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991.
Susana Gardete Choonkeun Kim Boris M. Hartmann Michael Mwangi Christelle M. Roux Paul M. Dunman Henry F. Chambers Alexander Tomasz 《PLoS pathogens》2012,8(2)
An isolate of the methicillin-resistant Staphylococcus aureus (MRSA) clone USA300 with reduced susceptibility to vancomycin (SG-R) (i.e, vancomycin-intermediate S. aureus, VISA) and its susceptible “parental” strain (SG-S) were recovered from a patient at the end and at the beginning of an unsuccessful vancomycin therapy. The VISA phenotype was unstable in vitro generating a susceptible revertant strain (SG-rev). The availability of these 3 isogenic strains allowed us to explore genetic correlates of antibiotic resistance as it emerged in vivo. Compared to the susceptible isolate, both the VISA and revertant strains carried the same point mutations in yycH, vraG, yvqF and lspA genes and a substantial deletion within an intergenic region. The revertant strain carried a single additional frameshift mutation in vraS which is part of two component regulatory system VraSR. VISA isolate SG-R showed complex alterations in phenotype: decreased susceptibility to other antibiotics, slow autolysis, abnormal cell division and increased thickness of cell wall. There was also altered expression of 239 genes including down-regulation of major virulence determinants. All phenotypic properties and gene expression profile returned to parental levels in the revertant strain. Introduction of wild type yvqF on a multicopy plasmid into the VISA strain caused loss of resistance along with loss of all the associated phenotypic changes. Introduction of the wild type vraSR into the revertant strain caused recovery of VISA type resistance. The yvqF/vraSR operon seems to function as an on/off switch: mutation in yvqF in strain SG-R turns on the vraSR system, which leads to increase in vancomycin resistance and down-regulation of virulence determinants. Mutation in vraS in the revertant strain turns off this regulatory system accompanied by loss of resistance and normal expression of virulence genes. Down-regulation of virulence genes may provide VISA strains with a “stealth” strategy to evade detection by the host immune system. 相似文献
992.
Sonja Schauer Regina Sommer Andreas H. Farnleitner Alexander K. T. Kirschner 《Applied and environmental microbiology》2012,78(20):7369-7375
A new protocol for rapid, specific, and sensitive cell-based quantification of Vibrio cholerae/Vibrio mimicus in water samples was developed. The protocol is based on catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) in combination with solid-phase cytometry. For pure cultures, we were able to quantify down to 6 V. cholerae cells on one membrane with a relative precision of 39% and down to 12 cells with a relative precision of 17% after hybridization with the horseradish peroxidase (HRP)-labeled probe Vchomim1276 (specific for V. cholerae and V. mimicus) and signal amplification. The corresponding position of the probe on the 16S rRNA is highly accessible even when labeled with HRP. For the first time, we were also able to successfully quantify V. cholerae/V. mimicus via solid-phase cytometry in extremely turbid environmental water samples collected in Austria. Cell numbers ranged from 4.5 × 101 cells ml−1 in the large saline lake Neusiedler See to 5.6 × 104 cells ml−1 in an extremely turbid shallow soda lake situated nearby. We therefore suggest CARD-FISH in combination with solid-phase cytometry as a powerful tool to quantify V. cholerae/V. mimicus in ecological studies as well as for risk assessment and monitoring programs. 相似文献
993.
Genetic manipulation of floral pigmentation genes 总被引:4,自引:0,他引:4
Joseph N. M. Mol Antoine R. Stuitje Alexander van der Krol 《Plant molecular biology》1989,13(3):287-294
994.
Alexander Kieneke Wilko H. Ahlrichs Pedro Martínez Arbizu Thomas Bartolomaeus 《Zoomorphology》2008,127(1):1-20
In an attempt to obtain detailed information on the entire protonephridial system in Gastrotricha, we have studied the protonephridial
ultrastructure of two paucitubulatan species, Xenotrichula carolinensis syltensis and Chaetonotus maximus by means of complete sets of ultrathin sections. In spite of some differences in detail, the morphology of protonephridia
in both examined species shows a common pattern: Both species have one pair of protonephridia that consist of a bicellular
terminal organ, a voluminous, aciliar canal cell and an adjacent, aciliar nephridiopore cell. The terminal organ consists
of two monociliar terminal cells each with a distal cytoplasmic lobe. These lobes interdigitate and surround cilia and microvilli
of the terminal cells. Where both lobes interdigitate, a meandering cleft is formed that is covered by the filtration barrier.
We here term the entire structure composite filter. The elongated, in some regions convoluted protonephridial lumen opens
distally to the outside via a permanent nephridiopore. A comparison with the protonephridia of other species of the Gastrotricha
allows hypothesising the following autapomorphies of the Paucitubulata: The bicellular terminal organ with a composite filter,
the convoluted distal canal cell lumen and the absence of cilia, ciliary basal structures and microvilli within the canal
cell. Moreover, this comparative survey could confirm important characteristics of the protonephridial system assumed for
the ground pattern of Gastrotricha like, for example, the single terminal cell with one cilium surrounded by eight microvilli. 相似文献
995.
During the RNA World, organisms experienced high rates of genetic errors, which implies that there was strong evolutionary
pressure to reduce the errors’ phenotypical impact by suitably structuring the still-evolving genetic code. Therefore, the
relative rates of the various types of genetic errors should have left characteristic imprints in the structure of the genetic
code. Here, we show that, therefore, it is possible to some extent to reconstruct those error rates, as well as the nucleotide
frequencies, for the time when the code was fixed. We find evidence indicating that the frequencies of G and C in the genome
were not elevated. Since, for thermodynamic reasons, RNA in thermophiles tends to possess elevated G+C content, this result
indicates that the fixation of the genetic code occurred in organisms which were either not thermophiles or that the code’s
fixation occurred after the rise of DNA.
Supplementary Materials Original data and programs are available at the author’s web site: . 相似文献
996.
Arturo Zenone Alexander Kovalev Fabio Badalamenti Stanislav N. Gorb 《Restoration Ecology》2024,32(3):e14084
Seagrasses provide various ecosystem functions in coastal areas of the world. In the Mediterranean Sea, Posidonia oceanica is an endemic species threatened by several activities despite being protected by national and international laws. Currently, several transplanting initiatives have been carried out using different methods, among which those including seeds and seedlings are considered the most ecological and low-cost ones. Beach-cast fruits and seeds can be found in spring and their appearance can easily be reported, through a citizen science approach, by the community. One of the obstacles in using these methods is identifying the best substrate in which to place P. oceanica seeds to facilitate root adhesion of the seedlings prior to their transplantation into the sea. In the present study, we analyzed, using a 3D surface optical microscope, the roughness of natural rocks to identify the availability of specific roughness ranges suitable for adhesion and root anchoring of P. oceanica seedlings. Conventional roughness parameters and roughness power spectral density were calculated for the inner and outer surfaces of 9 different rock samples. Among the rock samples examined, the calcarenitic ones and in particular marsala calcarenite, due to the presence of the “ideal roughness for seedlings” can be considered one of the best consolidated substrates to be used for the construction of ad hoc devices on which plantlet of P. oceanica can grow for the purpose of restoration. 相似文献
997.
The trans-Golgi network (TGN) is one of the main, if not the main, sorting stations in the process of intracellular protein trafficking.
It is therefore of central importance to understand how the key players in the TGN-based sorting and delivery process, the
post-Golgi carriers (PGCs), form and function. Over the last few years, modern morphological approaches have generated new
insights into the questions of PGC biogenesis, structure and dynamics. Here, we present a view by which the “lifecycle” of
a PGC consists of several distinct stages: the formation of TGN tubular export domains (where different cargoes are segregated
from each other and from the Golgi enzymes); the docking of these tubular domains onto molecular motors and their extrusion
towards the cell periphery along microtubules; the fission of the forming PGC from the donor membrane; and the delivery of
the newly formed PGC to its specific acceptor organelle. It is now important to add the many molecular machineries that have
been described as operating at the TGN to this “morphofunctional map” of the TGN export process. 相似文献
998.
Effects of chronic food restriction and treatments with leptin or ghrelin on different reproductive parameters of male rats 总被引:1,自引:0,他引:1
Sirotkin AV Chrenková M Nitrayová S Patras P Darlak K Valenzuela F Pinilla L Tena-Sempere M 《Peptides》2008,29(8):1362-1368
The existence of a close relationship between energy status and reproductive function is well-documented, especially in females, but its underlying mechanisms remain to be fully unfolded. This study aimed to examine the effects of restriction of daily calorie intake, as well as chronic treatments with the metabolic hormones leptin and ghrelin, on the secretion of different reproductive hormones, namely pituitary gonadotropins and prolactin, as well as testosterone, in male rats. Restriction (50%) in daily food intake for 20 days significantly reduced body weight as well as plasma PRL and T levels, without affecting basal LH and FSH concentrations and testicular weight. Chronic administration of leptin to rats fed ad libitum increased plasma PRL levels and decreased circulating T, while it did not alter other hormonal parameters under analysis. In contrast, in rats subjected to 50% calorie restriction, leptin administration increased plasma T levels and reduced testis weight. Conversely, ghrelin failed to induce major hormonal changes but tended to increase testicular weight in fed animals, while repeated ghrelin injections in food-restricted males dramatically decreased plasma LH and T concentrations and reduced testis weight. In sum, we document herein the isolated and combined effects of metabolic stress (50% food restriction) and leptin or ghrelin treatments on several reproductive hormones in adult male rats. Overall, our results further stress the impact and complex way of action of different metabolic cues, such as energy status and key hormones, in reproductive function also in the male. 相似文献
999.
Timothy A. McCaffrey Constantine Tziros Jannet Lewis Richard Katz Robert Siegel William Weglicki Jay Kramer I. Tong Mak Ian Toma Liang Chen Elizabeth Benas Alexander Lowitt Shruti Rao Linda Witkin Yi Lian Yinglei Lai Zhaoqing Yang Sidney W. Fu 《International journal of biological sciences》2013,9(4):350-360
1000.
Vladimir Sentchilo Antonia P Mayer Lionel Guy Ryo Miyazaki Susannah Green Tringe Kerrie Barry Stephanie Malfatti Alexander Goessmann Marc Robinson-Rechavi Jan R van der Meer 《The ISME journal》2013,7(6):1173-1186
Plasmids have long been recognized as an important driver of DNA exchange and genetic innovation in prokaryotes. The success of plasmids has been attributed to their independent replication from the host''s chromosome and their frequent self-transfer. It is thought that plasmids accumulate, rearrange and distribute nonessential genes, which may provide an advantage for host proliferation under selective conditions. In order to test this hypothesis independently of biases from culture selection, we study the plasmid metagenome from microbial communities in two activated sludge systems, one of which receives mostly household and the other chemical industry wastewater. We find that plasmids from activated sludge microbial communities carry among the largest proportion of unknown gene pools so far detected in metagenomic DNA, confirming their presumed role of DNA innovators. At a system level both plasmid metagenomes were dominated by functions associated with replication and transposition, and contained a wide variety of antibiotic and heavy metal resistances. Plasmid families were very different in the two metagenomes and grouped in deep-branching new families compared with known plasmid replicons. A number of abundant plasmid replicons could be completely assembled directly from the metagenome, providing insight in plasmid composition without culturing bias. Functionally, the two metagenomes strongly differed in several ways, including a greater abundance of genes for carbohydrate metabolism in the industrial and of general defense factors in the household activated sludge plasmid metagenome. This suggests that plasmids not only contribute to the adaptation of single individual prokaryotic species, but of the prokaryotic community as a whole under local selective conditions. 相似文献