全文获取类型
收费全文 | 893篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 531篇 |
晶体学 | 6篇 |
力学 | 24篇 |
数学 | 84篇 |
物理学 | 262篇 |
出版年
2021年 | 6篇 |
2020年 | 5篇 |
2018年 | 10篇 |
2016年 | 16篇 |
2015年 | 18篇 |
2014年 | 16篇 |
2013年 | 39篇 |
2012年 | 43篇 |
2011年 | 36篇 |
2010年 | 29篇 |
2009年 | 16篇 |
2008年 | 30篇 |
2007年 | 35篇 |
2006年 | 38篇 |
2005年 | 39篇 |
2004年 | 28篇 |
2003年 | 21篇 |
2002年 | 30篇 |
2001年 | 25篇 |
2000年 | 32篇 |
1999年 | 16篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 24篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 12篇 |
1971年 | 6篇 |
1969年 | 5篇 |
1918年 | 4篇 |
1908年 | 4篇 |
排序方式: 共有907条查询结果,搜索用时 15 毫秒
91.
K. G. Johnston 《Semigroup Forum》1994,49(1):131-135
Communicated by Norman R. Reilly 相似文献
92.
93.
The influence of an inhibitor (CF3Br or Halon 1301) on the propagation of high-speed turbulent flames, quasi-detonations and the transition to detonation has
been investigated for methane-air, propane-air and acetylene-air mixtures. The experiments are carried out in a 13 m tube
(15 cm diameter) filled with regularly spaced orifice plates (blockage ratio of 0.39) to ensure rapid flame acceleration.
In all cases, the addition of the inhibitor reduces the turbulent flame velocity and extinguishes the flame with sufficient
inhibitor concentration (2.7% and 7.5% for methane-air and propane-air, respectively). For acetylene-air mixtures, the quasi-detonation
speed is progressively reduced with increasing inhibitor concentration and eventually causes the failure of the quasi-detonation
and transition back to a fast turbulent flame. The inhibitor also narrows the propagation limits in all cases. To elucidate
the inhibition mechanism, detailed modelling of both the turbulent flame structure as well as the chemical kinetics are required. 相似文献
94.
Dr. Christopher J. Heard Prof. Roy L. Johnston Prof. Dr. J. Christian Schön 《Chemphyschem》2015,16(7):1461-1469
The energy landscapes of sub‐nanometre bimetallic coinage metal clusters are explored with the Threshold Algorithm coupled with the Birmingham Cluster Genetic Algorithm. Global and energetically low‐lying minima along with their permutational isomers are located for the Cu${_4 }$ Ag${_4 }$ cluster with the Gupta potential and density functional theory (DFT). Statistical tools are employed to map the connectivity of the energy landscape and the growth of structural basins, while the thermodynamics of interconversion are probed, based on probability flows between minima. Asymmetric statistical weights are found for pathways across dividing states between stable geometries, while basin volumes are observed to grow independently of the depth of the minimum. The DFT landscape is found to exhibit significantly more frustration than that of the Gupta potential, including several open, pseudo‐planar geometries which are energetically competitive with the global minimum. The differences in local minima and their transition barriers between the two levels of theory indicate the importance of explicit electronic structure for even simple, closed shell clusters. 相似文献
95.
Victoria L. Challinor Ryne C. Johnston Paul V. Bernhardt Reginald P. Lehmann Elizabeth H. Krenske James J. De Voss 《Chemical science》2015,6(10):5740-5745
A series of novel sesterterpenes (2–6) have been isolated from the roots of Aletris farinosa and structurally characterized by MS, NMR, and X-ray crystallography in conjunction with computational modeling. Their structures provide new insights into the mechanisms of sesterterpene biosynthesis. Specifically, we propose with support from density functional theory computations that the configuration at a single stereocenter determines the fate of a key tetracyclic carbocationic intermediate, derived from an oxidogeranylfarnesol precursor. Whereas one epimer of the carbocation undergoes H+ elimination to give 6, the other undergoes a spectacular cascade of seven 1,2-methyl and hydride migrations leading to the previously unreported carbon skeleton of 5. Theoretical calculations suggest that the cascade is triggered by substrate preorganization in the enzyme active site. 相似文献
96.
Well‐Defined Palladium Nanoparticles Supported on Siliceous Mesocellular Foam as Heterogeneous Catalysts for the Oxidation of Water
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Oscar Verho Dr. Torbjörn Åkermark Dr. Eric V. Johnston Karl P. J. Gustafson Dr. Cheuk‐W. Tai Henrik Svengren Dr. Markus D. Kärkäs Prof. Jan‐E. Bäckvall Prof. Björn Åkermark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5909-5915
Herein, we describe the use of Pd nanoparticles immobilized on an amino‐functionalized siliceous mesocellular foam for the catalytic oxidation of H2O. The Pd nanocatalyst proved to be capable of mediating the four‐electron oxidation of H2O to O2, both chemically and photochemically. The Pd nanocatalyst is easy to prepare and shows high chemical stability, low leaching, and recyclability. Together with its promising catalytic activity, these features make the Pd nanocatalyst of potential interest for future sustainable solar‐fuel production. 相似文献
97.
The vortex formed at the tip of a propeller interacting with the vortex formed at the tip of a stator vane provides a unique environment for the study of vortex interactions. Changes in the relative vortex strengths and vortex rotational directions were determined to impact the resulting vortex structures and are easily implemented with the experimental apparatus described herein. Study of the development of the vortex interaction was determined to be possible by increasing the initial separation between the two vortices. Vortex interaction phenomenon has been observed using smoke flow visualization.The authors would like to thank the NASA Lewis Research Center for their funding of propeller related research from which this experiment evolved and the National Sciences and Engineering Research Council of Canada for R. Johnston's Post Graduate Scholarships. 相似文献
98.
James P. Johnston Bruce P. Mosier Zia U. Khan 《International Journal of Heat and Fluid Flow》2002,23(6):744-749
An experimental study of flow downstream of round, pitched and skewed wall-jets (vortex generating jets) is presented to illustrate the effects of changing the geometric inlet conditions of the jet-holes. In one case the jet-hole has a smoothly contoured inlet, and in the other the inlet was a sharp-edged, sudden contraction. The test region geometry, mean jet flow and cross-flow conditions were otherwise identical. In both cases, dominant streamwise vortex structures are seen in the boundary layer downstream; the flow and turbulence is nearly the same in the far-field starting downstream of x/D=5. In the near-field, for x/D<5, there are significant differences; turbulence levels are higher, and the start of the dominant vortex shape is less clear for the sharp-edged case. This is believed to be the result of flow separation and free shear layer instability inside the jet-hole which are not present for the smoothly contoured case. 相似文献
99.
Over the last two decades the layer-by-layer (LbL) assembly technique has become a highly versatile platform for the synthesis of nanoengineered thin films and particles. The widespread need for highly functional and responsive materials for applications in biomedicine-such as drug and gene delivery-has recently led to considerable efforts in the assembly of LbL materials, particularly films that can be subsequently stabilised and functionalised through a range of chemistries. In this tutorial review, recent developments in hydrogen-bonded LbL-assembled materials will be discussed, focusing on the design of materials with enhanced stimuli-responsive characteristics. Emphasis will be given to materials engineered for biomedical applications, specifically films/capsules that afford controlled loading and release of therapeutic cargo for application in vitro and in vivo. 相似文献
100.
Ma LL Tam JO Willsey BW Rigdon D Ramesh R Sokolov K Johnston KP 《Langmuir : the ACS journal of surfaces and colloids》2011,27(12):7681-7690
The ability of smaller than 100 nm antibody (Ab) nanoparticle conjugates to target and modulate the biology of specific cell types may enable major advancements in cellular imaging and therapy in cancer. A key challenge is to load a high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. A versatile method called thin autocatalytic growth on substrate (TAGs) has been developed in our previous study to form ultrathin and asymmetric gold coatings on iron oxide nanocluster cores producing exceptional near-infrared (NIR) absorbance. AlexaFluor 488 labeled Abs were used to correlate the number of Abs conjugated to iron oxide/gold nanoclusters (nanoroses) with the hydrodynamic size. A transition from submonolayer to multilayer aggregates of Abs on the nanorose surface was observed for 54 Abs and an overall particle diameter of ~60-65 nm. The hydrodynamic diameter indicated coverage of a monolayer of 54 Abs, in agreement with the prediction of a geometric model, by assuming a circular footprint of 16.9 nm diameter per Ab molecule. The targeting efficacy of nanoclusters conjugated with monoclonal Abs specific for epidermal growth factor receptor (EGFR) was evaluated in A431 cancer cells using dark field microscopy and atomic absorbance spectrometry (AAS) analysis. Intense NIR scattering was achieved from both high uptake of nanoclusters in cells and high intrinsic NIR absorbance of individual nanoclusters. Dual mode imaging with dark field reflectance microscopy and fluorescence microscopy indicates the Abs remained attached to the Au surfaces upon the uptake by the cancer cells. The ability to load intense multifunctionality, specifically strong NIR absorbance, conjugation of an Ab monolayer in addition to a strong r2 MRI contrast that was previously demonstrated in a total particle size of only 63 nm, is an important step forward in development of theranostic agents for combined molecular specific imaging and therapy. 相似文献