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   569篇
  免费   31篇
  国内免费   3篇
林业   47篇
农学   42篇
基础科学   2篇
  141篇
综合类   48篇
农作物   61篇
水产渔业   82篇
畜牧兽医   108篇
园艺   12篇
植物保护   60篇
  2023年   6篇
  2022年   18篇
  2021年   29篇
  2020年   28篇
  2019年   31篇
  2018年   43篇
  2017年   29篇
  2016年   32篇
  2015年   28篇
  2014年   38篇
  2013年   44篇
  2012年   41篇
  2011年   43篇
  2010年   31篇
  2009年   18篇
  2008年   31篇
  2007年   13篇
  2006年   21篇
  2005年   12篇
  2004年   6篇
  2003年   5篇
  2002年   8篇
  2001年   3篇
  2000年   5篇
  1999年   3篇
  1998年   6篇
  1997年   4篇
  1996年   2篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   4篇
  1987年   1篇
  1986年   1篇
  1983年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
  1967年   1篇
  1964年   1篇
  1957年   1篇
排序方式: 共有603条查询结果,搜索用时 250 毫秒
1.
The objective of this study was to determine the effects of dietary supplementation of Nigella sativa L. seeds, Rosmarinus officinalis L. leaves and their combination on rumen metabolism, nutrient intake and digestibility, growth performance, immune response and blood metabolites in Dorper lambs. Twenty-four entire male Dorper lambs (18.68?±?0.6 kg, 4–5 months old) were randomly assigned to a concentrate mixture containing on a dry matter basis either, no supplement (control, T1), 1% R. officinalis leaves (T2), 1% N. sativa seeds (T3) or 1% R. officinalis leaves +1% N. sativa seeds (T4). The lambs had ad libitum access to urea-treated rice straw (UTRS) and were raised for 90 days. Supplemented lambs had greater (P?< 0.05) intake of DM and UTRS than the control lambs. The T4 lambs had lower (P?< 0.05) nutrient digestibility than those fed other treatments. Total and daily weight gain was greater (P?< 0.05) in T2 lambs than those fed other diets. The T3 and T4 lambs had greater (P?< 0.05) ruminal pH than the T1 and T2 lambs. Supplemented lambs had lower (P?<?0.05) ruminal total volatile fatty acids, acetate, propionate, NH3-N and C18:0 than the control lambs. The T4 lambs had lower (P?< 0.05) population of Fibrobacter succinogenes, Ruminococcus albus, methanogens and total protozoa compared with those fed other diets. Supplemented lambs had lower (P?< 0.05) neutrophils, basophils and serum urea and greater (P?<?0.05) serum IgA and IgG compared with the control lambs. The current results emphasised the variation in the efficacy of medicinal plants in ruminant nutrition.  相似文献   
2.
The present study assesses the effects of 5‐aminolevulinic acid (ALA, 0, 0.1, 1 and 10 mg l?1) on the growth of oilseed rape (Brassica napus L. cv. ZS758) seedlings under water‐deficit stress induced by polyethylene glycol (PEG 6000, 0 and ?0.3 MPa). Water‐deficit stress imposed negative effects on seedling growth by reducing shoot biomass, cotyledon water potential, chlorophyll content and non‐enzymatic antioxidants (glutathione and ascorbic acid) levels. On the other hand, water‐deficit stress enhanced the malondialdehyde (MDA) content, reactive oxygen species (ROS) production, enzymatic antioxidants activities, reduced/oxidized glutathione ratio (GSH/GSSG) and reduced/oxidized ascorbic acid (ASA/DHA) ratio in seedlings. Application of ALA at lower dosages (0.1 and 1 mg l?1) improved shoot weight and chlorophyll contents, and decreased MDA in rape seedlings, whereas moderately higher dosage of ALA (10 mg l?1) hampered the growth. The study also indicated that 1 mg l?1 ALA improved chlorophyll content, but reduced MDA content and ROS production significantly under water‐deficit stress. Lower dosages of ALA (0.1 and 1 mg l?1) also enhanced GSH/GSSG and ASA/DHA as compared to the seedlings under water‐deficit stress. The antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase and superoxide dismutase) enhanced their activities remarkably with 1 mg l?1 ALA treatment under water‐deficit stress. It was also revealed that 1 mg l?1 ALA treatment alone induced the expression of APX, CAT and GR substantially and under water‐deficit stress conditions ALA treatment could induce the expression of POD, CAT and GR to a certain degree. These results indicated that 0.1–1 mg l?1 ALA could enhance the water‐deficit stress tolerance of oilseed seedlings through improving the biomass accumulation, maintaining a relative high ratio of GSH/GSSG and ASA/DHA, enhancing the activities of the specific antioxidant enzymes and inducing the expression of the specific antioxidant enzyme genes.  相似文献   
3.
Interspecific hybrids between Trifolium uniflorum and cultivated white clover (Trifolium repens) have highly useful characteristics for temperate pastoral systems derived from both parent species. However, the early hybrids (F1 and BC1) also have unacceptably poor seed production for commerce. This study analysed the basis for the poor seed production and investigated breeding strategies for overcoming the problem. The BC1F1 generation produced lower‐than‐expected numbers of heads per plant and seeds per floret. Backcrossing of selected hybrids to white clover corrected these deficiencies and created new variation. Seed numbers were also returned to near target levels by recurrent selection within the BC1 generation. Thus, it was possible to retain a theoretical average of 25% of T. uniflorum genome and still achieve high seed production per plant. The BC1F2 and BC2F1 generations produced high seed numbers per plant, along with reasonable variation. Both of these second‐generation hybrid forms have high reproductive potential and should be the focus for the selection of the desired combinations of agronomic and seed production traits.  相似文献   
4.
Recent studies have demonstrated a strong relationship between the intestinal microbiota and the host health. As such, consumers are increasingly becoming more concerned about the potential effect of certain foods/feeds, particularly of transgenic origin on the gut microbiota. Although the European Food Safety Authority has recommended in their guidelines, to study the effect of transgenic food/feed on host-microbiota, yet, few studies have focused on the evaluation of such effects mainly due to culturing difficulties. Therefore, this study was intended to evaluate the potential adverse effects of transgenic diet consumption on some specific gut microflora (Lactobacillus group, Bifidobacterium genus, Escherichia coli subgroup and Enterococcus genus) of rabbits. A total of forty-eight rabbits were randomly assigned into four groups and fed a diet containing a variable proportion of transgenic cottonseeds at 0, 20, 30 and 40% inclusion level, respectively. Changes in the specific or total faecal bacterial population were monitored at five different experimental stages (i.e. 0, 45, 90, 135 and 180 days) using both the traditional plate count method (TM) and quantitative real-time PCR (qPCR). No significant differences (p > .05) were observed concerning numbers of specific bacteria or total bacteria between the control and experimental groups, though qPCR showed numerically higher values in terms of 16S rRNA gene copies as compared to the values obtained from TM. However, such numerical differences were biologically insignificant (p > .05). Similarly, no significant variations were noticed in the calculated B/E (log10 copies of Bifidobacterium per g faces/log10 copies of E. coli genome per g faeces) ratios in all the groups. All the ratios were in the range of 1.24 to 1.30 throughout the experiment, indicating a good balance of intestinal microflora and greater resistance to intestinal disorders. It is therefore concluded that feeding transgenic cottonseeds could not adversely affect the gut microflora of rabbits during a long-term study.  相似文献   
5.
6.
The aim of the present study was to evaluate the expression and localization of lymphangiogenic factors (VEGF-C and VEGF-D), their receptor (VEGFR3) and lymphatic endothelial marker (LYVE1) in buffalo placenta during early pregnancy [EP], and to investigate the functional role of lymphangiogenic growth factors in placental lymphangiogenesis. The mRNA and protein expression of VEGF-C, VEGF-D, their receptor VEGFR3 and LYVE1 showed significant expression in EP1 (29–42 days) and EP2 stages (51–82 days) both in caruncle (maternal part) and cotyledon (foetal part) of the buffalo placenta. Immunoreactivity of VEGF-C, VEGF-D and LYVE1 was observed around the endometrial gland, in lymphatics and trophoblast cells, whereas VEGFR3 mainly localized in lymphatics of the caruncle and cotyledons. Cultured trophoblast cells were treated with VEGF-C/VEGF-D (50, 100 and 150 ng/ml) and combined doses of VEGF-C and VEGF-D (150 ng/ml) each for different time durations (24, 48 and 72 h). The mRNA expression of LYVE1 and PCNA was significantly (p < .001) upregulated with VEGF-C and VEGF-D and combined treatment (@150 ng/ml), as well as significantly downregulating Caspase-3 at 48 and 72 h. Thus, the present study provides evidence that lymphangiogenic factors are expressed in buffalo placental compartments and they may play a significant role in the regulation of placental function in water buffaloes.  相似文献   
7.
Giant river prawn (Macrobrachium rosenbergii) farming plays an important role in the economy of Bangladesh. Presently, it is cultured in around 50 000 ha area with total annual production of 23 240 t. Traditional extensive prawn farming has been expanding over the last three decades through the introduction and adoption of improved culture systems, such as culture of prawn‐carps, prawn‐shrimp‐fish and prawn‐fish‐rice as concurrent and rotational systems. Efforts for the development of improved techniques on broodstock management, seed production and rearing and grow‐out of prawn have been made over the last decade. The outcomes are low‐cost feed for broodstock, production of post‐larvae in net cages (hapa), all‐male prawn culture, periphyton based prawn‐tilapia culture, C/N based prawn culture, organic prawn farming, prawn‐mola culture and prawn‐carp‐mola polyculture. Despite the development of culture technologies, a number of challenges for sustainable development of prawn farming need to be overcome to realize the potentials of this promising sector. Good aquaculture practises at all levels and application of measures for quality control and food safety would ensure sustainable development of prawn farming in Bangladesh.  相似文献   
8.
Boron is an essential plant micronutrient and the range between deficient and toxic levels of boron is narrow for most of the plants. Like other elements, boron becomes toxic to growth at high concentrations. High boron concentrations in soil reduce crop productivity in many areas of the world. The effect of increasing levels of boron (0, 0.50, 1.00, 1.50, 2.00 mm ) on oxidative stress, antioxidant defence response and changes in artemisinin content in Artemisia annua were investigated in the present study. Boron toxicity reduced the growth parameters viz. stem height, fresh weight and dry weight. Treatments induced oxidative stress resulting in lower net photosynthetic rate, stomatal conductance, internal CO2 and total chlorophyll content. The increased activities of antioxidant enzymes like CAT, POX and SOD were also noted in response to increasing levels of boron stress. However, H2O2 and artemisinin content were found to be high up to 1.00 mm concentration of boron compared to control, and on applying higher doses, further reduced contents were obtained. Thus, the results suggest that a mild stress of boron can be utilized for enhanced artemisinin production.  相似文献   
9.
The potential insecticidal activity of Spilanthes acmella Murr. (Compositae) extracts was assessed in this study. The extracts were shown to be toxic against adults of American cockroach, Periplaneta americana L. The active component in S. acmella extract was isolated and identified as N-isobutyl-2,6,8-decatrienamide (spilanthol). The results from topical application of spilanthol show that it has a high acute toxicity and spilanthol was the most potent compound when compared to three conventional insecticides. The potency was found to be 1.3, 2.6 and 3.8 times more toxic than carbaryl, bioresmethrin and lindane, respectively. Electrophysiological studies indicated immediate hyperexcitation followed by complete inhibition of the cockroach cercal nerve activity.  相似文献   
10.
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