全文获取类型
收费全文 | 546篇 |
免费 | 43篇 |
专业分类
589篇 |
出版年
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 33篇 |
2014年 | 27篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 16篇 |
2009年 | 18篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 32篇 |
2005年 | 15篇 |
2004年 | 23篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 9篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 13篇 |
1991年 | 2篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有589条查询结果,搜索用时 0 毫秒
101.
Invasive species may have negative impacts on many narrow range endemics and species restricted to oceanic islands. Predicting
recent impacts of invasive species on long-lived trees is difficult because the presence of adult plants may mask population
changes. We examined the impact of introduced black rats (Rattus rattus) on two palm species restricted to cloud forests and endemic to Lord Howe Island, a small oceanic island in the southern
Pacific. We combined estimates of the standing size distribution of these palms with the proximal impacts of rats on fruit
survival in areas baited to control rats and in unbaited areas. The size distribution of palms with trunks was comparable
across baited and unbaited sites. Small juvenile palms lacking a trunk (<50 cm tall) were abundant in baited areas, but rare
in unbaited sites for Lepidorrhachis mooreana, and rare or absent in 3 out of 4 unbaited Hedyscepe
canterburyana sites. All ripe fruits were lost to rats in the small fruited L. mooreana. Fruit removal was widespread but less (20–54%) in H. canterburyana. Both palms showed evidence of a reduced capacity to maintain a juvenile bank of palms through regular recruitment as a consequence
of over 90 years of rat impact. This will limit the ability of these species to take advantage of episodic canopy gaps. Baiting
for rat control reduced fruit losses and resulted in the re-establishment of a juvenile palm bank. Conservation of both endemic
palms necessitates control (or eradication) of rat populations on the unique cloud forest summits of the island. 相似文献
102.
103.
Helen Baines Margaret O Nwagwu Graham R Hastie Roman A Wiles Terry M Mayhew Francis JP Ebling 《Reproductive biology and endocrinology : RB&E》2008,6(1):4
Background
The hypogonadal (hpg) mouse is widely used as an animal model with which to investigate the endocrine regulation of spermatogenesis. Chronic treatment of these GnRH-deficient mice with estradiol is known to induce testicular maturation and restore qualitatively normal spermatogenesis. The aim of the current studies was to investigate whether these effects of estradiol are direct effects in the testis, or indirect actions via paradoxical stimulation of FSH secretion from the pituitary gland. 相似文献104.
Fischer-344 (F-344) rats differ from other common rat strains in that they
fail to show any preference for NaCl at any concentration in two- bottle
preference tests. Because 100 microM amiloride partially blocks the
NaCl-evoked chorda tympani (CT) response in electrophysiological studies,
we tested NaCl preference (0.068-0.273 M) in F-344 rats with and without
100 microM amiloride solution as the solvent. A third group was tested with
unadulterated NaCl solutions following CT transection. Amiloride had no
significant effect on the NaCl preference-aversion function, whereas CT
transection significantly reduced NaCl avoidance. These results suggest
that the amiloride-sensitive component of the NaCl response is not
necessary for F-344 rats to display avoidance of NaCl, but the entire CT
input is.
相似文献
105.
M Takahashi T Shimizu K Ooi H Noda T Nasu G Sakaguchi 《Japanese journal of medical science & biology》1988,41(1):21-26
Bacteriological examinations were performed on the first case of infant botulism in Japan (an infant boy aged 79 days at onset of illness). Clostridium botulinum type A toxin and organisms were detected continually in the stools of the infant for at least 31 days and 39 days, respectively. The highest levels of the toxin and of the population of the organisms, 7.8 X 10(4) LD50/g and 1.3 X 10(6) colony forming units (cfu)/g, were detected in the stool specimen taken on the 20th day of illness. Type A organisms were detected also in the honey fed to the infant before onset of illness, teats of his feeding bottle, soil specimens taken at the house entry and the vacuum-cleaner dust. Fecal excretion of the toxin and organisms was no longer detected from the 68th day of illness and he recovered. 相似文献
106.
107.
108.
Ooi H Cadogan E Sweeney M Howell K O'Regan RG McLoughlin P 《American journal of physiology. Heart and circulatory physiology》2000,278(2):H331-H338
Chronic hypercapnia is commonly found in patients with severe hypoxic lung disease and is associated with a greater elevation of pulmonary arterial pressure than that due to hypoxia alone. We hypothesized that hypercapnia worsens hypoxic pulmonary hypertension by augmenting pulmonary vascular remodeling and hypoxic pulmonary vasoconstriction (HPV). Rats were exposed to chronic hypoxia [inspiratory O(2) fraction (FI(O(2))) = 0.10], chronic hypercapnia (inspiratory CO(2) fraction = 0.10), hypoxia-hypercapnia (FI(O(2)) = 0.10, inspiratory CO(2) fraction = 0.10), or room air. After 1 and 3 wk of exposure, muscularization of resistance blood vessels and hypoxia-induced hematocrit elevation were significantly inhibited in hypoxia-hypercapnia compared with hypoxia alone (P < 0.001, ANOVA). Right ventricular hypertrophy was reduced in hypoxia-hypercapnia compared with hypoxia at 3 wk (P < 0.001, ANOVA). In isolated, ventilated, blood-perfused lungs, basal pulmonary arterial pressure after 1 wk of exposure to hypoxia (20.1 +/- 1.8 mmHg) was significantly (P < 0.01, ANOVA) elevated compared with control conditions (12.1 +/- 0.1 mmHg) but was not altered in hypoxia-hypercapnia (13.5 +/- 0.9 mmHg) or hypercapnia (11.8 +/- 1.3 mmHg). HPV (FI(O(2)) = 0.03) was attenuated in hypoxia, hypoxia-hypercapnia, and hypercapnia compared with control (P < 0.05, ANOVA). Addition of N(omega)-nitro-L-arginine methyl ester (10(-4) M), which augmented HPV in control, hypoxia, and hypercapnia, significantly reduced HPV in hypoxia-hypercapnia. Chronic hypoxia caused impaired endothelium-dependent relaxation in isolated pulmonary arteries, but coexistent hypercapnia partially protected against this effect. These findings suggest that coexistent hypercapnia inhibits hypoxia-induced pulmonary vascular remodeling and right ventricular hypertrophy, reduces HPV, and protects against hypoxia-induced impairment of endothelial function. 相似文献
109.
110.