全文获取类型
收费全文 | 1376篇 |
免费 | 71篇 |
国内免费 | 1篇 |
专业分类
1448篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 16篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 18篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 33篇 |
2014年 | 49篇 |
2013年 | 139篇 |
2012年 | 82篇 |
2011年 | 86篇 |
2010年 | 50篇 |
2009年 | 54篇 |
2008年 | 83篇 |
2007年 | 84篇 |
2006年 | 75篇 |
2005年 | 85篇 |
2004年 | 95篇 |
2003年 | 76篇 |
2002年 | 55篇 |
2001年 | 28篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 21篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有1448条查询结果,搜索用时 15 毫秒
981.
The size of the territory defended by the grazing fish ayu, Plecoglossus altivelis, often increases with decreasing intruder pressure. This territorial extension occurs even after additional growth of the fish reaches a plateau due to a surplus supply of algal food. This raises questions about the ecological advantages of defending an apparently enlarged territory. Enclosures were used to carry out observations on fish maintained as: (i) individuals with algae attached to the whole bottom area (2.4m2); (ii) individuals with algae covering 0.8m2; and (iii) with three conspecifics (competitive use) with algae attached to 2.4m2. In the competitive use enclosures, one (occasionally two) fish that exclusively foraged the area appeared in each of the groups. Algal resources were sufficiently renewable that no significant difference in growth rate was detected between the dominants of the competitive groups and the two types of solitary enclosures, indicating that the defended area supplied algal resources that exceeded the dominants ability to grow. All the territorial holders realized an increase in relative body weight, suggesting the occurrence of inhibition, which corresponds to Verners concept of superterritory. However, as inferred from the pheophytin/chlorophylla ratios, algae within a territory showed less senescence, perhaps owing to cropping by the dominant, and this was considered to be an adaptive response by the fish to an unpredictable food supply. In conclusion, the ayu conditionally defends a territory for long-term benefits, and inhibition is a consequence of facultative territory size and not a cause of it. 相似文献
982.
The asexual all-female Japanese crucian carp, Carassius auratus langsdorfii (Teleostei: Cypriniformes), reproduces gynogenetically, relying on the sperm of males of the sexual "host," C. auratus subspp. Theoretically, frequency-dependent mating preference of males to conspecific females can lead to the coexistence
of asexual and sexual fish, if all else is equal. Our specific questions are whether males prefer conspecific females over
asexual females and whether individuals show dominance hierarchies that potentially cause frequency-dependent mating preference.
In an individual choice experiment, a tank was partitioned into three compartments with the middle one for a single male and
the two outer ones for a sexual and an asexual female. The males of C. auratus
bürgeri demonstrated a significant preference for ovulated conspecific females over ovulated asexual females. In contrast, in a group
mating experiment, a single experimental tank included two males, a sexual female, and an asexual female together, and males
chased and mated with both asexual and sexual females equally. Male mate preference was weak in group mating, which is typical
in natural populations. Males and females of crucian carp showed no apparent agonistic behavior to each other in the group
mating experiment. This is different from other gynogenetic complexes with the dominance hierarchy of males showing strong
frequency-dependent mating preference (e.g., Poeciliopsis). We conclude that male mate preference is unlikely to be a strong frequency-dependent force maintaining the coexistence
of asexual–sexual complexes of Japanese crucian carp.
Received in revised form: 5 February 2001
Electronic Publication 相似文献
983.
We examined the effects of offspring food demand on parental regulation of food provisioning and body condition in a small long-lived seabird, Leachs storm-petrels (Oceanodroma leucorhoa). In one experimental group, food demand of chicks on their parents was increased by removing one parent (single), and in another group these food demands were decreased by supplementary feeding of chicks (supplement). A further unmanipulated group provided a control. Feeding frequencies by one parent were higher in the single but lower in the supplement than in the control group, in accordance with the food demand of chicks. The size of meals appeared to be not different among the experimental groups. However, as single parents did not compensate perfectly for the increase of chick food demand by food provisioning, single chicks grew at slower rates and fledged at smaller masses than control chicks. Supplement chicks grew at similar rates and fledged at similar masses as control chicks, because parents decreased food provisioning and food processing capacity of the chicks might be limited. The body condition of parents, which was determined by body mass loss and feather regrowth rate, did not differ among the groups. These results indicate that feeding frequency was regulated by parental decision in this storm-petrel species. Parents may adjust their food provisioning to match the food demand of chicks but within a certain range so as not to deteriorate their own body condition. 相似文献
984.
985.
Yoshitaka Saito Terutaka Ozawa Akinori Nishiyama 《The Journal of membrane biology》1987,98(2):135-144
Summary In the isolated, superfused mouse lacrimal gland, intracellular Na+ activities (aNa
i
) of the acinar cells were directly measured with double-barreled Na+-selective microelectrodes. In the nonstimulated conditionaNa
i
was 6.5±0.5 mM and membrane potential (V
m
) was –38.9±0.4 mV. Addition of 1 mM ouabain or superfusion with a K+-free solution slightly depolarized the membrane and caused a gradual increase inaNa
i
. Stimulation with acetylcholine (ACh, 1 M) caused a membrane hyperpolarization by about 20 mV and an increase inaNa
i
by about 9 mM in 5 min. The presence of amiloride (0.1 mM) reduced the ACh-induced increase inaNa
i
by approximately 50%, without affectingV
m
and input resistance in both nonstimulated and ACh-stimulated conditions. Acid loading the acinar cells by an addition/withdrawal of 20 mM NH4Cl or by replacement of Tris+-buffer saline solution with HCO
3
–
/CO2-buffered solution increasedaNa
i
by a few mM. Superfusion with a Cl–-free NO
3
–
solution or 1 mM furosemide or 0.5 mM bumetanide-containing solution had little effect on the restingaNa
i
levels, however, it reduced the ACh-induced increase inaNa
i
by about 30%. Elimination of metabolite anions (glutamate, fumarate and pyruvate) from the superfusate reduced both the restingaNa
i
and the ACh-induced increase inaNa
i
.The present results suggest the presence of multiple Na+ entry mechanisms activated by ACh, namely, Na+/H+ exchange, Na-K-Cl cotransport and organic substrate-coupled Na+ transport mechanisms. 相似文献
986.
We studied a mechanism of hemolysis induced by asbestos particles or silicic acid. This hemolysis was instantly initiated by mixing red blood cells with asbestos particles or silicic acid, and reached a plateau within 10 min. The hemolysis was suppressed by catalase, radical quenchers, deoxygenation, or phospholipids. The degree of the hemolysis was proportional to either the amount of asbestos added into red blood cell suspension or the amount of thiobarbituric acid-reacting substances formed. These findings suggest that in vitro hemolysis induced by asbestos particles (or silicic acid) is ascribed to membrane lipid peroxidation initiated by hydrogen peroxide which was generated by the interaction of the mineral particles with biological membranes. 相似文献
987.
Effect of incubation and preservation on resting egg hatching and mixis in the derived clones of the rotifer Brachionus plicatilis 总被引:3,自引:0,他引:3
The marine rotifer Brachionus plicatilis typicus (Clone 8105A, Univ. of Tokyo) was cultured in 500 ml beakers to form resting eggs. Tetraselmis tetrathele was used as a culture food. Just after formation, resting eggs were exposed to various temperature (5–25 °C) and light regimes (24L: OD and OL : 24D). When eggs were exposed to light just after formation, the eggs hatched sporadically over a month. No hatching was observed for six months when eggs were preserved under dark conditions regardless of the temperature. These eggs hatched simultaneously after being exposed to light and eggs preserved at 5 °C showed twice as high hatching rate (40%) as that of eggs preserved at 15–25 °C (24%). Clones from resting eggs that were kept under different temperature and light regimes were reared individually to the third generation. Incubation at 25 °C with lighting produced the highest (5.4% and 5.2 %) rate of mictic females during their 2nd and 3rd generations, respectively. The lowest rates (0 and 1.5%) were found when the eggs were kept at 5 °C in total darkness for six months. A lower rate of amictic female production was found in clones with higher rates of mixis. 相似文献
988.
T Iguchi S Kondo K Hisatsune 《Nihon saikingaku zasshi. Japanese journal of bacteriology》1989,44(6):805-812
Vibrio anguillarum, one of the causative agents of fish vibriosis, is serologically and biochemically divided into three groups (A, B and C). The chemical composition and molecular architecture of lipopolysaccharide (LPS) isolated from V. anguillarum PT 514, which belongs to serogroup B, were investigated. The LPS contained glucose (Glc), fructose (Fru), L-glycero-D-mannoheptose (L-D Hep), glucosamine (GlcN) and 4-amino-4,6-dideoxyglucose as sugar constituents in molar ratios of 8.9:0.7:3.0:1.1:1.6. Sephadex G-50 gel-chromatography of a degraded polysaccharide fraction separated from the LPS by 5% acetic acid hydrolysis suggested that the O-specific polysaccharide region consists of, in average, as much as 29 moles of Glc per 3 moles of L-D Hep, while the core polysaccharide contains at least Glc, L-D Hep and GlcN in molar ratios of 3.2 : 3.0 : 0.2. Fru and 4-amino-4,6-dideoxyglucose components were released from LPS on weak-acid hydrolysis, indicating that PT 514 LPS is distinguishable from those of Vibrio anguillarum belonging to the other serogroups. 2-Keto-3-deoxyoctonate (KDO), a common sugar constituent of gram-negative bacterial LPS, was not detected by Weissbach's color reaction under the conventional hydrolysis condition, but O-phosphoryl KDO was found in the strong-acid hydrolysate (4 M HCl, 100 C, 45 min). This substance was identical, at least in high-voltage paper electrophoresis, to 5-O-phosphoryl KDO.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
989.
990.