全文获取类型
收费全文 | 1920篇 |
免费 | 15篇 |
国内免费 | 4篇 |
专业分类
1939篇 |
出版年
2015年 | 10篇 |
2014年 | 8篇 |
2013年 | 51篇 |
2012年 | 41篇 |
2011年 | 58篇 |
2010年 | 98篇 |
2009年 | 89篇 |
2008年 | 77篇 |
2007年 | 112篇 |
2006年 | 81篇 |
2005年 | 73篇 |
2004年 | 43篇 |
2003年 | 26篇 |
2002年 | 15篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 26篇 |
1998年 | 55篇 |
1997年 | 51篇 |
1996年 | 42篇 |
1995年 | 44篇 |
1994年 | 43篇 |
1993年 | 44篇 |
1992年 | 35篇 |
1991年 | 55篇 |
1990年 | 34篇 |
1989年 | 53篇 |
1988年 | 35篇 |
1987年 | 41篇 |
1986年 | 23篇 |
1985年 | 40篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 20篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 31篇 |
1978年 | 17篇 |
1977年 | 25篇 |
1976年 | 27篇 |
1975年 | 38篇 |
1974年 | 23篇 |
1973年 | 20篇 |
1972年 | 40篇 |
1971年 | 42篇 |
1970年 | 13篇 |
1969年 | 7篇 |
1968年 | 9篇 |
1958年 | 6篇 |
1956年 | 5篇 |
排序方式: 共有1939条查询结果,搜索用时 15 毫秒
81.
LAUREN DICKIE MICHAEL HART RICHARD HELLING 《Invertebrate reproduction & development.》2013,57(3):229-232
Summary We compared prefeeding development times, from fertilized egg to prism larva, for Strongylocentrotus embryos from four clutches of eggs (each from a different species) differing in size. Development times did not vary consistently with egg diameter, and trends among eggs of different sizes varied with stage of development. In some cases, development times for eggs of intermediate diameter (S. franciscanus) were longer than those for larger or smaller eggs. Although mean egg diameters in clutches ranged from 84 μm (S. purpuratus) to 162 μm (S. pallidus), differences in development time to the last embryonic stage (prism) were very small. We conclude that the inverse relationship between parental investment in offspring and premetamorphic development time in echinoids depends only on the functional consequences of reduced size of feeding larval stages: effects of egg size on prefeeding development time are not evident. 相似文献
82.
CLEMENS KÜPPER GAVIN J. HORSBURGH DEBORAH A. DAWSON RICHARD FFRENCH‐CONSTANT TAMS SZKELY TERRY BURKE 《Molecular ecology resources》2007,7(1):35-39
We isolated 45 new Kentish plover (Charadrius alexandrinus) microsatellite loci. These were tested for polymorphism in 42 Kentish plovers breeding in the Çukurova Delta, Turkey. Thirty‐six of the 45 loci were polymorphic with observed heterozygosity varying between 0.22 and 0.93. Genotypes of individuals of known sex indicated that two loci were sex‐linked (Calex‐26 is located on the Z chromosome and Calex‐31 on the W chromosome). Additionally, we tested all loci for amplification in four other species of Charadridae (Kittlitz's plover, Madagascar plover, three‐banded plover and white‐fronted plover). On average 34 loci amplified per species (range 29–36). 相似文献
83.
KATSURA M. KAWANO KAZUHIRO EGUCHI KEISUKE UEDA RICHARD NOSKE 《Molecular ecology resources》2007,7(3):501-502
The grey‐crowned babbler (Pomatostomus temporalis) is a cooperative breeding bird species in which nonbreeding helpers of both sexes care for the young of breeding individuals. To measure the genetic relatedness between breeders and their offspring and helpers, we developed nine microsatellite markers. Most of the loci were highly polymorphic. These loci will be useful in understanding the evolution and maintenance of cooperative breeding and helping behaviour in this species. 相似文献
84.
LEANNA M. BIRGE STEVEN M. BOGDANOWICZ RICHARD G. HARRISON DANIEL J. HOWARD 《Molecular ecology resources》2007,7(6):1094-1096
Polymorphic di‐, tri‐ and tetranucleotide repeats were examined in Allonemobius to determine whether they could serve as useful markers in studies of sperm precedence, population genetics and hybrid zone structure. Ten microsatellite DNA loci were sufficiently polymorphic to be used for paternity tests and showed no evidence of linkage disequilibrium or deviations from Hardy–Weinberg equilibrium in Allonemobius socius. Nine of 10 of these microsatellites can be amplified from three other Allonemobius species, suggesting that these markers will have widespread utility in this ground cricket genus. 相似文献
85.
The effect of short-term weather fluctuations on temperatures inside lizard nests, and on the phenotypic traits of hatchling lizards 总被引:1,自引:0,他引:1
RICHARD SHINE MELANIE J. ELPHICK 《Biological journal of the Linnean Society. Linnean Society of London》2001,72(4):555-565
Can short‐term stochastic variation in local weather conditions modify the thermal conditions inside lizard nests, and thus (potentially) the developmental rates, hatching success, and phenotypic traits of hatchlings from these nests? This hypothesis requires that (i) natural nests are poorly buffered thermally, such that ambient regimes affect temperatures inside the nest, and (ii) short‐term thermal variations modify attributes of the offspring. Field data on natural nests of the sub‐alpine skink Bassiana duperreyi confirm the existence of this first effect, and laboratory experiments substantiate the latter. Exposure to warmer‐than‐usual temperatures for 2 wéeks during the 9‐ to 16‐wéek incubation period doubled hatching success, and significantly modified hatchling phenotypes (hatching dates, offspring size and locomotor performance). The proportion of development completed prior to this exposure influenced the degrée of response. Exposure to a brief ‘window’ of higher‐than‐usual temperatures soon after oviposition had more effect on hatching time, egg survival and hatchling phenotypes than if the exposure occurred later in development. Thus, minor variations in weather conditions during incubation may have substantial effects on reptile populations. 相似文献
86.
Developmental response to temperature during the critical early season growing period was investigated in two congeneric species of Craspedolepta feeding on Epilobium angustifolium at three sites at different altitudes in Norway and the UK. The larval development reaction norm to temperature, measured as accumulated day degrees, was not significantly different between Craspedolepta nebulosa and Craspedolepta subpunctata at sites where they co‐occurred but C. nebulosa development was consistently more advanced at any site. For individual species the reaction norms at the lowest site (Ainsdale, UK) were similar to the intermediate site (Geilo, Norway): and there were no differences between years. Insect size remained relatively constant. However, at the highest site (Haugastøl, Norway), where C. subpunctata is unable to complete its development, the reaction norm for C. nebulosa was significantly higher than at Geilo and the individual insects produced were smaller. These adaptations allow life‐history completion under limiting temperature conditions. An experiment at Ainsdale, to raise the mean temperature by around 2.5°C during the early growing season, resulted in accelerated development in both C. nebulosa and C. subpunctata but development in C. nebulosa was accelerated proportionately more. C. nebulosa thus displays the greater plasticity in developmental response to environmental temperature that allows it to occupy a greater altitudinal and latitudinal range than C. subpunctata, in which the response is less plastic and more canalized. The likely individualistic responses of the two species to climate warming are considered. 相似文献
87.
Morphometric comparison of populations of Orchis sitnia Lam. (Orchidaceae) from Oxfordshire and Kent
RICHARD M. BATEMAN ORPAH S. FARRINGTON 《Botanical journal of the Linnean Society. Linnean Society of London》1989,100(3):205-218
BATEMAN, R. M. & FARRINGTON, O. S., 1989. Morphometric comparison of populations of Orchis sitnia Lam. (Orchidaceae) from Oxfordshire and Kent. Univariate and multivariate morphometric analyses of Orchis simia Lam. from its two remaining naturally-founded populations in Britain (Goring, Oxfordshire and Faversham, Kent) reveal only minor morphological differences between the populations and suprisingly low levels of intra-population variation. This probably reflects recent founding from Continental seed at Faversham and penecontemporaneous, human-induced, catastrophic contraction of the gene pool at Goring. The apparently restricted gene pools of these populations may adversely effect their long-term survival. 相似文献
88.
89.
90.