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   428篇
  免费   30篇
  2021年   4篇
  2018年   4篇
  2016年   3篇
  2015年   8篇
  2014年   11篇
  2013年   13篇
  2012年   19篇
  2011年   13篇
  2010年   18篇
  2009年   12篇
  2008年   16篇
  2007年   18篇
  2006年   11篇
  2005年   19篇
  2004年   16篇
  2003年   14篇
  2002年   13篇
  2001年   18篇
  2000年   8篇
  1999年   14篇
  1998年   7篇
  1997年   5篇
  1996年   5篇
  1995年   5篇
  1994年   7篇
  1993年   10篇
  1992年   12篇
  1991年   6篇
  1989年   7篇
  1988年   7篇
  1987年   9篇
  1986年   5篇
  1985年   15篇
  1984年   8篇
  1983年   8篇
  1982年   4篇
  1980年   11篇
  1979年   4篇
  1978年   10篇
  1977年   10篇
  1976年   4篇
  1975年   3篇
  1973年   5篇
  1971年   4篇
  1964年   2篇
  1963年   2篇
  1961年   2篇
  1952年   2篇
  1950年   2篇
  1941年   2篇
排序方式: 共有458条查询结果,搜索用时 15 毫秒
441.
442.
The genus Melitaea consists of about 80 species, divided into ten species groups, which are all restricted to the Palaearctic region. The Melitaea phoebe group was defined by Higgins based on morphological characters such as wing pattern and genital structures. According to his interpretation, the M. phoebe group included seven species: M. phoebe, M. sibina, M. scotosia, M. aetherie, M. collina, M. consulis and M. turkmanica. The taxonomy of the phoebe species group has been poorly resolved and recent results on the species composition within the group suggest the need for a re‐evaluation. In this study molecular sequences (5985 bp) including one mitochondrial (COI) and up to six nuclear (CAD, EF, GAPDH, MDH, RpS5 and wingless) gene regions from 38 specimens of the Melitaea phoebe species group sensu Higgins and some closely related taxa from the Palaearctic region were analysed. The possible evolution of the processus posterior of the male genitalia was also reconstructed based on a shape mapping technique. The analysis of the combined data shows a very clear pattern and almost all relationships are highly supported. Based on the combined Bayesian tree and the shape of the processus posterior of the male genitalia, four main groups are recognised: (i) collina group, (ii) arduinna group, (iii) aetherie group and (iv) phoebe group. The status of M. ornata, M. zagrosi and M. scotosia as species is confirmed, and the results also indicate that M. telona (s.s.) from Israel is a separate species.  相似文献   
443.
444.
Chinese hamster cells (line CHO) were cloned in suspension with a carboxymethylcellulose-containing medium, and the colonies were counted with an electronic particle counter after enzymatically degrading the carboxymethylcellulose with cellulase. Survival of x-irradiated cells was determined by both the standard plating technique and the suspension technique, and comparable results were obtained.  相似文献   
445.
Two phases are distinguished in the α-amylase production in barley (Hordeum vulgare) grains. There is an increase in activity extended to the third or fourth day of germination, then a slight decrease follows. This decrease is accelerated by kinetin while it is prevented by IAA applied at the top of the embryo coleoptile. IAA reverses partially the kinetin action. IAA applied in the germination medium has practically no effect. Removal of the coleoptile stops further increase in α-amylase activity and induces complete insensitivity to hormone treatment. The results indicate that auxin metabolism in the coleoptile participates in the control of α-amylase evolution in the barley grain and that kinetin could act through auxin metabolism in this coleoptile.  相似文献   
446.
Cholinergic nerves are identified by labelling molecules in the ACh synthesis, release and destruction pathway. Recently, antibodies against another molecule in this pathway have been developed. Choline reuptake at the synapse occurs via the high-affinity choline transporter (CHT1). CHT1 immunoreactivity is present in cholinergic nerve fibres containing vesicular acetylcholine transporter (VAChT) in the human and rat central nervous system and rat enteric nervous system. We have examined whether CHT1 immunoreactivity is present in nerve fibres in human intestine and whether it is colocalised with markers of cholinergic, tachykinergic or nitrergic circuitry. Human ileum and colon were fixed, sectioned and processed for fluorescence immunohistochemistry with antibodies against CHT1, class III beta-tubulin (TUJ1), synaptophysin, common choline acetyl-transferase (cChAT), VAChT, nitric oxide synthase (NOS), substance P (SP) and vasoactive intestinal peptide (VIP). CHT1 immunoreactivity was present in many nerve fibres in the circular and longitudinal muscle, myenteric and submucosal ganglia, submucosa and mucosa in human colon and ileum and colocalised with immunoreactivity for TUJ1 and synaptophysin confirming its presence in nerve fibres. In nerve fibres in myenteric ganglia and muscle, CHT1 immunoreactivity colocalised with immunoreactivity for VAChT and cChAT. Some colocalisation occurred with SP immunoreactivity, but little with immunoreactivity for VIP or NOS. In the mucosa, CHT1 immunoreactivity colocalised with that for VIP and SP in nerve fibres and was also present in vascular nerve fibres in the submucosa and on epithelial cells on the luminal border of crypts. The colocalisation of CHT1 immunoreactivity with VAChT immunoreactivity in cholinergic enteric nerves in the human bowel thus suggests that CHT1 represents another marker of cholinergic nerves.  相似文献   
447.
The induction of rat liver microsomal monooxygenase by pretreatment of rats with dieldrin affords a 10-fold protection against the acute toxic effects of the organophosphorus insecticide, chlorfenvinphos. Metabolism studies were carried out to confirm that the protection was due to an enhanced rate of detoxification (via oxidative deethylation). At low doses of chlorfenvinphos (2.5 mg · kg?1), dieldrin pretreatment caused minimal changes in the metabolic profiles. However, at a higher dose (13.2 mg · kg?1), giving clinical signs of intoxication in the control animals, the dieldrin pretreated rats produced 5 times more deethylchlorofenvinphos than did the control animals. The results support the conclusion that the effect of enzyme induction on the metabolism of substrates of that enzyme are dosedependent. Alterations in metabolism, therefore, are not an automatic consequence of enzyme induction.  相似文献   
448.
Aqueous extracts from common tropical seaweeds were evaluated for their effect on the life cycle of the commercially important ectoparasite, Neobenedenia sp. (Platyhelminthes: Monogenea), through the survival of attached adult parasites, period of embryonic development, hatching success and oncomiracidia (larvae) infection success. There was no significant effect of any extract on the survival of adult parasites attached to fish hosts or infection success by oncomiracidia. However, the extracts of two seaweeds, Ulva sp. and Asparagopsis taxiformis, delayed embryonic development and inhibited egg hatching. The extract of A. taxiformis was most effective, inhibiting embryonic development of Neobenedenia sp. and reducing hatching success to 3% compared with 99% for the seawater control. Furthermore, of the 3% of eggs that hatched, time to first and last hatch was delayed (days 14 and 18) compared with the seawater control (days 5 and 7). Asparagopsis taxiformis shows the most potential for development as a natural treatment to manage monogenean infections in intensive aquaculture with the greatest impact at the embryo stage.  相似文献   
449.
450.
The distribution of iridoids, ellagitannins, proanthocyanidins and other compounds in the Cornaceae and related families is discussed in relation to the various taxonomic treatments. Analysis of the chemical data indicates that: (a) Benthamia and Cynoxylon are the most primitive sub-genera in Cornus, (b) Corokia possesses a chemical pattern consistent with that of the Cornaceae, but Helwingia might better be elevated to family rank, (c) Alangiaceae, Davidiaceae, Garryaceae and Nyssaceae broadly fall into the same pattern as the Cornaceaa and can be placed in a restricted order, Cornales, which excludes Araliaceae, Umbelliferae and Rhizophoraceae, and (d) the Cornales shows affinities to the Saxifragales and the Dipsacales.  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