全文获取类型
收费全文 | 2015篇 |
免费 | 50篇 |
国内免费 | 12篇 |
专业分类
化学 | 1319篇 |
晶体学 | 8篇 |
力学 | 92篇 |
数学 | 328篇 |
物理学 | 330篇 |
出版年
2022年 | 15篇 |
2021年 | 30篇 |
2020年 | 24篇 |
2019年 | 37篇 |
2018年 | 31篇 |
2017年 | 17篇 |
2016年 | 56篇 |
2015年 | 29篇 |
2014年 | 41篇 |
2013年 | 82篇 |
2012年 | 88篇 |
2011年 | 110篇 |
2010年 | 64篇 |
2009年 | 72篇 |
2008年 | 93篇 |
2007年 | 111篇 |
2006年 | 102篇 |
2005年 | 116篇 |
2004年 | 87篇 |
2003年 | 81篇 |
2002年 | 50篇 |
2001年 | 26篇 |
2000年 | 38篇 |
1999年 | 35篇 |
1998年 | 20篇 |
1997年 | 26篇 |
1996年 | 24篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 15篇 |
1992年 | 30篇 |
1991年 | 12篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1888年 | 10篇 |
排序方式: 共有2077条查询结果,搜索用时 62 毫秒
61.
Ketteler G Ogletree DF Bluhm H Liu H Hebenstreit EL Salmeron M 《Journal of the American Chemical Society》2005,127(51):18269-18273
Using a photoemission spectroscometer that operates close to ambient conditions of pressure and temperature we have determined the Pd-O phase diagram and the kinetic parameters of phase transformations. We found that on the (111) surface oxidation proceeds by formation of stable and metastable structures. As the chemical potential of O2 increases chemisorbed oxygen forms followed by a thin surface oxide. Bulk oxidation is a two-step process that starts with the metastable growth of the surface oxide into the bulk, followed by a first-order transformation to PdO. 相似文献
62.
The effects of storage of size-exclusion column packing materials in methanolic or azide-water solutions on subsequent separations were tested. Three commercially available columns were used in these studies; the Toyo-Soda Bio-Sil TSK 125, Bio-Sil TSK 250 and the DuPont Bio-Series GF-250. Upon initial chromatography, all three columns bound up to 760 micrograms of cytochrome c tryptic peptides. Sample binding to packing material is probably a function of the positively charged basic groups on peptides or proteins interacting with silanol groups. The larger the peptide, the less the opportunity for silanol-charged group interaction, hence, less binding. Initial samples introduced to a new column occupy the binding sites. Equilibration with neat methanol removes the bound protein revealing sites which bind sample. After absorption of peptides to binding sites on the packing material, storage in neat methanol regenerates the binding sites. Storage in 10% methanol diminished the binding phenomenon, but storage in azide-water reduced binding to a range below detection at the microgram level. Our recommendation to users of size-exclusion chromatographic columns is that one satisfy the absorption capacity of a new column by injecting a sufficient quantity of a basic peptide standard or other convenient sample to reduce available binding sites before using the column for important separations. Store columns in azide-water or 10% methanol to prevent the regeneration of exposed silanol groups. 相似文献
63.
The volatiles emitted by fresh whole flowers or isolated flower parts of mandarin, Citrus deliciosa Ten. (Rutaceae), were sampled using solid-phase micro-extraction (SPME). This technique offers several advantages over dynamic headspace sampling techniques used in previous investigations. In particular, SPME requires smaller sample sizes and very short sampling times, which can minimize the formation of artifacts due to damage to the plant, and contaminations or loss of compounds. This was especially applicable to the collection of volatiles from pollen. 相似文献
64.
[reaction: see text] A regioselective method for the preparation of 1,5-trisubstituted 1H-1,2,3-triazoles via a 1,3-dipolar cycloaddition of 1-trimethylsilylacetylenes with organoazides is described. Immobilization of the azide on REM resin and subsequent cycloaddition afforded a 2 x 2 x 4 x 3 membered 1,5-disubstituted 1H-1,2,3-triazole library with an average purified yield of 68%. 相似文献
65.
Two new uncommon nitrogenous sesquiterpenes, 11‐ethoxy‐3‐formamidotheonellin ( 1 ) and 7‐ethoxy‐3‐formamidobisabolane‐8,10‐diene ( 2 ), together with two known related sesquiterpenes, 3‐formamidotheonellin (=theonellin formamide; 3 ) and theonellin isothiocyanate ( 4 ), were isolated from the Hainan sponge Axinyssa aff. variabilis. Their structures were determined on the basis of extensive spectroscopic analysis and by comparison of their NMR data with those of known compounds. 相似文献
66.
67.
68.
Both single crystals of VCl3(THF)3 as well as isotypic cocrystals of the composition MCl3(THF)3, M=Ti/V 1/3, undergo a topotactic reversible phase transition to a hitherto unknown low-temperature modification. The close relationship between this new structure and the room-temperature phase determined by Cottonet al. is discussed from the molecular and the intermolecular point of view: Both modifications are built up by conformationally very similar molecules which change their arrangement during the phase transition. Lattice energy calculations confirm that these two alternative arrangements correspond to minima of almost the same packing energy.Dedicated to Professor Dr. G. E. Herberich on the occasion of his 60th birthday. 相似文献
69.
70.
Foltz C Stecker B Marconi G Bellemin-Laponnaz S Wadepohl H Gade LH 《Chemical communications (Cambridge, England)》2005,(40):5115-5117
Chiral C3-symmetric trisoxazolines are highly efficient stereodirecting ligands in enantioselective Cu(II) Lewis acid catalysis which is based on the concept of a stereoelectronic hemilability of the divalent copper; in direct comparison with the analogous bisoxazoline systems they are more efficient in the enantioselective alpha-amination as well as the enantioselective Mannich reaction of prochiral beta-ketoesters. 相似文献