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991.
992.
不同照度对棉铃虫蛾活动的影响 总被引:7,自引:2,他引:5
棉铃虫蛾分别在五个日龄(第二至第六天),各经过五个光照梯度的光照处理,结果表明,10-1~10-3lX照度范围是棉铃虫蛾比较合适的活动范围,计算同时表明,棉铃虫蛾在不同照度下的活动反应量差异显著,尤以在10-3lX照度下的活动反应量为最大,约88%左右。 相似文献
993.
光合作用的核心问题之一是光合作用的原初反应,即光能的高效吸收、转化和传递的机理。由于PSⅡ与水裂解、氧释放密切相关,因此,PSⅡ反应中心原初反应和能量传递的机理研究具有重要的理论意义。最近,PSⅡ捕光天线复合物以及细菌外周天线复合物的三维空间结构被揭示,反应中心及捕光天线的能量传递规律日益成为新的研究热点之一。近年来,国际上许多实验室采用时间分辨荧光光谱和吸收光谱等技术,利用不同层次的样品,对PSⅡ的原初反应包括能量传递过程的动力学性质进行了研究。但是,不同实验室得到的动力学数据以及对实验数据的解释都存在较大差异。我们实验 相似文献
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P Hardy D Lamireau X Hou I Dumont D Abran A M Nuyt D R Varma S Chemtob 《Journal of applied physiology》2001,91(4):1655-1662
We examined whether nitric oxide (NO) generated from neuronal NO synthase (nNOS) contributes to the reduced ability of the newborn to autoregulate retinal blood flow (RBF) and choroidal blood flow (ChBF) during acute rises in perfusion pressure. In newborn pigs (1-2 days old), RBF (measured by microsphere) is autoregulated over a narrow range of perfusion pressure, whereas ChBF is not autoregulated. N(G)-nitro-L-arginine methyl ester (L-NAME) or specific nNOS inhibitors 7-nitroindazole, 3-bromo-7-nitroindazole, and 1-(2-trifluoromethyl-phenyl)imidazole as well as ganglionic blocker hexamethonium, unveiled a ChBF autoregulation as observed in juvenile (4- to 6-wk old) animals, whereas autoregulation of RBF in the newborn was only enhanced by L-NAME. All NOS inhibitors and hexamethonium prevented the hypertension-induced increase in NO mediator cGMP in the choroid. nNOS mRNA expression and activity were three- to fourfold higher in the choroid of newborn pigs than in tissues of juvenile pigs. It is concluded that increased production of NO from nNOS curtails ChBF autoregulation in the newborn and suggests a role for the autonomic nervous system in this important hemodynamic function, whereas, for RBF autoregulation, endothelial NOS seems to exert a more important contribution in limiting autoregulation. 相似文献
997.
While fertigation can increase fertilizer use efficiency, there is an uncertainly as to whether the fertilizer should be introduced
at the beginning of the irrigation or at the end, or introduced during irrigation. Our objective was to determine the effect
of different fertigation schemes on nitrogen (N) uptake and N use efficiency (NUE) in cotton plants. A pot experiment was
conducted under greenhouse conditions in year 2004 and 2005. According to the application timing of nitrogen (N) fertilizer
solution and water (W) involved in an irrigation cycle, four nitrogen fertigation schemes [nitrogen applied at the beginning
of the irrigation cycle (N–W), nitrogen applied at the end of the irrigation cycle (W–N), nitrogen applied in the middle of
the irrigation cycle (W–N–W) and nitrogen applied throughout the irrigation cycle (N&W)] were employed in a completely randomized
design with four replications. Cotton was grown in plastic containers with a volume of 84 l, which were filled with a clay
loam soil and fertilized with 6.4 g of N per pot as unlabeled and 15N-labeled urea for 2004 and 2005, respectively. Plant total dry matter (DM) and N content in N–W was significantly higher
than in N&W in both seasons, but these were not consistent for W–N and W–N–W treatments. In year 2005, a significantly higher
nitrogen derived from fertilizer (NDFF) for the whole plant was found in W–N and N–W than that in W–N–W and N&W. Fertigation
scheme had a consistent effect on total NUE: N–W had the highest NUE for the whole plant, but this was not significantly different
from W–N. Treatments W–N and W–N–W had similar total NUE, and N&W had the lowest total NUE. After harvesting, the total residual
fertilizer N in the soil was highest in W–N, lowest in N–W, but this was not significantly different from N&W and W–N–W treatments.
Total residual NO3–N in the soil in N&W and W–N treatments was 20.7 and 21.2% higher than that in N–W, respectively. The total 15N recovery was not statistically significant between the four fertigation schemes. In this study, the fertigation scheme N–W
(nitrogen applied at the beginning of an irrigation cycle) increased DM accumulation, N uptake and NUE of cotton. This study
indicates that Nitrogen application at the beginning of an irrigation cycle has an advantage on N uptake and NUE of cotton.
Therefore, NUE could be enhanced by optimizing fertilization schemes with drip irrigation. 相似文献
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999.
Multiplicity of the Amino Acid Permeases in Saccharomyces cerevisiae IV. Evidence for a General Amino Acid Permease 总被引:36,自引:16,他引:20 下载免费PDF全文
Kinetic and genetic evidences are presented to show that, in addition to specific amino acid permeases, Saccharomyces cerevisiae has a general amino acid permease which catalyzes the transport of basic and neutral amino acids, but most probably not that of proline. The general amino acid permease appears to be constitutive, and its activity is inhibited when ammonium ions are added to the culture medium. A mutant which has lost the general amino acid permease activity was isolated. Its mutation, named gap (general amino acid permease), is not allelic to the aap (amino acid permease) mutation of Surdin et al., which has a quite different phenotype and cannot be considered as having selectively lost the general amino acid permease activity. 相似文献
1000.