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101.
102.
The relationship between the source strength and the “manifest vector” in the Einthoven Triangle is derived for a line and
a point dipole source and confirmed experimentally. The result permits the interpretation of the standard ECG leads in absolute
terms and corrected for body size. The manifest vector is shown to be approximately
times what it would be in an otherwise similar circular slab which circumscribes the triangle. 相似文献
103.
Morphology and Reproductive Processes of the L Forms of Bacteria II. Comparative Study of L Forms and Mycoplasma with the Electron Microscope 总被引:3,自引:0,他引:3
Representative electron micrographs, from the study of eight strains of L forms and one strain of Mycoplasma, are presented. A- and B-type L forms were derived from two strains of Proteus, two other L forms were derived from a diphtheroid and from a staphylococcus strain, and two strains (designated as LX) were isolated from L forms derived from a group A beta-hemolytic streptococcus and from a staphylococcus. The Mycoplasma strain was isolated from goats. Sections were made of young colonies grown within agar and from parts of surface colonies embedded in the agar. B-type L colonies of Proteus were produced by inoculation of bacteria into media containing penicillin. The large bodies developing from the bacteria and the organisms in B-type L colonies of Proteus, like the parent bacteria, had a cell wall consisting of a plasma membrane and an outer cell wall. The loss of rigidity in the cell wall indicated an alteration in its structure. The A-type L cultures of Proteus consisted of irregular branching masses extending in several directions, of small dense organisms corresponding to the elementary corpuscles present in cultures of Mycoplasma, and of intermediary forms. In contrast to the B-type, all organisms in the A-type colonies were surrounded by a single unit membrane corresponding to the plasma membrane of bacteria. The structures inside the cell membrane, both in the A- and B-type, seemed to correspond to the structure of the parent bacteria, which contained ribosomes and threads of DNA. The elementary corpuscles formed chains and filaments, and, apparently, these corpuscles took part in the multiplication by gradual enlargement. The organisms seen in the cultures of all L forms and Mycoplasma studied, except in the B-type L forms of Proteus, corresponded in size, shape, and structure, as well as in the development of elementary corpuscles, to the organisms in the A-type L form of Proteus. In contrast to the spherical organisms usually seen in broth cultures, the organisms in young cultures of Mycoplasma, which were grown within the agar, were similar in morphology, as well as in the discernible structure of the organisms, to L forms. Significant morphological and structural differences were not apparent between the L forms and Mycoplasma (in cultures grown within agar media) under the conditions of this investigation. 相似文献
104.
Cation Transport in Escherichia coli : VII. Potassium requirement for phosphate uptake 总被引:13,自引:1,他引:12
Paul L. Weiden Wolfgang Epstein Stanley G. Schultz 《The Journal of general physiology》1967,50(6):1641-1661
When Escherichia coli K-12 is grown in media containing limiting amounts of K, growth continues normally until all the extracellular K has been consumed. Thereafter the rates of growth, glucose consumption, and oxygen consumption decrease progressively, and the cell contents of K and P fall. These changes, referred to as K limitation, are all reversed by the addition of K. By specifically altering the ionic composition of the cells it was shown that these metabolic disturbances are not due to changes in the cell content of K or Na, but are directly related to the absence of K from the extracellular medium. The cell pool of inorganic P and the uptake of PO4 from the medium are low in K-limited cells and are immediately stimulated by the addition of K, suggesting that the primary effect of K limitation is to inhibit PO4 uptake. All the metabolic effects of K limitation can be attributed to inhibition of PO4 uptake. The requirement of extracellular K for PO4 uptake may be due to a coupling between the uptake of K and PO4. 相似文献
105.
106.
Stanley G. Schultz Ralph Zalusky Arthur E. Gass Jr. 《The Journal of general physiology》1964,48(2):375-378
Unidirectional Cl fluxes across in vitro segments of rabbit ileum have been determined both in the absence and in the presence of an electrochemical potential gradient. The results indicate that Cl transport in this preparation can be attributed to purely passive forces uninfluenced by solvent drag or exchange diffusion. Furthermore, on the basis of this and previous studies, it has been demonstrated that the sum of the partial ionic conductances of Na and Cl accounts for at least 90 per cent of the total tissue conductance. 相似文献
107.
The European corn borer, Ostrinia nubilalis (Hübn.), has been reared satisfactorily on a meridic diet containing no crude plant material. Ascorbic acid has been shown to be a necessary component of this diet for normal development of the larvae. Evidence is presented of the identity of the corn leaf factor (CLF), contained in spray-dried alfalfa juice, with ascorbic acid. The larvae grew better on a wheat germ supplemented diet than on the diets in which wheat germ was replaced with powdered cellulose, vitamin-free casein and corn oil or wheat germ oil. These data suggested that another factor, present in wheat germ, was required for optimal larval growth.
Approved for publication by the director of the Wisconsin Agricultural Experiment Station.
This study was supported in part by research grant (GM-05093) from the National Institutes of Health. 相似文献
Zusammenfassung Der Maiszünsler, Ostrinia nubilalis (Hübn.), wurde zufriedenstellend mit einer meridischen (meridic) Diät aufgezogen, die kein pflanzliches Rohmaterial enthielt. Es zeigte sich, daß zur normalen Entwicklung der Raupen zu dieser Diät Ascorbinsäure zugesetzt werden muß. Es wird wahrscheinlich gemacht, daß der Mais-Blattfaktor (CLF), der in sprühgetrocknetem Luzernesaft enthalten ist, mit Ascorbinsäure identisch ist.Die Larven wuchsen an der ergänzten Weizenkeimlingsdiät besser als an Diäten, bei denen die Weizenkeimlinge durch staubförmige Cellulose, vitaminfreies Kasein und Maisöl oder Weizenkeimlingsöl ersetzt war. Diese Befunde lassen vermuten, daß zum optimalen Wachstum ein anderer, in Weizenkeimlingen enthaltener Faktor erforderlich ist.Die Entdeckung der Ascorbinsäure als Mais-Blattfaktor ermöglicht die Entwicklung einer holidischen (holidic) Diät für dieses Insekt. Solch eine holidische Diät wird jedoch solange unteroptimal sein, bis der Faktor in Weizenkeim bestimmt ist.
Approved for publication by the director of the Wisconsin Agricultural Experiment Station.
This study was supported in part by research grant (GM-05093) from the National Institutes of Health. 相似文献
108.
109.
Effect of Osmotic Shock and Low Salt Concentration on Survival and Density of Bacteriophages T4B and T4Bo1 总被引:3,自引:0,他引:3
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Measurements of survival and buoyant densities of bacteriophages T4B, T4Bo(1), and T4D have demonstrated the following: (a) After suspension in a concentrated salt solution, T4B and T4D are sensitive both to osmotic shock and to subsequent exposure to low monovalent salt concentrations. (b) Sensitivity of T4B to dilution from a concentrated salt solution is dependent on dilution rate, that of T4D is less dependent, and that of T4Bo(1) is independent. (c) Sensitivity of all three phages to low salt concentrations depends on initial salt concentrations to a variable extent. (d) Density gradient profiles indicate that nearly half of osmotically shocked T4B retain their DNA. Similar analysis demonstrates that few, if any, T4Bo(1) lose DNA when subjected to a treatment causing 90% loss of infectivity. (e) The effective buoyant densities of T4B and T4Bo(1) depend significantly on the dilution treatments to which the phages are subjected prior to centrifugation in CsCl gradients. These data are explicable in terms of the different relative permeabilities of the phages to water and solutes, and of alterations in the counterion distribution surrounding the DNA within the phage heads. 相似文献
110.
Natural hybridization in the coccinellid genus chilocorus 总被引:1,自引:0,他引:1
Stanley G. Smith 《Chromosoma》1966,18(3):380-406
A population of lady-bird beetles at the head of the Crowsnest River valley on the immediate east side of the Rocky Mountains has been sampled regularly over the years 1961 to 1964. The 389 individuals studied had chromosome numbers ranging from 2n = 14 (58%) to 2n = 20 (3%). The former is the diploid number of C. hexacyclus, the latter that of C. tricyclus, species otherwise known respectively only in the Prairie Provinces and the interior of British Columbia plus the adjoining part of the State of Washington. About 19% of the beetles had the intermediate number of 17 chromosomes, males possessing either a hexacyclus-type or a morphologically distinct tricyclus-type Y chromosome. — In all numerical categories meiotic pairing was virtually perfect but the trivalents in heterozygotes were frequently linearly aligned. This assures production of aneuploid (duplicationdeficiency) gametes, only complementary recombinations of which are viable. Segregational sterility resulting from triple (92%), double (84%) and single (50%) heterozygotes is estimated to be ca 40%. Of four neo-diploids, with zero chromosomal sterility, predicted in the F2 only one materialized with certainty, the one with 13 + tricyclus-type Y. This is interpreted to mean that F2 progeny are rare; rare because (1) random mating, complete introgression, is the rule and (2) Segregational sterility is severest in triple heterozygotes. — Despite the population-depressing effect of the inviable aneuploid zygotes, it is calculated that segregation and crossing-over generate a minimum of 148 × 109 new recombinants (a minimum were crossing-over strictly localized); those acquiring beneficial attributes will be favoured by natural selection. — Topographically, it is evident that tricyclus adults invade the resident hexacyclus community year after year, borne on the prevailing westerly winds that funnel through Crowsnest Pass (elevation only 4463): hexacyclus is thereby constrained to the east of the Continental Divide and consequently does not penetrate into tricyclus territory.Dedicated to Prof. J. Seiler on the occasion of his eightieth birthday. 相似文献