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   594篇
  免费   32篇
  626篇
  2022年   10篇
  2021年   11篇
  2019年   8篇
  2018年   10篇
  2017年   6篇
  2016年   7篇
  2015年   14篇
  2014年   18篇
  2013年   14篇
  2012年   26篇
  2011年   31篇
  2010年   28篇
  2009年   18篇
  2008年   17篇
  2007年   16篇
  2006年   21篇
  2005年   17篇
  2004年   13篇
  2003年   21篇
  2002年   12篇
  2001年   13篇
  2000年   16篇
  1999年   12篇
  1998年   8篇
  1997年   6篇
  1996年   7篇
  1995年   4篇
  1994年   6篇
  1993年   7篇
  1992年   18篇
  1991年   23篇
  1990年   12篇
  1989年   12篇
  1988年   11篇
  1987年   11篇
  1986年   6篇
  1985年   13篇
  1984年   12篇
  1983年   13篇
  1981年   8篇
  1980年   7篇
  1979年   6篇
  1978年   8篇
  1977年   6篇
  1974年   8篇
  1973年   9篇
  1971年   5篇
  1970年   6篇
  1969年   5篇
  1963年   4篇
排序方式: 共有626条查询结果,搜索用时 15 毫秒
1.
Efficient plant regeneration via somatic embryogenesis has been developed in chickpea cultivar C235. Leaf explants, on MS medium supplemented with 1.25 mg/l 2,4-D and 0.25 mg/l kinetin, yielded somatic embryos with high efficiency during dark incubation. MS medium supplemented with B5 vitamins, 0.125 mg/l IBA and 2 mg/l BAP was found suitable for embryo maturation. The well formed embryos germinated into plantlets on basal B5 medium supplemented with 0.25 mg/l BAP. Further development into healthy plantlets was obtained on basal B5 medium. Hardened plantlets produced normal, fertile plants upon transfer to soil.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP 6-Benzyl-aminopurine - IAA IndoIe-3-acetic acid - IBA Indole-3-butyric acid - NAA 1-Naphthalene acetic acid - Kinetin 6-furfuryl aminopurine - Zeatin 6-(4-hydroxy-3-methylbut-2-enylamino)-purine  相似文献   
2.
Proteolytic thermophilic bacterial cultures (171 strains) were isolated from different milk and milk products. After screening these isolates for protease production in a liquid medium, fifty that exhibited enzyme activity in excess of 100 units/ml were selected and identified. Twenty-nine were Bacillus stearothermophilus (constituting 58% of the total), twelve were B. coagulans , five were B. circulans and four were B. licheniformis . Skim milk powder contributed the maximum number of B. stearothermophilus (64.7%) followed by raw milk (63.2%) and pasteurized milk (44.4%). When the culture supernatant liquids from the selected isolates were given heat treatment, five cultures retained 100% protease activity at 65°C for 30 min. Protease of B. stearothermophilus RM-67 had the maximum heat resistance because it retained 87.5% of its activity at 70°C for 30 min.  相似文献   
3.
D P Chopra 《In vitro》1978,14(11):939-944
Outgrowth cultures of normal human epidermis were used to study a possible relationship between growth inhibition and differentiated function. The effects of theophylline, epidermal chalone and x-irradiation on mitoses and the characteristic production of epidermal keratohyaline granules (KG) were examined at various intervals after the treatment. Theophylline (an inhibitor of cyclic nucleotide phosphodiesterase) or epidermal chalone inhibited mitoses and enhanced KG production. X-irradiation inhibited mitoses but had no effect on KG formation. These results indicate that inhibition of proliferation per se is not sufficient to enhance keratinization of human epidermal cells.  相似文献   
4.
5.
Genetic and developmental studies of wingless (wg1), a new second chromosome recessive mutation in Drosophila melanogaster, have shown that it affects not only wing and haltere development (giving rise to wingless and/or halterless flies), but also results in various abnormalities of the mesothorax. The larvae destined to develop into wingless and/or halterless flies possessed underdeveloped mesothoracic and/or metathoracic imaginal discs.  相似文献   
6.
Digestions of bovine skin proteodermatan sulphate with cathepsin C proved that the dermatan sulphate was located on Ser-4 in most of the molecules. A Ser-Gly sequence is essential for xylosylation of the serine residue and sulphated galactosaminoglycan synthesis in different proteoglycans. Variations in adjoining sequences may be significant in relation to the glycosylation process in different tissues.  相似文献   
7.
Now is the time to refocus efforts in urban research and design. A changing climate and extreme weather events are presenting unique challenges to urban systems around the world. These challenges illuminate the social barriers that accompany disruptive events such as resource inequities and injustices. In this perspective, we provide three research priorities for just and sustainable urban systems that help to address these matters. The three research priorities are: (1) social equity and justice, (2) circularity, and (3) digital twins. Conceptual context and future research directions are provided for each. For social equity and justice, the future directions are mandatory equity analysis and inclusionary practices, understanding and reconciling historical injustices, and intentional integration with diverse community stakeholders. For circularity applications, they are better metrics for integration, more robust evaluation frameworks, and dynamic modeling at multiple spatial and temporal scales. Future directions for digital twins include developing principles to reduce complexity, integrating model and system components, and reducing barriers to data access. These research priorities are core to meeting several of the United Nations Sustainable Development Goals (i.e., 1—No Poverty, 8—Decent Work and Economic Growth, 10—Reduced Inequalities, and 11—Sustainable Cities and Communities). Useful social and technical matters are discussed throughout, where we highlight the importance of prioritizing localized research efforts, provide guidance for community-engaged research and co-development practices, and explain how these priorities interact to align with the evolving field of industrial ecology.  相似文献   
8.
This study aims to establish an efficient protocol for development of seedlings of an endangered medicinally important forest tree Boswellia serrata Roxb., for mass plantation and consistent supply of salai guggul. The green mature fruits served as source of seeds. The excised green zygotic embryos were cultured on Gamborg (B5), McCown and Loyd (WPM) and Schenk and Hildebrandt (SH) media fortified with different concentration of sucrose and on Murashige and Skoog (MS) medium containing 3 % sucrose, polyvinylpyrrolidone (PVP) (0–300 mg l−l), Gibberellic acid (GA3), Indoleacetic acid (IAA), Naphthaleneacetic acid (NAA), Indole-3-Butyric acid (IBA) or 2,4-dichlorophenoxyacetic acid (2,4 D) and 6-benzylaminopurine (BA) or kinetin (Kin) individually. The highest frequency of embryo germination (96 %) and conversion into seedling was obtained on MS medium containing 3 % sucrose together with 200 mg l−l PVP; other media were either inferior or induced abnormalities in the seedlings including callus formation from the zygotic embryos. Fully developed seedlings could be successfully established in soil with about 94 % survival. The embryos from mature dry seeds did not respond for germination in any of the experiments. In conclusion, selection of zygotic embryo from green mature seeds and their in vitro germination is important for propagation of B. serrata.  相似文献   
9.
Human prenatal ethanol exposure that occurs during a period of increased synaptogenesis known as the 'brain growth spurt' has been associated with significant impairments in attention, learning and memory. Recent studies have shown that administration of ethanol to infant rats during the synaptogenesis period (first 2 weeks after birth) triggers extensive apoptotic neurodegeneration throughout many regions of the developing brain and results in cognitive dysfunctions as the animal matures. The present study was designed with an aim to investigate the effect of resveratrol, a polyphenolic phytoalexin (trans-3,5,4-trihydroxy stilbene) present in red wine on alcohol-induced cognitive deficits and neuronal apoptosis in rat pups postnatally exposed to ethanol. Pups were administered ethanol (5 g/kg, 12% v/v) by intragastric intubation on postnatal days 7, 8, and 9. Ethanol-exposed pups showed impaired memory performance in both Morris water maze elevated plus maze task recorded by using computer tracking with EthoVision software. Behavioral deficit in ethanol-exposed pups was associated with enhanced acetylcholinesterase activity, increased oxidative-nitrosative stress, cytokine (TNF-α, IL-1β and TGF-β), nuclear factor kappa beta and caspase 3 levels in both cerebral cortex and hippocampus. Chronic treatment with resveratrol (10 and 20 mg/kg) significantly attenuated all the behavioral, biochemical and molecular changes in different brain regions of ethanol administered pups. The major finding of the study is that resveratrol blocks activation of nuclear factor kappa beta pathway and apoptotic signaling and prevents cognitive deficits in rats postnatally exposed to ethanol.  相似文献   
10.
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