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   1137篇
  免费   67篇
  国内免费   9篇
林业   69篇
农学   78篇
基础科学   27篇
  426篇
综合类   108篇
农作物   110篇
水产渔业   65篇
畜牧兽医   187篇
园艺   28篇
植物保护   115篇
  2023年   16篇
  2022年   51篇
  2021年   73篇
  2020年   71篇
  2019年   93篇
  2018年   117篇
  2017年   107篇
  2016年   79篇
  2015年   38篇
  2014年   49篇
  2013年   137篇
  2012年   58篇
  2011年   73篇
  2010年   43篇
  2009年   28篇
  2008年   41篇
  2007年   27篇
  2006年   25篇
  2005年   11篇
  2004年   9篇
  2003年   7篇
  2002年   5篇
  2001年   1篇
  2000年   4篇
  1999年   1篇
  1998年   4篇
  1997年   5篇
  1996年   5篇
  1995年   1篇
  1994年   3篇
  1993年   3篇
  1992年   1篇
  1991年   3篇
  1990年   4篇
  1989年   3篇
  1987年   2篇
  1986年   2篇
  1985年   2篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1973年   1篇
排序方式: 共有1213条查询结果,搜索用时 890 毫秒
51.
The current experiment was conducted to find out the optimal conditions for mass rearing and developmental changes of Cyclosainsulana. The lab. conditions were maintained at(27±2)℃ and(65±5)% RH. The clear perplex cages and natural diet consisting of the aphids, larvae of the house fly and larvae of drosophila were used for rearing. C. insulana took(123.12±7.26) days to develop from eggs to adults passing through eight instars under prevailing vivo conditions. The eggs were greenish white in color with average size of 0.57 mm ±0.034. The eggs spent(7.52±1.64) days in emergence. Maximum number of spiderlings survived at the 5th instar(84%) and minimum at the 1st instar(34%). The measurements of different body parts including the total body length, cephalothorax and pedipalps of the both male and female C. insulana were done with the help of micrometer and presented as mean±SD. The measurements varied in the each developing instar. It was concluded that spiders were difficult to rear in the lab. conditions and each developing stage which was regarded as instars showed variations in size colors and body characteristics.  相似文献   
52.
Under the umbrella of WTO, the reduction in trade barriers has forced the policy makers to focus on the export competitiveness. Rice is an important source for foreign exchange earnings for the economy of Pakistan, keeping in mind of this fact, the competitiveness of Pakistan’s rice with other major exporters was examined by applying revealed competitive advantage. The domestic consumption trends of rice among the major rice exporting countries were also analyzed in the current study. The results revealed that as compare to other major exporters of rice in the world, Pakistan had high competitive and comparative advantage in the production of rice. The comparison of the movements in comparative advantage indices for Pakistan with the major world rice competitors/exporters showed that Pakistan possessed relatively high comparative and competitive advantages in rice production. The declining domestic per capita consumption of rice and increasing trends in competitiveness for Pakistan clearly revealed the expected potential of higher growth which meant that rice exports from Pakistan could continue to play an important role for the earnings of foreign exchange. In order to exploit the potential benefits of rice exports, we need to strengthen the competitiveness in rice sector of Pakistan.  相似文献   
53.
Irrigation of arable land with contaminated sewage waters leads to the accumulation of trace metals in soils with subsequent phyto‐/zootoxic consequences. In this study, biochar derived from cotton sticks was used to amend an agricultural silt‐loam soil that had been previously irrigated with trace metal contaminated sewage waters. Metal accumulation and toxicity to spinach (Spinacia oleracea) and fenugreek (Trigonella corniculata) was investigated by measuring concentrations of Cd and Ni in plant tissues and various photosynthetic and biochemical activities of plants. Positive impacts of biochar on both spinach and fenugreek were observed in terms of biomass production that increased from 29% to 36% in case of spinach, while for fenugreek this increase was 32% to 36%. In the control treatment there was an increase in malondialdihyde, soluble sugar, and ascorbic acid contents, indicating heavy metal stress. Biochar applications increased soluble proteins and amino acids in plants and reduced the uptake of Cd from 5.42 mg kg?1 at control to 3.45 mg kg?1 at 5% biochar amended soil and Ni (13.8 mg kg?1 to 7.3 mg kg?1 at 5% biochar) by the spinach plants. In fenugreek, the Cd was reduced from 7.72 mg kg?1 to 3.88 mg kg?1 and reduction in Ni was from 15.45 mg kg?1 to 9.46 mg kg?1 at 5% biochar treated soil, reducing the possibility of transfer up the food chain. This study demonstrates that the use of biochar made from cotton‐sticks, as an amendment to arable soils that have received contaminated irrigation water, could improve plant growth and decrease Cd and Ni uptake to crops, alleviating some of the negative impacts of using sewage waters on arable land.  相似文献   
54.
Extracts of proventriculus (PE) and small intestine (IE) of fowl were used, for the first time, as media for the in vitro hatching of infective eggs of Ascaridia galli. Hatching was successful in a mixture of equal parts of PE and IE (MIP) under normal air and under different concentrations of CO2, but not under 100% CO2. A very highly significant retardation (P less than 0.001) in the rate of hatching appeared as the concentration of CO2 was increased, indicating that high levels of CO2 inhibit the process of hatching. 100% of the eggs hatched in PE in 40.5 min whereas they did not hatch at all in IE, suggesting that IE alone has no influence on egg hatching. The shortest time taken for 100% of the eggs to hatch in this study suggests that the present method of hatching is faster than all previous methods used by different workers.  相似文献   
55.
56.
Imidacloprid has been used as a key insecticide for controlling sucking insect pests of cotton, whereas Spodoptera litura also has been indirectly exposed to this insecticide in Pakistan. To evaluate the risk of resistance evolution and to develop a better resistance management strategy, a field collected population was selected with imidacloprid in the laboratory. Thereafter, fitness cost, realized heritability and cross resistance of imidacloprid resistance in S. litura were investigated. After 14 generations of selection with imidacloprid, S. litura developed a 137.48-fold resistance to the insecticide. Bioassay revealed that this strain showed cross-resistance to acetamiprid (RR 8.52) and a little to lamdacyhalothrin (1.92) but negative cross-resistance was found to methomyl (−0.19). The resistant strain had a relative fitness of 0.38, with substantially lower rates of larval survival, larval duration, male pupal duration, development time, emergence rate of healthy adults, fecundity, hatchability, and prolonged larval and pupal duration. Mean relative growth rate of the larvae, intrinsic rate of population increase, and biotic potential was lower for the selected populations. The estimated realized heritability (h2) of imidacloprid resistance was 0.15 in the resistant strain of S. litura. Development of the resistance may cost significant fitness for the resistant population. This study provided valuable information for further understanding the impact of imidacloprid resistance on physiological parameters of S. litura and for facilitating the development of resistance management strategies.  相似文献   
57.
Estimating variation in grain mineral concentration and bioavailability in relation to grain yield and the year of cultivar release is important for breeding wheat with increased content of bioavailable minerals. The grain yield and yield components, grain phytate concentration, and concentration and bioavailability of minerals (zinc Zn, iron Fe and calcium Ca) in wheat grains were estimated in 40 wheat cultivars released in Punjab (Pakistan) during the last five decades. Mean grain Zn and Ca concentrations in current-cultivars were significantly lower (≥14%) than in obsolete cultivars released during the Green Revolution (1965–1976). Much of this variation was related to increased grain weight in current-cultivars. There was a positive correlation among minerals (r = 0.39 or higher, n = 40) and minerals with phytate in wheat grains (r = 0.38 or higher, n = 40). The tested cultivars varied widely in grain yield and grain phytate-to-mineral molar ratios (phytate:mineral). Compared to obsolete cultivars, the current-cultivars had a higher phytate:mineral ratio in grains, indicating poor bioavailability of minerals to humans. The study revealed a non-significant relationship between grain yield and phytate:mineral ratios in grains. Therefore, breeding for lower phytate:mineral ratios in wheat grains can ensure increased mineral bioavailability without significant reduction in the yield potential. Future breeding should be focused on developing new genotypes suitable for mineral biofortification and with increased mineral bioavailability in grains.  相似文献   
58.
Urea is a common ingredient of the diets of intensively fed lambs, but is increasingly required for industrial processes. Maize steep liquor (MSL) is a by-product of maize grain degradation to produce starch that may be a suitable replacement. Fifty growing lambs were fed on equinitrogenous diets in which between 0% and 80% of the urea was replaced by MSL; their growth and metabolism were recorded over 70 days. Increasing replacement of urea by MSL increased feed intake and nutrient digestibilities, leading to increased growth rates, more efficient feed conversion, and increased nitrogen retention. Concentrations of triiodothyroxin, thyroxin, glucose, and methionine were increased by replacement of urea by liquor, and plasma urea was reduced. This study suggests that MSL is a suitable replacement for up to 80% of urea in the diet of rapidly growing lambs.  相似文献   
59.
The present paper reports the prevalence of coccidiosis in industrial broiler chickens in Faisalabad, Punjab, Pakistan to determine the occurrence of different species of Eimeria in the area and to assess their correlation with the environmental conditions including temperature, humidity and rainfall. The study was conducted from January 2009 to December 2010. Examination of chicken guts revealed 43.89% (n = 3,283/7,480) prevalence of coccidiosis. The highest prevalence (27.04%) was recorded of Eimeria tenella followed by Eimeria maxima (22.42%), Eimeria acervulina (19.89%) and Eimeria necatrix (4.02%). The prevalence of disease was significantly higher (P < 0.05) in autumn (60.02 ± 4.38) followed by summer (47.42 ± 2.92), spring (36.92 ± 2.27) and winter (29.89 ± 3.43). Likewise, prevalence of different species of Eimeria also varied (P < 0.05) in different seasons of the year except that of E. necatrix. A strong correlation (P < 0.05) of environmental conditions with the overall and species-wise prevalence of coccidiosis was recorded except E. necatrix.  相似文献   
60.
Seroprevalence, clinical findings, and lesions of contagious caprine pleuropneumonia (CCPP) in Beetal goats were recorded during an outbreak. The overall seroprevalence of CCPP was 32.50%. Confirmation of Mycoplasma mycoides in serum was carried out using counter immunoelectrophoresis (CIE) technique. The highest CIE-positive cases were recorded in the older goats (51.72%) as compared to young ones. Nasal swabs collected from 39 goats showing respiratory signs were found positive for M. mycoides. The most consistent clinical findings were mild to severe cough, purulent nasal secretion, emaciation, dyspnea, increased respiration rate, and pyrexia. Mortality due to CCPP was 9.17%. Consolidation of lungs exhibited the highest frequency (100%), followed by alveolar exudation (90.90%) and pleural adhesion (72.72%). Among the microscopic lesions, septal peribronchiolar fibrosis exhibited the highest frequency (81.81%), followed by fibrinous pleuritis (63.63%) and peribronchiolar cuffing of mononuclear cells (54.54%) in lungs. From these results, it was concluded that CCPP under subtropical conditions has high prevalence in Beetal goats and leads to significant mortality.  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