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   742篇
  免费   29篇
  国内免费   1篇
林业   56篇
农学   58篇
基础科学   10篇
  152篇
综合类   26篇
农作物   67篇
水产渔业   48篇
畜牧兽医   275篇
园艺   12篇
植物保护   68篇
  2023年   8篇
  2022年   23篇
  2021年   31篇
  2020年   31篇
  2019年   25篇
  2018年   46篇
  2017年   43篇
  2016年   31篇
  2015年   20篇
  2014年   25篇
  2013年   68篇
  2012年   36篇
  2011年   53篇
  2010年   21篇
  2009年   18篇
  2008年   25篇
  2007年   26篇
  2006年   14篇
  2005年   10篇
  2004年   17篇
  2003年   18篇
  2002年   9篇
  2001年   14篇
  2000年   12篇
  1999年   10篇
  1998年   6篇
  1996年   3篇
  1995年   3篇
  1994年   3篇
  1993年   2篇
  1992年   4篇
  1991年   5篇
  1990年   15篇
  1989年   8篇
  1988年   16篇
  1987年   8篇
  1986年   10篇
  1985年   6篇
  1984年   10篇
  1983年   6篇
  1982年   3篇
  1981年   2篇
  1980年   5篇
  1979年   3篇
  1978年   2篇
  1976年   3篇
  1974年   2篇
  1972年   4篇
  1967年   2篇
  1966年   4篇
排序方式: 共有772条查询结果,搜索用时 15 毫秒
631.
This study aimed at investigating the effects of weaning kids abruptly at an average of 55 ± 13 days of age on intake, behavioral and serum parameters and, lasted for a total of six weeks; two weeks pre-weaning and four weeks post-weaning. Sixteen single kids with equal gender were used. Kids were only allowed to stay with their mothers for suckling (45 min/period) both in the morning and in the evening period during pre-weaning. Grower concentrate and hay were offered ad libitum . The duration of the study was divided into three periods for the sampling of behavioral and serum parameters; (i) pre-weaning period lasting for two weeks (P-BW) (ii) early post-weaning period lasting for one week (P-AW1) and (iii) late post-weaning period lasting for three weeks (P-AW2). Daily weight gain of kids gradually decreased as the observation period progressed ( P  = 0.001). However concentrate feed intake increased from 0.154 kg/day in P-BW to 0.479 kg/day in P-AW1 and 0.499 kg/day in P-AW2. Water intake, rumination and standing behaviors decreased in P-AW2 ( P  < 0.001), whereas activity towards concentrate feed (CF) ( P  < 0.001) and roughage ( P  = 0.012) increased as compared to P-BW and P-AW1. Abnormal oral activity was not affected by the periods ( P  = 0.906). CF was significantly higher in females ( P  = 0.003), whereas males displayed higher lying behavior ( P  = 0.007). Glucose, total protein, urea, cholesterol, HDL-cholesterol, LDL-cholesterol concentrations ( P  = 0.001) and ALP activity ( P  = 0.003) were significantly affected by the periods. The results of the present study suggest that behavioral and serum parameters across the periods describe changes in the nutritional conditions as a result of the transition from milk to solid feed in association with weaning.  相似文献   
632.
Gesunde Pflanzen - Globally, rationalizing and converting each drop of irrigation water into food is a&nbsp;crucial act in agricultural production, particularly with climatic change concerns....  相似文献   
633.
The aim of this study was to determine the changes in the pharmacokinetics of meloxicam in goat kids who were castrated following the administration of xylazine. Six goat kids were used for the study. The study was performed in two periods according to a longitudinal study, with a 15-day washout period between periods. In the first period (Control group), 1 mg/kg meloxicam was administered by i.v. route to kids. In the second period (Castration group), the kids were sedated with 0.3 mg/kg xylazine and castration was performed following meloxicam administration. Plasma meloxicam concentration was analyzed using HPLC-UV, and pharmacokinetic parameters were calculated by noncompartmental model. In the control group following the administration of meloxicam, mean elimination half-life (t1/2ʎz), area under the concentration–time curve (AUC0−∞), total body clearance (ClT), and volume of distribution at steady-state (Vdss) were 13.50 ± 0.62 hr, 41.10 ± 2.86 hr µg/ml, 24.43 ± 1.75 ml hr−1 kg−1, and 0.45 ± 0.03 L/kg, respectively. In the castration group, the t1/2ʎz of meloxicam prolonged, AUC0−∞ increased, and ClT and Vdss decreased. In conclusion, the excretion of meloxicam from the body slowed and the t1/2ʎz was prolonged in the castrated goat kids following xylazine administration. However, there is a need to determine the pharmacodynamics of meloxicam in castrated goat kids.  相似文献   
634.
The objective of this study was to investigate the effect of in ovo injection of threonine (THR) on immunoglobulin A (IgA) gene expression of Japanese quail on hatch day. A total of 540 Japanese quail eggs were assigned into nine groups of 60 each and were set in a single‐stage incubator. Treatments were as follows: non‐injected (control), two diluent levels (0.05 or 0.1 ml saline), two sites of injection (in or under the air sac) and with or without nutrients (0.5 mg/ml THR). Eggs were injected on d 11 of incubation. On hatch day, after euthanizing hatched quail chicks, the intestine was removed and the jejunum was separated. The relative mRNA expression of jejunal IgA increased (p < 0.05) by the injection of 0.05 ml THR under the air sac when compared to the control group or other treatments of injection. Compared to the control group, no differences were imputable to treatments of 0.1‐ml injections on IgA gene expression. Differences with other injected groups were not significant. It was concluded that injection of 0.05 ml saline containing 0.5 mg THR/ml under the air sac can improve jejunal IgA mRNA expression in newly hatched Japanese quail chicks.  相似文献   
635.
The effects of a diet containing a high proportion of rapeseed meal on the activity of certain plasma enzymes were studied in laying birds. The enzymes studied were alkaline phosphatase (AP), aspartate transaminase (AST), L-gamma-glutamyl-transferase (gamma-GT), isocitrate dehydrogenase (ICDH), leucine arylamidase (LAP), malate dehydrogenase (MDH) and sorbitol dehydrogenase (SDH). No notable differences were observed between the plasma AP, LAP or SDH activities of the birds given the rapeseed meal and the birds receiving a soyabean meal control diet throughout the experiment. However, the plasma AST and gamma-GT activities of the treated birds showed slight elevations while their plasma ICDH and MDH activities showed more marked elevations, which are indicative of liver damage, in response to the diet. Macroscopic observations of the livers of the birds at the end of the experiment were in fairly good accord with the elevation in plasma ICDH and MDH activities noted for the individual birds.  相似文献   
636.
Ovalbumin (OVA) was phosphorylated by dry-heating in the presence of pyrophosphate at pH 4.0 and 85 degrees C for 1 and 5 days, and the physicochemical and structural properties of phosphorylated OVA were investigated. The phosphorus content of OVA increased to 1.01% by phosphorylation, and the electrophoretic mobility of PP-OVA also increased. Although the solubility of dry-heated OVA decreased, the decrease was slightly depressed by phosphorylation. The circular dichroism spectra showed that the change of the secondary structure in the OVA molecule, as measured by alpha-helix content, was mild by phosphorylation. The exchange reaction between the sulfhydryl and disulfide groups was enhanced and the surface hydrophobicity of OVA increased by phosphorylation. The tryptophan fluorescence intensity of OVA decreased by phosphorylation, suggesting that the conformational change occurred in the OVA molecule by phosphorylation. Although the differential scanning calorimetry thermograms of OVA showed a lowering of the denaturation temperature from 78.3 to 70.1 degrees C by phosphorylation, the stability of OVA against heat-induced insolubility at pH 7.0 was improved. The results indicated molten (partially unfolded) conformations of OVA formed by dry-heating in the presence of pyrophosphate.  相似文献   
637.
Low pressure drip irrigation is being promoted in Sub Saharan Africa as an alternative to traditional methods of small scale irrigation of vegetables. The African Market Garden (AMG) is a horticultural production system for smallholders based on low-pressure drip irrigation combined with an improved crop management package. The agronomic and economic performance of the AMG is compared to two gardens irrigated manually with watering cans. One of these gardens is managed according to the same improved crop management package as in the AMG, this treatment is called Improved Management (IM). The other garden is managed according to common practices of vegetable producers in the area, this treatment is called the Farmer Practice (FP). Crop productivity, labor and water use were monitored for two vegetable species (okra and eggplants). The experiment was performed on-station in Niger on three adjacent 500 m2 plots in a sandy acid soil. It was found that improved crop management practices greatly enhance crop productivity over traditional methods at comparable production costs. The AMG gave higher crop yields and higher returns to investment than the treatments irrigated with watering cans. Labor accounts for up to 45% of the production cost in vegetable gardens irrigated by hand, where 80% of the producer time is spent on irrigation. The total labor requirement for the drip irrigated AMG was on average 1.1 man hours per day against 4.7 man hours per day for the Farmers Practice on a 500 m2 garden. Returns on labor are at least double for the AMG against the other treatments. The returns on land from eggplant were found to be US$ 1.7, 0.8 and 0.1 per m2 for the AMG, IM and FP respectively. The returns on water for the cultivation of eggplant are around US$ 2 per m3 in the AMG, against US$ 0.1 in the Farmers Practice. This experiment showed the strong positive impact of drip irrigation and improved crop management practices on profits at minimal environmental costs, indicating that transformation of existing practices poses a considerable potential towards sustainable agricultural development.  相似文献   
638.
A comparative study of the storage and reuse of immobilized yeast cells on apple pieces, kissiris, and gamma-alumina was carried out. The immobilized biocatalysts were allowed to remain in the fermented alcoholic liquid after the end of each fermentation batch for extended periods at 30 degrees C before reactivation in batch fermentation for wine-making. The results showed that the biocatalysts were able to reactivate and ferment after successively increased periods of storage compared to free cell systems both on glucose medium and on grape must. In glucose medium, apple-, kissiris-, and gamma-alumina-supported biocatalysts reactivated after 120, 80, and 83 days, respectively. Possible storage periods for grape must were lower but remained high. Immobilized yeast biocatalyst on apple pieces produced wines with an improved volatiles composition compared to kissiris- and gamma-alumina-supported biocatalysts. There were no significant negative effects on the fermentation activity and volatile byproduct composition.  相似文献   
639.
The effect of applying chemical fertilizers alone or in combination with biofertilizer on the growth, yield and fruit quality and leaf mineral nutrient content of Sewy date palm was investigated in three successive seasons from 2004 to 2006. This study was carried out at the Siwa Oasis in the western desert of Egypt between longitude 25°18′ and 26°06′ E and latitudes 29°05′ and 29°20′ N. Chemical fertilizer applications were 1.2 or 1.5 kg N/tree, 0.065 or 0.044 kg P/tree and 0.250 or 0.420 kg K/tree. Nitrogen and potassium were given as three split applications, whereas P was mixed with organic manure (40 kg/palm tree) and supplied as a single application. Biofertilizer treatments were applied at both rates of N, P and K. The control treatment was the existing nutrient application of just 40 kg of organic sheep manure/tree/year, given as a single application. The results indicated that the application of the larger amounts of N, P and K increased the number of leaves and bunches per palm, fruit yield and total sugar content with a high level of fruit quality and production economics. In addition, this treatment increased the mineral content of leaves and reduced the biennial bearing phenomenon of Sewy date palm.  相似文献   
640.
Nutrient deficiency, especially zinc (Zn) and phosphorus (P), is a common nutritional problem for the production of some crops in Turkey. This problem results in the application of increasing amounts of several fertilizers. Mycorrhizal inoculation or the indigenous potential of mycorrhizae in the soil is a critical factor in crop production under low supply of Zn and P. The effects of selected mycorrhizal inoculation on growth and Zn and P uptake of maize and green pepper were investigated in Zn- and P-deficient calcareous soils from Central Anatolia. Soils were sterilized by autoclaving and plants were grown for 7 weeks in pots under greenhouse conditions with inoculation of two selected arbuscular mycorrhizal (AM) species (Glommus moseea and G. etunicatum) at three rates of P (0, 25, 125 mg P kg?1 soil) and two rates of Zn (0 and 5 mg Zn kg?1soil). Without mycorrhizal inoculation, shoot and root dry matter production were severely affected by P and Zn deficiencies, and supply of adequate amounts of P and Zn significantly enhanced plant growth. When the soil was inoculated with mycorrhizal inoculation, the increasing effects of P and Zn fertilization on plant growth remained less pronounced. In accordance with growth data, mycorrhizae inoculation enhanced P and Zn concentration of plants, especially under low supply of P and Zn. The results obtained indicate that maize and green pepper are highly mycorrizal–dependent (MD) plant species under both low P and Zn supply and mycorrhizae play an essential role in P and Zn nutrition of plants in P and Zn-deficient soils. Although addition of P and Zn increased plant growth and plants are mycorrhizal dependent on P and Zn nutrition however dependence is much more dependent on P nutrition.  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