全文获取类型
收费全文 | 279篇 |
免费 | 1篇 |
出版年
2013年 | 7篇 |
2012年 | 3篇 |
2011年 | 2篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2003年 | 10篇 |
2001年 | 3篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 7篇 |
1970年 | 3篇 |
1969年 | 6篇 |
1952年 | 1篇 |
1938年 | 1篇 |
1937年 | 2篇 |
1936年 | 1篇 |
1929年 | 1篇 |
1927年 | 1篇 |
1925年 | 1篇 |
1924年 | 2篇 |
排序方式: 共有280条查询结果,搜索用时 15 毫秒
111.
MOHAPATRA SHYAM S.; POOLE RONALD J.; DHINDSA RAJINDER S. 《Journal of experimental botany》1987,38(10):1697-1703
Mohapatra, S. S., Poole, R. J. and Dhindsa, R. S. 1987. Coldacclimation, freezing resistance and protein synthesis in alfalfa(Medicago sativa L. cv. Saranac).J. exp. Bot. 38: 16971703. Changes in freezing resistance (percent survival at 10°C), pattern of protein synthesis and translatable mRNApopulation during cold acclimation of alfalfa (Medicago sativaL. cv. Saranac) have been examined. Two days of cold acclimationat 4 °C increased freezing resistance from about 6% to 40%,protein content by 200% and total RNA content by 100%. Acclimationfor longer periods did not cause further increases in freezingresistance, protein content or RNA content. Examination of proteinchanges by sodium dodecyl sulphate-polyacrylamide gel electrophoresis(SDS-PAGE) coupled with protein staining, and by fluorographyof in vivo labelled proteins separated by SDS-PAGE, showed thatseveral proteins are increasingly or newly synthesized duringcold acclimation. Analysis of in vitro translation productsby SDS-PAGE and fluorography shows changes in the populationof translatable mRNAs. It is concluded that in this varietyof alfalfa cold acclimation for only 2 d is sufficient to confermaximum freezing resistance, and that changes in proteins duringcold acclimation are regulated most probably at the transcnptionallevel. Key words: Freezing resistance, protein synthesis, cold acclimation, SDS-PAGE, Medicago sativa L. 相似文献
112.
Spatial and temporal variation in the diet of a predaceous stonefly (Plecoptera: Perlodidae) 总被引:1,自引:0,他引:1
SUMMARY. 1. Spatial and temporal variation in the diet of the univoltine predatory stonefly, Kogotus nonus , was studied over 3 years in a small Alberta stream to determine whether the relative abundance of prey types in the diet of Kogotus reflected relative prey densities in the stream and whether the variation in absolute feeding rate was related to either prey or predator density.
2. The seasonal shift from sole utilization of Orthocladiinae to inclusion of Baetis in the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.
3. Feeding rate on Baetis . as assessed by per capita gut contents, showed a seasonal shift from a positive correlation with Baetis density in winter to a negative relationship with predator density in spring. This suggested that feeding by small Kogotus is a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference. 相似文献
2. The seasonal shift from sole utilization of Orthocladiinae to inclusion of Baetis in the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.
3. Feeding rate on Baetis . as assessed by per capita gut contents, showed a seasonal shift from a positive correlation with Baetis density in winter to a negative relationship with predator density in spring. This suggested that feeding by small Kogotus is a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference. 相似文献
113.
BAUMGARTNER BRIAN J.; RILEY SEAN P.; KASSCHAU MARGARET R.; MILLS W. RONALD 《Journal of experimental botany》1988,39(11):1495-1504
Incorporation of [3H]TTP into DNA by pea chloroplast extractswas highly dependent on the age of the tissue from which plastidswere prepared. Catalytic activity was greatest in samples from6- to 9-d-old plants; preparations from more mature tissueswere much less effective. Moreover, activity was 3 to 10 timesgreater in younger tissues regardless of whether chlorophyll,protein or plastid number was used as the index of comparison.Enzymes from the first (oldest), second, third, and fourth (youngest)leaves of the same plants were also studied. Again, activitywas 4 to 10 times greater in samples from the youngest tissues.When plastid extracts from older leaves were mixed with thosefrom younger tissues, they did not reduce synthesis. Thus, thedecline in activity does not appear to be due to the productionof an inhibitor during plant development. One explanation forthese data is that enzymes of ctDNA replication, such as DNApolymerase, vary in activity during leaf development; thereforechanges in enzyme levels may be an important factor in controllingchloroplast DNA replication during development. We have alsoexamined the incorporation of [3H]TTP into DNA by isolated intactpea chloroplasts; in general, labelled TTP was less readilyincorporated into chloroplast DNA than was [3H]thymidine. Key words: Chloroplast DNA replication, chloroplast DNA polymerase 相似文献
114.
RONALD G. WILSON STEPHEN K. TAHIR RAPHAEL MECHOULAM SELMA ZIMMERMAN ARTHUR M. ZIMMERMAN 《Cell biology international》1996,20(2):147-157
The negative and positive enantiomers of 7-hydroxy- Δ6-tetrahydrocannabinol-dimethylheptyl (designated HU-210 and HU-211 respectively) differentially affect undifferentiated and differentiating cultured pheochromocytoma cells (PC-12 cells). In general, cell viability and cell proliferation were suppressed to a much greater extent with HU-210 than with HU-211 in differentiating cells. The effects of these synthetic cannabinoids on the cytoskeleton of PC-12 cells were examined by epifluorescence and confocal microscopy. In both undifferentiated and differentiating PC-12 cells, HU-211 has little effect on the cytoarchitecture whereas HU-210 disrupts the distribution of microtubules and microfilaments. Vacuoles (2–4 μm) were evident in the cytoplasm of HU-210-treated cells but not in the cytoplasm of HU-211-treated cells or in vehicle controls. Tubulin and actin mRNA levels were reduced to 5 and 40 %, respectively (relative to untreated controls) in 10 μmHU-210-treated cells whereas the same concentration of HU-211 reduced tubulin and actin mRNA levels to 90 and 95 %, respectively. A comparison of the effects of the paired enantiomers and Δ1-THC on the cellular parameters studied reveals that in differentiating cells the action of Δ1-THC is intermediate between that of HU-210 and HU-211. This study demonstrates that compared to HU-210 and Δ1-THC the positive enantiomer HU-211 has little cellular activity. 相似文献
115.
DE SCHUTTER ERIK; SIMON TED W.; ANGSTADT JAMES D.; CALABRESE RONALD L. 《Integrative and comparative biology》1993,33(1):16-28
SYNOPSIS. Heartbeat in the medicinal leech is paced by a neuraloscillator comprising two elemental oscillators whose activityis coordinated intersegmental coordinating fibers. The elementaloscillators each consist of a bilateral pair of heart interneuronslinked by reciprocal inhibitory synapses. The activity cycleof each elemental oscillator consists of alternating burstsof action potentials (plateau/burst phase) and periods inhibition(inactive phase). Oscillation ensues in the reciprocally inhibitorypairs because each neuron is able to escape from the inhibitionits contralateral partner and thus move on to the plateau/burstphase. We have identified and described membrane currents thatcontribute to oscillation and studied graded synaptic transmissionbetween the neurons, using discontinuous current clamp and switchingsingle electrode voltage clamp techniques. A hyperpolarization-activatedinward current, Ih, plays a major role in escape from inhibition,and Ca2+ currents produce plateau potentials that support burstformation and mediate graded synaptic transmission. To consolidate our knowledge and guide future research, we haveconstructed a first generation computer model of a neural oscillatorbased on reciprocal inhibition, using Hodgkin-Huxley equationsand a synaptic transfer model, derived from our biophysicalstudies, with Nodus software (De Schutter, 1989). This modelhas confirmed an important role for Ih in sustaining oscillationand has implicated a similarly important role for outward currents(particularly IA), which remain to be studied. Neural oscillatorsbased on reciprocal inhibition appear to be ubiquitous, andour studies, biophysical and computational, provide insightsinto how they may operate. 相似文献
116.
117.
118.
RONALD FAYER 《The Journal of eukaryotic microbiology》1981,28(2):266-267
Problems of the taxonomy and, especially, of the nomenclature of various species of coccidia of direct importance to humans are further discussed. The diversity of host potential and site selection is also mentioned, with the prediction that, hopefully, our knowledge will be much greater 15 years from now than it presently is. 相似文献
119.
120.
RONALD M. DOBSON 《Systematic Entomology》1972,41(2):145-150
A new species of Carpophilus is described from males and females taken in Florida, U.S.A. A lectotype male and paralectotype female are chosen for Carpophilus ophthalmicus, and a new species is described from material misidentified as ophthalmicus. 相似文献