全文获取类型
收费全文 | 1579篇 |
免费 | 163篇 |
出版年
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 22篇 |
2017年 | 17篇 |
2016年 | 32篇 |
2015年 | 42篇 |
2014年 | 44篇 |
2013年 | 64篇 |
2012年 | 90篇 |
2011年 | 98篇 |
2010年 | 54篇 |
2009年 | 57篇 |
2008年 | 84篇 |
2007年 | 74篇 |
2006年 | 81篇 |
2005年 | 82篇 |
2004年 | 68篇 |
2003年 | 76篇 |
2002年 | 70篇 |
2001年 | 53篇 |
2000年 | 49篇 |
1999年 | 36篇 |
1998年 | 24篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 26篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 25篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1985年 | 16篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1979年 | 12篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 17篇 |
1974年 | 12篇 |
1970年 | 16篇 |
1969年 | 25篇 |
1968年 | 11篇 |
1967年 | 15篇 |
1965年 | 11篇 |
排序方式: 共有1742条查询结果,搜索用时 15 毫秒
1.
Larisa R. G. DeSantis Jessica R. Scott Blaine W. Schubert Shelly L. Donohue Brian M. McCray Courtney A. Van Stolk Amanda A. Winburn Michael A. Greshko Mackie C. O’Hara 《PloS one》2013,8(8)
The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately. 相似文献
2.
3.
Liane Wehder Günther Ernst Anna C. Crecelius Orlando Guntinas-Lichius Christian Melle Ulrich S. Schubert Ferdinand von Eggeling 《The journal of histochemistry and cytochemistry》2010,58(10):929-937
Carcinoma tissue consists of not only tumor cells but also fibroblasts, endothelial cells or vascular structures, and inflammatory cells forming the supportive tumor stroma. Therefore, the spatial distribution of proteins that promote growth and proliferation in these complex functional units is of high interest. Matrix-assisted laser desorption/ionization imaging mass spectrometry is a newly developed technique that generates spatially resolved profiles of protein signals directly from thin tissue sections. Surface-enhanced laser desorption/ionization mass spectrometry (MS)combined with tissue microdissection allows analysis of defined parts of the tissue with a higher sensitivity and a broader mass range. Nevertheless, both MS-based techniques have a limited spatial resolution. IHC is a technique that allows a resolution down to the subcellular level. However, the detection and measurement of a specific protein expression level is possible only by semiquantitative methods. Moreover, prior knowledge about the identity of the proteins of interest is necessary. In this study, we combined all three techniques to gain highest spatial resolution, sensitivity, and quantitative information. We used frozen tissue from head and neck tumors and chose two exemplary proteins (HNP1–3 and S100A8) to highlight the advantages and disadvantages of each technique. It could be shown that the combination of these three techniques results in congruent but also synergetic data. (J Histochem Cytochem 58:929–937, 2010) 相似文献
4.
The microbial segment of food webs plays a crucial role in lacustrine food-web functioning and carbon transfer, thereby influencing carbon storage and CO2 emission and uptake in freshwater environments. Variability in microbial carbon processing (autotrophic and heterotrophic production and respiration based on glucose) with depth was investigated in eutrophic, methane-rich Lake Rotsee, Switzerland. In June 2011, 13C-labelling experiments were carried out at six depth intervals in the water column under ambient light as well as dark conditions to evaluate the relative importance of (chemo)autotrophic, mixotrophic and heterotrophic production. Label incorporation rates of phospholipid-derived fatty acid (PLFA) biomarkers allowed us to differentiate between microbial producers and calculate group-specific production. We conclude that at 6 m, net primary production (NPP) rates were highest, dominated by algal photoautotrophic production. At 10 m —the base of the oxycline— a distinct low-light community was able to fix inorganic carbon, while in the hypolimnion, heterotrophic production prevailed. At 2 m depth, high label incorporation into POC could only be traced to nonspecific PLFA, which prevented definite identification, but suggests cyanobacteria as dominating organisms. There was also depth zonation in extracellular carbon release and heterotrophic bacterial growth on recently fixed carbon. Large differences were observed between concentrations and label incorporation of POC and biomarkers, with large pools of inactive biomass settling in the hypolimnion, suggesting late-/post-bloom conditions. Net primary production (115 mmol C m?2 d?1) reached highest values in the epilimnion and was higher than glucose-based production (3.3 mmol C m?2 d?1, highest rates in the hypolimnion) and respiration (5.9 mmol C m?2 d?1, highest rates in the epilimnion). Hence, eutrophic Lake Rotsee was net autotrophic during our experiments, potentially storing large amounts of carbon. 相似文献
5.
6.
7.
Abstract: Schwannoma-derived growth factor (SDGF) is a potent mitogen and neuronal differentiation factor. Because of its relationship to epidermal growth factor (EGF) and the heregulins, it was asked if SDGF interacts with the EGF receptor or HER2/neu. SDGF binds to and causes the phosphorylation on tyrosine of the EGF receptor but not HER2/neu. 相似文献
8.
A. Vuillemin D. Ariztegui G. Nobbe C. J. Schubert the Pasado Science Team 《Geomicrobiology journal》2014,31(4):285-298
Methanogenic populations were investigated in subsaline Laguna Potrok Aike sediments, southern Argentina. Microbial density and activity were assessed via cell count and in situ ATP detection for the last ~11K years. Methanogen phylogenetics highlighted species stratification throughout depth, whereas CO2 reduction was the major pathway leading to methane production. Organic substrates, characterized using pore water analysis, bulk organic fractions and saturated fatty acids, showed a clear link between sediment colonization and initial organic sources. Concentrations and δ13C compositions of methane and fatty acids provided final evidence of a microbial imprint on Holocene organic proxies in the most colonized intervals. 相似文献
9.
10.
Comparative 16S rRNA oligonucleotide analyses and murein types of round-spore-forming bacilli and non-spore-forming relatives 总被引:6,自引:0,他引:6
E Stackebrandt W Ludwig M Weizenegger S Dorn T J McGill G E Fox C R Woese W Schubert K H Schleifer 《Journal of general microbiology》1987,133(9):2523-2529
The phylogenetic incoherency of the genus Bacillus as presently described is demonstrated by analysis of both published and new data from comparative 16S rRNA cataloguing of nine Bacillus species and a number of related non-Bacillus taxa, i.e. Caryophanon latum, Filibacter limicola and Planococcus citreus. While the ellipsoidal-spore-forming bacilli, e.g. B. subtilis and allied species, formed a coherent cluster, the round-spore-forming bacilli showed a higher degree of relationship to the non-spore-forming organisms than these bacilli show among each other. Thus B. sphaericus clustered with C. latum, B. globisporus grouped with F. limicola, B. pasteurii with Sporosarcina ureae, and 'B. aminovorans' with P. citreus, respectively. These organisms formed two related subclusters which, in their phylogenetic depth, are comparable to that of the B. subtilis subline. With the exception of 'B. aminovorans', the 16S rRNA phylogeny was entirely consistent with the distribution of murein types. Even more distantly related to and grouping outside the main Bacillus cluster was B. stearothermophilus, which displayed a moderate relationship to Thermoactinomyces vulgaris. Taxonomic problems arising from the new insights into the intrageneric relationships of Bacillus are discussed. 相似文献