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941.
Association of Vibrio cholerae O1 El Tor and O139 Bengal with the Copepods Acartia tonsa and Eurytemora affinis 下载免费PDF全文
The association of Vibrio cholerae with zooplankton has been suggested as an important factor in transmission of human epidemic cholera, and the ability to colonize zooplankton surfaces may play a role in the temporal variation and predominance of the two different serogroups (V. cholerae O1 El Tor and O139) in the aquatic environment. To date, interactions between specific serogroups and species of plankton remain poorly understood. Laboratory microcosm experiments were carried out to compare quantitatively the colonization of two copepod species, Acartia tonsa and Eurytemora affinis, by each of the epidemic serogroups. V. cholerae O1 consistently achieved higher abundances than V. cholerae O139 in colonizing adults of each copepod species as well as the multiple life stages of E. affinis. This difference in colonization may be significant in the general predominance of V. cholerae O1 in cholera epidemics in rural Bangladesh where water supplies are taken directly from the environment. 相似文献
942.
The intra-annual variability of soft-bottom macrobenthos abundance patterns in the North Channel of the Seine estuary 总被引:2,自引:0,他引:2
Nicolas Desroy Anne-Laure Janson Lionel Denis Gregory Charrier Sandric Lesourd Jean-Claude Dauvin 《Hydrobiologia》2007,588(1):173-188
Temporal and spatial variability of the Abra alba–Pectinaria koreni and Macoma balthica communities was examined in the northern part of the Seine estuary (North Channel) over different space and time scales in
order to assess the role that the hydrologic regime and/or anthropogenic influences play in defining benthic communities over
time. Sediment in the North Channel displayed strong spatial and temporal variability, sustained by intense sediment transport
episodes. Total macrobenthic abundances ranged widely on the course of the year and there was no evidence of a seasonal signal
for the density fluctuations, whatever the spatial scale considered. The bio-sedimentary dynamics can be divided into two
periods: the first corresponds to the high flow rate period (January–May) during which fauna is influenced by fine silt/clay
deposition, and the second to the low flow rate period (June–December) during which sandy deposits prevail. Despite the absence
of significant correlations between sediment composition and abundance, episodes of sediment transport seem to be an important
structuring mechanism in the Seine estuary. As a consequence, the faunal composition varied throughout the year. The winter
and spring fauna, characterised by species living on muddy fine-sands or muds, were enriched during the summer and autumn
by species living in clean fine sand, such as Donax vittatus, Nephtys cirrosa or Spio decoratus, mainly represented by adult individuals. Secondary settlement of drifters may explain the rapid structuration of assemblages
a few days after the sandy deposits. Our results suggest the importance of the bentho-pelagic coupling, primarily induced
by the sedimentary instability, on the macrobenthic fauna dynamics. The intra-annual variability of assemblages at the mouth
of the Seine river and the silted situation of the North Channel might simply be the result of the silting up and alteration
of the inner estuary, generated by several decades of man-made modifications and natural processes. 相似文献
943.
The protonation constants of 1,3,5-trideoxy-1,3,5-tris(2-hydroxyl-benzyl)amino-cis-inositol (thci) in I = 1 M (NaClO4) were determined to be: pKa1 5.96 ± 0.03, pKa2 7.21 ± 0.01, pKa3 8.32 ± 0.07, pKa4 8.95 ± 0.06. The solvent extraction studies were consistent with the formation of the Ln(thci)3+ and complexes. The log of the stability constants (log β1 and log β2) at 25 °C in 1 M (NaClO4) at pH 4 for formation of these complexes are reported. Laser luminescence measurements of the 7F0-5D0 transition of Eu(III) complexed by thci indicated two species. The shifts in the peaks relative to that of Eu(aq)3+ were comparable to the values reported for other complexes of Eu(III) with organic ligands, but the intensities were greater. Luminescence lifetime measurements of the fluorescence spectra indicated that the complex has 5 inner sphere water molecules bound to the Eu(III) cation at pH 6.71-8.52. This was consistent with bidentate chelation of Eu(III) with each thci molecule. gaussian view energy calculations indicated bonding for M(III) to the amino and hydroxyl groups of the cyclohexanetriol and (2-hydroxybenzyl)amino moieties in the Ln(thci)3+ complex. 相似文献
944.
PduL is an evolutionarily distinct phosphotransacylase involved in B12-dependent 1,2-propanediol degradation by Salmonella enterica serovar typhimurium LT2 下载免费PDF全文
Liu Y Leal NA Sampson EM Johnson CL Havemann GD Bobik TA 《Journal of bacteriology》2007,189(5):1589-1596
Salmonella enterica degrades 1,2-propanediol (1,2-PD) in a coenzyme B(12)-dependent manner. Previous enzymatic assays of crude cell extracts indicated that a phosphotransacylase (PTAC) was needed for this process, but the enzyme involved was not identified. Here, we show that the pduL gene encodes an evolutionarily distinct PTAC used for 1,2-PD degradation. Growth tests showed that pduL mutants were unable to ferment 1,2-PD and were also impaired for aerobic growth on this compound. Enzyme assays showed that cell extracts from a pduL mutant lacked measurable PTAC activity in a background that also carried a pta mutation (the pta gene was previously shown to encode a PTAC enzyme). Ectopic expression of pduL corrected the growth defects of a pta mutant. PduL fused to eight C-terminal histidine residues (PduL-His(8)) was purified, and its kinetic constants were determined: the V(max) was 51.7 +/- 7.6 micromol min(-1) mg(-1), and the K(m) values for propionyl-PO(4)(2-) and acetyl-PO(4)(2-) were 0.61 and 0.97 mM, respectively. Sequence analyses showed that PduL is unrelated in amino acid sequence to known PTAC enzymes and that PduL homologues are distributed among at least 49 bacterial species but are absent from the Archaea and Eukarya. 相似文献
945.
Contribution of the FtsQ transmembrane segment to localization to the cell division site 总被引:1,自引:0,他引:1 下载免费PDF全文
Scheffers DJ Robichon C Haan GJ den Blaauwen T Koningstein G van Bloois E Beckwith J Luirink J 《Journal of bacteriology》2007,189(20):7273-7280
The Escherichia coli cell division protein FtsQ is a central component of the divisome. FtsQ is a bitopic membrane protein with a large C-terminal periplasmic domain. In this work we investigated the role of the transmembrane segment (TMS) that anchors FtsQ in the cytoplasmic membrane. A set of TMS mutants was made and analyzed for the ability to complement an ftsQ mutant. Study of the various steps involved in FtsQ biogenesis revealed that one mutant (L29/32R;V38P) failed to functionally insert into the membrane, whereas another mutant (L29/32R) was correctly assembled and interacted with FtsB and FtsL but failed to localize efficiently to the cell division site. Our results indicate that the FtsQ TMS plays a role in FtsQ localization to the division site. 相似文献
946.
The alanine racemase of Mycobacterium smegmatis is essential for growth in the absence of D-alanine 下载免费PDF全文
Alanine racemase, encoded by the gene alr, is an important enzyme in the synthesis of d-alanine for peptidoglycan biosynthesis. Strains of Mycobacterium smegmatis with a deletion mutation of the alr gene were found to require d-alanine for growth in both rich and minimal media. This indicates that alanine racemase is the only source of d-alanine for cell wall biosynthesis in M. smegmatis and confirms alanine racemase as a viable target gene for antimycobacterial drug development. 相似文献
947.
A Novel indole compound that inhibits Pseudomonas aeruginosa growth by targeting MreB is a substrate for MexAB-OprM 下载免费PDF全文
Robertson GT Doyle TB Du Q Duncan L Mdluli KE Lynch AS 《Journal of bacteriology》2007,189(19):6870-6881
Drug efflux systems contribute to the intrinsic resistance of Pseudomonas aeruginosa to many antibiotics and biocides and hamper research focused on the discovery and development of new antimicrobial agents targeted against this important opportunistic pathogen. Using a P. aeruginosa PAO1 derivative bearing deletions of opmH, encoding an outer membrane channel for efflux substrates, and four efflux pumps belonging to the resistance nodulation/cell division class including mexAB-oprM, we identified a small-molecule indole-class compound (CBR-4830) that is inhibitory to growth of this efflux-compromised strain. Genetic studies established MexAB-OprM as the principal pump for CBR-4830 and revealed MreB, a prokaryotic actin homolog, as the proximal cellular target of CBR-4830. Additional studies establish MreB as an essential protein in P. aeruginosa, and efflux-compromised strains treated with CBR-4830 transition to coccoid shape, consistent with MreB inhibition or depletion. Resistance genetics further suggest that CBR-4830 interacts with the putative ATP-binding pocket in MreB and demonstrate significant cross-resistance with A22, a structurally unrelated compound that has been shown to promote rapid dispersion of MreB filaments in vivo. Interestingly, however, ATP-dependent polymerization of purified recombinant P. aeruginosa MreB is blocked in vitro in a dose-dependent manner by CBR-4830 but not by A22. Neither compound exhibits significant inhibitory activity against mutant forms of MreB protein that bear mutations identified in CBR-4830-resistant strains. Finally, employing the strains and reagents prepared and characterized during the course of these studies, we have begun to investigate the ability of analogues of CBR-4830 to inhibit the growth of both efflux-proficient and efflux-compromised P. aeruginosa through specific inhibition of MreB function. 相似文献
948.
949.
Rogers PA Chilian WM Bratz IN Bryan RM Dick GM 《American journal of physiology. Heart and circulatory physiology》2007,292(3):H1404-H1411
Previously, we demonstrated that coronary vasodilation in response to hydrogen peroxide (H(2)O(2)) is attenuated by 4-aminopyridine (4-AP), an inhibitor of voltage-gated K(+) (K(V)) channels. Using whole cell patch-clamp techniques, we tested the hypothesis that H(2)O(2) increases K(+) current in coronary artery smooth muscle cells. H(2)O(2) increased K(+) current in a concentration-dependent manner (increases of 14 +/- 3 and 43 +/- 4% at 0 mV with 1 and 10 mM H(2)O(2), respectively). H(2)O(2) increased a conductance that was half-activated at -18 +/- 1 mV and half-inactivated at -36 +/- 2 mV. H(2)O(2) increased current amplitude; however, the voltages of half activation and inactivation were not altered. Dithiothreitol, a thiol reductant, reversed the effect of H(2)O(2) on K(+) current and significantly shifted the voltage of half-activation to -10 +/- 1 mV. N-ethylmaleimide, a thiol-alkylating agent, blocked the effect of H(2)O(2) to increase K(+) current. Neither tetraethylammonium (1 mM) nor iberiotoxin (100 nM), antagonists of Ca(2+)-activated K(+) channels, blocked the effect of H(2)O(2) to increase K(+) current. In contrast, 3 mM 4-AP completely blocked the effect of H(2)O(2) to increase K(+) current. These findings lead us to conclude that H(2)O(2) increases the activity of 4-AP-sensitive K(V) channels. Furthermore, our data support the idea that 4-AP-sensitive K(V) channels are redox sensitive and contribute to H(2)O(2)-induced coronary vasodilation. 相似文献
950.
Egbertson MS Moritz HM Melamed JY Han W Perlow DS Kuo MS Embrey M Vacca JP Zrada MM Cortes AR Wallace A Leonard Y Hazuda DJ Miller MD Felock PJ Stillmock KA Witmer MV Schleif W Gabryelski LJ Moyer G Ellis JD Jin L Xu W Braun MP Kassahun K Tsou NN Young SD 《Bioorganic & medicinal chemistry letters》2007,17(5):1392-1398
A 1,6-naphthyridine inhibitor of HIV-1 integrase has been discovered with excellent inhibitory activity in cells, good pharmacokinetics, and an excellent ability to inhibit virus with mutant enzyme. 相似文献