全文获取类型
收费全文 | 2618篇 |
免费 | 103篇 |
国内免费 | 15篇 |
专业分类
化学 | 1767篇 |
晶体学 | 30篇 |
力学 | 69篇 |
数学 | 151篇 |
物理学 | 452篇 |
无线电 | 267篇 |
出版年
2023年 | 16篇 |
2022年 | 48篇 |
2021年 | 71篇 |
2020年 | 69篇 |
2019年 | 67篇 |
2018年 | 70篇 |
2017年 | 48篇 |
2016年 | 113篇 |
2015年 | 74篇 |
2014年 | 132篇 |
2013年 | 205篇 |
2012年 | 170篇 |
2011年 | 195篇 |
2010年 | 107篇 |
2009年 | 90篇 |
2008年 | 143篇 |
2007年 | 145篇 |
2006年 | 123篇 |
2005年 | 125篇 |
2004年 | 74篇 |
2003年 | 80篇 |
2002年 | 68篇 |
2001年 | 28篇 |
2000年 | 30篇 |
1999年 | 13篇 |
1998年 | 32篇 |
1997年 | 20篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有2736条查询结果,搜索用时 62 毫秒
971.
972.
New Insights into the Nature of Co‐components and Their Impact on Pd Structure: X‐ray Absorption Studies on Toluene Acetoxylation Catalysts
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. Suresh Gatla Dr. Jörg Radnik Dr. Neetika Madaan Dr. Marga‐Martina Pohl Dr. Olivier Mathon Dr. Andrei Rogalev Dr. Venkata Narayana Kalevaru Dr. Andreas Martin Dr. Sakura Pascarelli Prof. Dr. Angelika Brückner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15280-15289
Co‐components are a powerful tool to tune the performance of catalysts, but their nature and their impact on the catalysts is often controversially discussed. In this study X‐ray absorption spectroscopy (XAS) was employed to elucidate the nature of co‐components and their impact on the catalytic reaction. In anatase‐supported Pd‐based catalysts for the gas‐phase acetoxylation of toluene, less noble co‐components (e.g., Mn, Co, and Sb) spread over the support in their oxidic form and changed their valence state on stream. Incorporated atoms such as C or a small part of the Sb affect the electronic structure of Pd. For the noble Au, only a weak interaction with the support and Pd was observed during time on stream. Only XAS at the K‐edges together with investigations of the Pd L‐edge for a better understanding of the electronic structure, supplemented by STEM for elemental mapping, allow such detailed insights. 相似文献
973.
Singanaboina Rajaram Udugu Ramulu Seema Aravind Katragadda Suresh Babu 《Helvetica chimica acta》2015,98(5):650-656
An efficient and highly stereoselective synthesis of stagonolide E ( 1 ) starting from the readily available hexane‐1,6‐diol ( 8 ) was accomplished, employing MacMillan α‐hydroxylation, Horner? Wadsworth? Emmons olefination, (Z)‐selective Still? Gennari olefination, and Yamaguchi lactonization as key steps. 相似文献
974.
An Elegant Synthesis of a New Class of 1‐(Substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxides by Microwave Irradiation
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Radha Rani Chinthaparthi Chandra Sekhar Reddy Gangireddy Madhu Kumar Reddy Kandula Satheesh Krishna Balam Suresh Reddy Cirandur 《Journal of heterocyclic chemistry》2015,52(6):1876-1882
A simple and efficient one‐pot microwave‐assisted click formation of 1‐(substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxide derivatives via Huisgen regioselective [3+2]‐cycloaddition of an in situ generated organic azides and diphenyl(prop‐2‐yn‐1‐yl)phosphine oxide in highly polar DMSO‐H2O medium. This synthetic protocol is mild, requires shorter reaction time, and afforded products in excellent yields with high regioselectivity. 相似文献
975.
Precise fluorescence imaging of single λ-DNA molecules for base pair distance analysis requires a superresolution technique, as these distances are on the order of diffraction limit. Individual λ-DNA molecules intercalated with the fluorescent dye YOYO-1 were investigated at subdiffraction spatial resolution by direct stochastic optical reconstructionmicroscopy (dSTORM). Various dye-to-DNA base pair ratios were imaged by photoswitching YOYO-1 between the fluorescent state and the dark state using two laser sources. The acquired images were reconstructed into a super-resolution image by applying Gaussian fitting to the centroid of the point spread function. By measuring the distances between localized fluorophores, the base pair distances in single DNA molecules for dye-to-DNA base pair ratios of 1:50, 1:100, and 1:500 were calculated to be 17.1±0.8 nm, 34.3±2.2 nm, and 170.3±8.1 nm, respectively, which were in agreement with theoretical values. These results demonstrate that intercalating dye in a single DNA molecule can be photoswitched without the use of an activator fluorophore, and that super-localization precision at a spatial resolution of ~17 nm was experimentally achieved. 相似文献
976.
Synthesis,characterization and optical properties of graphene oxide–polystyrene nanocomposites
下载免费PDF全文
![点击此处可从《先进技术聚合物》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kattimuttathu Suresh I. Krishnappan Chidambaram Vellorathekkaepadil Vinod Nutenki Rajender Reddy Mandapati Venkateswara Černík Miroslav 《先进技术聚合物》2015,26(3):214-222
The synthesis of graphene oxide (GO)–polystyrene (PS) Pickering emulsions, as environment‐friendly nanostructures suitable for novel applications, has received significant attention in recent years. In this work, the synthesis and characterization of GO–PS nanocomposites through seeded emulsion polymerization and the selective light reflection properties of dry films have been reported. Amphiphilic molecule sulfonated 3‐pentadecyl phenol was used as a co‐surfactant to stabilize GO dispersions during the emulsion polymerization process. The particle size of the dispersions as measured by dynamic light scattering decreases from 540 nm, for PS without any GO, to 88 nm with 1 wt% GO content. Scanning electron microscopy studies show a uniform size distribution of the composite particles prepared with GO. The dried films show a structural color that varies with the GO content. The self‐assembly behavior of the dried film was further studied using reflectance spectroscopy, which shows a red shift of the reflectance maximum from 440 to 538 nm as the GO loading was increased from 0.2 to 0.5 wt%, respectively, indicating a different microstructure. X‐ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to study the morphology and structure of the composite particles on drying. The AFM study confirms the non‐spherical shape of the particles. Thermogravimetric analysis shows improved thermal decomposition characteristics of the nanocomposite films. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
977.
Spacer length controlled highly thermo reversible polyurethane–urea based on polystyrene: synthesis and crystallization studies
下载免费PDF全文
![点击此处可从《先进技术聚合物》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Poly(urethane–urea) (PUU) is prepared using dihydroxy functionalized polystyrene having Mw 2000 g/mol, 1,6 hexamethylene diisocyanate and three different diamines (1,2‐ethylenediamine, 1,4‐butanediamine and 1,6‐hexamethylene diamine) by melt polymerization method. The synthesized copolymer is characterized by viscosity measurements, Fourier transform infrared (FT‐IR) spectroscopy, wide angle 2D‐X‐ray scattering (WAXS) and differential scanning colorimetry (DSC). The inherent viscosity of the polymers is found to be in the range of 0.4–0.5 dl/g, suggesting that the polymers are of high molecular weight. FT‐IR results conclude that the urea groups form both monodendate and bidendate assemblies. Temperature‐dependent FT‐IR and WAXS data confirm that the crystallinity of the copolymer is highly reversible and depends on the spacer length. DSC data also confirm that the crystallization pattern depends on the spacer length. The swelling behavior in water and the solubility of the polymer in chloroform are depending on the type of chain extender used in the PUU synthesis. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
978.
Dr. Samir Das Dr. Arundhati Nag JingXin Liang Dr. David N. Bunck Dr. Aiko Umeda Blake Farrow Matthew B. Coppock Deborah A. Sarkes Amethist S. Finch Heather D. Agnew Suresh Pitram Bert Lai Mary Beth Yu Dr. A. Katrine Museth Dr. Kaycie M. Deyle Bianca Lepe Frances P. Rodriguez‐Rivera Amy McCarthy Belen Alvarez‐Villalonga Ann Chen John Heath Dimitra N. Stratis‐Cullum Prof. James R. Heath 《Angewandte Chemie (International ed. in English)》2015,54(45):13219-13224
We describe a general synthetic strategy for developing high‐affinity peptide binders against specific epitopes of challenging protein biomarkers. The epitope of interest is synthesized as a polypeptide, with a detection biotin tag and a strategically placed azide (or alkyne) presenting amino acid. This synthetic epitope (SynEp) is incubated with a library of complementary alkyne or azide presenting peptides. Library elements that bind the SynEp in the correct orientation undergo the Huisgen cycloaddition, and are covalently linked to the SynEp. Hit peptides are tested against the full‐length protein to identify the best binder. We describe development of epitope‐targeted linear or macrocycle peptide ligands against 12 different diagnostic or therapeutic analytes. The general epitope targeting capability for these low molecular weight synthetic ligands enables a range of therapeutic and diagnostic applications, similar to those of monoclonal antibodies. 相似文献
979.
Nagabhushana S. R. Sunilkumar Suresh S. Sannappa J. Srinivasa E. 《Journal of Radioanalytical and Nuclear Chemistry》2020,323(3):1393-1403
Journal of Radioanalytical and Nuclear Chemistry - The activity of radium (226Ra), radon (222Rn) and physicochemical parameters in ground water around study area were estimated by standard... 相似文献
980.
Decarboxylative Conjunctive Cross-coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis
Riccardo S. Mega Vincent K. Duong Dr. Adam Noble Prof. Dr. Varinder K. Aggarwal 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(11):4405-4409
The synthesis of complex alkyl boronic esters through conjunctive cross-coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross-coupling cascade of vinyl boronic esters. Excellent functional-group tolerance is displayed, and application of a range of carboxylic acids, including secondary α-amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross-coupling was also applied to the synthesis of sedum alkaloids. 相似文献