全文获取类型
收费全文 | 991篇 |
免费 | 37篇 |
国内免费 | 26篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 23篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 28篇 |
2013年 | 34篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 31篇 |
2008年 | 25篇 |
2007年 | 36篇 |
2006年 | 36篇 |
2005年 | 24篇 |
2004年 | 20篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 38篇 |
1998年 | 34篇 |
1997年 | 27篇 |
1996年 | 35篇 |
1995年 | 36篇 |
1994年 | 27篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 33篇 |
1988年 | 23篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有1054条查询结果,搜索用时 140 毫秒
951.
Eric F. Karlin 《Journal of bryology》2014,36(3):165-179
Sphagnum ×australe s.l. and S. ×falcatulum s.l. are both cryptic species complexes of gametophytically allodiploid and allotriploid cytotypes, with the allodiploid cytotype being one parent of the respective allotriploid cytotype. Phylogenetic analyses of S. ×australe s.l. and S. ×falcatulum s.l. were undertaken using sequences from two plastid loci and cloned sequences from three nuclear loci. Subgenomes from three subgenera were detected in allotriploid S. ×australe. The haploid parent of allotriploid S. ×australe was S. fimbriatum (subg. Acutifolia). One of the two subgenomes contributed by allodiploid S. australe was associated with S. strictum (subg. Rigida); the parental species associated with the other subgenome could not be identified, either at the species level or in terms of subgenus association. It may represent an early diverging lineage of subg. Sphagnum or a previously undetected subgenus. Allotriploid S. ×falcatulum has subgenomes from two subgenera. This study confirms prior findings that S. cuspidatum (subg. Cuspidata) was the haploid parent of allotriploid S. ×falcatulum. One of the two subgenomes contributed by allodiploid S. ×falcatulum was associated with subg. Cuspidata (species unidentified) and the second was associated with subg. Subsecunda (species unidentified). Recurrent allopolyploidy appears to have been associated with the complex evolutionary processes (inter-subgeneric hybridization, interploidal hybridization, double allopolyploidy) which resulted in each of these two allotriploids. The highest level of divergence detected among the subgenomes in each of these Sphagnum allotriploids is comparable to the average genetic divergence reported for angiosperm allopolyploids. 相似文献
952.
Francis O. Nwadukwe 《Aquatic Ecology》1995,29(2):177-182
Clarias gariepinus andHeterobranchus longifilis were successfully hybridized to produce reciprocal F1 progeny during a two-year study.C. gariepinus produced significantly heavier spawn thanH. longifilis during the same period. Fertilized eggs were incubated in aerated static-water in fibre-glass troughs, and hatching rates
were not found to be significantly different (P<0.05) between any two of the four catfish groups produced. Eight-day old fry
of each group were reared in fertilized nursery ponds, and F1 hybrids fromH. longifilis maternal parent had the best growth and survival rates at the end of 18 days. The reciprocal cross showed intermediate growth
rate between both parents. At harvest, differential growth was less pronounced among both hybrids than among the parents. 相似文献
953.
《Cell reports》2020,30(7):2094-2105.e9
- Download : Download high-res image (161KB)
- Download : Download full-size image
954.
A Colcemid-resistant Chinese hamster line with an altered form of β-tubulin was used in studies of the expression of spindle
proteins in interspecific cell hybrids. Eight hybrids between this line, and a Colcemid-sensitive mouse cell line, were studied.
The altered hamster β-tubulin was not expressed as an increased resistance to Colcemid in any hybrid. Since the complete hamster
chromosome complement was represented among the hybrids, the absence of altered β-tubulin is not due to segregation of the
mutant hamster β-tubulin gene. We suggest either that the hamster β-tubulin gene is repressed in hybrids, or that hamster
β-tubulin is excluded from the spindle in hybrid cells. We compare these findings with previous reports of the repression
of other highly active, moderately repeated constitutive genes in interspecific hybrids. 相似文献
955.
A study of intermediate forms betweenEulemur macaco macaco andE. m. flavifrons was performed on animals in different areas located to the north, south, and east of the known limits of distribution in
Maromandia. A large hybridization zone was defined and morphological and dermatoglyphic comparisons were done on the different
animals. 相似文献
956.
957.
M. T. M. N. Cornélio A. R. S. Figueirôa K. G. B. Santos R. Carvalho W. S. Soares Filho M. Guerra 《Plant Systematics and Evolution》2003,240(1-4):149-161
Karyotypes of 93 individuals belonging to 18 accessions of mandarins, mandarin hybrids and two related species were analysed with the fluorochromes CMA and DAPI, to identify marker chromosomes. The karyotypes revealed highly differentiated banding patterns and could be classified in four groups (I–IV) according to the presence/absence of chromosomes with three bands (type A) or with two bands (one proximal and one terminal, type B, or both terminal, type C). The accessions of group I exhibited the simplest and homozygous karyotypes (lacking chromosome types A, B and C), represented by `Sunki' and `Cleopatra'. Group II (lacking chromosome types A and B) included three accessions of Mediterranean mandarins and `Cravo' mandarin, all of them with very similar and almost completely homozygous karyotypes. All other karyotypes of groups II and III (lacking chromosome type A) were heterozygous for one or more chromosome pairs and most of them seemed to be hybrid derivatives from non-mandarin accessions. Group IV (with chromosome types A and B) was represented only by two heterozygous hybrids (`Murcott' and `King'). The karyotype of most hybrids agrees with one of the possible combinations resulting from chromosome types segregation from their putative ancestor karyotypes, but at least `Orlando' seemed to be a more complex hybrid. Comparing with banding patterns of other Citrus species, those of group I and the Mediterranean mandarins (group II) are the best candidates to represent C. reticulata (sensu Swingle) as a true species. 相似文献
958.
Yuri Lazebnik 《Cell cycle (Georgetown, Tex.)》2014,13(15):2323-2329
A common view is that an accidental increase in ploidy contributes to the evolution of neoplastic cells primarily by decreasing the fidelity of mitosis with extra chromosomes and centrosomes. This view implies that how neoplastic cells become polyploid is irrelevant, as it has been widely assumed. If this assumption is correct, then the oncogenic contribution of the pathways to polyploidy and thus their potential as targets for cancer prevention is determined by their incidence in the body. A lesson from plant evolution, in which an accidental increase in ploidy has a prevalent role, suggests that this assumption needs to be reconsidered. 相似文献
959.
A histochemical procedure has been developed for staining aminoacylase-1 (ACY-1) isozymes after electrophoresis on cellulose acetate membranes. N-Formyl-L-methionine and N-acetyl-L-methionine were excellent enzyme substrates in the staining reaction. The ACY-1 isozymes from tissue culture cells of several vertebrate species showed distinguishable electrophoretic patterns. The ACY-1 isozymes in extracts of mouse, human, owl monkey, and African green monkey kidney cells each had electrophoretic mobilities different from those of peptidases S, A, and C from the same cells. Except for African green monkey kidney (CV-1) cells, the animal species expressed a single anodally migrating ACY-1 band. Human-mouse somatic cell hybrids containing the short arm of human chromosome 3 expressed three ACY-1 bands, as would be predicted from the dimeric structure of the enzyme. CV-1 cells expressed two (or three) ACY-1 bands, suggesting the possibility that CV-1 cells contained two alleles at a single locus or two genetic loci for ACY-1.This research was aided by USPHS Grants CA-06656-17 and 1-K6KAI-2352-17 from the National Cancer Institute and the National Institute of Allergy and Infectious Diseases, and by Contract NO1-CP-71058 from the National Cancer Institute. 相似文献
960.
Twelve novel fenfuram-diarylether hybrids were designed, synthesized and characterized by 1H NMR and MS. Their in vitro antifungal activities were evaluated against five phytopathogenic fungi by mycelial growth inhibition method. Most compounds showed significant antifungal effect on Rhizoctonia solani and Sclerotinia sclerotiorum. Compound 1c exhibited the most potent antifungal effect on R. solani with an EC50 value of 0.242 mg/L, superior to the commercial fungicide boscalid (EC50 = 1.758 mg/L) and the lead fungicide fenfuram (EC50 = 7.691 mg/L). Molecular docking revealed that compound 1c featured a higher affinity for succinate dehydrogenase (SDH) than fenfuram. Furthermore, it was shown that the 2-chlorophenyl group of compound 1c formed a π-π stacking with D/Tyr-128 and a Cl-π interaction with B/His-249, which made compound 1c more active than fenfuram against SDH. 相似文献