全文获取类型
收费全文 | 1015篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
化学 | 609篇 |
晶体学 | 22篇 |
力学 | 11篇 |
数学 | 282篇 |
物理学 | 120篇 |
出版年
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 18篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 63篇 |
2012年 | 53篇 |
2011年 | 50篇 |
2010年 | 23篇 |
2009年 | 23篇 |
2008年 | 47篇 |
2007年 | 66篇 |
2006年 | 60篇 |
2005年 | 35篇 |
2004年 | 53篇 |
2003年 | 29篇 |
2002年 | 36篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1988年 | 8篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 12篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 16篇 |
1971年 | 12篇 |
1970年 | 14篇 |
1969年 | 13篇 |
1968年 | 14篇 |
1967年 | 10篇 |
排序方式: 共有1044条查询结果,搜索用时 578 毫秒
71.
Nassimbeni Luigi R. Niven Margaret L. Stuart Debra A. Zemke Klaus J. 《Journal of chemical crystallography》1986,16(4):557-567
The crystal structure of the 21 channel complex of desoxycholic acid and ethyl acetate has been investigated at 298 and 163 K. The space group isP212121(No. 19) with four molecules of desoxycholic acid in the unit cell. The ethyl acetate molecules are enclathrated along the 21 axes parallel toc and exhibit differing degrees of disorder in the low- and room-temperature structures. Differences in the disorder imply that it is both statistical and dynamic in nature. Our best model for each structure yieldsR=0.064 [R
w
=0.058,w=(
2
F)–1] andR=0.068 [R
w
=0.064,w=(
2
F)
–1
] for the ambient- and low-temperature studies respectively.IUPAC Nomenclature: 3, 12-dihydroxy-5-cholan-24-oic acid. 相似文献
72.
The infrared spectra (700–150 cm?1) of twenty-six complexes of 2-aminomethylpyridine (amp) with first transition series metal(II) ions are discussed. The complexes include the tris(amp) complexes [M(amp)3]2+ the bis(amp) compounds M(amp)2X2 and the mono(amp) complexes M(amp)X2. Assignments of the NH2 rocking modes, v(M-NH2), v(M-py) and ligand modes are based on the effects of isotopic labelling of the amino group and the effects of substitution of the metal ion and halide. The structural implications of the spectra are discussed. 相似文献
73.
74.
This paper describes the design, construction and use of a field-cycled proton-electron double-resonance imaging (FC-PEDRI) system for the detection and imaging of free radicals. The unique feature of this imager is its use of a 450-mT detection magnetic field in order to achieve good image quality and sensitivity. The detection magnetic field is provided by a superconducting magnet, giving high stability and homogeneity. Field cycling is implemented by switching on and off the current in an internal, coaxial, resistive secondary magnet that partially cancels the superconducting magnet's field at the sample; the secondary magnet is actively shielded to avoid eddy currents. EPR irradiation takes place at approximately 5 mT, following which the field is switched to 450 mT in 40 ms for NMR signal detection. Full details of the imager's subsystems are given, and experiments to image the distribution of stable free radical contrast agents in phantoms and in anesthetized rats are described. 相似文献
75.
Jenkins MA 《Electrophoresis》2004,25(10-11):1555-1560
Using capillary electrophoresis (CE) for serum protein electrophoresis, the quality of results begins with monitoring a well-functioning instrument, using scrupulously clean capillaries, well-calibrated methods as well as regular use of an internal quality control material. Quality assurance programs are available in countries such as Australia, United Kingdom, United States, and European countries such as Sweden and Germany. The present commercial control material that is available gives percentages of albumin, alpha 1, alpha 2, beta- and gamma-globulins, the gamma-component being of normal distribution, and not containing any monoclonal protein component. We feel that a quantitative commercial control material containing a monoclonal protein at decision level for treating myeloma patients would be beneficial to all laboratories as a serum protein electrophoresis control, whether the analysis is by CE or agarose gels. The same applies for control material for urinary protein electrophoresis. 相似文献
76.
[reaction: see text] The synthesis of the fused aromatic spiroketal core of gamma-rubromycin is described via addition of an aryl acetylide fragment to an aryl acetaldehyde fragment. In turn, the aryl acetylene precursor was readily prepared with use of a Sonogashira reaction. 相似文献
77.
78.
The stability of traveling wave solutions of scalar viscous conservation laws is investigated by decomposing perturbations into three components: two far-field components and one near-field component. The linear operators associated to the far-field components are the constant coefficient operators determined by the asymptotic spatial limits of the original operator. Scaling variables can be applied to study the evolution of these components, allowing for the construction of invariant manifolds and the determination of their temporal decay rate. The large time evolution of the near-field component is shown to be governed by that of the far-field components, thus giving it the same temporal decay rate. We also give a discussion of the relationship between this geometric approach and previous results, which demonstrate that the decay rate of perturbations can be increased by requiring that initial data lie in appropriate algebraically weighted spaces. 相似文献
79.
80.
Catherine Kealley Margaret Elcombe Arie Van Riessen 《Journal of synchrotron radiation》2008,15(1):86-90
Synchrotron radiation diffraction data were collected from hydroxyapatite–carbon nanotube bioceramic composites to determine the crystallite size and to measure changes in non‐uniform strain. Estimates of crystallite size and strain were determined by line‐profile fitting of discrete peaks and these were compared with a Rietveld whole‐pattern analysis. Overall the two analysis methods produced very similar numbers. In the commercial hydroxyapatite material, one reflection in particular, (0 2 3), has higher crystallite size and lower strain values in comparison with laboratory‐synthesized material. This could indicate preferential crystal growth in the [0 2 3] direction in the commercial material. From the measured strains in the pure material and the composite, there was a degree of bonding between the matrix and strengthening fibres. However, increasing the amount of carbon nanotubes in the composite has increased the strain in the material, which is undesirable for biomedical implant applications. 相似文献