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971.
Kjellmaniella crassifolia, the edible macro-brown alga in Japan contained nearly 27% of alginates of which nearly 7% was extractable from the fronds with boiling water for 6 h and the residual alginates in the frond were almost exhaustively extracted with a dilute alkali at 60 °C for 6 h. The alginates dissolved in all these extracts with both boiling water and dilute alkali were purified by fractionation with MgCl2 and alcohol.The content of MM blocks in the boiling water-soluble alginate sample increased remarkably during heating for 6 h while that of GG blocks from the same sample decreased. In contrast, MM blocks in the alkali-soluble alginate sample decreased during 6 h heating while GG blocks continued to increase. Since the amounts of MG blocks showed slight fluctation, the M:G ratio of alginates extracted with boiling water increased towards the end of extraction whereas the reverse is true for the alkali-soluble alginates. 相似文献
972.
Voltage-clamp experiments were performed on single bovine adrenal fasciculata cells in short-term primary culture using either
standard (broken membrane) or perforated whole-cell patch clamp recording. The membrane current measured with the perforated
method was dominated by a very stable transient outward current. By contrast, the transient outward current recorded using
the standard method was unstable. The reversal potential of the transient outward current varied linearly with the logarithm
of [K+]
e
with a slope of 47 mV per decade. The onset of activation was sigmoidal and was fitted with a power function where n= 4. Time constants ranged from 1 to 4 msec with a maximum at −25 mV. The steady-state activation curve spanned the voltage
range −50 to +80 mV without reaching a clear maximum. During a pulse, the current decayed in a biexponential manner. Time
constants τ1 and τ2 were voltage-dependent and ranged from 50 to 200 msec respectively for a voltage step at +50 mV. The steady-state inactivation
was dependent on the conditioning pulse duration. Using short conditioning pulses (1.2 sec), the curve which spanned the voltage
range −40 to −20 mV, was 15 mV more positive than that obtained with longer conditioning pulses (60 sec). Time constants of
this ``very slow inactivation' process (τvs) determined for voltage steps at −60 and −50 mV were 15 and 10 sec respectively. A ``facilitation process' of the peak current
was observed when the duration or the amplitude of conditioning pulses were increased in the voltage range −100 to −50 mV.
Recovery from inactivation followed a biexponential time course which seemed a mixture of both inactivation processes. In
some experimental conditions, isolated cells were able to produce overshooting action potentials. These results are discussed
in relation with the membrane electrogenesis of this cell type.
Received: 14 November 1994/Revised: 24 October 1995 相似文献
973.
UVM (ultravioletmodulation of mutagenesis) is a recently describedrecA-independent, inducible mutagenic phenomenon in which prior UV irradiation ofEscherichia coli cells strongly enhances mutation fixation at a site-specific 3-N4-ethenocytosine (C) lesion borne on a transfected single-stranded M13 DNA vector. Subsequent studies demonstrated that UVM is also induced by alkylating agents, and is distinct from both the SOS response and the adaptive response to alkylation damage. Because of the increasing significance being attributed to oxidative DNA damage, it is interesting to ask whether this class of DNA damage can also induce UVM. By transfecting M13 vector DNA bearing a site-specificC lesion into cells pretreated with inducing agents, we show here that the oxidative agent H2O2 is a potent inducer of UVM, and that the induction of UVM by H2O2 does not requireoxyR-regulated gene expression. UVM induction by H2O2 appears to be mediated by DNA damage, as indicated by the observation of a concomitant reduction in cellular toxicity and UVM response in OxyRc cells. Available evidence suggests that UVM represents a generalized cellular response to a broad range of chemical and physical genotoxicants, and that DNA damage constitutes the most likely signal for its induction. 相似文献
974.
François Bouteau Ulrike Bousquet Anne-Marie Pennarun Monique Convert Olivier Dellis Daniel Cornel Jean-Pierre Rona 《Physiologia plantarum》1996,98(1):97-104
The purpose of our work was to investigate the functioning of K+ channels in protoplasts of laticifers of Hevea brasiliensis Muell. Arg., anastomosed into a network devoid of large central vacuoles, after tapping stress. Physiological functions such as proton pump activity and uptake of sucrose (a rubber precursor) were maintained, when the voltage-clamp method was used in vivo to record the whole-cell K+ current during the stress response.
A time-dependent inward current was induced in 50 m M KCl and rapidly inactivated (about 100 ms). The activation potential of this inward K+ channel was not closely dependent on Ek . This would be coherent with the 'valve model' of Schroeder and Fang (1991, Proc. Natl. Acad. Sci. USA 88: 11583–11587) involving the activation of a H+ -pump accounting for the K+ uptake observed in laticiferous cells under stress. The activation half-time of outward currents was clearly voltage dependent: from about 350 to 60 ms for 125 and 155 mV, respectively. Time-dependent outward current sensitivity to 5 m M BaCl2 or CaCl2 or to 5 μ M Erythrosin B showed that the K+ channels could be Ca2+ -dependent. Because of the positive values of the activation potential of the outward current, the possibility opens that an action potential exists, these cells being specialized for stress response. 相似文献
A time-dependent inward current was induced in 50 m M KCl and rapidly inactivated (about 100 ms). The activation potential of this inward K
975.
E. Nenz F. Pupilli F. Damiani S. Arcioni 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(1-2):183-189
Interspecific somatic hybrid plants were obtained by symmetrical electrofusion of mesophyll protoplasts of Medicago sativa with callus protoplasts of Medicago arborea. Somatic hybrid calli were picked manually from semi-solid culture medium after they were identified by their dual color in fluorescent light. Twelve putative hybrid calli were selected and one of them regenerated plants. The morphogenesis of the somatic hybrid calli was induced by the synthetic growth regulator 1,2 benzisoxazole-3-acetic acid. Somatic hybrid plants showed intensive genome rearrangements, as evidenced by isozyme and RFLP analysis. The morphology of somatic hybrid plants was in general intermediate between the parents. The production of hybrids by protoplast fusion between sexually incompatible Medicago species is related to the in vitro respon siveness of the parental protoplasts. The possibility of using somatic hybrid plants in alfalfa breeding is discussed. 相似文献
977.
中国豆科植物区系新资料 总被引:1,自引:0,他引:1
报道了中国豆科一新记录属闭荚藤属和一新记录种滇西围涎树前者分布于我国西藏墨脱雅鲁藏布江峡谷热带山地雨林中,后者见于云南西部盈江亚热带山地常绿阔叶林中。 相似文献
978.
Isolated protoplasts from pulvinar motor cells of Mimosa pudica were studied using conventional whole-cell patch clamp techniques. With internal solutions weakly buffered for Ca2+ (0.2 mm EGTA), a run-down of the outward delayed rectifier K+ current was induced by hyperpolarizing the holding potential, and this effect was strongly promoted by high external Ca2+ concentrations. This rundown could be reversed by coming back to less hyperpolarized holding potentials or by lowering the external [Ca2+]. Such rundown was absent when pipette internal solutions strongly buffered (10 mm EGTA) for Ca2+ were used. Ionomycin induced run-down of the K+ current with internal solutions containing 0.2 mm but not 10 mm EGTA. The hyperpolarization-associated rundown was reversibly blocked by Gd3+ and La3+.We thank Christophe Untereiner and Denis Wagner for expert technical assistance in facilitating the experiments and data acquisition and analysis. 相似文献
979.
980.