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   622篇
  免费   25篇
  国内免费   1篇
  648篇
  2023年   8篇
  2022年   17篇
  2021年   25篇
  2020年   14篇
  2019年   9篇
  2018年   33篇
  2017年   14篇
  2016年   22篇
  2015年   32篇
  2014年   42篇
  2013年   54篇
  2012年   48篇
  2011年   45篇
  2010年   27篇
  2009年   23篇
  2008年   30篇
  2007年   32篇
  2006年   27篇
  2005年   20篇
  2004年   13篇
  2003年   12篇
  2002年   9篇
  2001年   12篇
  2000年   12篇
  1999年   4篇
  1998年   6篇
  1997年   5篇
  1996年   4篇
  1994年   5篇
  1991年   4篇
  1990年   3篇
  1986年   1篇
  1985年   3篇
  1984年   6篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1975年   4篇
  1974年   1篇
  1973年   1篇
  1972年   3篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1955年   1篇
排序方式: 共有648条查询结果,搜索用时 0 毫秒
21.
Chitinase, capable of degrading the cell walls of invading phytopathogenic fungi, plays an important role in plant defense response, particularly when this enzyme is overexpressed through genetic engineering. In the present study, Brassica plant (Brassica juncea L.) was transformed with chitinase gene tagged with an overexpressing promoter 35 S CaMV. The putative transgenics were assayed for their inhibitory activity against Alternaria brassicae, the inducer of Alternaria leaf spot of Brassica both in vitro and under polyhouse conditions. In in vitro fungal growth inhibition assays, chitinase inhibited the fungal colony size by 12-56% over the non-trangenic control. The bioassay under artificial epiphytotic conditions revealed the delay in the onset of disease as well as reduced lesion number and size in 35S-chitinase Brassica as compared to the untransformed control plants.  相似文献   
22.
Somatostatin suppresses ghrelin secretion from the rat stomach   总被引:6,自引:0,他引:6  
Ghrelin is an acylated peptide that stimulates food intake and the secretion of growth hormone. While ghrelin is predominantly synthesized in a subset of endocrine cells in the oxyntic gland of the human and rat stomach, the mechanism regulating ghrelin secretion remains unknown. Somatostatin, a peptide produced in the gastric oxyntic mucosa, is known to suppress secretion of several gastrointestinal peptides in a paracrine fashion. By double immunohistochemistry, we demonstrated that somatostatin-immunoreactive cells contact ghrelin-immunoreactive cells. A single intravenous injection of somatostatin reduced the systemic plasma concentration of ghrelin in rats. Continuous infusion of somatostatin into the gastric artery of the vascularly perfused rat stomach suppressed ghrelin secretion in both dose- and time-dependent manner. These findings indicate that ghrelin secretion from the stomach is regulated by gastric somatostatin.  相似文献   
23.
Glucocorticoids (GC) are usually considered to be immunosuppressive and anti-inflammatory. However, recent studies in mammals have demonstrated the diverse effects of GC on non-specific host-defense mechanism, depending on dose or duration of treatment. Hence, in the present study in vitro dose and time-related effects of glucocorticoid, i.e. hydrocortisone (HC) on phagocytosis and nitrite production by LPS-induced splenic macrophages in wall lizard Hemidactylus flaviviridis has been investigated. Hydrocortisone suppressed percentage phagocytosis, phagocytic index and nitrite production by splenic macrophages even at the lowest concentration (10(-13) M) for a short-term exposure (4 h). Hydrocortisone-induced suppression enhanced with the increase of concentration or duration of exposure time. The suppressive effect of hydrocortisone on phagocytic and cytotoxic activities of splenic macrophages was further corroborated since the pre-exposure of macrophages to glucocorticoid-receptor blocker (RU 486) considerably reduced the hydrocortisone-induced suppression of phagocytosis and nitrite production. The present study suggests that GC instead of diverse effects, has dose- and time-dependent immunosuppressive effect on non-specific host-defense immune responses in wall lizard H. flaviviridis.  相似文献   
24.
The hypothalamus is the most important region in the control of food intake and body weight. The ventromedial "satiety center" and lateral hypothalamic "feeding center" have been implicated in the regulation of feeding and energy homeostasis by various studies of brain lesions. The discovery of orexin peptides, whose neurons are localized in the lateral hypothalamus and adjacent areas, has given us new insight into the regulation of feeding. Dense fiber projections are found throughout the brain, especially in the raphe nucleus, locus coeruleus, paraventricular thalamic nucleus, arcuate nucleus, and central gray. Orexins mainly stimulate food intake, but by the virtue of wide immunoreactive projections throughout the brain and spinal cord, orexins interact with various neuronal pathways to potentiate divergent functions. In this review, we summarize recent progress in the physiological, neuroanatomical, and molecular studies of the novel neuropeptide orexins (hypocretins).  相似文献   
25.
26.

Background  

Rho subfamily GTPases are implicated in a large number of actin-related processes. They shuttle from an inactive GDP-bound form to an active GTP-bound form. This reaction is catalysed by Guanine nucleotide exchange factor (GEFs). GTPase activating proteins (GAPs) help the GTPase return to the inactive GDP-bound form. The social amoeba Dictyostelium discoideum lacks a Rho or Cdc42 ortholog but has several Rac related GTPases. Compared to our understanding of the downstream effects of Racs our understanding of upstream mechanisms that activate Rac GTPases is relatively poor.  相似文献   
27.
This study was undertaken to determine age and sex variations in the prevalence of underweight and stunting, and to assess the impact of some socio-economic variables on undernutrition among 6–16 year old school children of Bengalee ethnicity in Chapra, West Bengal, India. The subjects were selected randomly from various schools and madrassas of the Chapra Block. A total of 725 children (342 boys and 383 girls) aged 6–16 years were measured and data on their socio-economic status were collected. Age and sex combined rates of underweight and stunting were 44.40% and 37.20%, respectively. Weight-for-age Z-score (WAZ) showed significant association with per-capita income (PCI) among boys (F = 5.45) and girls (F = 8.14). Height-for-age Z-score (HAZ) has also shown the association with per-capita income among boys (F = 4.43) and girls (F = 9.69). The WAZ was significantly associated with fathers’ educational status (FOS) (t = ?2.95) and the number of living rooms (NLR) (t = ?2.91) among girls. The HAZ showed significant association with number of siblings (NS) among girls (F = 4.25). Linear regression analyses revealed that NLR (t = 2.04) and NS (t = 1.95) had a significant impact on HAZ among boys. Among girls, PCI (t = 3.38), FOS (t = 2.87) and NLR (t = 2.81) had a significant impact on WAZ and also PCI (t = 3.28) and FOS (t = 2.90) had a significant impact on HAZ. NLR had significant associations with underweight (χ2 = 3.59) and stunting (χ2 = 4.20) among boys. Among girls, PCI had significant associations with underweight (χ2 = 11.15) and stunting (χ2 = 11.64). FOS also showed significant associations with underweight (χ2 = 8.10) as well as stunting (χ2 = 8.28) among girls. NLR showed a significant association with underweight (χ2 = 7.75). Logistics regression analyses revealed that FOS (Wald = 8.00) and NLR (Wald = 4.09) were significant predictors of stunting among boys. Among girls, PCI was a significant predictor of underweight (Wald = 10.95) as well as stunting (Wald = 10.45). FOS, NLR and NS were also significant predictors of stunting (Wald = 8.16), underweight (Wald = 7.68) and stunting (Wald = 6.97) respectively. The present study revealed that the nutritional status of the children was unsatisfactory and it is of paramount importance not only to increase the amount of food supplementation given but also to promote gender equality.  相似文献   
28.
Extensively drug-resistant tuberculosis: current challenges and threats   总被引:1,自引:0,他引:1  
Extensively drug-resistant tuberculosis (XDR-TB) is defined as tuberculosis caused by a Mycobacterium tuberculosis strain that is resistant to at least rifampicin and isoniazid among the first-line antitubercular drugs (multidrug-resistant tuberculosis; MDR-TB) in addition to resistance to any fluroquinolones and at least one of three injectable second-line drugs, namely amikacin, kanamycin and/or capreomycin. Recent studies have described XDR-TB strains from all continents. Worldwide prevalence of XDR-TB is estimated to be c. 6.6% in all the studied countries among multidrug-resistant M. tuberculosis strains. The emergence of XDR-TB strains is a reflection of poor tuberculosis management, and controlling its emergence constitutes an urgent global health reality and a challenge to tuberculosis control activities in all parts of the world, especially in developing countries and those lacking resources and as well as in countries with increasing prevalence of HIV/AIDS.  相似文献   
29.
Hong  Sung Hyun  Singh  Sudhir  Tripathi  Bhumi Nath  Mondal  Suvendu  Lee  Sangmin  Jung  Hyun Suk  Cho  Chuloh  Kaur  Shubhpreet  Kim  Jin-Hong  Lee  Sungbeom  Bai  Hyoung-Woo  Bae  Hyeun-Jong  Lee  Sang Yeol  Lee  Seung Sik  Chung  Byung Yeoup 《Protoplasma》2020,257(3):807-817
Protoplasma - Alkyl hydroperoxide reductase subunit F (AhpF) is a well-known flavoprotein that transfers electrons from pyridine nucleotides to the peroxidase protein AhpC via redox-active...  相似文献   
30.
In this paper, the magnetohydrodynamic (MHD) axisymmetric stagnation-point flow of an unsteady and electrically conducting incompressible viscous fluid in with temperature dependent thermal conductivity, thermal radiation and Navier slip is investigated. The flow is due to a shrinking surface that is shrunk axisymmetrically in its own plane with a linear velocity. The magnetic field is imposed normally to the sheet. The model equations that describe this fluid flow are solved by using the spectral relaxation method. Here, heat transfer processes are discussed for two different types of wall heating; (a) a prescribed surface temperature and (b) a prescribed surface heat flux. We discuss and evaluate how the various parameters affect the fluid flow, heat transfer and the temperature field with the aid of different graphical presentations and tabulated results.  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