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   1390篇
  免费   134篇
  国内免费   49篇
  2024年   6篇
  2023年   54篇
  2022年   45篇
  2021年   111篇
  2020年   84篇
  2019年   135篇
  2018年   83篇
  2017年   73篇
  2016年   65篇
  2015年   68篇
  2014年   57篇
  2013年   178篇
  2012年   53篇
  2011年   47篇
  2010年   25篇
  2009年   44篇
  2008年   49篇
  2007年   51篇
  2006年   43篇
  2005年   40篇
  2004年   18篇
  2003年   29篇
  2002年   17篇
  2001年   11篇
  2000年   12篇
  1999年   10篇
  1998年   14篇
  1997年   10篇
  1996年   14篇
  1995年   15篇
  1994年   14篇
  1993年   9篇
  1992年   13篇
  1991年   10篇
  1990年   5篇
  1989年   11篇
  1988年   6篇
  1987年   6篇
  1986年   3篇
  1985年   5篇
  1984年   5篇
  1983年   5篇
  1982年   3篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1977年   1篇
  1976年   2篇
  1974年   2篇
排序方式: 共有1573条查询结果,搜索用时 250 毫秒
1.
Nutrition plays a key role in many aspects of health and dietary imbalances are major determinants of chronic diseases including cardiovascular disease, obesity, diabetes and cancer. Adequate nutrition is particularly essential during critical periods in early life (both pre- and postnatal). In this regard, there is extensive epidemiologic and experimental data showing that early sub-optimal nutrition can have health consequences several decades later.  相似文献   
2.
Onosma echioides Linn (Boraginaceae) is the most frequently used curative herb widely used for kidney obstruction, sciatic pain, and gout. The present study was designed to investigate the therapeutic effects of n-hexane bark extract of O. echioides (OE) L. root in vivo against Streptozotocin-induced diabetic neuropathy in SD rats. For in vivo activity, the experiment was categorized into five different groups (n = 5). Group-I was considered as nondiabetic/normal control (NC) treated with 0.5% carboxymethyl cellulose (CMC), Group II as diabetic control, Group-III, IV, and V served as diabetic treated with OE 50, OE 100, and pregabalin at a dose of 50, 100, and 10 mg/kg body weight, orally, respectively. Body weight, blood glucose, oral glucose tolerance test, behavioral studies (motor coordination test, thermal hyperalgesia, cold allodynia, locomotor activity, oxidative biomarkers (thio barbituric acid reactive substances [TBARS], superoxide dismutase [SOD], glutathione [GSH], and catalase), and histopathology of the sciatic nerve were performed. Treatment with OE showed a dose-dependent increase in neuroprotective activity by improving the myelination and decreasing the axonal swelling of nerve fibers. The verdicts of behavioral activities showed a remarkable effect on animals after the treatment of extract and standard drug pregabalin. In conclusion, our findings supported the traditional application of OE and explored its importance in the management of diabetic neuropathy. Additional clinical experiments may provide novel therapeutic drugs for diabetes and its complications.  相似文献   
3.
Nitrogen is the major growth-limiting nutrient for marine algae. One potential source of nitrogen for marine algae is ammonium released by invertebrates. Many mid-intertidal reefs in northeastern New Zealand are dominated by a close association between the honeycomb barnacle Chamaesipho columna and an encusting brown alga Pseudolithoderma sp. Growth of Pseudolithoderma was enhanced in the presence of live C. columna, which released ammonium at a greater rate than the maximum rate of ammonium uptake by Pseudolithoderma. Algal tissue on barnacle tests had a lower C:N ratio than tissue located more than 2 cm from the nearest barnacle, suggesting the barnacle is an important source of nitrogen for the alga. The role of nutrient exchange in determining ecological patterns of species in marine communities is discussed.  相似文献   
4.
This study is based on a sample of 9,134 children ranging in age from 2 to 17 years from which the excessively lean and fat children by skinfold thickness were excluded. This sample was derived from the combined data sets of the first and second National Health and Nutrition Examination Surveys (NHANES I and II) of 1971-1974 and 1976-1980. Means and percentiles of upper arm muscle area were calculated for 3 cm increments in stature from 84 to 184 cm for boys and from 84 to 176 cm for girls. Based on means, Z-score units, and percentile ranges of upper arm muscle area by stature, five operational categories of nutritional status have been established. It is recommended that these standards and this classification system be used to supplement current standards of weight for age and weight for height in order to obtain a more complete assessment of body composition and nutritional status.  相似文献   
5.
E. D. Fajer 《Oecologia》1989,81(4):514-520
Summary Little is known about the effects of enriched CO2 environments, which are anticipated to exist in the next century, on natural plant-insect herbivore interactions. To begin to understand such effects on insect growth and survival, I reared both early and penultimate instar larvae of the buckeye, Junonia coenia (Lepidoptera: Nymphalidae), on leaves from one of their major hostplants, plantain, Plantago lanceolata (Plantaginaceae), grown in either ambient (350 PPM) or high (700 PPM) CO2 atmospheres. Despite consuming more foliage, early instar larvae experienced reduced growth on high CO2-grown compared to ambient CO2-grown leaves. However, survivorship of early instar larvae was unaffected by the CO2 treatment. Larval weight gain was positively correlated with the nitrogen concentration of the plant material and consumption was negatively correlated with foliar nitrogen concentration, whereas neither larval weight gain nor consumption were significantly correlated with foliar water or allelochemical concentrations. In contrast, penultimate instar larvae had similar growth rates on ambient and high CO2-grown leaves. Significantly higher consumption rates on high CO2-grown plants enabled penultimate instar larvae to obtain similar amounts of nitrogen in both treatments. These larvae grew at similar rates on foliage from the two CO2 treatments, despite a reduced efficiency of conversion of ingested food (ECI) on the low nitrogen, high CO2-grown plants. However, nitrogen utilization efficiencies (NUE) were unaffected by CO2 treatment. Again, for late instar larvae, consumption rates were negatively correlated with foliar nitrogen concentrations, and ECI was also very highly correlated with leaf nitrogen; foliar water or allelochemical concentrations did not affect either of these parameters. Differences in growth responses of early and late instar larvae to lower nitrogen, high-CO2 grown foliage may be due to the inability of early instar larvae to efficiently process the increased flow of food through the gut caused by additional consumption of high CO2 foliage.  相似文献   
6.
A few reports have suggested the possibility that feeding conditions might affect the sexual maturation of free-ranging Japanese monkeys in provisionized troops. In the present study, the sexual maturation of male monkeys at Takasakiyama in 1984, nine years after the start of restriction of artificial feeding, was examined externally and histologically and the results were compared with data obtained in 1971, when artificial foods were abundantly given. Spermatogenesis was not observed in any of the males under 4.5 years old in the present study, whereas it was noted in some premature 3.5-year-old males and in all males over 4.5 years old in the 1971 study. The age of sexual maturation thus rose by one or more years over the 13-year period from 1971 to 1984. The lag in sexual maturation of the males at Takasakiyama in 1984 could have been induced by the restriction of artificial feeding.  相似文献   
7.
陆源  杨岚 《动物学研究》1992,13(1):67-71
本文报道笼养和野生白腹锦鸡机体营养成分及其差异。分析表明,笼养的比野生种营养成分含量高的有:腿肌蛋白质高11%,胸肌、腿肌、全血的氨基酸分别高2.64%,1.39%和4.68%,胸肌、腿肌和肝脏的碳水化合物分别高0.076%、0.092%和3.962%,胸肌和腿肌的维生素A分别高188.63和84.09 I.U.,胸肌和腿肌的维生素D分别高47.2和12.8 I.U.。但是胸肌蛋白质含量笼养的比野生的低26%。  相似文献   
8.
连续两年对鱼腥藻的六个品系进行了大量培养比较研究,在长江中下游气候条件下,HB1042和HB1105具有稳定的生产性能,5月下旬至九月中旬123d内,平均有效生长分别为114和100d;其次是HB1058,HB686和HB1017,平均有效生长天分别为73,58和71d;HB13适应性较差。生物量生产率在5月下旬、6月中旬至9月中旬较高,除HB13外,平均都在10g干重/m~2/d以上或接近10g/m~2/d。在不同的季节它们表现出了各自的最高生物量生产率。据此,提出了逐月逐旬采取藻种搭配生产,以获得最高生物量生产率的配合关系。营养成分分析表明它们的蛋白质含量在40%左右;氨基酸组成合理,除某些种类的含硫氨基酸略低外,都符合FAO/WHO的标准。  相似文献   
9.
肝细胞癌(hepatocellular carcinoma,HCC)治疗困难、预后很差,是肿瘤相关死亡中的第4大癌症,严重危害人类生命健康,但其具体发病机制却仍未完全阐明。因此,探索能调控肝细胞癌发生发展,作为肝细胞癌的诊断标志物或能预测患者预后的关键分子仍十分必要。环状RNA是前体mRNA通过反向剪接产生的由3′, 5′ 磷酸二酯键首尾连接形成的共价闭合环状结构,主要有外显子circRNA(exonic circRNA,ecircRNA)、环状内含子RNA(circular intronic RNA,ciRNA)及外显子 内含子circRNA(exon-intron circRNA,EIciRNA)三大类。由于环状RNA具有普遍性、高度保守性和稳定性,其可以参与多种癌症的发生发展过程,并且可作为肿瘤的早期诊断标志物及预后因子,因此,这是一类新型且非常有潜力应用于临床诊治各阶段的分子。近年来,有大量关于环状RNA与肝细胞癌的研究。这些研究表明,环状RNA在肝细胞癌发生发展进程中发挥的作用十分重要,并且其机制多样。因此,本文主要关注环状RNA在肝细胞癌中的最新进展,总结不同环状RNA分子对于肝细胞癌细胞恶性表型、肿瘤干细胞及肿瘤微环境中免疫细胞的作用,以及其在肝细胞癌临床转移、分期、诊断、预后等各阶段中发挥的功能及其具体作用机制。此外,本文还提出了目前研究中存在的一些问题和不足,以期为未来的研究提供一些新的思路及策略。  相似文献   
10.
Two lines of the red and pale yellow cell suspension cultures, prepared fromPrunus x yedoensis Matsum. callus induced by Murashige and Skoog's (1962) basal medium supplemented with 2, 4-dichlorophenoxyacetic acid (2, 4-D, 1.0 mg/l), kinetin (0.1 mg/l) and sucrose (30 g/l), were maintained on Schenk and Hildebrandt medium as modified by Mitchell and Gildow (1975). The red cell suspension culture produced cyanidin 3-monoglucoside, 5, 4′-dihydroxy-7-methoxyisoflavone 4′-glucoside (prunetrin), isoquercitrin, catechin, epicatechin, and procyanidin B-1, B-2, B-3 and B-4, while the pale yellow cells produced only a small amount of catechin and epicatechin as main flavonoids. These flavonoid compounds found in the red cell culture were present also in maturePrunus leaves. Maximum growth and maximum amount of total phenol and proanthocyanidin (procyanidins) were obtained with 0.3 mg/l of both 2,4-D and kinetin. Maximum concentration of anthocyanin was also obtained with 0.3 mg/l 2, 4-D regardless of kinetin concentration. Accumulation of proanthocyanidin was markedly stimulated by low concentrations of phosphate, which reduced growth by about half, and also by high concentrations of inorganic nitrogen. Production of both anthocyanin and proanthocyanidin was reduced by lowered nitrogen levels. Cell growth and production of all phenolics were inhibited when ammonium ion replaced nitrate in the medium.  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