全文获取类型
收费全文 | 459篇 |
免费 | 101篇 |
出版年
2021年 | 4篇 |
2018年 | 6篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 15篇 |
2008年 | 15篇 |
2007年 | 22篇 |
2006年 | 22篇 |
2005年 | 16篇 |
2004年 | 19篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 16篇 |
2000年 | 24篇 |
1999年 | 18篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1960年 | 6篇 |
1924年 | 3篇 |
排序方式: 共有560条查询结果,搜索用时 15 毫秒
481.
482.
R W Crow 《Plastic and reconstructive surgery》1983,71(2):205-208
483.
Why is mendelian segregation so exact? 总被引:6,自引:0,他引:6
J F Crow 《BioEssays : news and reviews in molecular, cellular and developmental biology》1991,13(6):305-312
The precise 1:1 segregation of Mendelian heredity is ordinarily taken for granted, yet there are numerous examples of 'cheating' genes that perpetuate themselves in the population by biasing the Mendelian process in their favor. One example is the Segregation Distortion system of Drosophila melanogaster, in which the distorting gene causes its homologous chromosome to produce a nonfunctional sperm. This system depends on three closely linked components, whose molecular basis is beginning to be understood. The system is characterized by numerous modifiers changing the degree of distortion. Mathematical theory shows that unlinked modifiers that change the degree of distortion in the direction of Mendelism always increase in the population. This provides a mechanism for removing cheaters and preserving the honesty of the Mendelian gene-shuffle. 相似文献
484.
485.
J F Crow 《Human biology; an international record of research》1989,61(5-6):763-75; discussion 776-80
486.
487.
The evolution of underwater flight: The redistribution of pectoral fin rays,in manta rays and their relatives (Myliobatidae)
下载免费PDF全文
![点击此处可从《Journal of morphology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kayla C. Hall Peter J. Hundt John D. Swenson Adam P. Summers Karen D. Crow 《Journal of morphology》2018,279(8):1155-1170
Batoids are a diverse clade of flat cartilaginous fishes that occur primarily in benthic marine habitats. The skates and rays typically use their flexible pectoral fins for feeding and propulsion via undulatory swimming. However, two groups of rays have adopted a pelagic or bentho‐pelagic lifestyle and utilize oscillatory swimming—the Myliobatidae and Gymnuridae. The myliobatids have evolved cephalic lobes, anteriorly extended appendages that are optimized for feeding, while their pectoral fins exhibit several modifications that likely arose in association with functional optimization of pelagic cruising via oscillatory flight. Here, we examine variation in fin ray distribution and ontogenetic timing of fin ray development in batoid pectoral fins in an evolutionary context using the following methods: radiography, computed tomography, dissections, and cleared and stained specimens. We propose an index for characterizing variation in the distribution of pectoral fin rays. While undulatory swimmers exhibit symmetry or slight anterior bias, we found a posterior shift in the distribution of fin rays that arose in two distinct lineages in association with oscillatory swimming. Undulatory and oscillatory swimmers occupy nonoverlapping morphospace with respect to fin ray distribution illustrating significant remodeling of pectoral fins in oscillatory swimmers. Further, we describe a derived skeletal feature in anterior pectoral fins of the Myliobatidae that is likely associated with optimization of oscillatory swimming. By examining the distribution of fin rays with clearly defined articulation points, we were able to infer evolutionary trends and body plan remodeling associated with invasion of the pelagic environment. Finally, we found that the number and distribution of fin rays is set early in development in the little skate, round stingray, and cownose ray, suggesting that fin ray counts from specimens after birth or hatching are representative of adults and therefore comparable among species. 相似文献
488.
489.
The effect of murine monoclonal antibodies binding monomorphic epitopes of Class II, HLA-DR molecules on responding human B lymphocytes stimulated by anti-immunoglobulin M (IgM) antibodies was studied. Goat F(ab')2 anti-human IgM coupled to Sepharose beads (insoluble), or in solution, was added to macrophage-depleted B cells in culture with, or without, anti-human HLA-DR monoclonal antibodies. The addition of monoclonal anti-HLA-DR antibodies to anti-human IgM-stimulated B lymphocytes inhibited this T-independent B-cell proliferation by 82-94%. The role of Class II, HLA-DR molecules on B cells may therefore exceed that of antigen presentation alone, to include responding B-cell activation induced by anti-immunoglobulin. 相似文献
490.
William T. Crow 《Journal of nematology》2014,46(4):331-335
One of the primary pests of bermudagrass (Cynodon spp.) on golf courses in the southeastern United States is Belonolaimus longicaudatus (sting nematode). In 2011, a commercial formulation of Bacillus firmus I-1582, Nortica 5WG, was launched in the United States for management of plant-parasitic nematodes on turfgrasses. To test the efficacy of late winter/early spring application of this biopesticide on B. longicaudatus, two field trials in 2009 compared B. firmus with fenamiphos and untreated control treatments. In 2011, two additional field trials compared treatment with B. firmus with untreated control only. These trials measured treatment effects on the population density of B. longicaudatus, turf root length, and turf percent green cover. In all four trials, treatment with B. firmus improved root length and decreased numbers of B. longicaudatus in contrast to the untreated. These results indicate that late winter/early spring application of B. firmus is an effective biopesticide treatment for management of B. longicaudatus on golf course bermudagrass. 相似文献