全文获取类型
收费全文 | 1504篇 |
免费 | 69篇 |
国内免费 | 149篇 |
出版年
2024年 | 4篇 |
2023年 | 26篇 |
2022年 | 29篇 |
2021年 | 48篇 |
2020年 | 45篇 |
2019年 | 51篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 28篇 |
2015年 | 37篇 |
2014年 | 49篇 |
2013年 | 104篇 |
2012年 | 66篇 |
2011年 | 94篇 |
2010年 | 64篇 |
2009年 | 71篇 |
2008年 | 70篇 |
2007年 | 105篇 |
2006年 | 75篇 |
2005年 | 75篇 |
2004年 | 78篇 |
2003年 | 70篇 |
2002年 | 64篇 |
2001年 | 56篇 |
2000年 | 38篇 |
1999年 | 29篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 25篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有1722条查询结果,搜索用时 15 毫秒
21.
β-Galactosidase (β-Galase, EC 3.2.1.23) activity has been detected in a culture medium of cell suspension cultures of carrot ( Daucus carota L. cv. Kintoki). The extracellular β-Galase (β-Galase-II) was purified to electrophoretic homogeneity from the concentrated medium using ammonium sulfate precipitation, chromatography on CM-Sephadex C-50. DEAE-Sepharose CL-6B and Sephacryl S-200HR, and preparative PAGE. The molecular mass of the purified enzyme was estimated to be 65 kDa by Sephacryl S-200HR gel-permeation, and 60 kDa by SDS-PAGE after treatment with SDS and 2-mercaptoethanol. The pI was 6.5. The Km and Vmax values for p -nitrophenyl (PNP)-β-D-galactopyranoside were 0.17 m M and 31.9 μmol (mg protein)-1 , h-1 , respectively. The optimal activity in McIlvaine's buffer occurred at pH 4.0–4.4. The enzyme activity was inhibited by Co24 , Cu2+ , Hg2- , p -chloromercuribenzoate (PCMB) and D-galactono-1,4-lactone. The enzyme acted on citrus galactan and larchwood arabinogalactan in an exo-fashion, and was slightly involved in the hydrolysis of an acidic pectic polymer containing arabinosyl and galactosyl residues and in the breakdown of cell walls isolated from carrot cell cultures. 相似文献
22.
23.
P. Michaud J. Courtois B. Courtois A. Heyraud P. Colin-Morel J.-P. Sguin J.-N. Barbotin 《International journal of biological macromolecules》1995,17(6):369-372
During fermentation, the mutant strain Rhizobium mefliloti M5N1 CS, which induces nodule formation on alfalfa roots, produces a partially acetylated (1 → 4)-β-d-glucuronan. In addition to this exopolysaccharide of high molecular weight, the mutant strain produces oligoglucoronates and cyclic (1 → 2)-β-d-glucans with degrees of polymerization from 17 to 30. Under the conditions applied, magnesium has no effect on cyclic glucan production by the mutant strain, but the succinoglycan production by the wild-type strain Rhizobium meliloti M5N1 increases. 相似文献
24.
Manganese supplementation resulted in higher polysaccharide levels and reduced cellular pigmentation by more than 8- or 17-fold after growth for 7d of the fungus Aureobasidium pullulans ATCC 42023 on sucrose or corn syrup, respectively, as a carbon source. The melanin content of the polysaccharide elaborated by ATCC 42023 cells also decreased if MnCl2 was added to the medium. The pullulan content of the polysaccharide synthesized by ATCC 42023 on sucrose was found to increase with increasing levels of manganese, whereas it was lower during growth on corn syrup if manganese was present. 相似文献
25.
Kenji Hara Henneke Pangkey Kiyoshi Osatomi Keiko Yatsuda Atsushi Hagiwara Katsuyasu Tachibana Tadashi Ishihara 《Hydrobiologia》1997,358(1-3):89-94
We examined some characteristics of hydrolyticenzymes, especially -1,3-glucanase, to obtain theinformation of cell wall lytic enzymes forrotifers.Crude enzyme (ammonium sulfate fraction) of rotifershydrolyzed starch, -1,3-glucan, glycol chitinand CM-cellulose. Optimum pH for hydrolysis ofstarch and CM-cellulose was 6.5, and that for -1,3glucan and glycol chitin was pH 6.0. Pectic acid,xylan and agarose were not hydrolyzed at pH 3–10.-1,3 glucanase was purified about 73-fold from crudeenzyme by ion-exchange chromatography and gelfiltration. Optimum pH and temperature of the enzymewere 6 and 60 °C, respectively. The molecular weight ofthe enzyme was estimated about 260 kDa by gelfiltration. The enzyme was inhibited byHgCl2 and MnCl_2. 相似文献
26.
The soluble extracellular polysaccharides (ECP) of suspension-cultured tobacco cells were fractionated by DEAE-Sephadex CC into seven sub-fractions. Su 相似文献
27.
A particulate enzymatic preparation, extracted from fenugreek seedlings (Trigonella foenum-graecum) catalyses the transfer of mannose from guanosine diphosphate-[U-14C]mannose and its incorporation into an alkali-soluble polysaccharide. Chemical and enzymatic study of this polysaccharide reveals the presence of only one type of osidic linkage, namely β-(1 → 4)-s-mannopyranosyl. The influence of some factors on this biosynthesis was studied, as well as the MW of the polysaccharide and the existence of an endogenous acceptor. 相似文献
28.
The polysaccharide component of the stigmatic exudate from Lilium longiflorum has the composition, arabinose (26%), rhamnose (6%), galactose (57%) and glucuronic acid (11%). The highly branched polysaccharide bears a striking resemblance to the acidic polysaccharide exudate from Araucaria bidwillii in belonging to the galactan group and in carrying outer chains terminated by arabinofuranose, rhamnopyranose, galactopyranose and glucuronic acid residues. Both polysaccharides contain the sequence O-rhamnopyranosyl-(1→4)-glucopyranosyluronic acid-(1→6)-galactopyranose in some of the outer chains. 相似文献
29.
1,3-β-Glucan synthase activity has been demonstrated in particulate fractions of bark extracts from Mexican lime. With respect to substrate, the enzyme kinetics did not conform to the Michaelis-Menten equation. The value of the Hill coefficient was 1.2 and S0.5 is 1.1 mM. The enzyme had an optimum pH of 7.5. Maltose, sucrose, and especially cellobiose and glucose, were enzyme activators when tested at physiological concentrations. In the presence of 15 mM MgCl2 the enzymic activity was stimulated at 10 μM UDP-glucose but decreased at 1 mM UDP-glucose, suggesting a minor 1,4-β-glucan synthase activity. 相似文献
30.
R. De Philippis C. Sili G. Tassinato M. Vincenzini R. Materassi 《Bioresource technology》1991,38(2-3)
Batch cultures of Cyanospira capsulata, a heterocystous cyanobacterium possessing a thick polysaccharidic capsule, were characterized by increasing viscosity owing to the continuous release of a soluble polysaccharide (EPS) into the culture medium. Both capsulated trichomes and solubilized EPS contributed to the flow properties of whole cultures. A typical pseudoplastic behaviour, the more marked the more aged were the cultures, was evidenced.The production of EPS was investigated under different growth conditions by changing some nutritional and physical parameters known to affect the synthesis of exopolysaccharides in algae and cyanobacteria. Among the factors tested (Ca2+, Mg2+ or PO4−4 deficiencies, salinity and pH) only Mg2+ shortage caused a significant enhancement of the EPS production. Under continuous illumination in open ponds, the EPS productivity of batch cultures on standard mineral medium was about 5·8 g m−2 day−1, whereas under Mg2+ deficiency with a consequent increase of the cultures' viscosity 相似文献