全文获取类型
收费全文 | 244篇 |
免费 | 20篇 |
国内免费 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 15篇 |
2012年 | 20篇 |
2011年 | 20篇 |
2010年 | 18篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 17篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 93 毫秒
161.
Dhanabalan Rajasekaran Prakash Jeevanandam Prabakar Sukumar Arulpandiyan Ranganathan Samdevakumar Johnjothi Vivekanandan Nagarajan 《Reports of Practical Oncology and Radiotherapy》2015,20(1):57-65
Aim
To evaluate the new Octavius 4D system for patient specific quality assurance and to study the correlation between plan complexity and gamma index analysis in patient specific quality assurance of VMAT using the Octavius 4D system.Background
McNiven (2010) proposed a study to evaluate the utility of a complexity metric, the Modulation Complexity Score, to evaluate the relationship of the metric with deliverability in IMRT.Materials and methods
Evaluation of the Octavius 4D system was carried out by gamma evaluation of user defined MLC created patterns and AAPM TG 119 benchmark plans. The relationship between plan complexity expressed as Modulation Complexity Score (MCS) and the gamma index analysis was established by a planar and volumetric gamma analysis of 106 clinically approved VMAT patient plans of different sites.Results
Average volumetric 3D global gamma evaluation (3 mm/3%) results for the evaluation plans was 97.41% for 6 MV X-rays and 98.30% for 15 MV X-rays. Average MCS values for the head and neck, pelvic and thoracic plans were 0.2224, 0.3615 and 0.1874. Average volumetric 3D global gamma analysis (3 mm/3%) results for the head and neck, pelvic and thoracic VMAT plans were 95.45%, 97.51% and 96.98%, respectively. Out of 90 correlation analyses between the MCS and gamma passing rate, only 3 had the r value greater than 0.5.Conclusions
The Octavius 4D system is a suitable device for patient specific pretreatment QA. Global and local gamma analysis results showed a weak correlation with the MCS. 相似文献162.
163.
Abstract: Incorporation of [1 H]fucose into the TCA-precipitable material from the particulate and soluble fractions of different regions of the brain in the 1-day-old chick was measured following training on a passive avoidance task. A significant increase in the level of incorporation of [3 H]fucose into the particulate fraction of the anterior forebrain roof was observed in the trained birds as compared with untrained controls. The percentage increases in radioactivity in the particulate fraction of the anterior forebrain roof were 29% ( p < 0.01), 16% ( p < 0.01), and 26% ( p < 0.01) in the trained birds as compared with controls, 30 min, 3 h, and 24 h following learning, respectively, but had returned to control levels after 48 h. These results suggest either increased production of glycoproteins or increased fucosylation of preexisting proteins following training, and suggest one of the possible localized neurochemical changes associated with the learning of the passive avoidance response. 相似文献
164.
The behavioural reaction of a tropical estuarine gastropod, Cerithidea cingulata (Gmelin), to different types of substrata was investigated by subjecting the snails to different mixtures of natural sediment. In addition the organic matter in the sediments was estimated, and an attempt has also been made to relate these results to the distribution of snails in the field. 相似文献
165.
166.
Takeshita F Tanaka T Matsuda T Tozuka M Kobiyama K Saha S Matsui K Ishii KJ Coban C Akira S Ishii N Suzuki K Klinman DM Okuda K Sasaki S 《Journal of virology》2006,80(13):6218-6224
Toll-like receptors (TLRs) recognize microbial components and trigger the signaling cascade that activates the innate and adaptive immunity. TLR adaptor molecules play a central role in this cascade; thus, we hypothesized that overexpression of TLR adaptor molecules could mimic infection without any microbial components. Dual-promoter plasmids that carry an antigen and a TLR adaptor molecule such as the Toll-interleukin-1 receptor domain-containing adaptor-inducing beta interferon (TRIF) or myeloid differentiation factor 88 (MyD88) were constructed and administered to mice to determine if these molecules can act as an adjuvant. A DNA vaccine incorporated with the MyD88 genetic adjuvant enhanced antigen-specific humoral immune responses, whereas that with the TRIF genetic adjuvant enhanced cellular immune responses. Incorporating the TRIF genetic adjuvant in a DNA vaccine targeting the influenza HA antigen or the tumor-associated antigen E7 conferred superior protection. These results indicate that TLR adaptor molecules can bridge innate and adaptive immunity and potentiate the effects of DNA vaccines against virus infection and tumors. 相似文献
167.
Mi X Swenson NG Valencia R Kress WJ Erickson DL Pérez ÁJ Ren H Su SH Gunatilleke N Gunatilleke S Hao Z Ye W Cao M Suresh HS Dattaraja HS Sukumar R Ma K 《The American naturalist》2012,180(1):E17-E30
Niche differentiation has been proposed as an explanation for rarity in species assemblages. To test this hypothesis requires quantifying the ecological similarity of species. This similarity can potentially be estimated by using phylogenetic relatedness. In this study, we predicted that if niche differentiation does explain the co-occurrence of rare and common species, then rare species should contribute greatly to the overall community phylogenetic diversity (PD), abundance will have phylogenetic signal, and common and rare species will be phylogenetically dissimilar. We tested these predictions by developing a novel method that integrates species rank abundance distributions with phylogenetic trees and trend analyses, to examine the relative contribution of individual species to the overall community PD. We then supplement this approach with analyses of phylogenetic signal in abundances and measures of phylogenetic similarity within and between rare and common species groups. We applied this analytical approach to 15 long-term temperate and tropical forest dynamics plots from around the world. We show that the niche differentiation hypothesis is supported in six of the nine gap-dominated forests but is rejected in the six disturbance-dominated and three gap-dominated forests. We also show that the three metrics utilized in this study each provide unique but corroborating information regarding the phylogenetic distribution of rarity in communities. 相似文献
168.
Ethylene modulates flavonoid accumulation and gravitropic responses in roots of Arabidopsis 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Plant organs change their growth direction in response to reorientation relative to the gravity vector. We explored the role of ethylene in Arabidopsis (Arabidopsis thaliana) root gravitropism. Treatment of wild-type Columbia seedlings with the ethylene precursor 1-aminocyclopropane carboxylic acid (ACC) reduced root elongation and gravitropic curvature. The ethylene-insensitive mutants ein2-5 and etr1-3 had wild-type root gravity responses, but lacked the growth and gravity inhibition by ACC found in the wild type. We examined the effect of ACC on tt4(2YY6) seedlings, which have a null mutation in the gene encoding chalcone synthase, the first enzyme in flavonoid synthesis. The tt4(2YY6) mutant makes no flavonoids, has elevated indole-3-acetic acid transport, and exhibits a delayed gravity response. Roots of tt4(2YY6), the backcrossed line tt4-2, and two other tt4 alleles had wild-type sensitivity to growth inhibition by ACC, whereas the root gravitropic curvature of these tt4 alleles was much less inhibited by ACC than wild-type roots, suggesting that ACC may reduce gravitropic curvature by altering flavonoid synthesis. ACC treatment induced flavonoid accumulation in root tips, as judged by a dye that becomes fluorescent upon binding flavonoids in wild type, but not in ein2-5 and etr1-3. ACC also prevented a transient peak in flavonoid synthesis in response to gravity. Together, these experiments suggest that elevated ethylene levels negatively regulate root gravitropism, using EIN2- and ETR1-dependent pathways, and that ACC inhibition of gravity response occurs through altering flavonoid synthesis. 相似文献
169.
An additive-dominance model to determine chromosomal effects in chromosome substitution lines and other gemplasms 总被引:1,自引:0,他引:1
Wu J Jenkins JN McCarty JC Saha S Stelly DM 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2006,112(3):391-399
When using chromosome substitution (CS) lines in a crop breeding improvement program, one needs to separate the effects of
the substituted chromosome from the remaining chromosomes. This cannot be done with the traditional additive-dominance (AD)
model where CS lines, recurrent parent, and their hybrids are used. In this study, we develop a new genetic model and software,
called a modified AD model with genotype × environment interactions, which can predict additive and dominance genetic effects
attributed to a substituted alien chromosome in a CS line as well as the overall genetic effects of the non-substituted chromosomes.
In addition, this model will predict the additive and dominance effects of the same chromosome of interest (i.e. chromosome
25 of cotton in this study) in an inbred line, as well as the effects of the remaining chromosomes in the inbred line. The
model requires a CS line, its recurrent parent and their F1 and/or F2 hybrids between the substitution lines and several inbred lines. Monte Carlo simulation results showed that genetic variance
components were estimated with no or slight bias when we considered this modified AD model as random. The correlation coefficient
between predicted effects and true effects due to the chromosomes of interest varied from zero to greater than 0.90 and it
was positively relative to the difference between the CS line and the recurrent line. To illustrate the use of this new genetic
model, an upland cotton, Gossypium hirsusum L, CS line (CS-B25), TM-1 (the recurrent parent), five elite cultivars, and the F2 hybrids from test-crossing these two lines with the five elite cultivars were grown in two environments in Mississippi. Agronomic
and fiber data were collected and analyzed. The results showed that the CS line, CS-B25, which has chromosome 25 from line
3 to 79, Gossypium barbadense substituted into TM-1, had positive genetic associations with several fiber traits. We also determined that Chromosome 25
from FiberMax 966 had significantly positive associations with fiber length and strength; whereas, chromosome 25 from TM-1
and SureGrow 747 had detectable negative genetic effects on fiber strength. The new model will be useful to determine effects
of the chromosomes of interest in various inbred lines in any diploid or amphidiploid crop for which CS lines are available. 相似文献
170.
Comparing tropical forest tree size distributions with the predictions of metabolic ecology and equilibrium models 总被引:2,自引:0,他引:2
Muller-Landau HC Condit RS Harms KE Marks CO Thomas SC Bunyavejchewin S Chuyong G Co L Davies S Foster R Gunatilleke S Gunatilleke N Hart T Hubbell SP Itoh A Kassim AR Kenfack D LaFrankie JV Lagunzad D Lee HS Losos E Makana JR Ohkubo T Samper C Sukumar R Sun IF Nur Supardi MN Tan S Thomas D Thompson J Valencia R Vallejo MI Muñoz GV Yamakura T Zimmerman JK Dattaraja HS Esufali S Hall P He F Hernandez C Kiratiprayoon S Suresh HS Wills C Ashton P 《Ecology letters》2006,9(5):589-602
Tropical forests vary substantially in the densities of trees of different sizes and thus in above-ground biomass and carbon stores. However, these tree size distributions show fundamental similarities suggestive of underlying general principles. The theory of metabolic ecology predicts that tree abundances will scale as the −2 power of diameter. Demographic equilibrium theory explains tree abundances in terms of the scaling of growth and mortality. We use demographic equilibrium theory to derive analytic predictions for tree size distributions corresponding to different growth and mortality functions. We test both sets of predictions using data from 14 large-scale tropical forest plots encompassing censuses of 473 ha and > 2 million trees. The data are uniformly inconsistent with the predictions of metabolic ecology. In most forests, size distributions are much closer to the predictions of demographic equilibrium, and thus, intersite variation in size distributions is explained partly by intersite variation in growth and mortality. 相似文献