全文获取类型
收费全文 | 440687篇 |
免费 | 3664篇 |
国内免费 | 1219篇 |
专业分类
化学 | 205665篇 |
晶体学 | 6035篇 |
力学 | 24068篇 |
综合类 | 9篇 |
数学 | 82913篇 |
物理学 | 126880篇 |
出版年
2020年 | 2532篇 |
2019年 | 2729篇 |
2018年 | 19166篇 |
2017年 | 19692篇 |
2016年 | 13423篇 |
2015年 | 4723篇 |
2014年 | 5383篇 |
2013年 | 12644篇 |
2012年 | 16224篇 |
2011年 | 30374篇 |
2010年 | 18559篇 |
2009年 | 18675篇 |
2008年 | 25159篇 |
2007年 | 29913篇 |
2006年 | 11010篇 |
2005年 | 16479篇 |
2004年 | 12998篇 |
2003年 | 12603篇 |
2002年 | 9871篇 |
2001年 | 8036篇 |
2000年 | 6563篇 |
1999年 | 4848篇 |
1998年 | 4375篇 |
1997年 | 4308篇 |
1996年 | 4323篇 |
1995年 | 3823篇 |
1994年 | 3906篇 |
1993年 | 3586篇 |
1992年 | 4006篇 |
1991年 | 4000篇 |
1990年 | 3889篇 |
1989年 | 3770篇 |
1988年 | 3906篇 |
1987年 | 3762篇 |
1986年 | 3563篇 |
1985年 | 4812篇 |
1984年 | 5069篇 |
1983年 | 4214篇 |
1982年 | 4404篇 |
1981年 | 4333篇 |
1980年 | 4293篇 |
1979年 | 4258篇 |
1978年 | 4541篇 |
1977年 | 4363篇 |
1976年 | 4418篇 |
1975年 | 4099篇 |
1974年 | 4128篇 |
1973年 | 4325篇 |
1972年 | 2970篇 |
1971年 | 2469篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
961.
G. Kh. Panova M. N. Khlopkin N. A. Chernoplekov A. A. Shikov 《Physics of the Solid State》2002,44(7):1218-1223
The specific heats of the Ni2B amorphous system and of its crystal analog were studied in the temperature range 3–270 K. The data obtained permitted us to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, determine the electronic density of states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ, and to calculate some average frequencies (moments) of the vibrational spectrum. The electronic density of states at the Fermi level increases under amorphization. An analysis of the temperature dependence of the lattice specific heat showed that amorphization brings about a substantial growth in the density of vibrational states at low frequencies, whereas the spectrum-averaged and rms frequencies change very little, which is in good agreement with neutron diffraction measurements. 相似文献
962.
A self-consistent model of the development of dendrites and partial discharges in a dielectric solid under a variable voltage
is suggested. Dendrites originate at sites with the enhanced local field strength and also where the dielectric is broken
down under the action of partial discharges. The numerical simulation is used to quantitatively describe the space-time dynamics
of the dendrites and partial discharges in epoxy resin for the tip-plane electrode configuration. The simulated data are compared
with electrical measurements of partial discharges and with optical images of dendrite growth under the same conditions. 相似文献
963.
Ivonin I. V. Krasil'nikova L. M. Lavrent'eva L. G. Porokhovnichenko L. P. 《Russian Physics Journal》2002,45(5):493-497
Experimental proofs of asymmetric trapping of atoms at the growth step in vapor-phase epitaxy of gallium arsenide in the GaAs–AsCl3–H2 system are given. The data obtained confirm the important role of the surface diffusion mass transfer in the growth of epitaxial GaAs layers on vicinals in the neighborhood of (111)A. The effective diffusion length is estimated. 相似文献
964.
The most promising next generation Image Velocimtry (IV) is the high-speed Dynamic PIV. It requires the development of innovative
high-speed video camera sensors. We started by specifying the required performance of these new sensors, for measurements
in air and water flows. These criteria founded on the most recent developments in PIV algorithms and incorporate results from
a large questionnaire survey of users of high-speed video cameras in Japan. The results suggest that the followings are required:
(1) frame rate of 1,000,000 fps, (2) pixel count of 1,000,000 pixels, (3) frame storage capacity of 100–200 frames for tracing
a single event and 10,000 frames for turbulent measurements, (4) gray levels of 4–8 bits for PTV; 12 bits for observation.
Finally, we reviewed the state of the art of high-speed video-image sensors. Currently the standard parallel-readout sensors
can operate at 1 Kfps with a pixel count of approximately 1 Kpixels. The In-situ Storage Image Sensor (ISIS) developed by
the authors has recently achieved frame rates of 1 Mfps. 相似文献
965.
Switching kinetics of uniaxial ferroelastic ferroelectrics (FFs) in external electric and stress fields is studied using classical theory of nucleation and growth. The stage in which the polarization and deformation reversal involves the main body of the FF and the final stage (Ostwald ripening) of the FF switching are studied with allowance for the change in the repolarization and redeformation during the phase transition. The time dependences of the repolarization and redeformation are found, and equations are derived from which the polarization current and the deformation flux, as well as their time dependence, can be calculated. The calculated main characteristics of the FF switching are compared with the experimental data for switching of Rochelle salt single crystals. 相似文献
966.
This paper reports on the results of experimental investigations into the thermal conductivity of GaS and GaSe layered semiconductor crystals in directions parallel and perpendicular to the crystal layers in the temperature range 5–300 K. Specific features of the thermal conductivity of these crystals are analyzed. 相似文献
967.
We clarify the way in which cosmological perturbations of quantum origin, produced during inflation, assume classical properties. Two features play an important role in this process: First, the dynamics of fluctuations which are presently on large cosmological scales leads to a very peculiar state (highly squeezed) that is indistinguishable, in a precise sense, from a classical stochastic process. This holds for almost all initial quantum states. Second, the process of decoherence by interaction with the environment distinguishes the field amplitude basis as the robust pointer basis. We discuss in detail the interplay between these features and use simple analogies such as the free quantum particle to illustrate the main conceptual issues. 相似文献
968.
G. D. Kartashov 《Journal of Mathematical Sciences》1995,75(1):1389-1393
A point estimator is proposed for certain numerical characteristics of a bivariate normal distribution with parameters that
cannot be observed simultaneously.
Translated fromStatisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 21–28, Perm, 1990. 相似文献
969.
This paper considers a problem of nonlinear programming in which the objective function is the ratio of two linear functions and the constraints define a bounded and connected feasible region. Using a coordinate transformation, this problem is transformed into a simpler one, whose geometric interpretation is of particular significance. The transformation leads to a characterization of some special vertices of the feasible region from both the theoretical and operational points of view. 相似文献
970.
Jati K. Sengupta 《The Journal of the Operational Research Society》1996,47(11):1387-1397
A method is developed here for characterizing the empirical distribution of the efficient units in data envelopment analysis. Two empirical applications illustrate the various uses of the distribution approach. One involves the cost frontier which exhibits increasing returns to scale and the other involves a dynamic production frontier, where technological change causes a shift of the production frontier over time. 相似文献