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排序方式: 共有152条查询结果,搜索用时 31 毫秒
1.
An instrument containing a linear variable differential transformer was constructed to obtain continuous, nondestructive measurements of both short term changes in stem diameter and long term growth. In cotton plants, stem diameter, leaf water potential, and leaf relative water content are all closely related to net radiation at the top of the canopy. Leaves from the east and west sides of a plant show slight, but consistent differences in diurnal water potential patterns. 相似文献
2.
Continuous transpiration and β-guage measurements were made on cotton plants, the stomatal apertures of which had been induced to oscillate, thus allowing a water balance to be made, and leaf potential to be measured as functions of time. 相似文献
3.
Nitrate reductase utilizing NADH or reduced flavin mononucleotide (FMNH2) as electron donor was extracted from the leaves, stems and petioles, and roots of apple seedlings. Successful extraction was made possible by the use of insoluble polyvinylpyrrolidone (Polyclar AT) which forms insoluble complexes with polyphenols and tannins. The level of nitrate reductase per gram fresh weight was highest in the leaf tissue although the nitrate content of the roots was much higher than that of the leaves. Nitrite reductase activity was detected only in leaf extracts and was 4 times higher than nitrate reductase activity. Nitrate was found in all parts of young apple trees and trace amounts were also detected in mature leaves from mature trees. Nitrate reductase was induced in young leaves of apple seedlings and in mature leaves from 3 fruit-bearing varieties. An inhibitor of polyphenoloxidase, 2-mercaptobenzothiazole was used in both the inducing medium and the extracting medium in concentrations from 10−3 to 10−5m with no effect upon nitrate reductase activity. 相似文献
4.
Cyclic fluctuations in stomatal aperture, transpiration rate and leaf water potential under constant environmental conditions have been investigated in intact plants of cotton, pepper, and sunflower. Stomatal aperture and transpiration rate were least when leaf water potential was high and were greatest when leaf water potential was low. Lowest leaf water potential values lagged behind the occurrence of highest transpiration rates, and high overall resistance to water flow occurred in cycling plants. Both of these are considered essential for the occurrence of persistent cyclic behaviour. Hydropassive opening of stomates as the leaves wilted facilitated cycling in cotton and pepper, but not in sunflower, where hydropassive opening did not occur. The roots were identified as the site of the major resistance to water flow in the plant and further experiments directly showed the importance of this root resistance in initiating cycling by causing water stress in the leaves as the stomates opened. Root resistance varied diurnally, becoming increasingly important at night. Root resistance naturally rose to high levels in cotton. High levels were induced in pepper or sunflower by having the roots in deionized water for several days or by anoxia. Quantitative measurements of overall plant resistance were made from leaf water potential and transpiration rate data. The results are discussed and it suggested that plant resistance may indirectly be of importance in the movement of water from the plant to the air. 相似文献
5.
Comparison between NO(x) Evolution Mechanisms of Wild-Type and nr(1) Mutant Soybean Leaves 总被引:6,自引:0,他引:6
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Klepper L 《Plant physiology》1990,93(1):26-32
The nr1 soybean (Glycine max [L.] Merr.) mutant does not contain the two constitutive nitrate reductases, one of which is responsible for enzymic conversion of nitrite to NOx (NO + NO2). It was tested for possible nonenzymic NOx formation and evolution because of known chemical reactions between NO2− and plant metabolites and the instability of nitrous acid. It did not evolve NOx during the in vivo NR assay, but intact leaves did evolve small amounts of NOx under dark, anaerobic conditions. Experiments were conducted to compare NO3− reduction, NO2− accumulation, and the NOx evolution processes of the wild type (cv Williams) and the nr1 mutant. In vivo NR assays showed that wild-type leaves had three times more NO3− reducing capacity than the nr1 mutant. NOx evolution from intact, anerobic nr1 leaves was approximately 10 to 20% that from wild-type leaves. Nitrite content of the nr1 mutant leaves was usually higher than wild type due to low NOx evolution. Lag times and threshold NO2− concentrations for NOx evolution were similar for the two genotypes. While only 1 to 2% of NOx from wild type is NO2, the nr1 mutant evolved 15 to 30% NO2. The kinetic patterns of NOx evolution with time weré completely different for the mutant and wild type. Comparisons of light and heat treatments also gave very different results. It is generally accepted that the NOx evolution by wild type is primarily an enzymic conversion of NO2− to NO. However, this report concludes that NOx evolution by the nr1 mutant was due to nonenzymic, chemical reactions between plant metabolites and accumulated NO2− and/or decomposition of nitrous acid. Nonenzymic NOx evolution probably also occurs in wild type to a degree but could be easily masked by high rates of the enzymic process. 相似文献
6.
Summary The cellular events during the primary immune response in T and B cell compartments in the splenic white pulp were analysed in germfree mice immunized with sheep erythrocytes. Light, fluorescence and electronmicroscopic studies revealed that the initial formation of lymphoid blast cells occurs in the thymus-dependent area, i.e. the central periarteriolar lymphatic sheath (central PALS), 2 days after immunization. Lymphoblasts were found in close relation with erythrocyte-containing macrophages and with interdigitating cells. With fluorescence microscopy these blast cells were Ig negative. Lymphoblasts in the central PALS showed many polyribosomes in the cytoplasm, but were virtually devoid of endoplasmic reticulum. The ultrastructure of lymphoblasts in the central PALS, and their relation with interdigitating cells, suggests that these cells are the progeny of antigen-activated T cells.Cells with a positive cytoplasmic fluorescence, plasmablasts, appeared 3 days after immunization in the peripheral part of the PALS. During the progress of the immune response these cells accumulated around branches of the central arteriole, and moved along marginal zone bridging channels towards the red pulp. In the electron microscope plasmablasts showed many polyribosomes, short strands of rough endoplasmic reticulum close to mitochondria, and a few electron-dense bodies. The cell organelles of plasmablasts were frequently gathered in a so called uropod, which is a morphological sign of active cell movement.Germinal center formation started within primary follicles, 4 days after immunization. Blast cells in germinal centers did not show cytoplasmic fluorescence. During the course of the immune response, germinal centers extended in diameter, and fluorescent dendritic cells appeared at the periphery of the germinal center.From the present observations we conclude that: (1) cellular cooperation between different lymphoid and non-lymphoid cell types during the immune response against SRBC takes place in the PALS, (2) the cellular cooperation in the PALS results in the differentiation of B cells into immunoglobulin-producing plasmablasts, (3) the cellular cooperation in the PALS preceeds the formation of germinal centers in primary follicles, hence germinal centers are not involved in early T-B cell cooperation. 相似文献
7.
Christophe Meyer Kristoff Corten Mariska Wesseling Koen Peers Jean-Pierre Simon Ilse Jonkers Kaat Desloovere 《PloS one》2013,8(11)
The burden of hip muscles weakness and its relation to other impairments has been well documented. It is therefore a pre-requisite to have a reliable method for clinical assessment of hip muscles function allowing the design and implementation of a proper strengthening program. Motor-driven dynamometry has been widely accepted as the gold-standard for lower limb muscle strength assessment but is mainly related to the knee joint. Studies focusing on the hip joint are less exhaustive and somewhat discrepant with regard to optimal participants position, consequently influencing outcome measures. Thus, we aimed to develop a standardized test setup for the assessment of hip muscles strength, i.e. flexors/extensors and abductors/adductors, with improved participant stability and to define its psychometric characteristics. Eighteen participants performed unilateral isokinetic and isometric contractions of the hip muscles in the sagittal and coronal plane at two separate occasions. Peak torque and normalized peak torque were measured for each contraction. Relative and absolute measures of reliability were calculated using the intraclass correlation coefficient and standard error of measurement, respectively. Results from this study revealed higher levels of between-day reliability of isokinetic/isometric hip abduction/flexion peak torque compared to existing literature. The least reliable measures were found for hip extension and adduction, which could be explained by a less efficient stabilization technique. Our study additionally provided a first set of reference normalized data which can be used in future research. 相似文献
8.
Mariska Batavia George Nguyen Kristine Harman Irving Zucker 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2013,183(2):269-277
Turkish hamsters (Mesocricetus brandti) are a model organism for studies of hibernation, yet a detailed account of their torpor characteristics has not been undertaken. This study employed continuous telemetric monitoring of body temperature (T b) in hibernating male and female Turkish hamsters at ambient temperatures (T as) of 5 and 13 °C to precisely characterize torpor bout depth, duration, and frequency, as well as rates of entry into and arousal from torpor. Hamsters generated brief intervals of short (<12 h), shallow test bouts (T b > 20 °C), followed by deep torpor bouts lasting 4–6 days at T a = 5 °C and 2–3 days at T a = 13 °C. Females at T a = 5 °C had longer bouts than males, but maintained higher torpor T b; there were no sex differences at T a = 13 °C. Neither body mass loss nor food intake differed between the two T as. Hamsters entered torpor primarily during the scotophase (subjective night), but timing of arousals was highly variable. Hamsters at both T as generated short, shallow torpor bouts between deep bouts, suggesting that this species may be capable of both hibernation and daily torpor. 相似文献
9.
Mariska Wesseling Lode Bosmans Christophe Van Dijck Jos Vander Sloten Roel Wirix-Speetjens Ilse Jonkers 《Computer methods in biomechanics and biomedical engineering》2019,22(4):376-385
To account for proximal femoral deformities in children with cerebral palsy (CP), subject-specific musculoskeletal models are needed. Non-rigid deformation (NRD) deforms generic onto personalized bone geometry and thereby transforms the muscle points. The goal of this study was to determine to what extent the models and simulation outcomes in CP patients differ when including subject-specific detail using NRD or Magnetic Resonance Imaging (MRI)-based models. The NRD models slightly overestimated hip contact forces compared to MRI models and differences in muscle point positions and moment arm lengths (MALs) remained, although differences were smaller than for the generic model. 相似文献
10.
Defective Glucose Transport Across Brain Tissue Barriers: A Newly Recognized Neurological Syndrome 总被引:6,自引:0,他引:6
Klepper J Wang D Fischbarg J Vera JC Jarjour IT O'Driscoll KR De Vivo DC 《Neurochemical research》1999,24(4):587-594
Impaired glucose transport across brain tissue barriers causes infantile seizures, developmental delay and acquired microcephaly. Since the first report in 1991 (De Vivo et al, NEJM, 1991) 17 patients have been identified with the glucose transporter protein syndrome (GTPS). The diagnostic feature of the syndrome is an unexplained hypoglycorrhachia in the clinical setting of an infantile epileptic encephalopathy. We review our clinical experience by highlighting one illustrative case: a 6-year old girl who presented at age 2 months with infantile seizures and hypoglycorrhachia. The CSF/blood glucose ratio was 0.33. DNA sequencing identified a missense mutation in exon 7 (C1108T). Erythrocyte GLUT1 immunoreactivity was normal. The time course of 3-0-methyl-glucose (3OMG) uptake by erythrocytes of the patient was 46% that of mother and father. The apparent Km was similar in all cases (2–4 mmol/L), but the apparent Vmax in the patient was only 28% that of the parents (500 versus 1,766 fmol/s/106RBC; p < 0.004). In addition, a 3-month trial of oral thioctic acid also benefited the patient and increased the Vmax to 935 fmol/s/106 RBC (p < 3 × 10–7). Uptake of dehydroascorbic acid by erythrocytes of the patient was impaired to the same degree as that of 3OMG (Vmax was 38% of that of the mother's), which supports previous observations of GLUT1 being multifunctional. These studies confirm the molecular basis of the GTPS and the multifunctional role of GLUT1. The need for more effective treatment is compelling. 相似文献