全文获取类型
收费全文 | 126397篇 |
免费 | 1595篇 |
国内免费 | 474篇 |
专业分类
化学 | 69360篇 |
晶体学 | 2039篇 |
力学 | 4989篇 |
综合类 | 5篇 |
数学 | 12363篇 |
物理学 | 39710篇 |
出版年
2016年 | 1311篇 |
2015年 | 1024篇 |
2014年 | 1365篇 |
2013年 | 4863篇 |
2012年 | 3473篇 |
2011年 | 4487篇 |
2010年 | 2791篇 |
2009年 | 2561篇 |
2008年 | 3997篇 |
2007年 | 4070篇 |
2006年 | 4116篇 |
2005年 | 4042篇 |
2004年 | 3509篇 |
2003年 | 3190篇 |
2002年 | 3084篇 |
2001年 | 3599篇 |
2000年 | 2702篇 |
1999年 | 2212篇 |
1998年 | 1895篇 |
1997年 | 1887篇 |
1996年 | 1831篇 |
1995年 | 1803篇 |
1994年 | 1578篇 |
1993年 | 1561篇 |
1992年 | 1778篇 |
1991年 | 1765篇 |
1990年 | 1693篇 |
1989年 | 1698篇 |
1988年 | 1697篇 |
1987年 | 1687篇 |
1986年 | 1610篇 |
1985年 | 2158篇 |
1984年 | 2294篇 |
1983年 | 1902篇 |
1982年 | 2237篇 |
1981年 | 2058篇 |
1980年 | 2091篇 |
1979年 | 2077篇 |
1978年 | 2208篇 |
1977年 | 2111篇 |
1976年 | 2138篇 |
1975年 | 2075篇 |
1974年 | 1910篇 |
1973年 | 2124篇 |
1972年 | 1287篇 |
1971年 | 976篇 |
1970年 | 918篇 |
1969年 | 927篇 |
1968年 | 1056篇 |
1967年 | 1106篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
32.
33.
Gas-phase 21Ne nuclear magnetic resonance spectra were measured at the natural abundance of 21Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B0 = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the 21Ne nuclear magnetic moment, μ(21Ne) = 0.6617774(10) μN. The present value of μ(21Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(21Ne). 相似文献
34.
35.
36.
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
37.
38.
39.
W. L. Liang B. K. A. Ngoi L. E. N. Lim K. Venkatakrishnan C. W. Hee 《Optics & Laser Technology》2003,35(4):285-290
In this paper, integration of interference phenomenon into femtosecond laser micromachining was reported as the femtosecond laser pulses were reshaped spatially to perform ablation. The generation of circular interference pattern was demonstrated by overlapping infrared femtosecond laser pulses. The interference pattern was subsequently focused on a copper substrate to ablate microstructures of concentric circular rings. The present technique is expected to open up new applications in the areas of rapid fabrication of micro-Fresnel lenses, hybrid microlenses and lens arrays. 相似文献
40.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献