全文获取类型
收费全文 | 413篇 |
免费 | 47篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 33篇 |
2011年 | 39篇 |
2010年 | 21篇 |
2009年 | 11篇 |
2008年 | 21篇 |
2007年 | 19篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 24篇 |
2003年 | 16篇 |
2002年 | 18篇 |
2001年 | 24篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有460条查询结果,搜索用时 15 毫秒
331.
Characterization of the Xanthophyll Cycle and Other Photosynthetic Pigment Changes Induced by Iron Deficiency in Sugar Beet (Beta vulgaris L.) 总被引:3,自引:1,他引:2
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this work we characterize the changes induced by iron deficiency in the pigment composition of sugar beet (Beta vulgaris L.) leaves. When sugar beet plants were grown hydroponically under limited iron supply, neoxanthin and β-carotene decreased concomitantly with chlorophyll a, whereas lutein and the carotenoids within the xanthophyll cycle were less affected. Iron deficiency caused major increases in the lutein/chlorophyll a and xanthophyll cycle pigments/chlorophyll a molar ratios. Xanthophyll cycle carotenoids in Fe-deficient plants underwent epoxidations and de-epoxidations in response to ambient light conditions. In dark adapted Fe-deficient plants most of the xanthophyll cycle pigment pool was in the epoxidated form violaxanthin. We show, both by HPLC and by in vivo 505 nanometers absorbance changes, that in Fe deficient plants and in response to light, the de-epoxidated forms antheraxanthin and zeaxanthin were rapidly formed at the expense of violaxanthin. Several hours after returning to dark, the xanthophyll cycle was shifted again toward violaxanthin. The ratio of variable to maximum chlorophyll fluorescence from intact leaves was decreased by iron deficiency. However, in iron deficient leaves this ratio was little affected by light conditions which displace the xanthophyll cycle toward epoxidation or de-epoxidation. This suggests that the functioning of the xanthophyll cycle is not necessarily linked to protection against excess light input. 相似文献
332.
Masson's vegetant hemangioendothelioma is a benign intravascular tumor, sometimes confused with such malignant vascular tumors as angiosarcoma, whose clinical appearance is nonspecific and whose diagnosis can only be established through microscopic examination. The fine needle aspiration (FNA) cytologic findings together with the histologic and immunohistochemical findings of such a tumor in a 22-year-old man are presented. Cytologically, the material obtained by FNA consisted of two distinct populations of cells. One type of cell had large nuclei (sometimes displaced towards the periphery), finely granular chromatin, prominent nucleoli and abundant globular cytoplasm. The second type of cell had spindle-shaped or oval nuclei, granular chromatin and scanty eosinophilic cytoplasm. Although these findings may permit the cytologic recognition of this entity, the aspirate in this case was interpreted as showing a vascular mesenchymal tumor of probable malignancy. Histologic examination of the excised tumor, aided by immunoperoxidase studies for factor VIII antigen that revealed the endothelial nature of the proliferating cells, established the correct diagnosis. 相似文献
333.
The APPswe/PS1A246E mutations in an astrocytic cell line leads to increased vulnerability to oxygen and glucose deprivation,Ca2+ dysregulation,and mitochondrial abnormalities
下载免费PDF全文
![点击此处可从《Journal of neurochemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
María Dolores Martin‐de‐Saavedra Elisa Navarro Ana J. Moreno‐Ortega Mauricio P. Cunha Izaskun Buendia Pablo Hernansanz‐Agustín Rafael León María F. Cano‐Abad Antonio Martínez‐Ruiz Ricardo Martínez‐Murillo Michael R. Duchen Manuela G. López 《Journal of neurochemistry》2018,145(2):170-182
334.
The effects of short-term administration of thyroid hormones (T3 and T4) and methyltiouracile (MTU) on liver and plasma lipid levels in female rats have been comparatively studied T3 increases the levels of all the studied liver lipids and decreases the plasma lipids. T4 produces smaller and even, in some cases (liver triglycerides and cholesterol esters), opposite effects. The administration of MTU produces, in general, opposite effects to T3 and T4. 相似文献
335.
The effect of progesterone upon several lipidic parameters on rat liver and plasma was studied. Progesterone administration led to a significant increase in the hepatic triacylglyceride and cholesterol esterified levels and to a decrease in the phospholipid content. After progesterone treatment decreases in plasma total lipids, phospholipids, cholesterol and cholesterol esterified were observed, whereas plasma triacylglyceride and free fatty acid levels increased. The hormonal treatment altered the lipoprotein pattern, which significantly reduced the beta-lipoprotein fraction. 相似文献
336.
Improving Sprint Performance in Soccer: Effectiveness of Jump Squat and Olympic Push Press Exercises
Irineu Loturco Lucas Adriano Pereira Ronaldo Kobal Thiago Maldonado Alessandro Fromer Piazzi Altamiro Bottino Katia Kitamura Cesar Cavinato Cal Abad Miguel de Arruda Fabio Yuzo Nakamura 《PloS one》2016,11(4)
Training at the optimum power load (OPL) is an effective way to improve neuromuscular abilities of highly trained athletes. The purpose of this study was to test the effects of training using the jump squat (JS) or Olympic push-press (OPP) exercises at the OPL during a short-term preseason on speed-power related abilities in high-level under-20 soccer players. The players were divided into two training groups: JS group (JSG) and OPP group (OPPG). Both groups undertook 12 power-oriented sessions, using solely JS or OPP exercises. Pre- and post-6 weeks of training, athletes performed squat jump (SJ), countermovement jump (CMJ), sprinting speed (5, 10, 20 and 30 m), change of direction (COD) and speed tests. To calculate the transfer effect coefficient (TEC) between JS and MPP OPP and the speed in 5, 10, 20, and 30 m, the ratio between the result gain (effect size [ES]) in the untrained exercise and result gain in the trained exercise was calculated. Magnitude based inference and ES were used to test the meaningful effects. The TEC between JS and VEL 5, 10, 20, and 30 m ranged from 0.77 to 1.29, while the only TEC which could be calculated between OPP and VEL 5 was rather low (0.2). In addition, the training effects of JS on jumping and speed related abilities were superior (ES ranging from small to large) to those caused by OPP (trivial ES). To conclude, the JS exercise is superior to the OPP for improving speed-power abilities in elite young soccer players. 相似文献
337.
We have isolated two yeast artificial chromosome (YAC) clones from Drosophila melanogaster that contain a small amount of dodeca satellite (a satellite DNA located in the centromeric region of chromosome 3) and sequences homologous to the telomeric retrotransposon HeT-A. Using these YACs as probes for fluorescence in situ hybridization
to mitotic chromosomes, we have localized these HeT-A elements to the centric heterochromatin of chromosome 3, at region h55. The possible origin of these telomeric elements in a centromeric position is discussed.
Received: 30 July 1999 / Accepted: 19 September 1999 相似文献
338.
339.
García de la Fuente R Carrión C Botella S Fornes F Noguera V Abad M 《Bioresource technology》2007,98(18):3561-3569
The biological oxidation of elemental sulphur (S(o)) added to three alkaline composts prepared with a range of organic wastes (CC, melon crop residues; MC, mixed manures; and BC, pine bark) to reduce their pH was studied. The titration curves showed that to achieve an equivalent pH drop, compost CC needed a larger dose of S(o) than did composts MC and BC. The acidification efficiency was high in the three composts (53%), but the pH reduction obtained from the titration curves in MC and BC composts was lower than expected. S(o) oxidation in amended composts was found to be related to pH and CaCO(3) content decreases, and to the rise in CaSO(4) and electrical conductivity levels. A remarkable increase in the autotrophic bacteria population and a slight increase in heterotrophic bacteria along with S(o) oxidation were recorded. Actinomycetes, fungi and yeasts were not affected by the addition of S(o) to composts. 相似文献
340.
Bioenergy production and sustainable development: science base for policymaking remains limited
下载免费PDF全文
![点击此处可从《Global Change Biology Bioenergy》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Carmenza Robledo‐Abad Hans‐Jörg Althaus Göran Berndes Simon Bolwig Esteve Corbera Felix Creutzig John Garcia‐Ulloa Anna Geddes Jay S. Gregg Helmut Haberl Susanne Hanger Richard J. Harper Carol Hunsberger Rasmus K. Larsen Christian Lauk Stefan Leitner Johan Lilliestam Hermann Lotze‐Campen Bart Muys Maria Nordborg Maria Ölund Boris Orlowsky Alexander Popp Joana Portugal‐Pereira Jürgen Reinhard Lena Scheiffle Pete Smith 《Global Change Biology Bioenergy》2017,9(3):541-556
The possibility of using bioenergy as a climate change mitigation measure has sparked a discussion of whether and how bioenergy production contributes to sustainable development. We undertook a systematic review of the scientific literature to illuminate this relationship and found a limited scientific basis for policymaking. Our results indicate that knowledge on the sustainable development impacts of bioenergy production is concentrated in a few well‐studied countries, focuses on environmental and economic impacts, and mostly relates to dedicated agricultural biomass plantations. The scope and methodological approaches in studies differ widely and only a small share of the studies sufficiently reports on context and/or baseline conditions, which makes it difficult to get a general understanding of the attribution of impacts. Nevertheless, we identified regional patterns of positive or negative impacts for all categories – environmental, economic, institutional, social and technological. In general, economic and technological impacts were more frequently reported as positive, while social and environmental impacts were more frequently reported as negative (with the exception of impacts on direct substitution of GHG emission from fossil fuel). More focused and transparent research is needed to validate these patterns and develop a strong science underpinning for establishing policies and governance agreements that prevent/mitigate negative and promote positive impacts from bioenergy production. 相似文献