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   2937篇
  免费   167篇
  国内免费   11篇
林业   267篇
农学   186篇
基础科学   43篇
  643篇
综合类   179篇
农作物   438篇
水产渔业   319篇
畜牧兽医   632篇
园艺   96篇
植物保护   312篇
  2024年   4篇
  2023年   21篇
  2022年   92篇
  2021年   122篇
  2020年   126篇
  2019年   172篇
  2018年   201篇
  2017年   195篇
  2016年   200篇
  2015年   108篇
  2014年   140篇
  2013年   295篇
  2012年   178篇
  2011年   210篇
  2010年   153篇
  2009年   99篇
  2008年   196篇
  2007年   88篇
  2006年   65篇
  2005年   61篇
  2004年   39篇
  2003年   44篇
  2002年   34篇
  2001年   24篇
  2000年   33篇
  1999年   18篇
  1998年   21篇
  1997年   14篇
  1996年   16篇
  1995年   15篇
  1994年   9篇
  1993年   7篇
  1992年   8篇
  1991年   6篇
  1990年   8篇
  1989年   9篇
  1988年   6篇
  1987年   7篇
  1986年   5篇
  1985年   5篇
  1984年   11篇
  1983年   8篇
  1981年   5篇
  1979年   5篇
  1978年   5篇
  1975年   3篇
  1973年   3篇
  1972年   3篇
  1971年   3篇
  1967年   4篇
排序方式: 共有3115条查询结果,搜索用时 0 毫秒
101.
This experiment was conducted to evaluate the effects of different levels of sweet orange (Citrus sinensis) peel extract (SOPE) on humoral immune system responses in broiler chickens. Three hundred 1‐day broilers (Ross‐308) were randomly allocated to treatments varying in supplemental SOPE added in the drinking water. The experimental groups consisted of three treatments fed for 42 days as follows: a control treatment without feed extract, a treatment containing 1000 ppm of SOPE and a treatment containing 1250 ppm of SOPE. All treatments were isocaloric and isonitrogenous. Broilers were vaccinated with Newcastle disease virus (NDV), avian influenza (AI), infectious bursal disease (IBD) and infectious bronchitis virus (IBV) vaccines. Antibody titer response to sheep red blood cells (SRBC) was higher in the group fed 1250 ppm of SOPE (P < 0.05) as well as for immunoglobulin G (IgG) and IgM. Similarly, antibody titer responses to all vaccines were constantly elevated (P < 0.05) by SOPE enrichment in a dose‐dependent manner. Relative weights of spleen and bursa of Fabricius were unaffected by treatments. Dietary SOPE supplementation may improve the immune response and diseases resistance, indicating that it can constitute a useful additive in broiler feeding. Thus, supplying SOPE in rations may help to improve relative immune response in broiler chickens.  相似文献   
102.
Two experiments were designed to evaluate the effect of silymarin on stored spermatozoa using four rams. In experiment 1, silymarin was evaluated as a supplement for Tris–glucose extender. Semen samples (n = 20) were diluted with extender containing 0, 50, 100, 150 and 200 μg/ml silymarin and incubated at 5°C for 72 h. Membrane integrity, acrosome integrity, sperm viability and motility were evaluated at 72 h. Concentration of malondialdehyde (MDA) was determined after 48 h. Membrane integrity was higher in 100 μg/ml silymarin (65.2%) than control group (43.2%, p < 0.05). Acrosome integrity was highest in 100 μg/ml silymarin (71.3%, p < 0.05). Progressive motility was higher in 100 (58.5%), 150 (60.62%) and 200 μg/ml silymarin (54.7%) than control group (30.7%, p < 0.05). The highest MDA concentration was observed in control group (400 mm /10 × 106 sperm; p < 0.05). The goal of experiment 2 was to determine the interaction between silymarin and caproic acid on ram stored sperm. Ejaculates (n = 20) were diluted by Tris–glucose extender, added 0 (S?) or 100 μg/ml (S+) silymarin and 0 (C?) or 0.3125% (C+) caproic acid, and thereafter, aliquots were incubated at 5°C for 72 h. Membrane integrity was lower in C?S? (57.6%) than C?S+ (73.2%), C+S? (80.2%) and C+S+ (72.1%, p > 0.05). The highest sperm viability and acrosome integrity were observed in C+S (82.4 and 80.1%, respectively; p < 0.05). There was no difference between CS+ and C+S+ on sperm viability and membrane integrity, progressive motility and MDA concentration (p > 0.05). Therefore, the supplementation of extender with silymarin and caproic acid improved sperm quality and caproic acid was superior to caproic acid plus silymarin.  相似文献   
103.
Restriction fragment length polymorphism (RFLP) genotyping was employed to analyze the population genetics of Mycobacterium bovis in Iran. One hundred and twenty-three isolates collected from slaughtered tuberculosis-suspect cattle and one clinically asymptomatic buffalo were subjected to RFLP analysis with probes of the polymorphic GC-rich sequence (PGRS) and the direct repeat sequence (DR) using DNA digested with PvuII and AluI. All these methods detected a large homogeneous population in which only a few isolates had variant genotypes. Only AluI-based RFLPs of both the PGRS and DR sequences were able to clearly differentiate between BCG and field strains of M. bovis. As in previous reports, these findings seem to reflect a recent dispersal of one or a few strains in Iran following the substantial expansion of Holstein-Friesian cattle over the last few decades.  相似文献   
104.
ObjectivesTo study the effect of pregnancy and lactation on echocardiographic parameters in Holstein dairy cows.AnimalsNine multiparous high milk producing (HMP) dairy cows (producing more than 40 kg of milk per day in peak production) and 9 low milk producing (LMP) cows (producing less than 30 kg or milk per day in peak production).MethodsEchocardiography was performed twice; one month before calving and two months after calving.ResultsThe heart rate of HMP cows in the early lactation period was significantly higher than in the dry period. In LMP cows, there was a significant increase in left ventricular dimension in the early lactation period as compared to the dry period, and the interventricular septum in systole (IVSs) in the dry period was significantly thicker than early lactation period. In HMP cows, there was an increase in the right ventricular diameter in systole in the early lactation period as compared to the dry period. Left ventricular and aortic dimensions in the dry period of HMP were significantly higher than those of LMP cows. When the data were corrected for body weight, comparison of values of the dry period of HMP and LMP cows showed that left ventricular volume in systole in HMP was significantly higher and that IVSs, left ventricular fractional shortening and ejection fraction were significantly lower than in LMP cows.ConclusionsThis study demonstrated that lactation influences the intracardiac dimensions. The amount of milk production can influence echocardiographic parameters in dairy cows.  相似文献   
105.
106.
OBJECTIVE: To evaluate effects of small intestinal submucosa (SIS) on elution properties of plaster of Paris (POP). SAMPLE POPULATION: 27 POP cylinders, 27 POP spheres, and 9 polymethylmethacrylate (PMMA) spheres. PROCEDURES: Pellets were loaded with gentamicin (50 mg/g) and divided into 7 groups of 9 beads each: PMMA spheres; POP cylinders coated with 0, 4, or 8 layers of SIS; and POP spheres coated with 0, 4, or 8 layers of SIS. Gentamicin concentration was measured 6, 12, 18, 24, 32, 40, and 48 hours and 3, 4, 5, 7, 14, 21, 28, 35, and 42 days after wrapping. Porosity was evaluated via scanning electron microscopy. Curvature factor of elution curves, total amount of drug released (TDR), time required to reach 50% of total release (TDR(t50)), and number of days with concentrations > or = 1 microg/mL were compared among groups. RESULTS: SIS decreased the curvature factor and increased the TDR(t50) and TDR of POP spheres and cylinders. Curvature factor of the PMMA-release curve remained lower than that for any POP group, but all POP groups wrapped in SIS released more gentamicin than PMMA spheres. Gentamicin concentrations remained > or = 1 microg/mL in SIS-wrapped POP and PMMA groups throughout the study. Wrapping POP in SIS minimized the increase in porosity of pellets. CONCLUSIONS AND CLINICAL RELEVANCE: Wrapping POP with SIS slows the release and increases the amount of gentamicin leaching from spheres and cylinders. All groups wrapped in SIS maintained antimicrobial concentrations greater than the minimum inhibitory concentration of most pathogens.  相似文献   
107.
108.
Xu Q  Song X  Xu L  Yan R  Shah MA  Li X 《Veterinary parasitology》2008,156(3-4):319-323
A fusion DNA vaccine co-expressed Eimeria tenella TA4 and chicken IL-2 (chIL-2) was constructed and its efficacy against E. tenella challenge was observed. TA4 gene of E. tenella and chIL-2 gene were cloned into expression vector pcDNA3.1 and pcDNA4.0c in different forms, producing vaccines pcDNA3.1-TA4-IL-2, pcDNA3.1-TA4 and pcDNA4.0c-IL-2. The expression of aim genes in vivo was detected by RT-PCR and western blot. Animal experiment was carried out to evaluate the immune efficacy of the vaccines. Results indicated these DNA vaccines were successfully constructed and the antigen genes could be expressed effectively in vivo. The animal experimental results showed that DNA vaccines could obviously alleviate cecal lesions, body weight loss and increase oocyst decrease ratio. The ACI of pcDNA3.0-TA4-IL-2 group was 192, higher than that of pcDNA3.1-TA4 group. The results suggested that TA4 was an effective candidate antigen for vaccine and co-expression of cytokine with antigen was an alternative method to enhance DNA vaccine immunity.  相似文献   
109.
Septoria tritici blotch (STB), caused by Mycosphaerella graminicola has recently become one of the devastating diseases in Iran causing significant yield losses on most commercial bread and durum wheat cultivars. Iran is located in the Fertile Crescent, a region where wheat was historically domesticated; and, thus, landraces derived from this region are of considerable global interest for identification of new sources of resistance to various stresses. Here, we report on the resistance responses of 45 tetraploid wheat landraces collected from different provinces of Iran to eight M. graminicola isolates. In total 138 isolate-specific resistances were found among all interactions (n = 360). The highest number of specific resistances (30 out of 32 interactions) was found in wheat landraces collected from West Azarbaijan. In contrast, all landraces from Kordestan were highly susceptible to M. graminicola isolates and only one isolate-specific resistance was identified among 106 isolate-wheat interactions. Kermanshah landraces showed the highest resistance variation against different isolates. About 57 isolate-specific resistances were identified among 104 interactions. Ilam landraces were highly resistant to STB as 28 specific resistances were observed among 32 interactions. Markazi (n = 2) and Sistan-Baluchestan (n = 1) were susceptible to all isolates tested. Landraces from Lorestan were generally susceptible to isolates tested as 26 susceptible responses were observed out of 32 interactions. Our results indicate that landraces collected from the Fertile Crescent region may possess diverse effective resistance genes or valuable broad spectrum resistance genes, and that their identification is of interest and can be exploited in breeding programs.  相似文献   
110.
Rusts and powdery mildews employ different strategies to suppress defense during penetration. We observed that a compatible interaction of barley-Puccinia hordei induced increased penetration resistance to a challenge infection by powdery mildew. This induced resistance is local and its level is not determined by the virulence spectrum of the challenger isolate. Our data suggest that the inducer effect is due to rust-stoma communication during penetration, to the presence of the rust hyphae in the apoplast, or to penetration resistance mounted by the rust attacked mesophyll cells. We hypothesized that the rust “primes” the basal defense prior to the mildew infection.  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