全文获取类型
收费全文 | 9108篇 |
免费 | 421篇 |
国内免费 | 2篇 |
出版年
2023年 | 21篇 |
2022年 | 49篇 |
2021年 | 109篇 |
2020年 | 66篇 |
2019年 | 78篇 |
2018年 | 121篇 |
2017年 | 108篇 |
2016年 | 163篇 |
2015年 | 255篇 |
2014年 | 240篇 |
2013年 | 328篇 |
2012年 | 754篇 |
2011年 | 867篇 |
2010年 | 306篇 |
2009年 | 256篇 |
2008年 | 749篇 |
2007年 | 738篇 |
2006年 | 696篇 |
2005年 | 632篇 |
2004年 | 585篇 |
2003年 | 572篇 |
2002年 | 497篇 |
2001年 | 285篇 |
2000年 | 334篇 |
1999年 | 183篇 |
1998年 | 51篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 31篇 |
1994年 | 25篇 |
1993年 | 33篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1974年 | 20篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1970年 | 11篇 |
1968年 | 9篇 |
排序方式: 共有9531条查询结果,搜索用时 46 毫秒
21.
Photobiont cells of the lichen Evernia prunastri have completely been separated from their fungal partner by filtration through a bed of Sepharose 2B. Both mannitol and ribitol have been quantified by gas-liquid chromatography in the different steps of the isolation procedure. Absence of mannitol, which is exclusively produced by the mycobiont, has been used as the best probe to monitor isolation. 相似文献
22.
Invertase immobilization via its carbohydrate moiety 总被引:1,自引:0,他引:1
After periodate oxidation of its glycosidic component, invertase was covalently bound onto three types of modified solid supports: glycidyl methacrylate, styrene-divinylbenzene copolymers, and bead cellulose. Direct reaction of the invertase aldehyde groups that were formed with amino groups of the support and use of the modified Ugi reaction have been employed as immobilization procedures. Apart from binding methods, the important effects of the buffer, support, conditions of periodate oxidation, and the length of the spacer on the activity of the enzyme conjugate have been investigated. Superior conjugate activity was obtained, via modified Ugi reaction, by the immobilization of a suitably oxidized invertase to a styrene-divinylbenzene copolymer having free amino groups. 相似文献
23.
24.
Meria E. Penttilä K. M. Helena Nevalainen Alain Raynal Jonathan K. C. Knowles 《Molecular & general genetics : MGG》1984,194(3):494-499
Summary The possibility of cloning filamentous fungal genes by expression in the yeast Saccharomyces cerevisiae has been studied. A genome bank of Aspergillus niger was made in E. coli using a yeast cosmid shuttle vector and over 10,000 different cosmid clones were individually isolated. Yeast transformants carrying Aspergillus DNA were screened for the expression of the genes for fungal secreted glycoproteins, -galactosidase, -glucosidase, and amyloglucosidase, and for the expression of fungal genes complementing yeast ura3 and leu2 mutations.Of the five Aspergillus genes studied, only one, -glucosidase, was found to be expressed in yeast, and this at a low level. This suggests that there are essential differences between the genes of yeast and filamentous fungi. 相似文献
25.
The title trisaccharide was synthesized using methyl 1-thioglycoside building blocks. An acyclic analogue, methyl 3-O-(α-D-glycopyranosyl-oxyethyl)-α-D-glucopyranoside, which has an ethylene bridge in place of the galactosyl residue, was also synthesized. 相似文献
26.
Emilio Román Galán Jaun A. Galbis Pérez Mariá A. Arévalo Arévalo 《Carbohydrate research》1983,116(2):255-262
The reaction between 2-(benzylamino)-2-deoxy-d-glycero-l-gluco-heptose and 5,5-dimethyl-1,3-cyclohexanedione yields 1-benzyl-4,5,6,7-tetrahydro-6,6-dimethyl-2-(d-galacto-pentitol-1-yl)-indol-4-one (2). Acid-catalyzed, intramolecular dehydration of 2 under kinetically controlled conditions gives 1-benzyl-4,5,6,7-tetrahydro-2-α-d-lyxofuranosyl-6,6-dimethylindol-4-one; the anomeric configuration of this compound is only suggested. When the dehydration reaction is conducted under thermodynamically controlled conditions, it produces a 1:1 mixture of the α- and β-d-lyxopyranosyl compounds. The structures of the new compounds were elucidated by chemical and physical methods. 相似文献
27.
Accumulation of pyrophosphate in Escherichia coli. Relationship to growth and nucleotide synthesis 总被引:1,自引:0,他引:1
Pyrophosphate (PPi) content of Escherichia coli is increased manyfold when the growth of the cells is limited by inhibition of the synthesis of nucleotides. The accumulated PPi is immediately degraded when inhibition is released and growth allowed to resume. Other tested nutritional deficiencies (starvation of carbon source, sulfate or an amino acid) fail to induce PPi accumulation. 相似文献
28.
29.
30.
1. Aspartate-carbamoyltransferase activity was concentrated from rat-liver preparations. Only l-aspartate, beta-benzyl-l-aspartate and beta-erythro-hydroxy-dl-aspartate were carbamoylated enzymically. The K(m) for l-aspartate and carbamoyl phosphate have been determined by three methods: colorimetric procedure, radioactive assay with [(14)C]aspartate and an assay with [(14)C]carbamoyl phosphate. 2. The K(m) for aspartate has been determined as a function of the pH; the pK of the functional group at the active site of the enzyme, pK(e), was at pH9.0. Enzymic activity was diminished in the presence of N-ethylmaleimide, p-hydroxymercuribenzoate and the heavy metals Ag(+), Hg(2+), or Zn(2+). The inhibitions could be prevented by mercaptoethanol. These findings suggested the association of a thiol group with the enzymic activity. 3. Enzymic activity was also decreased by sodium lauryl sulphate, urea and dioxan. Competitive inhibition (with l-aspartate) was manifested by maleate, succinate, oxaloacetate, beta-erythro-hydroxy-dl-aspartate and beta-benzyl-l-aspartate. The K(i) for most of these inhibitions has been determined. 4. The properties of the liver enzyme are compared with those of Escherichia coli aspartate carbamoyltransferase and the implications of the findings are discussed. 相似文献