全文获取类型
收费全文 | 121508篇 |
免费 | 7788篇 |
国内免费 | 95篇 |
出版年
2012年 | 12627篇 |
2011年 | 14360篇 |
2010年 | 2050篇 |
2009年 | 958篇 |
2008年 | 11507篇 |
2007年 | 12126篇 |
2006年 | 11389篇 |
2005年 | 10911篇 |
2004年 | 10737篇 |
2003年 | 9924篇 |
2002年 | 8844篇 |
2001年 | 6852篇 |
2000年 | 8969篇 |
1999年 | 3358篇 |
1998年 | 355篇 |
1997年 | 251篇 |
1996年 | 139篇 |
1995年 | 156篇 |
1994年 | 140篇 |
1993年 | 127篇 |
1992年 | 125篇 |
1991年 | 102篇 |
1990年 | 110篇 |
1989年 | 86篇 |
1988年 | 96篇 |
1987年 | 75篇 |
1986年 | 71篇 |
1985年 | 58篇 |
1984年 | 49篇 |
1983年 | 77篇 |
1982年 | 65篇 |
1981年 | 39篇 |
1980年 | 46篇 |
1974年 | 29篇 |
1972年 | 32篇 |
1971年 | 41篇 |
1970年 | 36篇 |
1969年 | 31篇 |
1959年 | 133篇 |
1958年 | 272篇 |
1957年 | 279篇 |
1956年 | 225篇 |
1955年 | 240篇 |
1954年 | 226篇 |
1953年 | 153篇 |
1952年 | 162篇 |
1951年 | 110篇 |
1950年 | 102篇 |
1949年 | 44篇 |
1948年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
84.
85.
The lipase produced by Pseudomonas fluorescens biotype I was selected for hydrolyzing beef tallow at 50-70 degrees C to more than 90% of reaction ratio. Using an amount of lipase sufficient to reach equilibrium, the final reaction ratio was decreased with increasing temperature and the apparent enthalpy of beef tallow hydrolysis obtained by the final reaction ratio was -1.93 x 10(4)cal/mol, and the final reaction ratio also decreased with increasing substrate concentration. The rising time, which is the reaction time up to one-half of the final reaction ratio, decreased remarkably with increasing temperature, and was closely related to the value of the maximum velocity by the Michaelis constant of this lipase. The final reaction ratio increased with increasing lipase amount up to equilibrium. Increasing the lipase above the amount required to reach equilibrium caused a decrease in the rising time. The feasibility of using parameters obtained by a hyperbolic simulation of the progress curve is discussed. 相似文献
86.
Invertase was ionically immobilized on the poly(ethylene-co-vinyl alcohol) hollow fiber inside surface, which was aminoacetalized with 2-dimethylaminoacetaldehyde dimethyl acetal. Immobilization and enzyme reaction were carried out by letting the respective solutions pass or circulate through the inside of the hollow fiber, and the activity of invertase was determined by the amount of glucose produced enzymatically from sucrose. Immobilization conditions were examined with respect to the enzyme concentration and to the time, and consequently the preferable conditions at room temperature were found to be 5 mug/mL of enzyme concentration and 4 h of immobilization time. Under those conditions the immobilization yield and the ratio of the activity of the immobilized invertase to that of the native one were 89 and 80%, respectively. For both repeating and continuous usages, the activity fell to ca. 60% of the initial activity in the early stage and after that almost kept that value. The apparent Michaelis constant K(m) (') for the immobilized invertase decreased with increasing the flow rate of the substrate solution, to be close to the value for the native one. Furthermore, the possibility of the separation of the enzymatically formed glucose from the reaction mixture through the hollow fiber membrane was preliminarily examined. 相似文献
87.
88.
Three growth inhibitors which might be involved in phototropism of Sakurajima radish (Raphanus sativus var. hortensis f. gigantissimus Makino) hypocotyls, were isolated as crystalline forms from light-exposed radish seedlings and identified as cis- and trans-raphanusanins and 6-methoxy-2,3,4,5-tetrahydro-1,3-oxazepin-2-one (designated raphanusamide). The cis- and trans-raphanusanins inhibited growth of etiolated radish hypocotyls at concentrations higher than 1.5 micromolar, raphanusamide at concentrations higher than 20 micromolar. 相似文献
89.
Hydroxamate-Stimulated O(2) Uptake in Roots of Pisum sativum and Zea mays, Mediated by a Peroxidase : Its Consequences for Respiration Measurements 总被引:4,自引:4,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Low concentrations of salicylhydroxamic acid (<5 millimolar) stimulate O2 uptake in intact roots of Pisum sativum. We demonstrate that the hydroxamate-stimulated O2 uptake does not reside in the mitochondria. We also show that the hydroxamate-stimulated O2 uptake is due to the activation of a peroxidase catalyzing reduction of O2. This peroxidase, which can use both NADH and NADPH as a substrate, is stimulated by low concentrations of monophenols, e.g. salicylhydroxamic acid and 2-methoxyphenol. It is inhibited by high (20 millimolar) concentrations of salicylhydroxamic acid, cyanide, and scavengers of the superoxide free radical ion, e.g. ascorbate, gentisic acid, and catechol. In the presence of gentisic acid, O2 uptake by intact pea roots was no longer stimulated by low concentrations of salicylhydroxamic acid. The consequence of the present finding for in vivo respiration measurements is that the use of low concentrations of salicylhydroxamic acid and uncoupler is reliable only in the presence of a suitable superoxide free radical scavenger which prevents activation of the peroxidase. It also confirms that high concentrations of salicylhydroxamic acid (20-25 millimolar) can be safely used in short-term experiments to assess the activity of the alternative path in intact roots. 相似文献
90.
Root cultures of various solanaceous plants grow well in vitro and produce large amounts of tropane alkaloids. Enzyme activity that converts hyoscyamine to 6β-hydroxyhyoscyamine is present in cell-free extracts from cultured roots of Hyoscyamus niger L. The enzyme hyoscyamine 6β-hydroxylase was purified 3.3-fold and characterized. The hydroxylation reaction has absolute requirements for hyoscyamine, 2-oxoglutarate, Fe2+ ions and molecular oxygen, and ascorbate stimulates this reaction. Only the l-isomer of hyoscyamine serves as a substrate; d-hyoscyamine is nearly inactive. Comparisons were made with a number of root, shoot, and callus cultures of the Atropa, Datura, Duboisia, Hyoscyamus, and Nicotiana species for the presence of the hydroxylase activity. Decarboxylation of 2-oxoglutarate during the conversion reaction was studied using [1-14C]-2-oxoglutarate. A 1:1 stoichiometry was shown between the hyoscyamine-dependent formation of CO2 from 2-oxoglutarate and the hydroxylation of hyoscyamine. Therefore, the enzyme can be classified as a 2-oxoglutarate-dependent dioxygenase (EC 1.14.11.-). Both the supply of hyoscyamine and the hydroxylase activity determine the amounts of 6β-hydroxyhyoscyamine and scopolamine produced in alkaloid-producing cultures. 相似文献