全文获取类型
收费全文 | 12993篇 |
免费 | 361篇 |
国内免费 | 1篇 |
出版年
2021年 | 114篇 |
2020年 | 95篇 |
2019年 | 121篇 |
2018年 | 263篇 |
2017年 | 233篇 |
2016年 | 314篇 |
2015年 | 334篇 |
2014年 | 409篇 |
2013年 | 546篇 |
2012年 | 531篇 |
2011年 | 548篇 |
2010年 | 349篇 |
2009年 | 256篇 |
2008年 | 394篇 |
2007年 | 430篇 |
2006年 | 403篇 |
2005年 | 404篇 |
2004年 | 345篇 |
2003年 | 388篇 |
2002年 | 312篇 |
2001年 | 281篇 |
2000年 | 233篇 |
1999年 | 178篇 |
1998年 | 94篇 |
1992年 | 238篇 |
1991年 | 232篇 |
1990年 | 182篇 |
1989年 | 217篇 |
1988年 | 234篇 |
1987年 | 238篇 |
1986年 | 219篇 |
1985年 | 252篇 |
1984年 | 202篇 |
1983年 | 166篇 |
1980年 | 83篇 |
1979年 | 234篇 |
1978年 | 158篇 |
1977年 | 136篇 |
1976年 | 135篇 |
1975年 | 170篇 |
1974年 | 269篇 |
1973年 | 260篇 |
1972年 | 253篇 |
1971年 | 248篇 |
1970年 | 258篇 |
1969年 | 246篇 |
1968年 | 192篇 |
1967年 | 196篇 |
1966年 | 173篇 |
1965年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 61 毫秒
971.
Agnieszka Fiuk Piotr T. Bednarek Jan J. Rybczyński 《Plant Molecular Biology Reporter》2010,28(3):413-420
Cytometric and molecular techniques were used to verify genetic uniformity among somatic embryo-derived plantlets of Gentiana pannonica Scop. Cytometric analysis of regenerants revealed absence of chromosomal changes and alterations in ploidy. However, reverse
phase high pressure liquid chromatography detected higher levels of methylation in regenerated plants than those of control
plants. These changes were further investigated using a quantitative molecular marker-based approach. This revealed that numerous
tissue culture-induced variations, ∼3% (epi)mutations, were observed, including sequence variation and changes in methylation
patterns. Moreover, complex patterns of variation, including combinations of genetic and epigenetic changes, were relatively
high (ca. 9%). Overall, tissue culture-induced variation reached 16%; while, demethylation was lower than de novo methylation
in heterozygotic material and similar in all regenerated plantlets. 相似文献
972.
Werner Ulrich Izabela Hajdamowicz Marcin Zalewski Marzena Stańska Wojciech Ciurzycki Piotr Tykarski 《Ecological Research》2010,25(2):375-381
Competition theory predicts that species of similar ecological niches are less likely to coexist than species with different
niches, a process called species assortment. In contrast, the concept of habitat filtering implies that species with similar
ecological requirements should co-occur more often than expected by chance. Here we use environmental and ecological data
to assess patterns of co-occurrence of regional communities of spiders distributed across two assemblies of lake islands in
northern Poland. We found aggregated and random co-occurrences of species of the same genus and a significant tendency of
species segregation across genera. We also found that species of the same genus react similarly to important environmental
variables. A comparison of ecological traits of species of the local communities with those expected from a random sample
from the regional Polish species pool corroborated partly the habitat filtering hypothesis. On the other hand, we did not
find evidence for species assortment. Our results also imply that at least some observed species co-occurrences result from
niche differentiation. 相似文献
973.
974.
Artur Mikiciński Piotr Sobiczewski Monika Sulikowska Joanna Puławska Jadwiga Treder 《Journal of Phytopathology》2010,158(4):201-209
Soft rot is the most important disease on calla lily in Poland. The isolation of the presumptive pathogen from symptomatic tubers on nutrient agar yielded bacteria with different colony morphology. Of 41 isolates collected, 10 showed pectolytic activity on crystal violet pectate medium and caused soft rot on potato slices. All pectolytic bacteria appeared to be Gram‐negative rods producing typical soft rot on inoculated leaf petioles of calla lily. Bacteria with colonies which morphologically resembled those used for inoculation were re‐isolated from diseased petioles. Their identification was based on phenotypic characters and sequence of the gene fragment coding 16S rRNA. It was found that, in addition to Pectobacterium carotovorum subsp. carotovorum, soft rot of calla lily can be caused by Pectobacterium carotovorum subsp. atrosepticum, Pseudomonas marginalis, Pseudomonas veronii and Chryseobacterium indologenes. The latter two are described for the first time as plant pathogens. The pectolytic activity of all identified bacteria, except that of P. carotovorum subsp. atrosepticum, was lower than that of P. carotovorum subsp. carotovorum, but strains of P. veronii showed a higher activity than P. marginalisand C. indologenes species. 相似文献
975.
Piotr Stefanowicz Monika Kijewska Katarzyna Kapczyńska Zbigniew Szewczuk 《Amino acids》2010,38(3):881-889
Two procedures of glycated peptides’ synthesis have been developed. The first method involves reductive alkylation of the
ε-amino groups of lysine with 2,3:4,5-di-O-isopropylidene-β-d-arabino-hexos-2-ulo-2,6-pyranose in the presence of sodium cyanoborohydride on solid support. The second one uses a new fully
protected lysine derivative, which is a building block designed for direct introduction of the glycated lysine moiety into
a peptide, according to the standard solid phase synthesis protocol. The applicability of the proposed methods for the synthesis
of peptide-derived Amadori products is discussed. The structure of the synthesized glycated peptides was confirmed by high-resolution
mass spectrometry and enzymatic hydrolysis. Circular dichroism studies, performed in water solution, revealed that the formation
of the Amadori rearrangement product in the lysine side chain does not influence significantly the conformational preferences
of the peptides studied. However, when the solvent was changed to trifluoroethanol, the glycated peptides preferred β-turn
conformation. 相似文献
976.
Relationship between genotype and soil environment during colonization of poplar roots by mycorrhizal and endophytic fungi 总被引:1,自引:0,他引:1
Leszek Karliński Maria Rudawska Barbara Kieliszewska-Rokicka Tomasz Leski 《Mycorrhiza》2010,20(5):315-324
Poplars are among the few tree genera that can develop both ectomycorrhizal (ECM) and arbuscular (AM) associations; however,
variable ratios of ECM/AM in dual mycorrhizal colonizations were observed in the roots of a variety of poplar species and
hybrids. The objective of our study was to analyze the effect of internal and external factors on growth and dual AM and ECM
colonization of poplar roots in three 12–15-year-old common gardens in Poland. We also analyzed the abundance of nonmycorrhizal
fungal endophytes in the poplar roots. The Populus clones comprised black poplars (Populus deltoides and P. deltoides × Populus nigra), balsam poplars (Populus maximowiczii × Populus trichocarpa), and a hybrid of black and balsam poplars (P. deltoides × P. trichocarpa). Of the three sites that we studied, one was located in the vicinity of a copper smelter, where soil was contaminated with
copper and lead. Poplar root tip abundance, mycorrhizal colonization, and soil fungi biomass were lower at this heavily polluted
site. The total mycorrhizal colonization and the ratio of ECM and AM colonization differed among the study sites and according
to soil depth. The influence of Populus genotype was significantly pronounced only within the individual study sites. The contribution of nonmycorrhizal fungal endophytes
differed among the poplar clones and was higher at the polluted site than at the sites free of pollution. Our results indicate
that poplar fine root abundance and AM and ECM symbiosis are influenced by environmental conditions. Further studies of different
site conditions are required to characterize the utility of poplars for purposes such as the phytoremediation of polluted
sites. 相似文献
977.
Ditkowski B Troć P Ginda K Donczew M Chater KF Zakrzewska-Czerwińska J Jakimowicz D 《Molecular microbiology》2010,78(6):1403-1415
Bacterial chromosome segregation usually involves cytoskeletal ParA proteins, ATPases which can form dynamic filaments. In aerial hyphae of the mycelial bacterium Streptomyces coelicolor, ParA filaments extend over tens of microns and are responsible for segregation of dozens of chromosomes. We have identified a novel interaction partner of S. coelicolor ParA, ParJ. ParJ negatively regulates ParA polymerization in vitro and is important for efficient chromosome segregation in sporulating aerial hyphae. ParJ-EGFP formed foci along aerial hyphae even in the absence of ParA. ParJ, which is encoded by sco1662, turned out to be one of the five actinobacterial signature proteins, and another of the five is a ParJ paralogue. We hypothesize that polar growth, which is characteristic not only of streptomycetes, but even of simple Actinobacteria, may be interlinked with ParA polymer assembly and its specific regulation by ParJ. 相似文献
978.
Pawel Sledz Heping Zheng Krzysztof Murzyn Maksymilian Chruszcz Matthew D Zimmerman Mahendra D Chordia Andrzej Joachimiak Wladek Minor 《Protein science : a publication of the Protein Society》2010,19(7):1395-1404
Surface lysine methylation (SLM) is a technique for improving the rate of success of protein crystallization by chemically methylating lysine residues. The exact mechanism by which SLM enhances crystallization is still not clear. To study these mechanisms, and to analyze the conditions where SLM will provide the optimal benefits for rescuing failed crystallization experiments, we compared 40 protein structures containing N,N-dimethyl-lysine (dmLys) to a nonredundant set of 18,972 nonmethylated structures from the PDB. By measuring the relative frequency of intermolecular contacts (where contacts are defined as interactions between the residues in proximity with a distance of 3.5 Å or less) of basic residues in the methylated versus nonmethylated sets, dmLys-Glu contacts are seen more frequently than Lys-Glu contacts. Based on observation of the 10 proteins with both native and methylated structures, we propose that the increased rate of contact for dmLys-Glu is due to both a slight increase in the number of amine-carboxyl H-bonds and to the formation of methyl C–H···O interactions. By comparing the relative contact frequencies of dmLys with other residues, the mechanism by which methylation of lysines improves the formation of crystal contacts appears to be similar to that of Lys to Arg mutation. Moreover, analysis of methylated structures with the surface entropy reduction (SER) prediction server suggests that in many cases SLM of predicted SER sites may contribute to improved crystallization. Thus, tools that analyze protein sequences and mark residues for SER mutation may identify proteins with good candidate sites for SLM. 相似文献
979.
In this study, we examined the response of glioma C6 cells to 2′,3′-O-(4-benzoylbenzoyl)-ATP (BzATP) and showed that the BzATP-induced calcium signaling does not involve the P2X7 receptor activity. We show here that in the absence of extracellular Ca2+, BzATP-generated increase in [Ca2+]i
via Ca2+ release from intracellular stores. In the presence of calcium ions, BzATP established a biphasic Ca2+ response, in a manner typical for P2Y receptors. Brilliant Blue G, a selective antagonist of the rat P2X7 receptor, did not reduce any of the two components of the Ca2+ response elicited by BzATP. Periodate-oxidized ATP blocked not only BzATP- but also UTP-induced Ca2+ elevation. Moreover, BzATP did not open large transmembrane pores. What is more, a cross-desensitization between UTP and
BzATP occurred, which clearly shows that in glioma C6 cells BzATP activates most likely the P2Y2 but not the P2X7 receptors. 相似文献
980.
Pawel Mazur Tomasz Magdziarz Andrzej Bak Zdzislaw Chilmonczyk Teresa Kasprzycka-Guttman Irena Misiewicz-Krzemińska Katarzyna Skupińska Jaroslaw Polanski 《Journal of molecular modeling》2010,16(7):1205-1212
Isothiocyanates (ITC) are well-known chemopreventive agents extracted from vegetables. This activity results from the activation
of human oxidoreductase. In this letter, the uncompetitive activatory mechanism of ITC was investigated using docking and
molecular dynamics simulations. This indicates that NAD(P)H:quinone oxidoreductase can efficiently improve enzyme-substrate
recognition within the catalytic site if the ITC activator supports the interaction in the uncompetitive binding site. 相似文献