全文获取类型
收费全文 | 201篇 |
免费 | 9篇 |
专业分类
化学 | 143篇 |
晶体学 | 7篇 |
力学 | 12篇 |
数学 | 14篇 |
物理学 | 34篇 |
出版年
2022年 | 1篇 |
2019年 | 9篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 16篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1961年 | 3篇 |
1900年 | 2篇 |
排序方式: 共有210条查询结果,搜索用时 31 毫秒
121.
Using the lubrication approximation we investigate two-dimensional steady flow of a thin film of fluid with temperature-dependent
viscosity on a uniformly heated or cooled horizontal cylinder, which may be stationary or rotating about its axis, in the
case when the Biot number (a measure of heat transfer at the free surface) is large.We show that the film thickness (but not
the fluid velocity) may be obtained from that in the isothermal case by a simple re-scaling. 相似文献
122.
Wenxin Mao Christopher R. Hall Anthony S. R. Chesman Craig Forsyth Yi‐Bing Cheng Noel W. Duffy Trevor A. Smith Udo Bach 《Angewandte Chemie (International ed. in English)》2019,58(9):2893-2898
Mixed organolead halide perovskites (MOHPs), CH3NH3Pb(BrxI1?x)3, have been shown to undergo phase segregation into iodide‐rich domains under illumination, which presents a major challenge to their development for photovoltaic and light‐emitting devices. Recent work suggested that phase‐segregated domains are localized at crystal boundaries, driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, a method for growing large (30×30×1 μm3) monocrystalline MAPb(BrxI1?x)3 single crystals is presented. The direct visualization of the growth of nanocluster‐like I‐rich domains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time‐resolved spectroscopy provided new insight into the nature of the phase‐segregated domains and the collective impact on the optoelectronic properties. 相似文献
123.
Noel McLaughlin Colm Duffy Francesco Alletto Andrea Ravelli Stefano Lancianesi Malachi Gillick-Healy Mauro F.A. Adamo 《Tetrahedron letters》2019,60(19):1313-1316
The diastereoselective reduction of γ-keto-sulfonates to afford α,γ-substituted γ-hydroxy sulfonates has been investigated. Herein we report the first example of a diastereoselective carbonyl reduction whereby hydride attack is directed via chelation of a neighbouring sulfonate group to a boron atom, thus affording prevalently trans γ-hydroxy sulfonates. 相似文献
124.
125.
Radial x-ray diffraction experiments were conducted under nonhydrostatic compression on SiO2 to 60 GPa in a diamond anvil cell. This ratio of differential stress to shear modulus t/G is 0.019(3)-0.037(5) at P=15-60 GPa. The ratio for octahedrally coordinated stishovite is lower by a factor of about 2 than observed in four-coordinated silicates. Using a theoretical model for the shear modulus, the differential stress of stishovite is found to be 4.5(1.5) GPa below 40 GPa and to decrease sharply as the stishovite-CaCl2-type phase transition boundary is approached. Inversion of measured lattice strains provides direct experimental evidence for softening of C11-C12. 相似文献
126.
In this article, we show that the Hurst parameter and a well-known wavelet estimator fail to distinguish on/off models with substantially different distributions of on-times. We identify the problem as arising when standard power spectrum techniques, which are well-defined for commonly considered processes, are applied to processes with extremely heavy tailed on-times. We provide an elementary mechanism whereby such extremely heavy-tailed on-time processes arise in a simple queuing model. 相似文献
127.
Fully suspended, five-axis, three-magnetic-bearing dynamic spin rig with forced excitation 总被引:2,自引:0,他引:2
C. R. Morrison A. Provenza A. Kurkov G. Montague K. Duffy O. Mehmed D. Johnson R. Jansen 《Experimental Mechanics》2005,45(3):226-237
A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform
vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has
three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust
bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature,
which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical,
electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated,
rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of
blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the
rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from
the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100
g A−1 was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip
displacement of 1.778×10−3m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative
to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm. 相似文献
128.
A.J. Rosakis J. Duffy L.B. Freund 《Journal of the mechanics and physics of solids》1984,32(6):443-460
Dynamic crack propagation experiments have been performed using wedge loaded double cantilever beam specimens of an austenitized, quenched and tempered 4340 steel. Measurements of the dynamic stress intensity factor have been made by means of the optical method of caustics. The interpretation of experimental data, obtained from the shadow spot patterns photographed with a Cranz-Schardin high speed camera, is based on an elastodynamic analysis. The instantaneous value of the dynamic stress intensity factor KdI is obtained as a function of crack tip velocity. Finally, the interaction of reflected shear and Rayleigh waves with the moving crack tip stress field is considered. 相似文献
129.
Johnson RD Navratil M Poe BG Xiong G Olson KJ Ahmadzadeh H Andreyev D Duffy CF Arriaga EA 《Analytical and bioanalytical chemistry》2007,387(1):107-118
Bulk studies are not suitable to describe and study cell-to-cell variation, which is of high importance in biological processes
such as embryogenesis, tissue differentiation, and disease. Previously, capillary electrophoresis with laser-induced fluorescence
detection (CE-LIF) was used to measure the properties of organelles isolated from millions of cells. As such, these bulk measurements
reported average properties for the organelles of cell populations. Similar measurements for organelles released from single
cells would be highly relevant to describe the subcellular variations among cells. Toward this goal, here we introduce an
approach to analyze the mitochondria released from single mammalian cells. Osteosarcoma 143B cells are labeled with either
the fluorescent mitochondrion-specific 10-N-nonyl acridine orange (NAO) or via expression of the fluorescent protein DsRed2. Subsequently, a single cell is introduced
into the CE-LIF capillary where the organelles are released by a combined treatment of digitonin and trypsin. After this treatment,
an electric field is applied and the released organelles electromigrate toward the LIF detector. From an electropherogram,
the number of detected events per cell, their individual electrophoretic mobilities, and their individual fluorescence intensities
are calculated. The results obtained from DsRed2 labeling, which is retained in intact mitochondria, and NAO labeling, which
labels all mitochondria, are the basis for discussion of the strengths and limitations of this single-cell approach.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users 相似文献
130.
An RP monolithic column coated with an amphoteric carboxybetaine type surfactant has been used with a combined triple eluent concentration, pH and flow gradient ion chromatography technique for the simultaneous separation of up to 18 nucleotides, nucleosides and nucleobases. The separation of up to eight precursors on a 1 cm long monolithic microcolumn using the combined gradient approach is also shown. The method was applied to the separation of the above nucleic acid precursors in perchloric acid extracts of yeastolates samples. 相似文献