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61.
Mihailovic A Vladescu I McCauley M Ly E Williams MC Spain EM Nuñez ME 《Langmuir : the ACS journal of surfaces and colloids》2006,22(10):4699-4709
Here we explore DNA binding by a family of ruthenium(II) polypyridyl complexes using an atomic force microscope (AFM) and optical tweezers. We demonstrate using AFM that Ru(bpy)2dppz2+ intercalates into DNA (K(b) = 1.5 x 10(5) M(-1)), as does its close relative Ru(bpy)2dppx2+ (K(b) = 1.5 x 10(5) M(-1)). However, intercalation by Ru(phen)3(2+) and other Ru(II) complexes with K(b) values lower than that of Ru(bpy)2dppz2+ is difficult to determine using AFM because of competing aggregation and surface-binding phenomena. At the high Ru(II) concentrations required to evaluate intercalation, most of the DNA strands acquire a twisted, curled conformation that is impossible to measure accurately. The condensation of DNA on mica in the presence of polycations is well known, but it clearly precludes the accurate assessment by AFM of DNA intercalation by most Ru(II) complexes, though not by ethidium bromide and other monovalent intercalators. When stretching individual DNA molecules using optical tweezers, the same limitation on high metal concentration does not exist. Using optical tweezers, we show that Ru(phen)2dppz2+ intercalates avidly (K(b) = 3.2 x 10(6) M(-1)) whereas Ru(bpy)3(2+) does not intercalate, even at micromolar ruthenium concentrations. Ru(phen)3(2+) is shown to intercalate weakly (i.e., at micromolar concentrations (K(b) = 8.8 x 10(3) M(-1))). The distinct differences in DNA stretching behavior between Ru(phen)3(2+) and Ru(bpy)3(2+) clearly illustrate that intercalation can be distinguished from groove binding by pulling the DNA with optical tweezers. Our results demonstrate both the benefits and challenges of two single-molecule methods of exploring DNA binding and help to elucidate the mode of binding of Ru(phen)3(2+). 相似文献
62.
Alexander J. Blake Paul J. Dyson Scott L. Ingham Brian F. G. Johnson Caroline M. Martin 《Transition Metal Chemistry》1995,20(6):577-582
Summary The [2.2]paracyclophane cluster, Ru6C(CO)14(
3-
2
2
2-C16H16) (1), undergoes reaction with Me3NO and triphenylphosphine to yield Ru6C(CO)13(
3-
2
2
2-C16H16)(PPh3) (2), which may also be produced from (1) by thermolysis with PPh3 in THF. Compound (2) has been fully characterized in solution by spectroscopy and in the solid state by a single crystal X-ray diffraction analysis at 277 K, and its structure is compared with that of the parent cluster, (1). Using the same synthetic procedures, the tricyclohexylphosphine analogue, Ru6C(CO)13(
3-
2
2
2-C16H16)(PCy3) (3), has also been prepared and characterized spectroscopically. A comparison of the chemical shifts of the 577-01 protons in the 1H-n.m.r. spectra of compounds (1)–(3) together with a variety of other [2.2]paracyclophane and benzene clusters has been made. 相似文献
63.
Photodynamic therapy (PDT) efficacy is a complex function of tissue sensitivity, photosensitizer (PS) uptake, tissue oxygen concentration, delivered light dose and some other parameters. To better understand the mechanisms and optimization of PDT treatment, we assessed two techniques for quantifying tissue PS concentration and two methods for quantifying pathological tumor damage. The two methods used to determine tissue PS concentration kinetic were in vivo fluorescence probe and ex vivo chemical extraction. Both methods show that the highest tumor to normal tissue PS uptake ratio appears 4 h after PS administration. Two different histopathologic techniques were used to quantify tumor and normal tissue damage. A planimetry assessment of regional tumor necrosis demonstrated a linear relationship with increasing light dose. However, in large murine tumors this finding was complicated by the presence of significant spontaneous necrosis. A second method (densitometry) assessed cell death by nuclear size and density. With some exceptions the densitometry method generally supported the planimetry results. Although the densitometry method is potentially more accurate, it has greater potential subjectivity. Finally, our research suggests that the tools or methods we are studying for quantifying PS levels and tissue damage are necessary for the understanding of PDT effect and therapeutic ratio in experimental in vivo tumor research. 相似文献
64.
Dawit Z. Bezabeh Todd M. Allen Eileen M. McCauley Peter B. Kelly A. Daniel Jones 《Journal of the American Society for Mass Spectrometry》1997,8(6):630-636
Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are widespread environmental pollutants that are generated by incomplete combustion and by atmospheric transformation of polycyclic aromatic hydrocarbons (PAHs). Many nitro-PAH compounds are potent genotoxins and some are direct acting mutagens. Detection of nitro-PAHs in aerosols is complicated by small sample sizes and nitro-PAH abundances that are 1–2 orders of magnitude less than analogous unsubstituted PAHs. Selective detection of several nitro-PAHs by using laser desorption ionization time-of-flight mass spectrometry in negative ion mode has been achieved. Desorption and ionization of nitro-PAHs were effected by using pulsed UV radiation at 266 and 213 ran. Intense molecular anions were observed in addition to fragments identified as CN? and NO 2 ? , which were characteristic indicators of the presence of nitro-PAHs. Selective detection of nitro-PAHs in negative ion mode was demonstrated in the analysis of a diesel particulate sample. 相似文献
65.
A rigorous investigation of the identification of a heterogeneousflexural rigidity coefficient in the Euler-Bernoulli steady-statebeam theory in the presence of a prescribed load is presented.Mathematically, this study is an extension to higher-order differentialequations of the coefficient identification problem analysedby Marcellini (1982) for the one-dimensional Poisson equation.In addition, various types of boundary conditions are discussed.Conditions for the well-posedness of these inverse problemsare established and, furthermore, numerical results obtainedusing a regularization algorithm are presented. 相似文献
66.
Airborne Nanostructured Particles and Occupational Health 总被引:7,自引:6,他引:1
Nanotechnology is leading to the development in many field, of new materials and devices in many fields that demonstrate nanostructure-dependent
properties. However, concern has been expressed that these same properties may present unique challenges to addressing potential
health impact. Airborne particles associated with engineered nanomaterials are of particular concern, as they can readily
enter the body through inhalation. Research into the potential occupational health risks associated with inhaling engineered
nanostructured particles is just beginning. However, there is a large body of data on occupational and environmental aerosols,
which is applicable to developing an initial assessment of potential risk and risk reduction strategies. Epidemiological and
pathological studies of occupational and environmental exposures to airborne particles and fibers provide information on the
aerosol-related lung diseases and conditions that have been observed in humans. Toxicological studies provide information
on the specific disease mechanisms, dose–response relationships, and the particle characteristics that influence toxicity,
including the size, surface area, chemistry or reactivity, solubility, and shape. Potential health risk will depend on the
magnitude and nature of exposures to airborne nanostructured particles, and on the release, dispersion, transformation and
control of materials in the workplace. Aerosol control methods have not been well-characterized for nanometer diameter particles,
although theory and limited experimental data indicate that conventional ventilation, engineering control and filtration approaches
should be applicable in many situations. Current information supports the development of preliminary guiding principles on
working with engineered nanomaterials. However critical research questions remain to be answered before the potential health
risk of airborne nanostructured particles in the workplace can be fully addressed.
Disclaimer
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National
Institute for Occupational Safety and Health 相似文献
67.
Angular distributions of protons from the 12C(α, p)15N reaction have been measured over the angular range from 10–70° at an α-particle bombarding energy of 96.8 MeV. Well defined particle groups are observed up to an excitation energy of 18 MeV in 15N. The relatively small number of states excited implies a selectivity both in the reaction mechanism and in structure effects. DWBA calculations using a semi-microscopic three-nucleon form factor have been performed using several different sets of wave functions. Good agreement in the ratio σexp/σth is obtained for most states using the 15N wave functions of de Meijer. The strongest state in the (α, p) spectrum is observed at 15.397 MeV in 15N and DWBA calculations give good agreement for a assignment. This state has been observed only in other three-nucleon transfer reactions involving heavy ions. The recent discovery of a state at 10.693 MeV in a p+14C resonance measurement is supported by our analysis. 相似文献
68.
The problem of the free convection boundary-layer flow over a semi-infinite vertical flat surface in a porous medium is considered,
in which the surface temperature has a constant value T1 at the leading edge, where T1 is above the ambient temperature, and takes a value T2 at a given distance L along the surface, varying linearly between these two values and remaining constant afterwards. Numerical solutions of the
boundary-layer equations are obtained as well as solutions valid for both small and large distance along the surface. Results
are presented for the three cases, when the temperature T2 is greater, equal or less than the ambient temperature T∞. In the first case, T2 > T∞, a boundary-layer flow develops along the surface starting with a flow associated with the temperature difference T1 − T∞ at the leading edge and approaching a flow associated with the temperature difference T2 − T∞ at large distances. In the second case, T2 = T∞, the convective flow set up on the initial part of the surface drives a wall jet in the region where the surface temperature
is the same as ambient. In the final case, T2 < T∞, a singularity develops in the numerical solution at the point where the surface temperature becomes T∞. The nature of this singularity is discussed. 相似文献
69.
In this paper the steady free convection boundary-layer along a semi-infinite, slightly inclined (both positive and negative)
to the horizontal plate embedded in a porous medium with the flow generated by Newtonian heating has been investigated. The
asymptotic solution near the leading edge and the full numerical solution along the whole plate domain have been obtained
numerically, whilst the asymptotic solution far downstream along the plate has been obtained analytically. For a positive
inclination the full numerical solution is in agreement with the asymptotic solutions. However, for a negatively inclined
plate, only the small asymptotic solution near the leading edge of the plate can be predicted giving an insight that the model
for a negatively inclined plate, whilst mathematically interesting, is not physically realistic. 相似文献
70.
In this paper we investigate the combined free and forced convection of a fully developed Newtonian fluid within a vertical channel composed of porous media when viscous dissipation effects are taken into consideration. The flow is analysed in the region of a first critical Rayleigh number in order to interpret the multiple-valued solutions and discuss their validity. The governing fourth-order, ordinary differential equation, which contains the Darcy and the viscous dissipation terms, is solved analytically using perturbation techniques and numerically using D02HBF NAG Library. A detailed investigation of the governing O.D.E. is performed on both clear fluid and porous medium for various values of the viscous dissipation parameter, , when the wall temperature decreases linearly with height, and the pressure gradient is both above and below its hydrostatic value. Although mathematically the results in all cases show that there are two solution branches, producing four possible solutions, the study of the velocity and buoyancy profiles together with the Darcy effect indicate that only one of the two solutions at any value of the Rayleigh number appears to be physically acceptable. It is shown that the effect of the Darcy number decreases as the critical Rayleigh numbers increase. 相似文献