全文获取类型
收费全文 | 955篇 |
免费 | 37篇 |
国内免费 | 7篇 |
专业分类
化学 | 624篇 |
晶体学 | 12篇 |
力学 | 36篇 |
综合类 | 1篇 |
数学 | 89篇 |
物理学 | 237篇 |
出版年
2023年 | 9篇 |
2022年 | 39篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 14篇 |
2016年 | 37篇 |
2015年 | 27篇 |
2014年 | 51篇 |
2013年 | 80篇 |
2012年 | 76篇 |
2011年 | 81篇 |
2010年 | 39篇 |
2009年 | 39篇 |
2008年 | 47篇 |
2007年 | 45篇 |
2006年 | 59篇 |
2005年 | 40篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 30篇 |
2001年 | 30篇 |
2000年 | 18篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1917年 | 1篇 |
1911年 | 2篇 |
排序方式: 共有999条查询结果,搜索用时 0 毫秒
221.
A new phenolic glucoside, isoconiferoside (1), was isolated from the seeds of Panax ginseng (Araliaceae). The structure was determined to be 9-O-[β-D-glucopyranosyl-(1 --> 6)-β-D-glucopyranosyl]-trans-coniferyl alcohol based on spectroscopic analyses (1H- and 13C-NMR, DEPT, COSY, HMQC, and HMBC) and acid hydrolysis. 相似文献
222.
The aggregation state of several lithium enolates were calculated in the gas phase and in THF solution by the B3LYP DFT and MP2 methods. The gas phase free energies of aggregate formation were underestimated by the DFT calculations, compared to those obtained by the G3MP2 method, although DFT did correctly predict the hexamer to be the major gas phase species. The DFT calculations correctly predicted the tetramer to be the major species in THF, while MP2 underestimated the stability of the tetramer relative to the dimer. 相似文献
223.
Choi SH Na HB Park YI An K Kwon SG Jang Y Park MH Moon J Son JS Song IC Moon WK Hyeon T 《Journal of the American Chemical Society》2008,130(46):15573-15580
Heterostructured nanoparticles composed of metals and Fe3O4 or MnO were synthesized by thermal decomposition of mixtures of metal-oleate complexes (for the oxide component) and metal-oleylamine complexes (for the metal component). The products included flowerlike-shaped nanoparticles of Pt-Fe3O4 and Ni-Fe3O4 and snowmanlike-shaped nanoparticles of Ag-MnO and Au-MnO. Powder X-ray diffraction patterns showed that these nanoparticles were composed of face-centered cubic (fcc)-structured Fe3O4 or MnO and fcc-structured metals. The relaxivity values of the Au-MnO and Au-Fe3O4 nanoparticles were similar to those of the MnO and Fe3O4 nanoparticles, respectively. Au-Fe3O4 heterostructured nanoparticles conjugated with two kinds of 12-base oligonucleotide sequences were able to sense a complementary 24-mer sequence, causing nanoparticle aggregation. This hybridization-mediated aggregation was detected by the overall size increase indicated by dynamic light scattering data, the red shift of the surface plasmon band of the Au component, and the enhancement of the signal intensity of the Fe3O4 component in T2-weighted magnetic resonance imaging. 相似文献
224.
Lee SH Son JK Jeong BS Jeong TC Chang HW Lee ES Jahng Y 《Molecules (Basel, Switzerland)》2008,13(2):272-300
Rutaecarpine is an indolopyridoquinazolinone alkaloid isolated from Evodia rutaecarpa and related herbs, which has shown a variety of intriguing biological properties such as anti-thrombotic, anticancer, anti-inflammatory and analgesic, anti-obesity and thermoregulatory, vasorelaxing activity, as well as effects on the cardiovascular and endocrine systems. Recent progress in the studies on the isolation, synthesis, structure-activity relationship studies, biological activities and metabolism of rutaecarpine are reviewed. 相似文献
225.
Mlanie M. Lorion Nikolaos Kaplaneris Jongwoo Son Rositha Kuniyil Lutz Ackermann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(6):1698-1702
Bioorthogonal late‐stage diversification of structurally complex peptides has enormous potential for drug discovery and molecular imaging. In recent years, transition‐metal‐catalyzed C?H activation has emerged as an increasingly viable tool for peptide modification. Despite major accomplishments, these strategies largely rely on expensive palladium catalysts. We herein report an unprecedented cobalt(III)‐catalyzed peptide C?H activation, which enables the direct C?H functionalization of structurally complex peptides, and sets the stage for a multicatalytic C?H activation/alkene metathesis/hydrogenation strategy for the assembly of novel cyclic peptides. 相似文献
226.
Truong Son Pham László Balázs Imre Petneházy Zsuzsa Jászay 《Tetrahedron: Asymmetry》2010,21(3):346-351
An enantioselective Michael addition of diethyl cyanomethyl phosphonate to chalcones catalysed by bifunctional catalysts based on cinchona alkaloids has been developed, producing enantiomerically enriched cyanophosphonate precursors of α-substituted β-aminophosphonates. 相似文献
227.
Youn-Suk Son Ki-Joon Kim Ji-Yong Kim Jo-Chun Kim 《Radiation Physics and Chemistry》2010,79(12):1270-1274
We applied a hybrid technique to assess the decomposition characteristics of ethylbenzene and toluene that annexed the catalyst technique with existing electron beam (EB) technology. The removal efficiency of ethylbenzene in the EB–catalyst hybrid turned out to be 30% greater than that of EB-only treatment. We concluded that ethylbenzene was decomposed more easily than toluene by EB irradiation. We compared the independent effects of the EB–catalyst hybrid and catalyst-only methods, and observed that the efficiency of the EB–catalyst hybrid demonstrated approximately 6% improvement for decomposing toluene and 20% improvement for decomposing ethylbenzene. The G-values for ethylbenzene increased with initial concentration and reactor type: for example, the G-values by reactor type at 2800 ppmC were 7.5–10.9 (EB-only) and 12.9–25.7 (EB–catalyst hybrid). We also observed a significant decrease in by-products as well as in the removal efficiencies associated with the EB–catalyst hybrid technique. 相似文献
228.
Rolczynski BS Szarko JM Son HJ Liang Y Yu L Chen LX 《Journal of the American Chemical Society》2012,134(9):4142-4152
Record-setting organic photovoltaic cells with PTB polymers have recently achieved ~8% power conversion efficiencies (PCE). A subset of these polymers, the PTBF series, has a common conjugated backbone with alternating thieno[3,4-b]thiophene and benzodithiophene moieties but differs by the number and position of pendant fluorine atoms attached to the backbone. These electron-withdrawing pendant fluorine atoms fine tune the energetics of the polymers and result in device PCE variations of 2-8%. Using near-IR, ultrafast optical transient absorption (TA) spectroscopy combined with steady-state electrochemical methods we were able to obtain TA signatures not only for the exciton and charge-separated states but also for an intramolecular ("pseudo") charge-transfer state in isolated PTBF polymers in solution, in the absence of the acceptor phenyl-C(61)-butyric acid methyl ester (PCBM) molecules. This led to the discovery of branched pathways for intramolecular, ultrafast exciton splitting to populate (a) the charge-separated states or (b) the intramolecular charge-transfer states on the subpicosecond time scale. Depending on the number and position of the fluorine pendant atoms, the charge-separation/transfer kinetics and their branching ratios vary according to the trend for the electron density distribution in favor of the local charge-separation direction. More importantly, a linear correlation is found between the branching ratio of intramolecular charge transfer and the charge separation of hole-electron pairs in isolated polymers versus the device fill factor and PCE. The origin of this correlation and its implications in materials design and device performance are discussed. 相似文献
229.
230.
2-Nitroaryl aldehydes, ketones, and imines were reductively cyclized to 2,1-benzisoxazoles with good yields in the presence of indium and iodine in MeOH. Under a similar condition, N-(2-nitrobenzylidene)anilines were produced mixtures of 2,1-benzisoxazoles and 3-anilino-2-phenyl-2H-indazoles. 相似文献