全文获取类型
收费全文 | 1992篇 |
免费 | 66篇 |
国内免费 | 11篇 |
专业分类
化学 | 1427篇 |
晶体学 | 29篇 |
力学 | 22篇 |
数学 | 114篇 |
物理学 | 477篇 |
出版年
2021年 | 21篇 |
2020年 | 13篇 |
2019年 | 29篇 |
2018年 | 24篇 |
2017年 | 11篇 |
2016年 | 31篇 |
2015年 | 31篇 |
2014年 | 47篇 |
2013年 | 90篇 |
2012年 | 99篇 |
2011年 | 91篇 |
2010年 | 58篇 |
2009年 | 48篇 |
2008年 | 98篇 |
2007年 | 126篇 |
2006年 | 95篇 |
2005年 | 120篇 |
2004年 | 136篇 |
2003年 | 88篇 |
2002年 | 99篇 |
2001年 | 50篇 |
2000年 | 52篇 |
1999年 | 32篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 42篇 |
1995年 | 31篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 30篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 30篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1972年 | 8篇 |
1970年 | 8篇 |
排序方式: 共有2069条查询结果,搜索用时 15 毫秒
61.
Transition of the radial electric field by electron cyclotron heating in the CHS heliotron/torsatron
62.
Fernandes SA Nachtigall FF Lazzarotto M Fujiwara FY Marsaioli AJ 《Magnetic resonance in chemistry : MRC》2005,43(5):398-404
'Non-covalent synthesis' of novel chiral hosts (calix[6]arene-chiral amine complexes) and its application to enantiomeric discrimination was investigated by (1)H NMR spectroscopy. The topology of a ternary complex was proposed for the calix[6]arene-amine-sulfoxide to rationalize the chiral recognition. 相似文献
63.
Alfaya RV Fujiwara ST Gushikem Y Kholin YV 《Journal of colloid and interface science》2004,269(1):32-36
3-n-propylpyridiniumsilsesquioxane chloride polymer, abbreviated as SiPy+Cl-, was used to coat a porous silica gel, SiO2, surface to form the chemically modified solid SiO2/SiPy+Cl-. The resulting polymer film was well adhered to the surface and presented an ion exchange capacity of 0.74 mmol g(-1). Metal halides, MClz [M=Fe(III), Cu(II), and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: mSiO2/SiPy+Cl-+ MClz <=> (SiO2/SiPy+)m[MCl(z+m)]m-, where the [MCl(z+m)]m- species adsorbed on the surface are FeCl4-, ZnCl4(2-), and CuCl4(2-). Accurate estimates of the specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures. 相似文献
64.
65.
Onodera K Nakamura H Oba Y Ohizumi Y Ojika M 《Journal of the American Chemical Society》2005,127(29):10406-10411
Zooxanthellamide Cs (ZAD-Cs), C(128)H(220)N(2)O(53)S(2) (ca. 2.7 kDa), was obtained from a cultured marine dinoflagellate of the genus Symbiodinium as an inseparable isomeric mixture of polyhydroxylated 61- to 66-membered macrolides. The chemical structures of the components were clarified by detailed 2D NMR analysis to be the macrolactonized analogues of zooxanthellamide A (ZAD-A), which had been previously isolated from the same microalgae. Chemical lability of ZAD-Cs suggests that ZAD-A is an artifact derived from ZAD-Cs during the isolation steps. Three of the components possess the largest (63-, 64-, and 66-membered) ring sizes found to date among the natural macrolides. ZAD-Cs exhibited higher vasoconstrictive activity than that of the zooxanthellatoxins, the first vasoconstrictive macrolides from Symbiodinium sp. The structure-activity relationship suggests that the huge macrolactone structure is important for biological activity. The relationship between the structures of the polyol metabolites and the phylogenetic systematics of Symbiodinium sp. is also discussed. 相似文献
66.
A stepwise reaction of p-tert-butylthiacalix[4]arene (TC4A-(OH)(4)) with [CpTiCl3]-NEt(3) and cis-[Mo(N(2))(2)(PMe(2)Ph)(4)] afforded a new Ti-Mo heterobimetallic complex [TC4A-(O)(4)Ti(micro2-C(5)H(5))MoH(PMe(2)Ph)(2)] which shows an unusual alpha-agostic micro2-eta5:eta2-coordination of a cyclopentadienyl ligand. 相似文献
67.
68.
Kyoichiro Shibatani Yuzuru Fujiwara Kiyoshi Fujii 《Journal of polymer science. Part A, Polymer chemistry》1970,8(7):1693-1703
High-resolution proton magnetic resonance and infrared spectra of poly(vinyl formal) were studied in comparison with those of the model formals obtained from stereoisomers of pentane-2,4-diol and heptane-2,4,6-triol in order to learn spectral changes due to differences of the steric structures of the polymer. In the NMR spectrum of transformal obtained from dl diol or dl,dl (syndiotactic) triol, all proton signals were well interpreted by assuming a rapid chair-chair inversion of the formal ring. On the other hand, no such inversion was observed spectroscopically in cis-formal obtained from the meso diol or meso,meso (isotactic) triol, and the cis-formal ring was supposed to take a diequatorial form preferentially. Consequently, dioxymethylene protons gave a single peak (equivalent) in trans-formal and an AB quartet (nonequivalent) in cis-formal. In the spectra of poly(vinyl formal), the dioxymethylene signal was an overlap of the singlet and quartet in dimethylsulfoxide solution. Observations of the spectra of various poly(vinyl formals) obtained from poly(vinyl alcohols) of different tacticities and study of temperature dependence of the signal have shown that the singlet and quartet are attributed to trans- and cis- formals, respectively, in the polymer spectrum also. In the infrared spectra of poly(vinyl formals), the 800 and 785 cm-1 bands were found to be related to cis- and trans-formal rings respectively. A linear relationship was confirmed between D785/D800 and trans/cis ratios determined from the peak intensities of the dioxymethylene proton signals. 相似文献
69.
Takaki K Itono Y Nagafuji A Naito Y Shishido T Takehira K Makioka Y Taniguchi Y Fujiwara Y 《The Journal of organic chemistry》2000,65(2):475-481
Three-component coupling of acylphosphonates and two carbonyl compounds leading to beta-hydroxyphosphonates has been achieved with low-valent samariums. Thus, acylphosphonates reacted with aldehydes in the presence of semicatalytic amounts of samarium metal or SmI(2) to give acyloxyphosphonates in good yields. The second coupling reaction of the acyloxyphosphonates with aldehydes or ketones promoted by SmI(2) afforded beta-hydroxyphosphonates instead of olefins. Moreover, these two reactions could be carried out in one pot. 相似文献
70.
[Reaction: see text] Cycloisomerization of 1,6-enynes proceeded smoothly in water under heterogeneous conditions in the presence of a palladium complex supported on polystyrene-poly(ethylene glycol) copolymer resin to give the corresponding cyclopentanes with a high level of chemical greenness. Multistep asymmetric synthesis of a hydrindane framework was achieved via palladium-catalyzed asymmetric pi-allylic alkylation, propargylation, and cycloisomerization of 1,6-enynes, where all three steps were performed in water with recyclable polymeric catalysts. 相似文献