全文获取类型
收费全文 | 163篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
安全科学 | 2篇 |
环保管理 | 5篇 |
综合类 | 9篇 |
基础理论 | 148篇 |
污染及防治 | 1篇 |
评价与监测 | 1篇 |
灾害及防治 | 1篇 |
出版年
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 1篇 |
1981年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有167条查询结果,搜索用时 15 毫秒
161.
The tilapiine cichlids Oreochromis leucostictus and Tilapia zillii were introduced into Lake Naivasha, Kenya, in 1956. Previous studies on data collected to 1987 revealed they were persistent
following establishment, despite environmental variability and exploitation. Recent data, however, suggest this persistence
is under threat as data indicate some significant declines in aspects of their abundance since 1999. The influence of changes
in lake level, allodiversity and fishing effort on this decline was tested and showed that a decline in lake level was a significant
causal factor. The recent change in allodiversity, with the establishment and dominance of Cyprinus carpio in the fishery, was not significant on the catch per unit effort of O. leucostictus but was on T. zillii. Since 1999, catches of tilapiines in the fishery have been independent of fishing effort, contrary to between 1975 and 1987,
suggesting their management through application of fishery models may no longer be applicable. As it was anthropogenic-mediated
lake level changes that were mainly responsible for their decline, then lake management should focus on sustainable water
utilization that maximizes lake levels in accordance with the basin-wide water balance. 相似文献
162.
Parker's seminal work brought attention to the possibility of postmating sexual selection by non-random fertilization success.
Mechanisms for these processes are still only partly understood and there is clearly a need for more studies of intraspecific
variation in sperm precedence. Here, we report results from an experimental study of the variation in fertilization success
between males of the water strider Gerris lacustris. Genital morphology, male body size, and copulation duration were examined as possible correlates of paternity. The significance
of guarding duration was also analysed. Only male genital morphology was correlated to fertilization success. This is one
of the first studies showing a relationship between male genital traits and fertilization success, supporting the view that
sexual selection may be responsible for the rapid and divergent evolution of genital structures in animals with internal fertilization.
The fertilization success of last males varied considerably after double matings with a short mating interval (10 min). Last-male
priority ranged from 0 to 100% and usually one of the males involved fertilized almost all the eggs. After double matings
with a short mating interval, the proportion of eggs fertilized by the last male averaged 0.68 and was greater than 0.5. In
contrast, the average fertilization success was biased towards the first male when the matings were more spread out over time
(24 h). These results do not support earlier suggestions of a widespread last-male sperm priority in water striders.
Received: 28 July 1998 / Received in revised form: 15 March 1999 / Accepted: 28 March 1999 相似文献
163.
Relative importance of male and territory quality in pairing success of male rock ptarmigan (Lagopus mutus) 总被引:4,自引:0,他引:4
We studied pairing success in male rock ptarmigan (Lagopus mutus) in northern Alaska to learn whether males obtaining more females possessed phenotypic traits that influenced female choice
directly, whether these traits permitted males to obtain territories favored by females, or whether both processes occurred.
The number of females per male varied from zero to three. Several male and territory traits were significantly correlated
with number of females per male. We used multiple regression to obtain a single measure of male quality and a single measure
of territory quality. These measures of male and territory quality correlated with each other and with male pairing success.
We used path analysis to separate direct effects of male quality on pairing success from indirect effects due to high-quality
males obtaining high-quality territories. Both direct and indirect pathways had significant effects on pairing success, and
direct and indirect effects of male traits on pairing success were about equal. This study illustrates an analytical approach
for estimating the relative importance of direct and indirect causal relationships in natural systems.
Received: 13 January 1998 / Accepted after revision: 7 November 1998 相似文献
164.
Male reproductive success in free-ranging feral horses 总被引:1,自引:0,他引:1
C. S. Asa 《Behavioral ecology and sociobiology》1999,47(1-2):89-93
In the social organization of feral horses, adult males compete to monopolize groups or bands of females, sometimes called
harems. Alternative male strategies are to remain alone or with other bachelors or, less commonly, to accept subordinate status
within a harem. The hypothesis that dominant harem stallion status confers a reproductive advantage was tested in free-ranging
feral horses. The presence of foals in harems headed by vasectomized (VSX) versus intact stallions was used to assess the
ability of these stallions to control reproduction in their harems. Of harems headed by VSX stallions, 17 and 33% contained
foals during years 2 and 3 post-treatment, respectively. In contrast, 86 and 80% of harems headed by non-VSX stallions contained
foals in those years. Acquisition of pregnant mares appeared more likely than sneak copulations by bachelor stallions to account
for foals in harems with a single stallion. However, most foals were born into harems that included a subordinate stallion,
an occurrence that was undoubtedly exacerbated by the extended breeding season resulting from the sterility of the harem stallion.
Thus, in comparing alternative reproductive tactics, bachelors appeared less successful than subordinate stallions within
a harem. However, the highest reproductive success was achieved by the harem stallion, further demonstrating that alternative
tactics are not equally profitable.
Received: 13 July 1999 / Received in revised form: 24 July 1999 / Accepted: 24 July 1999 相似文献
165.
Stephen T. Trumbo 《Behavioral ecology and sociobiology》2007,61(11):1717-1723
A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking
(as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis
that when the presence of a male partner increased the probability of successful defense from low to moderate that female
risk-taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal
male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired
females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide.
A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking.
A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but
from greater female defense against male intruders as well. It is hypothesized that the threat of infanticidal takeovers by
males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent
on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner
against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest
pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the
defending female. 相似文献
166.
Brood sex ratio is dependent on female mating status in polygynous great reed warblers 总被引:2,自引:0,他引:2
Isao Nishiumi 《Behavioral ecology and sociobiology》1998,44(1):9-14
Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In
polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females,
females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed
warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding
effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we
would predict that females which start breeding first within harems might produce more sons than those which start breeding
later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females
mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of
primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer
food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females
modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably
stronger than the latter factor.
Received: 11 March 1998 / Accepted after revision: 23 May 1998 相似文献
167.
高寒草甸藏嵩草种群繁殖对策的研究 总被引:17,自引:1,他引:17
对高寒草甸藏嵩草(Kobresia tibetica)种群的繁殖对策进行了初步研究。结果表明,藏嵩草属寒冷中生密丛短根茎地下芽植物,在高寒生境中采用了以营养繁殖为主,有性繁殖为辅的繁殖策略,具体体现在以几个方面:藏嵩草种子产量nA=200.1m^-2,但种子萌发率较低,室内和野外萌发率分别仅有4%和2%,经氢氧化钠溶液和赤霉素溶液处理后的种子萌发率分别为1%和6.7%,而剥去种皮后种子萌发率达47.3%,所以种皮坚硬是造成种子萌发率低的主要原因;进入种子库、保留至返青期且具有活性的种子仅占种子总数的31.49%,单位面积上理论实生苗数仅为1.26m^-2,与此相反,藏嵩草营养繁殖所形成的新个体数为101.32m^2,,远远多于种子萌发所形成的实生苗数,此外,藏嵩草营养繁殖效力也远高于有性繁殖效4力。营养繁殖效力占总数繁殖效力的83.46%(167)。表1参7 相似文献