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51.
52.
Amino groups at the surfaces of phospholipid vesicles 总被引:1,自引:0,他引:1
53.
54.
George H. Weiss 《Bulletin of mathematical biology》1968,30(3):427-435
Generalized equations are developed for the age structure of growing cell populations when other parameters besides chronological
age are taken into account. These are summarized in a parameter which we call “chronological age”. The theory is Markovian
in spirit and leads to an integro-differential equation for population density which generalizes several equations now appearing
in the literature. Approximations to the fundamental equation are suggested. 相似文献
55.
1. Monosaccharides, amino sugars and N-acetylneuraminic acid were determined by using an original colorimetric assay procedure, based on the detection of formaldehyde released after periodate oxidation. A range of these compounds was investigated by this method and they were all found to obey Beer's law within the concentration range 0-0.6mumole/ml. 2. A simple method for the determination of 6-deoxyhexose concentration in the presence of other monosaccharides is also described. 3. The optimum pH for the release of formaldehyde from sugars by periodate oxidation was 7.0-7.5. 4. The methods described have considerable advantages over existing assay systems and their particlar value in automatic colorimetry, where the use of concentrated acids is undesirable, is discussed. 相似文献
56.
Dynamic adhesion and separation of cells in vitro. II. Interactions of cells with hydrophilic and hydrophobic surfaces 总被引:2,自引:0,他引:2
Experiments made on the passage of cells through untreated and siliconized glass beads, and on the adhesion and spread of cultured cells on glass and Teflon surfaces show that, in the absence of serum and in its presence in low concentrations, cell adhesion and spread is sensitive to substratum wettability. On the other hand, in the presence of 100% serum, no differences in adhesive parameters are detectable. It is concluded that arguments correlating cell adhesion to surface wettability, and, by inference, surface free energy, are unsubstantiated in 100% serum, which may well approximate to the in vivo situation. The results also show no correlation between parameters of cell adhesion and cell separation, and thereby support the hypothesis that these are different processes. 相似文献
57.
Some Properties of Heat-Resistant and Heat-Sensitive Strains of Clostridium perfringens I. Heat Resistance and Toxigenicity 总被引:4,自引:2,他引:2 下载免费PDF全文
Heat resistance at 100 C (D-values), sporulating ratios, toxigenicity for mice, and lecithinase activity (as micrograms per milliliter of enzyme, ascertained by the lecithovitellin reaction) were determined for four strains of Clostridium perfringens. A definite inverse relationship between thermal resistance and toxigenicity was found. The D-values ranged from 17.6 for the most heat-resistant strain to 0.3 for the strain possessing the least heat resistance, with corresponding lecithinase activities from 25 to 133 mug/ml of enzyme. The sporulating ratios did not differ greatly between the strains. The heat stability of the toxin was greater at 100 C than at 75 C. There was a noticeable difference between the heat stabilities of the toxin in the culture fluids of the heat-sensitive and heat-resistant strains at pH 7.0 when the toxic filtrates were held at 100 C. At a holding temperature of 75 C, a similar but lesser difference was observed at pH 5.5. Heat resistance and lecithinase activity did not change when a substrain of the least heat-resistant parent strain was obtained through heat selection by a single transfer, or when the most heat-resistant strain was transferred serially 12 times. 相似文献
58.
Formation of Extracellular Sphingolipids by Microorganisms: IV. Pilot-Plant Production of Tetraacetylphytosphingosine by Hansenula ciferrii 下载免费PDF全文
Hanns G. Maister S. Peter Rogovin Frank H. Stodola Lynferd J. Wickerham 《Applied microbiology》1962,10(5):401-406
Tetraacetylphytosphingosine (TAPS) formation by the F-60-10 mating type strain of the yeast Hansenula ciferrii, previously observed on agar plates, has been shown to take place in submerged cultures. The optimal conditions for TAPS formation, and the correlation of TAPS production and sugar utilization under aerobic conditions, were studied in 10-liter fermentors. For each gram of glucose consumed, 5 mg of TAPS were formed; for each gram of yeast solids produced, 15 mg of TAPS were synthesized. A 750-liter pilot-plant run yielded 175 g of crude TAPS, which were obtained by hexane extraction of centrifuged yeast cells. 相似文献
59.
C Weiss 《Biophysical journal》1966,6(3):261-274
This paper analyzes the “energy switch” that has often been proposed to direct quanta absorbed by a given photosynthetic unit alternately to the site of one and then the other primary reaction. Such a device is essential to the Franck-Rosenberg theory, but not to the Duysens-Witt-Kok (DWK) model, which needs to assume only that the reactions occur in series. If there is no energy switch, an incident quantum absorbed at any time by any particular pigment molecule stands a chance of ending up in the reactive site of either primary reaction. The “separate packages” model is a special case of this general picture. Without an energy switch, a series model requires a storage device to insure that a quantum will not be wasted if it arrives at the site of one reaction while the photosynthetic unit is set up to perform the other. Such a storage device can be appended to the DWK model. Alternatively, this model can be augmented by an energy switch. This gives what is commonly known as the “spillover model,” a confusing name which we suggest be abandoned. As a clear-cut-though perhaps technically unfeasible-test of the energy switch hypothesis, we imagine a quantum injector, a hypothetical source of flashing light which delivers a single quantum to every photosynthetic unit with each flash. We aim this useful figment at an (equally hypothetical) photosynthetic system all of whose units are set up to perform the same primary reaction. If there is an energy switch, we can now prepare a “synchronous” photosynthetic apparatus in which each photosynthetic unit is undergoing the same reaction at the same time. 相似文献
60.
Adenosine Triphosphate and Other Requirements for the Utilization of Glucose by Agents of the Psittacosis-Trachoma Group. 总被引:11,自引:1,他引:10
E Weiss 《Journal of bacteriology》1965,90(1):243-253
Weiss, Emilio (Naval Medical Research Institute, Bethesda, Md.). Adenosine triphosphate and other requirements for the utilization of glucose by agents of the psittacosis-trachoma group. J. Bacteriol. 90:243-253. 1965.-The agent of meningopneumonitis cultivated in the allantoic cavity of chick embryos and purified by differential centrifugations was employed for most of the studies of the requirements for glucose utilization. The evolution of C(14)O(2) from glucose-1-C(14) was used as the criterion of metabolic activity in most experiments. The rate of glucose utilization increased somewhat during the first hour of incubation at 34.4 C and became approximately constant during the second hour. Changes in glucose concentration from 1 to 5 mm did not appreciably affect metabolic activity. More vigorous CO(2) production was obtained when the ratio of K(+)-Na(+) was >1 and, under certain conditions, when the concentration of inorganic phosphate was relatively high (0.05 m). Glucose utilization was entirely dependent on added adenosine triphosphate (ATP) and Mg(++). The effect of ATP was greatly reduced when the microorganisms were partially disrupted with sonic energy. Adenosine diphosphate (ADP) could be substituted for ATP, but the activity was reduced to less than 20%. ATP was not required when glucose-6-phosphate was substituted for glucose. With ADP and glucose, glucose-6-phosphate was an effective competitor of glucose utilization. Nicotinamide adenine dinucleotide phosphate (NADP) enhanced CO(2) production from carbon 1, but not from other carbons, with glucose and, especially, glucose-6-phosphate as substrates. ATP and NADP produced the above-described effects only when their concentrations were comparable to those of the substrates. These concentrations always exceeded the amount of CO(2) produced (0.05 to 0.5 mumole/mg of agent protein). The concentration of NADP could be reduced when oxidized glutathione was added. Diphosphothiamine had no effect on CO(2) production. Qualitatively similar results were obtained with the agent of trachoma purified from yolk sac. These experiments furnish evidence that agents of the psittacosistrachoma group, despite their enzymatic capabilities, require an exogenous source of energy. 相似文献