全文获取类型
收费全文 | 579577篇 |
免费 | 17917篇 |
国内免费 | 8476篇 |
专业分类
化学 | 305800篇 |
晶体学 | 8170篇 |
力学 | 28761篇 |
综合类 | 323篇 |
数学 | 78438篇 |
物理学 | 184478篇 |
出版年
2022年 | 4581篇 |
2021年 | 6319篇 |
2020年 | 7171篇 |
2019年 | 7301篇 |
2018年 | 14756篇 |
2017年 | 15099篇 |
2016年 | 15270篇 |
2015年 | 9439篇 |
2014年 | 12538篇 |
2013年 | 25363篇 |
2012年 | 25248篇 |
2011年 | 35010篇 |
2010年 | 23396篇 |
2009年 | 23093篇 |
2008年 | 30255篇 |
2007年 | 32256篇 |
2006年 | 20000篇 |
2005年 | 22776篇 |
2004年 | 18500篇 |
2003年 | 16425篇 |
2002年 | 14544篇 |
2001年 | 14947篇 |
2000年 | 11626篇 |
1999年 | 9462篇 |
1998年 | 7915篇 |
1997年 | 7630篇 |
1996年 | 7538篇 |
1995年 | 6608篇 |
1994年 | 6391篇 |
1993年 | 6037篇 |
1992年 | 6563篇 |
1991年 | 6577篇 |
1990年 | 6223篇 |
1989年 | 5922篇 |
1988年 | 5904篇 |
1987年 | 5733篇 |
1986年 | 5414篇 |
1985年 | 6844篇 |
1984年 | 6944篇 |
1983年 | 5487篇 |
1982年 | 5555篇 |
1981年 | 5520篇 |
1980年 | 5115篇 |
1979年 | 5484篇 |
1978年 | 5629篇 |
1977年 | 5457篇 |
1976年 | 5424篇 |
1975年 | 4991篇 |
1974年 | 4954篇 |
1973年 | 4998篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
M. P. Nosov V. A. Smirnova Yu. F. Zabashta A. Ya. Fridman M. P. Mokhnach 《Mechanics of Composite Materials》1989,25(1):8-12
Conclusion A method was proposed which makes it possible to study the low-frequency internal friction of complex fibers. This method was used to study the internal friction of complex composite fibers based on PCA and PE. We observed a relaxation process which is typical of the composite and is absent in the pure materials.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 11–15, January–February, 1989. 相似文献
983.
M. Faucher D. Garcia E. Antic-Fidancev M. Lemaitre-Blaise 《Journal of Physics and Chemistry of Solids》1989,50(12)
Some structural and spectroscopic features of rare earth orthoaluminates are examined.The trigonal→ orthorhombic transition is studied in a series of NdxSm1−xAlO3 compounds. The evolution of the crystal structure is followed by X-ray analysis and optical absorption. The free ion and crystal field parameters of Nd3+ (4f3 configuration) are determined in LuAlO3:Nd3+.The anomaly of the calculated splitting of the
levels is slight, but well characterized in NdAlO3. The spin correlated crystal field and orbitally correlated crystal field models are tested as well as an empirical correction which was proposed earlier. 相似文献
984.
In an effort to clarify the role of controlled oxygen exposure in the synthesis of LaBa2Cu3Oy samples which achieve zero resistivity above 90 K, we have prepared samples of La(1+x)Ba(2–x)Cu3Oy with x approximately equal to 0 and with y varying between 6.22 and 7.00. We find that for large values of y, 6.88相似文献
985.
D. B. Kayumova Yu. P. Syrnikov N. V. Penkina M. N. Rodnikova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(10):1634-1635
The structural relaxation time for series of various liquids (alkanes, aliphatic alcohols, and diols) are calculated from published data on the shear viscosity and the heat of evaporation per unit volume. Liquids having a 3D H-bond network (diols) are characterized by relaxation times one to two orders of magnitudes longer than those typical of liquids without such a network (alkanes and aliphatic alcohols). 相似文献
986.
Flávio A. Pavan Yoshitaka Gushikem Celso C. Moro Tania M. Costa Edilson V. Benvenutti 《Colloid and polymer science》2003,281(2):173-177
Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels. 相似文献
987.
Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations. 相似文献
988.
Based on the Fourier transform method, a simple closed-form expression for the on-axis power spectrum of ultrashort Gaussian pulsed beams in diffraction at a circular aperture is derived, which permits us to study spectral changes both analytically and numerically. It is shown that for diffracted pulsed beams there exist spectral red and blue shifts, spectral narrowing, and spectral switches in the near field. The aperture diffraction plays an important role in spectral switching, but both the truncation parameter and bandwidth (or equally, Fourier transform limited pulse duration) affect the behavior of spectral switches. 相似文献
989.
We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given. 相似文献
990.
A method of solving the problem of sound radiation from a plate with elements of different thickness in its plane is proposed, and the results obtained with this method are presented. It is shown that the main sources of sound radiation are the inhomogeneous flexural fields formed in the elements on both sides of their joint. 相似文献