全文获取类型
收费全文 | 83520篇 |
免费 | 436篇 |
国内免费 | 374篇 |
专业分类
化学 | 27149篇 |
晶体学 | 817篇 |
力学 | 6834篇 |
数学 | 33159篇 |
物理学 | 16371篇 |
出版年
2020年 | 49篇 |
2019年 | 58篇 |
2018年 | 10509篇 |
2017年 | 10326篇 |
2016年 | 6225篇 |
2015年 | 983篇 |
2014年 | 509篇 |
2013年 | 835篇 |
2012年 | 4042篇 |
2011年 | 10805篇 |
2010年 | 5787篇 |
2009年 | 6170篇 |
2008年 | 6870篇 |
2007年 | 9015篇 |
2006年 | 511篇 |
2005年 | 1501篇 |
2004年 | 1704篇 |
2003年 | 2091篇 |
2002年 | 1140篇 |
2001年 | 342篇 |
2000年 | 365篇 |
1999年 | 211篇 |
1998年 | 247篇 |
1997年 | 195篇 |
1996年 | 247篇 |
1995年 | 166篇 |
1994年 | 105篇 |
1993年 | 136篇 |
1992年 | 112篇 |
1991年 | 110篇 |
1990年 | 105篇 |
1989年 | 123篇 |
1988年 | 112篇 |
1987年 | 114篇 |
1986年 | 106篇 |
1985年 | 111篇 |
1984年 | 117篇 |
1983年 | 108篇 |
1982年 | 111篇 |
1981年 | 88篇 |
1980年 | 108篇 |
1979年 | 98篇 |
1978年 | 115篇 |
1977年 | 62篇 |
1976年 | 73篇 |
1975年 | 64篇 |
1974年 | 65篇 |
1973年 | 71篇 |
1972年 | 57篇 |
1914年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
At sufficiently high concentrations of methanol and of alkali salts in aqueous silica dispersions, the negative -potentials of the particles are decreased. This effect is more pronounced with lithium than with other alkali cations, and it is independent on the anion. The NMR spectra indicate lithium adsorption on silica from mixed solvents, but not in the absence of alcohol.Supported by a contract with the XMX Corporation, Burlington, Massachusetts, USA 相似文献
72.
Robert W. Ashford Peter Connard Robert Daniel 《The Journal of the Operational Research Society》1992,43(5):519-531
The time-consuming process of solving large-scale Mixed Integer Programming problems using the branch-and-bound technique can be speeded up by introducing a degree of parallelism into the basic algorithm. This paper describes the development and implementation of a parallel branch-and-bound algorithm created by adapting a commercial MIP solver. Inherent in the design of this software are certain ad hoc methods, the use of which are necessary in the effective solution of real problems. The extent to which these ad hoc methods can successfully be transferred to a parallel environment, in this case an array of at most nine transputers, is discussed. Computational results on a variety of real integer programming problems are reported. 相似文献
73.
74.
J. Žofka 《Czechoslovak Journal of Physics》1982,32(3):321-325
Hypernuclear structure models are briefly reviewed. Phenomena related to hypernuclear polarization are displayed. A discussion is given of nuclear and hypernuclear neutron orbitals extraction. Preliminary results on
– angular distributions for the reaction6Li(K
–, –)
6
Li are presented.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.The collaboration of Dr. M. Sotona and Dr. L. Majling in the speedy preparation of the AD results and discussions with them and with Prof. B. Povh are greatly acknowledged. 相似文献
75.
A study of chromium(III) ion adsorption on a stearic acid monomolecular layer (MML), spread on the surface of a51CrCl3 aqueous solution, is presented. From the analysis of the experimental results it can be concluded that MML saturation is achieved at CrCl3 concentrations above 10?6M. When the maximum adsorption pH value of Cr(III) ions on MML is 6.7, MML is completely ionized and chromium ion is bonded as Cr(OH) 2 + . The kinetics of Cr(III) ion adsorption on MML could be expressed as AS=A ∞ S (1?e?k t). 相似文献
76.
Jorge Pavez Maritza Páez Armelle Ringuedé Fethi Bedioui José H. Zagal 《Journal of Solid State Electrochemistry》2005,9(1):21-29
We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O2) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O2 reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O2 to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy. 相似文献
77.
Sorption of uranium by non-living water hyacinth roots 总被引:1,自引:0,他引:1
S. Shawky M. Abdel Geleel Ashraf Aly 《Journal of Radioanalytical and Nuclear Chemistry》2005,265(1):81-84
Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg . ml-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U6+ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm. 相似文献
78.
Tomislav P. Živković 《Journal of mathematical chemistry》2002,32(1):39-71
Interaction of quantum system S
a
described by the generalised × eigenvalue equation A|
s
=E
s
S
a
|
s
(s=1,...,) with quantum system S
b
described by the generalised n×n eigenvalue equation B|
i
=
i
S
b
|
i
(i=1,...,n) is considered. With the system S
a
is associated -dimensional space X
a
and with the system S
b
is associated an n-dimensional space X
n
b
that is orthogonal to X
a
. Combined system S is described by the generalised (+n)×(+n) eigenvalue equation [A+B+V]|
k
=
k
[S
a
+S
b
+P]|
k
(k=1,...,n+) where operators V and P represent interaction between those two systems. All operators are Hermitian, while operators S
a
,S
b
and S=S
a
+S
b
+P are, in addition, positive definite. It is shown that each eigenvalue
k
i
of the combined system is the eigenvalue of the × eigenvalue equation
. Operator
in this equation is expressed in terms of the eigenvalues
i
of the system S
b
and in terms of matrix elements
s
|V|
i
and
s
|P|
i
where vectors |
s
form a base in X
a
. Eigenstate |
k
a
of this equation is the projection of the eigenstate |
k
of the combined system on the space X
a
. Projection |
k
b
of |
k
on the space X
n
b
is given by |
k
b
=(
k
S
b
–B)–1(V–
k
P})|
k
a
where (
k
S
b
–B)–1 is inverse of (
k
S
b
–B) in X
n
b
. Hence, if the solution to the system S
b
is known, one can obtain all eigenvalues
k
i
} and all the corresponding eigenstates |
k
of the combined system as a solution of the above × eigenvalue equation that refers to the system S
a
alone. Slightly more complicated expressions are obtained for the eigenvalues
k
i
} and the corresponding eigenstates, provided such eigenvalues and eigenstates exist. 相似文献
79.
J. Jureta S. Cvejanović M. Kurepa D. Cvejanović 《Zeitschrift für Physik A Hadrons and Nuclei》1982,304(2):143-153
A high resolution electron impact threshold spectroscopy technique was used to examine the excitation of Cl2 in the 2–14 eV region. This study complements previous photon absorption and emission measurements, because it is capable of detecting transitions which are optically forbidden. In the region up to 7.5 eV, broad dissociative structures are correlated with optically active valence states, although relative intensities in the threshold spectrum differ considerably and indicate a substantial contribution from the optically forbidden transitions. At 7.46 eV a series of 5 equidistant sharp peaks is detected and interpreted as arising from the2 π g Feshbach resonance, which differs from the ground state positive ion Cl 2 + by a pair of Rydberg electrons: (4sσ)2. The decay channels responsible for the appearance of the resonance in a threshold spectrum are discussed and it is suggested that they include several valence states of the (2431) and (2341) configurations, whose potential energy curves cross the Cl 2 ? ,2πg curve in the region of energy at which the resonance state is formed. At higher incident electron energies and up to ionisation, Rydberg states predominate, starting with (2430) 4s3,1 π g states detected for the first time. The absence of broad peaks above 8 eV and the irregular appearance of Rydberg bands is consistent with the strong Rydberg-valence configuration mixing proposed by Peyerimhoff and Buenker. Where our resolution permits comparison, good general agreement is found with recent synchrotron radiation absorption measurements of optically allowed transitions. 相似文献
80.
L. F. Brum Malta Marta Eloisa Medeiros 《Journal of Thermal Analysis and Calorimetry》2005,81(1):149-152
Summary This work reports the room-temperature stabilization of the Bi4V2-xFexIIO11-1.5x γ ‘ phase, a promising ionic conductive material that finds application in solid oxide fuel cell and oxygen sensor devices. The Fe(II) cation proved to be a better stabilizer than Fe(III), which was previously used, since a lower substitution degree of V5+ is needed for the former. Powder X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry were used in these experiments. 相似文献