全文获取类型
收费全文 | 2901篇 |
免费 | 189篇 |
国内免费 | 2篇 |
专业分类
3092篇 |
出版年
2023年 | 7篇 |
2022年 | 17篇 |
2021年 | 35篇 |
2020年 | 33篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 39篇 |
2016年 | 62篇 |
2015年 | 92篇 |
2014年 | 131篇 |
2013年 | 167篇 |
2012年 | 204篇 |
2011年 | 190篇 |
2010年 | 145篇 |
2009年 | 135篇 |
2008年 | 176篇 |
2007年 | 193篇 |
2006年 | 190篇 |
2005年 | 176篇 |
2004年 | 156篇 |
2003年 | 149篇 |
2002年 | 138篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 42篇 |
1998年 | 47篇 |
1997年 | 33篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 23篇 |
1992年 | 27篇 |
1991年 | 26篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有3092条查询结果,搜索用时 15 毫秒
61.
The formamidopyrimidine-DNA glycosylase (Fpg, MutM) is a bifunctional base excision repair enzyme (DNA glycosylase/AP lyase) that removes a wide range of oxidized purines, such as 8-oxoguanine and imidazole ring-opened purines, from oxidatively damaged DNA. The structure of a non-covalent complex between the Lactoccocus lactis Fpg and a 1,3-propanediol (Pr) abasic site analogue-containing DNA has been solved. Through an asymmetric interaction along the damaged strand and the intercalation of the triad (M75/R109/F111), Fpg pushes out the Pr site from the DNA double helix, recognizing the cytosine opposite the lesion and inducing a 60 degrees bend of the DNA. The specific recognition of this cytosine provides some structural basis for understanding the divergence between Fpg and its structural homologue endo nuclease VIII towards their substrate specificities. In addition, the modelling of the 8-oxoguanine residue allows us to define an enzyme pocket that may accommodate the extrahelical oxidized base. 相似文献
62.
63.
Benamar Dahmani Daniel Krebs Saïd El Antri Frédéric Troalen Serge Fermandjian 《Journal of biomolecular structure & dynamics》2013,31(4):429-439
Abstract The peptide (35 residues) corresponding to the basic subdomain (bSD) of c-Jun (residues 252–281) and its fragments NP (N-terminal peptide, 1–19) and CP (C-terminal peptide, 1635) were synthesized in stepwise solid-phase using the tert-butyloxycarbonyl/benzyl strategy. In a previous paper, we have shown that during its binding to the DNA site CRE (cAMP- responsive element) the bSD structure was converted into α-helix from an initial random coil conformation [Krebs, D., Dahmani, B., El Antri, S., Monnot, M., Convert, O., Mauffret, O., Troalen, F. & Fermandjian, S. Eur. J. Biochem. 231, 370–380 (1995)]. Our results suggested both a high flexibility and a helical potential in bSD, these two properties seeming crucial for the accommodation of the basic subdomain of c-Jun to its specific DNA targets. In this work, we assessed the conformational variability of bSD through the study of the secondary structures of its NP and CP fragments in trifluoroethanol (TFE)/2H2O mixtures, using Fourier transform infrared (FTIR) spectroscopy. The IR results were critically analyzed in light of our previously reported circular dichroism (CD) and NMR data [Krebs, D., Dahmani, B., Monnot, M., Mauffret, O., Troalen, F. & Fermandjian, S. Eur. J. Biochem. 235, 699–712 (1996)]. Upon addition of TFE, the relative areas of the seven components of the amide I band (1700–1620 cm?1) reflected the conversion of a large amount of random coil conformation into α-helix for the two fragments and bSD. This effect was accompanied by more subtle variations of the less populated structures, in agreement with the results of CD and NMR experiments. The IR results stipulated the conservation of the parent bSD secondary structures in both fragments; however, NP and CP peptides did not display similar random-to-α-helix stabilization pattern upon additions of TFE to aqueous solutions. The profile from CD signal at 222 nm was found sigmoidal for NP and almost linear for CP, while that corresponding to the parent peptide bSD was just in between those of its fragments. Thus, the present study confirms the high flexibility and helix propensity of the c-Jun basic subdomain and suggests that the N- and C-terminal parts of the peptide do not follow the same random-to-helix conversion profile during their complexation with DNA. 相似文献
64.
Oula Shahin Nicolas Martin-St Paul Serge Rambal Richard Joffre Franck Richard 《Symbiosis (Philadelphia, Pa.)》2013,61(1):1-12
Understanding the factors underlying the distribution of biodiversity is a challenging issue in ecology. Here, we examined the distribution patterns of ectomycorrhizal fungal diversity across the soil profile in three Quercus ilex forests. Contact exploration type strongly dominated at all sites, but was most prevalent in the upper, organic-rich soil layers. At each site, three quarters of the ectomycorrhizal tips and 59 % of taxa were restricted to the ten first centimeters of the soil profile. The relative abundance of the dominant family Russulaceae increased with increasing soil depth. Species composition varied significantly among sites, with most species being rare. Species that occurred in only one of the three sites accounted for 78.9 % of all species, and 57.3 % of species were represented by a single ECM root tip. Our results suggest that (i) rare species at both local and regional scales contribute to the highly diverse fungal assemblages in Mediterranean forests and (ii) multi-sites studies including the whole soil profile are needed to provide comprehensive overviews of the taxonomic and functional diversities of ectomycorrhizal communities. 相似文献
65.
A field population of Typhlodromus pyri (Acari: Phytoseiidae) tolerant to mancozeb was selected in the laboratory. After 10 mancozeb selections the LC50 value for mancozeb was 73 times higher in the selected-10 strain compared to the standard susceptible strain. A genetic analysis
using reciprocal crosses and backcrosses of female F1 progeny found no maternal effect. Resistance in the selected-10 strain was codominant in expression, dominance value was
about −0.1. Backcrosses between F1 females and the susceptible strain indicate that the resistance to mancozeb could be principally conferred by a predominant
gene, but additional factors would also be involved. 相似文献
66.
67.
Jun Zheng Jun-Qiao Feng Lei Zhou Serge Maurice Mbadinga Ji-Dong Gu Bo-Zhong Mu 《World journal of microbiology & biotechnology》2018,34(2):34
Bacterial community and diversity in a long-term petroleum-contaminated soil of an oilfield were characterized using 16S rRNA gene-based Illumina MiSeq high-throughput sequencing. Results indicated that Proteobacteria (49.11%) and Actinobacteria (24.24%) were the most dominant phyla, and the most abundant genera were Pseudoxanthomonas (8.47%), Luteimonas (3.64%), Alkanindiges (9.76%), Acinetobacter (5.26%) and Agromyces (8.56%) in the soil. Meanwhile a series of cultivations were carried out for isolation of alkane degraders from petroleum-contaminated soil with gellan gum and agar as gelling agents. And the isolates were classified by their 16S rRNA genes. Nine of the isolates including Enterobacter, Pseudomonas,Acinetobacter, Rhizobium, Bacillus, Sphingomonas, Paenibacillus, Variovorax and Rhodococcus showed strong biodegradability of alkane mixture (C9–C30) in a wide range of chain-length, which could be potentially applied in enhancement of bioremediation. 相似文献
68.
Steve F. Perry Serge Thomas 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(5):489-497
Summary An extracorporeal circulation of rainbow trout (Oncorhynchus mykiss) was utilized to continuously monitor the rapid and progressive effects of endogenous or exogenous catecholamines on blood respiratory/acid-base status, and to provide in vivo evidence for adrenergic retention of carbon dioxide (CO2) in fish blood (cf. Wood and Perry 1985). Exposure of fish to severe aquatic hypoxia (final P
wO2=40–60 torr; reached within 10–20 min) elicited an initial respiratory alkalosis resulting from hypoxia-induced hyperventilation. However, at a critical arterial oxygen tension (P
aO2) between 15 and 25 torr, fish became agitated for approximately 5 s and a marked (0.2–0.4 pH unit) but transient arterial blood acidosis ensued. This response is characteristic of abrupt catecholamine mobilization into the circulation and subsequent adrenergic activation of red blood cell (RBC) Na+/H+ exchange (Fievet et al. 1987). Within approximately 1–2 min after the activation of RBC Na+/H+ exchange by endogenous catecholamines, there was a significant rise in arterial PCO2 (P
aCO2) whereas arterial PO2 was unaltered; the elevation of P
aCO2 could not be explained by changes in gill ventilation. Pre-treatment of fish with the -adrenoceptor antagonist phentolamine did not prevent the apparent catecholamine-mediated increase of P
aCO2. Conversely, pre-treatment with the -adrenoceptor antagonist sotalol abolished both the activation of the RBC Na+/H+ antiporter and the associated rise in P
aCO2, suggesting a causal relationship between the stimulation of RBC Na+/H+ exchange and the elevation of P
aCO2. To more clearly establish that elevation of plasma catecholamine levels during severe hypoxia was indeed responsible for causing the elevation of P
aCO2, fish were exposed to moderate hypoxia (final P
wO2=60–80 torr) and then injected intraarterially with a bolus of adrenaline to elicit an estimated circulating level of 400 nmol·l-1 immediately after the injection. This protocol activated RBC Na+/H+ exchange as indicated by abrupt changes in arterial pH (pHa). In all fish examined, P
aCO2 increased after injection of exogenous adrenaline. The effects on P
aO2 were inconsistent, although a reduction in this variable was the most frequent response. Gill ventilation frequency and amplitude were unaffected by exogenous adrenaline. Therefore, it is unlikely that ventilatory changes contributed to the consistently observed rise in P
aCO2. Pretreatment of fish with sotalol did not alter the ventilatory response to adrenaline injection but did prevent the stimulation of RBC Na+/H+ exchange and the accompanying increases and decreases in P
aCO2 and P
aO2, respectively. These results suggest that adrenergic elevation of P
aCO2, in addition to the frequently observed reduction of P
aO2 are linked to activation of RBC Na+/H+ exchange. The physiological significance and the potential mechanisms underlying the changes in blood respiratory status after addition of endogenous or exogenous catecholamines to the circulation of hypoxic rainbow trout are discussed.Abbreviations
P
aCO2
arterial carbon dioxide tension
-
P
aO2
arterial oxygen tension
-
P
da
dorsal aortic pressure
-
pHa
arterial pH
-
P
wO2
water oxygen tension
-
RBC
red blood cell
-
V
f
breathing frequency 相似文献
69.
Robin E. Everts Serge A. Versteeg Corinne Renier Francoise Vignaux Peter C. Groot Jan Rothuizen Bernard A. van Oost 《Mammalian genome》2000,11(9):741-747
Genomic Representational Difference Analysis (gRDA) is a subtractive DNA method to clone the differences between two related
genomes, called tester and driver. We have evaluated this method to obtain polymorphic DNA markers for pedigree dogs. Amplified
size-selected genomic restriction fragments (amplicons) of two dog littermates were repeatedly hybridized to each other in
order to remove (subtract) those restriction fragments common to both sibs. Already after two rounds of subtractive hybridization,
a clear enrichment of presumably tester-specific restriction fragments was observed, which was even more pronounced after
the third round of subtraction. A plasmid library of 3000 recombinant clones was constructed of the second round and of the
third round difference product. DNA sequence determination of randomly chosen clones of each difference product showed that
approximately 1000 unique clones were obtained in the second-round difference product and approximately 500 in the third-round
difference product. About half of the clones identified in the second-round difference product were also present in the third-round
difference product. Of the second-round difference product, 39 different gRDA fragments could be identified, of which 21 were
tester specific. In the third-round difference product, 22 different gRDA fragments were identified, of which 18 were tester
specific. There were 13 fragments in common, resulting in a total of 48 different fragments. In order to establish the localization
of these markers, we performed mapping using the dog radiation hybrid panel RHDF5000. Of 39 mapped clones, 29 were mapped
to 20 existing RH groups, and 10 remained unlinked. It is concluded that gRDA is suitable to generate DNA markers to track
disease genes within lines of pedigree dogs.
Received: 26 April 2000 / Accepted: 11 May 2000 相似文献
70.
Laetitia Plaisance Vincent Rousset Serge Morand D. Timothy J. Littlewood 《Journal of Biogeography》2008,35(1):76-87
Aim To investigate the phylogeographical patterns of two poorly dispersing but widely distributed monogenean species, Haliotrema aurigae and Euryhaliotrematoides grandis, gill parasites of coral reef fishes from the family Chaetodontidae. Location South Pacific Ocean (SPO). Methods Sequence data from the mitochondrial cytochrome oxidase subunit I (COI) gene were obtained from samples from five localities of the SPO (Heron Island, Lizard Island, Moorea, Palau and Wallis) for the two parasite species. Phylogenetic and genetic diversity analyses were used to reconstruct phylogeographical patterns, and dates of cladogenetic events were estimated. Results Overall, 50 individuals of 17 Haliotrema aurigae and 33 of Euryhaliotrematoides grandis were sequenced from five localities of the SPO for COI mtDNA (798 bp). Our results revealed a deep phylogeographical structure in the species Euryhaliotrematoides grandis. The molecular divergence between individuals from Moorea and individuals from the remaining localities (7.7%) may be related to Pleistocene sea‐level fluctuations. In contrast, Haliotrema aurigae shows no phylogeographical patterns with the presence of most of the mitochondrial haplotypes in every locality sampled. Main conclusions Our study shows contrasting phylogeographical patterns of the two monogenean parasite species studied, despite many shared characteristics. Both parasites are found on the same host family, share the same geographical range and ecology, and are phylogenetically close. We propose two hypotheses that may help explain the diparity: the hypotheses involve differences in the evolutionary age of the parasite species and their dispersal capabilities. Additionally, the lack of phylogeographical structure in Haliotrema aurigae contrasts with its apparently restricted dispersion, which is likely to occur during the egg stage of the life cycle, inducing a passive dispersal mechanism in butterflyfish monogeneans. 相似文献