全文获取类型
收费全文 | 346918篇 |
免费 | 3064篇 |
国内免费 | 1047篇 |
专业分类
化学 | 177388篇 |
晶体学 | 5884篇 |
力学 | 15505篇 |
综合类 | 7篇 |
数学 | 40400篇 |
物理学 | 111845篇 |
出版年
2021年 | 2645篇 |
2020年 | 2940篇 |
2019年 | 3291篇 |
2018年 | 4318篇 |
2017年 | 4299篇 |
2016年 | 6431篇 |
2015年 | 3911篇 |
2014年 | 6241篇 |
2013年 | 15620篇 |
2012年 | 11978篇 |
2011年 | 14433篇 |
2010年 | 10178篇 |
2009年 | 10083篇 |
2008年 | 13301篇 |
2007年 | 13275篇 |
2006年 | 12673篇 |
2005年 | 11346篇 |
2004年 | 10572篇 |
2003年 | 9401篇 |
2002年 | 9149篇 |
2001年 | 10496篇 |
2000年 | 7989篇 |
1999年 | 6198篇 |
1998年 | 5098篇 |
1997年 | 5028篇 |
1996年 | 4664篇 |
1995年 | 4389篇 |
1994年 | 4225篇 |
1993年 | 4028篇 |
1992年 | 4598篇 |
1991年 | 4533篇 |
1990年 | 4414篇 |
1989年 | 4162篇 |
1988年 | 4220篇 |
1987年 | 4252篇 |
1986年 | 3961篇 |
1985年 | 5200篇 |
1984年 | 5472篇 |
1983年 | 4653篇 |
1982年 | 4891篇 |
1981年 | 4700篇 |
1980年 | 4576篇 |
1979年 | 4771篇 |
1978年 | 4898篇 |
1977年 | 4838篇 |
1976年 | 4937篇 |
1975年 | 4686篇 |
1974年 | 4631篇 |
1973年 | 4894篇 |
1972年 | 3175篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
A brief account of applications of polarized inelastic neutron scattering in condensed matter research is given. We show that
full polarization analysis is the only tool allowing to discriminate unambiguously between different magnetic modes in various
magnetic materials. We show by means of recent results in the Heisenberg ferromagnet EuS that the effects of dipolar interactions
can be studied on a microscopic scale. Moreover, we have found for the first time indications for the divergence of the longitudinal
fluctuations belowT
c. In the itinerant antiferromagnet chromium we demonstrate that the dynamics of the longitudinal and transverse excitations
are very different, resolving a long standing puzzle concerning the slope of their dispersion. Finally, we show that a measurement
of the polarization-dependent part of the cross section of non-centrosymmetric MnSi proves directly that the chirality of
the magnetic fluctuations is left-handed. 相似文献
132.
Dedushenko S. K. Makhina I. B. Mar'in A. A. Mukhanov V. A. Perfiliev Yu. D. 《Hyperfine Interactions》2004,158(1-4):417-421
A colourless quartz crystal doped with 57Fe3+ was obtained by hydrothermal synthesis in an NH4F solution. The crystal was transformed into violet amethyst by gamma-irradiation. The change in colour was accompanied by changes in the Mössbauer spectrum that can be interpreted as the conversion of trivalent iron into the tetravalent state: Fe3+→Fe4+.
相似文献133.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献
134.
M. D. Srinivas 《Pramana》2003,60(6):1137-1152
We derive an optimal bound on the sum of entropic uncertainties of two or more observables when they are sequentially measured
on the same ensemble of systems. This optimal bound is shown to be greater than or equal to the bounds derived in the literature
on the sum of entropie uncertainties of two observables which are measured on distinct but identically prepared ensembles
of systems. In the case of a two-dimensional Hilbert space, the optimum bound for successive measurements of two-spin components,
is seen to be strictly greater than the optimal bound for the case when they are measured on distinct ensembles, except when
the spin components are mutually parallel or perpendicular 相似文献
135.
We perform a comparative analysis of two mechanisms for the formation of a synthetic aperture radar (SAR) image of the ocean, which are related to orbital velocities on the surface. It is shown that the mechanism of fluctuations of the effective density of scatterers, which is commonly accepted at present as the physical basis for the SAR diagnostics of roughness, actually works only in the case of a sufficiently flat swell. In the presence of wind roughness, the dominant role is played by another mechanism, namely, fluctuations of the number of surface elements whose images are randomly shifted and superimposed in the image plane due to orbital velocities. In the case of a developed wind roughness propagated in the azimuthal direction, the power contributions of two above-mentioned mechanisms to the SAR imaging of the ocean differ by about two orders of magnitude. 相似文献
136.
D. Ruiz 《Journal of Differential Equations》2004,199(1):96-114
In this paper we study the existence of positive solutions for a nonlinear Dirichlet problem involving the m-Laplacian. The nonlinearity considered depends on the first derivatives; in such case, variational methods cannot be applied. So, we make use of topological methods to prove the existence of solutions. We combine a blow-up argument and a Liouville-type theorem to obtain a priori estimates. Some Harnack-type inequalities which are needed in our reasonings are also proved. 相似文献
137.
We study the similarity of perturbed compact operators to operators of block-diagonal structure with respect to some family of orthogonal projection operators, which allows us to refine and essentially strengthen results due to R. Turner. We obtain information about the operator realizing the similarity transformation, present estimates for the eigenvalues and eigenvectors of the perturbed operator, and also study the inverse problem of spectral analysis. 相似文献
138.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
139.
Silica@copper (SiO2@Cu) core–shell nanoparticles were synthesized and well characterized by XRD, TEM, AFM, XPS, UV/Vis, TGA–MS, and ICP–AES techniques. The synthesized SiO2@Cu core–shell nanoparticles were employed as catalysts for the conjugate addition of amines to α,β‐unsaturated compounds in water to obtain β‐amino carbonyl compounds in excellent yields in shorter reaction times. Furthermore, the catalyst works well for hetero‐Michael addition reactions of heteroatom nucleophiles such as thiols to α,β‐unsaturated compounds. As the reaction is performed in water, it allows for easy recycling of the catalyst with consistent activity. 相似文献
140.
V. P. Ershov D. A. Kas’yanov V. I. Rodchenkov D. A. Sergeev 《Crystallography Reports》2008,53(2):339-343
The growth of the isolated (100) face of a KDP crystal at exposure of the phase boundary to the initial ultrasound field and a standing acoustic wave has been investigated. A significant growth response of this face, exposed to sound normally along the acoustic axis in the near zone of a piston-like half-wave vibrator with f = 20 kHz and tangentially in the pulsed two-frequency (f = 600 and 900 kHz) standing-wave mode, has been revealed. It is shown that the mechanisms of mass exchange enhancement in these acoustic modes are different. The results obtained show a fundamental possibility of controlling crystal growth and dissolution by varying the parameters of inhomogeneous acoustic field. 相似文献