全文获取类型
收费全文 | 318篇 |
免费 | 1篇 |
国内免费 | 8篇 |
出版年
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 8篇 |
2012年 | 3篇 |
2011年 | 1篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 7篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有327条查询结果,搜索用时 15 毫秒
1.
Most studies on selection in plants estimate female fitness components and neglect male mating success, although the latter
might also be fundamental to understand adaptive evolution. Information from molecular genetic markers can be used to assess
determinants of male mating success through parentage analyses. We estimated paternal selection gradients on floral traits
in a large natural population of the herb Mimulus guttatus using a paternity probability model and maximum likelihood methods. This analysis revealed more significant selection gradients
than a previous analysis based on regression of estimated male fertilities on floral traits. There were differences between
results of univariate and multivariate analyses most likely due to the underlying covariance structure of the traits. Multivariate
analysis, which corrects for the covariance structure of the traits, indicated that male mating success declined with distance
from and depended on the direction to the mother plants. Moreover, there was directional selection for plants with fewer open
flowers which have smaller corollas, a smaller anther–stigma separation, more red dots on the corolla and a larger fluctuating
asymmetry therein. For most of these traits, however, there was also stabilizing selection indicating that there are intermediate
optima for these traits. The large number of significant selection gradients in this study shows that even in relatively large
natural populations where not all males can be sampled, it is possible to detect significant paternal selection gradients,
and that such studies can give us valuable information required to better understand adaptive plant evolution.
Second affiliation for Mark Van Kleunen is temporary until February 2007. 相似文献
2.
Genetic variation in rural and urban populations of Epipactis helleborine (L.) Crantz. (Orchidaceae) in Britain 总被引:1,自引:0,他引:1
P.M. HOLLINGSWORTH J.H. DICKSON 《Botanical journal of the Linnean Society. Linnean Society of London》1997,123(4):321-331
Genetic variation in Epipactis helleborine in the British Isles was assessed using starch gel electrophoresis of isozymes; 273 individuals were sampled from 13 populations and examined for genetic variation using eight enzyme systems encoded for by 13 loci. Overall, 46% of the loci examined were polymorphic, with an average of 1.69 alleles per locus. Within populations, a mean of 33% of the loci were polymorphic, with a mean number of 1.46 alleles per locus. Levels of genetic variation were compared between urban and well established rural populations to assess the genetic consequences of colonization of the urban sites. The average levels of genetic variation detected in urban populations were lower than that found in rural populations, although there was a much greater range of variation among the urban populations. Large urban populations actually have patterns of variation similar to rural populations and show evidence of multiple founders. This indicates that the high dispersibility of Epipactis seeds can in some cases overcome the predicted loss of genetic variation associated with founder effects during colonization. Small urban populations, however, show significantly lower levels of genetic variation compared with these large urban populations and the rural populations, and it seems likely that this is attributable to single founding events and/or genetic drift. 相似文献
3.
E. M. Petchey R. M. D. Koebner M. D. Gale 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(3):294-296
Summary Isoelectric focussing in alkaline pH gels has permitted the identification of a new homoeoallelic series of genes,Est-6, encoding grain esterases in bread wheat,Triticum aestivum. Nullisomic analysis located these genes to the short arms of the homoeologous group 2 chromosomes. A search for polymorphism withinEst-6 revealed null alleles at each ofEst-A6,Est-B6 andEst-D6. A further homoeolocus,Est-M6, is present on chromosome arm2MS ofAegilops comosa. 相似文献
4.
Aubrieta columnae Guss. is currently divided into three subspecies: A. columnae subsp. columnae, A. columnae subsp. italica, both found as isolated and fragmented populations in rocky habitats of Central and Southern Apennines (Italy), and A. columnae subsp. croatica found in the Balkan region. In order to gain information about the degree of genetic variability and to clarify taxonomic relationships among these taxa, we studied the isozyme patterns at 8 marker loci of 376 individuals from 8 populations by means of starch gel electrophoresis. Data analysis by using Wright's F-statistics and UPGMA clustering method was performed. The results show: 1) a general deviation from Hardy–Weinberg equilibrium within each subspecies; 2) a lesser genetic variation in populations occurring in habitats characterized by milder climatic conditions and relatively small seasonal variations; 3) a relatively high degree of differentiation between the three subspecies; 4) the possible common transadriatic origin of A. columnae subsp. italica and A. columnae subsp. croatica; 5) the possible origin of A. columnae subsp. columnae from A. columnae subsp. italica; and 6) that the current taxonomic status of A. columnae may be substantially confirmed, even if the findings are from a limited number of loci explored. 相似文献
5.
Isozymes and random amplified polymorphic DNA (RAPD) markers were used for precocious identification of non-maternal plants in progenies of the facultative apomict Poa pratensis. Four progenies obtained from controlled crosses that showed different degrees of apomixis on isozyme analysis of phospho-gluco-isomerases, esterases and peroxidases were chosen for RAPD analysis to generate genomic fingerprints using species-specific primers. At an advanced vegetative stage, a morphological analysis was also performed and characteristics related to growth habit and leaf morphology were observed and recorded. On the basis of the isozyme and RAPD electrophoretic pattern and the morphological appearance, each plant was classified as maternal or aberrant. All three classes of genetic markers employed were able to identify plants that exhibited aberrant traits in the four progenies. Overall, the results of RAPD analysis supported those of isozyme and morphology studies. However, in each progeny, some plants which both isozyme and morphological analyses distinguished as of maternal origin were aberrant according to RAPD analysis. Therefore, the RAPD method proved the most precise screening technique. The greater cost of the molecular approach was offset by its higher accuracy. The use of either three isozyme systems or six primers for PCR amplification seems to be sufficient for reliable estimation of the degree of apomixis. Histological analyses were carried out and the aposporic development of the plant material studied. 相似文献
6.
G. W. Bates C. A. Hasenkampf 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1985,70(3):227-233
Summary Electrically-induced protoplast fusion has been used to produce somatic hybrids between Nicotiana plumbaginifolia and Nicotiana tabacum. Following fusion of suspension culture protoplasts (N. plumbaginifolia) with mesophyll protoplasts (N. tabacum) heterokaryons were identified visually and their development was followed in culture. Because electrical fusion is a microtechnique, procedures were developed for culturing the heterokaryons in small numbers and at low density. The fusion and culture procedures described are rapid, uncomplicated and repeatable. Good cell viabilities indicate that the fusion procedure is not cytotoxic. Fused material was cultured 1–2 days at high density in modified K3 medium (Nagy and Maliga 1976). The heterokaryons were isolated manually and grown, at low density in conditioned media. Calli have been regenerated. Esterase isozyme patterns confirm the hybrid character of calli and clonally-derived plantlets recovered from these fusions. 相似文献
7.
Mercedes Gonzlez-Wangüemert Fernando Cnovas Concepcin Marcos ngel Prez-Ruzafa 《Biochemical Systematics and Ecology》2009,37(4):325-333
Extreme conditions of coastal lagoons could directly modify the genetic patterns of species. The aim of this work was to investigate the influence of environmental conditions and small scale dispersal patterns on the phosphoglucose isomerase (PGI*) genetic variability of Cerastoderma glaucum from the Mar Menor coastal lagoon. For this purpose, 284 cockles were collected around the perimeter of the lagoon. Vertical polyacrylamide gel electrophoresis was used to scan for PGI* polymorphisms, giving a total of seven alleles. The spatial genetic distribution of the PGI* variability, which seems to be marked by the main circulation in the lagoon, discriminates four hydrological basins. In the central basin, a gradient of allelic composition reflects the circulation forced by the dominant winds and the main channel communicated to the open sea. This result is well supported by the salinity GAM model that defines this gradient.The other three basins are defined by the distribution of fine sand in a more complex model that tries to explain the isolation of the three sites localized inside these basins. The southern, western and northern basins show the lowest degree of interconnection and are considered the most confined areas of the Mar Menor lagoon. This situation agrees with the confinement theory for benthic assemblages in the lagoon. The greater degree of differentiation seen in the Isla del Ciervo population is probably due to recent human intervention on the nearby Marchamalo channel, which has been drained in recent years thus altering the influence of the Mediterranean Sea on the southern basin. 相似文献
8.
Mahmood- Ul-Hassan Zahid H. Chohan Andrea Scozzafava Claudiu T. Supuran 《Journal of enzyme inhibition and medicinal chemistry》2013,28(3):263-267
Schiff's bases were obtained from aromatic/heterocyclic sulfonamides and amino-sulfonamide derivatives, such as sulfanilamide, homosulfanilamide, 4-aminoethyl-benzenesulfonamide and 5-amino-1,3,4-thiadiazole-2-sulfonamide. Metal complexes of some of these Schiff's bases, incorporating Zn(II), Co(II), Ni(II) and Cu(II) ions, were also prepared and tested as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more specifically the red blood cell isozymes I and II. The Schiff's bases behaved as medium potency CA I and CA II inhibitors, whereas their metal complexes showed a highly enhanced potency, with several low nanomolar CA II inhibitors detected. 相似文献
9.
R. Ortiz Z. Huaman 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2001,103(5):792-796
The need for broadening a crop’s genetic base may be determined by comparing allele frequencies within the gene pools of farmer
selections in their centers of diversity with that of modern breeding populations. The genetic structure of Andean and Chilean
potato farmer selections was investigated with the aid of nine isozymes, which have been studied in detail and used to characterize
North American cultivars and advanced breeding lines. These isozymes are associated with the most-important agronomic or quality
characters in the North American gene pool. By comparing these data with previous analyses of the North American gene pool,
allozyme frequency changes for nine loci were monitored. Allozyme frequency changes were not always due to genetic drift,
but resulted also from directional selection of isozyme marker linked quantitative trait loci (QTLs) affecting agronomic or
quality characters. Changes in allozyme frequency can also occur as a consequence of pleiotropy, i.e. the isozyme itself may
be involved in the expression of a phenotype. These allozyme frequency changes may reflect the manipulation of the potato
genome by breeders. There were allozymes in some North American cultivars that were not observed in the farmer selections
from the Andes and Chile. This confirms that breeders have already introgressed exotic genes from wild and other primitive
cultivated tuber-bearing Solanum species. On this basis, the need for broadening the genetic base for specific chromosomes (or chromosome regions) should be
based on analysis with these and other genetic markers available in potato.
Received: 20 November 2000 / Accepted: 27 December 2000 相似文献
10.
The self-incompatibility (SI) system of a geophytic cactus (Echinopsis chamaecereus Friedrich & G. Rowley) was examined in a series of experiments. Pollination tests indicated that E. chamaecereus is an obligate outbreeding species with a functional SI system. Incompatible matings were characterized by stylar inhibition
of pollen tube growth and lack of fruit set. Two S1 seedlings were recovered when plants of one clone were exposed to 42°C for 16 h and flowers were selfed immediately after
incubation. The two S1 seedlings and the parental (S0) clone were crossed in a full diallel. Results were consistent with a one-locus, gametophytic SI system with two different
S alleles. Disturbed segregation at isozyme locus Lap-1 was attributed to close linkage with the S locus (recombination frequency = 11±8%). This is the second report of close linkage between Lap-1 and S in the Cactaceae.
Recevied: 1 February 2001 / Revision accepted: 13 March 2001 相似文献