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91.
Timothy J. Fahey Joseph B. Yavitt John A. Pearson Dennis H. Knight 《Biogeochemistry》1985,1(3):257-275
Storage and flux of nitrogen were studied in several contrasting lodgepole pine (Pinus contorta spp.latifolia) forests in southeastern Wyoming. The mineral soil contained most of the N in these ecosystems (range of 315–860 g · m–2), with aboveground detritus (37.5–48.8g · m–2) and living biomass (19.5–24.0 g · m–2) storing much smaller amounts. About 60–70% of the total N in vegetation was aboveground, and N concentrations in plant tissues were unusually low (foliage = 0.7% N), as were N input via wet precipitation (0.25 g · m–2 · yr–1), and biological fixation of atmospheric N (<0.03 g · m–2 · yr–1, except locally in some stands at low elevations where symbiotic fixation by the leguminous herbLupinus argenteus probably exceeded 0.1 g · m–2 · yr–1).Because of low concentrations in litterfall and limited opportunity for leaching, N accumulated in decaying leaves for 6–7 yr following leaf fall. This process represented an annual flux of about 0.5g · m–2 to the 01 horizon. Only 20% of this flux was provided by throughfall, with the remaining 0.4g · m–2 · yr–1 apparently added from layers below. Low mineralization and small amounts of N uptake from the 02 are likely because of minimal rooting in the forest floor (as defined herein) and negligible mineral N (< 0.05 mg · L–1) in 02 leachate. A critical transport process was solubilization of organic N, mostly fulvic acids. Most of the organic N from the forest floor was retained within the major tree rooting zone (0–40 cm), and mineralization of soil organic N provided NH4 for tree uptake. Nitrate was at trace levels in soil solutions, and a long lag in nitrification was always observed under disturbed conditions. Total root nitrogen uptake was calculated to be 1.25 gN · m–2 · yr–1 with estimated root turnover of 0.37-gN · m–2 · yr–1, and the soil horizons appeared to be nearly in balance with respect to N. The high demand for mineralized N and the precipitation of fulvic acid in the mineral soil resulted in minimal deep leaching in most stands (< 0.02 g · m–2 · yr–1). These forests provide an extreme example of nitrogen behavior in dry, infertile forests. 相似文献
92.
Effects of photoperiodicity and light irradiance on phosphate-limited Oscillatoria agardhii in chemostat cultures 总被引:1,自引:0,他引:1
Oscillatoria sp. strain 23 is a filamentous, non-heterocystous cyanobacterium that fixes nitrogen aerobically. Although, in this organism nitrogenase is inactivated by oxygen a high tolerance is observed. Up to a pO2 of 0.15 atm, oxygen does not have any measurable effects on acetylene reduction. Higher concentrations of oxygen inhibited the activity to a relatively high degree. Evidence for two mechanisms of oxygen protection of nitrogenase in this cyanobacterium was obtained. A high rate of synthesis of nitrogenase may allow the organism to maintain a certain amount of active enzyme under aerobic conditions. Secondly, a switch off/on mechanism may reversibly convert the active enzyme into a non-active form which is insensitive to oxygen inactivation after a sudden and short-term exposure to high oxygen concentrations. It is conceived that these mechanisms in addition to a temporal separation of nitrogen fixation from oxygenic photosynthesis sufficiently explain the regulation process of aerobic nitrogen fixation in this organism.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- CAP
chloramphenicol 相似文献
93.
The non-heterocystous cyanobacterium Oscillatoria sp. strain 23 fixes nitrogen under aerobic conditions. If nitrate-grown cultures were transferred to a medium free of combined nitrogen, nitrogenase was induced within about 1 day. The acetylene reduction showed a diurnal variation under conditions of continuous light. Maximum rates of acetylene reduction steadily increased during 8 successive days. When grown under alternating light-dark cycles, Oscillatoria sp. fixes nitrogen preferably in the dark period. For dark periods longer than 8 h, nitrogenase activity is only present during the dark period. For dark periods of 8 h and less, however, nitrogenase activity appears before the beginning of the dark period. This is most pronounced in cultures grown in a 20 h light – 4 h dark cycle. In that case, nitrogenase activity appears 3–4 h before the beginning of the dark period. According to the light-dark regime applied, nitrogenase activity was observed during 8–11 h. Oscillatoria sp. grown under 16 h light and 8 h dark cycle, also induced nitrogenase at the usual point of time, when suddenly transferred to conditions of continuous light. The activity appeared exactly at the point of time where the dark period used to begin. No nitrogenase activity was observed when chloramphenicol was added to the cultures 3 h before the onset of the dark period. This observation indicated that for each cycle, de novo nitrogenase synthesis is necessary. 相似文献
94.
Self-transmissible plasmids carryinghis andnif genes fromKlebsiella pneumoniae have been introduced into threehis mutants ofProteus mirabilis: strains 5006-1, WR19 and WR20. Expression ofhis by the transconjugants was unequivocal, if slightly temperature-sensitive, but none was Nif+ when tested for acetylene reduction in anaerobic glucose medium using inocula from rich or glucose-minimal aerobic agar cultures. Succinate or pyruvate in place of glucose, low glucose, lower temperature or elevated Na2MoO4 did not allownif expression and no nitrogenase MoFe-protein peptide was detected immunologically after exposure to conditions in which diazotrophic enterobacteria, normal or genetically constructed, derepressnif.One strain,P. mirabilis WR19, carrying thehis nif Kmr plasmid pMF250 was examined in detail. Thenif activator genenifA was introduced on the plasmid pCK1. Such derivatives remained Nif- when tested, after aerobic growth on rich agar media, with normal or low glucose, with succinate or with elevated Mo. However, pre-conditioning by aerobic growth on glucose-minimal agar led to subsequent anaerobic expression ofnif in glucose medium from pMF250 in WR19 carrying pCK1. NH
4
+
or proline could serve as N-source in the glucose-minimal agar. Maximum activity was about 5% of that ofK. pneumoniae in our assay conditions. Material cross-reacting with anti-serum to the nitrogenase MoFe protein was formed. Nitrogenase activity was not switched off by NH
4
+
.P. mirabilis WR19 (pCK1) showed NH
4
+
-constitutive temperature-sensitive kanamycin resistance (anif-related phenotype of this plasmid) in aerobic glucose minimal medium. Expression ofnif inP. mirabilis WR19 (pCK1, pMF250) was NH
4
+
-repressible despite the constitutivenifA character of pCK1 and introduction of thentrA
+ plasmid pMM17 did not alter this phenotype. However, pCK1 did not give rise to NH
4
+
-constitutive diazotrophy in the wild-typeK. pneumoniae M5al. A construct of WR19 carrying pMF250 and constitutiventrC plasmid (pMD45) remained Nif- even after pre-growth on glucose-minimal media.We conclude (a) thatP. mirabilis forms a gene product functionally equivalent to that ofntrA inK. pneumoniae, (b) that it forms no functional equivalent of thentrC product in our growth conditions. The need for pre-conditioning on aerobic glucose media remains perplexing.Non-common abbreviation NFDM
Nitrogen-free-Davis-Mingioli medium 相似文献
95.
Abstract The regulatory properties of Rhodospirillum rubrum nitrogenase reduced by either the endogenous electron donor (ferredoxin) or an artificial donor (dithionite) were examined. The nitrogenase obtained from glutamate-grown cells required activating enzyme for maximum activity with either reductant. The activating enzyme requirement of ferredoxin-dependent nitrogenase activity implies a physiological significance of the activating enzyme in R. rubrum. Rhodopseudomonas capsulata nitrogenase also required activating enzyme when dithionite was the reductant, but there appeared to be no activating enzyme requirement with ferredoxin as the reductant. Because the catalytic activity of the enzyme was very low under these conditions, the physiological significance of activating enzyme in this organism remains in question. 相似文献
96.
Corrado Fogher Ilona Dusha∗ Patricia Barbot Claudine Elmerich∗ 《FEMS microbiology letters》1985,30(1-2):245-249
Abstract Probes containing the nod and hsn regions of Rhizobium meliloti and the fixABC genes of Rhizobium japonicum were used to perform hybridization experiments with endonuclease-restricted DNA from Azospirillum brasilense strains and 2 Azospirillum lipoferum strains. Homology to nod, hsn and fixA was found in the 4 Azospirillum strains. 相似文献
97.
The phylogenetically related phototrophic bacteria Rhodospirillum tenue and Rhodocyclus purpureus modulate activity of their glutamine synthetases by adenylylation/deadenylylation. Evidence for covalent modification includes the inhibitory effect of Mg2+ on the activity of glutamine synthetase extracted from cells of either species grown on excess ammonia, and the lack of Mg2+ inhibition of activity of the enzyme isolated from N2-(R. tenue) or glutamine (R. purpureus)-grown cells. In addition, snake venom phosphodiesterase treatment of glutamine synthetase from either species grown on excess ammonia relieved Mg2+ inhibition of the enzyme (as measured via the -glutamyl transferase assay), and changed the cation specificity from Mn2+ to Mg2+ (in the biosynthetic assay). 相似文献
98.
Dr. Paul A. Lespinat Yves M. Berlier Guy D. Fauque Rene Toci Gerard Denariaz Jean LeGall 《Journal of industrial microbiology & biotechnology》1987,1(6):383-388
Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D2–H+ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism. 相似文献
99.
Michael J. Sadowsky Katalin Rostas Prakash R. Sista Howard Bussey Desh Pal S. Verma 《Archives of microbiology》1986,144(4):334-339
Four histidine auxotrophs of Bradyrhizobium japonicum strain USDA 122 were isolated by random transposon Tn5 mutagenesis. These mutants arose from different, single transposition events as shown by the comparison of EcoRI and XhoI-generated Tn5 flanking sequences of genomic DNA. The mutants grew on minimal medium supplemented with l-histidine or l-histidinol but failed to grow with l-histidinol phosphate. While two of the muants were symbiotically defective and did not form nodules on Glycine max cvs. Lee and Peking and on Glycine soja, the other two mutants were symbiotically competent. Reversion to prototrophy occurred at a frequency of about 10-7 on growth medium without added antibiotics, but prototrophs could not be isolated from growth medium containing 200 g/ml kanamycin and streptomycin. The prototrophic revertants formed nodules on all the soybean cultivars examined. When histidine was supplied to the plant growth medium, both nodulation deficient mutants formed effective symbioses. On histidine unamended plants, nodules were observed infrequently. Three classes of bacterial colonies were isolated from such infrequent nodules: class 1 were kanamycin resistant-auxotrophs; class 2 were kanamycin sensitive-prototrophs; and class 3 were kanamycin-sensitive auxotrophs. Our results suggest that two Tn5 insertion mutations in B. japonicum leading to histidine auxotrophy, affect nodulation in some way. These mutations are in regions that show no homology to the Rhizobium meliloti common nodulation genes. 相似文献
100.
B. Regensburger L. Meyer M. Filser J. Weber D. Studer J. W. Lamb H. -M. Fischer M. Hahn H. Hennecke 《Archives of microbiology》1986,144(4):355-366
The genome of the slow-growing Bradyrhizobium japonicum (strain 110) was mutagenized with transposon Tn5. A total of 1623 kanamycin/streptomycin resistant derivatives were screened in soybean infection tests for nodulation (Nod) and symbiotic nitrogen fixation (Fix). In this report we describe 14 strains possessing a stable, reproducible Nod+Fix- phenotype. These strains were also grown under microaerobic culture conditions to test them for free-living nitrogen fixation activity (Nif). In addition to strains having reduced Fix and Nif activities, there were also strains that had reduced symbiotic Fix activity but were Nif+
ex planta.Analysis of the genomic structure revealed that the majority of the strains had a single Tn5 insertion without any further apparent physical alteration. A few strains had additional insertions (by Tn5 or IS50), or a deletion, or had cointegrated part of the vector used for Tn5 mutagenesis. One of the insertions was found in a known nif gene (nifD) whereas all other mutations seem to affect different, hitherto unknown genes or operons.Several mutant strains had an altered nodulation phenotype, inducing numerous, small, widely distributed nodules. Light and electron microscopy revealed that most of these mutants were defective in different stages of bacteroid development and/or bacteroid persistence. The protein patterns of the mutants were inspected by two-dimensional gel electrophoresis after labelling microaerobic cultures with l-(35S)methionine. Of particular interest were mutants lacking a group of proteins the synthesis of which was known to be under oxygen control. Such strains can be regarded as potential regulatory mutants. 相似文献