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991.
We present an analysis of song type differences between populations of seven forest weaver (Ploceus bicolor) subspecies. Phonology and syntax of the melodious parts of song types differ between these populations to the same extent
as they differ between population-specific dialects within a subspecies. Phonological and syntactical song features are socially
transmitted; they can be transmitted even between representatives of taxonomically different subspecies. The Harsh Call, a
complex element embedded in the melody, is of similar structure in populations of four South African subspecies, but shows
markedly different characteristics in populations of the subspecies from Kenya and Cameroon. Song differences between populations
are suggested to result from cultural drift and geographic isolation. A correspondence between genetically determined morphological
structures on the one hand and socially transmitted song structure on the other seems to be a coincidence due to geographic
separation. 相似文献
992.
993.
Two GacA-dependent small RNAs modulate the quorum-sensing response in Pseudomonas aeruginosa 总被引:3,自引:0,他引:3
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Kay E Humair B Dénervaud V Riedel K Spahr S Eberl L Valverde C Haas D 《Journal of bacteriology》2006,188(16):6026-6033
In Pseudomonas aeruginosa, the GacS/GacA two-component system positively controls the quorum-sensing machinery and the expression of extracellular products via two small regulatory RNAs, RsmY and RsmZ. An rsmY rsmZ double mutant and a gacA mutant were similarly impaired in the synthesis of the quorum-sensing signal N-butanoyl-homoserine lactone, the disulfide bond-forming enzyme DsbA, and the exoproducts hydrogen cyanide, pyocyanin, elastase, chitinase (ChiC), and chitin-binding protein (CbpD). Both mutants showed increased swarming ability, azurin release, and early biofilm development. 相似文献
994.
The catabolism of citronellol and geraniol [acyclic terpene utilization (Atu) pathway] was investigated in Pseudomonas citronellolis. A 13.3-kb genomic DNA fragment was cloned and harboured a putative regulator gene atuR and a gene cluster consisting of eight genes (atuABCDEFGH). Sequence analysis of the atu gene products showed a high degree of amino acid similarity (78-91% identity) to products of a similar gene cluster previously identified in Pseudomonas aeruginosa. Insertion mutagenesis in atuA resulted in inability of the bacteria to utilize acyclic terpenes as a sole source of carbon and energy and confirmed the involvement of atuA in the Atu pathway. Western blot analysis of wild-type and atuA mutant cells of P. citronellolis and P. aeruginosa for biotin-containing proteins enabled the identification of geranyl-CoA carboxylase (GCase), which is the key enzyme of the Atu pathway. GCase subunits were encoded by atuC and atuF. Putative functions for the other Atu proteins in the catabolic pathway of acyclic terpenes are discussed. 相似文献
995.
Falcone V Mihm D Neumann-Haefelin D Costa C Nguyen T Pozzi G Ricci S 《FEMS immunology and medical microbiology》2006,48(1):116-122
A conserved fragment comprising amino acid residues 130-230 of the G glycoprotein of human respiratory syncytial virus subtype A was expressed in the commensal bacterium Streptococcus gordonii. Recombinant streptococci displaying the G domain at the cell surface were used to immunize mice via both parenteral and mucosal routes. Subcutaneous immunization induced respiratory syncytial virus-specific serum immunoglobin G (IgG) capable of partially controlling virus replication in the lungs. Intranasal immunization with live bacteria stimulated the production of IgA against both the whole virus and the G domain in serum and bronchoalveolar fluid. Upon challenge, immunized animals had significantly lower virus titres in the lungs than the controls. Our results show for the first time that the G domain-expressing S. gordonii strain elicits both systemic and mucosal immunity that reduced respiratory syncytial virus replication in the lungs of mice. 相似文献
996.
Andreas Hansch Ingrid Hilger Dieter Sauner Michael Haas Joachim Böttcher Werner A. Kaiser 《Journal of Experimental Animal Science》2006,43(3):129-139
The aim of the study was to visualize chronic experimental arthritis with near-infrared fluorescence imaging (NIRF) in a murine experimental arthritis model of rheumatoid arthritis (RA) (flare-up arthritis). The flare-up arthritis model is a modification of the primary antigen-induced arthritis (AIA) model. NIRF was done for two preparations of the fluorochrome Cy5.5, one native and the other albumin conjugated. Histological features of flare-up arthritis were evaluated.AIA was induced in 16 mice (strain C57/Bl6); flare-up arthritis was induced in a subgroup of eight. On day 7 after induction of flare-up arthritis, four mice received 50 nmol/kg native dye and four mice equimolar concentrations of the dye as albumin-dye conjugate intravenously. NIRF imaging was performed immediately before injection (baseline) and until 72 h thereafter. Arthritis severity was evaluated histologically for primary AIA and flare-up arthritis mice.NIRF imaging revealed higher fluorochrome uptake in all inflamed knees compared to contralateral ones. The signal intensities induced by native Cy5.5 were higher than those generated by albumin-Cy5.5 conjugate. Histological evaluation of arthritic joints showed similar abnormalities in flare-up arthritis and in primary AIA joints.Imaging of flare-up arthritis in the near-infrared range was successful for both fluorochrome preparations, but albumin conjugation prior to injection does not improve the uptake of dye in arthritic joints. Flare-up arthritis is a feasible model of chronic relapse of arthritis in human RA. 相似文献
997.
Wolinska J Bittner K Ebert D Spaak P 《Proceedings. Biological sciences / The Royal Society》2006,273(1596):1977-1983
Parasite driven time-lagged negative frequency-dependent selection of hosts has been studied in natural populations by following changes in host genotype frequencies over time. However, such dynamics have not been considered at higher taxonomic levels, for example, between parental species and their hybrids. In a field study on a Daphnia hybrid system, we observed that one Daphnia taxon first was relatively under-infected, but became over-infected after a strong increase in frequency. This finding is consistent with the idea of parasite evolution towards the most frequent host taxon. In two experiments, we investigated whether the assumptions made by a model of negative frequency-dependent selection apply to our host taxa system. First, we showed that the parasite can change the outcome of taxa competition and secondly, we confirmed that the over-infection of one host taxon observed in the field has a genetic basis. Our results indicate that the incorporation of host-parasite interactions at the species level may allow us to gain a more complete picture of forces driving dynamic taxa coexistence in Daphnia hybrid systems. More generally, we suggest that if hybrids coexist in sympatry with parental taxa, the infection patterns as observed under natural conditions may be rather temporal and unstable. 相似文献
998.
Stephen C. Maberly Lucy A. Ball John A. Raven Dieter Sültemeyer 《Journal of phycology》2009,45(5):1052-1061
Twelve species, representing 12 families of the chrysophytes sensu lato, were tested for their ability to take up inorganic carbon. Using the pH‐drift technique, CO2 compensation points generally varied between 1 and 20 μmol · L?1 with a mean concentration of 5 μmol · L?1. Neither pH nor alkalinity affected the CO2 compensation point. The concentration of oxygen had a relatively minor effect on CO2‐uptake kinetics, and the mean CO2 compensation point calculated from the kinetic curves was 3.6 μmol · L?1 at 10–15 kPa starting oxygen partial pressure and 3.8 μmol · L?1 at atmospheric starting oxygen partial pressure (21 kPa). Similarly, uptake kinetics were not affected by alkalinity, and hence concentration of bicarbonate. Membrane inlet mass spectrometry (MIMS) in the presence and absence of acetazolamide suggested that external carbonic anhydrase in Dinobryon sertularia Ehrenb. and Synura petersenii Korschikov was either very low or absent. Rates of net HCO3? uptake were very low (~5% of oxygen evolution) using MIMS and decreased rather than increased with increasing HCO3? concentration, suggesting that it was not a real uptake. The CO2 compensation points determined by MIMS for CO2 uptake and oxygen evolution were similar to those determined in pH‐drift and were >1 μmol · L?1. Overall, the results suggest that chrysophytes as a group lack a carbon‐concentrating mechanism (CCM), or an ability to make use of bicarbonate as an alternative source of inorganic carbon. The possible evolutionary and ecological consequences of this are briefly discussed. 相似文献
999.
1000.
Katrin Kuehnle Maria D. Ledesma Lucie Kalvodova Alicia E. Smith Arames Crameri Fabienne Skaanes-Brunner Karin M. Thelen Luka Kulic Dieter Lütjohann Frank L. Heppner Roger M. Nitsch M. Hasan Mohajeri 《Neurochemical research》2009,34(6):1167-1182
Cholesterol is a prominent modulator of the integrity and functional activity of physiological membranes and the most abundant
sterol in the mammalian brain. DHCR24-knock-out mice lack cholesterol and accumulate desmosterol with age. Here we demonstrate
that brain cholesterol deficiency in 3-week-old DHCR24−/− mice was associated with altered membrane composition including disrupted detergent-resistant membrane domain (DRM) structure.
Furthermore, membrane-related functions differed extensively in the brains of these mice, resulting in lower plasmin activity,
decreased β-secretase activity and diminished Aβ generation. Age-dependent accumulation and integration of desmosterol in
brain membranes of 16-week-old DHCR24−/− mice led to the formation of desmosterol-containing DRMs and rescued the observed membrane-related functional deficits. Our
data provide evidence that an alternate sterol, desmosterol, can facilitate processes that are normally cholesterol-dependent
including formation of DRMs from mouse brain extracts, membrane receptor ligand binding and activation, and regulation of
membrane protein proteolytic activity. These data indicate that desmosterol can replace cholesterol in membrane-related functions
in the DHCR24−/− mouse.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
An erratum to this article can be found at 相似文献