全文获取类型
收费全文 | 496286篇 |
免费 | 2930篇 |
国内免费 | 1072篇 |
专业分类
化学 | 226871篇 |
晶体学 | 6993篇 |
力学 | 29040篇 |
综合类 | 9篇 |
数学 | 86341篇 |
物理学 | 151034篇 |
出版年
2021年 | 3854篇 |
2020年 | 4260篇 |
2019年 | 5069篇 |
2018年 | 17244篇 |
2017年 | 17133篇 |
2016年 | 15557篇 |
2015年 | 5548篇 |
2014年 | 8952篇 |
2013年 | 17707篇 |
2012年 | 17629篇 |
2011年 | 26741篇 |
2010年 | 18671篇 |
2009年 | 19288篇 |
2008年 | 22249篇 |
2007年 | 24091篇 |
2006年 | 14544篇 |
2005年 | 13846篇 |
2004年 | 13326篇 |
2003年 | 12780篇 |
2002年 | 12030篇 |
2001年 | 11395篇 |
2000年 | 9063篇 |
1999年 | 6762篇 |
1998年 | 6258篇 |
1997年 | 6032篇 |
1996年 | 5552篇 |
1995年 | 5024篇 |
1994年 | 5029篇 |
1993年 | 4932篇 |
1992年 | 5107篇 |
1991年 | 5623篇 |
1990年 | 5380篇 |
1989年 | 5389篇 |
1988年 | 5127篇 |
1987年 | 5120篇 |
1986年 | 4751篇 |
1985年 | 5753篇 |
1984年 | 6076篇 |
1983年 | 5144篇 |
1982年 | 5484篇 |
1981年 | 5071篇 |
1980年 | 4787篇 |
1979年 | 5344篇 |
1978年 | 5567篇 |
1977年 | 5558篇 |
1976年 | 5666篇 |
1975年 | 5312篇 |
1974年 | 5227篇 |
1973年 | 5391篇 |
1972年 | 4261篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
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
12.
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
13.
14.
15.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
16.
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
17.
We prove a character formula for any finite-dimensional irreducible representationV of the “queer” Lie superalgebra g=q(n). It expresses chV in terms of the multiplicities of the irreducible g-subquotients of the cohomology groups of certain dominant g-bundles on
the Π-symmetric projective spaces (i.e., on the homogeneous superspacesG/P whose reduced space is a projective space, whereG=Q(n)). We also establish recurrent relations for the above multiplicities, and this enables us to compute explicitly chV for any givenV. This provides a complete solution to the Kac character problem for the Lie superalgebraq(n). Finally, we consider the particular cases ofq(2), q(3), andq(4) in which we compare the new character formula with the generic character formula of [12].
Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 41, Algebraic
Geometry-7, 1997. 相似文献
18.
19.
We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity,
which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish
at a critical density n
c
, 2∼2×1012 cm−2, and then to have the opposite sign at n>n
c
,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the
critical point, G
c
,2∼120e
2/h, sets an upper (low-temperature) limit on its conductivity.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
20.
S. A. Gurevich T. A. Zaraiskaya S. G. Konnikov V. M. Mikushkin S. Yu. Nikonov A. A. Sitnikova S. E. Sysoev V. V. Khorenko V. V. Shnitov Yu. S. Gordeev 《Physics of the Solid State》1997,39(10):1691-1695
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material. 相似文献