全文获取类型
收费全文 | 61623篇 |
免费 | 5398篇 |
国内免费 | 1832篇 |
出版年
2022年 | 433篇 |
2021年 | 1370篇 |
2020年 | 1044篇 |
2019年 | 1243篇 |
2018年 | 1399篇 |
2017年 | 1081篇 |
2016年 | 1520篇 |
2015年 | 2021篇 |
2014年 | 2392篇 |
2013年 | 2631篇 |
2012年 | 3129篇 |
2011年 | 2920篇 |
2010年 | 1827篇 |
2009年 | 1760篇 |
2008年 | 2241篇 |
2007年 | 2038篇 |
2006年 | 1983篇 |
2005年 | 1638篇 |
2004年 | 1462篇 |
2003年 | 1347篇 |
2002年 | 1249篇 |
2001年 | 3050篇 |
2000年 | 2724篇 |
1999年 | 2092篇 |
1998年 | 801篇 |
1997年 | 745篇 |
1996年 | 638篇 |
1995年 | 583篇 |
1994年 | 546篇 |
1993年 | 472篇 |
1992年 | 1451篇 |
1991年 | 1297篇 |
1990年 | 1236篇 |
1989年 | 1134篇 |
1988年 | 1014篇 |
1987年 | 1005篇 |
1986年 | 862篇 |
1985年 | 851篇 |
1984年 | 603篇 |
1983年 | 560篇 |
1979年 | 642篇 |
1978年 | 461篇 |
1975年 | 500篇 |
1974年 | 579篇 |
1973年 | 561篇 |
1972年 | 571篇 |
1971年 | 554篇 |
1970年 | 524篇 |
1969年 | 534篇 |
1968年 | 434篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Cognitive Changes during Prolonged Stay at High Altitude and Its Correlation with C-Reactive Protein
Hypersensitive C-reaction protein (hsCRP) may be a risk factor for cognitive impairment resulting from Alzheimer’s disease (AD), stroke, and vascular dementia. This study explored the correlation of peripheral blood hsCRP level with cognitive decline due to high altitude exposure. The study was conducted on 100 male military participants who had never been to high altitude. Cerebral oxygen saturation monitoring, event related potentials (P300, N200) detection, and neurocognitive assessment was performed and total hsCRP, interleukin-6 (IL-6), and homocysteine was estimated at 500m altitude, 3650m altitude, 3day, 1, and 3 month post arriving at the base camp (4400m), and 1 month after coming back to the 500m altitude. High altitude increased brain oxygen saturation, prolonged P300 and N200 latencies, injured cognitive functions, and raised plasma hsCRP levels. But they all recovered in varying degrees at 1 and 3 month post arriving at the base camp (4400m). P300 latencies and hsCRP levels were strongly correlated to cognitive performances. These results suggested that cognitive deterioration occurred during the acute period of exposure to high altitude and may recover probably owning to acclimatization after extended stay at high altitude. Plasma hsCRP is inversely correlated to neurological cognition and it may be a potential biomarker for the prediction of high altitude induced cognitive dysfunction. 相似文献
52.
Household‐level correlates of children's physical activity levels in and across 12 countries 下载免费PDF全文
Deirdre M. Harrington Fiona Gillison Stephanie T. Broyles Jean‐Philippe Chaput Mikael Fogelholm Gang Hu Rebecca Kuriyan Anura Kurpad Allana G. LeBlanc Carol Maher Jose Maia Victor Matsudo Timothy Olds Vincent Onywera Olga L. Sarmiento Martyn Standage Mark S. Tremblay Catrine Tudor‐Locke Pei Zhao Peter T. Katzmarzyk for the ISCOLE Research Group 《Obesity (Silver Spring, Md.)》2016,24(10):2150-2157
53.
The genetic structure of 65 chicken populations was studied using 29 simple sequence repeat loci. Six main clusters which corresponded to geographical origins and histories were identified: Brown Egg Layers; predominantly Broilers; native Chinese breeds or breeds with recent Asian origin; predominantly breeds of European derivation; a small cluster containing populations with no common history and populations that had breeding history with White Leghorn. Another group of populations that shared their genome with several clusters was defined as 'Multi-clusters'. Gallus gallus gallus (Multi-clusters), one of the subspecies of the Red Jungle Fowl, which was previously suggested to be one of the ancestors of the domesticated chicken, has almost no shared loci with European and White Egg layer populations. In a further sub-clustering of the populations, discrimination between all the 65 populations was possible, and relationships between each were suggested. The genetic variation between populations was found to account for about 34% of the total genetic variation, 11% of the variation being between clusters and 23% being between populations within clusters. The suggested clusters may assist in future studies of genetic aspects of the chicken gene pool. 相似文献
54.
55.
Jianping Zhang Houyuan Lu Wanfa Gu Naiqin Wu Kunshu Zhou Yayi Hu Yingjun Xin Can Wang 《PloS one》2012,7(12)
The Peiligang Culture (9000-7000 cal. yr BP) in the Middle Yellow River region, North China, has long been considered representative of millet farming. It is still unclear, however, if broomcorn millet or foxtail millet was the first species domesticated during the Peiligang Culture. Furthermore, it is also unknown whether millet was cultivated singly or together with rice at the same period. In this study, phytolith analysis of samples from the Tanghu archaeological site reveals early crop information in the Middle Yellow River region, China. Our results show that broomcorn millet was the early dry farming species in the Peiligang Culture at 7800 cal. yr BP, while rice cultivation took place from 7800 to 4500 cal. yr BP. Our data provide new evidence of broomcorn millet and rice mixed farming at 7800 cal. yr BP in the Middle Yellow River region, which has implications for understanding the domestication process of the two crops, and the formation and continuance of the Ancient Yellow River Civilization. 相似文献
56.
57.
G. S. C. BUSO Z. P. S. AMARAL R. P. V. BRONDANI M. E. FERREIRA 《Molecular ecology resources》2006,6(1):252-254
Efforts to develop molecular tools for genetic analysis and breeding of common bean in the tropics are still limited. The number of microsatellite markers available for the crop is small compared to other crops of similar social and economic importance. As part of a project to broaden the use of molecular tools in bean breeding, a genomic library enriched for AG/TC repeat sequences was constructed for Phaseolus vulgaris. Twenty microsatellite markers were initially developed and 10 were characterized using a panel of 85 representative accessions of the bean gene bank. The number of alleles per marker ranged from three to 10. The polymorphism information content (PIC) varied from 0.23 to 0.80. The results indicate that the new markers can be readily used in genetically analysis of common bean. 相似文献
58.
59.
60.
Z Jesenská I Sajbidorová 《Journal of hygiene, epidemiology, microbiology, and immunology》1991,35(1):41-49
The biodegradation of T-2 toxin was studied by strains of micromycetes which were isolated from the environment. The 26 tested strains were divided into three groups. Group contains strains which degraded T-2 toxin very fast. This toxin could not be chromatographically determined in the medium even after 48 hours of incubation and the antifungal activity of residua against Kluyveromyces fragilis CCY-51-1-2 was low or zero. There were strains of Alternaria sp., Ulocladium sp., Aspergillus candidus, Cladosporium cladosporioides, Rhodotorula sp., Aspergillus flavus and Cladosporium macrocarpum. Group II contains with a low activity and in group III the results were variable and non stable. 相似文献