全文获取类型
收费全文 | 1217篇 |
免费 | 25篇 |
国内免费 | 1篇 |
出版年
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 31篇 |
2011年 | 49篇 |
2010年 | 62篇 |
2009年 | 51篇 |
2008年 | 62篇 |
2007年 | 71篇 |
2006年 | 48篇 |
2005年 | 50篇 |
2004年 | 25篇 |
2003年 | 22篇 |
2002年 | 7篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 24篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 31篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 28篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1974年 | 15篇 |
1973年 | 18篇 |
1972年 | 27篇 |
1971年 | 31篇 |
1965年 | 7篇 |
1957年 | 6篇 |
1953年 | 5篇 |
1952年 | 11篇 |
排序方式: 共有1243条查询结果,搜索用时 125 毫秒
61.
62.
PAUL EGGLETON ROBERT BELSHAW 《Biological journal of the Linnean Society. Linnean Society of London》1993,48(3):213-226
We consider differences between dipteran, hymenopteran and coleopteran parasitoids in the following categories: taxonomic range and developmental stage of hosts attacked; habitats they are attacked in; developmental stage of the parasitoid contacting the host; occurrence of phoresy, and attacking hosts during flight. Using existing phylogenetic classifications we reconstruct possible ancestral conditions to the parasitoid clades in the three orders. By considering these as phylogenetic constraints and potentialities we attempt to account for the observed differences between the parasitoids within the orders. 相似文献
63.
64.
Dual and simultaneous sensitivity analysis for matched pairs 总被引:1,自引:0,他引:1
65.
B30.2-like domain proteins: update and new insights into a rapidly expanding family of proteins 总被引:5,自引:0,他引:5
Henry J; Mather IH; McDermott MF; Pontarotti P 《Molecular biology and evolution》1998,15(12):1696-1705
The B30.2 domain is a conserved region of around 170 amino acids associated
with several different protein domains, including the immunoglobulin folds
of butyrophilin and the RING finger domain of ret finger protein. We
recently reported several novel members of this family as well as
previously undescribed protein families possessing the B30.2 domain. Many
proteins have subsequently been found to possess this domain, including
pyrin/marenostrin and the midline 1 (MID1) protein. Mutations in the B30.2
domain of pyrin/marenostrin are implicated in familial Mediterranean fever,
and partial loss of the B30.2 domain of MID1 is responsible for Opitz G/BBB
syndrome, characterized by developmental midline defects. In this study, we
scrutinized the available sequence data bases for the identification of
novel B30.2 domain proteins using highly sensitive database-searching
tools. In addition, we discuss the chromosomal localization of genes in the
B30.2 family, since the encoded proteins are likely to be involved in other
forms of periodic fever, autoimmune, and genetic diseases.
相似文献
66.
Out of Africa and back again: nested cladistic analysis of human Y chromosome variation 总被引:18,自引:3,他引:15
Hammer MF; Karafet T; Rasanayagam A; Wood ET; Altheide TK; Jenkins T; Griffiths RC; Templeton AR; Zegura SL 《Molecular biology and evolution》1998,15(4):427-441
We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544
individuals from Africa, Asia, Europe, Oceania, and the New World.
Phylogenetic analyses of these nine sites resulted in a tree for 10
distinct Y haplotypes with a coalescence time of approximately 150,000
years. The 10 haplotypes were unevenly distributed among human populations:
5 were restricted to a particular continent, 2 were shared between Africa
and Europe, 1 was present only in the Old World, and 2 were found in all
geographic regions surveyed. The ancestral haplotype was limited to African
populations. Random permutation procedures revealed statistically
significant patterns of geographical structuring of this paternal genetic
variation. The results of a nested cladistic analysis indicated that these
geographical associations arose through a combination of processes,
including restricted, recurrent gene flow (isolation by distance) and range
expansions. We inferred that one of the oldest events in the nested
cladistic analysis was a range expansion out of Africa which resulted in
the complete replacement of Y chromosomes throughout the Old World, a
finding consistent with many versions of the Out of Africa Replacement
Model. A second and more recent range expansion brought Asian Y chromosomes
back to Africa without replacing the indigenous African male gene pool.
Thus, the previously observed high levels of Y chromosomal genetic
diversity in Africa may be due in part to bidirectional population
movements. Finally, a comparison of our results with those from nested
cladistic analyses of human mtDNA and beta-globin data revealed different
patterns of inferences for males and females concerning the relative roles
of population history (range expansions) and population structure
(recurrent gene flow), thereby adding a new sex-specific component to
models of human evolution.
相似文献
67.
RICHARD HARRINGTON SUZANNE J. CLARK SUE J. WELHAM PAUL J. VERRIER COLIN H. DENHOLM MAURICE HULLɆ DAMIEN MAURICE† MARK D. ROUNSEVELL‡ NADÈGE COCU‡ EUROPEAN UNION EXAMINE CONSORTIUM 《Global Change Biology》2007,13(8):1550-1564
Aphids, because of their short generation time and low developmental threshold temperatures, are an insect group expected to respond particularly strongly to environmental changes. Forty years of standardized, daily data on the abundance of flying aphids have been brought together from countries throughout Europe, through the EU Thematic Network 'EXAMINE'. Relationships between phenology, represented by date of first appearance in a year in a suction trap, of 29 aphid species and environmental data have been quantified using the residual maximum likelihood (REML) methodology. These relationships have been used with climate change scenario data to suggest plausible changes in aphid phenology. In general, the date of first record of aphid species in suction traps is expected to advance, the rate of advance varying with location and species, but averaging 8 days over the next 50 years. Strong relationships between aphid phenology and environmental variables have been found for many species, but they are notably weaker in species living all year on trees. Canonical variate analysis and principal coordinate analysis were used to determine ordinations of the 29 species on the basis of the presence/absence of explanatory variables in the REML models. There was strong discrimination between species with different life cycle strategies and between species feeding on herbs and trees, suggesting the possible value of trait-based groupings in predicting responses to environmental changes. 相似文献
68.
Abstract 1. The flexibility of hymenopteran sex ratios is well documented, particularly in structured populations featuring sib mating. 2. Using game theoretic models, the present study examines species producing single‐sex broods in which sib mating is unlikely, and focuses on the role of population density in determining evolutionarily stable oviposition strategies. 3. Since only mated females can produce offspring of both sexes while unmated females produce only male offspring, mated females are under selection to produce more females overall to balance the primary sex ratio. 4. As the proportion of all females that are mated should increase with density, offspring sex ratio of mated females is strongly linked to density at low to moderate densities. The present study shows that when density becomes low enough for fewer than half of all females to have mated, then female offspring generate higher fitness. 5. In this low density situation, females may gain a fitness benefit from waiting at their emergence site or from using other costly means to find and mate with males before ovipositing. 6. The predicted correspondence between females waiting at the emergence site and fewer than half of females in the population containing sperm, can be tested empirically, as can the somewhat counter‐intuitive prediction that greater access to males should yield a more male‐biased sex ratio in the offspring of mated females. 7. The present study also indicates how measuring the variance in giving up times by females waiting for males at low density, can provide insight into mechanisms determining waiting times. 相似文献
69.
DAVID M. IOVANNISCI C. PAUL PLESTED GREGORY R. MOE 《The Journal of eukaryotic microbiology》2010,57(5):405-414
ABSTRACT. Leishmania parasites, which afflict 12 million people in 88 countries, exist as promastigotes transmitted by insect vectors and as amastigotes residing in mammalian macrophages. Promastigote cells arranged in rosettes have also been described but universally disregarded as a distinct stage in the life cycle. We present evidence that only rosettes of Leishmania major promastigotes express cell surface poly‐α2,8 N‐acetyl neuraminic acid (PSA) and PSA containing de‐N‐acetyl neuraminic acid (NeuPSA). Expression of rosette‐specific PSA antigens was mosaic, with individual promastigotes expressing PSA, NeuPSA or both. A 50 kDa protein was detected by Western blot analysis of a detergent‐insoluble cell fraction with both PSA and NeuPSA‐reactive antibodies. Frequencies of rosette formation as well as cell surface PSA/NeuPSA expression were temperature dependent. Rosettes also engaged in an unusual swarming behavior, congregating into extended clusters. Distinct structures resembling cellular fusion bodies were formed in and released from rosettes. The results indicate that rosettes are an unrecognized stage in the life cycle of Leishmania. We hypothesize that rosettes initiate mating in Leishmania during which PSA/NeuPSA expression plays an important role. Recognizing rosettes as a distinct form of the Leishmania life cycle opens new possibilities for treatment or prevention of disease and, possibly, in vitro genetic recombination without passage of cells through insect vectors. 相似文献
70.
Genetic variation was assessed in Atlantic wolffish, Anarhichas lupus, across the North Atlantic Ocean using microsatellite and amplified fragment length polymorphism (AFLP) markers. Despite unusual life history attributes such as large benthic eggs, large larvae, a limited pelagic stage and relatively sedentary adults, which suggest potential for strong population structure, range‐wide FST values were comparable to other marine fishes (≤0.035). Nevertheless, both significant genetic differentiation among regions and isolation by distance were observed, suggesting limited dispersal in this species. AFLP loci, evaluated on a subset of samples, revealed slightly higher FST values, but similar patterns of differentiation and isolation‐by‐distance estimates, compared to microsatellites. The genetic structure of Atlantic wolffish has likely been shaped by its post‐glacial history of recolonization, North Atlantic current patterns and continuity of habitat on continental shelves. 相似文献