全文获取类型
收费全文 | 1121篇 |
免费 | 33篇 |
国内免费 | 10篇 |
专业分类
化学 | 645篇 |
晶体学 | 4篇 |
力学 | 35篇 |
数学 | 233篇 |
物理学 | 247篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 31篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 56篇 |
2012年 | 62篇 |
2011年 | 76篇 |
2010年 | 44篇 |
2009年 | 40篇 |
2008年 | 57篇 |
2007年 | 52篇 |
2006年 | 52篇 |
2005年 | 53篇 |
2004年 | 48篇 |
2003年 | 30篇 |
2002年 | 36篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 21篇 |
1993年 | 9篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 22篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1917年 | 4篇 |
排序方式: 共有1164条查询结果,搜索用时 0 毫秒
11.
S. J. Parry 《Journal of Radioanalytical and Nuclear Chemistry》1987,112(2):383-386
Cumulative neutron activation is used to determine mg/kg concentrations of gold in rock samples, weighing 10 g. Twenty 0.5 g replicates are irradiated in an epithermal-neutron flux for 5 s and counted for 14 s. The twenty spectra are summed, and gold is measured with the 279 keV gamma-ray of197mAu (7.2 s). Total analysis time for a 10 g sample is 400 s and detection limits around 2 mg/kg are achieved in gold ores, sulfides and silicates. 相似文献
12.
R. P. Hallett K. G. McKay S. P. Balm A. W. Allaf H. W. Kroto A. J. Stace 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,34(1):65-70
Reaction studies of carbon clustersC
n
in the rangen=8–37, produced by laser vaporisation in a supersonic nozzle, have been investigated using time-of-flight mass spectrometry. Clear differences in reaction products formed on hydrogenation are detected which show that even and odd clusters behave quite differently and furthermore thatat least two different types of even cluster appear to exist. The reactivity patterns for clusters C
n
withn=16, 18 and 22 are in a different class from those withn=20, 24, 26 ..., a behaviour consistent with the existence of closed cage fullerene structures for even clusters with 20 or more carbon atoms (other thann=22). 相似文献
13.
14.
Gordon McKay Stephen J. Allen Ian F. McConvey Michael S. Otterburn 《Journal of colloid and interface science》1981,80(2):323-339
A three-step model has been proposed for the adsorption of Astrazone Blue dye (Basic Blue 69) on peat. The initial rate of uptake of dye ions due to physical adsorption and chemisorption (ion exchange) has been correlated using a surface mass transfer coefficient. These coefficients have been determined and expressed in the dimensionless mass transfer form, Sh/Sc0.33, as a function of agitation, initial dye concentration, peat particle size range, dye solution temperature, and mass of peat. 相似文献
15.
16.
C. Yonezawa H. Matsue K. McKay P. Povinec 《Journal of Radioanalytical and Nuclear Chemistry》2001,248(3):719-725
Multi-element and isotopic analyses of oils and marine environmental samples were carried out to estimate a contamination source using a "finger printing" method. Elemental analyses were carried out using neutron-induced prompt gamma-ray analysis (PGA), instrumental neutron activation analysis (INAA) at the Japan Atomic Energy Research Institute, Tokai-mura, Japan (JAERI) and ICP-MS in the IAEA Marine Environment Laboratory, Monaco (MEL). Fifteen elements including light elements, H, B, N, Si and Ca, which cannot be determined by INAA and ICP-MS, were determined by PGA. A total of 47 elements were determined in the present study. The potential of PGA for the determination of isotopic ratios was tested by measuring 34S/32S ratios in oils. The evaluation of historical records of marine environmental conditions using annual bands in coral samples was also investigated. 相似文献
18.
We use molecular dynamics simulations to investigate the structure of the hydrated Na-Nafion membranes. The membrane is "prepared" by starting with the Nafion chains placed on a cylinder having the water inside it. Minimizing the energy of the system leads to a filamentary hydrophilic domain whose structure depends on the degree of hydration. At 5 wt % water the system does not have enough water molecules to solvate all the ions that could be formed by the dissociation of the -SO3Na groups. As a result, the -SO3Na groups aggregate with the water to form very small droplets that do not join into a continuous phase. The size of the droplets is between 5 and 8 A. As the amount of water present in the membrane is increased, the membrane swells, and SO3Na has an increasing tendency to dissociate into ions. Furthermore, a transition to a percolating hydrophilic network is observed. In the percolating structure, the water forms irregular curvilinear channels branching in all directions. The typical dimension of the cross section of these channels is about 10-20 A. Calculated neutron scattering from the simulated system is in qualitative agreement with experiment. In all simulations, the pendant sulfonated perfluorovinyl side chains of the Nafion hug the walls of the hydrophilic channel, while the sulfonate groups point toward the center of the hydrophilic phase. The expulsion of the side chains from the hydrophilic domain is favored because it allows better interaction between the water molecules. We have also examined the probability of finding water molecules around the Na+ and the -SO3(-) ions as well as the probability of finding other water molecules next to a given water molecule. These probabilities are much broader than those found in bulk water or for one ion in bulk water (calculated with the potentials used in the present simulation). This is due to the highly inhomogeneous nature of the material contained in the small hydrophilic pores. 相似文献
19.
20.