全文获取类型
收费全文 | 690篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
化学 | 423篇 |
晶体学 | 3篇 |
力学 | 25篇 |
数学 | 99篇 |
物理学 | 156篇 |
出版年
2022年 | 8篇 |
2021年 | 9篇 |
2019年 | 10篇 |
2018年 | 20篇 |
2017年 | 26篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 45篇 |
2012年 | 35篇 |
2011年 | 31篇 |
2010年 | 25篇 |
2009年 | 26篇 |
2008年 | 30篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 6篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1967年 | 4篇 |
1957年 | 7篇 |
1954年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有706条查询结果,搜索用时 423 毫秒
51.
A variety of thiocarbonyl derivatives (thioketone, thioester, thioamide, dithioester, and dithiocarbamate) were converted to the corresponding gem-difluorides in excellent yields on reaction with the fluorinating agent, bis(2-methoxyethyl)aminosulfur trifluoride, in the presence of SbCl(3). 相似文献
52.
The paper reports a structural study of some memory and threshold chalcogenides in terms of coordination numberC, defined byC=8−N, and is the average coordination number for covalently bonded materials. The average number of nearest neighbours surrounding
a central atom, obtained for As-Ge-Te (memory) and Se-Ge-Te (threshold) systems have been used to estimate the cohesive energies,
assuming simple additivity of bond energies. The bonding pattern so obtained, explains certain properties of these glasses. 相似文献
53.
The dissociation constants of some sulpha-drugs have been determined potentiometrically in 10–50% (v/v) dioxan—water media at 25° at ionic strength O.1M (NaClO4). Correlation of mole fraction of dioxan and pK gives a straight line. The pK values do not vary linearly with reciprocal of the dielectric constant of the medium at high percentage of dioxan. 相似文献
54.
S. Lal R. Raghavan T. N. Rangaswamy B. V. Sreekantan A. Subramanian S. D. Verma S. C. Tonwar R. H. Vatcha 《Proceedings Mathematical Sciences》1971,73(4):170-178
Detailed features of extremely collimated nuclear interactions induced by cosmic ray particles in carbon and brass (belonging to group I as classified in Part I of this series of papers) are presented. These extremely collimated nuclear interactions seem to be preferentially induced by pions rather than by nucleons; also the relative frequency of these seems to be less when brass is used as target compared to the case with carbon as target. The distribution of multiplicities of secondary particles emitted in the forward direction show certain regularities in the case of interactions induced by charged primaries. Observations on the γ-rays associated with these events give support to the interpretation that in these inelastic collisions pions are produced in pairs in the forward direction with low transverse momentum. It is suggested that such a low energy di-pion system could be the same as found in the so-called ABC effect. 相似文献
55.
Theoretical and experimental investigations of metal-jets, produced by interaction of a plane shock wave with a conical cavity at free surface of metals like aluminium, copper and mild steel, have been carried out and an attempt has been made to correlate the jet velocity with shock parameters. The velocity of the jet, obtained from the cavity of different half angles have been mostly measured with oscillographic technique. The experimental results agree with theory within experimental variations. The velocity of the jet increases monotonically with the particle velocity but decreases with increase in the angle of the cavity. 相似文献
56.
Hu X Jiao X Narayanan S Jiang Z K Sinha S Lurio LB Lal J 《The European physical journal. E, Soft matter》2005,17(3):353-359
We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion. 相似文献
57.
A comparative study with a vertically integrated model and the multi-level model has shown that the former can remain a good substitute for the latter in the prediction of sea-surface elevation as long as the bottom friction coefficients in the vertically integrated models are properly specified. 相似文献
58.
The k-higher Mahler measure of a non-zero polynomial P is the integral of log
k
|P| on the unit circle. In this note, we consider Lehmer’s question (which is a long-standing open problem for k=1) for k>1 and find some interesting formulas for 2- and 3-higher Mahler measure of cyclotomic polynomials. 相似文献
59.
Nd2O3-SiO2 binary oxide was prepared by solgel technique using tetra-ethoxysilane and neodymium nitrate as precursor materials and HCl as a catalyst. The prepared samples were subjected to heat treatment in the temperature range from 600 to 1100 °C for different time duration. Characterization of heat treated samples was carried out by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effect of sintering temperature and time on structural changes of Nd-doped silica has been discussed. The sample sintered at 1100 °C for 12 h shows the formation of monoclinic Nd2O3 nanocrystallites in silica matrix with average grain size ∼18 nm. 相似文献
60.
An operationally simple and high yielding procedure has been developed for the preparation of nitriles from aldoximes and primary amides using bromodimethylsulfonium bromide (BDMS) as a novel and efficient reagent in the absence of any added base or catalyst. The optimal protocol is applicable to access a wide range of cyano compounds including aromatic, heterocyclic, and aliphatic species. The conversion of aldoximes to nitriles takes place at room temperature in acetonitrile, whereas acetonitrile at reflux temperature is required for rapid conversion in the case of primary amides. 相似文献