全文获取类型
收费全文 | 6802篇 |
免费 | 404篇 |
国内免费 | 21篇 |
专业分类
化学 | 4794篇 |
晶体学 | 16篇 |
力学 | 185篇 |
数学 | 1073篇 |
物理学 | 1159篇 |
出版年
2023年 | 85篇 |
2022年 | 42篇 |
2021年 | 119篇 |
2020年 | 148篇 |
2019年 | 139篇 |
2018年 | 106篇 |
2017年 | 100篇 |
2016年 | 313篇 |
2015年 | 244篇 |
2014年 | 253篇 |
2013年 | 391篇 |
2012年 | 414篇 |
2011年 | 429篇 |
2010年 | 290篇 |
2009年 | 269篇 |
2008年 | 365篇 |
2007年 | 336篇 |
2006年 | 336篇 |
2005年 | 318篇 |
2004年 | 267篇 |
2003年 | 200篇 |
2002年 | 220篇 |
2001年 | 121篇 |
2000年 | 102篇 |
1999年 | 105篇 |
1998年 | 86篇 |
1997年 | 110篇 |
1996年 | 96篇 |
1995年 | 93篇 |
1994年 | 61篇 |
1993年 | 67篇 |
1992年 | 42篇 |
1991年 | 46篇 |
1990年 | 42篇 |
1989年 | 35篇 |
1988年 | 27篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 31篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 32篇 |
1980年 | 27篇 |
1979年 | 26篇 |
1978年 | 31篇 |
1977年 | 35篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 26篇 |
1973年 | 28篇 |
排序方式: 共有7227条查询结果,搜索用时 31 毫秒
1.
2.
3.
Markus Bödenler Ludovic de Rochefort P. James Ross Nicolas Chanet Geneviève Guillot Gareth R. Davies 《Molecular physics》2019,117(7-8):832-848
ABSTRACTFast field-cycling (FFC) nuclear magnetic resonance relaxometry is a well-established method to determine the relaxation rates as a function of magnetic field strength. This so-called nuclear magnetic relaxation dispersion gives insight into the underlying molecular dynamics of a wide range of complex systems and has gained interest especially in the characterisation of biological tissues and diseases. The combination of FFC techniques with magnetic resonance imaging (MRI) offers a high potential for new types of image contrast more specific to pathological molecular dynamics. This article reviews the progress in FFC-MRI over the last decade and gives an overview of the hardware systems currently in operation. We discuss limitations and error correction strategies specific to FFC-MRI such as field stability and homogeneity, signal-to-noise ratio, eddy currents and acquisition time. We also report potential applications with impact in biology and medicine. Finally, we discuss the challenges and future applications in transferring the underlying molecular dynamics into novel types of image contrast by exploiting the dispersive properties of biological tissue or MRI contrast agents. 相似文献
4.
Werner Leißner 《Results in Mathematics》1991,20(1-2):530-537
5.
Hans Maaß 《Mathematische Annalen》1941,118(1):312-318
Ohne Zusammenfassung 相似文献
6.
7.
Starch belongs to the polyglucan group. This type of polysaccharide shows a broad β-relaxation process in dielectric spectra at low temperatures, which has its molecular origin in orientational motions of sugar rings via glucosidic linkages. This chain dynamic was investigated for α(1,4)-linked starch oligomers with well-defined chain lengths of 2, 3, 4, 6, and 7 anhydroglucose units (AGUs) and for α(1,4)-polyglucans with average degrees of polymerization of 5, 10, 56, 70, and so forth (up to 3000; calculated from the mean molecular weight). The activation energy (Ea) of the segmental chain motion was lowest for dimeric maltose (Ea = 49.4 ± 1.3 kJ/mol), and this was followed by passage through a maximum at a degree of polymerization of 6 (Ea = 60.8 ± 1.8 kJ/mol). Subsequently, Ea leveled off at a value of about 52 ± 1.5 kJ/mol for chains containing more than 100 repeating units. The results were compared with the values of cellulose-like oligomers and polymers bearing a β(1,4)-linkage. Interestingly, the shape of the Ea dependency on the chain length of the molecules was qualitatively the same for both systems, whereas quantitatively the starch-like substances generally showed higher Ea values. Additionally, and for comparison, three cyclodextrins were measured by dielectric relaxation spectroscopy. The ringlike molecules, with 6, 7, and 8 α(1,4)-linked AGUs, showed moderately different types of dielectric spectra. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 188–197, 2004 相似文献
8.
In order to change the ion-exchange selectivity of anion-exchange resin, the surface of a gel-type anion exchange resin was modified with anionic polyelectrolyte, polystyrenesulfonic acid. Using this modified resin, the ion-exchange rate of nitrate was little decreased, but that of sulfate was evidently decreased. It is considered that the ion-exchange reaction of the multivalent anion is suppressed by the greater electrostatic repulsive force against the modification layer than that against the monovalent anion. Thus, this modified resin may be suitable for the selective separation of monovalent anions. The influence of the modified condition on the ion-exchange rate was examined. Furthermore, this modified resin was used to separate nitrate ions from sulfate ions in the aqueous solution. 相似文献
9.
10.