全文获取类型
收费全文 | 1349427篇 |
免费 | 29724篇 |
国内免费 | 7692篇 |
专业分类
化学 | 672188篇 |
晶体学 | 20455篇 |
力学 | 75116篇 |
综合类 | 105篇 |
数学 | 242618篇 |
物理学 | 376361篇 |
出版年
2021年 | 13507篇 |
2020年 | 15920篇 |
2019年 | 16047篇 |
2018年 | 13819篇 |
2016年 | 28415篇 |
2015年 | 20868篇 |
2014年 | 30452篇 |
2013年 | 74398篇 |
2012年 | 38523篇 |
2011年 | 36186篇 |
2010年 | 37737篇 |
2009年 | 40078篇 |
2008年 | 35017篇 |
2007年 | 31080篇 |
2006年 | 35942篇 |
2005年 | 28937篇 |
2004年 | 30073篇 |
2003年 | 28221篇 |
2002年 | 29150篇 |
2001年 | 29037篇 |
2000年 | 24948篇 |
1999年 | 22597篇 |
1998年 | 21090篇 |
1997年 | 21085篇 |
1996年 | 21118篇 |
1995年 | 19186篇 |
1994年 | 18640篇 |
1993年 | 18171篇 |
1992年 | 18228篇 |
1991年 | 18499篇 |
1990年 | 17707篇 |
1989年 | 17761篇 |
1988年 | 17317篇 |
1987年 | 17322篇 |
1986年 | 16262篇 |
1985年 | 22670篇 |
1984年 | 23876篇 |
1983年 | 20054篇 |
1982年 | 21691篇 |
1981年 | 20915篇 |
1980年 | 20265篇 |
1979年 | 20502篇 |
1978年 | 21747篇 |
1977年 | 21353篇 |
1976年 | 21059篇 |
1975年 | 19719篇 |
1974年 | 19368篇 |
1973年 | 19819篇 |
1972年 | 14304篇 |
1967年 | 12554篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
To investigate local ordering and segregation phenomenon in a Ni91Pt9-alloy after sputtering and annealing a 3D optical atom probe (OAP) has been used. The specimen tips have been prepared from polycrystalline samples. To sputter the samples a separate preparation chamber with a scannable Ar-sputter-gun is connected to the OAP vessel. When necessary, the sample can be electrically heated to induce segregation and cure the altered layer. After a heat treatment of a Ni91 at. %Pt 9 at.% specimen at 1100 K the surface of a (111)-oriented specimen is enriched in platinum by a factor of two in relation to the bulk. The phenomenon of short-range ordering has been investigated on the surface and in the subsurface volume. A 3D reconstruction of this annealed NiPt specimen shows regions with high concentration of platinum that gives an indication at short-range ordering. Uniform sputtering of the tip without a heat treatment induces a decisive depletion of Pt on the surface and the following subatomic layers. The atom-probe results of specimens in thermal equilibrium are in close agreement to further surface sensitive results obtained from Ion Scattering Spectroscopy (ISS) and Auger Electron Spectroscopy (AES). 相似文献
982.
983.
In electrodialysis using thin membranes and spacers, the compactness of the membrane cell-pairs leads to a small potential drop, and hence to energy saving. The spacer design itself has a great effect on the cost of the plants, since spacers act as turbulence promoters. A careful design, to increase the mass transfer coefficients, can reduce the membrane surface area required for a given application. Limiting current measurements, cell-pair resistance and pressure losses are presented for several thin spacers, for different flow-velocity values and feed water concentrations. It was possible to find an advantageous geometry of the separating mesh leading to substantial savings on investment and operation costs. 相似文献
984.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2]
n
·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993. 相似文献
985.
986.
987.
988.
Summary This paper is concerned with the problem of developing numerical integration algorithms for differential equations that, when
viewed as equations in some Euclidean space, naturally evolve on some embedded submanifold. It is desired to construct algorithms
whose iterates also evolve on the same manifold. These algorithms can therefore be viewed as integrating ordinary differential
equations on manifolds. The basic method “decouples” the computation of flows on the submanifold from the numerical integration
process. It is shown that two classes of single-step and multistep algorithms can be posed and analyzed theoretically, using
the concept of “freezing” the coefficients of differential operators obtained from the defining vector field. Explicit third-order
algorithms are derived, with additional equations augmenting those of their classical counterparts, obtained from “obstructions”
defined by nonvanishing Lie brackets. 相似文献
989.
A method using capillary gel electrophoresis with laser-induced fluorescence detection is described which permits complete sequence determination of antisense DNA analogues of unknown sequence. This method, originally created as a tool to confirm the sequence of antisense oligonucleotides being developed as therapeutic drugs, utilizes data collected under a range of experimental conditions described by the Ogston model as applied to gel electrophoresis. A linear relationship independent of experimental conditions between the relative electrophoretic migration time and the oligonucleotide base number was observed and is shown to be consistent with a simplified version of this model and can be used to facilitate the sequence determination. 相似文献
990.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献