全文获取类型
收费全文 | 2661篇 |
免费 | 111篇 |
国内免费 | 9篇 |
专业分类
化学 | 2245篇 |
晶体学 | 23篇 |
力学 | 23篇 |
数学 | 257篇 |
物理学 | 233篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 37篇 |
2021年 | 35篇 |
2020年 | 55篇 |
2019年 | 51篇 |
2018年 | 28篇 |
2017年 | 31篇 |
2016年 | 75篇 |
2015年 | 78篇 |
2014年 | 90篇 |
2013年 | 117篇 |
2012年 | 194篇 |
2011年 | 244篇 |
2010年 | 112篇 |
2009年 | 99篇 |
2008年 | 211篇 |
2007年 | 203篇 |
2006年 | 194篇 |
2005年 | 195篇 |
2004年 | 168篇 |
2003年 | 130篇 |
2002年 | 116篇 |
2001年 | 33篇 |
2000年 | 23篇 |
1999年 | 24篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 27篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 9篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1969年 | 4篇 |
1968年 | 2篇 |
排序方式: 共有2781条查询结果,搜索用时 15 毫秒
991.
Jaka Sunarso Youssof Shekibi Jim Efthimiadis Liyu Jin Jennifer M. Pringle Anthony F. Hollenkamp Douglas R. MacFarlane Maria Forsyth Patrick C. Howlett 《Journal of Solid State Electrochemistry》2012,16(5):1841-1848
Organic ionic plastic crystal (OIPC) electrolytes are among the key enabling materials for solid-state and higher than ambient
temperature lithium batteries. This work overviews some of the parameter studies on the Li|OIPC interface using lithium symmetrical
cells as well as the optimisation and performance of Li|OIPC|LiFePO4 cells. The effects of temperature and electrolyte thickness on the cycle performance of the lithium symmetrical cell, particularly
with respect to the interfacial and bulk resistances, are demonstrated. Whilst temperature change substantially alters both
the interfacial and bulk resistance, changing the electrolyte thickness predominantly changes the bulk resistance only. In
addition, an upper limit of the current density is demonstrated, above which irreversible processes related to electrolyte
decomposition take place. Here, we demonstrate an excellent discharge capacity attained on LiFePO4|10 mol% LiNTf2-doped [C2mpyr][NTf2]|Li cell, reaching 126 mAh g-1 at 50 °C (when the electrolyte is in its solid form) and 153 mAh g-1 at 80 °C (when the electrolyte is in its liquid form). Most remarkably, at high temperature operation, the capacity retention
at long cycles and high current is excellent with only a slight (3%) drop in discharge capacity upon increasing the current
from 0.2 C to 0.5 C. These results highlight the real prospects for developing a lithium battery with high temperature performance
that easily surpasses that achievable with even the best contemporary lithium-ion technology. 相似文献
992.
Thomas D Clark Mila Boncheva Jennifer M German Marcus Weck George M Whitesides 《Journal of the American Chemical Society》2002,124(1):18-19
This communication describes the fabrication of three-dimensional structures of organic polymers using principles of design inspired by protein folding. The structures consist of rigid polyhedral components with dimensions of a few millimeters ("microdomains"), representing alpha-helical and beta-sheet secondary structures, connected with flexible linkers representing loops or turns. These structures were fabricated from polyurethane using photolithographic and soft lithographic techniques. The surfaces of the microdomains were patterned into hydrophobic and hydrophilic regions, and a hydrophobic photocurable liquid (serving both as lubricant and adhesive) was selectively precipitated onto the hydrophobic areas. The unfolded structures were suspended in water and agitated by tumbling. Self-assembly occurred through coalescence of the thin films of hydrophobic liquid, and was caused by minimization of the free energy of the interface between the liquid adhesive and the water. The self-assembled structures were locked in place by curing the adhesive with UV light. These results demonstrate the use of concepts abstracted from the study of proteins-including attractive hydrophobic interactions, shape complementarity, and conformational constraint-in the self-assembly of complex, three-dimensional structures on the millimeter scale. 相似文献
993.
Lifei Zheng Alessio Marcozzi Dr. Jennifer Y. Gerasimov Prof. Dr. Andreas Herrmann 《Angewandte Chemie (International ed. in English)》2014,53(29):7599-7603
Cyclic peptides containing a disulfide bridge were identified as a simple and versatile coordination sphere for asymmetric catalysis. Upon complexation with Cu2+ ions they catalyze Diels–Alder and Friedel–Crafts reactions with high enantioselectivities of up to 99 % ee and 86 % ee, respectively. Moreover, the peptides ligands were systematically optimized with the assistance of “Alanine Scanning”. This biomolecular design could greatly expand the choice of peptide scaffolds for artificial metallopeptide catalysts. 相似文献
994.
Mark D. Straub Jennifer Leduc Michael Frank Aida Raauf Trevor D. Lohrey Stefan G. Minasian Sanjay Mathur John Arnold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5805-5809
Homoleptic uranium(IV) amidate complexes have been synthesized and applied as single‐source molecular precursors for the chemical vapor deposition of UO2 thin films. These precursors decompose by alkene elimination to give highly crystalline phase‐pure UO2 films with an unusual branched heterostructure. 相似文献
995.
Dr. Colin S. M. Kang Dr. Oliver E. Hutt Prof. Jennifer M. Pringle 《Chemphyschem》2022,23(13):e202200115
The implementation of next-generation batteries requires the development of safe, compatible electrolytes that are stable and do not cause safety problems. The difluoro(oxalato)borate ([DFOB]−) anion has been used as an electrolyte additive to aid with stability, but such an approach has most commonly been carried out using flammable solvent electrolytes. As an alternative approach, utilisation of the [DFOB]− anion to make ionic liquids (ILs) or Organic Ionic Plastic Crystals (OIPCs) allows the advantageous properties of ILs or OIPCs, such as higher thermal stability and non-volatility, combined with the benefits of the [DFOB]− anion. Here, we report the synthesis of new [DFOB]−-based ILs paired with triethylmethylphosphonium [P1222]+, and diethylisobutylmethylphosphonium [P122i4]+. We also report the first OIPCs containing the [DFOB]− anion, formed by combination with the 1-ethyl-1-methylpyrrolidinium [C2mpyr]+ cation, and the triethylmethylammonium [N1222]+ cation. The traditional synthetic route using halide starting materials has been successfully replaced by a halide-free tosylate-based synthetic route that is advantageous for a purer, halide free product. The synthesised [DFOB]−-based salts exhibit good thermal stability, while the ILs display relatively high ionic conductivity. Thus, the new [DFOB]−-based electrolytes show promise for further investigation as battery electrolytes both in liquid and solid-state form. 相似文献
996.
Billups WE Luo W Lee GA Chee J Arney BE Wiberg KB Artis DR 《The Journal of organic chemistry》1996,61(2):764-770
Bicyclo[4.1.0]hept-1,6-ene has been generated by elimination of 1-chloro-2-(trimethysilyl)bicyclo[4.1.0]heptane in the gas phase over solid fluoride at 25 degrees C. The cyclopropene dimerizes by a rapid ene reaction forming two diastereomeric cyclopropenes. In tetrahydrofuran or chloroform the ene dimers couple to form a single crystalline triene tetramer, whereas a mixture of tricyclohexane tetramers is formed when the neat dimers are allowed to warm to room temperature. Oxidation by dimethyldioxirane or dioxygen gives carbonyl products. Quantum mechanical calculations yielded an increase in strain of approximately 17 kcal/mol over that for 1,2-dimethylcyclopropene. The potential enegy barrier to flexing (folding) along the fused double bond of bicyclo[4.1.0]hept-1,6-ene is only approximately 1 kcal/mol at the highest level of theory investigated. 相似文献
997.
McCullagh JS Tripp JA Hedges RE 《Rapid communications in mass spectrometry : RCM》2005,19(22):3227-3231
The reconstruction of ancient diets using isotopic measurements of bone collagen, and other tissues, which survive in archaeological contexts, relies on known isotopic relationships between diet and body tissues. Examination of these relationships often requires the study of modern human and animal subjects. While hair keratin can act as a useful proxy for bone collagen in isotopic studies on living humans, where it is inappropriate to sample tissues such as collagen, it can, in addition, act as a chronological indicator of dietary change. This study investigates hair keratin delta13C values from current residents of the UK and the USA. Residents in the USA showed a clear bulk hair delta13C enrichment of approximately 3 per thousand over UK individuals, attributed to an elevated C4 dietary input from maize fed to livestock in North America. The keratin delta13C of subjects who moved between the UK and USA showed a pronounced change after relocation, taking approximately 4 months to reach isotopic equilibrium. To investigate these differences further, we measured delta13C values of dispensable and indispensable amino acids as a group, and selected individual amino acids. As a group, enrichment of dispensable amino acids compared with indispensable amino acids occurred in samples from both continents, averaging 7.2 per thousand in the UK and 7.9 per thousand in the USA. Dispensable and indispensable amino acids, as well as all individual amino acids measured, were enriched in samples from the USA compared with those from the UK. 相似文献
998.
999.
Zheng T Narayan RS Schomaker JM Borhan B 《Journal of the American Chemical Society》2005,127(19):6946-6947
A simple and efficient process to cyclize triols containing a 1,2-diol functionality with a pendant hydroxyl group is presented. The one-pot procedure converts the 1,2-diol into an ortho ester in situ, which upon treatment with a Lewis acid generates a cyclic acetoxonium intermediate. This intermediate is subsequently trapped by the pendant hydroxyl group to generate a cyclic ether. The stereochemistry of the 1,2-diol is transferred to the product with complete fidelity (inversion at the site of cyclization), and the reaction proceeds with high regioselectivity. The process is akin to the Lewis acid-catalyzed intramolecular ring-opening of epoxides with hydroxyl groups yielding cyclic ethers of various sizes with regio- and stereochemical control. 相似文献
1000.
Ragupathi G Koide F Livingston PO Cho YS Endo A Wan Q Spassova MK Keding SJ Allen J Ouerfelli O Wilson RM Danishefsky SJ 《Journal of the American Chemical Society》2006,128(8):2715-2725
Several novel, fully synthetic, carbohydrate-based antitumor vaccines have been assembled. Each construct consists of multiple cancer-related antigens displayed on a single polypeptide backbone. Recent advances in synthetic methodology have allowed for the incorporation of a complex oligosaccharide terminating in a sialic acid residue (i.e., GM2) as one of the carbohydrate antigens. Details of the vaccine synthesis as well as the results of preliminary immunological investigations are described herein. 相似文献