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91.
The speltoid series of mutations provides a genetic tool forinvestigating the control of flower development. In fertileGabo wheat and in St2 and St3 basal sterile speltoids, the changesin RNA staining patterns have been followed histochemicallyas a marker of cellular activity. Sterile floret sites are characterizedby a reduced RNA content. Use of dual-wavelength microspectrophotometryhas provided evidence that RNA content is similar in lemma primordiasubtending presumptive fertile and sterile primordia, but isstrikingly different in the floral meristems in the two types.The total nucleic acid content of the floral primordia has beenrelated to the number of epidermal cells in the subtending lemmaprimordium as a marker of development, using a linear modelanalysis of covariance. There is a linear increase in nucleicacid content during fertile floret development, but no significantincrease in RNA content in sterile St3 primordia. The rate constantis only 1/10th to 1/20th of that of Gabo. A stereological analysisshows that cell number in the floral meristems of Gabo increasesexponentially during development. In contrast, in St3, whilethere is a significant increase in cell number, it is at a drasticallyreduced rate. The intercept values are close to zero, indicatingthat only one or two cells initiate floral meristem development.The fertility-controlling alleles exert their effect prior tothe appearance of a visible floral primordium, and probablyafter initiation of the lemma. Triticum aestivum, wheat, floral development, histochemistry, nucleic acids, speltoids 相似文献
92.
Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium 总被引:11,自引:1,他引:10
RUFTY THOMAS W. Jr; JACKSON WILLIAM A.; RAPER C. DAVID Jr. 《Journal of experimental botany》1982,33(6):1122-1137
Experiments were conducted to investigate the effect of concentrationof NH4+ in nutrient solution on root assimilation of NO3and to determine whether the NH4+NO3 interaction wasmodified in the presence of K+. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO3)2and varying concentrations of (NH4)2SO4 in the absence or presenceof 0.15 mM K2SO4. The accelerated phase of NO3 uptakeappeared most sensitive to restriction by additions of 0.15mM (NH4)2SO4. In the absence of K+, the restriction increasedonly slightly even when solution (NH4)2SO4, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH4+in the tissue from about 7.0 to 35 µmol g1 fr.wt. of root. Increasing concentrations of solution NH4+ progressivelyinhibited net K+ uptake. At the highest solution NH4+ concentrations,there was an initial net efflux of K+ and no net influx occurredduring the treatment period. The severity of the NH4)SO4 restrictionof NO3 uptake was moderated considerably in the presenceof K+ as long as a net influx of K+ occurred. However, net influxof K+ was not associated with alteration of NH4+ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO3 uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH4+ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH4+. Several mechanisms were postulatedto account for the moderating influence of K+. In all experiments,root NO3 reduction was restricted by the presence ofambient NH4+. The quantitative decreases in reduction tendedto be less than decreases in NO3 uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded. 相似文献
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Serial dilutions: Error effects and optimal designs 总被引:1,自引:0,他引:1
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Soybeans [Glycine max(L.) Merr.] were harvested at various time periods after a 2-h exposure to either 0 or 0.5 μ1/1 ozone to determine the effects of ozone on selected enzymes. Carbohydrate metabolism was modified by a depression of glyceraldehyde 3-phaosphate dehydrogenase and an activation of glucose 6-phosphate dehydrogenase. Ozone did not alter the levels of RNase, protease, acid phosphatase or esterase as might be expected if ozone enhanced leaf senescence. The activities of phenylalanine ammonia lyase, polyphenol oxidase and peroxidase were initially depressed and then stimulated following the ozone exposure. The reactions of soybeans to an acute ozone stress were more nearly akin to those elicited in response to other stresses than to the process of senescence. 相似文献
100.
The importance of pre-thicket conifer plantations for nesting Hen Harriers Circus cyaneus in Ireland
MARK W. WILSON SANDRA IRWIN DAVID W. NORRISS STEPHEN F. NEWTON KEVIN COLLINS THOMAS C. KELLY & JOHN O'HALLORAN 《Ibis》2009,151(2):332-343
Hen Harriers Circus cyaneus are threatened across much of their range and their conservation requires appropriate habitat management. The locations of 148 Hen Harrier nests found in the Republic of Ireland during national breeding surveys in 2000 and 2005 were used to assess nest-site selection. The distribution of these nests was compared to distributions of randomly located points to investigate selection at the scale of the nest-site and landscape. The main nesting habitats selected were pre-thicket stage of first and, particularly, second rotation plantations, mostly of exotic conifers. There was no evidence that the area of post-closure plantations negatively affected Hen Harrier nest distribution. There was a positive correlation across study areas between changes in numbers of Hen Harrier nests between 2000 and 2005 and changes in the area of pre-thicket second rotation plantations over the same period. The overall effect of plantation forests on breeding Hen Harriers in Ireland therefore appears to be positive. However, this study did not consider the effects of plantation habitats on breeding success. Improved grassland was strongly avoided as a nesting habitat. Furthermore, after controlling for the influence of nesting habitat on nest location, landscapes with a high percentage cover of improved grassland were also avoided. Further agricultural intensification of grassland in areas where Hen Harriers breed is likely to have a negative impact on this species. These results are required for the development of management strategies for the conservation of this species. 相似文献