全文获取类型
收费全文 | 327篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
化学 | 203篇 |
晶体学 | 2篇 |
力学 | 19篇 |
数学 | 21篇 |
物理学 | 95篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 6篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 29篇 |
2010年 | 13篇 |
2009年 | 15篇 |
2008年 | 7篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有340条查询结果,搜索用时 390 毫秒
91.
Host phases of fallout239,240Pu and241Am were studied in the surface sediments obtained in 1994 from abyssal basins of relatively small area of the western North
Pacific. An analytical procedure involving sequential chemical extraction was employed for partitioning the host phases of
the nuclides in sediment into five fractions: (1) exchangeable (2) bound to carbonate, (3) bound to hydrous Fe-Mn oxides,
(4) bound to organic matter and (5) residual. Decrease of total239,240Pu concentration with decreasing association of239,240Pu with organic matter, high241Am/239,240Pu activity ratio in carbonate phase and somewhat high proportion of oxidized239,240Pu in leachable phases suggest a possibility of post-depositional diagenetic remobilization of Pu from sediment to water column. 相似文献
92.
Simple nitric acid leaching and alkali fusion techniques for the determination of the total content of fallout239,240Pu in deep-sea sediment were compared. Leaching neither with boiling conc. HNO3 nor with boiling conc. HNO3+H2O2 was found to be sufficient. The sodium hydroxide fusion technique yielded reproducible analytical results and is proposed
as an optimum dissolution method for quantitative determination of the total content of fallout239,240Pu in deep-sea sediment. 相似文献
93.
A predator–prey model with transmissible disease in the prey species is proposed and analysed. The essential mathematical features are analysed with the help of equilibrium, local and global stability analyses and bifurcation theory. We find four possible equilibria. One is where the populations are extinct. Another is where the disease and predator populations are extinct and we find conditions for global stability of this. A third is where both types of prey exist but no predators. The fourth has all three types of individuals present and we find conditions for limit cycles to arise by Hopf bifurcation. Experimental data simulation and brief discussion conclude the paper. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
94.
95.
A. K. M. Moinul Haque Meaze K. Devan Y. S. Lee Y. D. Oh G. N. Kim D. Son 《Pramana》2007,68(2):279-287
Experimental results of transmissions for the samples of natural molybdenum with thickness 0.0192 atoms/barn and for the four
samples of natural tantalum with thickness 0.0222, 0.0111, 0.0055 and 0.0025 atoms/barn are presented in this work. Measurements
were carried out at the Pohang Neutron Facility which consists of a 100 MeV Linac, water-cooled tantalum target, and 12 m
flight path length. Effective total cross-sections were extracted from the transmission data, and resonance parameters were
obtained by using the code SAMMY. The present measurements were compared with other measurements and with the evaluated nuclear
data file ENDF/B-VI.8.
相似文献
96.
The apparent dielectric constant, , of the hydrophobic pyrene binding sites in erythroid spectrin and human serum albumin (HSA) were estimated using the linear relationship [Turro, N.J., Kuo, P.L., Somasundaran, P. and Wong, K. (1986). J. Phys. Chem. 90, 288–291] between the ratio of the first (373 nm) and the third (384 nm) vibronic peak intensities (l1/l3) and the dielectric constant of the bulk medium. Binding of the hydrophobic fluorescent probe, pyrene, to erythroid spectrin and HSA was determined from concentration dependent change in the ratio l1/l3 from the emission spectra. Pyrene binds to spectrin (Kapp = 6.2 × 106 M–1) with a higher affinity than that of HSA (Kapp = 3.7 × 104 M–1) and the binding in both cases are saturable. The for spectrin and HSA was estimated to be 7 ± 2.1 and 5.4 ± 1.6 respectively. A case study with spectrin, covalently labeled with pyrene maleimide, have been presented for aging of pyrene-labelled spectrin showing the potential of the use of vibrational peak ratios (l1/l3) in the study of polarity of microenvironments in the neighborhood of cysteine residues of a protein. Large changes in the pyrene spectral components indicated conformational changes in the cysteine microenvironment of the protein upon storage at 4°C. 相似文献
97.
98.
99.
This note is concerned with the origin of secondary flow in straight noncircular ducts. A critical examination of the analytical expressions for the secondary flow production terms is made to show that the essential requirement for secondary flow is a finite gradient of the difference in the turbulent stresses in the plane of the duct cross section in a peripheral direction. This conclusion has been reached following an investigation of the turbulent stress distributions in unidirectional pipe flow and assumes that, in general, the normal stresses only are significant in secondary flow production. An observation is made on “vorticity reversal” in the immediate vicinity of the boundary of a noncircular duct. 相似文献
100.
A more general and realistic four-component magnetized plasma medium consisting of opposite polarity ions and nonthermal distributed positrons and electrons is considered to investigate the stable/unstable frequency regimes of modulated ion-acoustic waves (IAWs) in the D-F regions of Earth's ionosphere. A (3 + 1) -dimensional nonlinear Schrödinger equation, which leads to the modulation instability (MI) of IAWs, is derived. The parametric regimes for the existence of the MI, first- and second-order rogue waves, and also their basic features (viz., amplitude, width, and speed) are found to be significantly modified by the effect of physical plasma parameters and external magnetic field. It is found that the nonlinearity of the different types of electronegative plasma system depends on the positive to negative ion mass ratio. It is also shown that the presence of nonthermal distributed electrons and positrons modifies the nature of the MI of the modulated IAWs. The implication of our results for the laboratory plasma [e.g., (Ar+, F− ) electronegative plasma] and space plasma [e.g., (H+, H− ), () electronegative plasma in D-F regions of Earth's ionosphere] are briefly discussed. 相似文献