全文获取类型
收费全文 | 828篇 |
免费 | 67篇 |
国内免费 | 3篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 6篇 |
2019年 | 17篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 22篇 |
2015年 | 31篇 |
2014年 | 38篇 |
2013年 | 46篇 |
2012年 | 50篇 |
2011年 | 55篇 |
2010年 | 42篇 |
2009年 | 35篇 |
2008年 | 46篇 |
2007年 | 44篇 |
2006年 | 29篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 33篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 21篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1972年 | 5篇 |
1967年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有898条查询结果,搜索用时 31 毫秒
11.
Evidence for interference, coinfections, and intertypic virus enhancement of infection by ovine-caprine lentiviruses. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The ovine-caprine lentiviruses share nucleotide homology and serological properties in their gag-pol genes and gene products but constitute two distinct biological groups represented by ovine visna virus of Icelandic origin and by caprine arthritis-encephalitis and ovine progressive pneumonia viruses of U.S. origin. Two members of each group, visna 1514 and its antigenic variant LV1-1 in the first group and CAEV/CO and S93, a field isolate virus from a local arthritic sheep, in the second group, were examined in the present study in competitive-binding studies in fibroblast and macrophage cell cultures. The cultures were preinoculated with each of the four viruses and then reinoculated with either 1514 virus or CAEV/CO, labeled with [35S]methionine. Both 1514 and CAEV/CO caused homologous interference. LV1-1 and S93 viruses shared the interference patterns of 1514 and CAEV/CO, respectively. 1514 and LV1-1 did not interfere with binding of CAEV/CO. Similarly, CAEV/CO and S93 did not interfere with binding of 1514. Remarkably, certain combinations, such as S93 plus 1514, resulted in enhanced binding of the second virus. Other experiments showed that the enhancement in binding extended to enhancement in replication of the second virus. These latter data suggested that individual cells supported replication of both viruses. Further testing of this phenomenon showed that goats could be doubly infected with two noninterfering viruses, 1514 and CAEV/CO. The ability of noninterfering related lentiviruses to infect the same cell and also the same host animal may be important in the natural history of these viruses in providing ideal conditions for the development of new recombinant viruses. 相似文献
12.
13.
Alan V. Di Vittorio Kanishka B. Narayan Pralit Patel Katherine Calvin Chris R. Vernon 《Global Change Biology Bioenergy》2023,15(2):185-207
Projection of land use and land-cover change is highly uncertain yet drives critical estimates of carbon emissions, climate change, and food and bioenergy production. We use new, spatially explicit land availability data in conjunction with a model sensitivity analysis to estimate the effects of additional land protection on land use and land cover. The land availability data include protected land and agricultural suitability and is incorporated into the Moirai land data system for initializing the Global Change Analysis Model. Overall, decreasing land availability is relatively inefficient at preserving undeveloped land while having considerable regional land-use impacts. Current amounts of protected area have little effect on land and crop production estimates, but including the spatial distribution of unsuitable (i.e., unavailable) land dramatically shifts bioenergy production from high northern latitudes to the rest of the world, compared with uniform availability. This highlights the importance of spatial heterogeneity in understanding and managing land change. Approximately doubling the current protected area to emulate a 30% protected area target may avoid land conversion by 2050 of less than half the newly protected extent while reducing bioenergy feedstock land by 10.4% and cropland and grazed pasture by over 3%. Regional bioenergy land may be reduced (increased) by up to 46% (36%), cropland reduced by up to 61%, pasture reduced by up to 100%, and harvested forest reduced by up to 35%. Only a few regions show notable gains in some undeveloped land types of up to 36%. Half of the regions can reach the target using only unsuitable land, which would minimize impacts on agriculture but may not meet conservation goals. Rather than focusing on an area target, a more robust approach may be to carefully select newly protected land to meet well-defined conservation goals while minimizing impacts to agriculture. 相似文献
14.
Lisa Beltz Opendra Narayan Robert J. Adams Stephen J. Noga Albert D. Donnenberg 《Journal of medical primatology》1991,20(4):144-151
Rhesus progenitor-enriched BM was exposed overnight to SIV and cultured in a limiting dilution assay where the potential for progenitor interaction with lymphocytes or macrophages was low. Virus was consistently isolated late in culture, detection being aided by coculture with CEM174 lymphoblasts. Although infected cells had reduced clonogenic activity, colonies were indistinguishable from those derived from uninfected BM with respect to proliferative potential, morphology, and longevity in culture. Primate immunodeficiency viruses, therefore, may infect immature BM populations, directly affecting hematopoietic activity. 相似文献
15.
Among diploid Lathyrus species a threefold variation in nuclear DNA amount is attributable to differences in the amount of repetitive DNA. Cross reassociation among repetitive and among non-repetitive DNA fractions from different species shows substantial divergence in DNA composition. The divergence in base composition is correlated with nuclear DNA amount. The degree of divergence is of the same order of magnitude in both the repetitive and nonrepetitive fractions. 相似文献
16.
Naturally occurring antigenic variants of visna virus isolated from two persistently infected sheep have been compared using RNAase T1 fingerprint analysis of the viral RNAs. All the viruses examined have oligonucleotide changes in the 3′-terminal region of the viral genome and many of the alterations are common among the variants of both sheep. There is progressive accumulation of point mutations in the 3′-terminal region of antigenically altered viruses isolated from persistently infected animals. In addition, antigenic variants isolated independently from another sheep contain the same altered oligonucleotides; the nucleotide sequences of these oligonucleotides are identical. These data strongly suggest that the alterations observed in the nucleotide sequence of the variants are related to the change in their antigenic character. 相似文献
17.
18.
19.
Thirty-nine enterotoxigenic cultures of Clostridium perfringens type A were studied for enterotoxin and haemagglutinin production. Enterotoxin was quantitated by sandwich ELISA and DOT-ELISA techniques and haemagglutinin titres were determined using sheep and human erythrocytes. Haemagglutinins from only six cultures reacted against both sheep and human erythrocytes; a further 13 reacted only against human erythrocytes, and another five only against sheep cells.The authors are with the Department of Veterinary Public Health and Epidemiology, Ranchi Veterinary College, Birsa Agricultural University, Ranchi-834007 (Bihar), India. 相似文献
20.
Buoyant density gradient analysis of nuclear DNA of fourCucumis species showed asymmetric profiles indicating the presence of satellite DNA sequences in the nuclear genome. A highly repeated satellite DNA sequence was isolated from the nuclear genome ofC. metuliferus under neutral CsCl gradients. The satellite DNA constitutes about 4.96% of total nuclear DNA and has 48.06% guanine plus cytosine content. The kinetic complexity of satellite DNA is 150 times smaller than T4 phage DNA and the base sequence divergence is low.3H-labeled cRNA transcribed from satellite DNA hybridized clearly to six heterochromatic knobs of pachytene chromosomes. The knob heterochromatin can be distinguished by Giemsa C-banding of pachytene chromosomes. Restriction enzyme analysis and Southern blot hybridization indicated that the satellite DNA has a tandem arrangement and predominantly formed two bands of size 210 and 151 base pairs. Absence of knob satellite DNA ofC. metuliferus in the nuclear genomes ofC. melo, C. anguria andC. sativus showed thatC. metuliferus remains isolated within the genusCucumis. 相似文献