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排序方式: 共有236条查询结果,搜索用时 15 毫秒
1.
Genetically modified tobacco plants (Nicotiana tabacumSamsun)with antisense cinnamyl alcohol dehydrogenase DNA, produce secondaryxylem of a reduced tensile stiffness. These plants were grownalongside control plants. The stems of the plants were flexedor protected from flexing over a period of several weeks. Thetensile moduli and second moments of areas of the differenttissues inside the stems were measured and used to calculatethe bending stiffness of the plants. In tobacco, the cylinderof xylem was found to be the most important tissue in determiningthe bending stiffness of the plants. The thickness of the xylemtissue cylinder increased when plants were subjected to flexuralstimulation. This increased the bending stiffness of the stems.The response to mechanical stimulation was found to be correlatedwith tissue strain and the genetically modified plants wereable to exactly compensate for the reduced modulus of theirxylem tissue by increasing the thickness of the xylem tissuecylinder more than in control plants.Copyright 1999 Annals ofBotany Company. Tobacco plants, stem bending, xylem tissue, second moment of area, thigmomorphogenesis, mechanical strain. 相似文献
2.
Interactions between Marek's Disease Herpesvirus and Avian Leucosis Virus in Tissue Culture 总被引:3,自引:0,他引:3
A GROUP B herpesvirus is important in the aetiology of Marek's disease, a highly contagious lymphoproliferative disease of chickens1,2. Chicks inoculated with enveloped Marek's disease herpesvirus (MDHV), extracted from feather follicle epithelium of chickens with the disease, developed tumour-like aggregates of lymphoid cells in the viscera and frequently in the peripheral nerves3,4. Cultures of chicken embryo fibroblast (CEF) cells infected with MDHV develop discrete foci of altered cells5. Our data show that MDHV infection of cultures of CEF cells, previously infected with an avian leucosis virus (RAV-2), results in both a reduction in the number of MDHV foci and an increase in the complement fixing avian leucosis antigen (COFAL)6 titre. 相似文献
3.
Habitat and substrate influences on population and production dynamics of a stream caddisfly, Ceraclea ancylus (Leptoceridae) 总被引:1,自引:0,他引:1
VINCENT H. RESH 《Freshwater Biology》1977,7(3):261-277
SUMMARY. Population and production dynamics of Ceraclea ancylus (Vorhies), a leptocerid caddisfly with a univoltine life cycle, five larval instars, and a single cohort population, were examined in Brashears Creek, Kentucky. A systematic sampling approach that included analysis in riffle, pool, and waterwillow bed habitats was used and fourteen sampling transects were taken across Brashears Creek between May 1971 and July 1972. For each of the 70 m2 samples taken along a transect, the depth, habitat, and substrate type were recorded. The number of C. ancylus cases and numbers and dry weights of each larval instar were determined. The majority of the C. ancylus population was in the second larval instar in July, the third larval instar in August, the fourth larval instar in September, and the fifth larval instar from October through May. The spring population was 30% of the early instar maximum estimated the previous August. The spatial distribution of C. ancylus reflects a logarithmic pattern with early instar larvae more highly clumped than the late larval instar and pupal populations. Initial standing stock estimates were less than 1% of the standing stock biomass. A production estimate of 9.9 mg/m2·year (dry weight) was determined using the instantaneous growth method, Allen's Curve method, and the Hynes method of estimating secondary production. Turnover ratios (7.0 annual TR, 5.7 cohort TR) were higher than estimates reported as typical for benthic macroinvertebrates because of the low initial to final mean individual weight of the C. ancylus larvae (0.4%). Production estimates calculated for C. ancylus populations in waterwillow bed (4.4 mg/m2·year) and pool (13.7 mg/m2·year) habitats were less than calculated for the riffle population (19.9 mg/m2·year). The annual turnover ratio (10.2) was higher in the pool population than in other habitats because of spring larval migration into the pool from other habitats. A trend of higher production estimates with larger sized substrate particles and increased numbers of particles may reflect the increase in available food sources or attachment sites. The accuracy of production estimates and their applicability to water resource management may be limited by a failure to consider the spatial distributions of the population being sampled and the tendency for sampling procedures to be confined to single habitats. 相似文献
4.
Aggregation-dependent turnover of flagellar adhesion molecules in chlamydomonas gametes 总被引:8,自引:7,他引:1
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Previous studies on flagellar adhesion in chlamydomonas (Snell, W. and S. Roseman. 1979. J. Biol. Chem. 254:10820-10829.) have shown that as gametes adhere to flagella isolated from gametes of the opposite mating type, the adhsiveness of the added flagella but not of the gametes is lost. The studies reported here show that the addition of protein synthesis inhibitors (cycloheximide [CH] or anisomycin) to the medium of such cell- flagella mixtures causes the cells to lose their adhesiveness. This loss, however, occurs only after the cells have interacted with 4-8 flagella/cell and does not occur if the cells are kept in CH (7 h) without aggregating. The availability of an impotent (imp) mating type plus (MT(+)) mutant (provided by U.W. Goodenough), which adheres but is unable to undergo the fusion that normally follows adhesion, made it possible to determine whether a similar loss of adhesiveness occurs in mixtures of matting type minus (mt(-)) and imp mt(+) gametes. In the absence of inhibitor, mt(-) and imp mt(+) gametes adhered to each other (without fusing) for several hours; however, in the presence of CH or anisomycin, the gametes began to de-adhere 35 min after mixing, and, by 90 min, 100 percent of the cells were single again. This effect was reversible, and the rapid turnover of cells were single again. This effect was reversible, and the rapid turnover of molecules involved in adhesion occurred only during adhesion inasmuch as gametes pretreated for 4 h with CH were able to aggregate in CH for the same length of time as nonpretreated cells aggregated in CH. By the addition of CH at various times after the mt(-) and imp mt(+) gametes were mixed, measurements were made of the “pool size” of the molecules involved in adhesion. The pool reached a minimum after 25 min of aggregation, rapidly increased for the next 25 min, and then leveled off at the premixing level. These results suggest that flagellar adhesion in chlamydomonas causes modification of surface molecules (receptors, ligands), which brings about their inactivation and stimulates their replacement. 相似文献
5.
ALEXANDRA HOUSSAYE JEAN‐CLAUDE RAGE NATHALIE BARDET PEGGY VINCENT MBAREK AMAGHZAZ SAID MESLOUH 《Palaeontology》2013,56(3):647-661
Abstract: Palaeophis maghrebianus belongs to the Palaeophiinae (Palaeophiidae). This snake subfamily is relatively poorly known, and it is mainly represented by disarticulated vertebrae and ribs and by a few vertebral segments. Its intracolumnar variability remains also poorly understood. The discovery of new isolated vertebrae and vertebral segments of Palaeophis maghrebianus in the Ypresian (Lower Eocene) Phosphates of Morocco enables us to provide a more detailed diagnosis of this species and to describe its intracolumnar variability. Moreover, the new material reveals that this species could reach gigantic size being, with Palaeophis colossaeus, one of the two longer palaeophiids. The microanatomical and histological analysis of some vertebrae illustrating diverse positions along the vertebral column reveals the presence of osteosclerosis, especially in the anterior and mid‐precloacal regions. The occurrence of this osseous specialization implies a role in buoyancy and body trim control in this taxon, which is considered a shallow marine dweller based on its anatomical features and geological data. Palaeophis maghrebianus also displays a dense vascular network suggesting a growth speed, and thus a metabolic rate, much higher than in the biggest extant snakes. 相似文献
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8.
1. Field experiments were conducted to examine interactions between larvae of the caddisfly Gumaga nigricula and the algae (primarily diatoms) located on their sand grain cases. Floating experimental enclosures were placed in sunlit pools of a California stream. Treatments applied to occupied cases, or to those from which caddisflies had been removed, included variations in grazer density, addition of nutrients, and modification of illumination using shade cloth. 2. Neither faecal-enriched agar in empty cases nor injections of faecal material into plugged cases affected case chlorophyll a concentration; injected nutrients (N and P), however, did increase chlorophyll a concentration. Faecal material may be nutrient poor, or nutrients may not be readily released. In addition, the relatively impermeable case wall may reduce the likelihood that nutrients from caddisflies reach the algae on the outer case surface. 3. Although a Gumaga larva may graze algae from its own case, grazing by conspecifics and the caddisfly Helicopsyche borealis causes a greater reduction in the chlorophyll a content of cases. 4. Chlorophyll a content of empty cases was decreased by experimental reduction of light. Because of shading associated with burrowing, chlorophyll a content of cases occupied by Gumaga was low and was unaffected by experimental light reduction. 5. Removal of Gumaga from its case results in rapid accrual of algae. Thus, the net effect of larval presence is to diminish the algal content of its case. 相似文献
9.
Salt sensitivity in chickpea (Cicer arietinum L.): ions in reproductive tissues and yield components in contrasting genotypes
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LUKASZ KOTULA HAMMAD A. KHAN JOHN QUEALY NEIL C. TURNER VINCENT VADEZ KADAMBOT H. M. SIDDIQUE PETA L. CLODE TIMOTHY D. COLMER 《Plant, cell & environment》2015,38(8):1565-1577
The reproductive phase in chickpea (Cicer arietinum L.) is affected by salinity, but little is known about the underlying cause. We investigated whether high concentrations of Na+ and Cl– in the reproductive structures influence reproductive processes. Chickpea genotypes contrasting in tolerance were subjected to 0, 35 or 50 mm NaCl applied to soil in pots. Flower production and abortion, pod number, percentage of empty pods, seed number and size were evaluated. The concentrations of Na+, K+ and Cl– were measured in various plant tissues and, using X‐ray microanalysis, in specific cells of developing reproductive structures. Genotypic variation in reproductive success measured as seed yield in saline conditions was associated with better maintenance of flower production and higher numbers of filled pods (and thus seed number), whereas seed size decreased in all genotypes. Despite the variation in reproductive success, the accumulation of Na+ and Cl– in the early reproductive tissues of developing pods did not differ between a tolerant (Genesis836) and a sensitive (Rupali) genotype. Similarly, salinity tolerance was not associated with the accumulation of salt ions in leaves at the time of reproduction or in seeds at maturity. 相似文献
10.
Brooke R Snyder Pei-Hsun Cheng Jinjing Yang Shang-Hsun Yang Anderson HC Huang Anthony WS Chan 《BMC cell biology》2011,12(1):1-8