. We included the most important components present in a cell: (1) DNA and RNA bases (adenine, cytosine, guanine, thymine and uracil), (2) amino acids (glycine, L ‐alanine, L ‐valine, L ‐serine, L ‐glutamic acid, L ‐arginine, L ‐phenylalanine, L ‐tyrosine, L ‐tryptophan, L ‐histidine, L ‐proline), (3) fatty acids and fats (lauric acid, myristic acid, palmitic acid, stearic acid, 12‐methyltetradecanoic acid, 13‐methylmyristic acid, 14‐methylpentadecanoic acid, 14‐methylhexadecanoic acid, 15‐methylpalmitic acid, oleic acid, vaccenic acid, glycerol, triolein, trilinolein, trilinolenin), (4) saccharides (β‐D ‐glucose, lactose, cellulose, D ‐(+)‐dextrose, D ‐(+)‐trehalose, amylose, amylopectine, D ‐(+)‐mannose, D ‐(+)‐fucose, D ‐(−)‐arabinose, D ‐(+)‐xylose, D ‐(−)‐fructose, D ‐(+)‐galactosamine, N‐acetyl‐D ‐glucosamine, chitin), (5) primary metabolites (citric acid, succinic acid, fumarate, malic acid, pyruvate, phosphoenolpyruvate, coenzyme A, acetyl coenzyme A, acetoacetate, D ‐fructose‐6‐phosphate) and (6) others (β‐carotene, ascorbic acid, riboflavin, glutathione). Examples of Raman spectra of bacteria and fungal spores are shown, together with band assignments to the reference products. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
127.
128.
129.
A. M. Neville 《Applied Scientific Research》1960,9(1):71-84
Summary Test data on the recovery of creep of mortar specimens made with different cements are presented. It is shown that, whereas
creep depends on the strength of mortar (as influenced by the cement), the creep recovery is not a function of this strength.
From measurements on the change in weight of specimens, under load and free-standing, it is concluded that creep is not caused
by the movement of water from the cement paste into the surrounding medium. The possibility of creep being connected with
the removal of zeolitic water from calcium silicate hydrates is discussed, and reasons for the non-reversible character of
creep recovery are suggested. 相似文献
130.