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   678篇
  免费   28篇
  国内免费   3篇
林业   107篇
农学   36篇
基础科学   1篇
  79篇
综合类   32篇
农作物   24篇
水产渔业   122篇
畜牧兽医   253篇
园艺   11篇
植物保护   44篇
  2023年   2篇
  2022年   15篇
  2021年   26篇
  2020年   24篇
  2019年   15篇
  2018年   25篇
  2017年   25篇
  2016年   25篇
  2015年   37篇
  2014年   31篇
  2013年   43篇
  2012年   43篇
  2011年   48篇
  2010年   29篇
  2009年   27篇
  2008年   38篇
  2007年   34篇
  2006年   31篇
  2005年   36篇
  2004年   33篇
  2003年   32篇
  2002年   29篇
  2001年   14篇
  2000年   9篇
  1999年   11篇
  1998年   4篇
  1997年   4篇
  1996年   1篇
  1995年   1篇
  1993年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1979年   1篇
  1977年   1篇
  1973年   1篇
  1970年   1篇
排序方式: 共有709条查询结果,搜索用时 31 毫秒
701.
Matricaria chamomilla L., known as "chamomile", has been used as an herbal tea or supplementary food all over the world. We investigated the effects of chamomile hot water extract and its major components on the prevention of hyperglycemia and the protection or improvement of diabetic complications in diabetes mellitus. Hot water extract, esculetin (3) and quercetin (7) have been found to show moderate inhibition of sucrase with IC50 values of 0.9 mg/mL and 72 and 71 microM, respectively. In a sucrose-loading test, the administration of esculetin (50 mg/kg body weight) fully suppressed hyperglycemia after 15 and 30 min, but the extract (500 mg/kg body weight) and quercetin (50 mg/kg body weight) were less effective. On the other hand, a long-term feed test (21 days) using a streptozotocin-induced rat diabetes model revealed that the same doses of extract and quercetin showed significant suppression of blood glucose levels. It was also found that these samples increased the liver glycogen levels. Moreover, chamomile extract showed potent inhibition against aldose reductase (ALR2), with an IC50 value of 16.9 microg/mL, and its components, umbelliferone (1), esculetin (3), luteolin (6), and quercetin (7), could significantly inhibit the accumulation of sorbitol in human erythrocytes. These results clearly suggested that daily consumption of chamomile tea with meals could contribute to the prevention of the progress of hyperglycemia and diabetic complications.  相似文献   
702.
Polycrystalline MgGeO3 post-perovskite was plastically deformed in the diamond anvil cell between 104 and 130 gigapascals confining pressure and ambient temperature. In contrast with phenomenological considerations suggesting (010) as a slip plane, lattice planes near (100) became aligned perpendicular to the compression direction, suggesting that slip on (100) or (110) dominated plastic deformation. With the assumption that silicate post-perovskite behaves similarly at lower mantle conditions, a numerical model of seismic anisotropy in the D' region implies a maximum contribution of post-perovskite to shear wave splitting of 3.7% with an oblique polarization.  相似文献   
703.
We tested the hypothesis that sapling growth following a sudden increase in solar irradiance is related to recovery from photoinhibition and the balance between rate of production of new leaves and rate of abscision of old leaves. Leaf gas exchange, chlorophyll fluorescence and relative growth rate (RGR) of stem basal area were measured following the sudden exposure of shade-grown (7% of full sunlight) saplings of four Shorea species to full sunlight. Sudden exposure to full sunlight resulted in an immediate and substantial reduction in dark-adapted quantum yield of photosystem II (Fv/Fm), followed by a gradual recovery in all species. Near light-saturated net assimilation rate (A max) and area-based leaf chlorophyll concentration ([Chl area]) also declined immediately after exposure. Eleven days after exposure, A max had recovered to pre-exposure values in all species, whereas [Chl area] had not recovered. Across species, RGR of stem basal area increased with increasing RGR of the number of leaves following exposure to full sunlight. The interspecific variations in RGR of stem basal area suggest that new leaf production is crucial for determining the potential growth of saplings following gap formation.  相似文献   
704.
Soybeans planted in early to mid-June (early) are less affected by rainfall during rainy season than those conventionally planted in early to mid-July in southwestern Japan. Also, narrow row cultivation is expected to increase soybean yield and save labor for inter-tillage and ridging. Field experiments were performed in 2014 and 2015 to test the effect of plant density (high, middle, and low) under early planting condition on growth, yield, and several agronomical traits of Sachiyutaka A1 and three new genotypes (Sakukei 155, Kanto 127 and Shikoku 15). Early planting was performed in mid- to late June, even though rainy season started in early June. Higher plant densities produced 13% greater yield than low plant density through an increase in biomass accumulation, especially at R5. Among yield components, only pods m?2 was significantly and positively correlated with yield, indicating that an increase in pods m?2 led to a greater yield with higher plant densities. The yields of Sachiyutaka A1 were relatively stable for two years, but the lodging resistance should be further improved. Shikoku 15 had greater yield potential and lodging resistance, but its resistance to damping-off disease should be improved. Sakukei 155 with medium plant density produced relatively high and stable yield with less lodging. Although the yield of Kanto 127 fluctuated between experimental years, this genotype showed higher yield potential in higher plant densities with less lodging in 2015. Thus, Sakukei 155 and Kanto 127 with high or medium density may be suitable for early planting in this region.  相似文献   
705.
The present experiment was conducted to determine the effects of Molasses-Urea Supplementation (MUS) on weight gain, ruminal fermentation and major microbial populations in sheep on a winter grazing regime in Inner Mongolia. Total 40 sheep, allowed free consumption of MUS after grazing, served as a treatment group, while 30 sheep, fed only by pasture grazing, served as a control group. Ruminal fermentation parameters, consisted of pH, Bacterial Crude Protein (BCP) and ammonia nitrogen (NH3-N) were measured. In addition, numbers of five symbiotic bacteria were investigated. The results showed as follows: the average daily weight gain, concentration of NH3-N and numbers of protozoa were significantly higher (p<0.05) in the treatment group than those in the control group. Contrastingly, no significant difference was found in BCP concentration and pH between the two groups. At the end of the experiment, the populations of Selenomonas ruminantium,Anaerovibrio lipolytica,Fibrobacter succinogenes,Ruminococcus flaveciens and Ruminococcus albus in the treatment group were significantly higher than those of the control group (p<0.05). These results demonstrated that greater weight gain could be induced during winter in Inner Mongolia by improved nutritional status through promotion of microbial populations using urea and sugar.  相似文献   
706.
Studies on stress and its impacts on animals are very important in many fields of science, including animal science, because various stresses influence animal production and animal welfare. In particular, the social stresses within animal groups have profound impact on animals, with the potential to induce abnormal behaviors and health problems. In humans, social stress induces several health problems, including psychiatric disorders. In animal stress models, social defeat models are well characterized and used in various research fields, particularly in studies concerning mental disorders. Recently, we have focused on behavior, nutrition and metabolism in rodent models of social defeat to elucidate how social stresses affect animals. In this review, recent significant progress in studies related to animal social defeat models are described. In the field of animal science, these stress models may contribute to advances in the development of functional foods and in the management of animal welfare.  相似文献   
707.
708.
This study examines the relationship between spike morphology and natural habitat for 84 accessions of four Aegilops species, belongs to section Sitopsis, Ae. bicornis, Ae. longissima, Ae. searsii, and Ae. sharonensis in genus Aegilops, section Sitopsis, wild relatives of Triticum aestivum L. These species are considered valuable genetic resources for future cultivation and breeding of domesticated wheat. The goals of the study were to: (1) document variation in spike morphology among these four species; (2) examine the relationship between spike morphology and native habitat; (3) document geographical distribution of distinct spike morphology; and (4) examine the relationship between spike morphology and heading time and value for these four species. The results reveal significant differences in spike morphology among species of section Sitopsis. The most noteworthy variation involved the absence/presence of lateral awn, such that species with lateral awn were restricted in coastal, though species without lateral awn were mainly distributed in inland. This suggests that local climate may be a determinant of variation in lateral awn, and that this trait may be subject to convergent evolution. Differences in heading time in sympatric area were also observed. The differences may enhance species divergence and could represent a lead speciation event. The results of this study will facilitate identification of populations or accessions of wild wheat with favorable traits and/or novel adaptive genes.  相似文献   
709.
The aims of the present study were to identify the differences between two mouse lines (high (H)‐ and low (L)‐oxygen consumption) in terms of mitochondrial respiratory activity when GMP (glutamate, malate, and pyruvate) and succinic acid are used as substrates and to examine the relationship between mitochondrial respiration activity and feed efficiency in both lines. The average daily feed intake, feed conversion ratio (FCR), and residual feed intake (RFI) were significantly higher in the H than the L line. The correlation between FCR and RFI was significant (r = 0.60, p < 0.05). RFI was effective as an indicator of feed efficiency. When succinic acid was used as a substrate, mitochondrial respiration states 2–4, ACR, and proton leak were significantly higher in the H than the L line. When GMP was used as a substrate, respiration states 3 and 4 in the H line were significantly higher than those in the L line, and there were significant positive correlations between FCR and RFI and mitochondrial respiration states 2–4. The results indicated that selection for high or low OC changed the basal metabolic rates estimated from liver mitochondrial respiration activity and feed efficiency.  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