全文获取类型
收费全文 | 1670篇 |
免费 | 143篇 |
国内免费 | 2篇 |
出版年
2023年 | 11篇 |
2022年 | 31篇 |
2021年 | 38篇 |
2020年 | 33篇 |
2019年 | 34篇 |
2018年 | 36篇 |
2017年 | 51篇 |
2016年 | 57篇 |
2015年 | 84篇 |
2014年 | 95篇 |
2013年 | 95篇 |
2012年 | 149篇 |
2011年 | 191篇 |
2010年 | 142篇 |
2009年 | 97篇 |
2008年 | 96篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 71篇 |
2004年 | 71篇 |
2003年 | 59篇 |
2002年 | 50篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有1815条查询结果,搜索用时 390 毫秒
951.
Luke J. Harmon Karen Bauman Matt McCloud John Parks Shannon Howell Jonathan B. Losos 《Zoo biology》2005,24(3):197-213
Studies of urban wildlife are important because they can give us insight into both how animals adapt to novel environments and how some species survive and prosper in human‐dominated landscapes. Urban zoological institutions provide an ideal setting for research on such species. We report on a study of the behavior and ecology of opossums (Didelphis virginiana) on the grounds of the St. Louis Zoological Park. We used radio tracking to investigate the movement patterns and den site use of opossums on the grounds of the zoo and compared the results to data available for opossums elsewhere. We find that urban opossums in the St. Louis zoo have smaller home ranges and move shorter distances than their rural counterparts. We suggest that increased food availability and decreased risk of predation might explain such differences, and we suspect that conditions are even more favorable to opossums in a zoological setting than in cities in general. Our findings illustrate that there is much to be learned from scientific study of the free‐living animals found on zoological park grounds. Zoo Biol 00:1–17, 2005. © 2005 Wiley‐Liss, Inc. 相似文献
952.
Mortality of key fish species released by recreational anglers in an Australian estuary 总被引:1,自引:0,他引:1
Matt K. Broadhurst Charles A. Gray Michael E.L. Wooden James A. Haddy 《Journal of experimental marine biology and ecology》2005,321(2):171-179
A field experiment was done to quantify the mortality of fish released during a recreational angling tournament in Botany Bay, Australia. Participating boat-based anglers were divided into two groups, each representing different typical catch-and-release events. The first group (termed the ‘live weigh-in group’) retained the largest two individuals of 4 species (dusky flathead, Platycephalus fuscus, yellowfin bream, Acanthopagrus australis, sand whiting, Sillago ciliata, and trevally, Pseudocaranx dentex) in onboard holding tanks and then presented these to researchers at designated weigh-in times and stations. Gear, operational and handling data were collected before 125 fish were tagged using plastic t-bar tags, returned to the anglers and then released into two sea cages. The second group (termed the ‘immediate-release group’) immediately released 224 fish into two sea cages, after they were tagged and relevant data recorded by onboard observers. This group represented those fish routinely discarded (i) as part of catch-and-immediate-release tournaments and/or (ii) due to minimum legal sizes and/or personal quotas. Appropriate species and numbers of ‘control’ fish were seined and placed into two sea cages. All fish were monitored for mortalities over 10 days. Dusky flathead, yellowfin bream, trevally and snapper, Pagrus auratus accounted for more than 85% of the total catch. Their adjusted mortalities ranged between 0% and 36.6%. Irrespective of the treatment, most yellowfin bream and snapper deaths occurred within 3 h of being hooked and released into the cages, while trevally and dusky flathead showed a delayed mortality over 4 days. Owing to confounding effects due to their confinement, dusky flathead were excluded from further analyses. Anatomical hook location and the time between capture and release were significant predictors of mortality for yellowfin bream and trevally, respectively (p < 0.01), but none of the various gear, operational or handling factors examined were significant for snapper (p > 0.05). The results are discussed in terms of species-specific variabilities in mortalities, their causal effects and better management of catch-and-release events. 相似文献
953.
954.
Currently, there is a lack of knowledge about GHG emissions, specifically N2O and CH4, in subtropical coastal freshwater wetland and mangroves in the southern hemisphere. In this study, we quantified the gas fluxes and substrate availability in a subtropical coastal wetland off the coast of southeast Queensland, Australia over a complete wet-dry seasonal cycle. Sites were selected along a salinity gradient ranging from marine (34 psu) in a mangrove forest to freshwater (0.05 psu) wetland, encompassing the range of tidal influence. Fluxes were quantified for CH4 (range ?0.4–483 mg C–CH4 h?1 m?2) and N2O (?5.5–126.4 μg N–N2O h?1 m?2), with the system acting as an overall source for CH4 and N2O (mean N2O and CH4 fluxes: 52.8 μg N–N2O h?1 m?2 and 48.7 mg C–CH4 h?1 m?2, respectively). Significantly higher N2O fluxes were measured during the summer months (summer mean 64.2 ± 22.2 μg N–N2O h?1 m?2; winter mean 33.1 ± 24.4 µg N–N2O h–1 m?2) but not CH4 fluxes (summer mean 30.2 ± 81.1 mg C–CH4 h?1 m?2; winter mean 37.4 ± 79.6 mg C–CH4 h?1 m?2). The changes with season are primarily driven by temperature and precipitation controls on the dissolved inorganic nitrogen (DIN) concentration. A significant spatial pattern was observed based on location within the study site, with highest fluxes observed in the freshwater tidal wetland and decreasing through the mangrove forest. The dissolved organic carbon (DOC) varied throughout the landscape and was correlated with higher CH4 fluxes, but this was a nonlinear trend. DIN availability was dominated by N–NH4 and correlated to changes in N2O fluxes throughout the landscape. Overall, we did not observe linear relationships between CH4 and N2O fluxes and salinity, oxygen or substrate availability along the fresh-marine continuum, suggesting that this ecosystem is a mosaic of processes and responses to environmental changes. 相似文献
955.
956.
Many plants release allelopathic chemicals that can inhibit germination, growth, and/or survival in neighboring plants. These impacts appear magnified with the invasion of some non-native plants which may produce allelochemicals against which native fauna have not co-evolved resistance. Our objective was to examine the potential allelopathic impact of an invasive non-native shrub/tree on multiple plant species using field observation and experimental allelopathy studies. We surveyed and collected an invasive, non-native tree/shrub (Rhamnus cathartica) at Tifft Nature Preserve (a 107-ha urban natural area near Lake Erie in Buffalo, NY). We also surveyed understory plant communities in the urban forest to examine correlations between R. cathartica abundance and local plant community abundance and richness. We then used experimental mesocosms to test if patterns observed in the field could be explained by adding increased dosages of R. cathartica to soils containing five plant species, including native and non-native woody and herbaceous species. In the highly invaded urban forest, we found that herbaceous cover, shrubs and woody seedlings negatively covaried with R. cathartica basal area and seedlings density. In the mesocosm experiments, R. cathartica resulted in significant decreases in plant community species richness, abundance, and shifted biomass allocation from roots. Our results provide evidence that R. cathartica is highly allelopathic in its invaded range, that R. cathartica roots have an allelopathic effect and that some plant species appear immune. We suggest that these effects may explain the plant’s ability to form dense monocultures and resist competitors, as well as shift community composition with species-specific impacts. 相似文献
957.
Surawski PP Battersby BJ Lawrie GA Ford K Rühmann A Marcon L Kozak D Trau M 《Molecular bioSystems》2008,4(7):774-778
The concept of optically encoding particles for solid phase organic synthesis has existed in the literature for several years. However, there remains a significant challenge to producing particles that are capable of withstanding harsh solvents and reagents whilst maintaining the integrity and range of the optical encoding. In this study, a new generation of fluorescently encoded support particles was used for both solid phase peptide synthesis and on-particle analysis of proteolysis in a multiplexed, flow cytometric assay. The success of the assay was demonstrated through the use of a model protease, trypsin. Our results show that the use of solid supports with high peptide yield, high swellability in water and high penetration of the enzyme into the interior of the particle is not absolutely necessary for proteolysis assays. 相似文献
958.
959.
Kessner D Chambers M Burke R Agus D Mallick P 《Bioinformatics (Oxford, England)》2008,24(21):2534-2536
SUMMARY: The ProteoWizard software project provides a modular and extensible set of open-source, cross-platform tools and libraries. The tools perform proteomics data analyses; the libraries enable rapid tool creation by providing a robust, pluggable development framework that simplifies and unifies data file access, and performs standard proteomics and LCMS dataset computations. The library contains readers and writers of the mzML data format, which has been written using modern C++ techniques and design principles and supports a variety of platforms with native compilers. The software has been specifically released under the Apache v2 license to ensure it can be used in both academic and commercial projects. In addition to the library, we also introduce a rapidly growing set of companion tools whose implementation helps to illustrate the simplicity of developing applications on top of the ProteoWizard library. AVAILABILITY: Cross-platform software that compiles using native compilers (i.e. GCC on Linux, MSVC on Windows and XCode on OSX) is available for download free of charge, at http://proteowizard.sourceforge.net. This website also provides code examples, and documentation. It is our hope the ProteoWizard project will become a standard platform for proteomics development; consequently, code use, contribution and further development are strongly encouraged. 相似文献
960.
Question: How does regular management burning of a northern, Calluna vulgaris‐dominated heathland affect the lichen diversity at the patch and landscape scale? Location: Mar Lodge Estate, Scottish Highlands, United Kingdom. Methods: 26 fire sites of different ages and 11 long‐term unburnt stands were surveyed to create a chronosequence of changing lichen diversity following burning. Data were analysed graphically, with a GLM and using a CCA. Results: Though the immediate effect of fire was to significantly reduce lichen diversity, it generally recovered within 20 years. There was a significant difference in the population dynamics between wet and dry moorland areas with terricolous lichens in the former site being replaced by pleurocarpous mosses. Older stands, unburnt for 25 years or more, generally had lower diversity than stands 10 to 15 years old. Changes in lichen diversity and community composition can be attributed to the development of Calluna stand structure following burning. Conclusions: Fire can be seen to play an important role in maintaining the diversity of lichens in heathland areas by providing a variety of stand‐structures and ages across the landscape that favours the development of greater beta‐diversity. 相似文献