首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   716篇
  免费   133篇
  国内免费   4篇
  2019年   6篇
  2018年   16篇
  2017年   9篇
  2016年   27篇
  2015年   33篇
  2014年   38篇
  2013年   36篇
  2012年   37篇
  2011年   33篇
  2010年   27篇
  2009年   20篇
  2008年   16篇
  2007年   27篇
  2006年   24篇
  2005年   26篇
  2004年   22篇
  2003年   28篇
  2002年   25篇
  2001年   24篇
  2000年   27篇
  1999年   28篇
  1998年   14篇
  1997年   12篇
  1996年   12篇
  1995年   9篇
  1994年   7篇
  1993年   9篇
  1992年   12篇
  1991年   12篇
  1990年   8篇
  1989年   9篇
  1988年   7篇
  1987年   12篇
  1986年   11篇
  1985年   8篇
  1983年   10篇
  1982年   10篇
  1981年   16篇
  1980年   8篇
  1979年   11篇
  1978年   15篇
  1977年   7篇
  1976年   10篇
  1975年   6篇
  1974年   6篇
  1972年   12篇
  1971年   5篇
  1970年   12篇
  1967年   6篇
  1966年   5篇
排序方式: 共有853条查询结果,搜索用时 31 毫秒
31.
Cytochromes c 3 of different strains of sulfatereducing bacteria have been purified and tested for their capacity to reduce colloidal sulfur to hydrogen sulfide. The results are in good agreement with the activities reported for the whole cells. Cytochrome c 3 is the sulfur reductase of some strains of sulfate-reducing bacteria such as Desulfovibrio desulfuricans Norway 4 and sulfate-reducing bacterium strain 9974 from which the sulfur reductase activity can be purified with the cytochrome c 3. In contrast, Desulfovibrio vulgaris Hildenborough cytochrome c 3 is inhibited by the product of the reaction namely hydrogen sulfide. Chloramphenicol has no effect on the sulfur reductase activity of D. desulfuricans Norway 4 when resting cells grown on lactate-sulfate medium are put in the presence of colloidal sulfur. This shows that the sulfur reductase activity is constitutive and corresponds to the fact that colloidal sulfur grown cells do not contain more cytochrome c 3 (or another sulfur reductase) than lactate-sulfate-grown cells.  相似文献   
32.
Summary The authors studied the phenotypic distribution of -L-fucosidase in a random sample of the population of the area of Rennes (France). The frequencies of Fu 1 (0.64) and Fu 2 (0.36) genes are significantly different from the frequencies observed in New York whites and blacks.  相似文献   
33.
34.
New topics on ecology and systematics of recent and fossil Lingulids lead to an obvious revision of our knowledges on this zoological group. At first, the recent species need systematics and taxonomy on the bases of new described specific criteria (as, morphology of deltidial areas, muscle disposition); the results are briefly indicated. But, in fossil species, disorder and disparity of used characteristics are emphasized.The general conceiving on ecology of Lingulids are reviewed and discussed, especially on bathymetry and salinity; sediment and oxygenation conditions; taphocoenosis and lingulid «communities. On recent species, all these points are also studied, especially some ecological requirements (salinity, bathymetry, grain size), and mechanism of burrowing ability, burrow living positions in the sediments, as shell preservations after death and fossilization, to facilitate the paleobiotope interpretations. Recent animals are euryhalin, surviving at salinities from about 13 to 42‰; they could be considered as well adapted to waters with strong salinity fluctuations. They show preference to fine sand bottoms (lowest particle size about 40–60 μm). Their bathymetric distribution occurs between 0 and about 500 m (Lingula especially between 5–50 m; Glottidia 15–70 m). The isotherms 8–10°C seem to restrict their geographical and bathymetric distribution.Therefore, some post-palaeozoic lingulid bedsare studied or redescribed on the bases of the above discussed characteristics, and new interpretations on the environmental situation are given (Trias of Vosges Mountains; Oligocene from Japan; Eocene of London Basin). More caution must be used in study of fossil Lingulids that are not especially animals living in infralittoral bottoms with low salinity and deficient oxygenation, as generally accepted.  相似文献   
35.
36.
Three forms of ferredoxin FdI, FdI′, and FdII have been isolated from Desulfovibrio gigas, a sulfate reducer. They are separated by a combination of DEAE-cellulose and gel filtration chromatographic procedures. FdI and FdI′ present a slight difference in isoelectric point which enables the separation of the two forms over DEAE-cellulose, while FdII is easily separated from the two other forms by gel filtration. The three forms have the same amino acid composition and are isolated in different aggregation states. Molecular weight determinations by gel filtration gave values of 18 000 for FdI and FdI′ and 24 000 for FdII, whereas a value of 6000 is determined when dissociation is accomplished with sodium dodecyl sulfate. The electronic spectra are different and their ultraviolet-visible absorbance rations are 0.77, 0.87 and 0.68 respectively for FdI, FdI′ and FdII. Despite these differences, the physiological activities of the three forms are similar as far as the reduction of sulfite by molecular hydrogen is concerned.  相似文献   
37.
Satellite DNA amounts were examined in adult tissues of Drosophila virilis, a species whose DNA contains three prominent satellites. Satellite amounts in DNA from six of the seven tissues were lower than in DNA from diploid (adult brain) tissue. Satellite amounts in adult ovary DNA, however, were equivalent to or greater than diploid levels. When DNA from pupal ovaries was examined, a 30% increase in satellite amounts over diploid levels was found. An RNA-DNA hybridization experiment showed that the ribosomal RNA genes in pupal ovary DNA were under-replicated relative to diploid DNA levels.  相似文献   
38.
39.
One of the most important defenses for the eggs of ovipositing female organisms is to avoid being laid in the same habitat as their predators. However, for most organisms, completely avoiding an offspring's predators is not possible. One mechanism that has been largely overlooked is for females to partition an oviposition site into microhabitats that differ in quality for offspring survival. We conducted a series of experiments to examine whether female newts avoid microhabitats utilized by their offspring's primary predator, caddisfly larvae. Female newts avoided laying eggs near predatory caddisflies and shifted egg laying upward in the water column when provided with a vertical dimension. Caddisflies were attracted to chemical stimuli from female newts and their eggs, yet primarily used benthic areas in experimental chambers. Finally, results from a field experiment indicate that the behavioral strategy employed by female newts increases offspring survival. This subset of non‐genetic maternal effects, micro‐oviposition avoidance, is likely an important yet underexplored mechanism by which females increase offspring survival.  相似文献   
40.
Hydrodynamic limb vein injection is an in vivo locoregional gene delivery method. It consists of administrating a large volume of solution containing nucleic acid constructs in a limb with both blood inflow and outflow temporarily blocked using a tourniquet. The fast, high pressure delivery allows the musculature of the whole limb to be reached. The skeletal muscle is a tissue of choice for a variety of gene transfer applications, including gene therapy for Duchenne muscular dystrophy or other myopathies, as well as for the production of antibodies or other proteins with broad therapeutic effects. Hydrodynamic limb vein delivery has been evaluated with success in a large range of animal models. It has also proven to be safe and well‐tolerated in muscular dystrophy patients, thus supporting its translation to the clinic. However, some possible limitations may occur at different steps of the delivery process. Here, we have highlighted the interests, bottlenecks and potential improvements that could further optimize non‐viral gene transfer following hydrodynamic limb vein injection.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号