全文获取类型
收费全文 | 432280篇 |
免费 | 4168篇 |
国内免费 | 1324篇 |
专业分类
化学 | 222749篇 |
晶体学 | 7045篇 |
力学 | 19695篇 |
综合类 | 12篇 |
数学 | 49639篇 |
物理学 | 138632篇 |
出版年
2021年 | 3539篇 |
2020年 | 3871篇 |
2019年 | 4265篇 |
2018年 | 5697篇 |
2017年 | 5877篇 |
2016年 | 8400篇 |
2015年 | 4937篇 |
2014年 | 8094篇 |
2013年 | 19856篇 |
2012年 | 15007篇 |
2011年 | 18210篇 |
2010年 | 13123篇 |
2009年 | 12856篇 |
2008年 | 16282篇 |
2007年 | 16212篇 |
2006年 | 15205篇 |
2005年 | 13572篇 |
2004年 | 12482篇 |
2003年 | 11086篇 |
2002年 | 11024篇 |
2001年 | 12914篇 |
2000年 | 9626篇 |
1999年 | 7610篇 |
1998年 | 6425篇 |
1997年 | 6283篇 |
1996年 | 5947篇 |
1995年 | 5300篇 |
1994年 | 5065篇 |
1993年 | 4984篇 |
1992年 | 5557篇 |
1991年 | 5703篇 |
1990年 | 5468篇 |
1989年 | 5388篇 |
1988年 | 5198篇 |
1987年 | 5292篇 |
1986年 | 5024篇 |
1985年 | 6484篇 |
1984年 | 6643篇 |
1983年 | 5509篇 |
1982年 | 5881篇 |
1981年 | 5447篇 |
1980年 | 5444篇 |
1979年 | 5695篇 |
1978年 | 5829篇 |
1977年 | 5741篇 |
1976年 | 5751篇 |
1975年 | 5455篇 |
1974年 | 5269篇 |
1973年 | 5494篇 |
1972年 | 3762篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
A. S. Merkur'ev 《Journal of Mathematical Sciences》1991,57(6):3489-3497
This article considers the splitting properties of finite-dimensional division rings over universal splitting fields of quadratic forms. An example of a field with u-invariant equal to 6 is constructed, which contradicts Kaplansky's conjecture concerning u-invariants.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im, V. A. Steklova Akademii Nauk SSSR, Vol. 175, pp. 75–89, 1989. 相似文献
32.
The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies ωmw and ωrf, respectively, is analyzed. The effective time-independent Hamiltonian describing the “dressed” spin states of the “spin + bichromatic field” system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances ω0 = ωmw + rωrf (ω0 is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies. 相似文献
33.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
34.
35.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
36.
A successful application of ultrasound Doppler velocimetry in liquid sodium flows is described. To obtain sufficient Doppler
signals, different problems had to be solved: the transmission of the ultrasonic beam through the channel wall made of stainless
steel, the acoustic coupling between the transducer and the channel wall, and the wetting of the inner surface of the wall
by the liquid metal, respectively. A sodium flow in a square duct exposed to a transverse magnetic field is investigated.
In accordance with the existing knowledge about MHD channel flows, we found that the velocity profiles modified to a M-shape
owing to the effect of an inhomogeneous magnetic field.
Received: 12 June 2001/Accepted: 27 October 2001 相似文献
37.
38.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
39.
The variational problem of contact equilibrium of a punch and an elastic body is considered. An equivalent formulation of the problem is given in variational inequality form. Existence and uniqueness of the solution is investigated in a particular case. A penalty method is proposed for approximate solution of the problem.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 97–103, 1985. 相似文献
40.