全文获取类型
收费全文 | 302篇 |
免费 | 25篇 |
专业分类
化学 | 175篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 74篇 |
物理学 | 70篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 26篇 |
2019年 | 32篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 20篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 14篇 |
2011年 | 37篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 19篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1979年 | 1篇 |
1939年 | 2篇 |
排序方式: 共有327条查询结果,搜索用时 387 毫秒
161.
We demonstrate fiber distributed feedback (DFB) lasers using Raman gain in two germanosilicate fibers. Our DFB cavities were 124 mm uniform fiber Bragg gratings with a π phase shift offset from the grating center. Our pump was at 1480 nm and the DFB lasers operated on a single longitudinal mode near 1584 nm. In a commercial Raman gain fiber, the maximum output power, linewidth, and threshold were 150 mW, 7.5 MHz, and 39 W, respectively. In a commercial highly nonlinear fiber, these figures improved to 350 mW, 4 MHz, and 4.3 W, respectively. In both lasers, more than 75% of pump power was transmitted, allowing for the possibility of substantial amplification in subsequent Raman gain fiber. 相似文献
162.
Consider the semilinear wave equations in dimension 3 with a defocusing and superconformal power-type nonlinearity and with data lying in the Hs×Hs−1 (s<1) closure of smooth functions that are compactly supported inside a ball with fixed radius. We establish new bounds of the Sobolev norms of the solution. In particular, we prove that the Hs norm of the high frequency component of the solution grows like T∼(1−s)2+ in a neighborhood of s=1. In order to do that, we perform an analysis in a neighborhood of the cone, using the finite speed of propagation, an almost Shatah–Struwe estimate [17], an almost conservation law and a low–high frequency decomposition and .1 相似文献
163.
This work developed a computational process to predict noise radiation from gearboxes. It developed a system-level vibro-acoustic model of an actual gearbox, including gears, bearings, shafts, and housing structure, and compared the results to experiments. The meshing action of gear teeth causes vibrations to propagate through shafts and bearings to the housing radiating noise. The vibration excitation from the gear mesh and the system response were predicted using finite element and lumped-parameter models. From these results, the radiated noise was calculated using a boundary element model of the housing. Experimental vibration and noise measurements from the gearbox confirmed the computational predictions. The developed tool was used to investigate the influence of standard rolling element and modified journal bearings on gearbox radiated noise. 相似文献
164.
Thomas Y. George Dr. Tristan Asset Arezoo Avid Prof. Plamen Atanassov Prof. Iryna V. Zenyuk 《Chemphyschem》2020,21(6):469-475
Kinetic isotope effect (KIE) was used to study the rate-determining step for oxygen reduction reaction (ORR) on dispersed Pt/C electrocatalyst and polycrystalline Pt (Pt-poly). KIE is defined as the ratio of the kinetic current measured in protonated electrolyte versus deuterated electrolyte, with KIE values larger than one indicating proton participation in the rate-determining step. The effect of poisoning anions on the platinum rate determining step is investigated by assessing the KIE in perchloric (non-poisoning) and sulfuric acid-based electrolytes. The kinetics currents were calculated using the Koutechy-Levich and Tafel analysis. A KIE of 1 was observed for Pt/C (with a 40 wt.% Pt loading) and Pt-poly, thus indicating that, on 40 wt. % Pt/C and Pt-poly, the rate determining step is proton independent. 相似文献
165.
Neel A. Mansukhani Erica B. Peters Miranda M. So Mazen S. Albaghdadi Zheng Wang Mark R. Karver Tristan D. Clemons Jeffrey P. Laux Nick D. Tsihlis Samuel I. Stupp Melina R. Kibbe 《Macromolecular bioscience》2019,19(6)
The rising prevalence of cardiovascular disease worldwide necessitates novel therapeutic approaches to manage atherosclerosis. Intravenously administered nanostructures are a promising noninvasive approach to deliver therapeutics that reduce plaque burden. The drug liver X receptor agonist GW3965 (LXR) can reduce atherosclerosis by promoting cholesterol efflux from plaque but causes liver toxicity when administered systemically at effective doses, thus preventing its clinical use. The ability of peptide amphiphile nanofibers containing apolipoprotein A1–derived targeting peptide 4F to serve as nanocarriers for LXR delivery (ApoA1‐LXR PA) in vivo is investigated here. These nanostructures are found to successfully target atherosclerotic lesions in a mouse model within 24 h of injection. After 8 weeks of intravenous administration, the nanostructures significantly reduce plaque burden in both male and female mice to a similar extent as LXR alone in comparison to saline‐treated controls. Furthermore, they do not cause increased liver toxicity in comparison to LXR treatments, which may be related to more controlled release by the nanostructure. These findings demonstrate the potential of supramolecular nanostructures as safe, effective drug nanocarriers to manage atherosclerosis. 相似文献
166.
167.
168.
Tristan S. Kleine Taeheon Lee Kyle J. Carothers Meghan O. Hamilton Laura E. Anderson Liliana Ruiz Diaz Nicholas P. Lyons Keith R. Coasey Wallace O. Parker Ludovico Borghi Michael E. Mackay Kookheon Char Richard S. Glass Dennis L. Lichtenberger Robert A. Norwood Jeffrey Pyun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):17820-17824
Optical technologies in the long‐wave infrared (LWIR) spectrum (7–14 μm) offer important advantages for high‐resolution thermal imaging in near or complete darkness. The use of polymeric transmissive materials for IR imaging offers numerous cost and processing advantages but suffers from inferior optical properties in the LWIR spectrum. A major challenge in the design of LWIR‐transparent organic materials is that nearly all organic molecules absorb in this spectral window which lies within the so‐called IR‐fingerprint region. We report on a new molecular‐design approach to prepare high refractive index polymers with enhanced LWIR transparency. Computational methods were used to accelerate the design of novel molecules and polymers. Using this approach, we have prepared chalcogenide hybrid inorganic/organic polymers (CHIPs) with enhanced LWIR transparency and thermomechanical properties via inverse vulcanization of elemental sulfur with new organic co‐monomers. 相似文献
169.
170.
Dr. Juri Litterscheidt Prof. Dr. Jeffrey S. Bandar Max Ebert Robert Forschner Dr. Korinna Bader Prof. Dr. Tristan H. Lambert Dr. Wolfgang Frey Dr. Andrea Bühlmeyer Marcus Brändle Finn Schulz Prof. Dr. Sabine Laschat 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10644-10652
Aminocyclopropenium ions have raised much attention as organocatalysts and redox active polymers. However, the self-assembly of amphiphilic aminocyclopropenium ions remains challenging. The first deltic ionic liquid crystals based on aminocyclopropenium ions have been developed. Differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction provided insight into the unique self-assembly and nanosegregation of these liquid crystals. While the combination of small headgroups with linear p-alkoxyphenyl units led to bilayer-type smectic mesophases, wedge-shaped units resulted in columnar mesophases. Upon increasing the size and polyphilicity of the aminocyclopropenium headgroup, a lamellar phase was formed. 相似文献