全文获取类型
收费全文 | 833篇 |
免费 | 16篇 |
专业分类
化学 | 669篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 39篇 |
物理学 | 131篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 51篇 |
2011年 | 45篇 |
2010年 | 41篇 |
2009年 | 30篇 |
2008年 | 57篇 |
2007年 | 51篇 |
2006年 | 53篇 |
2005年 | 39篇 |
2004年 | 27篇 |
2003年 | 15篇 |
2002年 | 20篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 20篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1935年 | 2篇 |
排序方式: 共有849条查询结果,搜索用时 15 毫秒
841.
María A. RamírezMaría V. Corona Gisela OrtizAlejandra Salerno Isabel A. PerilloMaría M. Blanco 《Tetrahedron letters》2011,52(13):1466-1468
A new approach for the synthesis of selectively N-substituted tetra- and pentamethylenediamines 1 (n = 4,5) is described. The method uses N-substituted ω-haloalkanamides 2 as precursors and involves the microwave-promoted conversion into ω-azidocarboxamides 3 and later the reduction of both azido and carboxamide groups with diborane. 相似文献
842.
Rodríguez-Solla H Concellón C Blanco EG Sarmiento JI Díaz P Soengas RG 《The Journal of organic chemistry》2011,76(13):5461-5465
A chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,β-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective β-elimination reaction is proposed to explain these results. 相似文献
843.
Kelly B O'Donovan DH O'Brien J McCabe T Blanco F Rozas I 《The Journal of organic chemistry》2011,76(22):9216-9227
The synthesis and conformational analysis of a series of pyridin-2-yl guanidine derivatives using NMR, X-ray crystallography, and B3LYP/6-31+G** theoretical studies are reported. A remarkable difference was observed in the (1)H NMR spectra of the guanidinium salts as compared with their N,N'-di-Boc protected and neutral analogues. This difference corresponds to a 180° change in the dihedral angle between the guanidine/ium moiety and the pyridine ring in the salts as compared to the Boc-protected derivatives, a conclusion that was supported by theoretical studies, X-ray data, and NMR analysis. Moreover, our data sustain the existence of two intramolecular hydrogen-bonding systems: (i) between the pyridine N1 atom and the guanidinium protons in the salts and (ii) within the tert-butyl carbamate groups of the Boc-protected derivatives. To verify that the observed conformational control arises from these intramolecular interactions, a new series of N-Boc-N'-propyl-substituted pyridin-2-yl guanidines were also prepared and studied. 相似文献
844.
Exchange-bias and superparamagnetic behaviour of Fe nanoparticles embedded in a porous carbon matrix
M.P. Fernández D.S. Schmool A.S. Silva M. Sevilla A.B. Fuertes P. Gorria J.A. Blanco 《Journal of Non》2008,354(47-51):5219-5221
Combining different experimental techniques, the physical properties of Fe nanoparticles (NPs) randomly dispersed in a porous carbon have been investigated. From the analysis of TEM images and the broad maximum observed in ZFC–FC magnetization measurements under an applied magnetic field of 2.5 mT, a broad-size distribution NPs (5–50 nm) is estimated. The nature of these NPs (α-Fe and γ-Fe) was determined from X-ray diffraction. Furthermore, magnetization measurements suggest that these Fe-NPs remain completely blocked below 60 K due to a magnetic exchange-bias coupling induced on the surface of these NPs. However, the true nature of the core–shell responsible for this exchange bias within the NPs, is not totally understood yet. In addition, the system begins to be magnetically unblocked above 60 K, becoming almost superparamagnetic above 200 K. Room temperature Mössbauer spectroscopy confirms the existence of both α- and γ-Fe phases; an additional quadrupole component is required to properly fit the spectrum, which could be associated with the NP’s shell or to an oxide phase probably located on the surface of the NPs. 相似文献
845.
A. Fernández-Martínez D. Martínez-Blanco M.J. Pérez G.J. Cuello G.R. Castro P. Gorria J.A. Blanco 《Journal of Non》2008,354(47-51):5156-5158
The temperature dependence of magnetization together with neutron powder thermo-diffraction show that nominal ball milled Fe30Cr70 for 110 h is formed of two mixed phases (Fe20Cr80 + Fe), both of them with body centered cubic crystal structure and very close values for the lattice parameter (~2.87 Å). On heating above 900 K, the system exhibits an irreversible structural transformation, giving rise to the homogenization of the material, and then recovering the well-defined starting composition Fe30Cr70. Subsequent heating-cooling neutron thermo-diffraction cycles do not show any additional transformation, thus explaining the overlapping M(T) curves after the first heating. 相似文献
846.
Ignazio Blanco Gianluca Cicala Giuseppe Recca Claudio Tosto 《Entropy (Basel, Switzerland)》2022,24(5)
This research focuses on the thermal characterization of 3D-printed parts obtained via fused filament fabrication (FFF) technology, which uses a poly(lactic acid) (PLA)-based filament filled with milled carbon fibers (MCF) from pyrolysis at different percentages by weight (10, 20, 30 wt%). Differential scanning calorimetry (DSC) and thermal conductivity measurements were used to evaluate the thermal characteristics, morphological features, and heat transport behavior of the printed specimens. The experimental results showed that the addition of MCF to the PLA matrix improved the conductive properties. Scanning electron microscopy (SEM) micrographs were used to obtain further information about the porosity of the systems. 相似文献
847.
Using time-resolved static and dynamic light scattering (DLS) we have studied the kinetics of phase separation in an aqueous gelatin/maltodextrin mixture upon fast cooling. The time evolution of the droplet radius is modelled for the monodisperse case under reaction-limited and diffusion-limited conditions and compared with the observed evolution of the mode associated with the droplet diffusion. For quenches to above the gelatin ordering temperature, nucleation and rather reaction-limited than diffusion-limited growth and late-stage coalescence of droplets with diameters up to 90 μm were concluded. Quenches to well below the gelatin ordering temperature seem to induce diffusion-limited growth or (delayed) spinodal decomposition (SD) to a phase-separated microstructure with slow late-stage coarsening. In deep quenches, a second slow SD or diffusion-limited cluster aggregation (DLCA) process becomes apparent from the evolution of the static structure factor; the process seems to be related to the maltodextrin gelation in the composite. 相似文献
848.
849.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献