全文获取类型
收费全文 | 1928篇 |
免费 | 439篇 |
国内免费 | 64篇 |
专业分类
2431篇 |
出版年
2024年 | 4篇 |
2023年 | 52篇 |
2022年 | 32篇 |
2021年 | 57篇 |
2020年 | 118篇 |
2019年 | 149篇 |
2018年 | 125篇 |
2017年 | 141篇 |
2016年 | 126篇 |
2015年 | 143篇 |
2014年 | 156篇 |
2013年 | 153篇 |
2012年 | 109篇 |
2011年 | 130篇 |
2010年 | 95篇 |
2009年 | 108篇 |
2008年 | 113篇 |
2007年 | 85篇 |
2006年 | 65篇 |
2005年 | 75篇 |
2004年 | 68篇 |
2003年 | 47篇 |
2002年 | 47篇 |
2001年 | 43篇 |
2000年 | 36篇 |
1999年 | 20篇 |
1998年 | 36篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2431条查询结果,搜索用时 31 毫秒
21.
Calcification process dynamics in coral primary polyps as observed using a calcein incubation method
Yoshikazu Ohno Akira Iguchi Chuya Shinzato Mikako Gushi Mayuri Inoue Atsushi Suzuki Kazuhiko Sakai Takashi Nakamura 《Biochemistry and Biophysics Reports》2017
Calcification processes are largely unknown in scleractinian corals. In this study, live confocal imaging was used to elucidate the spatiotemporal dynamics of the calcification process in aposymbiotic primary polyps of the coral species Acropora digitifera. The fluorophore calcein was used as a calcium deposition marker and a visible indicator of extracellular fluid distribution at the tissue-skeleton interface (subcalicoblastic medium, SCM) in primary polyp tissues. Under continuous incubation in calcein-containing seawater, initial crystallization and skeletal growth were visualized among the calicoblastic cells in live primary polyp tissues. Additionally, the distribution of calcein-stained SCM and contraction movements of the pockets of SCM were captured at intervals of a few minutes. Our experimental system provided several new insights into coral calcification, particularly as a first step in monitoring the relationship between cellular dynamics and calcification in vivo. Our study suggests that coral calcification initiates at intercellular spaces, a finding that may contribute to the general understanding of coral calcification processes. 相似文献
22.
23.
M. Wall L. Putchim G. M. Schmidt C. Jantzen S. Khokiattiwong C. Richter 《Proceedings. Biological sciences / The Royal Society》2015,282(1799)
Tropical scleractinian corals are particularly vulnerable to global warming as elevated sea surface temperatures (SSTs) disrupt the delicate balance between the coral host and their algal endosymbionts, leading to symbiont expulsion, mass bleaching and mortality. While satellite sensing of SST has proved a reliable predictor of coral bleaching at the regional scale, there are large deviations in bleaching severity and mortality on the local scale that are poorly understood. Here, we show that internal waves play a major role in explaining local coral bleaching and mortality patterns in the Andaman Sea. Despite a severe region-wide SST anomaly in May 2010, frequent upslope intrusions of cold sub-pycnocline waters due to breaking large-amplitude internal waves (LAIW) mitigated coral bleaching and mortality in shallow waters. In LAIW-sheltered waters, by contrast, bleaching-susceptible species suffered severe bleaching and total mortality. These findings suggest that LAIW benefit coral reefs during thermal stress and provide local refugia for bleaching-susceptible corals. LAIW are ubiquitous in tropical stratified waters and their swash zones may thus be important conservation areas for the maintenance of coral diversity in a warming climate. Taking LAIW into account can significantly improve coral bleaching predictions and provide a valuable tool for coral reef conservation and management. 相似文献
24.
A comparison of life history traits of sexual and asexual strains of the parasitoid wasp,Lysiphlebus fabarum (Braconidae: Aphidiinae) 下载免费PDF全文
1. This study examined biological characteristics of sexual and asexual strains of the parasitoid wasp, Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae). 2. Strains were reared in different instar hosts (the black bean aphid, Aphis fabae Scopoli) under identical environmental conditions (21 °C, 65–75% RH, and LD 16:8 h). 3. Results showed that the second instar of the aphid is the most suitable growth stage for both strains, as the wasps that emerged from the second instar hosts were larger, more fecund, and had larger egg size. Trade‐offs between the fitness components of the parasitoid were clearer when the parasitoids were reared in suboptimal instars. 4. According to the results, sexual females emerged around 1 day earlier and lived around 0.5 day less than asexual females. Also, sexual females emerged with a lower initial egg load, although these wasps tend to have larger eggs than asexual females. Asexual females may enjoy greater longevity and higher developmental plasticity which suggests a higher degree of synchronization with pest population dynamism. 5. The results suggest that sexual wasps, in contrast to asexual wasps, invest more in egg size than in egg load. This study suggests strain‐specific adaptations of L. fabarum to different instars of the black bean aphid by which the allocation of nutritional resources to various functions differs between strains. 6. Furthermore, differences in life history traits between strains can greatly influence the population dynamics of each strain, and hence their effectiveness in suppressing pest populations. 相似文献
25.
Gradients of disturbance and environmental conditions shape coral community structure for south‐eastern Indian Ocean reefs 下载免费PDF全文
Jens Zinke James P. Gilmour Rebecca Fisher Marji Puotinen Joseph Maina Emily Darling Michael Stat Zoe T. Richards Timothy R. McClanahan Maria Beger Cordelia Moore Nicholas A. J. Graham Ming Feng Jean‐Paul A. Hobbs Scott N. Evans Stuart Field George Shedrawi Russ C. Babcock Shaun K. Wilson 《Diversity & distributions》2018,24(5):605-620
26.
Eyal Ben‐Hur Ori Fragman‐Sapir Rivka Hadas Alon Singer Ronen Kadmon 《Ecology letters》2012,15(11):1276-1282
Functional trade‐offs have long been recognised as important mechanisms of species coexistence, but direct experimental evidence for such mechanisms is extremely rare. Here, we test the effect of one classical trade‐off – a negative correlation between seed size and seed number – by establishing microcosm plant communities with positive, negative and no correlation between seed size and seed number and analysing the effect of the seed size/number correlation on species richness. Consistent with theory, a negative correlation between seed size and seed number led to a higher number of species in the communities and a corresponding wider range of seed size (a measure of functional richness) by promoting coexistence of large‐ and small‐seeded species. Our study provides the first direct evidence that a seed size/number trade‐off may contribute to species coexistence, and at a wider context, demonstrates the potential role of functional trade‐offs in maintaining species diversity. 相似文献
27.
Claudia Pogoreutz Nils Rädecker Anny Cárdenas Astrid Gärdes Christian R. Voolstra Christian Wild 《Global Change Biology》2017,23(9):3838-3848
The disruption of the coral–algae symbiosis (coral bleaching) due to rising sea surface temperatures has become an unprecedented global threat to coral reefs. Despite decades of research, our ability to manage mass bleaching events remains hampered by an incomplete mechanistic understanding of the processes involved. In this study, we induced a coral bleaching phenotype in the absence of heat and light stress by adding sugars. The sugar addition resulted in coral symbiotic breakdown accompanied by a fourfold increase of coral‐associated microbial nitrogen fixation. Concomitantly, increased N:P ratios by the coral host and algal symbionts suggest excess availability of nitrogen and a disruption of the nitrogen limitation within the coral holobiont. As nitrogen fixation is similarly stimulated in ocean warming scenarios, here we propose a refined coral bleaching model integrating the cascading effects of stimulated microbial nitrogen fixation. This model highlights the putative role of nitrogen‐fixing microbes in coral holobiont functioning and breakdown. 相似文献
28.
Genetic connectivity of a coral reef ecosystem predator: the population genetic structure and evolutionary history of the Caribbean reef shark (Carcharhinus perezi) 下载免费PDF全文
29.
Sergei V. Drovetski Sargis A. Aghayan Vanessa A. Mata Ricardo J. Lopes Nicolle A. Mode Johanna A. Harvey Gary Voelker 《Molecular ecology》2014,23(13):3322-3329
Two hypotheses have been proposed to explain the abundance–occupancy relationship (AOR) in parasites. The niche breadth hypothesis suggests that host generalists are more abundant and efficient at colonizing different host communities than specialists. The trade‐off hypothesis argues that host specialists achieve high density across their hosts' ranges, whereas generalists incur the high cost of adaptation to diverse immuno‐defence systems. We tested these hypotheses using 386 haemosporidian cytochrome‐b lineages (1894 sequences) recovered from 2318 birds of 103 species sampled in NW Africa, NW Iberia, W Greater Caucasus and Transcaucasia. The number of regions occupied by lineages was associated with their frequency suggesting the presence of AOR in avian Haemosporidia. However, neither hypothesis provided a better explanation for the AOR. Although the host generalist Plasmodium SGS1 was over three times more abundant than other widespread lineages, both host specialists and generalists were successful in colonizing all study regions and achieved high overall prevalence. 相似文献
30.
Debra?L.?Abercrombie Shelley?C.?Clarke Mahmood?S.?ShivjiEmail author 《Conservation Genetics》2005,6(5):775-788
The future status of sharks is an issue of widespread conservation concern due to declines in many species in the face of
high levels of exploitation to satisfy market demands for products, especially fins. Substantial declines in the large-bodied
hammerhead sharks, Sphyrna lewini, S. mokarran and S. zygaena, even in regions where some management occurs, indicate that informed conservation measures are warranted for these circumglobally
distributed species. Despite the importance of assessing shark catch and trade on a species-specific basis to detect potential
overexploitation of individual species, achieving this goal for hammerheads has proven elusive due to difficulties in identification
of their products. Here, we present the development and application of a diagnostic, streamlined, five-primer multiplex polymerase
chain reaction assay utilizing species-specific primers based on nuclear ribosomal ITS2 for the three hammerhead species throughout
their global distribution. Application of this assay to investigations of the fin market confirmed the presence of hammerhead
fins in the international trade. A study of the world’s largest fin market in Hong Kong revealed a high concordance between
specific Chinese-name trade categories and fins from these three species (“Bai Chun” with S. lewini, “Gui Chun” with S. zygaena and “Gu Pian” with S.␣mokarran), and clear species preferences. This concordance information allows the use of market records for monitoring species-specific
trends in trade and exploitation rates. The assay is also proving useful for identification of shark body parts in U.S. fisheries
law-enforcement activities. Screening of morphologically identified “ S. lewini” from globally distributed areas using this assay with subsequent whole ITS2 sequencing suggests a cryptic species closely
related to S. lewini occurs off the SE USA coast. 相似文献