全文获取类型
收费全文 | 2331篇 |
免费 | 101篇 |
国内免费 | 56篇 |
出版年
2023年 | 40篇 |
2022年 | 45篇 |
2021年 | 63篇 |
2020年 | 41篇 |
2019年 | 63篇 |
2018年 | 58篇 |
2017年 | 34篇 |
2016年 | 38篇 |
2015年 | 55篇 |
2014年 | 63篇 |
2013年 | 136篇 |
2012年 | 67篇 |
2011年 | 63篇 |
2010年 | 42篇 |
2009年 | 76篇 |
2008年 | 93篇 |
2007年 | 80篇 |
2006年 | 87篇 |
2005年 | 89篇 |
2004年 | 81篇 |
2003年 | 75篇 |
2002年 | 82篇 |
2001年 | 76篇 |
2000年 | 69篇 |
1999年 | 48篇 |
1998年 | 61篇 |
1997年 | 67篇 |
1996年 | 57篇 |
1995年 | 54篇 |
1994年 | 40篇 |
1993年 | 44篇 |
1992年 | 46篇 |
1991年 | 41篇 |
1990年 | 34篇 |
1989年 | 37篇 |
1988年 | 38篇 |
1987年 | 28篇 |
1986年 | 31篇 |
1985年 | 45篇 |
1984年 | 39篇 |
1983年 | 36篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1972年 | 5篇 |
1971年 | 9篇 |
排序方式: 共有2488条查询结果,搜索用时 896 毫秒
981.
Ghassan Bkaily Nadine Gros-Louis Radha Naik Doris Jaalouk Pierre Pothier 《Molecular and cellular biochemistry》1996,154(2):113-121
In the present study, Fluo-3 Ca2+ measurement and confocal microscopy techniques were used in order to localize cytosolic [ ]c and nuclear [ ]n free Ca2+ distribution in resting and spontaneously contracting single heart cells from 10-day-old chick embryos. In resting single cells, the concentration of Ca2+ in the cytoplasm was lower than that in the nucleus. Increasing cytosolic free Ca2+ from 100–1600 nM gradually increased [Ca2+]n with a maximum capacity near 1200 nM. Results from Fura-2 microfluorometry and Fluo-3 confocal microscopy suggest a potential cross talk between the increase of cytosolic free Ca2+ and the uptake and release of Ca2+ by the nucleus during spontaneous contraction of single myocytes. Calcium waves in spontaneously contracting cells were found to spread from one cell to the next with the nucleus acting as a fluorescent beacon in which Ca2+ levels remained elevated for several milliseconds even after cytosolic Ca2+ had returned to near basal values. These results strongly suggest that the nucleus plays a negative and positive feedback role in controlling cytosolic free Ca2+ concentration during excitation-contraction coupling in heart cells. 相似文献
982.
已知大鼠外膝体内有中脑上丘来的含P-物质的神经末梢,其机能不明。在离休的大鼠外膝体脑片上用单电极电压箝位的方法研究了P-物质对外膝体神经元电压依赖性离子通道的作用。结果表明,P-物质可以使静息膜去极化,并降低膜电导。这提示P-物质抑制了线性钾漏电流。此外,P-物质还抑制去极化激活的慢失活的钾电流、低阈值钙电流和超极化激活的内向整流(H或Q)电流。P-物质还可能抑制早钾(A)电流。因此,P-物质在外膝体视觉信号传递中的作用是使外膝体神经元从爆发反应方式或振荡状态转化为中继反应方式,易化突触传递,使视网膜的视觉信号忠实地传递到大脑皮层。 相似文献
983.
984.
Nifedipine对烟草花粉萌发、花粉管生长及生殖核分裂的影响 总被引:1,自引:0,他引:1
用细胞学和统计学方法研究了Ca2+ 通道专一性阻滞剂nifedipine(Nif)对烟草(Nicotiana tabacumL.)离体花粉萌发、花粉管生长及生殖核分裂的影响。10- 4 m ol/LNif可抑制花粉萌发。Nif对花粉管生长的影响与其浓度和处理持续时间有关,10- 4 m ol/L Nif始终抑制花粉管生长;而10- 7~10- 5 m ol/LNif在较短时间内起不同程度的促进作用,之后逐渐过渡为抑制花粉管生长。较高浓度处理可使花粉管形态趋向异常,细胞质流动趋于停滞。Nif抑制生殖核的有丝分裂,相对推迟分裂高峰。Nif使花粉管中的金霉素(CTC)荧光趋于减弱,表明Nif通过抑制Ca2+ 通道活性产生生理效应。着重讨论了Nif抑制生殖核分裂的可能原因 相似文献
985.
通过以山羊草等23种不同异源胞质的中国春为母本,以小偃6号为父本,经过七代核置换回交,培育成功了23种不同细胞质的小偃6号核质杂种。和对照小偃6号比较分析,发现不同的异源细胞质对小偃6号的抽穗期,条锈抗性、结实率等9个农艺性状都有着较明显的影响。 相似文献
986.
Joseph L. Scott Sharon T. Broadwater Bill D. Saunders Jewel P. Thomas Paul W. Gabrielson 《Journal of phycology》1992,28(5):649-660
This study suggests that the genus Rhodella be restricted to that set of features currently observed only in Rhodella maculata Evans and Rhodella violacea (Korn-mann) Wehrmeyer, that a new genus Dixoniella be established to accommodate the unicellular red alga, Rhodella grisea (Geitler) Fresnel, Billard, Hindák et Pekár-ková, and that Rhodella cyanea Billard et Fresnel be further studied for probable reclassification. These conclusions are based on ultrastructural comparisons of Dixoniella grisea with published information on the genus Rhodella. The presence of thylakoids in the pyrenoid, a peripheral encircling thylakoid in the chloroplast, a dictyosome/nuclear envelope association, and the lack of a specialized pyrenoid/nucleus association in D. grisea separate this alga from the genus Rhodella. Cell division in D. grisea is not demonstrably different from that in Rhodella, although the unusually well-defined material of the presumptive microtubule organizing center (MTOC) made it possible to follow the development and behavior of the MTOC to a greater degree than in previously studied red algal cells. The surprising amount of conformity in cell division characters between D. grisea and the genus Rhodella prompted a comparison of cell division characteristics in all red algal unicells studied to date. All unicells show a remarkable degree of similarity except for differences in interzonal spindle length, dissimilarities in size of the nucleus-associated organelle (NAO), and the unusual NAO of Porphyridium purpureum (Bory) Drew et Ross. 相似文献
987.
988.
Ghosh Suchandra Patel Amrish H. Cousins Michael Grasing Kenneth 《Neurochemical research》1998,23(6):875-885
The purpose of these experiments was to further characterize changes in dopaminergic function that follow withdrawal from chronic opiate treatment. Withdrawal after treatment to a maximum dose of 120 mg/kg of morphine did not alter dopamine concentrations in the substantia nigra, ventral tegmental area, striatum, or nucleus accumbens; but did decrease concentrations of DOPAC and the ratio of DOPAC to dopamine in the lateral striatum and nucleus accumbens. Uptake of tritiated dopamine was diminished for withdrawn slices obtained from the striatum with no effect observed for tissue from the nucleus accumbens. Deficits of in vitro release of tritiated dopamine also occurred following withdrawal, with the nucleus accumbens being sensitive to dependence produced by a lower dose of morphine. In conclusion, opiate withdrawal produces a complex pattern of effects on dopaminergic function that is specific for the striatum and nucleus accumbens. 相似文献
989.
中缝核与阻塞性睡眠呼吸暂停关系的实验研究 总被引:3,自引:0,他引:3
本实验在64只氨基甲酸乙酯麻醉、断双侧迷走神经、自主呼吸的健康家兔上进行,观察电、化学刺激中缝背核(NRD)、中缝大核(NRM)对颏舌肌和膈肌肌电、以及窒息增幅反应(AARA)的作用。结果如下:1.长串电脉冲刺激NRD,颏舌肌和膈肌肌电幅度明显升高,在刺激过程中呈持续性吸气相放电。长串电脉冲刺激NRM,颏舌肌和膈肌肌电幅度显著抑制,呼吸节律减弱或消失;2.于NRD微量注入谷氨酸钠,颏舌肌和膈肌肌电幅度升高,频率加快。在NRM微量注射谷氨酸钠,AARA降低。上述结果与电刺激NRD、NRM的效应基本一致;3.NRM内微量注入吗啡,颏舌肌和膈肌的AARA峰值被抑制,潜伏期延长,恢复期缩短。若注射吗啡后5min再微量注入纳络酮,则吗啡的抑制效应减弱。结果提示:中缝核和阿片肽类物质对颏舌肌有重要的调制作用,可能与阻塞性睡眠呼吸暂停的发生有关 相似文献
990.
氧自由基对大鼠心肌细胞核钙转运系统的影响 总被引:6,自引:1,他引:5
观察氧自由基对心肌细胞核钙转运系统的影响。方法;大鼠心肌细胞核采用蔗糖密度梯度心分离纯化,用酶学方法测定了ATPase活性,用^45Ca^2+同位素法测定下摄取。结果;低浓度的H2O2短时间作用使核钙泵活性增加31.6%,高浓度H2O2使核钙泵活性降低,呈时间和剂量信赖性。 相似文献