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   305篇
  免费   10篇
  2023年   3篇
  2022年   9篇
  2021年   39篇
  2020年   11篇
  2019年   18篇
  2018年   22篇
  2017年   7篇
  2016年   19篇
  2015年   28篇
  2014年   21篇
  2013年   25篇
  2012年   32篇
  2011年   16篇
  2010年   12篇
  2009年   9篇
  2008年   6篇
  2007年   8篇
  2006年   5篇
  2005年   2篇
  2004年   5篇
  2003年   1篇
  2002年   3篇
  2001年   1篇
  1999年   4篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1982年   1篇
  1971年   1篇
排序方式: 共有315条查询结果,搜索用时 917 毫秒
221.
Apis mellifera jemenitica is the indigenous race of honey bees in the Arabian Peninsula and is tolerant to local drought conditions. Experiments were undertaken to determine the differences in associative learning and memory of honey bee workers living in the arid zone of Saudi Arabia, utilizing the proboscis extension response (PER). These experiments were conducted on the indigenous race (A. m. jemenitica) along with two introduced European races (A. m. carnica and A. m. ligustica). The data revealed that A. m. jemenitica is amenable to PER conditioning and may be used in conditioning experiments within the olfactory behavioral paradigm. The results also demonstrated that the three races learn and retain information with different capacities relative to each other during the experimental time periods. Native Arabian bees (A. m. jemenitica) exhibited significantly lower PER percentage during second and third conditioning trials when compared to exotic races. Apis mellifera jemenitica also exhibited reduced memory retention at 2?h and 24?h when compared to A. m. carnica and A. m. ligustica. Therefore, the native Arabian bees were relatively slow learners with reduced memory retention compared to the other two races that showed similar learning and memory retention. Three or five conditioning trials and monthly weather conditions (October and December) had no significant effects on learning and memory in A. m. jemenitica. These results emphasized a novel line of research to explore the mechanism and differences in associative learning as well as other forms of learning throughout the year among bee races in the harsh arid conditions of Saudi Arabia. This is the first study in Saudi Arabia to demonstrate inter-race differences regarding olfactory associative learning between native Arabian bees and two introduced European honey bee races.  相似文献   
222.
Spirulina platensis has been advocated as safe food for human use by several investigators. In this study its beneficial dietary effect against liver injuries caused by d-galactosamine (d-GalN) was studied ensuring safety to human health using animal model. Acute hepatotoxicity was induced in Wister rats with d-GalN followed by treatment with butylated hydroxytoluene (BHT) and with Spirulina aqueous extract at various concentrations. The effect of Spirulina at different concentrations were tried and compared with BHT treatment. The animals treated with d-GalN on subsequent treatment by supplementation with Spirulina (6, 9%) in the diets, led to significant reversal in the levels of the antioxidant enzymes through hepatocytes by suppression of negative effect. Spirulina aqueous extract at 9% resulted in a significant decrease in the levels of alkaline phosphatase and infalmatory markers TNFα, IL6 and IL1β and also decreased TBARS, while it showed an increase in oxidative stress marker such as GR, GSH, GST, SOD, GPX and CAT and total protein when compared to the levels recorded with that group treated with d-GalN. Results also indicated that Spirulina aqueous extract at 9% concentration was equally effective in protecting liver damage as it was observed with BHT. Histological studies on liver treated with d-GalN, BHT and Spirulina aqueous extract showed that S. platensis is effective as diet in providing beneficial protective effect. The results obtained in the present study very clearly indicated the positive beneficial protective effect of Spirulina, when used as diet, on the safety and protection of liver from injuries caused by toxicants.  相似文献   
223.
The presented experiments evaluated the symbiotic performance of soybean genotypes with contrasting salt stress tolerance to arbuscular mycorrhizal fungi (AMF) inoculation. In addition, the physiological stress tolerance mechanisms in plants derived from mutualistic interactions between AMF and the host plants were evaluated. Plant growth, nodulation, nitrogenase activity and levels of endogenous growth hormones, such as indole acetic acid and indole butyric acid, of salt-tolerant and salt-sensitive soybean genotypes significantly decreased at 200 mM NaCl. The inoculation of soybean with AMF improved the symbiotic performance of both soybean genotypes by improving nodule formation, leghemoglobin content, nitrogenase activity and auxin synthesis. AMF colonization also protected soybean genotypes from salt-induced membrane damage and reduced the production of hydrogen peroxide, subsequently reducing the production of TBARS and reducing lipid peroxidation. In conclusion, the results of the present investigation indicate that AMF improve the symbiotic performance of soybean genotypes regardless of their salt stress tolerance ability by mitigating the negative effect of salt stress and stimulating endogenous level of auxins that contribute to an improved root system and nutrient acquisition under salt stress.  相似文献   
224.
Gupta V  Khurana R  Tyagi AK 《Plant cell reports》2007,26(11):1919-1931
Differential screening of a stage-specific cDNA library of Indica rice has been used to identify two genes expressed in pre-pollination stage panicles, namely OSIPA and OSIPK coding for proteins similar to expansins/pollen allergens and calcium-dependent protein kinases (CDPK), respectively. Northern analysis and in situ hybridizations indicate that OSIPA expresses exclusively in pollen while OSIPK expresses in pollen as well as anther wall. Promoters of these two anther-specific genes show the presence of various cis-acting elements (GTGA and AGAAA) known to confer anther/pollen-specific gene expression. Organ/tissue-specific activity and strength of their regulatory regions have been determined in transgenic systems, i.e., tobacco and Arabidopsis. A unique temporal activity of these two promoters was observed during various developmental stages of anther/pollen. Promoter of OSIPA is active during the late stages of pollen development and remains active till the anthesis, whereas, OSIPK promoter is active to a low level in developing anther till the pollen matures. OSIPK promoter activity diminishes before anthesis. Both promoters show a potential to target expression of the gene of interest in developmental stage-specific manner and can help engineer pollen-specific traits like male-sterility in plants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Accessions: OSIPA cDNA, AF220610; OSIPK cDNA, AF312920; OSIPA partial gene and upstream promoter region, AY166659; OSIPK gene-specific and upstream sequence, AY168440.  相似文献   
225.
The genus Euphorbia attracted the attention of many researchers worldwide from natural products, bioactivity, and ecological perspective. The essential oils (EOs) of Euphorbia heterophylla are poorly studied. Therefore, the present study aimed to provide a detailed profile of the E. heterophylla EOs as well as to determine their antioxidant and allelopathic activities. The EOs from aerial parts of E. heterophylla were extracted using hydrodistillation and analyzed via GC/MS. The antioxidant activity was determined based on scavenging of the free radical, 1,1‐diphenyl‐2‐picrylhydrazyl and H2O2. Various concentrations of the EOs were tested against the noxious weed, Cenchrus echinatus. Thirty‐five compounds were identified representing 100 % of the total mass. Four classes of components were characterized, among which terpenoids were the main components (88.70 %). Monoterpenes represented the main class (69.48 %), followed by sesquiterpenes (18.63 %), and only one diterpenoid, kaur‐16‐ene, was identified. 1,8‐Cineole (32.03 %), camphor (16.54 %), β‐elemene (5.92 %), endo‐borneol (4.94 %), limonene (4.27 %), pentatriacontane (3.91 %), and α‐pinene (3.89 %) were the major compounds. The EOs composition of Egyptian E. heterophylla ecospecies was comparable to that of other reported Euphorbia species, although it showed no correlation with Nigerian E. heterophylla ecospecies. The EOs from E. heterophylla aerial parts exhibited significant antioxidant activity. Moreover, a concentration of 100 μL L?1 of the EOs reduced the germination, root, and shoot growth of C. echinatus by about 93.95 %, 84.6 %, and 57.8 %, respectively. Therefore, the EOs from E. heterophylla could be integrated into the control of this weed, as eco‐friendly biocontrol method. Further study is needed to characterize their allelopathic activity under field conditions as well as to evaluate their durability and biosafety.  相似文献   
226.
It has been suggested that pyrogenic toxins of Staphylococcus aureus are involved in the series of events leading to some cases of sudden infant death syndrome (SIDS). The objectives of the study were to screen tissues from SIDS infants for pyrogenic toxins and to compare incidence of identification of these toxins among these infants from different countries. An enzyme-linked immunosorbent assay (ELISA) and a flow cytometry method were used to screen body fluids and frozen or formalin-fixed tissues for pyrogenic toxins of S. aureus, toxic shock syndrome toxin 1 (TSST), staphylococcal enterotoxins A (SEA), B (SEB), and C1 (SEC). Toxins were identified in tissues of 33/62 (53%) SIDS infants from three different countries: Scotland (10/ 19, 56%); France (7/13, 55%); Australia (16/30, 53%). In the Australian series, toxins were identified in only 3/19 (16%) non-SIDS deaths (chi2 = 5.42, P < 0.02). The flow cytometry method was useful for toxin detection in both frozen and fixed tissues, but ELISA was suitable only for frozen tissues or those fixed for less than 12 months. Identification of pyrogenic toxins in > 50% of SIDS infants from three different countries indicated further investigation into the role the toxins play in cot deaths might result in development of additional measures to reduce further the incidence of these infant deaths.  相似文献   
227.
Recent studies have indicated that microRNA and VEGF are considered to be genetic modifiers and are associated with elevated levels of fetal haemoglobin HbF, and thus they reduce the clinical impact of sickle haemoglobin (HbS) patients. This cross-sectional study was performed on clinical confirmed subjects of SCD cases. miR-423-rs6505162 C>T and VEGF-2578 C>A genotyping was conducted by ARMS-PCR in SCD and healthy controls. A strong clinical significance was reported while comparing the association of miR-423 C>T genotypes between SCD patients and controls (p = 0.031). The microRNA-423 AA genotype was associated with an increased severity of SCD in codominant model with odd ratio (OR = 2.36, 95% CI, (1.15–4.84), p = 0.018) and similarly a significant association was observed in recessive inheritance model for microRNA-423 AA vs (CC+CA) genotypes (OR = 2.19, 95% CI, (1.32–3.62), p < 0.002). The A allele was associated with SCD severity (OR = 1.57, 95% CI, (1.13–2.19), p < 0.007). The distribution of VEGF-2578 C>A genotypes between SCD patients and healthy controls was significant (p < 0.013). Our results indicated that in the codominant model, the VEGF-2578-CA genotype was strongly associated with increased SCD severity with OR = 2.56, 95% CI, (1.36–4.82), p < 0.003. The higher expression of HbA1 (65.9%), HbA2 (4.40%), was reported in SCD patients carrying miR-423-AA genotype than miR-423 CA genotype in SCD patients carrying miR-423 CA genotype HbA1 (59.98%), HbA2 (3.74%) whereas SCD patients carrying miR-423 CA genotype has higher expression of HbF (0.98%) and HbS (38.1%) than in the patients carrying AA genotype HbF (0.60%), HbS (36.1%). ARMS-PCR has been proven to be rapid, inexpensive and is highly applicable to gene mutation screening in laboratories and clinical practices. This research highlights the significance of elucidating genetic determinants that play roles in the amelioration of the HbF levels that is used as an indicator of severity of clinical complications of the monogenic disease. Further well-designed studies with larger sample sizes are necessary to confirm our findings.  相似文献   
228.
The iron repressible nature of Haemophilus influenzae transferrin binding proteins suggests a regulatory role for elemental iron in their expression. The existence of a Haemophilus ferric uptake repressor (Fur) binding motif identified in the promoter region of both tbpA and tbpB further supports this hypothesis. However, a recent study using brain heart infusion growth medium suggested that transferrin binding protein synthesis in H. influenzae was haem- rather than iron-regulated. The present study re-investigates this observation and using a chemically defined medium, we demonstrate that elemental iron haem or protoporphyrin IX can each regulate Haemophilus influenzae transferrin, haemopexin and haemoglobin receptor expression.  相似文献   
229.
Technology has been revolutionizing health care. The current article is split into three parts, the first portion discusses the usage of technological devices in stuttering treatment, the scan of technical devices may be used specifically in treatment or can be used to offer guidance and thereby improve the pace of expression. They will even help to create physiological improvements. The second section of the article refers to telehealth as a means of providing services to people with stuttering. This approach has become a simple benevolence of technology and has managed to enter the unreached. Teletherapy can also be utilized for individuals who are robbed of treatment owing to isolation from financial restrictions. The third part of the analysis is regarding the apps. Apps may be used as an adjunct to speech language training or can be used during the repair process.  相似文献   
230.
This study surveyed 205 wetland sites in the Southwestern Saudi Arabia. We found seven species of amphibians (Anura), which belong to four families: Bufonidae; which includes four species, Sclerophrys tihamica; S. Arabica, Duttaphrynus dhufarensis, and Bufotes viridis; Hylidae, represented by only one species, the tree frog Hyla savignyi; Ranidae, which represented by one species, Pelophylax ridibundus and finally the Dicroglossidae, represented by one species, Euphlyctis ehrenbergii. The reasonable amount of rain received in southwest Arabia, and habitat diversity contribute to the relative abundance of amphibians in the region. Five types of wetland habitats were found in the study area. Valley streams, irrigated farms, seasonal ponds, dam reservoir and lagoons of treated sewage water. The current study revealed the wide spread of amphibians in southwestern Saudi Arabia than what had been reported earlier and confirmed the presence of the Bufotes viridis at three new sites in Asir Heights. It also showed the wide spread of S. arabica in all types of habitats in the southwestern region of Saudi Arabia. Habitat degradation was evident in the region, which might lead to species loss.  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