全文获取类型
收费全文 | 393169篇 |
免费 | 4975篇 |
国内免费 | 1913篇 |
专业分类
化学 | 220012篇 |
晶体学 | 6165篇 |
力学 | 16000篇 |
综合类 | 65篇 |
数学 | 41629篇 |
物理学 | 116186篇 |
出版年
2018年 | 3611篇 |
2017年 | 3624篇 |
2016年 | 5658篇 |
2015年 | 3952篇 |
2014年 | 5680篇 |
2013年 | 16000篇 |
2012年 | 12154篇 |
2011年 | 15037篇 |
2010年 | 10416篇 |
2009年 | 10258篇 |
2008年 | 13928篇 |
2007年 | 14196篇 |
2006年 | 13428篇 |
2005年 | 12265篇 |
2004年 | 11061篇 |
2003年 | 9895篇 |
2002年 | 9733篇 |
2001年 | 11512篇 |
2000年 | 8831篇 |
1999年 | 6711篇 |
1998年 | 5449篇 |
1997年 | 5453篇 |
1996年 | 5432篇 |
1995年 | 4878篇 |
1994年 | 4847篇 |
1993年 | 4616篇 |
1992年 | 5336篇 |
1991年 | 5268篇 |
1990年 | 5036篇 |
1989年 | 5018篇 |
1988年 | 4908篇 |
1987年 | 4885篇 |
1986年 | 4687篇 |
1985年 | 6257篇 |
1984年 | 6335篇 |
1983年 | 5269篇 |
1982年 | 5669篇 |
1981年 | 5385篇 |
1980年 | 5129篇 |
1979年 | 5447篇 |
1978年 | 5822篇 |
1977年 | 5698篇 |
1976年 | 5649篇 |
1975年 | 5273篇 |
1974年 | 5360篇 |
1973年 | 5427篇 |
1972年 | 3924篇 |
1971年 | 3195篇 |
1968年 | 3483篇 |
1967年 | 3644篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
961.
The oxide films formed on AISI 304L stainless steel at 300 °C in the oxidation time range between 2 and 4 h have been studied by photoelectrochemistry. Photocurrents were investigated as a function of the wavelength of the incident light and the electrode potential. The investigation allowed the determination of the semiconductive properties of the oxides. The oxide films showed n-type behaviour. A duplex structure of the oxide films has been suggested on the basis of the photocurrent spectra, with an internal oxide layer having an optical gap (Eg2 = 2.16-2.3 eV) depending on the applied potential and oxidation time, higher to that of the external oxide layer (Eg1 ≈ 1.9 eV). Significant variations in the amplitude of the photocurrent were detected as a function of the applied potential and the oxidation time. 相似文献
962.
Yu. D. Perfiliev V. S. Rusakov L. A. Kulikov A. A. Kamnev K. Alkhatib 《Hyperfine Interactions》2006,167(1-3):881-885
To explain line broadening in emission Mössbauer spectra as compared to the corresponding absorber measurements, the model of trapped electrons has been proposed. Auger electrons (emitted, e.g. after electron capture by 57Co or after the converted isomeric transition of 119mSn), as well as secondary electrons, may be trapped in the proximity to the nucleogenic ion. Electrons captured by lattice traps at different distances from the daughter ion induce an asymmetric distribution of quadrupole splitting in the resulting emission spectra, as shown in a few examples. This model is supported by estimates of quadrupole splitting values which may be caused by such trapped electrons located at specified distances from the nucleogenic atom. 相似文献
963.
Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic
energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping
to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties
in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been
evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic
domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural
and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm
in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron
scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films. 相似文献
964.
The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found. 相似文献
965.
We have characterized multidielectric scaled SONOS nonvolatile memory structures with the quasi-static linear voltage ramp (LVR) technique and dynamic pulse measurements. We have formulated physically-based ERASE/WRITE and retention methods with deep level amphoteric traps which capture and emit carriers to the bands in the silicon nitride film. Amphoteric trap parameters are extracted by the LVR technique. ERASE/WRITE and retention amphoteric trap model simulations agree well with the experimental dynamic pulse measurements. Experimental scaled SONOS structures have been fabricated with tunnel oxide XOT=20 Å, nitride XN=30 Å and blocking oxide XOB=55 Å and demonstrated a static flatband shift of 3.6 V with ±5 V programming voltages. These structures may be used as the nonvolatile memory element in high density VLSI circuits. 相似文献
966.
967.
968.
969.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
970.