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   599篇
  免费   42篇
林业   98篇
农学   25篇
基础科学   4篇
  85篇
综合类   19篇
农作物   27篇
水产渔业   68篇
畜牧兽医   267篇
园艺   6篇
植物保护   42篇
  2023年   6篇
  2022年   6篇
  2021年   18篇
  2020年   36篇
  2019年   31篇
  2018年   29篇
  2017年   21篇
  2016年   31篇
  2015年   17篇
  2014年   25篇
  2013年   44篇
  2012年   41篇
  2011年   30篇
  2010年   21篇
  2009年   16篇
  2008年   29篇
  2007年   36篇
  2006年   31篇
  2005年   24篇
  2004年   17篇
  2003年   12篇
  2002年   14篇
  2001年   14篇
  2000年   13篇
  1999年   6篇
  1998年   1篇
  1997年   11篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   11篇
  1991年   8篇
  1990年   5篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1986年   4篇
  1985年   4篇
  1983年   1篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   3篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1969年   1篇
  1968年   2篇
排序方式: 共有641条查询结果,搜索用时 15 毫秒
1.
Plant Foods for Human Nutrition - Argan oil is prepared by cold pressing argan kernels collected from fully ripe fruit. Argan oil market price is particularly elevated. Consequently, efficient...  相似文献   
2.
Use of nutrient efficient crop species or cultivars within species in combination with improved crop production practices offer the best option for meeting the future food requirements of growing world populations. Efficiency improvement has a key role for nutrient use and it improves both productivity of yield and minimizes risks of losses that potentially harm the environment. To improve nutrient use efficiency (NUE), one strategy is to select cultivars of crops with high NUE. Both nitrogen (N) and phosphorus (P) are among essential macronutrients commonly applied to agricultural crops to optimize yields. Evaluation of potato cultivars with high N and P efficiency is essential for sustainable production of the crop. In Ethiopia, however, little research has been done to elucidate better NUE of potato crop until recently. This study was, thus, designed to evaluate selected potato cultivars (Belete, Gudene, Jalene, Marachere and one local check) for NP use efficiency under low levels of the nutrients in Wolaita Sodo University, Ethiopia during 2014 and 2015. Factorial combination of 3 levels of each N (0, 55.5 and 111 kg N ha?1 ) and P (0, 19.5 and 39 kg P ha?1 ) were assigned to the main plots and the 5 cultivars to subplots of split-plot design in three replications. Efficiency indices such as agronomic efficiency, physiological efficiency and recovery efficiency were computed for combined NP nutrients. Results showed that agronomic nitrogen use efficiency, apparent phosphorus use efficiency and phosphorus use efficiencies were significantly influenced by the interaction effect of rates of NP nutrition and variety. Application of NP more than 55.5:19.5 kg ha?1 will not beneficial due to their less or equal use and recovery efficiencies to 55.5:19.5 kg NP ha?1. Belete was the most NP efficient variety followed by Jalene and Gudene in all efficiency indices. Therefore, Belete, Jalene and Gudene return better for NP at 55.5:19.5 kg ha?1 for economical use of fertilizes while obtaining satisfactory yield. It can be concluded that yield response variation of the varieties was related to their differences in NP uptake and use efficiencies; and the improved potato varieties were superior to local check in using NP nutrients efficiently.  相似文献   
3.
Polypyrrole (PPy) film was prepared via in-situ chemical polymerization of pyrrole monomer on the surface of red-clay-brick (RCB) substrate. The deposited PPy film was characterized and used as an adsorbent for removal of benzene polycarboxylic acids from aqueous solutions. The effects of solution pH, contact time, initial concentration, and temperature on the adsorption process were systematically investigated to find the optimum operating conditions. Adsorption kinetic data were best fitted by pseudo-second order kinetic model. The adsorption equilibrium data were most represented by the Freundlich isotherm model. The maximum adsorption amounts of Trimellitic, Hemimellitic, and Pyromellitic acids were 189.27, 177.26, and 203.31 mg/g, respectively. The thermodynamic studies indicate that the adsorption was an endothermic and spontaneous process. Also, the PPy-RCB film was successfully regenerated using sodium hydroxide solution. The regenerated PPy-RCB can be reused for more than four successive cycles with a low reduction in adsorption efficiency.  相似文献   
4.
5.
6.

Effects of exposing quail eggs to high temperature on the heat tolerance ability and productivity of birds were investigated. Four groups of 600 fertile eggs were randomly selected; the first group was incubated under 37.5 °C and the hatched chicks were reared under a gradual decrease in temperature from 35 to 24 °C (Control). The second group was exposed to 39.1 °C for 2 h/day during 4–14 days of embryogenesis and the hatched chicks were reared under a gradual decrease in temperature from 35 to 24 °C. The third group was incubated under 37.5 °C and the hatched chicks were exposed to 39?±?1 °C for 2 h/day during 4–14 days of age. The fourth group was exposed to 39?±?1 °C for 2 h during 4–14 days of embryogenesis and the hatched chicks were exposed to 39?±?1 °C for 2 h/day during 4–14 days of age. The temperature applied changed (P?<?0.01) embryo weight and incubation period. Birds exposed to high temperature during brooding had superior growth performance, dressed carcass, body temperature and health traits. Birds subjected to 39?±?1 °C during brooding exhibited decreased feed consumption and body weight gain. Finally, this work suggests that thermal acclimation during embryogenesis might offer a practical method for easing heat stress.

  相似文献   
7.
A total of 17 microsatellite deoxyribonucleic acid loci used routinely for horse parentage control were used to evaluate genetic diversity among normal Arabian horses and severe combined immunodeficiency (SCID) carrier Arabian horses (ArS) and normal Arab-Barb horses and SCID carrier Arab-Barb horses (ArbeS). On the basis of the genotype of 186 horses, mean allelic diversity was estimated as 6.82, 5.53, and 6.7059 in normal Arabian horses, ArS, and for both groups of Arab-Barb horses, respectively. Five specific alleles were observed in ArS and ArbeS, with one common with ArS at HMS6, whereas five alleles common between ArS and ArbeS had a high frequency. Expected and observed heterozygosity showed great heterogeneity in the population studied and were similar or higher when compared with other studies on Arabian horses. Coefficient of gene differentiation Gst of Nei associated with Nei’s genetic distance and multivariate correspondence analysis indicated a possible differentiation between the studied populations when analyzed separately according to breed. Probability of assignment of a horse to a specific group was assessed using a full and partial Bayesian approach. In all, 80.6% of Arab horses and 78.2% of Arab-Barb horses were assigned properly with a partial Bayesian test, which provided better results than the full one. These findings will be useful for identification of SCID carrier horses by using the microsatellite deoxyribonucleic acid loci used routinely for horse parentage control in our laboratory.  相似文献   
8.
The effects of the aqueous extract of Cistus ladaniferus leaves and stems were studied on the rodent isolated jejunum. The extract produced a reversible concentration dose-dependent (0.1-3 mg/ml) inhibition of the spontaneous motility of the rabbit jejunum. The inhibitory effects of the extract were not affected by pretreatment with the inhibitors of the alpha and beta adrenergic receptors yohimbine, prazosin or propranolol. The extract also inhibited K(+)-induced contractions in rabbit and rat jejunum at a similar concentration range. This result suggests that the antispasmodic action of the extract is mediated through calcium channel blockade. The results confirm the traditional use of C. ladaniferus in treating intestinal ache.  相似文献   
9.
Detailed studies have been undertaken to define pruning regimes for Eucalyptus nitens, but little is known of E. globulus responses to pruning although this is a more commonly planted species. This paper describes experiments that aimed to identify (a) levels of pruning that reduce E. globulus growth, (b) physiological processes contributing to those growth responses, (c) the incidence of decay and factors influencing decay incidence following pruning of E. globulus, and (d) comparative responses of E. nitens and E. globulus to live branch pruning. Results of a field experiment indicated that removal of between 30 and 50% of the crown length was appropriate for E. globulus plantations verging on canopy closure. The significant reduction in height growth associated with removal of 50 or 70% of crown length suggested pruning should remain below 50% of crown length if reduced stem growth of pruned trees was to be avoided. Stem volume was only significantly reduced over the period of the experiment by 70% pruning, but it was estimated that standing volume following removal of 50% of crown length would be reduced by 82 m3 ha−1 over a 20-year rotation if there were no other silvicultural interventions. The growth responses observed were probably related to large reductions in leaf area following 50 or 70% removal of crown length. Trees responded to pruning by changing patterns of biomass partitioning to favour stem growth at the expense of branch growth. A glasshouse study determined that light-saturated net CO2 uptake (Amax) increased following pruning. E. nitens seedlings had both a higher baseline Amax and higher Amax following pruning than did E. globulus, which could partially explain the greater effect of pruning on E. globulus growth than has been observed for E. nitens in other studies. This result, as well as apparently different patterns of foliage distribution through the crowns of E. globulus and E. nitens, suggested that models of pruning responses need to be parameterised for both species. In addition, a more conservative pruning regime may be appropriate for E. globulus than E. nitens. Pruning increased the frequency of branch traces with decay infection, and there was a trend towards increasing decay outbreaks with increasing pruning severity. Decay outbreaks were more likely to occur following pruning of high angle or larger diameter branches.  相似文献   
10.
Infection of heartwood by decay fungi (heartrot) is a concern for growers of Acacia mangium for solid‐wood products as the incidence can be high in some regions of Indonesia. Variation of heartrot incidence for different provenances of A. mangium was determined using two field trials in Sumatra, Indonesia. In a Riau Province trial of 21 provenances, the effect of provenance was statistically significant for natural heartrot incidence, which ranged from 1.6% to 27.2%. In a smaller trial using artificial inoculation in South Sumatra, heartwood infection incidence ranged from 39.4% to 70.8% across six provenances and both wound type and provenance were statistically significant factors. There was also significant variation in sapwood infection length related to provenance. Wood extractives (yield, total phenols, protein‐precipitable tannin and 2,3‐trans‐3,4′,7,8‐tetrahydroxyflavanone) were quantified from a subsample of trees for each trial. However, no significant differences in extractive concentration were detectable according to provenance and evidence for a relationship between heartwood extractives and heartrot incidence was generally poor. While further studies need to be completed to establish the basis for heartrot incidence, results from these trials allow for recommendations on provenance selection to reduce heartrot incidence and provide information for further genetic selection programmes.  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