全文获取类型
收费全文 | 2354篇 |
免费 | 95篇 |
国内免费 | 12篇 |
专业分类
化学 | 2019篇 |
晶体学 | 10篇 |
力学 | 16篇 |
数学 | 242篇 |
物理学 | 174篇 |
出版年
2023年 | 16篇 |
2022年 | 43篇 |
2021年 | 61篇 |
2020年 | 62篇 |
2019年 | 55篇 |
2018年 | 29篇 |
2017年 | 43篇 |
2016年 | 89篇 |
2015年 | 75篇 |
2014年 | 84篇 |
2013年 | 125篇 |
2012年 | 161篇 |
2011年 | 178篇 |
2010年 | 100篇 |
2009年 | 101篇 |
2008年 | 143篇 |
2007年 | 136篇 |
2006年 | 149篇 |
2005年 | 120篇 |
2004年 | 103篇 |
2003年 | 95篇 |
2002年 | 84篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 21篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1973年 | 3篇 |
1958年 | 55篇 |
1957年 | 20篇 |
1934年 | 4篇 |
排序方式: 共有2461条查询结果,搜索用时 15 毫秒
991.
Steady-state fluorescence imaging can be used in conjunction with selective exogenous or endogenous fluorescent compounds for the diagnosis of skin lesions, for example cancer. Depending on the excitation and emission properties of the fluorescent compound used, various excitation and/or emission wavelengths can be chosen in order to allow fluorescence imaging. Unwanted background signals such as autofluorescence and scattering can decrease the image quality and, hence, the diagnosis potential of this imaging method. We have used an inexpensive dual excitation and/or emission wavelength approach in order to suppress the unwanted background signal and allow contrast enhanced fluorescence imaging. One excitation and/or emission wavelength is at the corresponding maximum of the fluorescent compound, while the second is at a nearby excitation/emission minimum. The first image contains the emission from the fluorescent compound used combined with the signal from the unwanted background. The second image provides an image of just the unwanted background signal. The difference of both images taken, thus gives a contrast enhanced image of the skin lesion. The method relies on the assumption that the background signal does not change significantly due to the small changes in wavelength for excitation or emission. Image ratio methods have already been applied towards diagnosis of basal cell carcinomas after administration of aminolevulinic acid-induced protoporphyin IX. In this study, we describe in vivo measurements in mice where the second image, usually the background signal only, contains new unwanted image data. This simple method can successfully resolve the desired image, thus demonstrating the versatility of the image processing procedure. 相似文献
992.
We consider an integrable Hamiltonian system with n degrees of freedom whose first integrals are invariant under the symplectic action of a compact Lie group G. We prove that the singular Lagrangian foliation associated to this Hamiltonian system is symplectically equivalent, in a G-equivariant way, to the linearized foliation in a neighborhood of a compact singular nondegenerate orbit. We also show that the nondegeneracy condition is not equivalent to the nonresonance condition for smooth systems. 相似文献
993.
Jean M. J. Tronchet Joëlle Ojha-Poncet Eva Winter-Mihaly Boris Kohler Michel Geoffroy 《Helvetica chimica acta》1977,60(3):888-891
Some more examples of stable free radicals of carbohydrate heterocyclic derivatives 2-Glycosyl-4,4,5,5-tetramethylimidazoline- 3-oxide-1-oxyls and 2-glycosyl-4,4,5,5-tetramethylimidazoline 1-oxyls have been prepared in nine carbohydrate series, which proves the generality of the method. The hyperfine coupling constant between the free electron and the α-proton of the glycosyl group is never very large (0-2.3 G) but a correlation between its value and the structure of the aglycone has been noted. Free radicals of that type, stable in aqueous solutions, are potentially interesting for biological studies. 相似文献
994.
Eva Lowen-Colebunders 《Acta Mathematica Hungarica》1984,44(3-4):181-189
995.
996.
997.
Photolabile linkers are very useful in the generation of combinatorial libraries as they offer compound cleavage under mild conditions directly into a solvent suitable for biological testing. Six new photolabile linkers have been developed which allow coupling of building blocks with a carboxy, amino, hydroxy and sulfonyl group. Photolytic cleavage of these building blocks will give libraries with carboxy, amido, methylamido, amino, ureido, hydroxy, aminocarbonyloxy and aminosulfonyl terminal groups. Coupling conditions for these reactions were elucidated and the photolytic cleavage reaction was studied. 相似文献
998.
Walter Dummler Eva Siegmund und Friedrich Hauzeur 《Fresenius' Journal of Analytical Chemistry》1988,330(4-5):374-375
Ohne Zusammenfassung
Diagnostic validity of the secretin-CCK test in the diagnosis of exocrine pancreatic insufficiency — results of a leaving-one-out-study相似文献
999.
1000.
Eva Ferrara Dentice 《Journal of Geometry》1996,55(1-2):73-85
In this paper a complete classification of finite matroids with one more hyperplane than points is obtained.Dedicated to Professor Maria Scafati Tallini on the occasion of her 65th birthday 相似文献