全文获取类型
收费全文 | 579篇 |
免费 | 99篇 |
出版年
2022年 | 6篇 |
2021年 | 10篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 25篇 |
2014年 | 14篇 |
2013年 | 26篇 |
2012年 | 29篇 |
2011年 | 23篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 15篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 28篇 |
2002年 | 20篇 |
2001年 | 8篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1973年 | 6篇 |
1971年 | 10篇 |
1970年 | 9篇 |
1969年 | 9篇 |
1967年 | 8篇 |
1966年 | 10篇 |
1965年 | 5篇 |
1964年 | 6篇 |
1959年 | 9篇 |
1956年 | 5篇 |
1954年 | 6篇 |
1953年 | 5篇 |
1952年 | 8篇 |
排序方式: 共有678条查询结果,搜索用时 15 毫秒
101.
When the kinetics of the acid phosphatase enzyme system from the posterior reproductive tract of the female housefly, Musca domestica, were studied, enzyme activity was zero order for 2 hr and was temperature-dependent. Orthophosphate release was linearily related to enzyme concentration, and pH optima between pH 3·3 to 3·7, 4·2 to 4·8, and 5·2 to 5·7 were observed. Magnesium and calcium ions were enzyme activators; arsenate, phosphate, fluoride, and hydroxymalonate ions were inhibitors. Sodium azide had little effect. The similarity of activity exhibited on the test substrates indicated that the soluble enzymes corresponded to the non-specific phosphomonoesterases.Disk electrophoresis showed that at least 6 proteins had acid phosphatase activity and were pH-dependent. Also, electrophoresis of extracts of the various structures of the reproductive tract showed that there was a tissue specificity in the distribution of the acid phosphatase isoenzymes. 相似文献
102.
Timing of growth regulator responses in peas 总被引:11,自引:0,他引:11
103.
104.
105.
Folia Microbiologica - The above-described method for purification of conidia of a strain ofAspergillus niger from the conidia of the parasitic fungusPenicillium purpurogenum consists in employing... 相似文献
106.
To characterize synchronisation strategies in the tracking of auditory rhythm with rhythmic finger tapping, the adaptation
process after unexpected step changes of an interstimulus interval (ISI) of 500 ms was investigated. Step changes of 2% (10
ms), 4% (20 ms), and 10% (50 ms) of ISI were applied to the stimulus sequence. Synchronisation patterns of 5 subjects were
analyzed based on synchronisation error (SE) and interresponse intervals (IRI). A strategy shift contigent upon the size of
the introduced step change was detected. After small ISI changes, rapid IRI matching to the new ISI was accompanied by temporarily
enlarged SE values, which slowly returned to preferred SE values before the step change. Large ISI changes showed quick SE
adaptations accompanied by a temporary overcorrection of IRI. Response asymmetry between ISI decreases and increases emerged,
showing a stronger adaptation during ISI increases. A two-dimensional difference equation was formulated to simulate the time
series of intertap intervals and explain the control process during IRI and SE adjustments. The system constants were optimized
to minimalize the deviations between the computed and the observed response trajectories, consisting of the time series of
SE and IRI. It was shown that a successful model fit using a linear two-dimensional difference equation was based on the size
and direction of the ISI changes. MANOVA procedures showed that differences in equation parameters during small and large
step changes were statistically significant (P<0.05). It is therefore suggested that a uniform model accounting for synchronization responses to all step changes would
require the introduction of nonlinear system properties.
Received: 20 August 1997/Accepted in revised form: 9 June 1998 相似文献
107.
Summary The effect of a direct-current electric field on cephalin and lecithin films was measured using infrared spectral techniques. The intensities of the spectral bands assigned to the vibrations of the phosphate and the fatty acid chain increased to a maximum as the applied potential was increased. These changes were observed only with brain cephalin and brain lecithin films and not with synthetic lipid films. These observations may be due to changes in the alignments of the phosphate and base dipoles in the lipid molecule as the applied field is changed. The electric field strengths at which the maximum intensities of the spectral bands are observed increase as the thickness decreases. Extrapolation to the thickness of the nerve membrane yields a value of the field strength that is much larger than is to be expected in the neuron. This suggests that only the phosphate group and the hydrocarbon chain change conformation during the passage of the nerve impulse.Presented in part at the First Meeting of the International Society for Neurochemistry, 1967, and the 156th Meeting of the American Chemical Society, 1968. 相似文献
108.
109.
110.
Experiments with green seedlings of sunflower (Helianthus annuns L.) indicate the existence of a phototropic mechanism which involves the leaves or cotyledons, and which can produce an asymmetry of auxin content without the involvement of lateral auxin transport, the classic explanation of phototropism in etiolated seedlings. The basic lines of evidence for the leaf-mediated tropism are: 1) darkening of one cotyledon will cause curvature of the stem toward the lighted cotyledon: 2) the darkened cotyledon sustains an enhanced growth rate in the stem below it: 3) conversely, light suppresses the growth-stimulating effects of a single cotyledon: and 4) more diffusible auxin is obtained from the stem below darkened cotyledons than below lighted ones. 相似文献