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   1087篇
  免费   78篇
林业   80篇
农学   138篇
基础科学   22篇
  206篇
综合类   65篇
农作物   76篇
水产渔业   65篇
畜牧兽医   402篇
园艺   17篇
植物保护   94篇
  2023年   11篇
  2022年   11篇
  2021年   32篇
  2020年   35篇
  2019年   23篇
  2018年   44篇
  2017年   53篇
  2016年   46篇
  2015年   34篇
  2014年   43篇
  2013年   70篇
  2012年   81篇
  2011年   61篇
  2010年   43篇
  2009年   35篇
  2008年   45篇
  2007年   38篇
  2006年   26篇
  2005年   32篇
  2004年   17篇
  2003年   23篇
  2002年   29篇
  2001年   21篇
  2000年   12篇
  1999年   13篇
  1998年   11篇
  1996年   7篇
  1994年   11篇
  1992年   12篇
  1991年   9篇
  1990年   12篇
  1989年   9篇
  1988年   17篇
  1987年   18篇
  1986年   11篇
  1985年   7篇
  1984年   9篇
  1983年   11篇
  1982年   9篇
  1981年   13篇
  1980年   6篇
  1979年   14篇
  1978年   8篇
  1975年   13篇
  1973年   8篇
  1972年   6篇
  1971年   7篇
  1970年   11篇
  1969年   13篇
  1968年   6篇
排序方式: 共有1165条查询结果,搜索用时 328 毫秒
991.
In sodic soils, excessive amounts of salts have an adverse effect on soil biological activity and stability of soil organic matter. The study analyzes the role of silvopastoral systems to improve soil organic matter and microbial activity with a view for effective management of soil fertility. The silvopastoral systems for the present study (located at Saraswati Reserved Forest, Kurukshetra; 29°4′ to 30°15′ N and 75°15′ to 77°16prime; E) are characterized by tree species of Acacia nilotica, Dalbergia sissoo and Prosopis juliflora along with grass species of Desmostachya bipinnata and Sporobolus marginatus. Soil microbial biomass carbon was measured using the fumigation extraction technique and nitrogen mineralization rates using aerobic incubation method. The microbial biomass carbon in the soils of D. bipinnata and S. marginatus treatments were low. In silvopastoral systems, microbial biomass carbon increased due to increase in the carbon content in the soil – plant system. A significant relationship was found between microbial biomass carbon and plant biomass carbon (r = 0.83) as well as the flux of carbon in net primary productivity (r = 0.92). Nitrogen mineralization rates were found greater in silvopastoral systems compared to 'grass-only' system. Soil organic matter was linearly related to microbial biomass carbon, soil N and nitrogen mineralization rates (r = 0.95 to 0.98, p < 0.01). On the basis of improvement in soil organic matter, enlarged soil microbial biomass pool and greater soil N availability in the tree + grass systems, agroforestry could be adopted for improving the fertility of highly sodic soil. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
992.
Ram G  Bhan MK  Gupta KK  Thaker B  Jamwal U  Pal S 《Fitoterapia》2005,76(2):143-147
Phenotypic and genotypic coefficient of variability, heritability in broad sense and genetic advance were determined investigating the characters of 15 accessions of Silybum marianum. Seed yield/plant and number of capsules/plant had highest estimates of genotypic variation, heritability and genetic advance which suggest that direct selection for these traits is suitable for the improvement of this crop. Number of capsules/plant had a significant positive correlation with the number of branches/plant and leaf length (r=0.3398, 0.7547), whereas seed yield/plant had a positive significant correlation with leaf length, stem diameter, capsule diameter and silymarin content (r=0.6830, 0.3140, 0.3484, 0.2925).  相似文献   
993.
Three hundred 1-day-old Japanese quail (Coturnix coturnix japonica) were divided into two groups of 150 each. One group was maintained on quail mash alone, whereas Fusarium verticillioides culture material (FCM) was added to quail mash in the second group from 5 days of age and supplied 150 mg FB1/kg mash. At day 21, each group was further subdivided into two groups, yielding four groups with 75 birds apiece, which served as the control (group CX), the Salmonella Gallinarum alone group (group CS), the FB1 alone group (group FX), and the group fed FB1 and infected with Salmonella Gallinarum (group FS). An oral challenge with Salmonella Gallinarum organisms (2 x 10(4) colony-forming units [cfu]/ml) was given to groups CS and FS at 21 days of age. Three quail each, were necropsied on day 21 (0 day interval) from groups CX and FX, whereas at subsequent intervals, i.e., 1, 2, 3, 5, 7, 10, 14, and 21 days postinfection (DPI), they were sacrificed from all four groups (CX, CS, FX, and FS) to study the agglutinin response to Salmonella Gallinarum and pathologic changes. The agglutinin titers to Salmonella Gallinarum in the combination group (FS) were generally lower when compared with those in group CS. A reduction in the size of spleen along with depletion of white pulp, thinning of cardiomyocytes, lymphoid cell depletion from bursal follicles, and renal tubular nephrosis were characteristic pathologic changes in group FX. In contrast, there was mild to severe enlargement of spleen accompanied by necrosis and reticuloendothelial cell hyperplasia, pericarditis, myocarditis, and focal interstitial nephritis in groups CS. Similar but more severe lesions were observed in the combination group (FS). In addition, the flabby texture of heart, hydropericardium, and ascites were mainly observed in group FS. It is concluded that continuous presence of fumonisins at 150 mg/kg diet increases the severity of Salmonella Gallinarum infection in young Japanese quail.  相似文献   
994.
Brucellosis causes serious economic losses to goat farmers by way of reproductive losses in the form of abortions and stillbirths. Nucleic acid vaccines provide an exciting approach for antigen presentation to the immune system. In this study, we evaluated the ability of DNA vaccine encoding the omp31 protein of Brucella melitensis 16M to induce cellular and humoral immune responses in mice. We constructed eukaryotic expression vectors called pTargeTomp31, encoding outer membrane protein (omp31) of B. melitensis 16M. pTargeTomp31 was injected intramuscularly three times, at 3-week intervals in groups of mice 6 weeks of age. pTargeTomp31 induced good antibody response in ELISA . pTargeTomp31 elicited a T-cell-proliferative response and also induced a strong gamma interferon production upon restimulation with either the omp31 antigen or B. melitensis 16M extract. We also demonstrate that animals immunized with this plasmid elicited a strong and long-lived memory immune response. Furthermore, pTargeTomp31 elicited a typical T-helper 1-dominated immune response in mice, as determined by immunoglobulin G isotype analysis. This vaccine also provided the moderate degree of protection to the mice. This study for the first time focuses on DNA immunization of a gene from B. melitensis. These results may lead to the development of a DNA-based vaccine for the control of brucellosis in goats.  相似文献   
995.
996.
997.

Background

The process for obtaining monoclonal antibodies against a specific antigen is very laborious, involves sophisticated technologies and it is not available in most research laboratories. Considering that most cytokines remain partially conserved among species during evolution, the search for antibody cross-reactivity is an important strategy for immunological studies in veterinary medicine. In this context, the amino acid sequence from human and canine cytokines have demonstrated 49–96 % homology, suggesting high probability of cross-reactivity amongst monoclonal antibodies. For this, 17 commercially available anti-human monoclonal antibodies [IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8 (#1, #2), IL-10, IL-12, IL-13, IL-17A, IFN-γ (#1, #2), TNF-α (#1, #2) and TGF-β], were evaluated in vitro for intracellular cytokine detection in a stimulated canine blood culture by flow cytometry and confocal microscopy. Lymphocytes from peripheral blood of healthy and two unhealthy dogs were analyzed.

Results

Eleven anti-human mAbs [IL-1α, IL-4, IL-5, IL-6, IL-8 (#1, #2), IL-12, IL-17A, TNF-α (#1, #2) and TGF-β] cross-reacted against canine intracellular cytokines. The specificity of the assays was not affected after Fc-blocking. Three anti-human cytokine mAbs [IL-4, IL-8 (#2) and TGF-β] when evaluated by confocal microscopy also cross-reacted with intracellular canine cytokines. The identification of human mAbs that cross-reacted with canine cytokines may support their use as immunological biomarkers in veterinary medicine studies.

Conclusion

The identification of these 11 anti-human cytokine mAbs that cross-reacted with canine cytokines will be useful immunological biomarkers for pathological conditions by flow cytometry and fluorescence microscopy in dogs.  相似文献   
998.
Histological analysis of the gonadal development of Leporinus copelandii Steindachner, 1875, a rheophilic Characiformes species in the Paraiba do Sul River, South‐eastern Brazil, was described. We expect that this species adapt gonadal development to succeed in this river basin that has its longitudinal profile blocked by several impoundments. Fishes were examined by routine macroscopic and histological techniques. Stages of oocyte and spermatocyte development were described, and gonadal maturation was proposed. Mean oocyte diameter obtained from histological observations increased from the pre‐spawning (4.2–175.5 μm) to spawning (148.5–262.0 μm) phases, followed by a sharp decrease in the post‐spawning (27.0–56.7 μm) phase. Based on occurrence of different oocytes phases and oocyte size distribution, this species has group‐synchronic development of oocytes. Further studies are necessary to clarify the spawning grounds for L. copelandii in the Paraíba do Sul River basin, especially considering that several impoundments obliterate the natural river course and this could limit spawning grounds.  相似文献   
999.
1000.
Exploitation of wild gene pool for breeding is a common practice in an increasing number of cultivated plants. The cultivated lentil could not attain the substantial improvement in the yield potential due to loss of genes for higher productivity and lack of resistance against biotic and abiotic stresses. The absence of evaluation data of wild lentils for characters of economic importance, besides biotic and abiotic stresses, is one of the constraints in their use in lentil breeding programme. In the present study, 70 wild accessions from four wild Lens subsp./sp. (L. culinaris subsp. orientalis, L. odomensis, L. ervoides and L. nigricans) along with 3 checks (Precoz, PL-406 and PL-639) were evaluated for phenological and agro-morphological characters, for their reaction to three fungal diseases (wilt, powdery mildew and rust) and screened for tolerance to moisture stress. The wild accessions showed higher performance for branches/plant as compared to cultivated genotypes. Similarly, a few accessions of L. culinaris subsp. orientalis were earlier to flower and had higher seeds and seed yield/plant as compared to cultivated lentil. However, some were comparable with cultivated genotypes for flowers/peduncle, peduncle length and plant height. The mean performance for flowers per peduncle, leaflets per leaf, plant height, seeds and seed yield per plant increased, while decreased for days to flowering and maturity, and branches per plant during the evolution of cultivated lentil from the wild Lens taxa. Of Lens taxa, L. nigricans had the maximum resistant accessions for biotic and tolerance to abiotic stresses. The valuable variation existing among wild accessions can be exploited following introgression with cultivated lentils. It will help in the flow of useful genes from wild to cultivated lentil for generating wide spectrum of variability and its subsequent use in genetic restructuring of lentil.  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