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51.
In chloroplasts and a number of prokaryotes, -aminolevulinic acid (ALA), the universal precursor of porphyrins, is synthesized by a multistep enzymatic pathway with glutamyl-tRNAGlu as an intermediate. The ALA synthesizing system from barley chloroplasts is highly specific in its tRNA requirement for chloroplast tRNAGlu; a number of other Glu-tRNAs are inactive in ALA formation although they can be glutamylated by chloroplast aminoacyl-tRNA synthetases. In order to obtain more information about the structural features defining the ability of a tRNA to be recognized by the ALA synthesizing enzymes, we purified and sequenced two cytoplasmic tRNAGlu species from barley embryos which are inactive in ALA synthesis. By using glutamylated tRNAs as a substrate for the overall reaction, we showed that Glu-tRNA reductase is the enzyme responsible for tRNA discrimination. 相似文献
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Characteristics and epitope mapping of a cloned human autoantigen La 总被引:13,自引:0,他引:13
A D Sturgess M G Peterson L J McNeilage S Whittingham R L Coppel 《Journal of immunology (Baltimore, Md. : 1950)》1988,140(9):3212-3218
The La (SS-B) polypeptide is a ribonucleoprotein against which high titer antinuclear antibodies (ANA) react in the human autoimmune disease primary Sj?gren's syndrome. To identify the autoepitopes with which the ANA anti-La (anti-SS-B) reacts, we isolated a 1.4-kb cDNA clone for La from a lambda gt10 library made from a human Burkitt's cell line. This clone contained an open reading frame of 1065 bp, encoding a 40.1-kDa polypeptide that corresponded to the carboxyl-terminal end of the La protein. The predicted polypeptide sequence of the recombinant protein was highly charged and unrelated to any previously published sequence. We also compared this clone to a previously published cDNA sequence for La and demonstrated significant differences, particularly that the open reading frame in our cDNA continued for 926 additional bases 3' to a putative termination codon in the previously reported sequence. The recombinant La protein was expressed in Escherichia coli and tested for reactivity with 200 sera containing ANA of various specificities. Only the sera containing anti-La antibodies reacted with the cloned La. By expressing subclones of the La cDNA as fusion proteins with beta-galactosidase, we have localized at least one epitope for the binding of anti-La antibodies to the carboxyl-terminal 103 amino acids of the La protein. No anti-La binding could be demonstrated to the region of the La protein that had previously been predicted to contain an autoepitope for the binding of anti-La (SS-B) antibodies. Studies of cloned autoepitopes could provide important clues to the role ANA play in disease and lead to targeted intervention in the treatment of primary Sj?gren's syndrome. 相似文献
55.
Summary The relative hydraulic conductivities of major and minor longitudinal veins, and the apoplastic permeability of the bundle sheaths surrounding all longitudinal and transverse veins were investigated in representatives of the C3, C4/NAD-ME, C4/NAD-ME/PCK intermediate, C4/PCK and C4/NADP-ME photosynthetic types. Using the Hagen-Poiseuille equation and measurements of tracheary element diameters, the number of elements in each vein type and the numbers of each vein type, we calculated that 87–99% of the water flow in a longitudinal direction would be expected to occur in the major veins. The permeability of the mestome sheaths and parenchymatous bundle sheaths surrounding the veins was tested using the negatively-charged, fluorescent dye, trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS). This dye proved nontoxic to plant tissue at a concentration of 0.5%, according to a deplasmolysis test with onion epidermal strips. The PTS concentration achieved in the tested grass leaves was about 0.035%, well below the toxic limit. When a solution of PTS was fed to the leaves by means of a basal cut, the dye moved into the veins of all orders. From there, it moved outward into the surrounding tissues, indicating that the sheaths surrounding the veins of all orders in all species tested were permeable. Therefore, contrary to previous predictions based on structural observations and some tracer studies, bundle sheaths with suberized cell walls do not function as endodermal layers. 相似文献
56.
A berberine-aniline blue fluorescent staining procedure for suberin,lignin, and callose in plant tissue 总被引:17,自引:0,他引:17
Summary A fluorescent staining procedure to detect suberin, lignin and callose in plants has been developed. This procedure greatly improves on previous methods for visualizing Casparian bands in root exodermal and endodermal cells, and performs equally well on a variety of other plant tissues. Berberine was selected as the most suitable replacement forChelidonium majus root extract after comparing the staining properties of the extract with those of four of its constituent alkaloids. Aniline blue counterstaining efficiently quenched unwanted background fluorescence and nonspecific berberine staining, while providing a fluorochrome for callose. When used with multichambered holders which allow simultaneous processing of freehand sections, this efficient staining procedure facilitates morphological studies involving large numbers of samples.Abbreviations ISCC-NBS
Inter-Society Color Council-National Bureau of Standards
- UV
ultraviolet light 相似文献
57.
Simultaneous determination of ascorbic acid and dehydroascorbic acid in cultures of C3H/10T1/2 cells
Luminita L. V. Ibric William F. Benedict Andrew R. Peterson 《In vitro cellular & developmental biology. Plant》1988,24(7):669-676
Summary A reproducible method is described for the separation and quantification of ascorbic acid and dehydroascorbic acid by ion-pairing
reverse-phase high performance liquid chromatography and detection by absorbance at 232 nm. Lowest detectable concentrations
with a linear response of detection were 5 nmol for ascorbic acid and 50 nmol for dehydroascorbic acid. This method was applied
to the analysis of C3H/10T1/2 cells and culture medium after influx or efflux experiments and single or multiple treatments
with ascorbic acid. Subsequent measurement of the radioactivity in the eluted fractions increased the detectability of both
ascorbic acid and dehydroascorbic acid to 10 to 20 pmol.
This research was supported by grant CA 09320 and CA 31574 from the National Cancer Institute, Bethesda, MD, and grant BC441
from The American Cancer Society. 相似文献
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Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe 总被引:27,自引:2,他引:25
Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales. 相似文献
60.
Agrobacterium tumefaciens is established as a vector for gene transfer in many dicotyledonous plants but is not accepted as a vector in monocotyledonous plants, especially in the important Gramineae. The use of Agrobacterium to transfer genes into monocot species could simplify the transformation and improvement of important crop plants. In this report we describe the use of Agrobacterium to transfer a gene into corn, the regeneration of plants, and detection of the transferred genes in the F1 progeny. Shoot apices of Zea mays L. variety Funk's G90 were cocultivated with A. tumefaciens EHA 1, which harbored the plasmid pGUS3 containing genes for kanamycin resistance (NPT II) and β-glucuronidase (GUS). Plants developed from these explants within 4 to 6 weeks. Fluorometric GUS assays of leaves and immature seeds from the plants exhibited low GUS activity. Both NOS and GUS gene fragments were amplified by polymerase chain reaction in the DNA isolated from the F1 generations of one of the original transformed plants. Southern analysis showed both GUS and NPT probes hybridized to DNA in several of the F1 progeny, demonstrating the incorporation of GUS and NPT II genes into high molecular weight DNA. These data establish successful gene transfer and sexual inheritance of the genes. 相似文献