全文获取类型
收费全文 | 4533篇 |
免费 | 244篇 |
国内免费 | 275篇 |
出版年
2023年 | 64篇 |
2022年 | 76篇 |
2021年 | 106篇 |
2020年 | 125篇 |
2019年 | 137篇 |
2018年 | 90篇 |
2017年 | 108篇 |
2016年 | 116篇 |
2015年 | 134篇 |
2014年 | 218篇 |
2013年 | 301篇 |
2012年 | 180篇 |
2011年 | 225篇 |
2010年 | 158篇 |
2009年 | 175篇 |
2008年 | 222篇 |
2007年 | 230篇 |
2006年 | 203篇 |
2005年 | 181篇 |
2004年 | 178篇 |
2003年 | 163篇 |
2002年 | 128篇 |
2001年 | 124篇 |
2000年 | 115篇 |
1999年 | 121篇 |
1998年 | 78篇 |
1997年 | 71篇 |
1996年 | 73篇 |
1995年 | 80篇 |
1994年 | 75篇 |
1993年 | 63篇 |
1992年 | 55篇 |
1991年 | 51篇 |
1990年 | 40篇 |
1989年 | 45篇 |
1988年 | 42篇 |
1987年 | 43篇 |
1986年 | 50篇 |
1985年 | 51篇 |
1984年 | 31篇 |
1983年 | 34篇 |
1982年 | 42篇 |
1981年 | 26篇 |
1980年 | 43篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 24篇 |
1972年 | 16篇 |
排序方式: 共有5052条查询结果,搜索用时 218 毫秒
991.
Yoshiyuki Kawakami Takayuki Akahane Akira Gotoh Yukie Okimura Kozue Oana Tsutomu Katsuyama 《Microbiology and immunology》1997,41(9):703-708
We have successfully developed and evaluated a new susceptibility testing procedure against Helicobacter pylori strains using air-dried microplates “HP-Plates” containing eight serially-diluted anti-H. pylori agents. HP-Plate wells were reconstituted by the inoculation of 100 μl of H. pylori cell suspensions. After incubation at 37 C for 48 hr under humidified microaerophilic conditions, HP-Plates were read visually with a circular mirror. We investigated the within-day reproducibility tests of HP-Plates using the six quality control (QC) strains we proposed. Of the 20 testings, determining the minimum inhibitory concentrations (MICs) of all the QC strains fell within ± 1 log2 dilution ranges. When 200 clinical isolates were tested with HP-Plates and compared with the results obtained with the modified broth macrodilution method of NCCLS, more than 90% of the MICs also fell within ±1 log2 dilution ranges. We concluded that the HP-Plate susceptibility test method is a practical and easily applicable alternative of susceptibility testing for clinical microbiology laboratories in determining the MICs of H. pylori isolates. 相似文献
992.
Genetic variation at allozyme and RAPD loci in sessile oak Quercus petraea (Matt.) Liebl.: the role of history and geography 总被引:7,自引:0,他引:7
The nuclear genetic variation within and among 21 populations of sessile oak was estimated at 31 RAPD loci in conjunction with previous estimates of variation at eight allozyme loci. The aim of the study was to assess the relative role of isolation-by-distance and postglacial history on patterns of nuclear variation. Because of its small effective population size and maternal transmission, the chloroplast genome is a good marker of population history. Both kinds of nuclear variation (RAPD and allozyme) were therefore compared, first, to the geographical distances among populations and, secondly, to chloroplast DNA restriction polymorphism in the same populations. Multiple Mantel tests were used for this purpose. Although RAPDs revealed less genetic diversity than allozymes, levels of genetic differentiation ( G ST ) were identical. The standard genetic distance calculated at all RAPD loci was correlated with geographical distances but not with the genetic distance calculated from chloroplast DNA data. Conversely, allozyme variation was correlated with chloroplast DNA variation, but not with geography. Possibly, divergent selection at two allozyme loci during the glacial period could explain this pattern. Because of its greater number of loci assayed, RAPDs probably provided a less biased picture of the relative role of geography and history. 相似文献
993.
While bilateral trait asymmetry is widely recognized to estimate developmental instability, much controversy exists over which types of asymmetry (fluctuating, directional, and/or antisymmetry) to use. Recently it has been hypothesized that the three types are strongly interrelated, and that increased developmental instability may be reflected in a transition from fluctuating to directional asymmetry and/or antisymmetry. Alternatively, habitat disturbance might change the genetic expression of directional asymmetry. We present herein the first empirical evidence for stress-mediated shifts in types of asymmetry in natural populations, by using mixture analysis to model tarsus asymmetry in bird populations exposed to different levels of habitat disturbance. Observed asymmetry patterns almost exclusively consisted of true fluctuating asymmetry in the least disturbed populations, but became progressively mixed with directional asymmetry under increasing disturbance. Failing to unravel these mixtures of different forms of asymmetry may have critical implications for the analysis and interpretation of asymmetry data. 相似文献
994.
995.
996.
An information‐theoretic approach to estimating the composite genetic effects contributing to variation among generation means: Moving beyond the joint‐scaling test for line cross analysis 下载免费PDF全文
Heath Blackmon Jeffery P. Demuth 《Evolution; international journal of organic evolution》2016,70(2):420-432
The pace and direction of evolution in response to selection, drift, and mutation are governed by the genetic architecture that underlies trait variation. Consequently, much of evolutionary theory is predicated on assumptions about whether genes can be considered to act in isolation, or in the context of their genetic background. Evolutionary biologists have disagreed, sometimes heatedly, over which assumptions best describe evolution in nature. Methods for estimating genetic architectures that favor simpler (i.e., additive) models contribute to this debate. Here we address one important source of bias, model selection in line cross analysis (LCA). LCA estimates genetic parameters conditional on the best model chosen from a vast model space using relatively few line means. Current LCA approaches often favor simple models and ignore uncertainty in model choice. To address these issues we introduce Software for Analysis of Genetic Architecture (SAGA), which comprehensively assesses the potential model space, quantifies model selection uncertainty, and uses model weighted averaging to accurately estimate composite genetic effects. Using simulated data and previously published LCA studies, we demonstrate the utility of SAGA to more accurately define the components of complex genetic architectures, and show that traditional approaches have underestimated the importance of epistasis. 相似文献
997.
998.
Aya Onoda Masaharu Asanoma Haruo Nukaya 《Bioscience, biotechnology, and biochemistry》2016,80(5):833-839
To identify the major mutagen in pyroligneous acid (PA), 10 wood and 10 bamboo pyroligneous acids were examined using the Ames test in Salmonella typhimurium strains TA100 and TA98. Subsequently, the mutagenic dicarbonyl compounds (DCs), glyoxal, methylglyoxal (MG), and diacetyl in PA were quantified using high-performance liquid chromatography, and the mutagenic contribution ratios for each DC were calculated relative to the mutagenicity of PA. Eighteen samples were positive for mutagens and showed the strongest mutagenicity in TA100 in the absence of S9 mix. MG had the highest mutagenic contribution ratio, and its presence was strongly correlated with the specific mutagenicity of PA. These data indicate that MG is the major mutagen in PA. 相似文献
999.
1000.
Kunduru is an important Anatolian landrace having peculiar traits that are appreciated by farmers and breeders. 33 accessions known as Kunduru collected by ICARDA from six geographical provinces of Turkey, were used to study the phenotypic and genotypic intra-diversity. Kunduru landraces exhibited high intra-diversity for most of the studied morphological traits. GPC (12.10–14.90%), vitreousness (75–100%), TKW (31.80–56.70 g), YP (4.70–8.00 ppm), b*-value (14.30–19.50), ash content (1.60–2.0%) and gluten strength (14–60 ml) showed marked variations. Gliadin and glutenin banding patterns showed high polymorphism. 65 alleles were detected with 14 SSR markers, giving a mean of 6.77 alleles per locus. The average PIC value was 0.44 and ranged from 0.11 to 0.70. The average genetic distance between pairs of landraces was 0.47 and ranged between 0.11 and 0.72. This study showed that Kunduru landraces maintains high allelic variation. PCoA indicated that eco-geographical variables have a significant effect on SSR diversity as well as morphological traits. Many of the landraces studied are in danger of disappearing from the local farmers' fields; this study demonstrates the importance of maintaining and conserving this precious genetic resources. 相似文献