全文获取类型
收费全文 | 384273篇 |
免费 | 3664篇 |
国内免费 | 1802篇 |
专业分类
化学 | 178374篇 |
晶体学 | 5002篇 |
力学 | 20803篇 |
综合类 | 61篇 |
数学 | 76341篇 |
物理学 | 109158篇 |
出版年
2020年 | 1902篇 |
2019年 | 2046篇 |
2018年 | 18836篇 |
2017年 | 19406篇 |
2016年 | 12307篇 |
2015年 | 4133篇 |
2014年 | 4175篇 |
2013年 | 9906篇 |
2012年 | 14884篇 |
2011年 | 29172篇 |
2010年 | 17723篇 |
2009年 | 17967篇 |
2008年 | 24065篇 |
2007年 | 28901篇 |
2006年 | 9522篇 |
2005年 | 15652篇 |
2004年 | 11994篇 |
2003年 | 11470篇 |
2002年 | 8685篇 |
2001年 | 7232篇 |
2000年 | 5785篇 |
1999年 | 3996篇 |
1998年 | 3399篇 |
1997年 | 3346篇 |
1996年 | 3560篇 |
1995年 | 2976篇 |
1994年 | 3030篇 |
1993年 | 2879篇 |
1992年 | 3082篇 |
1991年 | 3151篇 |
1990年 | 2940篇 |
1989年 | 2854篇 |
1988年 | 2820篇 |
1987年 | 2767篇 |
1986年 | 2752篇 |
1985年 | 3664篇 |
1984年 | 3708篇 |
1983年 | 3098篇 |
1982年 | 3410篇 |
1981年 | 3109篇 |
1980年 | 2974篇 |
1979年 | 3135篇 |
1978年 | 3355篇 |
1977年 | 3303篇 |
1976年 | 3314篇 |
1975年 | 3005篇 |
1974年 | 3111篇 |
1973年 | 3203篇 |
1972年 | 2434篇 |
1971年 | 1954篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
E. Goering M. Justen J. Geissler U. Rüdiger M. Rabe G. Güntherodt G. Schütz 《Applied Physics A: Materials Science & Processing》2002,74(6):747-753
Highly a-axis-textured CrO2 films have been deposited on Al2O3 (0001) substrates by chemical vapor deposition. CrO2 has been found to have highly a-axis (010)-oriented columnar growth on a Cr2O3 (0001) initial layer. The six-fold surface symmetry of the Cr2O3 initial layer leads to three equivalent in-plane orientations of the a-axis-oriented CrO2 unit cell. We report Cr L2,3 X-ray magnetic circular dichroism data along the surface normal and at 60° off-normal sample orientation. For a 60° sample
alignment, a strong increase of the projected orbital moment could be observed for unoccupied majority t2g states using moment analysis. Therefore, the c axis is identified as the intrinsic magnetic easy axis of CrO2. In addition, a small spin moment and a very strong magnetic dipole term Tz have been found.
Received: 8 January 2002 / Accepted: 8 January 2002 相似文献
982.
983.
M. M. Zaripov V. F. Tarasov V. A. Ulanov G. S. Shakurov 《Physics of the Solid State》2002,44(11):2050-2054
The bivalent chromium impurity centers in CdF2 and CaF2 crystals are investigated using electron paramagnetic resonance (EPR) in the frequency range 9.3–300 GHz. It is found that Cr2+ ions in the lattices of these crystals occupy cation positions and form [CrF4F4]6? clusters whose magnetic properties at low temperatures are characterized by orthorhombic symmetry. The parameters of the electron Zeeman and ligand interactions of the Cr2+ ion with four fluorine ions in the nearest environment are determined. The initial splittings in the system of spin energy levels of the cluster are measured. 相似文献
984.
Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
985.
The potential and polarization distributions in a planar emitting layer of PLZT-9/65/35 ferroelectric ceramic with a set of conductive strip electrodes on the emitting side and a continuous electrode on the opposite side are studied by numerical methods. The state arising immediately after polarization switching at the leading edge of an applied voltage pulse (i.e., before the polarization charges are screened by free charges) is considered. When the pulsed field strength far exceeds the double coercive field, regions with alternating polarization are found to form in the surface layer between the strips. The normal component of the polarization at its maxima is close to saturation. The electric field on both sides of the surface varies as the polarization vector and reaches 200 kV/cm. At surface microirregularities, the electric field strength is much higher. This means that field emission is responsible for electron escape from the ferroelectric ceramic during pulsed polarization switching. 相似文献
986.
V. I. Strunin A. A. Lyakhov G. Zh. Khudaibergenov V. V. Shkurkin 《Technical Physics》2002,47(6):760-766
A model of silane decomposition in a radio-frequency argon plasma is constructed. The concentrations of SiH4 decomposition products, as well as products of synthesis (higher silanes), are calculated. The role of metastable argon atoms in the formation of SiH3 radicals and the higher silanes is analyzed. 相似文献
987.
Several variations of two-dimensional (workers x jobs) and three-dimensional (workers x jobs x machines) time- as well as cost-minimizing assignment problems, which arise owing to (i) precedence relations of some form among the jobs or (ii) capacity restrictions on workers/machines imposed by the requirement that the surplus resources have to be fully employed, have been considered in the literature. In this paper, an algorithm is presented for time-cost trade-off analysis which is applicable to any general pair of such constrained problems. The algorithm is also illustrated by a numerical example. 相似文献
988.
This note discusses the need to use various data-compaction schemes in the implementation of sophisticated large-scale linear programming codes on modest personal computers. It demonstrates a method whereby the overhead of using these schemes is significantly reduced on Intel 80 x 86 processors. 相似文献
989.
The optimal return function for a Borel measurable gambling problem with a bounded utility function was shown by Strauch (1967)
to be universally measurable when the problem is leavable in the sense that the gambler may terminate play at any time. The
same is shown here for the more general class of nonleavable problems.
Research supported by National Science Foundation Grant DMS-8801085. 相似文献
990.