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281.
Microbial consumption of dimethyl sulfide and methanethiol in coastal marine sediments 总被引:3,自引:0,他引:3
Abstract: Samples were taken from oxic and anoxic zones of three ecosystems: a cyanobacterial mat, a diatom film and a carbonate sediment. Dimethylsulfide (DMS) concentrations were determined by headspace analysis of sediment slurries; maximal amounts were in the upper 5–10 mm of the sediments of 20 μM (cyanobacterial mat), 8 μM (diatom film) and < 1 μM in the carbonate sediment. Dissolved DMS in the cyanobacterial mat, determined by centrifugation and cryogenic trapping, was about two orders of magnitude lower than from slurry estimations but its variation with depth was similar. CH3 SH concentrations in slurried samples, determined after treatment with tributylphosphine, ranged from 2 to 7 μM in the diatom mat and was below the limit of detection (< 0.1 μM) in the carbonate sediment. MPN counts of bacteria that grew on DMS under oxic and anoxic (nitrate added) conditions were determined at all three sites. Aerobic DMS utilizers peaked in the surface and decreased with depth, while the population of anaerobic DMS utilizers was relatively constant in the top 20 mm. Populations of DMS utilizers were highest in the cyanobacterial mat and lowest in the carbonate sediment. MPN's of thiosulfate utilizers, aerobic and anaerobic (nitrate added) were determined in the cyanobacterial mat. Populations of aerobic and anaerobic S2 O3 2− utilizers were similar throughout the top 20 mm and comparable to those of DMS utilizers in the top 5 mm, but higher by about 100-fold below that zone. DMS and CH3 SH consumption rates were measured in slurries of sediments and aerobic rates were similar or only slightly higher than anaerobic rates; the latter were stimulated by nitrate. 相似文献
282.
Romain Leroy Marie-Noël de Visscher Oudou Halidou Amadou Boureima 《Biodiversity and Conservation》2009,18(10):2663-2677
The giraffe population (Giraffa camelopardalis) in Niger is the last representative of the peralta sub-species which lived throughout West Africa at the beginning of the twentieth century. Protected since the 1970s, giraffes
cohabit with humans in cultivated landscapes. This may not have appeared to pose many problems in the past, but the relationship
between farmers and giraffes has deteriorated with the expansion of cultivated land and that of the giraffe population, with
reported cases of giraffes damaging crops. A survey was conducted in all the affected villages in the Kouré area to establish
the nature, severity and distribution of the damage and to evaluate the local populations’ perception of the problem. Cowpeas
are fed upon in the field at harvest time and in the granaries, as well as ripe mangoes, during the most critical period for
giraffes’ nutrition. The vast majority of farmers interviewed consider giraffes to be rather a problem in spite of tourism
revenues they can obtain from them. This opinion has individually little correlation with damage rate on crops or easy access
to tourism revenues. The damage risk factors are first and foremost considered as uncontrollable by the farmers, even if technical
protection measures could easily be put in place locally. The inter-relationships between the socio-economic context and the
way the problem is perceived are discussed. 相似文献
283.
Characteristics and turnover of exopolymeric substances in a hypersaline microbial mat 总被引:2,自引:0,他引:2
Olivier Braissant Alan W. Decho Kristen M. Przekop Kimberley L. Gallagher Christina Glunk Christophe Dupraz & Pieter T. Visscher 《FEMS microbiology ecology》2009,67(2):293-307
The properties and microbial turnover of exopolymeric substances (EPS) were measured in a hypersaline nonlithifying microbial mat (Eleuthera, Bahamas) to investigate their potential role in calcium carbonate (CaCO3 ) precipitation. Depth profiles of EPS abundance and enzyme activities indicated that c . 80% of the EPS were turned over in the upper 15–20 mm. Oxic and anoxic mat homogenates amended with low-molecular-weight (LMW) organic carbon, sugar monomers, and different types of EPS revealed rapid consumption of all substrates. When comparing the consumption of EPS with that of other substrates, only marginally longer lag times and lower rates were observed. EPS (5–8%) were readily consumed during the conversion of labile to refractory EPS. This coincided with a decrease in glucosidase activity and a decrease in the number of acidic functional groups on the EPS. Approximately half of the calcium bound to the EPS remained after 10 dialyses steps. This tightly bound calcium was readily available to precipitate as CaCO3 . We present a conceptual model in which LMW organic carbon complexed with the tightly bound calcium is released upon enzyme activity. This increases alkalinity and creates binding sites for carbonate and allows CaCO3 to precipitate. Therefore, this model explains interactions between EPS and CaCO3 precipitation, and underscores the critical role of aerobic and anaerobic microorganisms in early diagenesis and lithification processes. 相似文献
284.
M. Luciano F. Miyajima P. A. Lind T. C. Bates M. Horan S. E. Harris M. J. Wright W. E. Ollier C. Hayward N. Pendleton A. J. Gow P. M. Visscher J. M. Starr I. J. Deary N. G. Martin and A. Payton 《Genes, Brain & Behavior》2009,8(2):218-227
The association between DTNBP1 genotype and cognitive abilities was investigated in three population samples (1054 Scottish, 1806 Australian and 745 English) of varying age. There was evidence in each of the cohorts for association ( P < 0.05) to single nucleotide polymorphisms ( SNPs) and haplotypes previously shown to relate to cognition. By comparison with previous findings, these associations included measures of memory, and there was at best equivocal evidence of association with general cognitive ability. Of the SNPs typed in all three cohorts, rs2619528 and rs1011313 showed significant association with measures of executive function in two cohorts, rs1018381 showed significant association with verbal ability in one cohort and rs2619522 showed significance/marginal significance with tests of memory, speed and executive function in two cohorts. For all these SNPs, the direction and magnitude of the allelic effects were consistent between cohorts and with previous findings. In the English cohort, a previously untested SNP (rs742105) located in a distinct haplotype block upstream of the other SNPs showed the strongest significance ( P < 0.01) for measures of memory but weaker significance for general cognitive ability. Our results therefore support involvement of the dysbindin gene in cognitive function, but further work is needed to clarify the specific functional variants involved and the cognitive abilities with which they are associated. 相似文献
285.
286.
287.
The patterns of synonymous codon usage in 91 Drosophila melanogaster genes
have been examined. Codon usage varies strikingly among genes. This
variation is associated with differences in G+C content at silent sites,
but (unlike the situation in mammalian genes) these differences are not
correlated with variation in intron base composition and so are not easily
explicable in terms of mutational biases. Instead, those genes with high
G+C content at silent sites, resulting from a strong "preference" for a
particular subset of the codons that are mostly C- ending, appear to be the
more highly expressed genes. This suggests that G+C content is reduced in
sequences where selective constraints are weaker, as indeed seen in a
pseudogene. These and other data discussed are consistent with the effects
of translational selection among synonymous codons, as seen in unicellular
organisms. The existence of selective constraints on silent substitutions,
which may vary in strength among genes, has implications for the use of
silent molecular clocks.
相似文献
288.
Alan W. Schwartz J. Visscher C. G. Bakker J. Niessen 《Origins of life and evolution of the biosphere》1987,17(3-4):351-357
Activated derivatives of purine-containing deoxynucleoside- diphosphates spontaneously oligomerize to produce pyrophosphate-
linked oligodeoxynucleotide analogues. These analogues are of potential interest as models of primitive, polynucleotide precursors.
The efficiency of oligomerization (ImpdGpIm and ImpdApIm much greater than ImpdIpIm) appears to reflect a combination of stacking
forces and the specific geometric orientations of the stacked units. Under favorable conditions, chain lengths greater than
20 have been obtained for oligomers containing pdGp in the absence of a template. In the presence of a complementary template,
the activated derivatives of pdGp and pdAp oligomerize much more extensively. An acyclo-analogue of G has also been shown
to undergo template-directed oligomerization on poly(C). These observations suggest the possibility that primitive information
transfer might have evolved in much simpler systems and that this function was taken over by polynucleotides at a later stage
in evolution.
For the previous paper in this series see Schwartz and Orgel, 1985a. 相似文献
289.
A Computer-aided noninterfering on-line technique for monitoring oxygen-transfer characteristics during fermentation processes 总被引:1,自引:0,他引:1
Spriet JA Botterman J Buyser DR De Visscher PL Vandamme EJ 《Biotechnology and bioengineering》1982,24(7):1605-1621
The role of computers in the monitoring and control of fermentation processes has increased steadfastly. The ultimate utility of the machines will not depend on the availability of online sensors but also on the availability of techniques that combine direct measurements, leading towards estimates of variable closely related to the microbial process or its control. In this article, a methodology for on-line and noninterfering evaluation of the volumetric mass-transfer coefficient K(l)a is developed. A detailed presentation of the procedure, called "the static method," is given. Its feasibility is proved through implementation of the method on an antibiotic fermentation process. These experiments indicate that operator actions meant to modify the oxygen-transfer conditions can be checked on-line. The quantitative value of the static method is ascertained by comparing the experimental results with K(l)a estimates obtained with the "gassing-out" method. A sensitivity analysis was carried out, revealing the need for temperature and pressure corrections and showing that the precision of the oxygen analyzer determines the precision of the static method. 相似文献
290.
NICO PM. SMIT WIETE WESTERHOF WILMA J. MENKO NETTY M. VERBEEK STAN PAVEL 《Pigment cell & melanoma research》1995,8(1):19-27
Melanocyte cultures were established and maintained routinely in Ham's F-10 medium containing 12-O-tetradecanoyl-phorbol-13-acetate (TPA), isobutylmethylxanthine (IBMX), cholera toxin (CT) and fetal calf serum (FCS). Three serum substitutes (Ultroser-G, Nutridoma-Hu and Nutricyte-H) were tested in order to obtain a medium without FCS having a more constant composition. Melanocyte proliferation was examined in long-term culture experiments by in situ cell counts at different periods of time. Only with Ultroser-G (1-2%) was the proliferation of melanocytes maintained without both FCS and CT, whereas the addition of the other two serum substitutes resulted in stabilization of melanocyte densities in the cultures up to 28 days. In the medium containing 1% Ultroser-G and IBMX without TPA minimal or no increases in melanocyte density were found. Addition of basic fibroblast growth factor (bFGF, 1 ng/ml) to the medium without TPA resulted in a partial restimulation of growth in different experiments. In this system with 1% Ultroser-G and 1 ng/ml bFGF, IBMX could also be replaced by other factors (dbcAMP LTC4 and a purified form of α-melanocyte stimulating hormone). The culture medium with 1% Ultroser-G containing TPA and IBMX is now used for routine melanocyte culture. In this medium TPN/IBMX can easily be replaced by bFGF/dbcAMP with optimal growth stimulation. The combination bFGF/α-MSH and other more physiological stimulators offers an alternative to study responses of melanocytes in culture with respect to proliferation, metabolism, and phenotype. 相似文献