全文获取类型
收费全文 | 363篇 |
免费 | 5篇 |
出版年
2019年 | 2篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 9篇 |
2011年 | 18篇 |
2010年 | 24篇 |
2009年 | 29篇 |
2008年 | 29篇 |
2007年 | 19篇 |
2006年 | 21篇 |
2005年 | 19篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1971年 | 5篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 6篇 |
1956年 | 3篇 |
1955年 | 1篇 |
1954年 | 3篇 |
1952年 | 2篇 |
1939年 | 1篇 |
排序方式: 共有368条查询结果,搜索用时 15 毫秒
71.
The results of a long-term capture-mark-recapture ringing programme carried out on a coastal population of breeding Redshanks Tringa totanus between 1974 and 1988 are presented.
Both sexes were equally likely to be recaptured in subsequent years, as were birds captured for the first time compared with those that had been captured previously. Older birds were more frequently recaptured than were young birds. There was no significant difference in male and female adult survival rates, with a mean of 72% of females and 75% of males surviving each year.
The breeding population fluctuated annually with estimated breeding densities of 122–285 pairs per km2 . Variation in breeding numbers (males), but not survival, was partially attributable to winter air temperature. 相似文献
Both sexes were equally likely to be recaptured in subsequent years, as were birds captured for the first time compared with those that had been captured previously. Older birds were more frequently recaptured than were young birds. There was no significant difference in male and female adult survival rates, with a mean of 72% of females and 75% of males surviving each year.
The breeding population fluctuated annually with estimated breeding densities of 122–285 pairs per km
72.
CHARLES A. NOCK PATRICK J. BAKER WOLFGANG WANEK ALBRECHT LEIS MICHAEL GRABNER SARAYUDH BUNYAVEJCHEWIN PETER HIETZ 《Global Change Biology》2011,17(2):1049-1063
Rising atmospheric carbon dioxide [CO2] can accelerate tree growth by stimulating photosynthesis and increasing intrinsic water‐use efficiency (iWUE). Little evidence exists, however, for the long‐term growth and gas‐exchange responses of mature trees in tropical forests to the combined effects of rising [CO2] and other global changes such as warming. Using tree rings and stable isotopes of carbon and oxygen, we investigated long‐term trends in the iWUE and stem growth (basal area increment, BAI) of three canopy tree species in a tropical monsoon forest in western Thailand (Chukrasia tabularis, Melia azedarach, and Toona ciliata). To do this, we modelled the contribution of ontogenetic effects (tree diameter or age) and calendar year to variation in iWUE, oxygen isotopes, and BAI using mixed‐effects models. Although iWUE increased significantly with both tree diameter and calendar year in all species, BAI at a given tree diameter was lower in more recent years. For one species, C. tabularis, differences in crown dominance significantly influence stable isotopes and growth. Tree ring Δ18O increased with calendar year in all species, suggesting that increasing iWUE may have been driven by relatively greater reductions in stomatal conductance – leading to enrichment in Δ18O – than increases in photosynthetic capacity. Plausible explanations for the observed declines in growth include water stress resulting from rising temperatures and El Niño events, increased respiration, changes in allocation, or more likely, a combination of these factors. 相似文献
73.
SHAUN C. CUNNINGHAM JAMES R. THOMSON RALPH MAC NALLY JENNIFER READ PATRICK J. BAKER 《Freshwater Biology》2011,56(8):1494-1508
1. Regulation of rivers for human demands has led to extensive forest dieback on many floodplains. If these important ecosystems are to be maintained under future drier climates, we need accurate tools for predicting forest dieback. In the absence of spatially explicit flooding histories for many floodplains, changes in groundwater conditions may be a good indicator of water availability and, therefore, an important environmental indicator. 2. Eucalyptus camaldulensis forests of Australia are an acute example of forest dieback, with 70% of the Victorian Murray River floodplain dying back. We quantified the relationship between forest dieback and ground water across this extensive floodplain (c. 100 000 ha of forest over 1500 km of river length). 3. A combination of extensive ground surveys, remotely sensed data and modelling methods was used to predict forest dieback at the time of the survey and in the past. This approach provides a valuable tool for accurately monitoring forest condition over large spatial scales. Forest dieback was estimated to have increased from 45 to 70% of the floodplain between 1990 and 2006. 4. Accurate groundwater data (depth and salinity) over a 20‐year period were obtained for 289 bores and summarised using nonlinear regression. Groundwater depth and salinity were strong predictors of stand condition. This suggests that changes in groundwater conditions could be used to signal areas vulnerable to forest dieback and prioritise the limited water available for managed flooding. 5. In the upper Murray, where ground water is predominantly fresh (<15 mS cm?2), dieback increased with increasing groundwater depth. In contrast, the condition of stands in the lower Murray improved with increases in groundwater depth due its high salinity (>30 mS cm?2). These regional differences in response of the same tree species to groundwater conditions show that our understanding of the drivers of forest dieback is best achieved at spatial and temporal scales representative of the problem. 相似文献
74.
Phylogenetic relationships among microgastrine braconid wasp genera based on data from the 16S, COI and 28S genes and morphology 总被引:3,自引:0,他引:3
JAMES B. WHITFIELD PATRICK MARDULYN† REW D. AUSTIN‡ MARK DOWTON§ 《Systematic Entomology》2002,27(3):337-359
Abstract Phylogenetic relationships among the genera of the large braconid wasp subfamily Microgastrinae were explored using DNA sequence data from the mitochondrial large ribosomal subunit (16S), nuclear large ribosomal subunit (28S) and mitochondrial cytochrome oxidase (COI) genes, along with morphological characters, both new and from previous studies. The taxonomic history of this group of wasps is reviewed, along with a critique of previous phylogenetic studies on the group. Molecular data were sampled from forty-six species representing twenty-six genera of microgastrines, plus three species representing the close outgroup taxa Cardiochilinae and Miracinae. Some 2300 base pairs of aligned sequence were obtained per taxon from the three genes. In addition, fifty-three morphological characters were coded for all known genera, including two undescribed genera, except Semionis Nixon (known from only a single male type specimen). Relationships among several groups of genera are clarified and challenge some major assumptions made in earlier classifications. In particular, it is clear that dependence on one or a few major morphological character systems oversimplifies relationships, and can lead to misleading results. Despite the large amount of data analysed, basal divergences within the subfamily remain poorly resolved and essentially unsupported in any rigorous statistical sense. 相似文献
75.
THEODORE J. ABATZOPOULOS ILIAS KAPPAS PETER BOSSIER PATRICK SORGELOOS JOHN A. BEARDMORE 《Biological journal of the Linnean Society. Linnean Society of London》2002,75(3):333-344
The brine shrimp Artemia consists of a number of bisexual species and a large number of parthenogenetic forms, which collectively, inhabit a wide range of hypersaline habitats. A recently described species (A. tibetiana) from a carbonate lake (Lagkor Co) in Tibet at an altitude of 4490 m has been tested with New World (A. franciscana USA, and A. franciscana feral population Vietnam) and Old World species (A. salina, A. urmiana, A. sinica) for cross fertility. These tests show complete infertility between A. tibetiana and A. franciscana . Between A. tibetiana and A. urmiana, A. sinica partial fertility through to F2 and F3 generations is evident. Allozyme and RAPD comparison of A. tibetiana with A. franciscana (USA), A. franciscana (Vietnam), A. sinica (Mongolia) and A. urmiana (Iran) show that A. tibetiana is similar to other bisexual species in mean heterozygosity (0.074) but has a somewhat higher proportion of polymorphic loci (40%, similar to that of A. urmiana ). The genetic distance between A. tibetiana and A. franciscana is 0.730, between A. tibetiana and A. urmiana is 0.475 and that between A. tibetiana and A. sinica is 0.114. FIS estimates for A. tibetiana differ significantly from zero for six loci, mainly because of lack of fit to Hardy-Weinberg expectations. This may suggest that even within the limited area of Lagkor Co there are Genétically distinct populations. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 333–344. 相似文献
76.
RUTH PATRICK 《The Journal of eukaryotic microbiology》1954,1(1):34-37
The results of these studies indicate that the first diatom flora developed at the 13-meter level. The flora at 12 meters increased. At the 11- and 9-meter levels the lake became increasingly eutrophic. Both plankton and benthic forms were present. At the 8- and 7-meter levels the lake was in a transitional stage from lake to bog conditions. From 6 meters to the surface bog conditions were present. 相似文献
77.
78.
PATRICK A. DARROW RAMONA T. SKIRPSTUNAS S. WADE CARLSON JOHN A. SHIVIK 《The Journal of wildlife management》2009,73(8):1441-1444
ABSTRACT We compared injury rates among captured coyotes (Canis latrans) to determine if modifications to cable foot-restraints would decrease resulting injuries. Mean International Standardization Organization's injury scores of coyotes caught in 3 types of cable foot-restraints were 22.2, 37.9, and 60.4 (F2,41 = 4.63, P = 0.015) for a chain-loop, standard cable, and sleeved cable, respectively. These results may be important for trappers and researchers to consider when using a cable foot-restraint device to capture wildlife. 相似文献
79.
MAREK ELIAS NICOLA J. PATRON PATRICK J. KEELING 《The Journal of eukaryotic microbiology》2009,56(4):348-356
ABSTRACT. The RAB GTPases, which are involved in regulation of endomembrane trafficking, exhibit a complex but incompletely understood evolutionary history. We elucidated the evolution of the RAB1 subfamily ancestrally implicated in the endoplasmic reticulum-to-Golgi traffic. We found that RAB1 paralogs have been generated over the course of eukaryotic evolution, with some duplications coinciding with the advent of major eukaryotic lineages (e.g. Metazoa, haptophytes). We also identified a unique, derived RAB1 paralog, orthologous to the Plasmodium Rab1A, that occurs in stramenopiles, alveolates, and Rhizaria, represented by the chlorarachniophyte Gymnochlora stellata . This finding is consistent with the recently documented existence of a major eukaryotic clade ("SAR") comprising these three lineages. We further found a Rab1A-like protein in the cryptophyte Guillardia theta , but it exhibits unusual features among RAB proteins: absence of a C-terminal prenylation motif and an N-terminal extension with two MSP domains; and its phylogenetic relationships could not be established convincingly due to its divergent nature. Our results nevertheless point to a unique membrane trafficking pathway shared by at least some lineages of chromalveolates and Rhizaria, an insight that has implications towards interpreting the early evolution of eukaryotes and the endomembrane system. 相似文献
80.
MATTHEW RAMON IVE DE SMET LIES VANDESTEENE MIRANDE NAUDTS BARBARA LEYMAN PATRICK VAN DIJCK FILIP ROLLAND TOM BEECKMAN & JOHAN M. THEVELEIN 《Plant, cell & environment》2009,32(8):1015-1032
Trehalose metabolism has profound effects on plant growth and metabolism, but the mechanisms involved are unclear. In Arabidopsis , 21 putative trehalose biosynthesis genes are classified in three subfamilies based on their similarity with yeast TPS1 (encoding a trehalose-6-phosphate synthase, TPS) or TPS2 (encoding a trehalose-6-phosphate phosphatase, TPP). Although TPS1 (Class I) and TPPA and TPPB (Class III) proteins have established TPS and TPP activity, respectively, the function of the Class II proteins (AtTPS5-AtTPS11) remains elusive. A complete set of promoter- β -glucurinidase/green fluorescent protein reporters demonstrates their remarkably differential tissue-specific expression and responsiveness to carbon availability and hormones. Heterologous expression in yeast furthermore suggests that none of the encoded enzymes displays significant TPS or TPP activity, consistent with a regulatory rather than metabolic function for this remarkable class of proteins. 相似文献