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   300篇
  免费   14篇
  国内免费   1篇
林业   34篇
农学   13篇
  76篇
综合类   24篇
农作物   20篇
水产渔业   66篇
畜牧兽医   43篇
园艺   3篇
植物保护   36篇
  2023年   5篇
  2022年   10篇
  2021年   6篇
  2020年   9篇
  2019年   8篇
  2018年   12篇
  2017年   7篇
  2016年   9篇
  2015年   9篇
  2014年   11篇
  2013年   29篇
  2012年   18篇
  2011年   20篇
  2010年   11篇
  2009年   10篇
  2008年   17篇
  2007年   8篇
  2006年   12篇
  2005年   13篇
  2004年   9篇
  2003年   6篇
  2002年   5篇
  2001年   3篇
  2000年   7篇
  1998年   5篇
  1997年   4篇
  1996年   4篇
  1995年   5篇
  1994年   5篇
  1993年   2篇
  1991年   3篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   4篇
  1986年   3篇
  1985年   2篇
  1982年   2篇
  1981年   1篇
  1979年   3篇
  1977年   2篇
  1973年   1篇
  1968年   1篇
  1966年   2篇
  1964年   1篇
  1963年   1篇
  1961年   1篇
  1959年   1篇
  1948年   1篇
排序方式: 共有315条查询结果,搜索用时 46 毫秒
1.
2.
This study was conducted to evaluate the comparative effect of maggot meal, silkworm meal and mealworm as dietary protein source on the production performance and some aspects of meat quality in broilers. In this regard, maggot meal was reared on chicken offal and poultry waste. Silkworm meal was obtained from silk industry, while mealworm was developed through beetles rearing. A total of 120‐day‐old broiler chicks were randomly divided into four groups where soya bean meal (M0) was replaced with maggot meal (M1), silkworm meal (M2) and mealworm (M3) respectively. Each group was further divided into three replicates. The study was carried out for a period of 5 weeks. Diets containing mealworm significantly reduced overall feed consumption and resulted into higher weight gain (p < .05). Lowest feed conversion ratio (FCR) was recorded for birds fed with mealworm diet (p < .05). Tenderness and juiciness of meat were higher (p < .05) in M3 compared to the control and other treatments. Mortality did not vary between the control and the treated groups. Therefore, it is concluded that insect meal is rich in essential nutrients and could be successfully used in broiler ration without compromising acceptability. In the light of this study, mealworm is the best choice in broiler ration, in comparison with maggot and silkworm.  相似文献   
3.
Effects of simulated acid rain and root-knot nematode on tomato   总被引:1,自引:1,他引:1  
Effects were examined of simulated acid rain and of root-knot nematode, Meloidogyne incognita race 1, on plant growth, yield, photosynthetic pigments and leaf epidermal characters of tomato ( Lycopersicon esculentum cv. Pusa Ruby). Sequential inoculation exposures (pre-, post-, and concomitant with nematode inoculation) were carried out in a greenhouse. Intermittent treatments of simulated acid rain at pH 3.2 caused white-to-tan irregular lesions on both the upper and lower surfaces of tomato leaves. The foliar symptoms were more pronounced on nematode-infected plants. Simulated acid rain (pH 3.2) and/or nematode infection suppressed plant growth, yield and pigment synthesis, the effects being greatest in post-inoculation treatments compared with simulated acid rain at pH 6.8. The total weight of fruits per plant was greatly suppressed owing to simulated acid rain or nematode infection. Chlorophyll a was found to be more sensitive to simulated acid rain or nematode infection than other leaf pigments. Root penetration, galling, egg mass production, and fecundity (number of eggs per egg mass) of M. incognita were enhanced at pH 5.6 and suppressed at pH 3.2 compared with pH 6.8. Nematode infection or simulated acid rain at pH 3.2 suppressed stomata and trichome development (number and size). Simulated acid rain treatments at pH 5.6 had a positive effect on number and size of trichomes, but a negative effect on stomata. The apertures of stomata were wider on tomato leaves exposed to simulated acid rain, especially at pH 3.2, than at pH 6.8.  相似文献   
4.
Glutathione (GSH) at concentrations of 0.0 (control), 0.5, 1.0, 2.0 and 3.0 mM was added to chilled bull semen to determine its effects on the keeping quality of semen used for artificial insemination (AI). The semen was preserved with egg yolk citrate extender. All samples were stored at 4-8 degrees C for 5 days. Sperm motility and proportion of abnormal acrosome were assessed daily. Sperm motility was significantly (p < 0.01) higher in the semen treated with 0.5 mM glutathione than in untreated semen on each day. The optimum sperm motility (>or=50%) for AI was retained significantly (p < 0.01) for 3 days in 0.0, 0.5, 1.0 and 2.0 mM glutathione treated semen, whereas in 0.3 mM glutathione-treated semen, sperm motility was 46.8% for 3 days. Acrosomal damage was significantly (p < 0.01) reduced after addition of 0.5 mM GSH in the preserved semen. Bull semen can be preserved in chilled condition for 5 days with 0.5 mM GSH with sperm motility above 40% and 12% acrosome abnormality.  相似文献   
5.
Root-exudates of Neem/Margosa and Bakain/Persian lilac brought about considerable mortality ofHoplolaimus indicus, Helicotylenchus indicus, Tylenchus filiformis, Tylenchorhynchus brassicae, Rotylenchulus reniformis andMeloidogyne incognita, however, to varying extent. The root-exudate of Neem was more toxic to nematodes than that of Bakain. The root-exudates also inhibited larval hatch ofM. incognita.  相似文献   
6.
Inhibins are members of the TGFβ superfamily and act as suppressors of follicle stimulating hormone (FSH) secretion from pituitary glands via a negative feedback mechanism to regulate folliculogenesis. In this study, the INHBB gene was knocked down by three RNAi-Ready pSIREN-RetroQ-ZsGreen vector- mediated recombinant plasmids to explore the effects of INHBB silencing on granulosa cell (GC) cell cycle, apoptosis and steroid production in vitro. Quantitative real-time polymerase chain reaction, Western blot, flow cytometry and ELISA were performed to evaluate the role of INHBB in the mouse GC cell cycle, apoptosis and steroid production in vitro. The results showed that the relative mRNA and protein expression of INHBB in mouse GCs can be significantly reduced by RNAi with pshRNA-B1, pshRNA-B2 and pshRNA-B3 plasmids, with pshRNA-B3 having the best knockdown efficiency. Downregulation of the expression of INHBB significantly arrests cells in the G1 phase of the cell cycle and increases the apoptosis rate in GCs. This was further confirmed by downregulation of the protein expressions of Cyclin D1, Cyclin E and Bcl2, while the protein expression of Bax was upregulated. In addition, specific downregulation of INHBB markedly decreased the concentration of estradiol and progesterone, which was further validated by the decrease in the mRNA levels of CYP19A1and CYP11A1. These findings suggest that inhibin βB is important in the regulation of apoptosis and cell cycle progression in granulosa cells. Furthermore, the inhibin βB subunit has a role in the regulation of steroid hormone biosynthesis. Evidence is accumulating to support the concept that inhibin βB is physiologically essential for early folliculogenesis in the mouse.  相似文献   
7.
Transgenic cotton carrying the Cry1Ac gene has revolutionized insect pest control since its adoption, although the development of resistance in insect pests has reduced its efficacy.  After 10 years of cultivating Bacillus thuringiensis (Bt) cotton with a single Cry1Ac gene, growers are on the verge of adopting Bt cotton that carries the double gene (Cry1Ac+Cry2A) due to its better effectiveness against insect pests.  Thus, the current study was designed to evaluate the role of each gene in the effectiveness of Bt cotton carrying the double gene.  The expression levels of the Cry1Ac and Cry2A genes were evaluated in the leaves of 10 genotypes (2 parents and 8 F1 hybrids) at 30 days after sowing (DAS), while samples of leaves, bolls and flowers were taken from the upper and lower canopies at 70 and 110 DAS.  The F1 hybrids were developed through reciprocal crosses between two Bt (CKC-1, CKC-2) and two non-Bt (MNH-786, FH-942) parents.  The differential expression of transgenes was evaluated through Enzyme Linked Immuno-Sorbent Assay (ELISA).  The results showed that the MNH786×CKC-1 hybrid had the highest concentrations of Cry1Ac gene at 30 DAS (3.08 µg g–1) and 110 DAS (1.01 µg g–1) in leaves.  In contrast, the CKC-2×MNH-786 hybrid showed the lowest concentrations of Cry1Ac gene at 30 DAS (2.30 µg g–1) and 110 DAS (0.86 µg g–1).  The F1 hybrid FH-942×CKC-2 showed the highest concentrations of Cry2A gene at 30 DAS (8.39 µg g–1) and 110 DAS (7.74 µg g–1) in leaves, while the CKC-1×MNH-786 hybrid expressed the lowest concentrations of Cry2A gene at 30 DAS (7.10 µg g–1) and 110 DAS (8.31 µg g–1).  A comparison between the two stages of plant growth showed that leaves had the highest concentrations at 30 DAS, whereas the lowest concentrations were observed at 110 DAS for both genes in leaves.  When the expression pattern was compared between various plant parts in genotype CKC-2, it was found that leaves had higher concentrations of Cry1Ac (3.12 µg g–1) and Cry2A (8.31 µg g–1) at 70 DAS, followed by bolls (Cry1Ac (1.66 µg g–1) and Cry2A (8.15 µg g–1)) and flowers (Cry1Ac (1.07 µg g–1) and Cry2A (7.99 µg g–1)).  The genotype CKC-2 had higher concentrations of Cry1Ac (3.12 µg g–1) and Cry2A (8.31 µg g1) in the upper canopy but less accumulation (2.66 µg g–1 of Cry1Ac, 8.09 µg g–1 of Cry2A) in the lower canopy at 70 DAS.  Similarly, at 110 DAS, the expression levels of Cry1Ac and Cry2A in upper and lower canopy leaves were 1.52 and 7.92 µg g–1, and 0.99 and 7.54 µg g–1, respectively.  Hence, the current study demonstrates that different genotypes showed variable expression for both of the Cry1Ac and Cry2A genes during plant growth due to different genetic backgrounds.  The Cry2A gene had three-fold higher expression than Cry1Ac with significant differences in expression in different plant parts.  The findings of this study will be helpful for breeding insect-resistant double-gene genotypes with better gene expression levels of Cry1Ac and Cry2A for sustainable cotton production worldwide.  相似文献   
8.
Soil organic carbon (SOC) and nitrogen (N) are two of the most important indicators for agricultural productivity. The primary objective of this study was to investigate the changes in SOC and N in the deep soil profile (up to 100 cm) and their relationships with crop productivity under the influence of long-term (since 1990) fertilization in the wheat-maize cropping system. Treatments included CK (control), NP (inorganic N and phosphorus (P) fertilizers), NPK (inorganic N, P and potassium fertilizers), NPKM (NPK plus manure), and M (manure). Crop yield and the properties of topsoil were measured yearly from 2001 to 2009. C and N contents were measured at five different depths in 2001 and 2009. The results showed that wheat and maize yields decreased between 2001 and 2009 under the inorganic fertilizer (NP and NPK) treatments. The average yield between 2001 and 2009 under the NP, NPK, NPKM, and M treatments (compared with the CK treatment) increased by 38, 115, 383, and 381%, respectively, for wheat and 348, 891, 2 738, and 1 845%, respectively, for maize. Different long-term fertilization treatments significantly changed coarse free particulate (cfPOC), fine free particulate (ffPOC), intramicroaggregate particulate (iPOC), and mineral-associated (mSOC) organic carbon fractions. In the experimental years of 2001 and 2009, soil fractions occurred in the following order for all treatments: mSOC>cfPOC>iPOC>ffPOC. All fractions were higher under the manure application treatments than under the inorganic fertilization treatments. Compared to the inorganic fertilization treatments, manure input enhanced the stocks of SOC and total N in the surface layer (0–20 cm) but decreased SOC and N in the deep soil layer (80–100 cm). This reveals the efficiency of manure in increasing yield productivity and decreasing risk of vertical loss of nutrients, especially N, compared to inorganic fertilization treatments. The findings provide opportunities for understanding deep soil C and N dynamics, which could help mitigate climate change impact on agricultural production and maintain soil health.  相似文献   
9.

Though Biofloc Technology is a new concept in Bangladesh, it provides advantages for improving aquaculture production in many countries, leading to achieve sustainable development goals. The objectives of this study were to determine the effects of stocking densities on the growth performance of stinging catfish (Heteropneustes fossilis) under Biofloc Technology and assess the economic prospects and business feasibilities. Fingerlings were stocked in unique 5000-L tanks with three stocking densities, i.e., 3500 fish/tank (Treatment-I), 4000 fish/tank (Treatment-II), 4500 fish/tank (Treatment-III). The treatments showed significant differences (P?<?0.05) considering the species-specific growth rate, feed conversion ratio, and protein efficiency ratio. Treatment-I had significantly ((P?<?0.05) higher final biomass (29.51 ± 0.04 kg/m3) than the other treatments. The present findings revealed that using a lower stocking density, the Biofloc Technology reduced ammonia (NH3), nitrite (NO2), nitrate (NO3), TDS, and floc volume but significantly increased the dissolved oxygen. As a result, Treatment-I had generated significantly higher net income (BANGLADESHI TAKA—BDT 86,278.90) over the other treatments. Moreover, the NPV, net BCR, and RoR with 4% and 9% opportunity cost were also significantly higher in Treatment-I than other treatments. The internal rate of return (IRR) and SWOT analysis index indicates that investing in Biofloc Technology is far superior, and a stocking density of 3500 fish/tank (Treatment-I) resulted in a faster investment return.

  相似文献   
10.
The dietary protein requirement of the freshwater prawn Macrobrachium rosenbergii to obtain the maximum body protein retention was assessed by the estimated protein needed daily for maintenance (M) and body protein increment (G). The body protein increment was estimated by quantifying body nitrogen increments when the prawn was fed high‐protein diets composed primarily of casein. The protein required for maintenance was estimated by regressing weight gains in feeding experiments using graded dietary levels of casein. The true daily retention (R) or increase in body protein of the prawn corresponds to the sum of M and G. The values of M, G, and R determined in the present study were 3.86, 0.24, and 4.10 g/kg body weight/d, respectively. On the basis of the daily body protein increment and the net protein utilization of casein (58%), dietary protein requirement of the juvenile M. rosenbergii for maximum body protein retention was suggested to be about 7.1 g/kg body weight/d.  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