全文获取类型
收费全文 | 47篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
49篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2006年 | 4篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有49条查询结果,搜索用时 15 毫秒
31.
32.
Improving the performance of the EPT Index to accommodate multiple stressors in Afrotropical streams
The EPT index (Ephemeroptera, Plecoptera and Trichoptera) may be skewed by the wide tolerance to multiple stressors of the Baetid, Caenid and Hydropsychid families, which affects the performance of the EPT index as an indicator of multiple stressors in aquatic ecosystems. The effect of the BCH families on the EPT index was evaluated and alternatives were considered to improve its performance. The hypothesis that the removal of the BCH families improves sensitivity of the EPT index to human-induced stressors in streams and rivers was tested. Macroinvertebrates were collected in January–March 2009 at 22 sites in the Nyando and Nzoia Rivers, Lake Victoria basin, Kenya. Nine derivatives and modifications of the EPT index were tested for responses to a disturbance gradient, ranked into three condition categories (reference, intermediate and impaired). The sensitivity of the proportionate abundance derivative of the EPT index improved when the BCH families were removed, whereas that of the richness derivative improved marginally. Other modifications considered performed poorly when compared with the EPT-BCH metrics. Wide distribution of the BCH across all sites, irrespective of the level of disturbance, reduced the sensitivity of the EPT index in the studied streams. The removal of the BCH families enhanced the sensitivity of the index to multiple stressors in Afrotropical streams and rivers. 相似文献
33.
Bioenergy crops currently provide the only source of alternative energy with the potential to reduce the use of fossil transportation fuels in a way that is compatible with existing engine technology,including in developing countries.Even though bioenergy research is currently receiving considerable attention,many of the concepts are not new,but rather build on intense research efforts from 30 years ago.A major difference with that era is the availability of genomics tools that have the potential to acceler... 相似文献
34.
PO TIEN XIUHUA ZHANG BINGSHENG QIU BINGYI QIN GUSUI WU 《The Annals of applied biology》1987,111(1):143-152
Two virus-protecting strains, S51 and S52, were obtained for the control of cucumber mosaic virus (CMV) by local lesion selection after adding satellite RNA to the RNA genome of CMV. Both were found to protect pepper plants against a virulent strain of CMV under greenhouse and field conditions. Results from 14 localities in China indicated that the use of protective strains decreased the disease index by 21.6% to 82.8% and increased fruit yields by 10.8% to 55.6%. The host reactions and safety of S51 and S52 were tested, and the effects of the strains on plant growth were also investigated. Possible mechanisms of control of CMV-caused plant diseases by mild strains are discussed. 相似文献
35.
A genetic algorithm for maximum-likelihood phylogeny inference using nucleotide sequence data 总被引:4,自引:2,他引:4
Phylogeny reconstruction is a difficult computational problem, because the
number of possible solutions increases with the number of included taxa.
For example, for only 14 taxa, there are more than seven trillion possible
unrooted phylogenetic trees. For this reason, phylogenetic inference
methods commonly use clustering algorithms (e.g., the neighbor-joining
method) or heuristic search strategies to minimize the amount of time spent
evaluating nonoptimal trees. Even heuristic searches can be painfully slow,
especially when computationally intensive optimality criteria such as
maximum likelihood are used. I describe here a different approach to
heuristic searching (using a genetic algorithm) that can tremendously
reduce the time required for maximum-likelihood phylogenetic inference,
especially for data sets involving large numbers of taxa. Genetic
algorithms are simulations of natural selection in which individuals are
encoded solutions to the problem of interest. Here, labeled phylogenetic
trees are the individuals, and differential reproduction is effected by
allowing the number of offspring produced by each individual to be
proportional to that individual's rank likelihood score. Natural selection
increases the average likelihood in the evolving population of phylogenetic
trees, and the genetic algorithm is allowed to proceed until the likelihood
of the best individual ceases to improve over time. An example is presented
involving rbcL sequence data for 55 taxa of green plants. The genetic
algorithm described here required only 6% of the computational effort
required by a conventional heuristic search using tree
bisection/reconnection (TBR) branch swapping to obtain the same
maximum-likelihood topology.
相似文献
36.
V. V. Bogomolov I. B. Kozlovskaya I. V. Alferova A. D. Egorov I. V. Kovachevich 《Human physiology》2010,36(7):766-772
Established with the personal participation of O.G. Gazenko, the Russian system of medical care for cosmonauts has been largely
preserved to this day. The system was fully functional on board the orbital complex Mir and, with appropriate modifications, has been adopted as the core of the medical care for Russian members of ISS crews. In
2000–2008, 22 cosmonauts were members of 17 ISS missions lasting from 140 to 216 days. The main functions of the medical care
system were to control health, physical, and mental performance, and to support space research. Readaptation to normal gravity
was, in most cases, similar to what has been typical on the return from Russian orbital stations; some deviations are accounted
for by the use of in-flight countermeasures. The paper presents some aspects of the theoretical work of Academician Gazenko
in the field of medical care in space flights. It outlines the principles of ISS medical management. The integrated medical
support system combines medical equipment and items available in the Russian and U.S. segments; the integrated medical group
consists of flight surgeons, medical experts, and biomedical engineers of international partners and coordinates the planning
and implementation of medical operations. In addition, challenges of health care in the phase of ISS operation are defined. 相似文献
37.
I. M. Zhdanko V. N. Zinkin S. K. Soldatov A. V. Bogomolov P. M. Sheshegov 《Human physiology》2016,42(7):705-714
Aviation noise is discussed as a harmful physical factor with ecological, hygienic, clinical, and social implications. Noise contributes to the development of general and occupational pathologies, chronic diseases, and reduction of professional longevity. The present-day knowledge of aviation noise sources and dynamics and effects on environment, population, and aviation personnel is overviewed, as well as strategies to prevent noise consequences including muffling techniques as the key ones. 相似文献
38.
39.
Biological control agents (BCAs) composed of attenuated cucumber mosaic (CMV) and its satellite RNA for controlling CMV diseases were found to induce plant resistance to a number of fungal diseases. Tests conducted in both the field and greenhouse showed evident protective effects against fungal infections by the BCAs. Artificial inoculation with a fungal spore suspension using BCA-treated plants, satellite transgenic plants and plants infected with CMV alone indicated that the resistance to fungi was induced by the virus infection, not by the presence of satellite RNA. 相似文献
40.
O. L. Kurbatova E. Yu. Pobedonostseva V. D. Prokhorovskaya O. N. Kholod A. N. Evsyukov V. V. Bogomolov Yu. I. Voronkov L. M. Filatova O. N. Larina L. A. Sidorenko V. V. Morgun R. R. Kaspransky Yu. P. Altukhov 《Russian Journal of Genetics》2006,42(10):1189-1198
Genetic demographic characteristics and immunogenetic markers (blood groups ABO, Rhesus, MNSs, P, Duffy, Kidd, and Kell) have been studied in a group of 132 Russian cosmonauts and test subjects (CTSG). Analysis of pedigrees has shown a high exogamy in the preceding generations: almost half of the subjects have mixed ethnic background. According to the results of genetic demographic analysis, a sample from the Moscow population was used as control group (CG). Comparison between the CTSG and CG has demonstrated significant differences in genotype frequencies for several blood group systems. The CTSG is characterized by a decreased proportion of rare interlocus genotypic combinations and an increased average heterozygosity. Analysis of the distributions of individual heterozygosity for loci with codominant expression of alleles has shown that the carriers of highly heterozygous genotypes are more frequent in the CTSG. Taking into account that the CTSG has been thoroughly selected from the general population, it is concluded that heterozygosity is related to successful adaptation to a space flight. 相似文献