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951.
Tonic GABAergic inhibition of taste-responsive neurons in the nucleus of the solitary tract 总被引:4,自引:1,他引:3
The effects of gamma-aminobutyric acid (GABA) and the GABAA receptor
antagonist bicuculline methiodide (BICM) on the activity of taste-
responsive neurons in the nucleus of the solitary tract (NST) were examined
electrophysiologically in urethane-anesthetized hamsters. Single neurons in
the NST were recorded extracellularly and drugs (21 nl) were microinjected
into the vicinity of the cell via a multibarrel pipette. The response of
each cell was recorded to lingual stimulation with 0.032 M NaCl, 0.032 M
sucrose, 0.0032 M citric acid and 0.032 M quinine hydrochloride (QHCl).
Forty-six neurons were tested for the effects of GABA; the activity of 29
cells (63%) was inhibited by 5 mM GABA. Whether activity was elicited in
these cells by repetitive anodal current stimulation (25 microA, 0.5 s, 0.1
Hz) of the tongue (n = 13 cells) or the cells were spontaneously active (n
= 13 cells), GABA produced a dose-dependent (1, 2 and 5 mM) decrement in
activity. Forty- seven NST neurons were tested for the effects of BICM on
their responses to chemical stimulation of the tongue; the responses of 28
cells (60%) were enhanced by 10 mM BICM. The gustatory responses of 26 of
these cells were tested with three concentrations (0.2, 2 and 10 mM) of
BICM, which produced a dose-dependent increase in both spontaneous activity
and taste-evoked responses. Nine of these neurons were sucrose- best, seven
were NaCl-best, eight were acid-best and two responded best to QHCl. The
responses to all four tastants were enhanced, with no difference among
neuron types. For 18 cells that were tested with two or more gustatory
stimuli, BICM increased their breadth of responsiveness to their two most
effective stimuli. These data show that approximately 60% of the
taste-responsive neurons in the rostral NST are inhibited by GABA and/or
subject to a tonic inhibitory influence, which is mediated by GABAA
receptors. The modulation of these cells by GABA provides a mechanism by
which the breadth of tuning of the cell can be sharpened. Modulation of
gustatory activity following a number of physiological changes could be
mediated by such a GABAergic circuit.
相似文献
952.
Fowler M; Ong L; Russinova E; Atanassov A; Scott N; Slater A; Elliott M 《Journal of experimental botany》1998,49(319):249-253
A procedure for direct production of somatic embryos from alfalfa leaf
explants has been developed. Wounding followed by 2,4-D treatment induces
competent cells in the leaf to produce embryos. Changes in gene expression
following induction of direct somatic embryogenesis were investigated by
RNA arbitrarily primed PCR (RAP-PCR) with a view to identifying genes
involved in controlling the onset of somatic embryo development. Amongst
the induced sequences identified were a calnexin-like sequence (which was
induced within 2 d), and a novel plant homologue of the yeast SN12
multi-drug resistance protein (which did not appear until 10 d after
induction). RT-PCR amplification of these sequences confirmed the
expression patterns revealed by RAP-PCR and was used to show that the
calnexin-like gene is induced by 2,4-D, but that the level of expression is
enhanced by wounding. The technique of RAP-PCR has the potential to isolate
genes of interest by identifying specific expression patterns during
complex developmental processes. 相似文献
953.
954.
955.
The Land and Sea Dayaks of Sarawak were surveyed for several erythrocyte enzymes. The gene frequency of 6PGDC in 132 Land Dayaks and 127 Sea Dayaks were 0.045 and 0.047, respectively. The gene frequency of PGM1-1 IN 285 Land Dayks and 240 Sea Dayaks were 0.716 and 0.779, respectively. The ADA2 gene frequency in 283 Land Dayaks and 188 Sea Dayaks were 0.154 and 0.090. ADA 5-1 was found once in the Land Dayaks and once in the Sea Dayaks. AK 2-1 was found once in 221 Sea Dayaks but not in any of 270 Land Dayaks. No PHI, LDH or CA variants were found among the Land or Sea Dayaks. 相似文献
956.
Mutagenicity of aflatoxins in Neurospora crassa 总被引:2,自引:0,他引:2
T Ong 《Mutation research》1970,9(6):615-618
957.
A method using sister-chromatid exchanges (SCEs) for genotoxic testing of gaseous compounds is described. Human peripheral lymphocyte cultures previously stimulated with phytohemagglutinin were placed in sterile dialysis tubing and then put in an enclosed flask containing additional culture media. Air, with or without ethylene dibromide (EDB), was bubbled through the flask for up to 8 h. The cultures were harvested 75 h after culture initiation, and second-division cells were scored for induction of SCEs according to established procedures. The SCE frequency was approximately doubled in cultures treated with EDB. A similar experiment with air alone resulted in only slight increases in SCEs. The results indicate that this system is potentially useful for detecting genotoxicity of gases and vapors and may be useful for the detection of genotoxic agents in occupational settings. 相似文献
958.
I.Kofi Adzamli Henry Ong Wah Kim A.Geoffrey Sykes George V. Buxton 《Journal of inorganic biochemistry》1982,16(4):311-317
The reaction of parsley 2Fe-2S ferredoxin in the normal oxidized state with eaq? generated by pulse radiolysis techniques has been studied at ~25°C, pH 7–8, I = 0.10 M (NaClO4). Rate constants ke (eaq? decay) and kp (protein absorbance change) are the same, second-order rate constant 9.7 × 109 M?1 sec?1. The reaction exhibits close to 100% efficiency. With 8Fe-8S ferredoxin from Clostridium pasteurianum under identical conditions it now appears that kp (although sometimes significantly smaller) is equal to ke. Varying efficiencies are also observed with this protein depending on the batch used. The reasons for such variable behavior are not fully understood. With oxidized and reduced forms of Chromatium v. high-potential iron-sulfur protein (HIPIP), ke and kp are essentially the same, but the highest efficiency observed is only ~50%. The prevailing pattern is therefore that rate constants ke and kp are generally in step for proteins having a single (or identical) active site(s). When the active site is buried as with HIPIP the efficiency of the reaction appears to decrease. 相似文献
959.
Although it is now apparent that the intracellular pH may rise considerably above neutrality under physiological conditions, information on the effect of alkaline pH on microtubule assembly and disassembly is still quite fragmentay. We have studied the assembly/disassembly of bovine brain microtubule protein at alkaline pH in vitro. When microtubules are assembled to a new steady state at pH less than 7 and pH is then made more alkaline, they undergo a rapid disassembly to a new steady state. This disassembly is reversed by acidification. The degree of disassembly is determined largely by the pH- dependence of the critical concentration, which increases five to eight times, from pH 7 to 8. A fraction of assembly-incompetent tubulin is identified that increases with pH, but its incompetency is largely reversed with acidification. Measurements of microtubule lengths are used to indicate that disassembly occurs by uniform shortening of microtubules. A comparison of shortening by alkalinization with dilution suggests that the intrinsic rate of disassembly is accelerated by increasing pH. The capacity for initiating assembly is progressively lost with incubation at alkaline pH (although some protection is afforded by sulfhydryl-reducing agents). However, direct assembly from depolymerized mixtures is possible at least up to pH 8.3, and the steady state achieved at these alkaline pH values is stable. Such preparations are readily disassembled by cold and podophyllotoxin (PLN). Disassembly induced by PLN is also markedly enhanced at alkaline pH, suggesting a corresponding enhancement of “treadmilling.” The implications of physiological events leading to alkaline shifts of pH for microtubule assembly/disassembly are discussed, particularly in the light of recent hypotheses regarding treadmilling and its role in controlling the distribution of microtubules in vivo. 相似文献
960.
Summary The Land Dayaks and the Sea Dayaks of Sarawak were surveyed for haptoglobin, transferrin and serum albumin variants. The Hp1 gene frequency was 0.385 in 283 Land Dayaks as well as in 205 Sea Dayaks. The TfDChi gene frequency in 283 Land Dayaks was 0.030 and in 188 Sea Dayaks it was 0.040. Serum albumin Medan was found in one of the 188 Sea Dayaks.This work was supported in part by the University of California International Center for Medical Research (UC ICMR) through research grant AI 10051, and in part by research grant HL 10486, both from the National Institutes of Health, U.S. Public Health Service. 相似文献