全文获取类型
收费全文 | 460135篇 |
免费 | 4043篇 |
国内免费 | 1323篇 |
专业分类
化学 | 229400篇 |
晶体学 | 6401篇 |
力学 | 23995篇 |
综合类 | 15篇 |
数学 | 73547篇 |
物理学 | 132143篇 |
出版年
2019年 | 3245篇 |
2018年 | 14246篇 |
2017年 | 14030篇 |
2016年 | 12259篇 |
2015年 | 4701篇 |
2014年 | 6505篇 |
2013年 | 16213篇 |
2012年 | 15462篇 |
2011年 | 24580篇 |
2010年 | 15763篇 |
2009年 | 15989篇 |
2008年 | 19955篇 |
2007年 | 22203篇 |
2006年 | 13336篇 |
2005年 | 13111篇 |
2004年 | 12183篇 |
2003年 | 11574篇 |
2002年 | 10605篇 |
2001年 | 10824篇 |
2000年 | 8510篇 |
1999年 | 6510篇 |
1998年 | 5736篇 |
1997年 | 5656篇 |
1996年 | 5335篇 |
1995年 | 4904篇 |
1994年 | 4999篇 |
1993年 | 4613篇 |
1992年 | 5255篇 |
1991年 | 5344篇 |
1990年 | 5110篇 |
1989年 | 5013篇 |
1988年 | 5041篇 |
1987年 | 4871篇 |
1986年 | 4630篇 |
1985年 | 6081篇 |
1984年 | 6433篇 |
1983年 | 5371篇 |
1982年 | 5673篇 |
1981年 | 5501篇 |
1980年 | 5423篇 |
1979年 | 5502篇 |
1978年 | 5920篇 |
1977年 | 5725篇 |
1976年 | 5820篇 |
1975年 | 5434篇 |
1974年 | 5530篇 |
1973年 | 5668篇 |
1972年 | 3943篇 |
1971年 | 3378篇 |
1970年 | 3075篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Demixing during film casting of blends of polystyrene, polymethylmethacrylate, and a symmetric diblock copolymer of styrene and methylmethacrylate is discussed. The concentration fluctuations in the homogeneous solutions were calculated in mean field approximation. The structures in the homogeneous and demixed solutions and in the dry films were measured by small-angle x-ray scattering, and the morphologies of the dry films were characterized by transmission electron microscopy. The structure of the dry blends is evidently already pre-formed in solution. 相似文献
192.
D. J. Plazek C. A. Bero S. Neumeister G. Floudas G. Fytas K. L. Ngai 《Colloid and polymer science》1994,272(11):1430-1438
By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT
g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems 相似文献
193.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased. 相似文献
194.
The lidar equation for the vibrational backscattering of neodymium laser radiation and its harmonics by hydrogen molecules
is solved numerically. Inclined paths in the atmosphere are investigated with the aim of selecting the transmitter wavelength
for detecting the lowest concentrations of hydrogen.
Zh. Tekh. Fiz. 68, 20–22 (January 1998) 相似文献
195.
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
196.
G. Ch. Shushkevich 《Technical Physics》1998,43(7):743-748
The electrostatic problem for a thin, unclosed spherical shell and a torus is reduced to paired summation equations in the
Legendre polynomials by means of formulas relating the spherical and toroidal harmonic functions. The paired equations are
transformed to a Fredholm integral equation of the second kind. Formulas are obtained for computing the charges of the conductors
in the form of a series in a small parameter. The capacitance is computed for certain geometrical parameters of the conductors.
Zh. Tekh. Fiz. 68, 1–6 (July 1998) 相似文献
197.
P. Seelig A. Dax S. Faber M. Gerlach G. Huber T. Kühl D. Marx P. Merz W. Quint F. Schmitt H. Winter M. Würtz 《Hyperfine Interactions》1998,114(1-4):135-139
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric
and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique
using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics
from an ion beam at relativistic velocities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
198.
The dependence of distribution functions of quarks, antiquarks, diquarks and their fragmentation into hadrons on the transverse momentumk t is discussed in the frame of the quark-gluon string model. We then discuss the division ofk t between 2n-quark-antiquark chains, orn-pomeron showers. Hadron and hadron-nuclear processesp?p,p?A,K +?p,K +?A are analysed. A strong dependence of the observed values on the numbern is derived by this method, which is of special importance for the analysis of hadron-nucleus collisions. Our method is compared with the regulark t division method. 相似文献
199.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
200.
A. Negr n-Mendoza G. Albarran S. Ramos-Bernal 《Radiation Physics and Chemistry》1993,42(4-6):1003-1006
The effect of clay on the radiolysis of malonic acid solutions was studied. The results showed an enhanced of decarboxylation rather than condensation reactions. 相似文献