全文获取类型
收费全文 | 1707篇 |
免费 | 106篇 |
国内免费 | 2篇 |
专业分类
1815篇 |
出版年
2023年 | 7篇 |
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 37篇 |
2015年 | 53篇 |
2014年 | 70篇 |
2013年 | 100篇 |
2012年 | 130篇 |
2011年 | 123篇 |
2010年 | 92篇 |
2009年 | 79篇 |
2008年 | 94篇 |
2007年 | 86篇 |
2006年 | 98篇 |
2005年 | 99篇 |
2004年 | 107篇 |
2003年 | 79篇 |
2002年 | 70篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1971年 | 6篇 |
排序方式: 共有1815条查询结果,搜索用时 0 毫秒
31.
32.
Ana Beloqui Taras Y. Nechitaylo Nieves López-Cortés Azam Ghazi María-Eugenia Guazzaroni Julio Polaina Axel W. Strittmatter Oleg Reva Agnes Waliczek Michail M. Yakimov Olga V. Golyshina Manuel Ferrer Peter N. Golyshin 《Applied and environmental microbiology》2010,76(17):5934-5946
The guts and casts of earthworms contain microbial assemblages that process large amounts of organic polymeric substrates from plant litter and soil; however, the enzymatic potential of these microbial communities remains largely unexplored. In the present work, we retrieved carbohydrate-modifying enzymes through the activity screening of metagenomic fosmid libraries from cellulose-depleting microbial communities established with the fresh casts of two earthworm species, Aporrectodea caliginosa and Lumbricus terrestris, as inocula. Eight glycosyl hydrolases (GHs) from the A. caliginosa-derived community were multidomain endo-β-glucanases, β-glucosidases, β-cellobiohydrolases, β-galactosidase, and β-xylosidases of known GH families. In contrast, two GHs derived from the L. terrestris microbiome had no similarity to any known GHs and represented two novel families of β-galactosidases/α-arabinopyranosidases. Members of these families were annotated in public databases as conserved hypothetical proteins, with one being structurally related to isomerases/dehydratases. This study provides insight into their biochemistry, domain structures, and active-site architecture. The two communities were similar in bacterial composition but significantly different with regard to their eukaryotic inhabitants. Further sequence analysis of fosmids and plasmids bearing the GH-encoding genes, along with oligonucleotide usage pattern analysis, suggested that those apparently originated from Gammaproteobacteria (pseudomonads and Cellvibrio-like organisms), Betaproteobacteria (Comamonadaceae), and Alphaproteobacteria (Rhizobiales).Microorganisms producing diverse glycosyl hydrolases (GHs) are widespread and typically thrive in environments where plant materials tend to accumulate and deteriorate (42, 73). The habitats of microorganisms with great GH diversity are the ruminant animal rumen, mouse bowel, and rabbit cecum (10, 24, 26, 28, 49, 74). Microorganisms associated with soil invertebrates in general and with soil earthworms in particular carry out metabolic processes that contribute to element cycling and are essential in sustaining processes which their hosts are unable to perform (20, 52, 72, 76). Although some species of earthworms produce cellulases (15, 55), they generally rely on microbes inhabiting their gastrointestinal (GI) tracts to perform cellulose utilization processes (31, 47, 77). Casts are of special interest in this respect. Considering that the overall numbers of cellulolytic microbes in earthworm casts are greater than those in soil (57), earthworm casts seem to play an important role in the decomposition of plant litter, serving as an inoculum for cellulosic substrates (9). It is important to note that microorganisms from preingested substratum (soil or plant litter) are predominant in the gut lumen (20); however, microbial populations in earthworm casts differ from those in soil in terms of diversity and the relative abundance of different taxa (29, 57, 63). It is anticipated that the enzymatic repertoire of such microbial communities must be especially broad toward diverse sugar-based polymeric, oligomeric, and monomeric substrates; however, among approximately 115 families of GHs with thousands of members known to date (12), none of the GHs have been derived from microorganisms of earthworm-associated microbial communities.The aim of the present work was therefore to examine the diversity of GHs in metagenome libraries derived from fresh casts of Aporrectodea caliginosa and Lumbricus terrestris earthworms via functional screening. Other important tasks of this work were to characterize individual enzymes and to gain insight into their structural-functional features. Finally, we performed sequence analysis of large contiguous DNA fragments of fosmids harboring the genes for GHs to associate them with the organism(s) that may produce them, which was complemented by conventional small-subunit (SSU) rRNA clone library sequencing analysis. 相似文献
33.
Methyl transfer from methyl vitamin B 12 总被引:1,自引:0,他引:1
G Agnes H A Hill J M Pratt S C Ridsdale F S Kennedy R J Williams 《Biochimica et biophysica acta》1971,252(1):207-211
34.
Patients with HIV not only have to deal with the challenges of living with an incurable disease but also with the dilemma of whether or not to disclose their status to their partners, families and friends. This study explores the extent to which sub-Saharan African (SSA) migrant women in Belgium disclose their HIV positive status, reasons for disclosure/non-disclosure and how they deal with HIV disclosure. A qualitative study consisting of interviews with twenty-eight SSA women with HIV/AIDS was conducted. Thematic content analysis was employed to identify themes as they emerged. Our study reveals that these women usually only disclose their status to healthcare professionals because of the treatment and care they need. This selective disclosure is mainly due to the taboo of HIV disease in SSA culture. Stigma, notably self-stigma, greatly impedes HIV disclosure. Techniques to systematically incorporate HIV disclosure into post-test counseling and primary care services are highly recommended. 相似文献
35.
Rosanna Pescini Gobert Monique van den Eijnden Cedric Szyndralewiez Catherine Jorand-Lebrun Dominique Swinnen Linfeng Chen Corine Gillieron Fiona Pixley Pierre Juillard Patrick Gerber Caroline Johnson-L��ger Serge Halazy Montserrat Camps Agnes Bombrun Margaret Shipp Pierre-Alain Vitte Vittoria Ardissone Chiara Ferrandi Dominique Perrin Christian Rommel Rob Hooft van Huijsduijnen 《The Journal of biological chemistry》2009,284(17):11385-11395
36.
Influence of soil type on the transfer of plasmid RP4p from Pseudomonas fluorescens to introduced recipient and to indigenous bacteria 总被引:1,自引:0,他引:1
Agnes Richaume Eric Smit Geneviève Faurie Jan D. van Elsas 《FEMS microbiology letters》1992,101(4):281-291
Abstract Transfer of plasmid RP4p from introduced Pseudomonas fluorescens to a co-introduced recipient strain or to members of the indigenous bacterial population was studied in four different soils of varying texture planted with wheat. Donor and recipient strains showed good survival in the four soils throughout the experiment. The numbers of transconjugants found in donor and recipient experiments in two soils, Ede loamy sand and Löss silt loam were significantly higher in the rhizosphere than in corresponding bulk soil. In the remaining two soils, Montrond and Flevo silt loam, transconjugant numbers were not significantly higher in the rhizosphere than in the bulk soil.
The combined utilization of a specific bacteriophage eliminate the donor strain and the pat sequence as a specific marker to detect RP4p was found to be very efficient in detecting indigenous transconjugants under various environmental conditions. The numbers of indigenous transconjugants were consistently higher in rhizosphere than bull soil. A significant rhizosphere effect on transconjugant numbers of transconjugants were recovered from Flevo and Montrond silt loam; these soils possess characteristics such as clay or organic matter contents which may be favorable to conjugation. 相似文献
The combined utilization of a specific bacteriophage eliminate the donor strain and the pat sequence as a specific marker to detect RP4p was found to be very efficient in detecting indigenous transconjugants under various environmental conditions. The numbers of indigenous transconjugants were consistently higher in rhizosphere than bull soil. A significant rhizosphere effect on transconjugant numbers of transconjugants were recovered from Flevo and Montrond silt loam; these soils possess characteristics such as clay or organic matter contents which may be favorable to conjugation. 相似文献
37.
Identification and simian immunodeficiency virus infection of CD1d-restricted macaque natural killer T cells 下载免费PDF全文
Motsinger A Azimzadeh A Stanic AK Johnson RP Van Kaer L Joyce S Unutmaz D 《Journal of virology》2003,77(14):8153-8158
Natural killer T (NKT) cells express a highly conserved T-cell receptor (TCR) and recognize glycolipids in the context of CD1d molecules. We recently demonstrated that CD4+ NKT cells are highly susceptible to human immunodeficiency virus type 1 (HIV-1) infection and are selectively depleted in HIV-infected individuals. Here, we identified macaque NKT cells using CD1d tetramers and human Valpha24 antibodies. Similar to human NKT cells, alpha-galactosylceramide (alpha-GalCer)-pulsed dendritic cells activate and expand macaque NKT cells. Upon restimulation with alpha-GalCer-pulsed CD1d(+) cells, macaque NKT cells secreted high levels of cytokines, a characteristic of these T cells. Remarkably, the majority of resting and activated macaque NKT cells expressed CD8, and a smaller portion expressed CD4. Macaque NKT cells also expressed the HIV-1/simian immunodeficiency virus (SIV) coreceptor CCR5, and the CD4+ subset was susceptible to SIV infection. Identification of macaque NKT cells has major implications for delineating the role of these cells in nonhuman primate disease models of HIV as well as other pathological conditions, such as allograft rejection and autoimmunity. 相似文献
38.
Agnes Dettai Cyril Gallut Sophie Brouillet Joel Pothier Guillaume Lecointre Régis Debruyne 《PloS one》2012,7(12)
Background
Researchers sorely need markers and approaches for biodiversity exploration (both specimen linked and metagenomics) using the full potential of next generation sequencing technologies (NGST). Currently, most studies rely on expensive multiple tagging, PCR primer universality and/or the use of few markers, sometimes with insufficient variability.Methodology/Principal Findings
We propose a novel approach for the isolation and sequencing of a universal, useful and popular marker across distant, non-model metazoans: the complete mitochondrial genome. It relies on the properties of metazoan mitogenomes for enrichment, on careful choice of the organisms to multiplex, as well as on the wide collection of accumulated mitochondrial reference datasets for post-sequencing sorting and identification instead of individual tagging. Multiple divergent organisms can be sequenced simultaneously, and their complete mitogenome obtained at a very low cost. We provide in silico testing of dataset assembly for a selected set of example datasets.Conclusions/Significance
This approach generates large mitogenome datasets. These sequences are useful for phylogenetics, molecular identification and molecular ecology studies, and are compatible with all existing projects or available datasets based on mitochondrial sequences, such as the Barcode of Life project. Our method can yield sequences both from identified samples and metagenomic samples. The use of the same datasets for both kinds of studies makes for a powerful approach, especially since the datasets have a high variability even at species level, and would be a useful complement to the less variable 18S rDNA currently prevailing in metagenomic studies. 相似文献39.
The inhibitory activity of natural products on plant p-hydroxyphenylpyruvate dioxygenase 总被引:3,自引:0,他引:3
Meazza G Scheffler BE Tellez MR Rimando AM Romagni JG Duke SO Nanayakkara D Khan IA Abourashed EA Dayan FE 《Phytochemistry》2002,60(3):281-288
The inhibitory activity of 34 natural products of various structural classes on hydroxyphenylpyruvate dioxygenase (HPPD), the target site for triketone herbicides, and the mode of interaction of selected natural products were investigated. Recombinant HPPD from arabidopsis is sensitive to several classes of natural compounds including, in decreasing order of sensitivity, triketones, benzoquinones, naphthoquinones and anthraquinones. The triketone natural products acted as competitive tight-binding inhibitors, whereas the benzoquinones and naphthoquinones did not appear to bind tightly to HPPD. While these natural products may not have optimal structural features required for in vivo herbicidal activity, the differences in their kinetic behavior suggest that novel classes of HPPD inhibitors may be developed based on their structural backbones. 相似文献