全文获取类型
收费全文 | 10432篇 |
免费 | 51篇 |
国内免费 | 140篇 |
专业分类
安全科学 | 42篇 |
废物处理 | 804篇 |
环保管理 | 1277篇 |
综合类 | 1246篇 |
基础理论 | 3280篇 |
环境理论 | 1篇 |
污染及防治 | 1942篇 |
评价与监测 | 1057篇 |
社会与环境 | 951篇 |
灾害及防治 | 23篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 57篇 |
2021年 | 35篇 |
2020年 | 45篇 |
2019年 | 38篇 |
2018年 | 1497篇 |
2017年 | 1404篇 |
2016年 | 1246篇 |
2015年 | 163篇 |
2014年 | 83篇 |
2013年 | 70篇 |
2012年 | 514篇 |
2011年 | 1401篇 |
2010年 | 725篇 |
2009年 | 647篇 |
2008年 | 922篇 |
2007年 | 1261篇 |
2006年 | 31篇 |
2005年 | 48篇 |
2004年 | 50篇 |
2003年 | 79篇 |
2002年 | 118篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1935年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
981.
982.
Neill A. Herbert Jon E. Skjæraasen Trygve Nilsen Anne G. V. Salvanes John F. Steffensen 《Marine Biology》2011,158(4):737-746
The frequency of low O2 (hypoxia) has increased in coastal marine areas but how fish avoid deleterious water masses is not yet clear. To assess whether
the presence and oxygen pressure (PO2) level of an O2 refuge affects the hypoxia avoidance behaviour of fish, individual Atlantic cod (Gadus morhua L.) were exposed to a range of O2 choices in a 2-way choice chamber at 11.4°C over two different experiments. Cod in the first experiment were allowed access
to a fixed O2 refuge (fully air-saturated seawater) whilst oxygen pressure (PO2) on the other side was reduced in steps to a critically low level, i.e. 4.3 kPa—a point where cod can no longer regulate
O2 consumption. Under these conditions, cod did not avoid any level of hypoxia and fish swimming speed also remained unchanged.
In contrast, strong avoidance reactions were exhibited in a second experiment when fish were again exposed to 4.3 kPa but
the safety, i.e. PO2, of the refuge was reduced. Fish not only spent less time at 4.3 kPa as a result of fewer sampling visits but they also swam
at considerably slower speeds. The presence of an avoidance response was thus strongly related to refuge PO2 and it is unlikely that cod, and possibly other fish species, would enter low O2 to feed in the wild if a sufficiently safe O2 refuge was not available. It is therefore hypothesized that the feeding range of fish may be heavily compressed if hypoxia
expands and intensifies in future years. 相似文献
983.
Northern and Spotted Wolffishes (Anarhichas denticulatus and A. minor) are demersal marine fishes listed as “threatened” in Canadian waters. Both species have unusually large benthic eggs and
large size at hatch, which should reduce passive dispersal. We examined population differentiation with microsatellite and
AFLP loci across the ranges of both species in the North Atlantic Ocean. Although significant population structure was documented,
differentiation was less than expected based on knowledge of life history characteristics. Significant differentiation was
found in Northern Wolffish between the Barents Sea and other samples based on both microsatellite and AFLP data. In contrast,
population structure in the Spotted Wolffish was notably weaker, particularly with microsatellites. Both species were characterized
by low genetic diversity for marine fishes and had significantly lower genetic diversity than the congeneric Atlantic Wolffish.
This finding was consistent with the conservation status of these three species and suggests potential vulnerability to over-exploitation
in Northern and Spotted Wolffishes. 相似文献
984.
The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the
upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important
prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the
summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m).
The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio.
δ15N and δ13C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance
of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7
for M. hubbsi was estimated using δ15N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels. 相似文献
985.
Anthony J. Gaston Paul A. Smith Laura McFarlane Tranquilla William A. Montevecchi David A. Fifield H. Grant Gilchrist April Hedd Mark L. Mallory Gregory J. Robertson Richard A. Phillips 《Marine Biology》2011,158(9):1929-1941
The non-breeding movements of marine birds were poorly known until recently, but this information is essential to understanding
the risk to different geographical populations from events on the wintering grounds. We tracked the migration routes and wintering
areas of Thick-billed Murre Uria lomvia from two breeding colonies in eastern Canada: Coats Island in northern Hudson Bay and The Minarets, Baffin Island, during
the period August 2007–May 2008 using geolocation loggers. Birds from The Minarets moved south rapidly post-breeding and wintered
principally off Newfoundland and southern Labrador, or between Newfoundland and southern Greenland, remaining south of 55°N
until at least the spring equinox. Those from Coats Island remained in Hudson Bay until at least mid-November, after which
they moved rapidly through Hudson Strait to winter in southern Davis Strait and the northern Labrador Sea, mostly north of
55°N. Many individuals stayed throughout the winter in areas of heavy ice cover. Adults from the two colonies appear to be
completely segregated in winter and those from Coats Island probably did not enter the area of the winter hunt in Newfoundland.
Unexpectedly, some birds from The Minarets wintered in waters beyond the continental slope and outside the distribution of
pack ice, demonstrating that particular individuals can be wholly pelagic throughout the winter. Coats Island birds returned
through Hudson Strait as soon as open water areas became available in spring. Their sojourn in Hudson Bay coincided very closely
with the occurrence of areas with <90% ice cover. In spite of the relatively large error in positions obtained from geolocation
loggers, our results demonstrated the value of these devices by uncovering a number of previously unknown aspects of Thick-billed
Murre non-breeding ecology in the Northwest Atlantic. Comparison of the non-breeding ecology based on SST experienced in winter
show that the winter niche is broader than hitherto assumed, demonstrating that separate populations may experience different
selection in the face of climate change. 相似文献
986.
We present a new system for microscopic multicolour variable chlorophyll fluorescence imaging of aquatic phototrophs. The
system is compact and portable and enables microscopic imaging of photosynthetic performance of individual cells and chloroplasts
using different combinations of blue, green, red or white light. Automated sequential exposure of microscopic samples to the
three excitation colours enables subsequent deconvolution of the resulting fluorescence signals and colour marking of cells
with different photopigmentation, i.e., cyanobacteria, green algae, red algae and diatoms. The photosynthetic activity in
complex mixtures of phototrophs and natural samples can thus be assigned to different types of phototrophs, which can be quantified
simultaneously. Here, we describe the composition and performance of the new imaging system and present applications with
both natural phytoplankton and microalgal culture samples. 相似文献
987.
Shrimp trawling is common throughout the southeastern and Gulf of Mexico coasts of the USA and is the primary contributor
to fisheries discards in these regions. Tens of thousands of nearshore seabirds nest near shrimp trawling grounds in the USA,
but to date, there has been no assessment of the relationship between seabirds and shrimp trawlers. We examined the taxonomic
composition of bycatch, rate at which seabirds scavenged bycatch, and energy density of discarded bycatch in a nearshore commercial
shrimp fishery. Bycatch was primarily comprised of demersal fish that are not typically accessible to the plunge-diving and
surface-feeding seabirds that occur in the area. Hence, seabird diets in the region appear to be broadened taxonomically by
the availability of discards. Results from discard experiments indicated that 70% of the nearly 5,500 items discarded by hand
were scavenged by seabirds and that the fate of a discarded item was most strongly predicted by its taxonomic order. Laughing
gulls scavenged the greatest proportion of discards, although brown pelicans were the only species to scavenge more discards
than predicted based upon their abundance. Because this is the first such study in the region, it is difficult to ascertain
the extent or intensity of the impact that discards have on nearshore seabirds. Nonetheless, our results suggest that it will
be difficult for managers to clearly understand fluctuations in local seabird population dynamics without first understanding
the extent to which these species rely upon discards. This may be especially problematic in situations where seabird populations
are recovering following natural or anthropogenic stressors. 相似文献
988.
Variation in female sperm storage is explained, in part, by the amount of sperm transferred at mating. Laboratory mating experiments
were conducted on Eurypanopeus depressus and Rhithropanopeus harrisii from the Chesapeake Bay and Pachygrapsus transversus from Florida, while mated pairs of Uca beebei and U. terpsichores were collected from mudflats in Panama. All experiments and collections were conducted during the summer of 2006 and 2007.
More sperm was transferred to larger than smaller females, and by species with long copulation durations (R. harrisii and E. depressus). These two species live in cryptic habitats, have high sperm/egg ratios, and likely store sperm across multiple broods.
In contrast, P. transversus and U. beebei mate conspicuously, have short copulations, transfer fewer sperm, and have low sperm/egg ratios. Comparisons of sperm transfer
across different mating strategies and habitats provide a better understanding of female sperm storage in the Brachyura. 相似文献
989.
In this paper, we argue that understanding marine ecosystem functioning requires a thorough appreciation of the role of intraguild
predation to system dynamics. The theoretical predictions of intraguild predation models might explain some of the community
features observed in marine ecosystems such as low diversity in upwelling and productive systems and species alternation in
response to moderate external forcing. Finally, we argue that an ecosystem approach to fisheries requires that the size–structure
of fish populations should be taken into account and that it is extremely important to account for the predators of early
stages (eggs and larvae) to gain a thorough understanding of the key interactions between species. 相似文献
990.
Gloria Massamba-N’Siala Roberto Simonini Piero Cossu Ferruccio Maltagliati Alberto Castelli Daniela Prevedelli 《Marine Biology》2011,158(7):1523-1535
The spatial scale of life-history and demographic variation was investigated in the opportunistic polychaete Ophryotrocha labronica La Greca and Bacci. Individuals were collected along the Italian coasts from three thermally different biogeographical regions
of the Mediterranean Sea. For each region, populations from four harbours were considered, and for each harbour, two sites
were examined. Life-history and demographic traits were investigated after one generation under a common garden experiment,
and their variation at the three spatial scales was assessed. All the traits showed high variability with regard to site.
A number of life-history and all demographic traits also varied according to the biogeographical region. Conversely, no differences
were found between harbours, suggesting that geographical isolation did not contribute to phenotypic variation. Results confirmed
the central role of local conditions for the evolution of life history in species colonizing heterogeneous environments, but
they also pointed to the importance of large-scale factors in shaping the phenotypic responses of O. labronica, demonstrating the need for a multi-scale approach for obtaining a good measure of natural variation in widespread opportunistic
species. 相似文献