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   1376篇
  免费   146篇
  国内免费   1篇
  2023年   12篇
  2022年   20篇
  2021年   60篇
  2020年   28篇
  2019年   26篇
  2018年   44篇
  2017年   39篇
  2016年   51篇
  2015年   94篇
  2014年   84篇
  2013年   104篇
  2012年   133篇
  2011年   112篇
  2010年   76篇
  2009年   53篇
  2008年   78篇
  2007年   58篇
  2006年   61篇
  2005年   56篇
  2004年   43篇
  2003年   37篇
  2002年   38篇
  2001年   6篇
  2000年   12篇
  1999年   8篇
  1998年   9篇
  1997年   4篇
  1996年   4篇
  1995年   10篇
  1994年   5篇
  1992年   16篇
  1991年   6篇
  1990年   14篇
  1989年   9篇
  1988年   8篇
  1987年   9篇
  1986年   5篇
  1985年   8篇
  1984年   7篇
  1983年   10篇
  1982年   10篇
  1981年   5篇
  1980年   5篇
  1979年   5篇
  1976年   5篇
  1975年   4篇
  1973年   3篇
  1970年   4篇
  1962年   2篇
  1928年   2篇
排序方式: 共有1523条查询结果,搜索用时 15 毫秒
21.
Utilizing a combination of preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and sodium dodecyl sulfate-hydroxylapatite column chromatography, we have separated and purified the gA and gB glycoproteins of the major virus-specific glycoprotein region from herpes simplex virus type 1-infected cells. By using purified antigen preparations, antisera specific to each of these glycoproteins were produced. Immunoprecipitation from detergent extracts of infected cells and radioimmune precipitation of the purified antigens have shown that the anti-gA and anti-gB sera each recognize both the gA and the gB glycoproteins. The anti-gA serum was also shown to neutralize virus despite the presence of only minute quantities of the gA glycoprotein in virions. Pulse-chase studies have indicated that the gA and gB glycoproteins are synthesized from a common precursor polypeptide. Together, these data demonstrate that the gA and gB glycoproteins of herpes simplex virus type 1 are antigenically similar but not identical and probably represent two different forms of the same polypeptide which differ in their degree of glycosylation.  相似文献   
22.
Juvenile turbot,Scophthalmus maximus (L.), were exposed to 0.58 μg 1−1 Aroclor 1254 in seawater, to sediments containing 100, 60 and 1 ppm or fed with cockle containing 20 ppm PCB (polychlorinated biphenyls). Concentration factors for liver and muscle were 104 and 103, respectively, for uptake of PCB from seawater. Contamination of muscle was similar to that of sediments containing 1 and 60 ppm PCB to which turbot were exposed, but less than the 20 ppm in their experimental diet. Contamination of flatfish in the North Sea area is compared with the levels of PCB in the flounder,Platichthys flesus (L.), in the River Thames and predictable values for uptake of PCB from different pathways discussed.  相似文献   
23.
Temperature-sensitive mutants of herpes simplex virus type 1 belonging to four DNA- complementation groups exhibited two distinct patterns of viral DNA synthesis after shift-up to the nonpermissive temperature. In cultures infected with mutants belonging to complementation groups A, C, and D, little or no viral DNA was synthesized after shift-up. In cultures infected with a mutant in complementation group B, nearly normal amounts of viral DNA were synthesized after shift-up.  相似文献   
24.
25.
26.
Eucalyptin and 8-desmethyleucalyptin have been isolated from the leaf wax coatings of several species of Eucalyptus, from Syncarpia glomulifera, Lophostemon confertus and an Angophora hybrid indicating that C-methylated flavones may be fairly distinctive of the family Myrtaceae. Ursolic acid has been isolated from the leaf waxes of E. youmanii, S. glomulifera, Leptospermum petersonii and Melaleuca quinquenervia, friedelin from Lophostemon confertus and 4,6-dimethoxy-2-hydroxyacetophenone from E. michaeliana.  相似文献   
27.
28.
In herbivores, survival and reproduction are influenced by quality and quantity of forage, and hence, diet and foraging behavior are the foundation of an herbivore's life history strategy. Given the importance of diet to most herbivores, it is imperative that we know the species of plants they prefer, especially for herbivorous species that are at risk for extinction. However, it is often difficult to identify the diet of small herbivores because: (a) They are difficult to observe, (b) collecting stomach contents requires sacrificing animals, and (c) microhistology requires accurately identifying taxa from partially digested plant fragments and likely overemphasizes less‐digestible taxa. The northern Idaho ground squirrel (Urocitellus brunneus) is federally threatened in the United States under the Endangered Species Act. We used DNA metabarcoding techniques to identify the diet of 188 squirrels at 11 study sites from fecal samples. We identified 42 families, 126 genera, and 120 species of plants in the squirrel's diet. Our use of three gene regions was beneficial because reliance on only one gene region (e.g., only trnL) would have caused us to miss >30% of the taxa in their diet. Northern Idaho ground squirrel diet differed between spring and summer, frequency of many plants in the diet differed from their frequency within their foraging areas (evidence of selective foraging), and several plant genera in their diet were associated with survival. Our results suggest that while these squirrels are generalists (they consume a wide variety of plant species), they are also selective and do not eat plants relative to availability. Consumption of particular genera such as Perideridia may be associated with higher overwinter survival.  相似文献   
29.

The Avian Vampire Fly, Philornis downsi, has invaded the Galapagos Islands, where it causes high mortality of endemic and native landbird species, including most species of Darwin’s finches. Control methods are under development, but key information is missing about the reproductive biology of P. downsi and the behavior of flies in and near nests of their hosts. We used external and internal nest cameras to record the behavior of P. downsi adults within and outside nests of the Galapagos Flycatcher, Myiarchus magnirostris, throughout all stages of the nesting cycle. These recordings showed that P. downsi visited flycatcher nests throughout the day with higher fly activity during the nestling phase during vespertine hours. The observations also revealed that multiple P. downsi individuals can visit nests concurrently, and that there are some interactions among these flies within the nest. Fly visitation to nests occurred significantly more often while parent birds were away from the nest than in the nest, and this timing appears to be a strategy to avoid predation by parent birds. We report fly mating behavior outside the nest but not in the nest cavity. We discuss the relevance of these findings for the adaptive forces shaping P. downsi life history strategies as well as rearing and control measures.

  相似文献   
30.
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