全文获取类型
收费全文 | 156篇 |
免费 | 5篇 |
专业分类
化学 | 116篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 6篇 |
物理学 | 29篇 |
出版年
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 8篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 1篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 9篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1933年 | 1篇 |
排序方式: 共有161条查询结果,搜索用时 15 毫秒
81.
The use of stimuli to induce reversible structural transformations in metallosupramolecular systems is of keen interest to chemists seeking to mimic the way that Nature effects conformational changes in biological machinery. While a wide array of stimuli have been deployed towards this end, stoichiometric changes have only been explored in a handful of examples. Furthermore, switching has generally been between only two distinct states. Here we use a simple 2‐(1‐(pyridine‐4‐methyl)‐1H‐1,2,3‐triazol‐4‐yl)pyridine “click” ligand in combination with PdII in various stoichiometries and concentrations to quantitatively access and cycle between three distinct species: a [PdL2]2+ monomer, a [Pd2L2]4+ dimer, and a [Pd9L12]18+ cage. 相似文献
82.
Rate coefficients for the reactions of CH3 + Br2 (k2), CH3CO + Br2 (k3), and Cl + Br2 (k5) were measured using the laser‐pulsed photolysis method combined with detection of the product Br atoms using resonance fluorescence. For the reactions involving organic radicals, the rate coefficients were observed to increase with decreasing temperature and within the temperature range explored, were adequately described by Arrhenius‐like expressions: k2 (224–358 K) = 1.83 × 10?11 exp(252/T) and k3 (228–298 K) = 2.92 × 10?11 exp(361/T) cm3 molecule?1 s?1. The total, temperature‐independent uncertainty for each reaction (including possible systematic errors in Br2 concentration measurement) was estimated as ~7% for k2 and 10% for k3. Accurate data on k5 was obtained at 298 K, with a value of 1.88 × 10?10 cm3 molecule?1 s?1 obtained (with an associated error of 6%). A limited data set at 228 K suggests that k5 is, within experimental uncertainty, independent of temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 575–585, 2010 相似文献
83.
Brooke E. Crowley Claudia Wultsch Marcella J. Kelly 《Isotopes in environmental and health studies》2013,49(5):478-498
ABSTRACTFaecal isotopic analysis may complement other non-invasive wildlife survey tools for monitoring landscape use by carnivores, such as motion-detecting cameras and non-invasive genetic sampling. We analysed carbon, nitrogen, and strontium isotopes in faecal matter produced by jaguars (Panthera onca) as well as bones from consumed prey at the Mountain Pine Ridge Forest Reserve (MPR) in Belize, Central America. The MPR is ideally suited for a spatial isotope study as vegetation and geology both vary considerably. The isotopic composition of faecal matter should reflect the habitat and geology where consumed prey lived. We used bone from consumed prey recovered from jaguar scats as a proxy for diet. Faecal matter and bone showed comparable spatial isotopic trends, suggesting that the isotopic composition of jaguar faeces can be used to detect foraging in different habitats (pine forest versus broadleaf forest) or on different geologies (Mesozoic carbonates; Palaeozoic granite, contact metamorphics, and metasediments). This result is reassuring as bones are not always present in carnivore scats. Studying landscape use by cryptic and wide-ranging carnivore species like jaguars remains challenging. Isotopic analysis of faecal matter complements the existing array of non-invasive spatial monitoring tools. 相似文献
84.
Scott SØ Gavey EL Lind SJ Gordon KC Crowley JD 《Dalton transactions (Cambridge, England : 2003)》2011,40(45):12117-12124
Readily synthesised and functionalised di-1,2,3-triazole "click" ligands are shown to self-assemble into coordinatively saturated, quadruply stranded helical [Pd(2)L(4)](BF(4))(4) cages with Pd(II) ions. The cages have been fully characterised by elemental analysis, HR-ESMS, IR, (1)H, (13)C and DOSY NMR, DFT calculations, and in one case by X-ray crystallography. By exploiting the CuAAC "click" reaction we were able to rapidly generate a small family of di-1,2,3-triazole ligands with different core spacer units and peripheral substituents and examine how these structural modifications affected the formation of the [Pd(2)L(4)](BF(4))(4) cages. The use of both flexible (1,3-propyl) and rigid (1,3-phenyl) core spacer units led to the formation of discrete [Pd(2)L(4)](BF(4))(4) cage complexes. However, when the spacer unit of the di-1,2,3-triazole ligand was a 1,4-substituted-phenyl group steric interactions led to the formation of an oligomeric/polymeric species. By keeping the 1,3-phenyl core spacer constant the effect of altering the "click" ligands' peripheral substituents was also examined. It was shown that ligands with alkyl, phenyl, electron-rich and electron-poor benzyl substituents all quantitatively formed [Pd(2)L(4)](BF(4))(4) cage complexes. The results suggest that a wide range of functionalised palladium(II) "click" cages could be rapidly generated. These novel molecules may potentially find uses in catalysis, molecular recognition and drug delivery. 相似文献
85.
Khamaganov V Karunanandan R Rodriguez A Crowley JN 《Physical chemistry chemical physics : PCCP》2007,9(31):4098-4113
The formation of CH(3) in the 248 or 266 nm photolysis of acetone (CH(3)C(O)CH(3)), 2-butanone (methylethylketone, MEK, CH(3)C(O)C(2)H(5)) and acetyl bromide (CH(3)C(O)Br) was examined using the pulsed photolytic generation of the radical and its detection by transient absorption spectroscopy at 216.4 nm. Experiments were carried out at room temperature (298 +/- 3 K) and at pressures between approximately 5 and 1500 Torr N(2). Quantum yields for CH(3) formation were derived relative to CH(3)I photolysis at the same wavelength in back-to-back experiments. For acetone at 248 nm, the yield of CH(3) was greater than unity at low pressures (1.42 +/- 0.15 extrapolated to zero pressure) confirming that a substantial fraction of the CH(3)CO co-product can dissociate to CH(3) + CO under these conditions. At pressures close to atmospheric the quantum yield approached unity, indicative of almost complete collisional relaxation of the CH(3)CO radical. Measurements of increasing CH(3)CO yield with pressure confirmed this. Contrasting results were obtained at 266 nm, where the yields of CH(3) (and CH(3)CO) were close to unity (0.93 +/- 0.1) and independent of pressure, strongly suggesting that nascent CH(3)CO is insufficiently activated to decompose on the time scales of these experiments at 298 K. In the 248 nm photolysis of CH(3)C(O)Br, CH(3) was observed with a pressure independent quantum yield of 0.92 +/- 0.1 and CH(3)CO remained below the detection limit, suggesting that CH(3)CO generated from CH(3)COBr photolysis at 248 nm is too highly activated to be quenched by collision. Similar to CH(3)C(O)CH(3), the photolysis of CH(3)C(O)C(2)H(5) at 248 nm revealed pressure dependent yields of CH(3), decreasing from 0.45 at zero pressure to 0.19 at pressures greater than 1000 Torr with a concomitant increase in the CH(3)CO yield. As part of this study, the absorption cross section of CH(3) at 216.4 nm (instrumental resolution of 0.5 nm) was measured to be (4.27 +/- 0.2) x 10(-17) cm(2) molecule(-1) and that of C(2)H(5) at 222 nm was (2.5 +/- 0.6) x 10(-18) cm(2) molecule(-1). An absorption spectrum of gas-phase CH(3)C(O)Br (210-305 nm) is also reported for the first time. 相似文献
86.
D.J. Hoarty S.F. James C.R.D. Brown B.M. Williams H.K. Chung J.W.O. Harris L. Upcraft B.J.B. Crowley C.C. Smith R.W. Lee 《High Energy Density Physics》2010,6(1):105-108
Heating of thin foil targets by an high power laser at intensities of 1017–1019 W/cm2 has been studied as a method for producing high temperature, high density samples to investigate X-ray opacity and equation of state. The targets were plastic (parylene-N) foils with a microdot made of a mixture of germanium and titanium buried at depth of 1.5 μm. The L-shell spectra from the germanium and the K-shell spectra from the titanium were taken using crystal spectrometers recording onto film and an ultra fast X-ray streak camera coupled to a conical focussing crystal with a time resolution of 1 ps. The conditions in the microdot were inferred by comparing the measured spectra to synthetic spectra produced by the time-dependent collisional–radiative (CR) models FLY and FLYCHK. The data were also compared to simulated spectra from a number of opacity codes assuming local thermodynamic equilibrium (LTE). Temperature and density gradients were taken into account in the comparisons. The sample conditions were inferred from the CR modelling using FLYCHK to be 800 ± 100 eV and 1.5 ± 0.5 g/cc. The best fit to the LTE models was at a temperature 20% lower than with the CR model. Though the sample departs from LTE significantly useful spectral comparisons can still be made. The results and comparisons are discussed along with improvements to the experimental technique to achieve conditions closer to LTE. 相似文献
87.
Charles D. Immanuel Timothy J. Crowley Edward S. Meadows Cajetan F. Cordeiro Francis J. Doyle 《Journal of polymer science. Part A, Polymer chemistry》2003,41(14):2232-2249
This article presents a study on the engineering of multimodal distributions in semibatch emulsion polymerizations with nonionic surfactants. Various methods of producing multimodal distributions are demonstrated, and the sensitivity of the process to the properties of the reagents are analyzed. A test‐bed emulsion polymerization system, equipped with instrumentation to measure particle size distribution (capillary hydrodynamic fractionator) and monomer conversion (densitometer and flow meters), is used for this purpose. The process is monitored and controlled with an industrial distributed control system, which enables the automated operation of the process through sequential or logic controllers operating over lower level proportional integral derivative controllers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2232–2249, 2003 相似文献
88.
T R?ckmann J Kaiser C A Brenninkmeijer W A Brand R Borchers J N Crowley M Wollenhaupt P J Crutzen 《Isotopes in environmental and health studies》2001,37(2):91-95
The position dependent 15N fractionation of nitrous oxide (N2O), which cannot be obtained from mass spectrometric analysis on molecular N2O itself, can be determined with high precision using isotope ratio mass spectrometry on the NO+ fragment that is formed on electron impact in the source of an isotope ratio mass spectrometer. Laboratory UV photolysis experiments show that strong position dependent 15N fractionations occur in the photolysis of N2O in the stratosphere, its major atmospheric sink. Measurements on the isotopic composition of stratospheric N2O indeed confirm the presence of strong isotope enrichments, in particular the difference in the fractionation constants for 15N14NO and 14N15NO. The absolute magnitudes of the fractionation constants found in the stratosphere are much smaller, however, than those found in the lab experiments, demonstrating the importance of dynamical and also additional chemical processes like the reaction of N2O with O(1D). 相似文献
89.
A perturbative semiclassical approximation for the elastics-matrix is used to derive simple and accurate formulae describing the effects of a nuclear quadrupole deformation on the elastic scattering of aligned nuclei. Expressions are derived for the second rank tensor components of the analysing power, the ratios of which turn out to be simple trigonometric functions of the scattering angle in agreement with experimental observations. The approximations are discussed in some detail and higher order corrections are derived. In an appendix we derive a semiclassical first-order perturbation formula describing the effect of a non-central complex perturbation in the presence of a non-perturbatively treated central term. Our formula is in disagreement with some earlier published formulae which fail to treat the real part of the perturbation correctly. 相似文献
90.