全文获取类型
收费全文 | 1910篇 |
免费 | 74篇 |
国内免费 | 7篇 |
专业分类
化学 | 1115篇 |
晶体学 | 39篇 |
力学 | 49篇 |
数学 | 180篇 |
物理学 | 319篇 |
无线电 | 289篇 |
出版年
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 40篇 |
2020年 | 43篇 |
2019年 | 40篇 |
2018年 | 26篇 |
2017年 | 40篇 |
2016年 | 63篇 |
2015年 | 32篇 |
2014年 | 63篇 |
2013年 | 116篇 |
2012年 | 88篇 |
2011年 | 105篇 |
2010年 | 59篇 |
2009年 | 58篇 |
2008年 | 78篇 |
2007年 | 95篇 |
2006年 | 76篇 |
2005年 | 82篇 |
2004年 | 71篇 |
2003年 | 64篇 |
2002年 | 54篇 |
2001年 | 34篇 |
2000年 | 33篇 |
1999年 | 39篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 30篇 |
1995年 | 36篇 |
1994年 | 28篇 |
1993年 | 27篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 14篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 14篇 |
1972年 | 11篇 |
1971年 | 12篇 |
排序方式: 共有1991条查询结果,搜索用时 177 毫秒
71.
Rajendran Arunachalam Eswaran Chinnaraja Arto Valkonen Kari Rissanen Palani S. Subramanian 《应用有机金属化学》2019,33(11)
The multidentate ligand H2 L upon complexation with Zn (II) and Cd (II) provide a one‐dimensional polymeric networks. These coordination polymers (CPs) CP‐1 and CP‐2 containing Zn (II) and Cd (II) metals respectively are well characterized. The single crystal structural analysis confirms the formation of one‐dimensional coordination polymer with zigzag fashion in CP‐1 and ladder chain CP‐2 . Both the CPs are applied as catalysts to synthesize various cyclic carbonates from epoxides and carbon dioxide. The catalysts are giving better conversion under solvent‐free and additive‐free condition using 10 bar CO2 and 100 °C as optimized pressure and temperature. The detailed kinetic experiments suggesting the first order kinetics, the energy of activation (Ea) is calculated for this catalytic conversion. 相似文献
72.
Wei Wang Dr. Parthasarathi Subramanian Oscar Martinazzoli Jun Wu Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10585-10589
Late-stage C−H glycosylations of structurally complex amino acids and peptides were accomplished by means of racemization-free manganese(I)-catalyzed C−H activation. Thus, glycosylative modifications proved to be viable by a linch-pin approach, featuring chemo- and site-selective C−H transformations. The peptide–saccharide conjugation provided modular access to structurally complex glycopeptides, likewise enabling the assembly of fluorescent-labelled glycopeptides. 相似文献
73.
74.
75.
Kodgirwar Vidya P. Deosarkar Shankar B. Joshi Kalyani R. 《Wireless Personal Communications》2020,110(1):423-444
Wireless Personal Communications - Applications of wireless sensor networks (WSNs) are increasing tremendously to facilitate and establish a link between the physical world and information system.... 相似文献
76.
77.
78.
Abstract In this study, the molecular weights of the polymer from vinyl benzoate has been reported for different dose rates and different temperatures. The mol.wt. remains around 4000. With increasing dose, the molecular weight increases to about 14,000. The degrees of polymerization and the kinetic chain lengths calculated from the experimentally determined G R values have been compared which show that the kinetic chain length is larger than the D ? Pn. From a plot of the (D ? Pn)?1 vs. R p , an intercept is obtained which is equal to 3.25 × 10?2 which is higher than obtained in conventional polymerization. By examining the effect of temperature on mol.wt., the dependence of R p on dose rate and the absence of induction period it has been concluded that chain transfer occurs to impurities that are generated during radiolysis. 相似文献
79.
80.
Synthesis and characterization of supramolecular optically active bisamides derived from amino acids
The synthesis and phase transitional behaviour of three pairs of enantiomeric supramolecular hexacatenar liquid crystals (LCs) derived from natural α-amino acids such as l/d-alanine, l/d-leucine and l/d-valine are described. Their preparation with high enantiomeric purity was accomplished by condensing optically active (amino acid residue containing) trialkoxy amines with a 3,4,5-trialkoxy cinnamic acid core using a peptide coupling reagent namely, 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyl-uronium hexafluorophosphate (HBTU). The mesomorphic behaviour of these self-complementing mesogens was ascertained by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. The compounds exhibit columnar (Col) phase over a wide thermal range. Particularly, a pair of enantiomers derived from l/d-leucine residues notably stabilize hexagonal Col (Colh) phase over a wide temperature range of ?5 °C to 180 °C. Circular dichroism (CD) and FTIR studies suggest the chiral (helical) organization of mesogens within the columns through intermolecular hydrogen bonding; thus, these enantiomers represent one of the rarely reported examples of LCs exhibiting supramolecular Colh phase at room temperature. The gelation studies reveal the ability of these bisamides to form stable supramolecular gels in ethanol caused through H-bonding interactions. 相似文献