全文获取类型
收费全文 | 1919篇 |
免费 | 264篇 |
国内免费 | 191篇 |
专业分类
化学 | 1167篇 |
晶体学 | 22篇 |
力学 | 98篇 |
综合类 | 31篇 |
数学 | 306篇 |
物理学 | 750篇 |
出版年
2024年 | 4篇 |
2023年 | 36篇 |
2022年 | 49篇 |
2021年 | 59篇 |
2020年 | 81篇 |
2019年 | 53篇 |
2018年 | 58篇 |
2017年 | 57篇 |
2016年 | 70篇 |
2015年 | 73篇 |
2014年 | 97篇 |
2013年 | 117篇 |
2012年 | 154篇 |
2011年 | 168篇 |
2010年 | 131篇 |
2009年 | 118篇 |
2008年 | 137篇 |
2007年 | 106篇 |
2006年 | 83篇 |
2005年 | 83篇 |
2004年 | 58篇 |
2003年 | 61篇 |
2002年 | 51篇 |
2001年 | 46篇 |
2000年 | 39篇 |
1999年 | 57篇 |
1998年 | 62篇 |
1997年 | 45篇 |
1996年 | 38篇 |
1995年 | 35篇 |
1994年 | 29篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有2374条查询结果,搜索用时 46 毫秒
151.
A previous study on the deleterious effect of triphenyltin chloride (TPTCl) on the alga Spirulina subsalsa reported on four physiological and biochemical indices (or parameters): growth rate, chlorophyll content, phycocyanin content and nitrate reductase activity. In the present study, further research was performed to confirm the findings reported in the previous paper, using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM images show significant changes in the screw‐pitch of S. subsalsa, suggesting that TPTCl may damage the inheritance characteristics of S. subsalsa. The TEM images illustrate that the external pectin theca, limiting membrane and inter photosynthetically active lamella in the S. subsalsa cell are those targets that can be easily damaged. Reversible and irreversible cell damage (cell necrosis) are also observed. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
152.
Circulators play a significant role in radar and microwave communication systems.This paper proposes a broadband and highly efficient plasmonic circulator,which consists of spoof surface plasmon polaritons(SSPPs)waveguides and ferrite disks to support non-reciprocal mode coupling.The simulated performance of symmetrically designed circulator shows that it has an insertion loss of roughly 0.5 dB while the isolation and return loss is more than 12 dB in the frequency range of 6.0 GHz–10.0 GHz(relative bandwidth of 50%).Equivalent circuit model has been proposed to explain the operating mechanism of the plasmonic circulator.The equivalent circuit model,numerical simulations,and experimental results are consistent with each other,which demonstrates the good performance of the proposed plasmonic circulator. 相似文献
153.
Wide-Angle Ultra-Broadband Metamaterial Absorber with Polarization-Insensitive Characteristics
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An ultra-wideband metamaterial absorber is developed,which is polarized-insensitive and angular-stable.Three layers of square resistive films comprise the proposed metamaterial.The optimal values of geometric parameters are obtained,such that the designed absorber can achieve an ultra-broadband absorption response from 4.73 to 39.04 GHz(relative bandwidth of 156.7%)for both transverse electricity and transverse magnetic waves.Moreover,impedance matching theory and an equivalent circuit model are utilized for the absorption mechanism analysis.The compatibility of equivalent circuit calculation results,together with both full-wave simulation and experimental results,demonstrates the excellent performance and applicability of the proposed metamaterial absorber. 相似文献
154.
Chuanlei Liu Kurt Ungar Dylan Pierce Ian Hoffman Weihua Zhang 《Journal of Radioanalytical and Nuclear Chemistry》2017,312(3):471-478
In assistance of radionuclide measurements at Canada’s Comprehensive Nuclear-Test-Ban Treaty (CTBT) laboratory, a Geant4 Monte Carlo application has been developed in simulating a broad-energy germanium detector and calculating detection efficiencies. The detector model was optimized in a reliable and non-biased manner through simultaneous tuning on gap distance and detector dimension, and was validated over various realistic measurement scenarios. All work is based on a series of experiments which covers the typical energy range of gamma radiation in environmental analysis, and considers the variety of the CTBT sample type, dimension and distance-to-detector. In all cases, the predicted efficiencies are consistent with the empirical ones within 5%, with a typical deviation of 3% in majority. 相似文献
155.
We use a Monte Carlo method to study the phase and interfacial behaviors of A-b-B diblocks in a blend of homopolymers, A and B, which are confined between two asymmetric hard and impenetrable walls. Our results show that, when the interaction strength is weak, the block copolymersare uniformly distributed in the ternary mixtures under considered concentrations. Under strong interaction strength, distribution region of the block copolymers changes from a single smooth interface to a curved interface or multi-layer interface in the ternary mixtures. Furthermore, our findings show that with increasing volume fraction of A-b-B diblock copolymer(фC), copolymer profiles broaden while фC≥ 0.4, a lamellar phase is formed and by further increasing фC, more thinner layers are observed. Moreover, the results show that, with the increase of фC, the phase interface first gradually transforms from plane to a curved surface rather than micelle or lamellar phase while with the increase of the interaction between A and B segments(ε_(AB)), the copolymer chains not only get stretched in the direction perpendicular to the interface, but also are oriented. The simulations also revealthat the difference between symmetric and asymmetric copolymers is negligible in statistics if the lengths of two blocksare comparable. 相似文献
156.
The density functional method is used to study the structure, electronic properties, static linear polarizabilities, and optical absorption spectra of two seven‐membered unconventional fullerene derivatives C58F17CF3 and C58F18. It is calculated that three sites chosen to locate the CF3 are isoenergetic. The energy gaps of C58F18 and C58F17CF3 are much larger than that of C58, indicating the fluorination and trifluoromethylation of C58 can remarkably enhance the kinetic stability. The density of states explore that the influence of CF3 to the energy levels is mainly distributed in the energy range from ?10 to ?2 eV. However, when the CF3 substitutes for F in C58F18, the bond lengths, energy gaps, static linear polarizabilities, and optical absorption spectra all show small variety. 相似文献
157.
Two novel asymmetric salen ligands H2L1 [N‐phenyl‐N‐(2‐hydroxy‐5‐methylphenyl)‐N′‐(2‐hydroxy‐3‐meth‐ oxylphenyl)‐o‐phenyldiamine] and H2L2 [N‐phenyl‐N‐(2‐hydroxy‐5‐chlorophenyl)‐N′‐(2‐hydroxy‐3‐methoxyl‐ phenyl)‐o‐phenyldiamine] and their metal complexes MLn (M=Zn, Co, Ni, Cu; n=1, 2) have been prepared and characterized by elemental analyses, 1H NMR, ESI‐MS, FT‐IR and UV‐Vis spectra. In particular, the complex ZnL1, the binuclear monosalphen complex, was synthesized and studied in detail using 1H NMR and ESI‐MS techniques. For other metal complexes under the same reaction conditions, only mononuclear complexes were obtained. The results are relevant to both the metal ions and the structure of ligands. 相似文献
158.
159.
The first, general, and highly efficient catalytic system that allows a wide range of activated and unactivated aryl chlorides to couple regioselectively with olefins has been developed. The Heck arylation reaction is likely to be controlled by the oxidative addition of ArCl to Pd(0). Hence, an electron-rich diphosphine, 4-MeO-dppp, was introduced to facilitate the catalysis. Solvent choice is critical, however; only sluggish arylation is observed in DMF or DMSO, whereas the reaction proceeds well in ethylene glycol at 0.1-1 mol % catalyst loadings, displaying excellent regioselectivity. Mechanistic evidence supports that the arylation is turnover-limited by the oxidative addition step and, most importantly, that the oxidative addition is accelerated by ethylene glycol, most likely via hydrogen bonding to the chloride at the transition state as shown by DFT calculations. Ethylene glycol thus plays a double role in the arylation, facilitating oxidative addition and promoting the subsequent dissociation of chloride from Pd(II) to give a cationic Pd(II)-olefin species, which is key to the regioselectivity observed. 相似文献
160.
Chunhua Fu Changshun Ruan Ya Fu Yuanliang Wang 《Polymer Degradation and Stability》2010,95(4):485-490
The multi-arm star polymer (ESOPLA) was obtained by ring-opening polymerization of dl-lactide using multifunctional epoxidized soybean oil (ESO) as an initiator in the presence of a stannous actuate (SnOct2) catalyst. Gel permeation chromatography with multi-angle laser light scattering (GPC-MALLS), FTIR, 1H NMR, thermal analysis and in vitro degradation were used to qualitatively characterize the synthesized polymers. The results revealed that ESO plays an important role in increasing the molecular weight, polymerization rate and monomer conversion rate. Degradation analysis demonstrated that the decrease in molecular weight and the weight loss ratio of the star-shaped ESOPLA were lower than that of linear poly(dl-lactide) (PDLLA). The surface topography of pre- and post-degradation materials was characterized by scanning electron microscopy (SEM). These SEM images showed that the linear PDLLA films underwent water erosion more readily than the star-shaped polymer films. 相似文献