全文获取类型
收费全文 | 8151篇 |
免费 | 313篇 |
国内免费 | 4篇 |
专业分类
化学 | 4424篇 |
晶体学 | 73篇 |
力学 | 149篇 |
数学 | 1727篇 |
物理学 | 2095篇 |
出版年
2023年 | 67篇 |
2021年 | 107篇 |
2020年 | 125篇 |
2019年 | 104篇 |
2018年 | 184篇 |
2017年 | 194篇 |
2016年 | 434篇 |
2015年 | 282篇 |
2014年 | 319篇 |
2013年 | 728篇 |
2012年 | 434篇 |
2011年 | 527篇 |
2010年 | 303篇 |
2009年 | 262篇 |
2008年 | 281篇 |
2007年 | 210篇 |
2006年 | 170篇 |
2005年 | 105篇 |
2004年 | 119篇 |
2003年 | 125篇 |
2002年 | 123篇 |
2001年 | 102篇 |
2000年 | 89篇 |
1999年 | 100篇 |
1998年 | 97篇 |
1997年 | 97篇 |
1996年 | 89篇 |
1995年 | 85篇 |
1994年 | 77篇 |
1993年 | 71篇 |
1992年 | 76篇 |
1991年 | 72篇 |
1989年 | 69篇 |
1988年 | 69篇 |
1987年 | 74篇 |
1986年 | 69篇 |
1985年 | 94篇 |
1984年 | 94篇 |
1983年 | 78篇 |
1982年 | 76篇 |
1981年 | 78篇 |
1980年 | 88篇 |
1979年 | 76篇 |
1978年 | 86篇 |
1977年 | 87篇 |
1976年 | 68篇 |
1974年 | 70篇 |
1973年 | 81篇 |
1966年 | 64篇 |
1965年 | 66篇 |
排序方式: 共有8468条查询结果,搜索用时 234 毫秒
31.
Given disjoint setsP
1,P
2, ...,P
d
inR
d
withn points in total, ahamsandwich cut is a hyperplane that simultaneously bisects theP
i
. We present algorithms for finding ham-sandwich cuts in every dimensiond>1. Whend=2, the algorithm is optimal, having complexityO(n). For dimensiond>2, the bound on the running time is proportional to the worst-case time needed for constructing a level in an arrangement
ofn hyperplanes in dimensiond−1. This, in turn, is related to the number ofk-sets inR
d−1
. With the current estimates, we get complexity close toO(n
3/2
) ford=3, roughlyO(n
8/3
) ford=4, andO(n
d−1−a(d)
) for somea(d)>0 (going to zero asd increases) for largerd. We also give a linear-time algorithm for ham-sandwich cuts inR
3 when the three sets are suitably separated.
A preliminary version of the results of this paper appeared in [16] and [17]. Part of this research by J. Matoušek was done
while he was visiting the School of Mathematics, Georgia Institute of Technology, Atlanta, and part of his work on this paper
was supported by a Humboldt Research Fellowship. W. Steiger expresses gratitude to the NSF DIMACS Center at Rutgers, and his
research was supported in part by NSF Grants CCR-8902522 and CCR-9111491. 相似文献
32.
33.
V. V. Panić A. B. Dekanski S. K. Milonjić V. B. Mišković-Stanković B. Ž. Nikolić 《Russian Journal of Electrochemistry》2006,42(10):1055-1060
Electrocatalytic properties of RuO2/Ti anode with different coating masses, which are prepared by the alkoxide sol-gel procedure, are investigated in chlorine
and oxygen evolution reactions by polarization measurements and electrochemical impedance spectroscopy in H2SO4 and NaCl electrolytes. According to polarization measurements, the activity of anodes at overpotentials below 100 mV is independent
of coating mass. However, impedance measurements above 100 mV reveal changes in the activity of anodes in chlorine evolution
reaction for different coating masses. The diffusion limitations related to the evolved chlorine are registered in low-frequency
domain at 1.10 V (SCE), diminishing with the increase in potential to the 1.15 V (SCE). The observed impedance behavior is
discussed with respect to the activity model for activated titanium anodes in chlorine evolution reaction involving formation
of gas channels within porous coating structure. Gas channels enhance the mass transfer rate similarly to the forced convection,
which also increases the activity of anode. This is more pronounced for the anode of greater coating mass due to its more
compact surface structure. The more compact structure appears to be beneficial for gas channels formation.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 10, pp. 1173–1179.
The text was submitted by the authors in English. 相似文献
34.
35.
A two-fraction model that makes it possible to calculate analytically the complex dielectric permittivity of ice in the far infrared and submillimeter wavelength ranges is proposed. The librational and vibrational fractions are considered. The first fraction, consisting of rigid dipoles executing anharmonic reorientations in defects of the structure, gives rise to the librational band of ice at 800 cm?1. The second fraction consists of elastically vibrating oppositely charged H-bonded molecules. This fraction describes two bands of ice in the range 100–300 cm?1, and the nonresonant background of dielectric losses in the submillimeter wavelength range. The dielectric permittivity spectra of ice calculated for the temperature of ?7°C are consistent with the experimental spectra. The spectra of ice at the temperature ?30°C are predicted. 相似文献
36.
K. Prokeš 《Czechoslovak Journal of Physics》2002,52(2):253-258
Many materials exhibit various magnetic phenomena as a function of magnetic field, temperature and/or pressure. Usually, bulk magnetic measurements provide first information on the magnetic state of the material by measuring their response on the applied magnetic field. However, it is necessary to investigate materials also on a microscopic scale. This is often done by means of neutron scattering. In this contribution we discuss basic ideas of this method and we report on few experimental results obtained with a split-pair coil 14.5 T superconducting magnet which can be combined with dilution stick offering temperatures as low as 30 mK and/or with a small clamped-type pressure cell which offers pressure up to 1.0 GPa. 相似文献
37.
We have investigated the structure of spider dragline silk by X-ray diffraction over a broad temperature range from room temperature
up to thermal denaturation conditions. The dominating signal from the β-sheet crystallites is analyzed. Pronounced changes
of scattering intensity starting at temperatures around 150 °C are observed. These changes are discussed in view of the respective
lattice constants, crystal size, size distribution, crystallite number density and amino acid composition.
PACS 87.68.+z; 87.15.-v; 87.64.Bx 相似文献
38.
Certain condition on the second fundamental form of CR submanifolds of maximal CR dimension of complex Euclidean space 总被引:1,自引:0,他引:1
We treat m-dimensional real submanifolds M of complex space forms ̿M when the maximal holomorphic tangent subspace is (m−1)-dimensional. On these manifolds there exists an almost contact structure F which is naturally induced from the ambient space and in this paper we study the condition h(FX,Y)−h(X,FY) = g(FX,Y)η, η∊ T⊥(M), on the structure F and on the second fundamental form h of these submanifolds. Especially when the ambient space ̿M is a complex Euclidean space, we obtain a complete classification of submanifolds M which satisfy these conditions.Mathematics Subject Classifications (2000): 53C15, 53C40, 53B20. 相似文献
39.
Various approaches and standards for transferring mathematical objects between different computer programs in multimedia environment in the framework of the OpenMath project are described. The use of these standards might revolutionize the exchange of mathematical information caused by the development of computer algebra tools and telecommunication possibilities. The standards make it possible to create databases and easily save and use mathematical objects obtained in different applications, e.g., to exchange the data obtained in different computer algebra systems and place information on the Internet. Bibliography: 9 titles. 相似文献
40.
The validity of local parton-hadron duality within the framework of HERWIG and JETSET event generators is investigated. We concentrate one
+
e
– annihilations in LEP 2 energy range as these interactions provide theoretically the cleanest condition for the discussion of this concept. We conclude that the concept of local parton-hadron duality is not valid in either of the two generators considered. 相似文献