全文获取类型
收费全文 | 805篇 |
免费 | 44篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 11篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 50篇 |
2012年 | 47篇 |
2011年 | 35篇 |
2010年 | 32篇 |
2009年 | 34篇 |
2008年 | 46篇 |
2007年 | 51篇 |
2006年 | 53篇 |
2005年 | 52篇 |
2004年 | 52篇 |
2003年 | 44篇 |
2002年 | 44篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 17篇 |
1998年 | 10篇 |
1997年 | 15篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有849条查询结果,搜索用时 25 毫秒
841.
Conduction of action potentials in Chara internodal cells wasblocked at a 5%-urethane treated region. The action potentialscould be propagated beyond this region when an electric bridgewas built across it with a low enough resistance that the actioncurrent across it could depolarize the membrane at the distaljunction of the bridge up to the threshold level. After recoveryof propagation, the configuration of the action current flowingthrough the bridge changed from monophasic to diphasic. Coursesof the monophasic action current and the depolarizing potentialof the resting membrane were in parallel with the course ofaction potential, although they were slightly out of phase witheach other. The magnitudes of the current and depolarizing potentialagreed well with those estimated using a simplified equivalentcircuit of the bridge arrangement or with those observed usingan electric model circuit.
1Present address: Department of Physiology, Tohoku UniversitySchool of Dentistry, Seiryo-machi, Sendai 980, Japan.
2Present address: Biology Laboratory, Kyoritsu Women's University,Hachioji, Tokyo 193, Japan. (Received December 18, 1985; Accepted March 26, 1986) 相似文献
842.
843.
844.
Reproductive interference, interspecific sexual interactions that affect reproductive success, is found in various taxa and has been considered as a fundamental source of reproductive character displacement (RCD). Once RCD has occurred, persistent interspecific sexual interactions between species pairs are expected to diminish. However, reproductive interference has been reported from some species pairs that sympatrically coexist. Thus, the question arises, can reproductive interference persist even after RCD? We modeled the evolutionary dynamics of signal traits and mate recognition that determine whether interspecific sexual interactions occur. Our models incorporate male decision making based on the recognition of signal traits, whereas most previous models incorporate only female decision making in mate selection. Our models predict the following: (1) even when male decision making is incorporated, males remain promiscuous; (2) nevertheless, the frequency of interspecific mating is maintained at a low level after trait divergence; (3) the rarity of interspecific mating is due to strict female mate recognition and the consequent refusal of interspecific courtship by females; and (4) the frequency of interspecific mating becomes higher as the cost to females of refusing interspecific courtship increases. These predictions are consistent with empirical observations that males of some species engage in infrequent heterospecific mating. Thus, our models predict that reproductive interference can persist even after RCD occurred. 相似文献
845.
846.
Purification and properties of NADH dehydrogenase from a thermoacidophilic archaebacterium, Sulfolobus acidocaldarius 总被引:3,自引:0,他引:3
An NADH dehydrogenase was purified to electrophoretical homogeneity from Sulfolobus acidocaldarius, a thermoacidophilic archaebacterium optimally growing at pH 2-3 and 75 degrees C. A 2,100-fold purification was achieved. The purified enzyme is an acidic protein with an isoelectric point of 5.6 and a molecular weight of 95,000, consisting of two 50,000-dalton subunits. The enzyme showed an absorption spectrum characteristic of flavoproteins, with maxima at 272, 372, and 448 nm. The enzyme is highly thermostable, is specific for NADH as an electron donor, and is capable of using 2,6-dichlorophenolindophenol, ferricyanide, benzoquinone, and naphthoquinone as electron acceptors. Though at a low rate, caldariellaquinone, a unique and sole benzothiophenequinone in the genus Sulfolobus, was also reduced by the enzyme, suggesting that the enzyme is a possible member of the respiratory chain of the thermoacidophilic archaebacterium. 相似文献
847.
Exercise training enhances in vivo tuberculosis purified protein derivative response in the elderly.
Mitsuharu Okutsu Yuko Yoshida Xiumin Zhang Akira Tamagawa Takayoshi Ohkubo Ichiro Tsuji Ryoichi Nagatomi 《Journal of applied physiology》2008,104(6):1690-1696
We investigated the effect of 25 wk of exercise training on in vivo immune measures that depend on T helper 1 (Th1) and T helper 2 (Th2) immune responses in the elderly as a substudy of a randomized controlled trial to investigate health benefits of regular exercise training for the elderly. Sixty-five healthy elderly volunteers were randomly assigned to either an exercise training group (n = 32) or a sedentary control group (n = 33). The area of skin reaction to purified protein derivative (PPD) of tuberculin that depends on Th1 activation and the concentrations of serum IgG subclasses and IgE were evaluated before and after 25-wk intervention. All participants completed 25 wk of training. Thirty-one participants of the exercise group and all control group underwent immunological analyses, but only 30 from the exercise group and 21 from the control group had the PPD skin reaction assessment. Repeated-measures ANOVA revealed a significant interaction between time and exercise intervention, which appeared as an enhanced skin reaction to tuberculin PPD (P < 0.05) and a reduced serum IgG4 concentration, the production of which depends on Th2-dependent class switching (P < 0.05), in the exercise group after 25 wk. No immune variables changed in the control group. These result supports the hypothesis that exercise training favors in vivo Th1 immune response in elderly persons. 相似文献
848.
The phenology and leaf traits ofDaphne kamtschatica Maxim. var.jezoensis (Maxim.) Ohwi, the only summer deciduous shrub (20–40 cm) in the temperate forest of northern Japan, are examined. This plant
carries through the winter mature leaves and well formed flower buds. It flowers in early spring during snowmelt and begins
photosynthesis under relatively high irradiance under an open forest canopy. Our results show that there is significant carbon
gain during the period when new leaves and fruit maturation also take place. Beginning in June, as the forest canopy closes,
leaves onDaphne shoots senesce acropetally and the plants become completely bare in mid-July. After a period of 20-day dormancy, the shoots
begin to resprout. Leaves become mature in early October and remain on the stem over winter. Leaf traits and photosynthesis
measurements suggest as follows. 1) By becoming summer deciduous,D. kamtschatica avoids the cost of maintaining leaves inefficient under deep shade. 2) The onset and breaking of the summer dormancy is triggered
by photoperiod since plants at the forest edge also become dormant even when light remained relatively high. However, the
decreased duration of dormancy with higher light levels suggests that there is a tendency towards shorter dormancy where summer
shade is absent and this could eventually lead to an evergreen habit such as that found in the alpine speciesDaphne miyabeana. 相似文献
849.