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2.
R D Keynes N G Greeff I C Forster J M Bekkers 《Proceedings. Biological sciences / The Royal Society》1991,246(1316):135-140
The effect of tetrodotoxin (TTX) on the sodium gating current in the squid giant axon was examined by recording the current that flowed at the pulse potential at which the ionic current fell to zero, first in the absence and then in the presence of TTX. The addition of 1 microM TTX to the bathing solution had no consistent effect on the size of the initial peak of the gating current, but resulted in small changes in the timecourse of its subsequent relaxation which were mainly caused by a reduction of about one quarter in the component that has a delayed onset and may possibly arise from changes in the state of ionization of groups in the channel wall when the lumen fills with water. Our findings suggest that the binding of TTX at the outer face of the sodium channel does not interfere with the mechanisms of activation and inactivation by the voltage sensors, but has an allosteric effect on the access of internal cations to the inside of the channel. 相似文献
3.
The mechanism of chromosome 14 inversion in a human T cell lymphoma 总被引:16,自引:0,他引:16
4.
Cystinotic fibroblasts transferred from 37 degrees C to 28 degrees C accumulated additional cystine over the period from 4 to 7 days of incubation at 28 degrees C, after which the additional cystine was lost; warming (to 37 degrees C) of cells with elevated cystine stores led to rapid cystine loss. These results, taken together with previously published data showing cystine release from cystinotic fibroblasts incubated at above-normal temperature, are interpreted as indicating the presence in the cystinotic fibroblast lysosome membrane of a cystine-porter whose efficacy is increased by an increase in membrane fluidity. This porter may be the residual activity of the cystine porter that is known to be deficient in cystinosis, or it may be a second as yet unrecognized porter. It is further proposed that this porter is responsible for the presumed efflux of cystine from cystinotic lysosomes. 相似文献
5.
The complete nucleotide sequence of the potexvirus white clover mosaic virus. 总被引:5,自引:1,他引:4 下载免费PDF全文
The complete nucleotide sequence (5845 nucleotides) of the genomic RNA of the potexvirus white clover mosaic virus (WC1MV) has been determined from a set of overlapping cDNA clones. Forty of the most 5'-terminal nucleotides of WC1MV showed homology to the 5' sequences of other potexviruses. The genome contained five open reading frames which coded for proteins of Mr 147, 417, Mr 26,356, Mr 12,989, Mr 7,219 and Mr 20,684 (the coat protein). The Mr 147,417 protein had domains of amino acid sequence homology with putative polymerases of other RNA viruses. The Mr 26,356 and Mr 12,989 proteins had homology with proteins of the hordeivirus barley stripe mosaic virus RNA beta and the furovirus beet necrotic yellow vein virus (BNYVV) RNA-2. A portion of the Mr 26,356 protein was also conserved in the cylindrical inclusion proteins of two potyviruses. The Mr 7,219 protein had homology with the 25K putative fungal transmission factor of BNYVV RNA-3. 相似文献
6.
Goats were prepared so that one carotid body (CB) could be perfused with blood in which the gas tensions could be controlled independently from the blood perfusing the systemic arterial system, including the brain. Since one CB is functionally adequate, the nonperfused CB was excised. To determine whether systemic arterial hypoxemia is necessary for ventilatory acclimatization to hypoxia (VAH), the CB was perfused with hypoxic normocapnic blood for 6 h [means +/- SE: partial pressure of carotid body O2 (PcbO2), 40.6 +/- 0.3 Torr; partial pressure of carotid body CO2 (PcbCO2), 38.8 +/- 0.2 Torr] while the awake goat breathed room air to maintain systemic arterial normoxia. In control periods before and after CB hypoxia the CB was perfused with hyperoxic normocapnic blood. Changes in arterial PCO2 (PaCO2) were used as an index of changes in ventilation. Acute hypoxia (0.5 h of hypoxic perfusion) resulted in hyperventilation sufficient to reduce average PaCO2 by 6.7 Torr from control (P less than 0.05). Over the subsequent 5.5 h of hypoxic perfusion, average PaCO2 decreased further, reaching 4.8 Torr below that observed acutely (P less than 0.05). Acute CB hyperoxic perfusion (20 min) following 6 h of hypoxia resulted in only partial restoration of PaCO2 toward control values; PaCO2 remained 7.9 Torr below control (P less than 0.05). The progressive hyperventilation that occurred during and after 6 h of CB hypoxia with concomitant systemic normoxia is similar to that occurring with total body hypoxia. We conclude that systemic (and probably brain) hypoxia is not a necessary requisite for VAH. 相似文献
7.
8.
Hydroxyl ion movements across the human erythrocyte membrane. Measurement of rapid pH changes in red cell suspensions 总被引:9,自引:3,他引:6 下载免费PDF全文
A stopped flow rapid reaction apparatus capable of following changes of ±0.02 pH unit in 0.1 ml of solution in less than 0.005 sec has been developed, utilizing a commercially available pH-sensitive glass electrode. Using this instrument, extracellular pH at 37°C was followed from less than 0.025 sec to 300 sec after mixing equal volumes of the following CO2-free solutions: (A) normal human red cells, washed three times and resuspended in 150 mM NaCl at pH 7.2 with a hematocrit of 18%; and, (B) 150 mM NaCl adjusted with HCl or NaOH to pH 2.1 to pH 10.3. A minimum of 2 ml of mixture had to flow through the electrode chamber to ensure complete washout. The mixing process produced a step change in the pH of the extracellular fluid, after which exchanges across the red cell membrane and buffering by intracellular hemoglobin caused it to return toward pH 7.2 with an approximately exponential time course. Under the assumption that pH changes after mixing represent exchanges of hydroxyl for chloride ions across the cell membrane, hydroxyl ion permeabilities (P
OH
- in cm/sec) were calculated and found to vary from 2 x 10-4 at pH 9 to 4 x 10-1 at pH 4 according to the empirical relationship P
OH
- = 170 exp (-1.51 pH). The form of the dependence of P
OH
- on extracellular pH does not appear compatible with a simple fixed charge theory of membrane permselectivity. 相似文献
9.
Summary 1. In solution culture with oats (Avena sativa) the effect of the K concentration of the nutrient solution on yield and K uptake rates has been investigated. The K concentration
of the different treatments were: 0.1, 0.3, 0.9 and 2.7 me K/l. These concentrations were kept constant during the whole growing
period.
2. The growth of the plants in all treatments was normal. Even with the lowest K concentration no visible symptoms of K deficiency
occurred. The highest grain yield was obtained with a K concentration of 0.9 me K/l. This yield was about 40% higher than
the yield with the lowest K concentration and about 5% higher than the grain yield with the highest K concentration.
3. The increasing K supply had a favorable effect on the fat and crude protein content of the grains. The highest K concentration
(2.7 me K/l) resulted in the highest content of crude protein (20%) and of fat (6.2%).
4. The rates of K uptake throughout the growing period differed considerably. The highest rates were measured during the shooting
stage and the blossom stage. The K concentration of the nutrient solution influenced the uptake rates significantly. High
yields were obtained if the K uptake at the beginning of the blossom stage was higher than 50% of the total K uptake.
5. The optimal K concentration for the yield performance, 0.9 me K/l, found in this experiment cannot be compared with K concentrations
of the soil solution under field conditions without reservations. Under field conditions root growth and the contact surface
between soil solution and root surface are different. Assuming that under field condition this contact surface nutrient solution/root
surface is not larger than in solution culture, also a K concentration of 1 me K/l of the soil solution should meet the K
demand of the plants, necessary for the production of high grain yields.
相似文献
10.