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61.
62.
Taras Antal Heta Mattila Marja Hakala-Yatkin Taina Tyystjärvi Esa Tyystjärvi 《Planta》2010,232(4):887-898
Nitrogen deficiency diminishes consumption of photosynthates in anabolic metabolism. We studied adjustments of the photosynthetic
machinery in nitrogen-deficient bean plants and found four phenomena. First, the number of chloroplasts per cell decreased.
Chloroplasts of nitrogen starved leaves contained less pigments than those of control leaves, but the in vitro activities
of light reactions did not change when measured on chlorophyll basis. Second, nitrogen deficiency induced cyclic electron
transfer. The amounts of Rubisco and ferredoxin-NADP+ reductase decreased in nitrogen starved plants. Low activities of these enzymes are expected to lead to increase in reduction
of oxygen by photosystem I. However, diaminobenzidine staining did not reveal hydrogen peroxide production in nitrogen starved
plants. Measurements of far-red-light-induced redox changes of the primary donor of photosystem I suggested that instead of
producing oxygen radicals, nitrogen starved plants develop a high activity of cyclic electron transport that competes with
oxygen for electrons. Nitrogen starvation led to decrease in photochemical quenching and increase in non-photochemical quenching,
indicating that cyclic electron transport reduces the plastoquinone pool and acidifies the lumen. A third effect is redistribution
of excitation energy between the photosystems in favor of photosystem I. Thus, thylakoids of nitrogen starved plants appeared
to be locked in state 2, which further protects photosystem II by decreasing its absorption cross-section. As a fourth response,
the proportion of non-QB-reducing photosystem II reaction centers increased and the redox potential of the QB/QB− pair decreased by 25 mV in a fraction of photosystem II centers of nitrogen starved plants. 相似文献
63.
The aim of this study was to unravel the historical biogeography of the speciose land snail genus Chondrina. To this end phylogenetic hypotheses were tested using mitochondrial DNA sequence data.Mitochondrial DNA sequences of the Cytochrome Oxidase subunit I region were obtained for 89 individuals, representing just over 70% of the extant Chondrina species. The extent of molecular genetic diversity and phylogeographical patterns were investigated by using neighbour joining, parsimony and bayesian methods for phylogeny reconstructions. The resulting data were used to infer historical biogeographical patterns for the genus Chondrina.The three phylogenetic methods yielded congruent topologies for the phylogeny reconstruction. Six clades were identified, each of which with at least one taxon that is known from the Iberian peninsula. The most parsimonious scenario indicates at least three waves of dispersal out of the Iberian peninsula into the North and East of Europe and Northern Africa.The phylogenetic relationships combined with the distributional patterns of the various species, indicate that only vicariance events cannot explain the actual situation. Apparently, separate waves of dispersal and subsequent speciation occurred, each time starting from the southwestern part of the present generic range. Until recently, this was obscured by repetitive cases of parallel or convergent evolution in shell characters, as became evident with the use of molecular methods. 相似文献
64.
Koski Marja; Moller Eva F.; Maar Marie; Visser Andre W. 《Journal of plankton research》2007,29(7):641-654
Despite the potential importance of zooplankton in degradationof marine snow, the association of colonising zooplankton withdiscarded appendicularian houses has not been investigated innorthern areas. We sampled the vertical distributions of appendicularians,houses and potential zooplankton colonisers at two stationsin the central North Sea during late summer. In addition, grazingexperiments were performed with the copepod Microsetella norvegica,which was assumed to be the main contributor to house degradation.The results were used in (i) inverse modelling, to estimatethe factors which were significant in shaping the vertical distributionof houses and (ii) calculations to estimate potential housedegradation rates. M. Norvegica was able to feed on appendicularianhouses, with feeding rates up to 0.42 g C (g C)1 day1(0.14 µg C ind.1 day1). The model resultssuggested that the vertical distribution of houses was shapedby sinking of houses, bacterial degradation and feeding of M.norvegica and invertebrate larvae. The estimated community degradationrate by M. norvegica was low, whereas invertebrate larvae haddegradation rates close to bacterial degradation. We concludethat at the typical concentrations of M. norvegica in the NorthSea (104 ind. m2), its role in marine snow degradationis likely to be small. Degradation by other zooplankton groups,such as invertebrate larvae, can, however, be substantial. 相似文献
65.
Consider an infectious disease which is endemic in a population divided into several large sub-communities that interact. Our aim is to understand how the time to extinction is affected by the level of interaction between communities. We present two approximations of the expected time to extinction in a population consisting of a small number of large sub-communities. These approximations are described for an SIR epidemic model, with focus on diseases with short infectious period in relation to life length, such as childhood diseases. Both approximations are based on Markov jump processes. Simulations indicate that the time to extinction is increasing in the degree of interaction between communities. This behaviour can also be seen in our approximations in relevant regions of the parameter space. 相似文献
66.
Arnell R Johannisson R Lindholm J Fornstedt T Ersson B Ballagi A Caldwell K 《Preparative biochemistry & biotechnology》2007,37(4):309-321
The steroid 9alpha-hydroxylase gene has been cloned from Mycobacterium smegmatis into Escherichia coli BL21. Progesterone added to bioreactors was subjected to in vivo transformation into 9alpha-hydroxyprogesterone. In 7 days, 43.6 mg 9alpha-hydroxyprogesterone was formed from 53.8 mg/L progesterone. The enzyme also has shown evidence of processing 4-androstene-3,17-dione in vivo. An extensive analytical method development, including LLE, HPLC-DAD, MS, and NMR was performed to verify the product and to enable a quantitative analysis. Protocols for analytical and preparative separation have been developed, using binaphtol as internal standard. Both the growth pattern and the bioconversion rate were unaffected by the presence of binaphtol in the bioreactor. The enzyme was purified by immobilised metal affinity and ion exchange chromatography, resulting in low in vitro activity. 相似文献
67.
Oderda G Shcherbakov P Bontems P Urruzuno P Romano C Gottrand F Gómez MJ Ravelli A Gandullia P Roma E Cadranel S De Giacomo C Canani RB Rutigliano V Pehlivanoglu E Kalach N Roggero P Celinska-Cedro D Drumm B Casswall T Ashorn M Arvanitakis SN;European Pediatric Task Force on Helicobacter pylori 《Helicobacter》2007,12(2):150-156
BACKGROUND AND AIM: Data on the eradication treatment for childhood Helicobacter pylori are scanty. A register was established on the European Society for Pediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) website to collect data on treatment performed by European pediatricians to ascertain what is practiced in the field. SUBJECTS: From January 2001 to December 2002, information on 597 children were entered by 23 European Centers, but only data of 518 treated children were completed and analyzed (86.7%, 262 male subjects, median age 9 years, range 1-14). According to their nationality, 226 children were from Southern Europe, 132 from Eastern Europe, 68 from Western Europe, and 4 from northern Europe, 68 from North Africa, and 20 from Asia. At endoscopy, 454 children had gastritis and 64 had ulcer (12.3%). Antibiotic sensitivity, tested in 361 cases, revealed 18% clarithromycin-resistant and 19% metronidazole-resistant H. pylori strains. RESULTS: Treatment was performed for 1 week in 388 and for 2 weeks in 130 children. Antibiotics were associated with proton pump inhibitors (PPI) in 345 and with bismuth in 121 children. Triple therapy was given to 485 children, dual therapy to 26, quadruple to 7. Follow-up data, by (13)C-Urea-Breath Test or histology or both, were available for 480 children. Overall eradication rate was 65.6%, significantly higher in children with ulcer (79.7%) than without (63.9%, p = .001). When given as first treatment, bismuth-containing triple therapies were more efficacious than PPI-containing ones (77% versus 64%, p = .02, OR 1.88, 95% CI 1.1-3.3). Twenty-seven different treatment regimens were used, but only six were administered to at least 18 children (range 18-157). There was no difference between treatments given for 1 or 2 weeks, or given as first or second therapies. CONCLUSION: European pediatricians entering data in the register used 27 different regimens. Bismuth-containing therapies resulted in higher eradication rate. Omeprazole-containing triple therapies were the most used although their efficacy was low. Therapies recommended for adults do not appear to be suitable for children. 相似文献
68.
Genetic basis of skin appendage development 总被引:1,自引:0,他引:1
Mikkola ML 《Seminars in cell & developmental biology》2007,18(2):225-236
Morphogenesis of hair follicles, teeth, and mammary glands depends on inductive epithelial-mesenchymal interactions mediated by a conserved set of signalling molecules. The early development of different skin appendages is remarkably similar. Initiation of organogenesis is marked by the appearance of a local epithelial thickening, a placode, which subsequently invaginates to produce a bud. These early developmental stages require many of the same genes and signalling circuits and consequently alterations in them often cause similar phenotypes in several skin appendages. After the bud stage, these organs adopt diverse patterns of epithelial growth, reflected in the usage of more divergent genes in each. 相似文献
69.
Porphyromonas gingivalis is considered an important pathogen in periodontal disease. While this organism expresses a number of virulence factors, no study combining different virulence polymorphisms has, so far, been conducted. The occurrence of combined virulence (Cv) genotypes in 62 isolates of P. gingivalis was investigated from subjects displaying either chronic periodontitis or periodontal abscess. The Cv genotypes, based on gene variation of fimbriae (fimA), Lys-specific cystein proteinase (kgp) and Arg-specific cystein proteinase (prpR1/rgpA), were evaluated by PCR. The isolates were also subjected to capsular polysaccharide K-serotyping. A total of 18 Cv genotype variants based on fimA: kgp: rgpA were identified, of which II:I:A and II:II:A Cv genotypes (53.3%) were the two most frequently detected combinations. Moreover, 36% of the isolates were K-typeable, with the K6 serotype being the most prevalent (23%). Two isolates had the same genotype as the virulent strain W83. The results indicate that chronic periodontitis is not associated with a particularly virulent clonal type. A highly virulent genotype (e.g. strain W83) of P. gingivalis can be found in certain periodontitis patients. 相似文献
70.
Palmroth MR Koskinen PE Kaksonen AH Münster U Pichtel J Puhakka JA 《Biodegradation》2007,18(6):769-782
In the current study, the microbial ecology of weathered hydrocarbon and heavy metal contaminated soil undergoing phytoremediation
was studied. The relationship of functional diversity, measured as carbon source utilisation in Biolog plates and extracellular
enzymatic activities, and genetic diversity of bacteria was evaluated. Denaturing gradient gel electrophoresis was used for
community analyses at the species level. Bulk soil and rhizosphere soil from pine and poplar plantations were analysed separately
to determine if the plant rhizosphere impacted hydrocarbon degradation. Prevailing microbial communities in the field site
were both genetically and metabolically diverse. Furthermore, both tree rhizosphere and fertilisation affected the compositions
of these communities and increased activities of extracellular aminopeptidases. In addition, the abundance of alkane hydroxylase
and naphthalene dioxygenase genes in the communities was low, but the prevalence of these genes was increased by the addition
of bioavailable hydrocarbons. Tree rhizosphere communities had greater hydrocarbon degradation potential than those of bulk
soil. Hydrocarbon utilising communities were dominated generally by the species Ralstonia eutropha and bacteria belonging to the genus Burkholderia. Despite the presence of viable hydrocarbon-degrading microbiota, decomposition of hydrocarbons from weathered hydrocarbon
contaminated soil over four years, regardless of the presence of vegetation, was low in unfertilised soil. Compost addition
enhanced the removal of hydrocarbons. 相似文献