全文获取类型
收费全文 | 2615篇 |
免费 | 132篇 |
专业分类
2747篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 48篇 |
2021年 | 71篇 |
2020年 | 48篇 |
2019年 | 77篇 |
2018年 | 105篇 |
2017年 | 75篇 |
2016年 | 125篇 |
2015年 | 155篇 |
2014年 | 162篇 |
2013年 | 219篇 |
2012年 | 246篇 |
2011年 | 221篇 |
2010年 | 140篇 |
2009年 | 97篇 |
2008年 | 174篇 |
2007年 | 178篇 |
2006年 | 161篇 |
2005年 | 108篇 |
2004年 | 79篇 |
2003年 | 100篇 |
2002年 | 68篇 |
2001年 | 3篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2747条查询结果,搜索用时 15 毫秒
951.
952.
953.
One of the goals in oilseed rape programs is to develop genotypes producing oil with low linolenic acid content (C18:3, ≤3%).
Low linolenic mutant lines of canola rapeseed were obtained via chemical mutagenesis at the Plant Breeding and Acclimatization Institute – NRI, in Poznan, Poland, and allele-specific SNP
markers were designed for monitoring of two statistically important single nucleotide polymorphisms detected by SNaPshot analysis
in two FAD3 desaturase genes, BnaA.FAD3 and BnaC.FAD3, respectively. Strong negative correlation between the presence of mutant alleles of the genes and linolenic acid content
was revealed by analysis of variance. In this paper we present detailed characteristics of the markers by estimation of the
additive and dominance effects of the FAD3 genes with respect to particular fatty acid content in seed oil, as well as by calculation of the phenotypic variation of
seed oil fatty acid composition accounted by particular allele-specific marker. The obtained percentage of variation in fatty
acid composition was considerable only for linolenic acid content and equaled 35.6% for BnaA.FAD3 and 39.3% for BnaC.FAD3, whereas the total percentage of variation in linolenic acid content was 53.2% when accounted for mutations in both genes
simultaneously. Our results revealed high specificity of the markers for effective monitoring of the wild-type and mutated
alleles of the Brassica napus FAD3 desaturase genes in the low linolenic mutant recombinants in breeding programs. 相似文献
954.
955.
Synowiec E Szaflik J Chmielewska M Wozniak K Sklodowska A Waszczyk M Dorecka M Blasiak J Szaflik JP 《Molecular biology reports》2012,39(3):2081-2087
Iron may be implicated in the generation of oxidative stress by the catalyzing the Haber–Weiss or Fenton reaction. On the
other hand, oxidative stress has been implicated in the pathogenesis of age-related macular degeneration (AMD) and heme oxygenase-1
(HO-1), encoded by the HMOX1 gene and heme oxygenase-2 (HO-2), encoded by the HMOX2 gene are important markers of iron-related oxidative stress and its consequences. Therefore, variability of the HMOX1 and HMOX2 genes might be implicated in the pathogenesis of AMD through the modulation of the cellular reaction to oxidative stress.
In the present work, we investigated the association between AMD and a G → C transversion at the 19 position in the HMOX1 gene (the 19G>C-HMOX1 polymorphism, rs2071747) and a A → G transition at the −42 + 1444 position in the HMOX2 gene (the −42 + 1444A>G-HMOX2 polymorphism, rs2270363) and its modulation by some environmental factors. 279 patients with AMD and 105 controls were recruited
in this study and the polymorphisms were typed by restriction fragment length polymorphism and allele-specific polymerase
chain reaction (PCR). We observed an association between the occurrence of dry AMD and the G/A genotype of the −42 + 1444A>G-HMOX2 polymorphism (odds ratio (OR) 2.72), whereas the G/G genotype reduced the risk of dry AMD (OR 0.41). The G/C genotype and
the C allele of the 19 G>C-HMOX1 polymorphism and the G/G genotype and the G allele of the −42 + 1444A>G-HMOX2 polymorphism were associated with progression of AMD from dry to wet form (OR 4.83, 5.20, 2.55, 1.69, respectively). On the
other hand, the G/G genotype and the G allele of the 19 G>C-HMOX1 polymorphism and the A/G genotype and the A allele of the −42 + 1444A>G-HMOX2 polymorphism protected against AMD progression (OR 0.19, 0.19, 0.34, 0.59, respectively). Therefore, the 19G>C-HMOX1 and the −42 + 1444A>G-HMOX2 polymorphisms may be associated with the occurrence and progression of AMD. 相似文献
956.
Popenda M Szachniuk M Antczak M Purzycka KJ Lukasiak P Bartol N Blazewicz J Adamiak RW 《Nucleic acids research》2012,40(14):e112
Understanding the numerous functions that RNAs play in living cells depends critically on knowledge of their three-dimensional structure. Due to the difficulties in experimentally assessing structures of large RNAs, there is currently great demand for new high-resolution structure prediction methods. We present the novel method for the fully automated prediction of RNA 3D structures from a user-defined secondary structure. The concept is founded on the machine translation system. The translation engine operates on the RNA FRABASE database tailored to the dictionary relating the RNA secondary structure and tertiary structure elements. The translation algorithm is very fast. Initial 3D structure is composed in a range of seconds on a single processor. The method assures the prediction of large RNA 3D structures of high quality. Our approach needs neither structural templates nor RNA sequence alignment, required for comparative methods. This enables the building of unresolved yet native and artificial RNA structures. The method is implemented in a publicly available, user-friendly server RNAComposer. It works in an interactive mode and a batch mode. The batch mode is designed for large-scale modelling and accepts atomic distance restraints. Presently, the server is set to build RNA structures of up to 500 residues. 相似文献
957.
Katarzyna Lamparska Jarrod Clark Gail Babilonia Victoria Bedell Wesley Yip Steven S. Smith 《Nucleic acids research》2012,40(19):9788-9801
5-Aza-2′-deoxycytidine (5azaC-dR) has been employed as an inhibitor of DNA methylation, a chemotherapeutic agent, a clastogen, a mutagen, an inducer of fragile sites and a carcinogen. However, its effects are difficult to quantify because it rapidly breaks down in aqueous solution to the stable compound 2′-deoxyriboguanylurea (GuaUre-dR). Here, we used a phosphoramidite that permits the introduction of GuaUre-dR at defined positions in synthetic oligodeoxynucleotides to demonstrate that it is a potent inhibitor of human DNA methyltransferase 1 (hDNMT1) and the bacterial DNA methyltransferase (M.EcoRII) and that it is a mutagen that can form productive base pairs with either Guanine or Cytosine. Pure GuaUre-dR was found to be an effective demethylating agent and was able to induce 5azaC-dR type fragile sites FRA1J and FRA9E in human cells. Moreover, we report that demethylation associated with C:G → G:C transversion and C:G → T:A transition mutations was observed in human cells exposed to pure GuaUre-dR. The data suggest that most of the effects attributed to 5azaC-dR are exhibited by its stable primary breakdown product. 相似文献
958.
Igor J. Chybicki Andrzej Oleksa Katarzyna Kowalkowska Jaroslaw Burczyk 《Plant Systematics and Evolution》2012,298(6):1045-1056
Peripheral populations may be crucial for understanding processes underlying adaptive genetic variation. Their evolution and ecology are driven by various genetic and demographic processes, such as selection, gene flow and bottleneck. Peripheral populations often experience a reduction in density resulting in the Allee effect. The presence of interfertile species increases the opportunity for hybridisation, which allows for a rescue from the Allee effect, but at the risk of genetic extinction through introgression. In this article we investigated a peripheral population of Quercus pubescens, a European tree species. The study population is located in Poland, several hundred kilometres northwards from the main species range. Due to geographic separation, the study population exists under strong pressure of introgression from potentially inter-fertile Q. petraea and Q. robur, which are the only common oaks in Poland. The intermediate morphology between typical Q. pubescens and a common oak species found in the study population supports the introgression hypothesis, which could be in line with the earlier studies of this species complex conducted in the main range of Q. pubescens. Alternatively, the intermediate morphology could reflect the founder effect or selection at an ecological extreme. We attempted to verify these hypotheses using microsatellites and a reference of common oak species. The results showed that the study population is genetically distinct from both Q. petraea and Q. robur. Additionally, the population is characterised by a low effective population size and limited gene dispersal. This suggests that the study population reveals strong reproductive isolation from common species, implying alternative sources of atypical morphology. 相似文献
959.
Comparative analysis of antioxidant capacity was performed using FRAP and DPPH methods on extracts containing carotenoids acquired from fruits of Sea buckthorn. The examination included nine varieties of Sea buckthorn growing in the comparative cultivation. Conducted analysis allowed to compare the antioxidant capacity with carotenoids content measured with spectrophotometric and HPLC methods. Three of the examined cultivars indicating high antioxidant activity in both, FRAP and DPPH methods, also revealed highest ('Aromatnaya') and high ('Botanicheskaya', 'Arumnyj') total carotenoids content in HPLC analysis. 相似文献
960.
The Nodal signaling pathway is known from earlier work to be an essential mediator of oral ectoderm specification in the sea urchin embryo, and indirectly, of aboral ectoderm specification as well. Following expression of the Nodal ligand in the future oral ectoderm during cleavage, a sequence of regulatory gene activations occur within this territory which depend directly or indirectly on nodal gene expression. Here we describe additional regulatory genes that contribute to the oral ectoderm regulatory state during specification in Strongylocentrotus purpuratus, and show how their spatial expression changes dynamically during development. By means of system wide perturbation analyses we have significantly improved current knowledge of the epistatic relations among the regulatory genes of the oral ectoderm. From these studies there emerge diverse circuitries relating downstream regulatory genes directly and indirectly to Nodal signaling. A key intermediary regulator, the role of which had not previously been discerned, is the not gene. In addition to activating several genes earlier described as targets of Nodal signaling, the not gene product acts to repress other oral ectoderm genes, contributing crucially to the bilateral spatial organization of the embryonic oral ectoderm. 相似文献