全文获取类型
收费全文 | 24430篇 |
免费 | 3677篇 |
国内免费 | 3110篇 |
专业分类
化学 | 17727篇 |
晶体学 | 235篇 |
力学 | 2505篇 |
综合类 | 124篇 |
数学 | 1667篇 |
物理学 | 8959篇 |
出版年
2024年 | 61篇 |
2023年 | 286篇 |
2022年 | 551篇 |
2021年 | 1081篇 |
2020年 | 1184篇 |
2019年 | 978篇 |
2018年 | 781篇 |
2017年 | 850篇 |
2016年 | 1193篇 |
2015年 | 1032篇 |
2014年 | 1226篇 |
2013年 | 2233篇 |
2012年 | 1433篇 |
2011年 | 1416篇 |
2010年 | 1226篇 |
2009年 | 1424篇 |
2008年 | 1522篇 |
2007年 | 1606篇 |
2006年 | 1443篇 |
2005年 | 1207篇 |
2004年 | 1109篇 |
2003年 | 1036篇 |
2002年 | 826篇 |
2001年 | 711篇 |
2000年 | 717篇 |
1999年 | 648篇 |
1998年 | 605篇 |
1997年 | 451篇 |
1996年 | 378篇 |
1995年 | 348篇 |
1994年 | 334篇 |
1993年 | 222篇 |
1992年 | 199篇 |
1991年 | 133篇 |
1990年 | 104篇 |
1989年 | 105篇 |
1988年 | 79篇 |
1987年 | 76篇 |
1986年 | 57篇 |
1985年 | 70篇 |
1984年 | 49篇 |
1983年 | 24篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
981.
Simulation of local ion transport in lamellar block copolymer electrolytes based on electron micrographs 下载免费PDF全文
Mahati Chintapalli Kenneth Higa X. Chelsea Chen Venkat Srinivasan Nitash P. Balsara 《Journal of Polymer Science.Polymer Physics》2017,55(3):266-274
A method is presented to relate local morphology and ionic conductivity in a solid, lamellar block copolymer electrolyte for lithium batteries, by simulating conductivity through transmission electron micrographs. The electrolyte consists of polystyrene‐block‐poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl) imide salt (SEO/LiTFSI), where the polystyrene phase is structural phase and the poly(ethylene oxide)/LiTFSI phase is ionically conductive. The electric potential distribution is simulated in binarized micrographs by solving the Laplace equation with constant potential boundary conditions. A morphology factor, f, is reported for each image by calculating the effective conductivity relative to a homogenous conductor. Images from two samples are examined, one annealed with large lamellar grains and one unannealed with small grains. The average value of f is 0.45 ± 0.04 for the annealed sample, and 0.37 ± 0.03 for the unannealed sample, both close to the value predicted by effective medium theory, 1/2. Simulated conductivities are compared to published experimental conductivities. The value of fUnannealed/fAnnealed is 0.82 for simulations and 6.2 for experiments. Simulation results correspond well to predictions by effective medium theory but do not explain the experimental measurements. Observation of nanoscale morphology over length scales greater than the size of the micrographs (~1 μm) may be required to explain the experimental results. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 266–274 相似文献
982.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(15):1757-1767
The synthesis, characterization, and solar cell application of newly developed two semiconducting polymers containing phenanthro[1,2‐b:8,7‐b′]dithiophene (PDT) and an isoindigo (IID) unit are described. In addition, a relationship between substitution position of side chains and molecular weights of the polymers and their solar cell performance are also discussed. Because of the installation of alkyl side chains onto sterically less hindered positions, PDT‐IID copolymers 12OD‐2 and 8OD‐2 have stronger intermolecular interaction than that of the previously reported copolymer 12OD . In low‐Mn polymers 12OD‐2 and 8OD‐2 formed high‐crystalline thin film with higher face‐on ratio than that of 12OD , but their unsuitable large‐scale phase separation suppressed their efficient photocurrent generation, leading to poor PCE of 2–3%. However, the surface morphology of 12OD‐2 and 8OD‐2 blended films are drastically improved by increasing Mn, which leads to the enhancement of Jsc and higher PCE of up to 4.3%. However, high‐Mn polymers 12OD‐2 and 8OD‐2 formed high‐crystalline film with about 10–15% lower face‐on ratio than that of high‐Mn polymer 12OD , leading to poor hole transporting ability, and thus lower Jsc and PCE. From this result, too much strong intermolecular interaction promotes the formation of unsuitable edge‐on orientation in blended films. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1757–1767 相似文献
983.
Tom Miclot Dr. Camille Corbier Prof. Alessio Terenzi Cécilia Hognon Prof. Stéphanie Grandemange Prof. Giampaolo Barone Prof. Antonio Monari 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(34):8865-8874
Human telomeric DNA, in G-quadruplex (G4) conformation, is characterized by a remarkable structural stability that confers it the capacity to resist to oxidative stress producing one or even clustered 8-oxoguanine (8oxoG) lesions. We present a combined experimental/computational investigation, by using circular dichroism in aqueous solutions, cellular immunofluorescence assays and molecular dynamics simulations, that identifies the crucial role of the stability of G4s to oxidative lesions, related also to their biological role as inhibitors of telomerase, an enzyme overexpressed in most cancers associated to oxidative stress. 相似文献
984.
The gas dynamics in an exhaust pipe is studied. In particular we focus on the warm up of the catalytic converter in very short times after the engine start. This is done by combustion a small unburnt part of the exhaust gas. This process is classically modelled by gas dynamic equations. Compared to the existing literature we improve the (one-dimensional) modelling approach using a small Mach number technique and a network ansatz for the full exhaust pipe. The final simplified model on one hand still describes the main features and on the other hand it is computationally a few orders of magnitude faster than the original model. Performing numerical simulations we compare the new model to the (classical) full model and to experimental results in the literature. 相似文献
985.
986.
In this contribution, we present two new united‐atom force fields (UA‐FFs) for 1‐alkyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide [CnMIM][NTf2] (n=1, 2, 4, 6, 8) ionic liquids (ILs). One is parametrized manually, and the other is developed with the gradient‐based optimization workflow (GROW). By doing so, we wanted to perform a hard test to determine how researchers could benefit from semiautomated optimization procedures. As with our already published all‐atom force field (AA‐FF) for [CnMIM][NTf2] (T. Köddermann, D. Paschek, R. Ludwig, ChemPhysChem 2007, 8, 2464 ), the new force fields were derived to fit experimental densities, self‐diffusion coefficients, and NMR rotational correlation times for the IL cation and for water molecules dissolved in [C2MIM][NTf2]. In the manual force field, the alkyl chains of the cation and the CF3 groups of the anion were treated as united atoms. In the GROW force field, only the alkyl chains of the cation were united. All other parts of the structures of the ions remained unchanged to prevent any loss of physical information. Structural, dynamic, and thermodynamic properties such as viscosity, cation rotational correlation times, and heats of vaporization calculated with the new force fields were compared with values simulated with the previous AA‐FF and the experimental data. All simulated properties were in excellent agreement with the experimental values. Altogether, the UA‐FFs are slightly superior for speed‐up reasons. The UA‐FF speeds up the simulation by about 100 % and reduces the demanded disk space by about 78 %. More importantly, real time and efforts to generate force fields could be significantly reduced by utilizing GROW. The real time for the GROW parametrization in this work was 2 months. Manual parametrization, in contrast, may take up to 12 months, and this is, therefore, a significant increase in speed, though it is difficult to estimate the duration of manual parametrization. 相似文献
987.
988.
989.
990.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(7):732-740
This work presents a two‐step, one‐pot process to make star polymers with polywedge arms. In a one‐pot reaction, after the polywedge arms are synthesized, crosslinker species are added to the reaction, rapidly forming star polymers. Crosslinker species with different degrees of conformational freedom were designed and synthesized and their capacity to generate star polymers was evaluated. Mass conversions up to 92% and stars with up to 17 arms were synthesized with the most rigid crosslinker. The effects of arm molecular weight and molar ratio of crosslinker to arm on mass conversion and arms per star were explored further. Finally, the size‐molecular weight scaling relationship for polywedges with linear and star architectures was compared, corroborating theoretical results regarding star polymers with arms much larger than their core. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 732–740 相似文献