全文获取类型
收费全文 | 341篇 |
免费 | 18篇 |
国内免费 | 1篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 26篇 |
2011年 | 26篇 |
2010年 | 20篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 33篇 |
2006年 | 8篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 21篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有360条查询结果,搜索用时 46 毫秒
111.
Kucukarabaci B Gunes HV Ozdemir G Cosan D Ozbabalik D Dikmen M Degirmenci I 《Genetic testing》2008,12(3):443-451
Aim: This study was carried out to determine if there is any association between plasminogen activator inhibitor type-1 (PAI-1) gene 4G/5G polymorphism and plasma PAI-1 enzyme activity in acute stroke patients. Methods: In this study, 333 genomic DNAs (from 253 acute stroke patients and 80 healthy subjects) were analyzed. Genomic DNAs were prepared from peripheral blood using a saline method. These DNAs were amplified by PCR method using primers specific for 4G and 5G alleles. PCR products were separated by 2% agarose gel electrophoresis and visualized by a charge coupled device (CCD) camera. PAI-1 enzyme activities were measured by ELISA method. The results were evaluated statistically with Student's t-test, chi(2)-test, one-way analysis of variance, and stepwise regression analysis. Results: In this study, frequency of PAI-1 gene 4G5G genotype was found to be low both in patients and controls. PAI-1 enzyme activities were significantly increased in acute stroke patients compared to controls. Although PAI-1 gene 4G5G genotype frequencies were low, the patients carrying this allele had highest plasma PAI-1 enzyme activity; likewise, although PAI-1 gene 4G4G genotype frequencies were high, the patients carrying this allele had lowest plasma PAI-1 enzyme activities. Homocysteine levels had a positive effect of 65% on plasma PAI-1 enzyme activities. Conclusion: Consequently, in this study, we may assert that PAI-1 gene, 4G4G and 5G5G genotypes, PAI-1 activity, and homocysteine level determination are significant criteria for identifying patients who are likely to develop stroke; on the other hand, a direct relation does not exist between gene polymorphism and enzyme activity. 相似文献
112.
Predicting extinction risks under climate change: coupling stochastic population models with dynamic bioclimatic habitat models 总被引:4,自引:0,他引:4
Keith DA Akçakaya HR Thuiller W Midgley GF Pearson RG Phillips SJ Regan HM Araújo MB Rebelo TG 《Biology letters》2008,4(5):560-563
Species responses to climate change may be influenced by changes in available habitat, as well as population processes, species interactions and interactions between demographic and landscape dynamics. Current methods for assessing these responses fail to provide an integrated view of these influences because they deal with habitat change or population dynamics, but rarely both. In this study, we linked a time series of habitat suitability models with spatially explicit stochastic population models to explore factors that influence the viability of plant species populations under stable and changing climate scenarios in South African fynbos, a global biodiversity hot spot. Results indicate that complex interactions between life history, disturbance regime and distribution pattern mediate species extinction risks under climate change. Our novel mechanistic approach allows more complete and direct appraisal of future biotic responses than do static bioclimatic habitat modelling approaches, and will ultimately support development of more effective conservation strategies to mitigate biodiversity losses due to climate change. 相似文献
113.
Characterization of Sugar and Polyphenolic Diversity in Floral Nectar of Different ‘Oblačinska’ Sour Cherry Clones 下载免费PDF全文
Basem Guffa Nebojša M. Nedić Dragana Č. Dabić Zagorac Tomislav B. Tosti Uroš M. Gašić Maja M. Natić Milica M. Fotirić Akšić 《化学与生物多样性》2017,14(9)
‘Obla?inska’ sour cherry, an autochthonous cultivar, is the most planted cultivar in Serbian orchards. Since fruit trees in temperate zone reward insects by producing nectar which ‘quality’ affects the efficiency of insect pollination, the aim of this study was analyzing of sugars and polyphenolics in floral nectar of 16 ‘Obla?inska’ sour cherry clones with different yielding potential. The contents of sugars and sugar alcohols were analyzed by ion chromatography, while polyphenolic profile was established using liquid chromatography/mass spectrometry technique. Fourteen sugars and six sugar alcohols were detected in nectar samples and the most abundant were fructose, glucose, and sucrose. Eleven polyphenols were quantified using available standards, while another 17 were identified according to their exact masses and characteristic fragmentations. Among quantified polyphenols, rutin, naringenin, and chrysin were the most abundant in nectar. Principal component analysis showed that some polyphenol components (naringin, naringenin, and rutin) together with sugars had high impact of spatial distribution of nectar samples on score plot. 相似文献
114.
Süleyman Akçay 《Journal of biological education》2017,51(1):52-65
In this study, Turkish prospective elementary science teachers’ understanding of photosynthesis and cellular respiration has been analysed within the contexts of ecosystem knowledge, organism knowledge and interconnection knowledge (IK). In the analysis, concept maps developed by 74 prospective teachers were used. The study was carried out with prospective teachers in their final year who were enrolled in the special teaching methods course. The results show that prospective teachers’ understanding of photosynthesis, cellular respiration, energy flow and matter cycling is quite different from one another’s. In addition, the present study revealed that prospective elementary science teachers showed weak understanding of energy flow and matter, cycling and cellular respiration concepts and IK category but they had strong understanding of photosynthesis concept. Prospective teachers also experience difficulties in understanding connections between macro- and microbiological systems. The study concludes with suggestions for more meaningful biology education. 相似文献
115.
Synephrine and phenylephrine act as α‐amylase, α‐glycosidase,acetylcholinesterase, butyrylcholinesterase,and carbonic anhydrase enzymes inhibitors 下载免费PDF全文
Parham Taslimi Hülya Akıncıoglu İlhami Gülçin 《Journal of biochemical and molecular toxicology》2017,31(11)
In this paper, synephrine and phenylephrine compounds showed excellent inhibitory effects against human carbonic anhydrase (hCA) isoforms I and II, α‐amylase, α‐glycosidase, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE). Synephrine and phenylephrine had Ki values of 199.02 ± 16.01 and 65.01 ± 5.00 μM against hCA I and 336.02 ± 74.01 and 92.04 ± 18.03 μM against hCA II, respectively. On the other hand, their Ki values were found to be 169.10 ± 80.03 and 88.03 ± 5.01 nM against AChE and 177.06 ± 6.01 and 78.03 ± 3.05 nM against BChE, respectively. α‐Amylase and α‐glycosidase enzymes were easily inhibited by these compounds. α‐Glycosidase inhibitors, generally defined to as starch blockers, are anti‐diabetic drugs that help to decrease post comestible blood glucose levels. 相似文献
116.
G. Bringmann H. Rischer J. Schlauer L. Aké Assi 《Plant Cell, Tissue and Organ Culture》1999,57(1):71-73
Ancistrocladus abbreviatus Airy Shaw (Ancistrocladaceae), a West African liana producing naphthylisoquinoline alkaloids, was
successfully raised from seeds in vitro. Clonal propagation was best achieved growing nodal stem segments on 1/5 Linsmaier
and Skoog medium with full strength organics and supplemented with 0.02 μM thidiazuron, 4.44 μM 6-benzylaminopurine and 0.05
μM 1-naphthaleneacetic acid. Detached axillary shoots were grown on Anderson's Rhododendron medium devoid of phytohormones
and rooted within one month when dipped in 4.92 μM indole-3-butyric acid. Rooted plants became acclimatized to nonsterile
greenhouse conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
117.
118.
Damien A. Fordham H. Resit Akçakaya Miguel B. Araújo David A. Keith Barry W. Brook 《Ecography》2013,36(9):956-964
Ecological niche models (ENMs) are the primary tool used to describe and forecast the potential influence of climate change on biodiversity. However, ENMs do not directly account for important biological and landscape processes likely to affect range dynamics at a variety of spatial scales. Recent advances to link ENMs with population models have focused on the fundamental step of integrating dispersal and metapopulation dynamics into forecasts of species geographic ranges. Here we use a combination of novel analyses and a synthesis of findings from published plant and animal case studies to highlight three seldom recognised, yet important, advantages of linking ENMs with demographic modelling approaches: 1) they provide direct measures of extinction risk in addition to measures of vulnerability based on change in the potential range area or total habitat suitability. 2) They capture life‐history traits that permit population density to vary in different ways in response to key spatial drivers, conditioned by the processes of global change. 3) They can be used to explore and rank the cost effectiveness of regional conservation alternatives and demographically oriented management interventions. Given these advantages, we argue that coupled methods should be used preferentially where data permits and when conservation management decisions require intervention, prioritization, or direct estimates of extinction risk. 相似文献
119.
The study was performed in 2003 to obtain baseline information on married women's knowledge of AIDS/HIV in Malatya, Turkey. The aim was to reach 1% of the population by covering 1200 married women out of 120,034 whose ages ranged from 15-49. Stratified systematic random sampling was used according to 17 health center lists. Although median HIV/AIDS knowledge score was found to be 70 (highest score was 100), it was also seen that clinical properties of the disease were not recognized adequately. The main resources of knowledge were visual (93%) and printed material (35%). These findings show that media based information does not seem to be sufficient. Therefore, it is recommended that health education should be inserted in the school curriculum and health personnel should inform the women. 相似文献
120.