全文获取类型
收费全文 | 22424篇 |
免费 | 2370篇 |
国内免费 | 6篇 |
出版年
2022年 | 109篇 |
2021年 | 237篇 |
2020年 | 171篇 |
2019年 | 199篇 |
2018年 | 235篇 |
2017年 | 240篇 |
2016年 | 457篇 |
2015年 | 738篇 |
2014年 | 802篇 |
2013年 | 1000篇 |
2012年 | 1376篇 |
2011年 | 1419篇 |
2010年 | 914篇 |
2009年 | 866篇 |
2008年 | 1176篇 |
2007年 | 1290篇 |
2006年 | 1113篇 |
2005年 | 1121篇 |
2004年 | 1154篇 |
2003年 | 1085篇 |
2002年 | 1029篇 |
2001年 | 383篇 |
2000年 | 355篇 |
1999年 | 421篇 |
1998年 | 349篇 |
1997年 | 273篇 |
1996年 | 276篇 |
1995年 | 253篇 |
1994年 | 261篇 |
1993年 | 234篇 |
1992年 | 337篇 |
1991年 | 300篇 |
1990年 | 277篇 |
1989年 | 261篇 |
1988年 | 273篇 |
1987年 | 245篇 |
1986年 | 247篇 |
1985年 | 256篇 |
1984年 | 259篇 |
1983年 | 202篇 |
1982年 | 235篇 |
1981年 | 176篇 |
1980年 | 178篇 |
1979年 | 170篇 |
1978年 | 168篇 |
1977年 | 149篇 |
1976年 | 153篇 |
1975年 | 123篇 |
1974年 | 143篇 |
1973年 | 134篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
D T Sharpe A H Roberts T L Barclay W A Dickson J A Settle D J Crockett M G Mossad 《BMJ (Clinical research ed.)》1985,291(6500):945-948
On 11 May 1985 the main stand of Bradford City Football Club caught fire. Within four minutes the stand was alight from end to end. Fifty three people were burnt to death and about 250 injured; 83 required admission to hospital, and 55 of these were treated by primary excision of their burns and skin grafting. In such disasters the help of staff from other hospitals and areas is essential. Patients should be assessed to see whether they have burns that will ultimately be fatal; if they have they should not be sent to regional burns units, where they would take up beds that could be used for patients with treatable burns. All districts should ensure that their plans for accidents in which burns injuries predominate are adequate. 相似文献
42.
The membrane environments in normal and tumor rat tissue and the effect of hyperthermia thereon are studied with 19F-NMR spectroscopy of the general anesthetic halothane. Normal and tumor cell types are clearly differentiated by the halothane resonance. A hydrophobic environment prominent in tumor tissue is more sensitive to heat treatment than the corresponding environments of normal cells. Studies of extracted lipids suggest that this may be due in part to the considerable difference in lipid temperature response which exists between normal and kidney tumor cells. 相似文献
43.
44.
45.
46.
47.
48.
49.
Abstract. Southern Appalachian high-elevation outcrops harbour six regionally rare Northern Appalachian taxa usually considered relicts of a Pleistocene alpine flora. For five of the six taxa, minimum elevation in the south was 367–1113 m higher than in the north. While habitats compared between the two regions share only 9% of their total flora, individual plots had up to 70% of their species occurring in the opposite region. The northern affinity of southern outcrops increased with elevation, slope steepness, soil Cu, B and SO4 and decreased with potential solar radiation and soil Na. As a result, communities above 1600 m on felsic bedrock, and above 1350 m on mafic bedrock, were most northern in composition. Northern affinity of southern outcrops also increased with latitude, which may partly result from closer geographic proximity to past communities that provided progenitors for the current northern flora. Northern treeless habitats increased in southern affinity with increased slope steepness, perennial seepage, vegetation height, shade, soil pH, Al, Mn, Na and decreased elevation and organic matter. As a result, northern outcrop communities below treeline were most similar to those on southern outcrops. This suggests that southern outcrop vegetation may be more similar to Pleistocene outcrop vegetation than to Pleistocene alpine vegetation. Partial constrained ordination showed that while compositional differences between the Northern and Southern Appalachian habitats were largely explained by environmental differences, there was a significant component of residual variation explained by north or south position that was unrelated to environment. These residual compositional differences may result from historical influences on community structure involving stochastic extinction and colonization processes. 相似文献
50.
Stephen M. Techtmann Julian L. Fortney Kati A. Ayers Dominique C. Joyner Thomas D. Linley Susan M. Pfiffner Terry C. Hazen 《PloS one》2015,10(3)
The waters of the Eastern Mediterranean are characterized by unique physical and chemical properties within separate water masses occupying different depths. Distinct water masses are present throughout the oceans, which drive thermohaline circulation. These water masses may contain specific microbial assemblages. The goal of this study was to examine the effect of physical and geological phenomena on the microbial community of the Eastern Mediterranean water column. Chemical measurements were combined with phospholipid fatty acid (PLFA) analysis and high-throughput 16S rRNA sequencing to characterize the microbial community in the water column at five sites. We demonstrate that the chemistry and microbial community of the water column were stratified into three distinct water masses. The salinity and nutrient concentrations vary between these water masses. Nutrient concentrations increased with depth, and salinity was highest in the intermediate water mass. Our PLFA analysis indicated different lipid classes were abundant in each water mass, suggesting that distinct groups of microbes inhabit these water masses. 16S rRNA gene sequencing confirmed the presence of distinct microbial communities in each water mass. Taxa involved in autotrophic nitrogen cycling were enriched in the intermediate water mass suggesting that microbes in this water mass may be important to the nitrogen cycle of the Eastern Mediterranean. The Eastern Mediterranean also contains numerous active hydrocarbon seeps. We sampled above the North Alex Mud Volcano, in order to test the effect of these geological features on the microbial community in the adjacent water column. The community in the waters overlaying the mud volcano was distinct from other communities collected at similar depths and was enriched in known hydrocarbon degrading taxa. Our results demonstrate that physical phenomena such stratification as well as geological phenomena such as mud volcanoes strongly affect microbial community structure in the Eastern Mediterranean water column. 相似文献