全文获取类型
收费全文 | 751篇 |
免费 | 61篇 |
出版年
2023年 | 4篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 17篇 |
2015年 | 34篇 |
2014年 | 49篇 |
2013年 | 45篇 |
2012年 | 55篇 |
2011年 | 45篇 |
2010年 | 41篇 |
2009年 | 28篇 |
2008年 | 35篇 |
2007年 | 40篇 |
2006年 | 36篇 |
2005年 | 25篇 |
2004年 | 27篇 |
2003年 | 30篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 15篇 |
1998年 | 4篇 |
1997年 | 14篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有812条查询结果,搜索用时 9 毫秒
101.
Lien T.P. Nguyen Anh D. Nguyen Trang T.P. Nguyen Adrien Perrard James M. Carpenter 《Journal of Asia》2018,21(2):638-644
This study provides the first molecular phylogeny of the social wasp subgenus Polistella (Hymenoptera: Vespidae: Polistes) from Vietnam. Fragments of the mitochondrial COI and 16S rRNA genes were used to reconstruct the phylogenetic trees among 38 Polistes species plus two out-group species (Vespa soror du Buysson and Ropalidia fasciata (Fabricius)). Our results support the existence of several species-groups, including two that are congruent with the previous stigma and Stenopolistes groups defined on the basis of morphology. Moreover, we recovered a clade including the stigma group and the two species P. humilis and P. variabilis that was sister to all other species of Polistella. However, the results also challenged the definition of other groups of Polistella based on morphological data, as well as the definition of two species: P. brunus and P. affinis. This first study calls for further analyses including morphological characters to clarify the taxonomy and the classification of the group. 相似文献
102.
Atef A. H. Mansour Donald W. Mkay Jon Lien James C. Orr Joseph H. Banoub Nils Øien Garry Stenson 《Marine Mammal Science》2002,18(1):112-120
Measurement of progesterone concentration in blubber was developed as a method to detect pregnancy in minke whales. Progesterone was extracted and quantified from blubber samples of minke whale carcasses by radioimmunoassay. Results showed a highly significant difference (almost 60-fold) between blubber progesterone concentrations of anatomically determined pregnant females versus non-pregnant female or male carcasses. The results of the study suggest that the blubber progesterone concentrations might be used to determine pregnancy status in free-ranging whales. 相似文献
103.
The biosynthesis of dehydrotremetone in Eupatorium rugosum has been investigated by feeding radioactive precursors to intact plants. The carbon atoms of acetate-[1-14C] and acetate-[2-14C] were identified in dehydrotremetone by degradation of the molecule. From the pattern of labeling it was concluded that the acetophenone moiety was derived from acetate via the polyacetate pathway. From the incorporation of mevalonate it appeared that the furan ring and its side chain were formed from an isoprenoid compound. Potential aromatic intermediates were chemically synthesized and also fed to plants but only tremetone was found to be efficiently incorporated into dehydrotremetone. Neither 4-hydroxyacetophenone nor 4-hydroxy-3[isopenten-(2)-yl]-acetophenone were efficiently incorporated into dehydrotremetone. 相似文献
104.
105.
106.
Temporal variation in habitat selection breaks the catch‐22 of spatially contrasting predation risk from multiple predators 下载免费PDF全文
Karen Lone Atle Mysterud Terje Gobakken John Odden John Linnell Leif Egil Loe 《Oikos》2017,126(5):624-632
Predator avoidance depends on prey being able to discern how risk varies in space and time, but this is made considerably more complicated if risk is simultaneously present from multiple predators. This is the situation for an increasing number of mammalian prey species, as large carnivores recover or are reintroduced in ecosystems on several continents. Roe deer Capreolus capreolus in southern Norway illustrate a case in which prey face two predators with contrasting patterns of predation risk. They face a catch‐22 situation: spatially avoiding the risk from one predator (lynx Lynx lynx in dense habitat) implies exposure to the other (hunters in open habitat). Using GPS‐data from 29 roe deer, we tested for daily and seasonal variation in roe deer selection for habitat with respect to the habitats’ year‐round average risk level. Generally, roe deer altered their habitat selection between night and day in a pattern consistent with being able to avoid predicted risk from the nocturnal lynx during night and predicted risk from human hunters during day. However, seasonal variation in habitat selection only partially corresponded with the predicted seasonal variation in risk. Whereas roe deer avoided areas with high risk from hunters more strongly during the hunting season than in other seasons, there was a lack of selection towards areas and time periods lowering the risk of lynx predation during winter. It seems likely that the risk of starvation and thermal stress constrain roe deer habitat selection during this energetically challenging season with cold temperatures, snow cover and limited natural forage. The habitat selection pattern of roe deer fits thus only partly with the two contrasting risk gradients they face. Adjusting risk‐avoidance behavior temporally can be an adaptive response in the case of several predators whose predation patterns differ in space and time. 相似文献
107.
Exploiting whole genome sequence data to fine map and characterize candidate genes within a quantitative trait loci region affecting androstenone on porcine chromosome 5 下载免费PDF全文
Male piglets are routinely castrated to eliminate boar taint. However, this treatment is undesirable, and alternative approaches, including genetic strategies to reduce boar taint, are demanded. Androstenone is one of the causative agents of boar taint, and a QTL region affecting this pheromone has previously been reported on SSC5: 22.6–24.8 Mb in Duroc. The QTL region is one of the few reported for androstenone that does not simultaneously affect levels of other sex steroids. The main objective of this study was to fine map this QTL. Whole genome sequence data from 23 Norwegian Duroc boars were analyzed to detect new polymorphisms within the QTL region. A subset of 161 SNPs was genotyped in 834 Duroc sires and analyzed for association with androstenone in adipose tissue and testosterone, estrone sulphate and 17β‐estradiol in blood plasma. Our results revealed 100 SNPs significantly associated with androstenone levels in fat (P < 0.001) with 94 of the SNPs being in strong linkage disequilibrium in the region 23.03–24.27 Mb. This haplotype block contains at least four positional candidate genes (HSD17B6, SDR9C7, RDH16 and STAT6) involved in androstenone biosynthesis. No significant associations were found between any of the SNPs and levels of testosterone and estrogens, confirming previous findings. The amount of phenotypic variance explained by single SNPs within the haplotype block was as high as 5.4%. As the SNPs in this region significantly affect levels of androstenone without affecting levels of other sex steroids, they are especially interesting as genetic markers for selection against boar taint. 相似文献
108.
Egil Karlsbakk 《Marine Biology Research》2005,1(2):140-148
Marine fish from several locations along the west coast of Norway were examined for leeches. Seven leech species were detected, Calliobdella nodulifera (Malm, 1863) from codfish, flatfish and a ray, Calliobdella lophii van Beneden & Hesse, 1863 from Lophius piscatorius L., Platybdella anarrhichae (Diesing, 1859) on Anarhichas lupus L., Platybdella quadrioculata Malm, 1863 on Symphodus melops (L.), Oceanobdella sp. on Zeugopterus punctatus (Bloch), Malmiana brunnea (Johansson, 1896) on Myoxocephalus scorpius (L.) and Malmiana bubali Srivastava, 1966 on Taurulus bubalis (Euphrasen). Calliobdella nodulifera infected unrelated hosts (euryxenic); the others appeared to be host specialists (oio- or stenoxenic). Details on the occurrence of Calliobdella nodulifera on Enchelyopus cimbrius (L.) during 1 year are given, which together with other observations suggest that its life cycle exceeds a year. A brief account on the morphology of “Platybdella” quadrioculata is provided, justifying its transfer to the genus Oceanobdella Caballero, 1956 as O. quadrioculata comb. nov. With the new additions, the Norwegian marine piscicolid fauna contain 12 species. At least ten additional species, known from adjoining areas, also probably occur along the Norwegian coast. 相似文献
109.
Daniel F. Austin Richard Felger Karol Chandler-Ezell Michael J. Balick Kurt Allerslev Reynertson Alfredo Gomez-Beloz My Lien T. Nguyen Rob Dean Neil A. Harriman Dorothea Bedigian Mary Theresa Bonhage-Freund Wendy Applequist Linda M. Lyon John Klock My Lien T. Nguyen 《Economic botany》2005,59(2):197-209
110.
Nathan R. Lien 《Inorganica chimica acta》2005,358(4):1284-1288
The crystal structure of Na[Co(NC6H6O6)] · H2O is reported. The structure is compared to similar transition-metal nitrilotriacetate complexes containing different alkali cations and transition metals (Cu2+ and Zn2+). Inner-sphere coordination of the metals is similar, but the arrangement of counter-ions and water molecules in the unit cells vary with the size of the alkali cation. 相似文献