全文获取类型
收费全文 | 5111篇 |
免费 | 349篇 |
国内免费 | 5篇 |
专业分类
5465篇 |
出版年
2024年 | 4篇 |
2023年 | 44篇 |
2022年 | 81篇 |
2021年 | 161篇 |
2020年 | 91篇 |
2019年 | 117篇 |
2018年 | 178篇 |
2017年 | 118篇 |
2016年 | 194篇 |
2015年 | 287篇 |
2014年 | 297篇 |
2013年 | 372篇 |
2012年 | 457篇 |
2011年 | 482篇 |
2010年 | 307篇 |
2009年 | 237篇 |
2008年 | 270篇 |
2007年 | 340篇 |
2006年 | 269篇 |
2005年 | 248篇 |
2004年 | 228篇 |
2003年 | 193篇 |
2002年 | 166篇 |
2001年 | 42篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 33篇 |
1997年 | 23篇 |
1996年 | 22篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有5465条查询结果,搜索用时 15 毫秒
101.
Cyanobacterial NDH-1 is a multisubunit complex involved in proton translocation, cyclic electron flow around photosystem I and CO2 uptake. The function and location of several of its small subunits are unknown. In this work, the location of the small subunits NdhL, -M, -N, -O and CupS of Synechocystis 6803 NDH-1 was established by electron microscopy (EM) and single particle analysis. To perform this, the subunits were enlarged by fusion with the YFP protein. After classification of projections, the position of the YFP tag was revealed; all five subunits are integrated in the membrane domain. The results on NDH-1 demonstrate that a GFP tag can be revealed after data processing of EM data sets of moderate size, thus showing that this way of labeling is a fast and reliable way for subunit mapping in multisubunit complexes after partial purification. 相似文献
102.
Camilla Dornfeld Alexandra J. Weisberg Ritesh K C Natalia Dudareva John G. Jelesko Hiroshi A. Maeda 《The Plant cell》2014,26(7):3101-3114
The aromatic amino acid Phe is required for protein synthesis and serves as the
precursor of abundant phenylpropanoid plant natural products. While Phe is
synthesized from prephenate exclusively via a phenylpyruvate intermediate in model
microbes, the alternative pathway via arogenate is predominant in plant Phe
biosynthesis. However, the molecular and biochemical evolution of the plant arogenate
pathway is currently unknown. Here, we conducted phylogenetically informed
biochemical characterization of prephenate aminotransferases (PPA-ATs) that belong to class-Ib aspartate aminotransferases
(AspAT Ibs) and catalyze the first
committed step of the arogenate pathway in plants. Plant PPA-ATs and succeeding arogenate dehydratases (ADTs) were found to be most closely related to
homologs from Chlorobi/Bacteroidetes bacteria. The Chlorobium
tepidum
PPA-AT and ADT homologs indeed efficiently converted prephenate and arogenate into
arogenate and Phe, respectively. A subset of AspAT
Ib enzymes exhibiting PPA-AT
activity was further identified from both Plantae and prokaryotes and, together with
site-directed mutagenesis, showed that Thr-84 and Lys-169 play key roles in specific
recognition of dicarboxylic keto (prephenate) and amino (aspartate) acid substrates.
The results suggest that, along with ADT, a gene encoding
prephenate-specific PPA-AT was transferred
from a Chlorobi/Bacteroidetes ancestor to a eukaryotic ancestor of Plantae, allowing
efficient Phe and phenylpropanoid production via arogenate in plants today. 相似文献
103.
104.
Jimenez N Canals R Lacasta A Kondakova AN Lindner B Knirel YA Merino S Regué M Tomás JM 《Journal of bacteriology》2008,190(9):3176-3184
By the isolation of three different Aeromonas hydrophila strain AH-3 (serotype O34) mutants with an altered lipopolysaccharide (LPS) migration in gels, three genomic regions encompassing LPS core biosynthesis genes were identified and characterized. When possible, mutants were constructed using each gene from the three regions, containing seven, four, and two genes (regions 1 to 3, respectively). The mutant LPS core structures were elucidated by using mass spectrometry, methylation analysis, and comparison with the full core structure of an O-antigen-lacking AH-3 mutant previously established by us. Combining the gene sequence and complementation test data with the structural data and phenotypic characterization of the mutant LPSs enabled a presumptive assignment of all LPS core biosynthesis gene functions in A. hydrophila AH-3. The three regions and the genes contained are in complete agreement with the recently sequenced genome of A. hydrophila ATCC 7966. The functions of the A. hydrophila genes waaC in region 3 and waaF in region 2 were completely established, allowing the genome annotations of the two heptosyl transferase products not previously assigned. Having the functions of all genes involved with the LPS core biosynthesis and most corresponding single-gene mutants now allows experimental work on the role of the LPS core in the virulence of A. hydrophila. 相似文献
105.
Natalia Kuczyńska-Kippen 《Hydrobiologia》2007,593(1):27-37
The distribution of rotifer communities between emergent (Typha angustifolia) and submerged (Chara tomentosa) vegetation and a comparatively open water zone were compared during the spring, summer and autumn seasons at three macrophyte-dominated
lakes. This survey identified 107 rotifera species of which 58% of the taxonomical structure was common for the three examined
lakes. Stoneworts with a more complicated spatial and morphological structure (having a much longer stem length than the narrow
leaf cattail), supported higher rotifer densities. The stem length appeared to be the best predictor of all the macrophyte
parameters and pH and chlorophyll a for the chemical variables, for explaining the variation of rotifer densities using the stepwise multiple forward regressions.
The distribution of pelagic species did not differ between particular sites, which may have reflected the behavioural requirements
of those rotifers. Some of them remained in the open water zone while others seeking an anti-predator refuge, gathered within
macrophyte stands during the daytime. Moreover, there were nine Chara-associated species recorded and only one Typha-associated species was noted. The similarity of rotifer communities was most strongly influenced by particular habitat and
season.
Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez
Advances in Rotifer Research 相似文献
106.
Moore CM Hubbard GB Dick E Dunn BG Raveendran M Rogers J Williams V Gomez JJ Butler SD Leland MM Schlabritz-Loutsevitch NE 《American journal of primatology》2007,69(10):1105-1118
Trisomy 13 in humans is the third most common autosomal abnormality at birth, after trisomy 21 and trisomy 18. It has a reported incidence of between 1:5,000 and 1:30,000 live births. It is associated with multiple abnormalities, many of which shorten lifespan. We describe here the first reported case of a baboon (Papio hamadryas) with trisomy of chromosome 17, which is homologous to human chromosome 13. The trisomic infant was born to a consanguineous pair of baboons and had morphological characteristics similar to those observed in human trisomy 13, including bilateral polydactyly in the upper limbs, a patent foramen ovale, and pyelectasis. Molecular DNA analysis using human chromosome 13 markers was consistent with the affected infant inheriting two copies of chromosome 17 derived from the same parental chromosome. This trisomy was, therefore, due to either an error in meiosis II or the result of postzygotic nondisjunction. The parental origin, however, could not be determined. 相似文献
107.
Effects of structural imperfection on gelatinization characteristics of amylopectin starches with A- and B-type crystallinity 总被引:1,自引:0,他引:1
The aim of the present work was to investigate the effect of physical structures on the properties of starch granules. Starches with a high amylopectin content possessing A- and B-type crystallinity were chosen for the study. The gelatinization temperature decreased in the following order: maize (A) > potato (B) > wheat (A) > barley (A), which did not reflect a correlation with the type of crystallinity. Low values of gelatinization temperature were accompanied with high free surface energy of the crystallites. It is proposed that these data are caused by different types of imperfections in starch crystals. Annealing resulted in an enhancement of the gelatinization temperature and a decrease of the free surface energy of the crystallites for all starches reflecting a partial improvement of crystalline perfection. A limited acid hydrolysis (lintnerization) of the starches decreased the gelatinization temperature because of a partial disruption of the crystalline lamellae and an increase of the amount of defects on the edges of the crystallites. Annealing of the lintnerized starches improved the structure of maize and potato starch, giving them similar structural and physicochemical parameters, which was opposite the behavior of the annealed sample from wheat. The possible nature of removable and nonremovable defects inside the crystalline region of the starch granules is discussed. It is concluded that, besides the allomorphic A- and B-types of crystal packing, physical defects in the crystals possess a major impact on starch gelatinization. 相似文献
108.
T. Sasaki Natalia A. Pronina M. Maeshima I. Iwasaki N. Kurano S. Miyachi 《Plant biology (Stuttgart, Germany)》1999,1(1):68-75
Abstract: The number and cross-sectional area of vacuoles in Chlorococcum littorale cells visualized with a differential interfer ence fluorescence microscope increased after their transfer from air to 40% CO2 . An immunological observation indicated that the level of subunit B of vacuolar H*ATPase also increased under 40% CO2 conditions. The activity of nitrate-sensitive ATP-ase associated with the vacuolar membrane was 2–fold higher in 40% CO2 -- grown cells than in air-grown cells. The effects of inhi bitors on the ATPase activity confirmed that these activities were derived from vacuolar-type H-ATPase. These results sug gest that vacuole development associated with that of vacuolar H+ -ATPase occurred during the acclimatization of C. littorale cells to extremely high CO2 conditions. 相似文献
109.
Complex epidemiological situation, nosocomial infections, microbial contamination, and infection risks in hospital and dental
equipment have led to an ever-growing need for prevention of microbial infection in these various areas. Macromolecular systems,
due to their properties, allow one to efficiently use them in various fields, including the creation of polymers with the
antimicrobial activity. In the past decade, the intensive development of a large class of antimicrobial macromolecular systems,
polymers, and copolymers, either quaternized or functionalized with bioactive groups, has been continued, and they have been
successfully used as biocides. Various permanent microbicidal surfaces with non-leaching polymer antimicrobial coatings have
been designed. Along with these trends, new moderately hydrophobic polymer structures have been synthesized and studied, which
contain protonated primary or secondary/tertiary amine groups that exhibited rather high antimicrobial activity, often unlike
their quaternary analogues. This mini-review briefly highlights and summarizes the results of studies during the past decade
and especially in recent years, which concern the mechanism of action of different antimicrobial polymers and non-leaching
microbicidal surfaces, and factors influencing their activity and toxicity, as well as major applications of antimicrobial
polymers. 相似文献
110.
Mavromatis K Ivanova N Barry K Shapiro H Goltsman E McHardy AC Rigoutsos I Salamov A Korzeniewski F Land M Lapidus A Grigoriev I Richardson P Hugenholtz P Kyrpides NC 《Nature methods》2007,4(6):495-500
Metagenomics is a rapidly emerging field of research for studying microbial communities. To evaluate methods presently used to process metagenomic sequences, we constructed three simulated data sets of varying complexity by combining sequencing reads randomly selected from 113 isolate genomes. These data sets were designed to model real metagenomes in terms of complexity and phylogenetic composition. We assembled sampled reads using three commonly used genome assemblers (Phrap, Arachne and JAZZ), and predicted genes using two popular gene-finding pipelines (fgenesb and CRITICA/GLIMMER). The phylogenetic origins of the assembled contigs were predicted using one sequence similarity-based (blast hit distribution) and two sequence composition-based (PhyloPythia, oligonucleotide frequencies) binning methods. We explored the effects of the simulated community structure and method combinations on the fidelity of each processing step by comparison to the corresponding isolate genomes. The simulated data sets are available online to facilitate standardized benchmarking of tools for metagenomic analysis. 相似文献