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41.
Elisabeth Tschermak-Woess Gertrude Hasitschka-Jenschke 《Plant Systematics and Evolution》1958,104(4-5):577-582
Zusammenfassung In den Fäden der GrünalgenMicrospora amoena undSpirogyra crassa wechseln geschlossene Abschnitte von eigentlich ruhenden Zellen mit Abschnitten von präprophasischen, das sind Mitose-bereiten, mitotisch aktiven und posttelophasischen, also unmittelbar nach der Mitose stehenden Zellen ab. Nur ausnahmsweise schieben sich Zellen des einen Typus in Abschnitte von Zellen des anderen Typus ein.Dieses Verhalten wird hypothetisch mit dem Auftreten und der Weiterleitung teilungsinduzierender Hormone erkärt. Daß die Teilungsstadien einschließlich der vor- und nachmitotischen Stadien nicht entsprechend einem Gefälle streng geordnet aufeinanderfolgen, beruht wahrscheinlich auf der Verschiedenartigkeit der äußeren und inneren Faktoren, die auf die einzelnen Zellen einwirken. Genealogische Faktoren spielen offenbar eine untergeordnete Rolle. 相似文献
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The metabolism of glucose in brains during sustained hypoglycemia was studied. [U-14C]Glucose (20 microCi) was injected into control rats, and into rats at 2.5 hr after a bolus injection of 2 units of insulin followed by a continuous infusion of 0.2 units/100 g rat/hr. This regimen of insulin injection was found to result in steady-state plasma glucose levels between 2.5 and 3.5 mumol per ml. In the brains of control rats carbon was transferred rapidly from glucose to glutamate, glutamine, gamma-aminobutyric acid and aspartate and this carbon was retained in the amino acids for at least 60 min. In the brains of hypoglycemic rats, the conversion of carbon from glucose to amino acids was increased in the first 15 min after injection. After 15 min, the specific activity of the amino acids decreased in insulin-treated rats but not in the controls. The concentrations of alanine, glutamate, and gamma-amino-butyric acid decreased, and the concentration of aspartate increased, in the brains of the hypoglycemic rats. The concentration of pyridoxal-5'-phosphate, a cofactor in many of the reactions whereby these amino acids are formed from tricarboxylic acid cycle intermediates, was less in the insulin-treated rats than in the controls. These data provide evidence that glutamate, glutamine, aspartate, and GABA can serve as energy sources in brain during insulin-induced hypoglycemia. 相似文献
43.
ULTRASTRUCTURAL OBSERVATIONS OF VITELLOGENESIS IN THE SPIDER CRAB, LIBINIA EMARGINATA L 总被引:2,自引:1,他引:1
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Ovaries from the spider crab, Libinia emarginata L. were studied to learn more of vitellogenesis in crustaceans. Oogonia and previtellogenic oocytes were found in the core of the ovaries. Vitellogenic oocytes are located more peripherally. Profiles of the endoplasmic reticulum are abundant in the vitellogenic oocytes. The granular and agranular reticulum as well as the Golgi complex are active in yolk synthesis. As vitellogenesis proceeds, yolk precursors are incorporated into the egg by micropinocytosis at the egg surface. Thus, in Libinia, yolk materials appear to be derived from both intra- and extraoocytic sources. 相似文献
44.
Guido A. Schoenenberger Susanne Buser Lorenz Cueni Heinz Döbeli Dieter Gillesen William Lergier Gertrude Schöttli Hans J. Tobler Kenneth Wilson 《Regulatory peptides》1980,1(3):223-244
Two different peptides have been purified from human liver, similar to those previously reported (Schoenenberger, G.A., and Wacker, W.E.C. (1966) Biochemistry 5, 1375–1379) to be present in human urine, which may serve as metabolic regulators of lactate dehydrogenase (EC 1.1 1.27) isoenzymes (LDH-M4 = muscle type; LDH-H4 = heart type). By trichloroacetic acid precipitation, ultrafiltration, Sephadex G-25 and Bio-Gel P-2 columns, affinity chromatography on immobilized LDH-isozymes and HPLC two peptides which differed with respect to molecular weight, retention on the affinity columns and amino acid composition were isolated. No effect was observed when native, tetrameric lactate dehydrogenase was incubated with these peptides. However, when lactate dehydrogenase was dissociated to monomers at low pH and allowed to reassociate by adjusting the pH to 7.5 complete inhibition of the reactivation occurred when the inhibitors were incubated together with respective reassociating monomeric isozymes. The two peptides showed no cross-specificity, i.e. each peptide exhibited inhibitory activity only on one of the two isozymes LDH-M4 or LDH-H4. From the amino acid analyses, gel-filtration and PAGE + SDS, molecular weight of 1800 for the M4 and ≈2700 for the H4 inhibitor were calculated. An apparent Ki of ≈3 × 10?5 mM for the H4 and ≈7 × 10?5 mM for the H4 inhibitor was estimated. The interaction of the inhibitors with the enzyme system showed strong cooperativity with Hill coefficients of 2.9 (LDH-M4-specific) and 2.4 (LDH-H4-specific). Mathematical modelling of the reassociation and reactivation of lactate dehydrogenase and its specific inhibition by the peptides led to the conclusion that the peptides reacts with monomers, dimers or a transition state during the tetramerisation process. k1 for the dimerisation step of M4 = 2.0 × 105 M?1 · s?1 and of H4 = 8.2 × 104 M?1 · s?1; k2 for the tetramerisation step of M4 = 2.8 × 105 M?1 · s?1 and of H4 = 1.2 × 105 · M?1 · s?1, were calculated, the second step still being the faster one. 相似文献
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Summary A multiple series of alleles of the gene MZ exist inSaccharomyces. The members of this series are differentiated from one another by their adaptive response to maltose, turanose, sucrose, melezitose and alpha-methyl glucoside. The more capable members of the series can ferment all five sugars while various multiple alleles are characterized by loss of ability to act on alpha-methyl glucoside, melezitose or sucrose. MZ is linked to the gene MA which controls the production of a specific maltase and to the gene MG which controls the production of a specific alpha-methyl glucosidase. All members of the series of multiple alleles produce the same enzyme showing that the gene and the enzyme are not identical. The enzyme is produced in three different steps, the initial one being a specific reaction of gene with substrate and the final one being a non-specific elicitation of enzyme.This work has been supported by research grants from The National Cancer Institute of the National Institutes of Health, U.S. Public Health Service and Anheuser-Busch, Inc. 相似文献
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