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51.
A five year study was conducted in a 100–120 year old even-aged sugar maple stand in southern Quebec (46°07N 73° 56W; 305 m altitude) to explore the effect of different fertilization formulations aimed at 1) correcting the most common nutrient deficiencies observed in declining maple stands (K and Mg), 2) decreasing soil acidity, and 3) simulating enrichment with atmospheric N. Seven fertilizer mixtures were applied in the spring of 1987: 400 kg ha-1 of K2SO4, CaCO3, CaMg(CO3)2, (NH4)2SO4, complete fertilizer (Maplegro) and 800 kg ha-1 of an equal mixture of K2SO4+CaCO3 or K2SO4+CaMg(CO3)2. The site was divided into twenty-four 25×25 m plots and treatments including control were replicated three times. Leaves and soils (organic and mineral) were sampled in 1987, 1988 and 1991. Trees were cored at 1.2 m to measure their response in diameter growth. The application of K2SO4+CaMg(CO3)2 was the only treatment that significantly increased (+13%) the average growth rate over the five year period after fertilization. The application of (NH4)2SO4, Maplegro, CaMg(CO3)2 and K2SO4 reduced growth relative to the control for the five year period by 29, 24, 20 and 12 %, respectively. Positive and negative effects on growth can be explained mainly in terms of changes in leaf K. Both the application of Maplegro and (NH4)2SO4 increased soil P availability. Overall, the rate of growth showed a cubic pattern of change over the 5 year period with peaks in 1988 and 1991. Trees in control plots went from a limiting foliar status of Ca and Mg, and surplus N in 1987 to a surplus of Ca and Mg, and lower N concentration in 1991. Our results suggest that nutrient deficiencies observed at our site were associated with a disturbance of the biogeochemical cycle of nutrients rather than soil nutrient depletion.Abbreviations BS
base saturation
- CEC
cation exchange capacity
- DRIS
diagnosis and recommendation integrated system 相似文献
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53.
Isolation and characterization of the mycobacterial phagosome: segregation from the endosomal/lysosomal pathway 总被引:5,自引:0,他引:5
Zahra Hasan Claudia Schlax Lotte Kuhn Ivan Lefkovits Douglas Young Jelle Thole & Jean Pieters 《Molecular microbiology》1997,24(3):545-553
Mycobacteria have the ability to persist within host phagocytes, and their success as intracellular pathogens is thought to be related to the ability to modify their intracellular environment. After entry into phagocytes, mycobacteria-containing phagosomes acquire markers for the endosomal pathway, but do not fuse with lysosomes. The molecular machinery that is involved in the entry and survival of mycobacteria in host cells is poorly characterized. Here we describe the use of organelle electrophoresis to study the uptake of Mycobacterium bovis bacille Calmette Guerin (BCG) into murine macrophages. We demonstrate that live, but not dead, mycobacteria occupy a phagosome that can be physically separated from endosomal/lysosomal compartments. Biochemical analysis of purified mycobacterial phagosomes revealed the absence of endosomal/lysosomal markers LAMP-1 and β-hexosaminidase. Combining subcellular fractionation with two-dimensional gel electrophoresis, we found that a set of host proteins was present in phagosomes that were absent from endosomal/lysosomal compartments. The residence of mycobacteria in compartments outside the endosomal/lysosomal system may explain their persistence inside host cells and their sequestration from immune recognition. Furthermore, the approach described here may contribute to an improved understanding of the molecular mechanisms that determine the intracellular fate of mycobacteria during infection. 相似文献
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56.
Ivan Laprevotte Sophie Brouillet Christophe Terzian Alain Hénaut 《Journal of molecular evolution》1997,44(2):214-225
A computer-assisted analysis was made of 24 complete nucleotide sequences selected from the vertebrate retroviruses to represent
the ten viral groups. The conclusions of this analysis extend and strengthen the previously made hypothesis on the Moloney
murine leukemia virus: The evolution of the nucleotide sequence appears to have occurred mainly through at least three overlapping
levels of duplication: (1) The distributions of overrepresented (3–6)-mers are consistent with the universal rule of a trend
toward TG/CT excess and with the persistence of a certain degree of symmetry between the two strands of DNA. This suggests
one or several original tandemly repeated sequences and some inverted duplications. (2) The existence of two general core
consensuses at the level of these (3–6)-mers supports the hypothesis of a common evolutionary origin of vertebrate retroviruses.
Consensuses more specific to certain sequences are compatible with phylogenetic trees established independently. The consensuses
could correspond to intermediary evolutionary stages. (3) Most of the (3–6)-mers with a significantly higher than average
frequency appear to be internally repeated (with monomeric or oligomeric internal iterations) and seem to be at least partly
the cause of the bias observed by other researchers at the level of retroviral nucleotide composition. They suggest a third
evolutionary stage by slippage-like stepwise local duplications.
Received: 3 January 1996 / Accepted: 27 March 1996 相似文献
57.
Capillary recruitment and transit time in the rat lung 总被引:1,自引:0,他引:1
Presson Robert G. Jr.; Todoran Thomas M.; De Witt Bracken J.; McMurtry Ivan F.; Wagner Wiltz W. Jr. 《Journal of applied physiology》1997,83(2):543-549
Presson, Robert G., Jr., Thomas M. Todoran, Bracken J. DeWitt, Ivan F. McMurtry, and Wiltz W. Wagner, Jr.Capillary recruitment and transit time in the rat lung.J. Appl. Physiol. 83(2): 543-549, 1997.Increasing pulmonary blood flow and the associated rise incapillary perfusion pressure cause capillary recruitment. The resultingincrease in capillary volume limits the decrease in capillary transittime. We hypothesize that small species with relatively high restingmetabolic rates are more likely to utilize a larger fraction ofgas-exchange reserve at rest. Without reserve, we anticipate thatcapillary transit time will decrease rapidly as pulmonary blood flowrises. To test this hypothesis, we measured capillary recruitment andtransit time in isolated rat lungs. As flow increased, transit timedecreased, and capillaries were recruited. The decrease in transit timewas limited by an increase in the homogeneity of the transit time distribution and an increased capillary volume due, in part, to recruitment. The recruitable capillaries, however, were nearly completely perfused at flow rates and pressures that were less thanbasal for the intact animal. This suggests that a limited reserve ofrecruitable capillaries in the lungs of species with high restingmetabolic rates may contribute to their inability to raiseO2 consumption manyfold abovebasal values. 相似文献
58.
Summary
Clostridium acetobutylicum ATCC 824 was used to produce butanol and acetone by fermenting acid whey. Results showed that both autoclaving and agitation played roles in solvent production. Maximum production was obtained in 120 h using autoclaved, pH adjusted (6.0) acid whey at 37 °C in a fermentor that was not agitated. 相似文献
59.
An account is given of the morphology and the taxonomy of the Asian, Australian and Pacific genus Archidendron (Leguminosae – Mimosoideae). A new infrageneric classification based on morphological data is presented, the genus being subdivided in 8 series. The phylogeny of the genus is discussed, the base of discussion being all available morphological, palynological and wood–anatomical characters. The presence/absence of stipules, the length of the staminal tube compared with that of the corolla–tube, the sessile/stipitate ovary(–ies), the morphology of the pods and the wood–anatomy have been particularly useful in determining the evolutionary trends within the genus. Analyses of the geographical range of selected character states are presented. The data suggest a Central – W. Malesian origin of the genus. The series endemic to the E. Malesian – Australian area have probably evolved more recently. The pluricarpellate condition of the flowers in several species endemic to the E. Malesian and Australian area is considered to be a derived character state. The following new taxa are proposed: Ser. Calycinae Nielsen, ser. Ptenopae Nielsen, ser. Bellae Nielsen, Archidendron falcatum Nielsen, A. cockburnii Nielsen, A. sabahense Nielsen, A. fagifolium (Bl. ex Miq.) Nielsen var. borneense Nielsen, A. kunsrteri (Prain) Nielsen subsp. ashtonii Nielsen, A. ellipticum (Bl.) Nielsen subsp. cordifoliolatum Nielsen. New combinations are proposed in the Malesian species formerly referred to Abarema, Zygia and Morolobium by Kostermans. Keys to and an enumeration of the species are presented. 相似文献
60.
Wistar-derived rats were raised and maintained either on a normal- (25% casein) or on a low-protein (8% casein) diet until the age of 100 to 114 days. Both diets were isocaloric and contained an adequate supply of salts and vitamins. There were gross differences in body, brain and pituitary weight between the two groups. In addition, the brain and pituitary content of β-endorphin like immunoreactivity was lower in the protein malnourished rats, and three different forms of training (50 tone-footshock shuttle avoidance trials; 50 tones alone (habituation); 50 footshocks alone) caused a depletion of brain β-endorphin like immunoreactivity in the normal, but not in the malnourished rats. Footshock stimulation caused, in addition, a pituitary decrease and a plasma increase of β-endorphin like immunoreactivity, also restricted to the normal diet group. Performance in the habituation and in the shuttle avoidance tasks was similar in the two groups, despite the different responsiveness of their brain and pituitary β-endorphin systems to training and/or stimulation. In view of the possible involvement of these systems in learning suggested by these and by previous data, it seems likely that the neurohumoral regulation of habituation and avoidance learning may be different in rats submitted to protein malnutrition when compared to controls. 相似文献