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   208篇
  免费   12篇
林业   13篇
农学   11篇
基础科学   1篇
  56篇
综合类   8篇
农作物   52篇
水产渔业   25篇
畜牧兽医   40篇
园艺   4篇
植物保护   10篇
  2022年   14篇
  2021年   15篇
  2020年   12篇
  2019年   11篇
  2018年   14篇
  2017年   22篇
  2016年   21篇
  2015年   6篇
  2014年   9篇
  2013年   26篇
  2012年   14篇
  2011年   17篇
  2010年   5篇
  2009年   6篇
  2008年   15篇
  2007年   2篇
  2006年   3篇
  2005年   3篇
  2004年   1篇
  2000年   1篇
  1985年   1篇
  1983年   2篇
排序方式: 共有220条查询结果,搜索用时 0 毫秒
31.
Background:Immobilization is an approach in industry to improve stability and reusability of urease. The efficiency of this technique depends on the type of membrane and the method of stabilization. Methods:The PEI-modified egg shell membrane was used to immobilize urease by absorption and glutaraldehyde cross-linking methods. The membranes were characterized by FTIR and AFM, and Nessler method was applied to measure the kinetic of the immobilized enzymes. Finally, the storage stability (6 °C for 21 days) and reusability (until enzyme activity reached to zero) of the immobilized enzymes were investigated. Results:Based on FTIR, three new peaks were observed in both the absorption- (at 1389.7, 1230.8, and 1074.2 cm-1) and the cross-linking (at 1615-1690, 1392.7, 1450 cm-1) immobilized enzymes. The surface roughness of the native membrane was altered after PEI treatment and enzyme immobilization. The optimal pH of cross-linking immobilized enzymes was shifted to a more neutral pH, while it was alkaline in adsorption-immobilized and free enzymes. The reaction time decreased in all immobilized enzymes (100 min for free enzyme vs. 60 and 30 min after immobilizing by adsorption and cross-linking methods, respectively). The optimal temperature for all enzymes was 70 °C and they had a higher Km and a lower Vmax than free enzyme. The stability and reusability of urease were improved by both methods. Conclusion:Our findings propose these approaches as promising ways to enhance the urease efficiency for its applications in industries and medicines. Key Words: Egg shell, Immobilization, Polyethylenimine, Urease  相似文献   
32.
Background: Multiple sclerosis (MS) is known as a progressive central nervous system inflammatory disease. Certain factors, such as interleukins, inflammatory cells, and oxidative stress are supposed to involve in MS etiology. Because of the important role of oxidative stress, antioxidant therapy for MS has received more attention. Although coenzyme Q10 (CoQ10) acts as an antioxidant, there is a lack of enough research on its effects on MS. Therefore, the present research was designed. Methods: C57BL/6 female adult mice (n = 30) were used in this study. The animals were randomly divided into trial and control groups. To induce MS, routine procedure for experimental autoimmune encephalomyelitis (EAE) was used, and scoring was performed based on clinical signs. By detecting score one, CoQ10 administration was started (10 mg/kg/three weeks). By using ELISA and real-time PCR, the brain levels of TNF-, IL-10, IL-4, and IL-12 were studied. Statistical tests were used to analyze the data and the P value less than 0.05 was considered to be significant. Results: Clinical symptoms in EAE animals were significantly decreased (P<0.05) as compared to control ones. In addition, the level of the TNF- was significantly decreased following CoQ10 administration versus IL-10. The ratio of TH1/TH2 interleukins in treated animals was significantly less than that in non-treated animals (P<0.01). Conclusion: Our findings showed that CoQ10 is capable of suppressing the inflammatory pathway of MS. Key Words: Experimental autoimmune encephalomyelitis (EAE), Multiple Sclerosis (MS), Coenzyme Q10 (CoQ10)  相似文献   
33.
The paper develops methods to construct a one-stage optimal design of dilution experiments under the total available volume constraint typical for biomedical applications. We consider various design criteria based on the Fisher information both in Bayesian and non-Bayesian settings and show that the optimal design is typically one-atomic meaning that all the dilutions should be of the same size. The main tool is variational analysis of functions of a measure and the corresponding steepest descent-type numerical methods. Our approach is generic in the sense that it allows for inclusion of additional constraints and cost components, like the cost of materials and of the experiment itself.  相似文献   
34.
Caspian roach (Rutilus rutilus caspicus), a spring spawning teleost, were subjected to various photoperiod and temperature regimes to study the feasibility of shifting the timing of spawning for artificial propagation purposes. A total of 650 female reproductively mature R. rutilus caspicus were subjected to different photoperiod and temperature regimes including four light regimes (natural light (NL), 16 hr of light (L):8 hr of darkness (D), 9L:15D, 11L:13D), each affected by three temperature regimes (14, 20 and 24°C) for 70 days. Five fish per tank were randomly sampled on Feb. 10, Feb. 20, March 28, April 15 and April 30 (natural spawning time). Ovarian tissue sections were studied using light microscope and transmission electron microscope (TEM). The levels of 17‐β estradiol (E2) and 17αhydroxyprogesterone (OHP) were also measured in the serum samples. In late winter (March 28th), the gonadal maturation and spawning were accelerated in fish treated with the long day length (16L/8D) and warm temperature (20°C). While, the maturation of oocytes and spawning delayed in fish exposed to low temperature (14°C) and short day length (9L/15D and 11L/13D). Photoperiod seems to play a more important role in the ovarian development of the R. rutilus caspicus compared to temperature; since even among the fish treated with the lowest temperature (14°C), those exposed to a longer day length (16L/8D), matured and spawned earlier than the others. Considering that the earliest spawning occurred in R. rutilus caspicus treated with 16L/8D at 20°C and the latest spawning occurred in fish exposed to low temperature and short photoperiod, it can be concluded that temperature and photoperiod play an important role in accelerating oocyte maturation and spawning.  相似文献   
35.
Background:This study investigated the antinociceptive effect of cumin and its biosynthesized AuNPs. Methods:Cumin extract (E) and cumin-AuNPs (GN) were prepared and administered intraperitoneally at the concentrations of 200, 500, and 1000 mg/ml to 27 male rats. UV–Vis spectroscopy and AFM were applied for AuNPs synthesis confirmation. The nociceptive behavior was assessed, and IL-6 serum levels were measured. Results:Cumin-AuNPs showed a peak absorption of 515 nm, and a size of about 40 nm. Three different concentrations of extract had no significant effect on acute and chronic nociceptive behavior. GN + E200 (46.00 ± 10.59) showed a significant acute anti-nociceptive effect compared to the control (98.66 ± 4.91; p = 0.029) and SS300 (98.33 ± 20.30; p = 0.029) groups. Also, GN + E500 (42.00 ± 11.84) significantly reduced acute nociceptive behavior compared to the control (98.66 ± 4.91; p = 0.019), SS300 (98.33 ± 20.30; p = 0.020), and GN + E1000 (91.00 ± 26.00; p = 0.040) groups. IL-6 serum levels reduced significantly in GN + E500 (24.65 ± 10.38; p = 0.002) and SS300 (33.08 ± 1.68; p = 0.039) compared to the controls (46.24 ± 3.02). Chronic nociceptive behavior was significantly lower in the SS300 (255.33 ± 26.30) compared to E200 (477.00 ± 47.29; p = 0.021), E500 (496.25 ± 46.29; p = 0.013), and GN + E500 (437.00 ± 118.03; p = 0.032) groups. Conclusion: Our findings suggest the potential effects of cumin-AuNPs on formalin-induced nociceptive behavior, which is independent of IL-6serum levels.Key Words: Interleukin-6, Pain, Cuminum cyminum L., Gold Nanoparticles, Green Synthesis  相似文献   
36.
Dinitroanilines represent a class of compounds that are widely used in herbicide formulations as they depolymerise plant microtubles, causing chromosome doubling. The potential of microtubule depolymerising herbicides trifluralin, oryzalin, and amiprophosmethyl (APM) for in vitro chromosome doubling of Rosa was studied. Five concentrations (0, 3, 6, 12 and 24 μM) and three exposure periods (12, 24 and 48 h) for each of the compounds were compared. Oryzalin, trifluralin and APM were not significantly different in their ability to induce chromosome doubling of R. hybrida cv Iceberg. At concentration of 6 μM and exposure period of 24 h, chromosome doubling of R. hybrida cv Iceberg was not significantly different with each of the polyplodising agents. At higher concentration (24 μM) and longer exposure period (48 h), 66.7% and 62.5% chromosome doubling was achieved with APM and trifluralin, respectively. However, the application of 6 μM oryzalin to R. persica (2n = 2x), R. hybrida cv Iceberg (2n = 3x) and R. hybrida cv Akito (2n = 4x), resulted in 60.0%, 6.3% and 0% chromosome doubling, respectively, which suggest that chromosome doubling is genotype dependent and plants with lower ploidy level have a higher propensity for chromosome doubling. Flow cytometry results at 18 and 24 weeks after herbicide treatment, indicated that the best time to test the treated plants was after 24 weeks.  相似文献   
37.
This experiment was conducted as a factorial based on complete randomized design (CRD) to study the effects of mycorrhiza inoculation density on cucumber cv. Super N3 irrigated with different salinity sodium chloride (NaCl) levels. Treatments were mycorrhiza inoculations; M1 (non mycorrhizal plant), M2 and M3 (mycorrhiza inoculations with 1000 and 2000 spores) and saline water was provided by S1, S2, S3, and S4 (control, 50, 75, and 100 mM NaCl) with 4 replications. The results showed that saline water reduced root, shoot, and fruit weights, and increased proline and electrolyte leakage. Photosynthesis rate, stomata and mesophyll conductance significantly decreased with increased NaCl concentrations. Mycorrhiza inoculation with 2000 spores increased fruit fresh and dry weights, proline and electrolyte leakage, and both mycorrhiza inoculations increased root and shoot dry weights, photosynthesis and stomata conductance. Root volume increased by mycorrhiza inoculation with 2000 spores under non-stress condition, and root length was stimulated by both mycorrhiza inoculations at all saline water levels. Fruit fresh and dry weights were enhanced by mycorrhiza inoculation with 1000 spores at all saline water levels. Photosynthesis rate was reduced by saline water stress and mycorrhiza inoculation stimulated photosynthesis rate. Mycorrhiza inoculation with 2000 spores increased transpiration under saline and non-saline conditions. Proline content of cucumber leaves increased under saline water application. Electrolyte leakage increased by saline water and mycorrhiza inoculation could not improve it. Both mycorrhiza inoculations (1000 and 2000 spores) at all salinity levels, and mycorrhiza inoculation with 1000 spores at 100 mM NaCl enhanced fruit weight, photosynthesis, and proline content of the cucumber leaves.  相似文献   
38.
39.
For studying the effect of LHRH-A2 hormone on the induction of final maturation and ovulation of Persian sturgeon, 71 matured females and 20 matured males were used. Five groups of breeders were injected with sturgeon pituitary gland hormone (50 mg per fish) and LHRH-A2 in dosages of 3.5, 7, 8 and 10 μg kg−1 for females and 3 and 5 μg kg−1 for males. Results showed that LHRH-A2 successfully induced final maturation and ovulation in females, and there was no significant difference between five groups of breeders in ovulation proportion, fertilization rate, survival rate of incubation, survival of yolk-sac absorption period and active feeding period of larvae. It can be concluded that the LHRH-A2 is a proper alternative for pituitary gland hormone in artificial propagation of Persian sturgeon.  相似文献   
40.
The purpose of this study was to investigate the dietary effects of using essential oil from sour lemon peel (Citrus limon) on growth performance, carcass composition, blood and serum parameters, and liver enzymes of juvenile rainbow trout (Oncorhynchus mykiss) exposed to deltamethrin (DMN) pesticide. Treatments with no lemon peel essential oil (LPEO) and without DMN (control), as well as four treatments with 10% of 96‐h lethal concentration of DMN were prepared with dietary supplementation of LPEO (zero, 200, 400, and 600 mg/kg). Trout juveniles (95.12 ± 0.53 g) were randomly allocated to the treatments (each with three replicates). The results showed that dietary LPEO inclusion improved fish growth parameters in the DMN‐containing treatments. The highest fat content was found in zero LPEO treatment with no DMN while it was lowest in DMN treatments containing 400 and 600 mg/kg of LPEO. Carcass protein content was the highest in DMN treatment with 400 mg/kg of LPEO. Blood and serum biochemical parameters showed statistical differences between no LPEO treatment with DMN exposure and those detected in the control fish (p < .05). Overall, the results indicate that dietary inclusion of LPEO at 400 mg/kg level can decrease some negative effects of DMN exposure.  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