全文获取类型
收费全文 | 1358133篇 |
免费 | 25791篇 |
国内免费 | 7706篇 |
专业分类
化学 | 682636篇 |
晶体学 | 20080篇 |
力学 | 74688篇 |
综合类 | 104篇 |
数学 | 242385篇 |
物理学 | 371737篇 |
出版年
2021年 | 13511篇 |
2020年 | 15925篇 |
2019年 | 16060篇 |
2016年 | 27522篇 |
2015年 | 20719篇 |
2014年 | 30483篇 |
2013年 | 74508篇 |
2012年 | 39173篇 |
2011年 | 36011篇 |
2010年 | 36732篇 |
2009年 | 38890篇 |
2008年 | 35284篇 |
2007年 | 30810篇 |
2006年 | 38326篇 |
2005年 | 29610篇 |
2004年 | 31143篇 |
2003年 | 29303篇 |
2002年 | 30550篇 |
2001年 | 30119篇 |
2000年 | 25831篇 |
1999年 | 23040篇 |
1998年 | 21284篇 |
1997年 | 21206篇 |
1996年 | 21200篇 |
1995年 | 19250篇 |
1994年 | 18681篇 |
1993年 | 18235篇 |
1992年 | 18377篇 |
1991年 | 18623篇 |
1990年 | 17823篇 |
1989年 | 17842篇 |
1988年 | 17437篇 |
1987年 | 17314篇 |
1986年 | 16321篇 |
1985年 | 22713篇 |
1984年 | 23899篇 |
1983年 | 20050篇 |
1982年 | 21762篇 |
1981年 | 20958篇 |
1980年 | 20282篇 |
1979年 | 20508篇 |
1978年 | 21798篇 |
1977年 | 21396篇 |
1976年 | 21145篇 |
1975年 | 19875篇 |
1974年 | 19576篇 |
1973年 | 20040篇 |
1972年 | 14512篇 |
1968年 | 12344篇 |
1967年 | 12672篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
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
142.
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
143.
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
144.
145.
146.
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
147.
A. J. Maroulis P. D. Akrivos C. P. Hadjiantoniou-Maroulis 《Journal of heterocyclic chemistry》1993,30(4):913-916
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity. 相似文献
148.
T. A. Beu 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(3):263-266
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented. 相似文献
149.
We develop an approach to the solution of the spinless Bethe-Salpeter equation for the different-mass case. Although the calculations are developed for spinzero particles in any arbitratry spherically symmetric potential, the non-Coulombic effective power-law potential is used as a kernel to produce the spin-averaged bound states of the non-self-conjugate mesons. The analytical formulas are also applicable to the self-conjugate mesons in the equal-mass case. The flavor-independent case is investigated in this work. The calculations are carried out to the third-order correction of the energy series. Results are consistent with those obtained before. 相似文献
150.