全文获取类型
收费全文 | 666123篇 |
免费 | 6755篇 |
国内免费 | 2041篇 |
专业分类
化学 | 358334篇 |
晶体学 | 9867篇 |
力学 | 29244篇 |
综合类 | 22篇 |
数学 | 79671篇 |
物理学 | 197781篇 |
出版年
2021年 | 5421篇 |
2020年 | 6075篇 |
2019年 | 6638篇 |
2018年 | 8628篇 |
2017年 | 8510篇 |
2016年 | 12763篇 |
2015年 | 7997篇 |
2014年 | 12265篇 |
2013年 | 30120篇 |
2012年 | 22813篇 |
2011年 | 27932篇 |
2010年 | 19804篇 |
2009年 | 19619篇 |
2008年 | 25972篇 |
2007年 | 25902篇 |
2006年 | 24237篇 |
2005年 | 21831篇 |
2004年 | 19953篇 |
2003年 | 17839篇 |
2002年 | 17625篇 |
2001年 | 19803篇 |
2000年 | 15147篇 |
1999年 | 11832篇 |
1998年 | 9766篇 |
1997年 | 9579篇 |
1996年 | 9245篇 |
1995年 | 8172篇 |
1994年 | 8112篇 |
1993年 | 7825篇 |
1992年 | 8826篇 |
1991年 | 9021篇 |
1990年 | 8589篇 |
1989年 | 8370篇 |
1988年 | 8399篇 |
1987年 | 8258篇 |
1986年 | 7720篇 |
1985年 | 10113篇 |
1984年 | 10433篇 |
1983年 | 8273篇 |
1982年 | 8570篇 |
1981年 | 8340篇 |
1980年 | 7853篇 |
1979年 | 8552篇 |
1978年 | 8909篇 |
1977年 | 8727篇 |
1976年 | 8661篇 |
1975年 | 8050篇 |
1974年 | 8058篇 |
1973年 | 8202篇 |
1972年 | 5676篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
A. M. Stokolos 《Mathematical Notes》1998,64(5):646-657
It is proved that there exists an integrable function on [0, 1]2 whose integral is nondifferentiable in each direction belonging to a set everywhere dense in [0, 2π] but is strongly differentiable.
Translated fromMatematicheskie Zametki, Vol. 64, No. 5, pp. 749–762, November, 1998. 相似文献
872.
The problem of calculating the noise factor of a traveling-wave gyrotron is solved for a model of a thin annular multistart-helical
electron flux taking into account the effect of the quasistatic space-charge field. Plots of the gain and the noise factor
of the traveling-wave gyrotron versus the electrical parameters of the amplifier are obtained.
Zh. Tekh. Fiz. 68, 130–132 (February 1998) 相似文献
873.
V. T. Astrelin A. V. Burdakov V. S. Koidan K. I. Mekler P. I. Mel’nikov V. V. Postupaev M. A. Shcheglov 《Journal of Experimental and Theoretical Physics》1998,86(3):489-500
This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the
GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 1017 cm−3 was created in the main plasma, whose density was 1015 cm−3. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse
along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions.
Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released
in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which
is inhomogeneous in density and temperature, including the appearance of pressure waves.
Zh. éksp. Teor. Fiz. 113, 897–917 (March 1998) 相似文献
874.
The problems of choosing the optimal mathematical model for a prescribed range of parameters of a pulsed action are discussed.
A preliminary analysis performed by similarity and dimensional-analysis methods using interpolation equations of state of
the matter shows that the complete system of equations of gasdynamics can be simplified by dropping individual terms which
are not important in a given parameter range. The results of an analysis are presented in the form of nomograms, which also
make it possible to identify the class of fast and energy-intensive gasdynamic processes more accurately than at an intuitive
level.
Zh. Tekh. Fiz. 68, 44–47 (May 1998) 相似文献
875.
876.
877.
Underdoped manganites: Canted antiferromagnetic ordering or two-phase ferro-antiferromagnetic state?
E. L. Nagaev 《Journal of Experimental and Theoretical Physics》1998,87(6):1214-1220
We calculate the energy of charge-carrier-induced canted ordering in conducting layered antiferromagnetic systems with double
exchange. The quantum approach to the d-spins is used. In the jellium model the energy of the canted state is lower than the energies of both collinear ferro-and
antiferromagnetic states over a certain range of charge carrier densities, beginning with arbitrarily small densities. Nevertheless,
the canted state cannot be realized, because it is unstable against charge-carrier density fluctuations. The two-phase ferro-antiferromagnetic
state can play the role of an alternative to canting. The case of an intermediate electronic-impurity phase separation is
investigated.
Zh. éksp. Teor. Fiz. 114, 2225–2237 (December 1998)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
878.
The solvent extraction of cobalt(II), nickel(II) and copper(II) using 2,4-pent-dione (Hacac) and 4-phenyl-2, 4-but-dione (Hbzac)
is carried out by varying the reagent concentration and pH of the aqueous phase. Each of these metals is quantitatively separated
(≈ 98%) from their binary mixtures with monovalent (Ag), divalent (Mn, Zn, Cd, Hg, Mg, Sn, Pb) and trivalent (Cr, Fe) metals.
The extraction constants are calculated from the metal distribution data using linear regression analysis. The extracted species
is MA2 in each case. A most significant result is separation of copper(II) from iron(III) which otherwise interferes when extracted
from the acidic medium. 相似文献
879.
The orientational ordering of several liquid crystals containing a difluorosubstituted phenyl ring has been studied through the use of C-13 NMR. The fluorinated phenyl ring of these liquid crystals have Cs symmetry, so three order parameters are required to completely describe the ordering of this ring. All three of these order parameters have been calculated from carbon-fluorine dipolar coupling constants obtained from the carbon-fluorine splittings in the C-13 NMR spectra. Because of the complexity of the fluorine-coupled spectra, variable angle spinning (VAS) was used to resolve the carbon-fluorine splittings. In order to study the orientational ordering over wide ranges of temperature, we have developed an empirical correlation between the order parameter and the value of a carbon-fluorine dipolar coupling constant. This enabled us to study the change in the order parameter with temperature. The results of applying this method to several structurally similar liquid crystals containing the same type of difluorinated phenyl ring are presented. A comparison is made to a similar mono-fluorinated liquid crystal. 相似文献
880.
The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents. 相似文献