全文获取类型
收费全文 | 935篇 |
免费 | 106篇 |
国内免费 | 4篇 |
专业分类
1045篇 |
出版年
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2017年 | 13篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 39篇 |
2013年 | 24篇 |
2012年 | 48篇 |
2011年 | 49篇 |
2010年 | 25篇 |
2009年 | 12篇 |
2008年 | 46篇 |
2007年 | 41篇 |
2006年 | 22篇 |
2005年 | 37篇 |
2004年 | 24篇 |
2003年 | 33篇 |
2002年 | 40篇 |
2001年 | 18篇 |
2000年 | 23篇 |
1999年 | 27篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 21篇 |
1991年 | 35篇 |
1990年 | 12篇 |
1989年 | 25篇 |
1988年 | 14篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 17篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1972年 | 7篇 |
1968年 | 7篇 |
1959年 | 6篇 |
1957年 | 7篇 |
排序方式: 共有1045条查询结果,搜索用时 15 毫秒
41.
G R Bartlett 《Biochemical and biophysical research communications》1976,70(4):1055-1062
The concentrations of glycolytic intermediates, including 2,3-diphosphoglycerate, were similar in rat reticulocytes and erythrocytes. There were striking differences, however, in the content and kind of water-soluble nucleotides. Reticulocytes contained much higher concentrations of ATP, GTP, UTP and CTP and had nucleotides not detected in the mature cell including UDP-acetylhexosamine, guanosine diphosphomannose and an unidentified cytidine compound. A large fraction of the total GTP found in the reticulocyte was in the form of a 1:1 complex of ferric iron with GTP. 相似文献
42.
43.
Repeated insemination in Michigan Holstein-Friesian cattle: Incidence, descriptive epidemiology and estimated economic impact 总被引:1,自引:0,他引:1
Twenty-two Michigan dairy herds participating in a computerized herd-health program were studied to determine the incidence and epidemiologic characteristics of repeat-breeder syndrome. A cow with repeat-breeder syndrome was defined as having been inseminated three or more times within the same lactation. Repeat-breeder syndrome was observed in 24% of 3,309 lactations. Cost components associated with unsuccessful inseminations included costs of delayed conception, extra inseminations, extra veterinary service and losses due to culling. Lactations with repeat-breeder syndrome were associated with a loss of approximately $385. An estimated extra cost of $140 was associated with a second insemination, $279 with three inseminations, $429 with four inseminations and $612 with five inseminations. 相似文献
44.
The molecular biology of barophilic bacteria 总被引:3,自引:1,他引:3
Many microorganisms from the deep-sea display high-pressure-adapted — also described as barophilic or piezophilic — growth
characteristics. Phylogenetic studies have revealed that a large proportion of the barophilic bacteria currently in culture
collections belong to a distinct subgroup of the genus Shewanella, referred to as the “barophile branch.“ Many of the basic properties of barophiles that enable their survival at extremes
of pressure remain to be elucidated. However, several genes whose expression is regulated by pressure, or which appear to
be critical to baroadaptation, have been uncovered. One such operon, whose presence appears to be restricted to the “barophile
branch,” has been identifed in DNA samples obtained from sediments recovered in the deepest ocean trench. In the case of another
set of pressure-regulated genes, regulatory elements required for pressure signaling have been uncovered. The nature and regulation
of these genes is discussed.
Received: February 19, 1997 / Accepted: March 3, 1997 相似文献
45.
The metabolic potential of the single cell genomes obtained from the Challenger Deep,Mariana Trench within the candidate superphylum Parcubacteria (OD1)
下载免费PDF全文
![点击此处可从《Environmental microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rosa León‐Zayas Logan Peoples Jennifer F. Biddle Sheila Podell Mark Novotny James Cameron Roger S. Lasken Douglas H. Bartlett 《Environmental microbiology》2017,19(7):2769-2784
Candidate phyla (CP) are broad phylogenetic clusters of organisms that lack cultured representatives. Included in this fraction is the candidate Parcubacteria superphylum. Specific characteristics that have been ascribed to the Parcubacteria include reduced genome size, limited metabolic potential and exclusive reliance on fermentation for energy acquisition. The study of new environmental niches, such as the marine versus terrestrial subsurface, often expands the understanding of the genetic potential of taxonomic groups. For this reason, we analyzed 12 Parcubacteria single amplified genomes (SAGs) from sediment samples collected within the Challenger Deep of the Mariana Trench, obtained during the Deepsea Challenge (DSC) Expedition. Many of these SAGs are closely related to environmental sequences obtained from deep‐sea environments based on 16S rRNA gene similarity and BLAST matches to predicted proteins. DSC SAGs encode features not previously identified in Parcubacteria obtained from other habitats. These include adaptation to oxidative stress, polysaccharide modification and genes associated with respiratory nitrate reduction. The DSC SAGs are also distinguished by relative greater abundance of genes for nucleotide and amino acid biosynthesis, repair of alkylated DNA and the synthesis of mechanosensitive ion channels. These results present an expanded view of the Parcubacteria, among members residing in an ultra‐deep hadal environment. 相似文献
46.
Holly Croft Jing M. Chen Xiangzhong Luo Paul Bartlett Bin Chen Ralf M. Staebler 《Global Change Biology》2017,23(9):3513-3524
Improving the accuracy of estimates of forest carbon exchange is a central priority for understanding ecosystem response to increased atmospheric CO2 levels and improving carbon cycle modelling. However, the spatially continuous parameterization of photosynthetic capacity (Vcmax) at global scales and appropriate temporal intervals within terrestrial biosphere models (TBMs) remains unresolved. This research investigates the use of biochemical parameters for modelling leaf photosynthetic capacity within a deciduous forest. Particular attention is given to the impacts of seasonality on both leaf biophysical variables and physiological processes, and their interdependent relationships. Four deciduous tree species were sampled across three growing seasons (2013–2015), approximately every 10 days for leaf chlorophyll content (ChlLeaf) and canopy structure. Leaf nitrogen (NArea) was also measured during 2014. Leaf photosynthesis was measured during 2014–2015 using a Li‐6400 gas‐exchange system, with A‐Ci curves to model Vcmax. Results showed that seasonality and variations between species resulted in weak relationships between Vcmax normalized to 25°C () and NArea (R2 = 0.62, P < 0.001), whereas ChlLeaf demonstrated a much stronger correlation with (R2 = 0.78, P < 0.001). The relationship between ChlLeaf and NArea was also weak (R2 = 0.47, P < 0.001), possibly due to the dynamic partitioning of nitrogen, between and within photosynthetic and nonphotosynthetic fractions. The spatial and temporal variability of was mapped using Landsat TM/ETM satellite data across the forest site, using physical models to derive ChlLeaf. TBMs largely treat photosynthetic parameters as either fixed constants or varying according to leaf nitrogen content. This research challenges assumptions that simple NArea– relationships can reliably be used to constrain photosynthetic capacity in TBMs, even within the same plant functional type. It is suggested that ChlLeaf provides a more accurate, direct proxy for and is also more easily retrievable from satellite data. These results have important implications for carbon modelling within deciduous ecosystems. 相似文献
47.
48.
Jeremy Bartlett 《BMJ (Clinical research ed.)》1963,2(5373):1653-1654
49.
50.