全文获取类型
收费全文 | 1814篇 |
免费 | 28篇 |
国内免费 | 15篇 |
专业分类
安全科学 | 53篇 |
废物处理 | 67篇 |
环保管理 | 300篇 |
综合类 | 304篇 |
基础理论 | 433篇 |
环境理论 | 4篇 |
污染及防治 | 473篇 |
评价与监测 | 135篇 |
社会与环境 | 83篇 |
灾害及防治 | 5篇 |
出版年
2023年 | 19篇 |
2022年 | 20篇 |
2021年 | 25篇 |
2020年 | 24篇 |
2019年 | 23篇 |
2018年 | 39篇 |
2017年 | 47篇 |
2016年 | 43篇 |
2015年 | 46篇 |
2014年 | 51篇 |
2013年 | 127篇 |
2012年 | 74篇 |
2011年 | 108篇 |
2010年 | 77篇 |
2009年 | 93篇 |
2008年 | 95篇 |
2007年 | 116篇 |
2006年 | 85篇 |
2005年 | 74篇 |
2004年 | 72篇 |
2003年 | 67篇 |
2002年 | 79篇 |
2001年 | 33篇 |
2000年 | 26篇 |
1999年 | 19篇 |
1998年 | 19篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1955年 | 5篇 |
1954年 | 8篇 |
排序方式: 共有1857条查询结果,搜索用时 93 毫秒
431.
Alternative male mating tactics in a cichlid, Pelvicachromis pulcher: a comparison of reproductive effort and success 总被引:2,自引:0,他引:2
Pelvicachromis pulcher is a small African cichlid which breeds in holes. Males may either reproduce monogamously (pair males), polygynously (harem
males), or be tolerated as helpers in a harem territory (satellite males). These helpers share in defence of the territory
against conspecifics, heterospecific competitors and predators. There are two male colour morphs that are fixed for life and
are apparently genetically determined. These differ in their potential mating strategy. Red morph males may become harem owners,
while yellow morph males may become satellite males, and males of both morphs may alternatively pair up monogamously. We compared
the reproductive effort and success of these three male reproductive strategies. Effort was measured as attack rates, time
expenditure and the risk of being injured or killed when attacking competitors or predators of three sympatric fish species.
Reproductive success was measured by observing how many eggs were fertilized by each male when this was possible, and by using
genetic markers. The number of fry surviving to independence of parental care was used as a criterion of success. The reproductive
success of harem males was 3.3 times higher than that of pair males and 7 times higher than that of the average satellite
male. Dominant satellite males, however, were as successful as monogamous pair males, using the measure of fertilized eggs.
To our knowledge, this has not been found previously in any fish species. Both harem and pair males had lower parental defence
costs per sired offspring, however, than males using the alternative satellite tactic. Defence effort was significantly related
to the risk of injury.
Received: 17 January 1996 / Accepted after revision: 9 June 1997 相似文献
432.
433.
The geographic distribution of mercury concentrations in the California mussel Mytilus californianus, collected from 1977–1978 at 43 sites along the western coastline of the continental United States is marked by consistently elevated levels at two locations. These two sites, which are relatively isolated from anthropogenic inputs and mercuryrich minerals, both contain large pinniped and marine bird populations. The relatively elevated mercury levels measured in the excrement of a pinniped from one of those locales indicate that the concentrated discharge of mercuryrich waste products from the marine ecosystem's top carnivores is contaminating lower trophic levels. 相似文献
434.
Ian Johnson 《生态毒理学报》2003,25(2):25-28
考虑货币指标信息的利害,关系到一个国家的财富,它对于保护国家财富、维护国家经济命脉是不可或缺的 .生物物理学指标的考虑,则关系到国内和全球天然资产的使用 .经济命脉的维护有赖于基本的生态贡献,诸如可更新和不可更新资源、废物的消纳与稳定的气候条件等 .这两项计量指标共同为决策者们提供了经济与生态生存能力的详尽资料 .这样一种方法也可以用来解释国家与全球之间的可持续性关系,以及参与政策的制定 . 相似文献
435.
Martin Claussen 《Environmental Sciences Europe》2003,15(1):21-30
In this overview two definitions of climate are presented, from the meteorological point of view and from the climate system’s point of view. The origin of climate change is discussed, i.e., externally forced variability and free, or internal variability that is caused without external trigger by internal instabilities of the system. Both, forced and free variability can appear as periodic, randomly quasi-periodic, and abrupt climate change. Finally, various possibilities of climate forecast are considered. 相似文献
436.
The Hamilton–Zuk hypothesis proposes that females prefer male secondary sexual traits because they are honest indicators of
parasite resistance. Despite the attention that this hypothesis has received, its role in sexual selection remains equivocal.
This study presents the first field test in guppies of two key predictions of the Hamilton–Zuk hypothesis: (1) that within
populations, the most highly ornamented males have the fewest parasites and (2) that among populations, males in high parasite
populations have the most conspicuous ornaments. Five hundred male guppies from 19 distinct populations in the Northern Range
of Trinidad were inspected for Gyrodactylus parasites and photographed. Eight measures of orange spot ornamentation were used to test the predictions: hue, saturation,
lightness, relative area, number, and area-weighted hue, saturation, and lightness. Parasite load had no significant effect
on any of these measures. There was also no relationship between orange spot ornamentation and parasite abundance among populations.
Guppies from high-predation environments had significantly more parasites, and their orange coloration was lighter and less
saturated than that in guppies from low-predation environments. Despite previous lab results, this study found no relationship
between parasite load and male orange spot ornamentation. 相似文献
437.
?ystein?HolandEmail author Robert?B.?Weladji Hallvard?Gj?stein Jouko?Kumpula Martin?E.?Smith Mauri?Nieminen Knut?H.?R?ed 《Behavioral ecology and sociobiology》2004,57(1):69-76
In polygynous mammals, high-quality females may increase their fitness by providing superior care to their offspring. Based on the agonistic interactions of female reindeer in an experimental herd during two consecutive years (1997 and 1998), we tested whether maternal social rank influenced: (1) winter body-mass change of females, (2) preparturition reproductive effort (measured as fecundity, the birth mass and the birth date of their calves), (3) preweaning maternal effort (measured as calves preweaning mortality, early preweaning and late preweaning growth rate and September body mass of calves), and (4) postweaning maternal effort (measured as calves body-mass change during their first winter). In the models, we included September females body mass as a covariate to separate the effects of maternal rank and body mass. We also tested whether the effect of social rank on maternal efforts was dependent on offspring sex. High-ranked females gained body mass whereas low-ranked females lost weight during the winter. Fecundity was higher and date of birth was earlier in high-ranked females than in subordinates, whereas no effect of females rank on birth mass of calves was found. Early preweaning growth rate and September body mass of calves increased with increasing females social rank, whereas late preweaning daily growth rate of calves was not influenced by females rank. Calves preweaning mortality was only influenced by year, which also explained most of the variance in the winter body-mass change of calves. The effects of females rank on the reproductive-efforts parameters studied were not specific to offspring sex. These findings suggest that females rank influences reproductive effort during the preparturition, as well as the preweaning, period, the effect being sex independent.Communicated by R. Gibson 相似文献
438.
Patrik Lindenfors Birgitta S. Tullberg Martin Biuw 《Behavioral ecology and sociobiology》2002,52(3):188-193
Pinnipedia contains some of the most spectacular examples of sexual size dimorphism, examples that are therefore frequently used to illustrate the theory of sexual selection. This paper addresses the question of whether a significant relationship between sexual selection and size dimorphism exists in a comparative context. Thus, harem size and body size data gathered from the literature were analysed with independent contrasts analyses. These investigations showed that sexual size dimorphism is not a consequence of an allometric relationship between male and female size. Instead, there is a clear relationship between harem size and sexual size dimorphism. Further analyses also revealed a significant relationship between harem size and male size whereas no such relationship existed for females. These results support the hypothesis that sexual size dimorphism in pinnipeds is the product of an exclusively male response to sexual selection. 相似文献
439.
In this paper, we present the hierarchical variable dependencies that were obtained from raw data with the use of two machine learning techniques on an ecological data set. The data set contains features of field margins and the corresponding number of spider species inhabiting them. This data set was used before by domain experts to construct a fuzzy qualitative model with hierarchical variable dependencies, which we use for comparison with our results. One of the machine learning methods constructs a hierarchical structure similar to the one in the experts’ model, while revealing some additional interesting relations of environmental features with respect to the number of spider species. The other method constructs a different hierarchy from the one proposed by the experts, which, according to our classification performance experiments, might be even more appropriate. 相似文献
440.
Central-place foraging theory has been unable to explain the load selection behavior of leaf-cutting ants (Atta spp., Attini: Formicidae). We suggest that this is due to incomplete consideration of the sequence of behaviors involved in resource acquisition by these ants. Unlike most central-place foragers, leaf-cutting ants do not return to their nests with food. Instead, the leaf fragments they gather must be processed within the nest to convert them to substrate for fungal gardens. We have shown previously that leaf fragment size affects the rate of distribution and processing of leaf tissue inside laboratory nests of Atta colombica. Including these tasks in the calculation of foraging rate may help explain load selection and other features of central-place foraging by Atta colonies. Here we develop a mathematical model of the complete sequence of external and internal tasks that lead to addition of substrate to fungal gardens. Using realistic parameter values, the leaf fragment sizes predicted to maximize a colony's rate of foraging in this broad sense correspond well with the mean fragment sizes actually collected by Atta colonies in the field. The optimal fragment size for global performance in the model is below the size that would maximize the delivery rate by above-ground foragers. The globally optimal size also fails to maximize the rate of either fragment distribution or fragment processing within the nest. Our results show how maximum collective performance of an ensemble of linked tasks may require behavior that would appear suboptimal in a piecemeal analysis of tasks. 相似文献