全文获取类型
收费全文 | 297篇 |
免费 | 1篇 |
专业分类
化学 | 258篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 4篇 |
物理学 | 24篇 |
出版年
2019年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 15篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 8篇 |
2007年 | 6篇 |
2006年 | 2篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 17篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1966年 | 4篇 |
1965年 | 1篇 |
1956年 | 1篇 |
1917年 | 1篇 |
1912年 | 1篇 |
1890年 | 2篇 |
排序方式: 共有298条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
On the Chemical Transport of Cr2O3 with CrI3/I2 – Experiments and Model-Calculations for Participation of CrOI2,g Gaseous chromium oxyiodides that were unknown up to now cause the migration of Cr2O3 in the temperature gradient 1 000°C→900°C when iodine (e. g. 0.1 mmol/ml) and CrI3 is added (eq. (1)). Transport agent for Cr2O3 is gaseous CrI4. With a smaller concentration of iodine (D(I2) ? 0.016 mmol/ml) and lower temperatures (e.g. T? = 850°C) the influence of H2O (from the wall of the silica ampoule) becomes more important. Under these conditions the transport of Cr2O3 is a result from the endothermic reactions (2), (3) and (4). H2,g has on the basis of the decomposition of HIg a positive difference of the solubility and H2,g should not to be considered as a transport agent. Because of the range of equilibrium-values the reaction 4 has to be taken into consideration. Estimated value of the enthalpie for CrOI2,g is fixed more precisely by thermodynamic model calculation to ΔfH°298(CrOI2,g) = ?51.4 kcal/mol. The estimated limit of error for the enthalpie of formation is smaller than ± 5 kcal/mol. Without an addition of CrI3 is in the system Cr2O3/I2 a migration of Cr2O3 not observable. 相似文献
5.
8,15,23,30-Tetramethyl[2.1.2.1]metacyclophane,4, is synthesised. Variable temperature 1Hmr and 13Cmr spectra indicate that 4e is the most likely conformation and that at temperatures above 50°C the molecule is fluxional (ΔG≠323 = 15.4 kcal/mole). 相似文献
6.
Single-crystal X-ray analyses have defined the structures and solid-state conformations of (±)-N-benzoyl-3-methylaminocycloheptanone [(±)-]and (+)-N-benzoyl-4-methylaminocycloheptanone [(±)]. Resolution of (±)-[4- methylaminocycloheptanone α 1-hydroxytropane]to yield the (+)-enantiomer. Identical in all respects with the free base from natural (+)-physoperuvine, was achieved via the di-p-toluoyl-(+)-tartrate salt. 相似文献
7.
Reginald B. Little 《Journal of Cluster Science》2003,14(2):135-185
The discovery, synthesis, characterization, and applicability of carbon nanotubes have produced tremendous excitement and interest among scientists and engineers. In particular, the use of these unique tubular nanostructures for new strong lightweight materials, nanoelectronics, fuel storage and cells, electron emitters and bio, scanning probe microscopy, and chemical sensing devices has created an intense effort to advance the synthesis so as to mass produce carbon nanotubes with control over diameter and helicity. The massive and controlled synthesis of this heralded nanostructure has been a great challenge. Although significant progress has advanced the preparation, more synthetic development is required. The syntheses have so far involved three main approaches: arc discharge vaporization, laser vaporization, and catalytic chemical vapor deposition. The synthetic trend has progressed to a point where further advancement with these techniques will require a better understanding of the mechanism of nucleation and growth. The mechanics of carbon nanotube nucleation and growth involve very complex and diverse phenomena occurring under extreme conditions and on the mesoscopic scale. As yet the detail mechanism is unknown. Difficulties with experimental probing and computational simulation have increased the mystery of this mechanism. This review presents an account of research on the synthesis of carbon nanotubes and the mechanism of formation. This overview includes all three mentioned synthetic approaches and hybrids thereof. On the basis of this broad account a comprehensive mechanism for carbon nanotube nucleation and growth naturally arises. This mechanism is qualitative and it hopes to inspire more quantitative exploration and synthetic advancement. 相似文献
8.
On the Chemical Transport of Tungsten Oxides WO2 and W18O49 with Hgl2. Experiments and Calculations Transport experiments with WO2 or W + WO2 or WO2 + W18O49 show that HgI2 is a transport agent as suitable as I2. We observed transport rates up to 47 mg/h. We investigated the dependence of the transport rate on the concentration of the transport agent n°(HgI2) as well as on the temperature. We also investigated the time dependence of the transport rates during transport experiments on a “transport balance”. Starting with WO2 + W18O49, WO2 is transported before W18O49. Thermodynamic calculations show that transport of W18O49 is understandable if the presence of small amounts of H2O from the quartz glass wall are taken into consideration, while transport of WO2 is possible with HgI2 in the presence of H2O as well as in absence of H2O. is the most important reaction for the transport of WO2. 相似文献
9.
Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXI. On the Understanding of the Chemical Transport of Ti4O7, Ti5O9, and Ti6O11 in the Presence of the Transporting Agents HgCl2 and TeCl4 Transport experiments starting with a phase TinO2n?1 (e.g. Ti4O7) and with HgCl2 as transporting agent show, that in a temperature gradient at the lower temperature T1 the neighbour phase with a higher oxygen content Tin+1O2n+1 (e.g. Ti5O9) is deposited. As we know from previous investigations, results of experiments with TeCl4 as transporting agent are comparable. Now on the basis of thermodynamical calculations it could be proved that in dry systems Ti/O/HgCl2 and Ti/O/TeCl4 (O/Ti < 2,0) a measurable transport of a TiOx phase resulting in the deposition of a higher phase cannot take place. Observed and calculated results agree, if small amounts of H2O are present resulting in the formation of HCl from HgCl2 or TeCl4 added as transporting agent. The refinement of the model now makes it possible to calculate the composition of the compound deposited at the temperature T1 also in systems with numerous closely neighbouring phases and for given experimental conditions. 相似文献
10.
Kimball DB Haley MM Mitchell RH Ward TR Bandyopadhyay S Williams RV Armantrout JR 《The Journal of organic chemistry》2002,67(25):8798-8811
The synthesis and study of dehydrobenzoannulene (DBA)-dimethyldihydropyrene (DDP) hybrids as models for the investigation of aromaticity in weakly diatropic systems is reported. Three new monofused DBA-DDP hybrids have been synthesized, and their NMR spectra are discussed with regard to quantifying the aromaticity remaining in multibenzene-fused DBAs. Nucleus-independent chemical shifts, determined at a series of locations for each compound, bond lengths, and (1)H and (13)C NMR chemical shifts were calculated and used to probe the aromaticity of these hybrids. Systems where more than one annulene/DBA is fused to the DDP core have also been obtained, and their potential use in photoinduced isomerization applications is discussed. 相似文献