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261.
D. Daby 《Hydrobiologia》2006,556(1):47-60
The oceanography around Mauritius (in the Western Indian Ocean) remains largely unstudied, hence there is an acute scarcity
of marine environmental data for management purposes. Rigorous water depth and current measurements were made on a system
of grids inside Le Morne lagoon (in the south western part of Mauritius) in March–April 2000 to generate semi-quantitative
models of general flow pattern in the form of contour maps using SURFER 6 computer programme. A simultaneous survey on composition
of bottom cover was conducted to examine possible relationships with current speed. A separate investigation recorded surface
and bottom currents prevailing amongst various habitat types to demonstrate the nature of the resulting damping effect on
surface current speed. Significant correlations generated from data analysis were discussed as a basis for real biophysical
relationships. Some of the limitations in the current analysis and some of the seemingly contradictory results are acknowledged
and addressed in the light of the general assumption that the structure of the lagoon is conditioned by current speeds. Much
stronger current speeds just outside the reef (e.g. >0.5 m s−1) than inside the lagoon (e.g. <0.32 m s−1) indicated a substantial slow-down of water current by the reef barrier. Inshore bottom currents were weaker than at the
surface and current speed correlated well with water depth. Bottom and surface current directions were generally similar,
i.e. going northward during flood tide and southward during ebb. The lagoon would be classified as ‘restricted’, exhibiting
well-defined tidal circulation, which is modified by wind forcing. Dense fields of branching Acropora corals slowed down surface current speed by as much as 87%, but the relationship between current speed and bottom cover appears
to be variable, depending on the specific location within the lagoon under consideration. The contour plots of the flow pattern
model generated reasonably high qualitative modelling of spatial current speed pattern in the lagoon, with stronger currents
generally along the reef areas, at the reef passes and in the deeper zones. However, these plots did not match closely those
displaying distribution of bottom cover, thus confirming results obtained from pair-wise correlation tests, namely the lack
of a significant relationship between current speed and bottom cover. Most of the correlations would appear to represent biological
relationships, with different types of communities enabling or excluding other types. Thus, the biophysical structure of the
lagoon would be driven a priori by the distribution and abundance of corals rather than current speeds, which contradicts the above hypothesis. Recurrent
natural hazards subject the benthic communities to a state of ‘perpetual knock-down and recovery’. Recovery, however, can
be seriously impaired by the chronic ongoing degradation of the coastal marine environment of Mauritius. An urgent review
of its coastal zone management and protection strategy would be desirable for the island. 相似文献
262.
Derek W. Keats 《Phycological Research》1995,43(3):151-160
A new species of semi-endophytic coralline alga, Lithophyllum cuneatum (Corallinaceae: Lithophylloideae), is described from Fiji. The species is characterized by a wedge-like thallus that is partially buried in the thallus of the host coralline, Hydrolithon onkodes (Heydrich) Penrose et Woelkerling or occasionally Neogoniolithon sp., and that appears at the surface of the host as a small pustule that is usually paler in color than the host. The thallus consists of erect filaments that are derived from a single cell. The basal cell, when visible, is non-palisade, and areas of bistratose margin are absent. Cells of contiguous erect filaments are joined by secondary pit connections. Epithallial cells are present in 2–3 layers, and individual trichocytes are common. Gametangial plants are dioecious. Male conceptacles have simple spermatangial systems that are confined to the floors of their elliptical chambers. Carposporangial conceptacles contain 5–8 celled gonimoblast filaments that are borne at the margin of a more-or-less discoid fusion cell, and so occupy the periphery of the elliptical conceptacle chambers. Tetrasporangial conceptacles are uniporate, with roofs formed from peripheral filaments, and chambers lack a central columella of sterile filaments. Despite its semi-endophytic nature, haustorial cells are absent, and plastids and pigmentation are present. 相似文献
263.
264.
S. Comeau R. C. Carpenter P. J. Edmunds 《Proceedings. Biological sciences / The Royal Society》2013,280(1753)
Central to evaluating the effects of ocean acidification (OA) on coral reefs is understanding how calcification is affected by the dissolution of CO2 in sea water, which causes declines in carbonate ion concentration [CO32−] and increases in bicarbonate ion concentration [HCO3−]. To address this topic, we manipulated [CO32−] and [HCO3−] to test the effects on calcification of the coral Porites rus and the alga Hydrolithon onkodes, measured from the start to the end of a 15-day incubation, as well as in the day and night. [CO32−] played a significant role in light and dark calcification of P. rus, whereas [HCO3−] mainly affected calcification in the light. Both [CO32−] and [HCO3−] had a significant effect on the calcification of H. onkodes, but the strongest relationship was found with [CO32−]. Our results show that the negative effect of declining [CO32−] on the calcification of corals and algae can be partly mitigated by the use of HCO3− for calcification and perhaps photosynthesis. These results add empirical support to two conceptual models that can form a template for further research to account for the calcification response of corals and crustose coralline algae to OA. 相似文献
266.
Smith JE Shaw M Edwards RA Obura D Pantos O Sala E Sandin SA Smriga S Hatay M Rohwer FL 《Ecology letters》2006,9(7):835-845
Declines in coral cover are generally associated with increases in the abundance of fleshy algae. In many cases, it remains unclear whether algae are responsible, directly or indirectly, for coral death or whether they simply settle on dead coral surfaces. Here, we show that algae can indirectly cause coral mortality by enhancing microbial activity via the release of dissolved compounds. When coral and algae were placed in chambers together but separated by a 0.02 μ m filter, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patterns of increasing coral stress with proximity to algae. Our results suggest that as human impacts increase and algae become more abundant on reefs a positive feedback loop may be created whereby compounds released by algae enhance microbial activity on live coral surfaces causing mortality of corals and further algal growth. 相似文献
267.
Shinji Yabuta 《Ichthyological Research》1997,44(2-3):177-182
Spawning and related behavior of a monogamous butterflyfish,Chaetodon trifasciatus, were observed at Kuroshima Island, Okinawa, Japan. Each heterosexual pair defended a feeding territory in the daytime. Spawning occurred at dusk on the days around full or new moon in the daytime. Spawning occurred at dusk on the days around full or new moon in the vicinity of offshore tidal currents. Spawning migration to such sites occurred in pairs, the feeding territories of which were located in areas of inshore currents. In the evening each pair established a small temporary territory, which they spawned adjacent to and slept within until the next morning. The distribution of sleeping sites as well as tidal current directions may determine the spawning sites of this butterflyfish. 相似文献
268.
Natsuko Adachi Ayaka Kotani Yoichi Ezaki Jianbo Liu 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2015,48(3):405-416
The Cambrian Series 3 Zhangxia Formation in Shandong Province, North China, includes small‐scale lithistid sponge–microbial reefs. The lithistid sponges grew on oolitic and bioclastic sediments, which were stabilized by microbial activities. The relative abundances of microbial components (e.g. calcimicrobe Epiphyton and stromatolites) vary among the reefs. However, the microbial components commonly encrusted or bound the lithistid sponges, formed remarkable encrustations on the surfaces of the sponges. Epiphyton especially grew upward and downward. The lithistid sponges thus provided substrates for the attachment and development of microbes, and the microbes played essential roles as consolidators, by encrusting reef‐building sponges. Additionally, the lithistid sponges were prone to degradation via microbial activities and diagenetic processes, and were thus preserved as micritic bodies, showing faint spicular networks or abundant spicules. Such low preservation potential within the reef environment obscured the presence of the sponges and their widespread contribution as reef‐building organisms during the Cambrian. During the prolonged interval after the demise of archaeocyaths, purely microbial reefs, such as stromatolites and thrombolites have been considered to be the principal reef builders, in association with rare lithistid sponge–microbial associations. However, recent findings, including those from Shandong Province and Korea, suggest that the lithistid sponge‐bearing reefs were more extensive during the Epoch 3 to the Furongian than previously thought. These lithistid sponge–microbial reefs were precursors of the sponge–microbial reefs that dominated worldwide in the Early Ordovician. 相似文献
269.
270.
Coral reef species are frequently the focus of bio-prospecting, and when promising bioactive compounds are identified there
is often a need for the development of responsible harvesting based on relatively limited data. The Caribbean gorgonian Pseudopterogorgia elisabethae has been harvested in the Bahamas for over a decade. Data on population age structure and growth rates in conjunction with
harvest data provide an opportunity to compare fishery practices and outcomes to those suggested by a Beverton-Holt fishery
model. The model suggests a minimum colony size limit of 7–9 years of age (21–28 cm height), which would allow each colony
2–4 years of reproduction prior to harvesting. The Beverton-Holt model assumes that colonies at or above the minimum size
limit are completely removed. In the P. elisabethae fishery, colonies are partially clipped and can be repeatedly harvested. Linear growth of surviving colonies was up to 3
times that predicted for colonies that were not harvested and biomass increase was up to 9 times greater than that predicted
for undisturbed colonies. The survival of harvested colonies and compensatory growth increases yield, and yields at sites
that had previously been harvested were generally greater than predicted by the Beverton-Holt model. The model also assumes
recruitment is independent of fishing intensity, but lower numbers of young colonies in the fished populations, compared to
unfished populations, suggest possible negative effects of the harvest on reproduction. This suggests the need for longer
intervals between harvests. Because it can be developed from data that can be collected at a single time, the Beverton-Holt
model provides a rational starting point for regulating new fisheries where long-term characterizations of population dynamics
are rarely available. However, an adaptive approach to the fishery requires the incorporation of reproductive data. 相似文献