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51.
52.
Lucas A. Cernusak Margaret M. Barbour Stefan K. Arndt Alexander W. Cheesman Nathan B. English Taylor S. Feild Brent R. Helliker Meisha M. Holloway‐Phillips Joseph A.M. Holtum Ansgar Kahmen Francesca A. McInerney Niels C. Munksgaard Kevin A. Simonin Xin Song Hilary Stuart‐Williams Jason B. West Graham D. Farquhar 《Plant, cell & environment》2016,39(5):1087-1102
Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases. Models describing evaporative enrichment of leaf water have become increasingly complex over time, reflecting enhanced spatial and temporal resolution. We recommend that practitioners choose a model with a level of complexity suited to their application, and provide guidance. At the same time, there exists some lingering uncertainty about the biophysical processes relevant to patterns of isotopic enrichment in leaf water. An important goal for future research is to link observed variations in isotopic composition to specific anatomical and physiological features of leaves that reflect differences in hydraulic design. New measurement techniques are developing rapidly, enabling determinations of both transpired and leaf water δ18O and δ2H to be made more easily and at higher temporal resolution than previously possible. We expect these technological advances to spur new developments in our understanding of patterns of stable isotope fractionation in leaf water. 相似文献
53.
A study of bacterial surface oligosaccharides were investigated among
different strains of Neisseria gonorrhoeae to correlate structural features
essential for binding to the MAb 2C7. This epitope is widely expressed and
conserved in gonococcal isolates, characteristics essential to an effective
candidate vaccine antigen. Sample lipooligosaccharides (LOS), was prepared
by a modification of the hot phenol-water method from which de-O-acetylated
LOS and oligosaccharide (OS) components were analyzed by ES-MS-CID-MS and
ES-MSnin a triple quadrupole and an ion trap mass spectrometer,
respectively. Previously documented natural heterogeneity was apparent from
both LOS and OS preparations which was admixed with fragments induced by
hydrazine and mild acid treatment. Natural heterogeneity was limited to
phosphorylation and antenni extensions to the alpha-chain. Mild acid
hydrolysis to release OS also hydrolyzed the beta(1-->6) glycosidic
linkage of lipid A. OS structures were determined by collisional and
resonance excitation combined with MS and multistep MSn which provided
sequence information from both neutral loss, and nonreducing terminal
fragments. A comparison of OS structures, with earlier knowledge of MAb
binding, enzyme treatment, and partial acid hydrolysis indicates a generic
overlapping domain for 2C7 binding. Reoccurring structural features include
a Hepalpha(1-->3)Hepbeta(1-->5)KDO trisaccharide core branched on the
nonreducing terminus (Hep-2) with an alpha(1-->2) linked GlcNAc
(gamma-chain), and an alpha-linked lactose (beta-chain) residue. From the
central heptose (Hep-1), a beta(1-->4) linked lactose (alpha-chain),
moiety is required although extensions to this residue appear unnecessary.
相似文献
54.
M A Diversé-Pierluissi T Fischer J D Jordan M Schiff D F Ortiz M G Farquhar L De Vries 《The Journal of biological chemistry》1999,274(20):14490-14494
Norepinephrine inhibits omega-conotoxin GVIA-sensitive presynaptic Ca2+ channels in chick dorsal root ganglion neurons through two pathways, one mediated by Go and the other by Gi. These pathways desensitize at different rates. We have found that recombinant Galpha interacting protein (GAIP) and regulators of G protein signaling (RGS)4 selectively accelerate the rate of desensitization of Go- and Gi-mediated pathways, respectively. Blockade of endogenous RGS proteins using antibodies raised against Galpha interacting protein and RGS4 slows the rate of desensitization of these pathways in a selective manner. These results demonstrate that different RGS proteins may interact with Gi and Go selectively, giving rise to distinct time courses of transmitter-mediated effects. 相似文献
55.
On the metabolic origin of the carbon isotope composition of CO2 evolved from darkened light-acclimated leaves in Ricinus communis 总被引:1,自引:1,他引:0
56.
Vertical niche overlap by two ocean giants with similar diets: Ocean sunfish and leatherback turtles 总被引:1,自引:0,他引:1
Graeme C. Hays Michael R. Farquhar Paolo Luschi Steven L.H. Teo Tierney M. Thys 《Journal of experimental marine biology and ecology》2009,370(1-2):134-143
We used satellite tags to record the patterns of depth utilisation for four ocean sunfish (Mola mola) and two leatherback turtles (Dermochelys coriacea) moving in broadly the same area off South Africa. Individuals were tracked for between 2 and 8 months and dive data relayed via satellite. For all the sunfish and one of the turtles, we received binned data on depth distribution, while for the second turtle we received individual dive profiles along with the proportion of time spent diving. Leatherback turtles dived almost exclusively within the upper 200 m, spending only 0.6 and 0.2% of their time > 200 m. There were times when sunfish likewise occupied these relatively shallow depths. However, there were also protracted periods when sunfish spent the majority of their time much deeper, with one individual remaining around 500 m for many hours at a time. These results suggest that sunfish sometimes exploit deeply distributed prey which is beyond the foraging range of leatherback turtles. We conclude that while both species are believed to feed predominantly on gelatinous zooplankton, the fact that sunfish do not need to come to the surface to breathe means that they can occupy an expanded vertical niche compared to the leatherback turtle. 相似文献
57.
Flint M von Hahn T Zhang J Farquhar M Jones CT Balfe P Rice CM McKeating JA 《Journal of virology》2006,80(22):11331-11342
Hepatitis C virus (HCV) entry is dependent on CD81. To investigate whether the CD81 sequence is a determinant of HCV host range, we expressed a panel of diverse CD81 proteins and tested their ability to interact with HCV. CD81 large extracellular loop (LEL) sequences were expressed as recombinant proteins; the human and, to a low level, the African green monkey sequences bound soluble HCV E2 (sE2) and inhibited infection by retrovirus pseudotype particles bearing HCV glycoproteins (HCVpp). In contrast, mouse or rat CD81 proteins failed to bind sE2 or to inhibit HCVpp infection. However, CD81 proteins from all species, when expressed in HepG2 cells, conferred susceptibility to infection by HCVpp and cell culture-grown HCV to various levels, with the rat sequence being the least efficient. Recombinant human CD81 LEL inhibited HCVpp infectivity only if present during the virus-cell incubation, consistent with a role for CD81 after virus attachment. Amino acid changes that abrogate sE2 binding (I182F, N184Y, and F186S, alone or in combination) were introduced into human CD81. All three amino acid changes in human CD81 resulted in a molecule that still supported HCVpp infection, albeit with reduced efficiency. In summary, there is a remarkable plasticity in the range of CD81 sequences that can support HCV entry, suggesting that CD81 polymorphism may contribute to, but alone does not define, the HCV susceptibility of a species. In addition, the capacity to support viral entry is only partially reflected by assays measuring sE2 interaction with recombinant or full-length CD81 proteins. 相似文献
58.
Juengel JL O'Connell AR French MC Proctor LE Wheeler R Farquhar PA Dodds KG Galloway SM Johnstone PD Davis GH 《Biology of reproduction》2011,85(1):113-120
Sheep lines with mutations in single genes that have major effects on ovulation rate have been very useful in gaining a better understanding of pathways important in controlling follicular development and ovulation rate. To date however, all known mutations are in the transforming growth factor beta (TGFB) superfamily. Ovulation rates were measured in 720 progeny of 20 rams that were descendants of a single prolific ewe. Evaluation of ovulation rates of daughters of closely related sires suggests the presence of a segregating major gene Fecundity Davisdale (FECD) that increases ovulation rate between 0.4 and 0.8 in heterozygous daughters. Key features of mutations in genes of the TGFB superfamily pathway, such as synergistic interactions with other family members, infertility in homozygous carriers, and increased responsiveness to exogenous gonadotropins, were not observed in this line; thus, the mutation does not appear to be acting in the TGFB pathway. Hence, there is likely a novel mutation being carried in this line of sheep that alters ovulation rate. Future identification of the causative mutation may provide new insights into regulation of follicular development and ovulation rate. 相似文献
59.
Bonander N Jamshad M Hu K Farquhar MJ Stamataki Z Balfe P McKeating JA Bill RM 《Biochemical Society transactions》2011,39(2):537-540
Tetraspanins are thought to exert their biological function(s) by co-ordinating the lateral movement and trafficking of associated molecules into tetraspanin-enriched microdomains. A second four-TM (transmembrane) domain protein family, the Claudin superfamily, is the major structural component of cellular TJs (tight junctions). Although the Claudin family displays low sequence homology and appears to be evolutionarily distinct from the tetraspanins, CD81 and Claudin-1 are critical molecules defining HCV (hepatitis C virus) entry; we recently demonstrated that CD81-Claudin-1 complexes have an essential role in this process. To understand the molecular basis of CD81-Claudin-1 complex formation, we produced and purified milligram quantities of full-length CD81 and Claudin-1, alone and in complex, in both detergent and lipid contexts. Structural characterization of these purified proteins will allow us to define the mechanism(s) underlying virus-cell interactions and aid the design of therapeutic agents targeting early steps in the viral life cycle. 相似文献
60.
Effect of temperature on the CO2/O2 specificity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the rate of respiration in the light 总被引:1,自引:0,他引:1
Responses of the rate of net CO2 assimilation (A) to the intercellular partial pressure of CO2 (p
i
) were measured on intact spinach (Spinacia oleracea L.) leaves at different irradiances. These responses were analysed to find the value of p
i
at which the rate of photosynthetic CO2 uptake equalled that of photorespiratory CO2 evolution. At this CO2 partial pressure (denoted ), net rate of CO2 assimilation was negative, indicating that there was non-photorespiratory CO2 evolution in the light. Hence was lower than the CO2 compensation point, . Estimates of were obtained at leaf temperatures from 15 to 30°C, and the CO2/O2 specificity of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (E.C. 4.1.1.39) was calculated from these data, taking into account changes in CO2 and O2 solubilities with temperature. The CO2/O2 specificity decreased with increasing temperature. Therefore we concluded that temperature effects on the ratio of photorespiration to photosynthesis were not solely the consequence of differential effects of temperature on the solubilities of CO2 and O2. Our estimates of the CO2/O2 specificity of RuBP carboxylase/oxygenase are compared with in-vitro measurements by other authors. The rate of nonphotorespiratory CO2 evolution in the light (R
d
) was obtained from the value of A at . At this low CO2 partial pressure, R
d
was always less than the rate of CO2 evolution in darkness and appeared to decrease with increasing irradiance. The decline was most marked up to about 100 mol quanta m-2 s-1 and less marked at higher irradiances. At one particular irradiance, however, R
d
as a proportion of the rate of CO2 evolution in darkness was similar in different leaves and this proportion was unaffected by leaf temperature or by [O2] (ambient and greater). After conditions of high [CO2] and high irradiance for several hours, the rate of CO2 evolution in darkness increased and R
d
also increased.Abbreviations and symbols A
rate of net CO2-assimilation
-
CO2 compensation point
-
CO2 compensation point in the absence of R
d
-
p
i
intercellular partial pressure of CO2
-
R
d
(day respiration)
rate of non-photorespiratory CO2 evolution in the light
-
R
n
(night respiration)
rate of CO2 evolution in darkness
- RuBP
ribulose-1,5-bisphosphate
- Rubisco
RuBP carboxylase/oxygenase 相似文献