全文获取类型
收费全文 | 26821篇 |
免费 | 1854篇 |
国内免费 | 9篇 |
出版年
2023年 | 194篇 |
2022年 | 389篇 |
2021年 | 784篇 |
2020年 | 594篇 |
2019年 | 670篇 |
2018年 | 847篇 |
2017年 | 763篇 |
2016年 | 1061篇 |
2015年 | 1456篇 |
2014年 | 1605篇 |
2013年 | 1808篇 |
2012年 | 2154篇 |
2011年 | 1959篇 |
2010年 | 1216篇 |
2009年 | 1138篇 |
2008年 | 1466篇 |
2007年 | 1408篇 |
2006年 | 1246篇 |
2005年 | 1155篇 |
2004年 | 1074篇 |
2003年 | 957篇 |
2002年 | 872篇 |
2001年 | 353篇 |
2000年 | 295篇 |
1999年 | 292篇 |
1998年 | 209篇 |
1997年 | 187篇 |
1996年 | 162篇 |
1995年 | 151篇 |
1994年 | 152篇 |
1993年 | 98篇 |
1992年 | 148篇 |
1991年 | 174篇 |
1990年 | 140篇 |
1989年 | 115篇 |
1988年 | 103篇 |
1987年 | 96篇 |
1986年 | 108篇 |
1985年 | 101篇 |
1984年 | 117篇 |
1983年 | 70篇 |
1982年 | 72篇 |
1981年 | 64篇 |
1980年 | 55篇 |
1979年 | 54篇 |
1978年 | 60篇 |
1977年 | 55篇 |
1976年 | 45篇 |
1975年 | 61篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
31.
Jan Dirk van Elsas Alexander V Semenov Rodrigo Costa Jack T Trevors 《The ISME journal》2011,5(2):367-183
In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health. 相似文献
32.
33.
Jamilly de Souza Costa Maria de Fátima Arruda 《Marine and Freshwater Behaviour and Physiology》2016,49(6):375-389
This study characterized the behavioral activity of Macrobrachium rosenbergii in the early stages of development, under different stocking densities (25 and 40 animals/m2), and during the light and dark phases of a 24-h cycle. Observations of individuals were made in 8 aquariums. Behavioral recording lasted 15 min/aquarium, 4 times/day and 4 days/week, 4 weeks in total. Food was offered twice daily. Observational methods included a combination of behavioral sampling and scan sampling. During the light phase, inactivity, cleaning and remaining in a shelter were the most frequent behaviors. During the dark phase the subjects displayed a higher frequency of feeding, exploration, swimming, and digging. At low density, the animals gained more weight and exhibited greater growth overall. These results indicate a behavioral pattern that is more favorable to animals in the lower density cultivation environment that can also create better living conditions for these shrimp, favor survival rates and therefore improve management success. 相似文献
34.
35.
36.
37.
38.
Samples of microphytobenthos from the Tagus estuary were analysed for photosynthetic pigments by spectrophotometry and High
Performance Liquid Chromatography (HPLC). Chlorophyll a values obtained with HPLC and spectrophotometry methods presented a highly significant positive correlation for both spectrophotometric
methods used (with and without the correction for pheopigments), but this relationship depended on the type of sediment. We
concluded that spectrophotometric methods give reliable Chl-a values, being suited for routine analysis, when a vast number of replicates is needed. However, for the correct estimation
of pheopigments, HPLC analysis is indispensable. In the literature, Chl-a estimations are expressed per content (μg g−1) or concentration (mg m−2). We discuss the influence of sediment type on the results depending on the type of unit used, and propose a simple conversion
factor based on sediment water content. 相似文献
39.
40.
Javier J Gonzalez-Rosa Manuel Vazquez-Marrufo Encarnacion Vaquero Pablo Duque Monica Borges Carlos M Gomez-Gonzalez Guillermo Izquierdo 《BMC neurology》2011,11(1):64-19