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   1139篇
  免费   69篇
  国内免费   2篇
林业   60篇
农学   15篇
基础科学   2篇
  110篇
综合类   164篇
农作物   27篇
水产渔业   135篇
畜牧兽医   637篇
园艺   18篇
植物保护   42篇
  2021年   12篇
  2020年   8篇
  2019年   18篇
  2018年   17篇
  2017年   13篇
  2016年   16篇
  2015年   14篇
  2014年   13篇
  2013年   50篇
  2012年   34篇
  2011年   50篇
  2010年   26篇
  2009年   31篇
  2008年   48篇
  2007年   43篇
  2006年   48篇
  2005年   30篇
  2004年   36篇
  2003年   31篇
  2002年   53篇
  2001年   29篇
  2000年   42篇
  1999年   36篇
  1998年   14篇
  1997年   16篇
  1996年   9篇
  1992年   22篇
  1991年   23篇
  1990年   34篇
  1989年   13篇
  1988年   25篇
  1987年   17篇
  1986年   18篇
  1985年   20篇
  1984年   15篇
  1983年   17篇
  1982年   11篇
  1981年   12篇
  1980年   12篇
  1979年   20篇
  1978年   14篇
  1977年   11篇
  1975年   16篇
  1974年   8篇
  1973年   15篇
  1972年   15篇
  1971年   10篇
  1970年   16篇
  1969年   8篇
  1968年   7篇
排序方式: 共有1210条查询结果,搜索用时 62 毫秒
991.
In the course of a larger screen of 1800 plant and fungal extracts, the ethyl acetate extract of Saussurea costus roots potently inhibited the growth of Trypanosoma brucei rhodesiense. Subsequent HPLC based activity profiling led to the identification of the sesquiterpene lactones arbusculin B (1), α-cyclocostunolide (2), costunolide (3), and dehydrocostuslactone (4). They were tested for in vitro antitrypanosomal activities and cytotoxicity alongside the structurally related sesquiterpene lactones parthenolide (5), zaluzanin D (6), and eupatoriopicrin (7), and had IC50s between 0.8 and 22 μM. Cytotoxic IC50s were from 1.6 to 19 μM, and selectivity indices from 0.5 to 6.5.  相似文献   
992.
Freezing and prolonged frozen storage of dough results in constant deterioration in the overall quality of the final product. In this study the effect of wheat bran and wheat aleurone as sources of arabinoxylan (AX) on the quality of bread baked from yeasted frozen dough was investigated. Wheat fiber sources were milled to pass through a 0.5 mm screen, prehydrated for 15 min, and incorporated into refined wheat flour at 15% replacement level. Dough products were prepared from refined flour (control A), whole wheat flour (control B), aleurone composite flour (composite flour A), and bran composite flour (composite flour B) and stored at –18°C for 28 weeks. Dough samples were evaluated for breadmaking quality at zero time, 14 weeks, and 28 weeks of storage. Quality parameters evaluated were loaf weight, loaf specific volume, and crumb firmness. Composite flour bread samples showed the most resistance to freeze damage (less reduction in the overall product quality), indicating a possible role of some fiber components (e.g., AX) in minimizing water redistribution in the dough system and therefore lessening adverse modifications to the gluten structure. The data suggest that the shelf life of frozen dough and quality of obtained bread can be improved with the addition of an AX source.  相似文献   
993.
994.
OBJECTIVE: To determine whether clinical signs or magnetic resonance imaging findings were associated with outcome in dogs with presumptive ischemic myelopathy. DESIGN: Retrospective case series. ANIMALS: 50 dogs. PROCEDURES: Medical records and magnetic resonance images were reviewed. A neurologic score from 1 (normal) to 5 (most severe degree of dysfunction) was assigned on the basis of neurologic signs at the time of initial examination. Follow-up information was obtained from the medical records and by means of a telephone questionnaire completed by owners and referring veterinarians. RESULTS: Median neurologic score at the time of initial examination was 3 (range, 2 to 5). Median follow-up time was 584 days (range, 4 to 2,090 days). Neurologic score at the time of initial examination and extent of the lesion seen on magnetic resonance images (quantified as the lesion length-to-vertebral length ratio and as the percentage cross-sectional area of the lesion) were significantly associated with outcome. Sensitivity of using a lesion length-to-vertebral length ratio > 2.0 or a percentage cross-sectional area of the lesion > or = 67% to predict an unsuccessful outcome was 100%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that severity of neurologic signs at the time of initial examination and extent of the lesions seen on magnetic resonance images were associated with outcome in dogs with ischemic myelopathy.  相似文献   
995.
A six-month-old, female, domestic shorthair cat was presented with a history of failure to grow and bilateral corneal opacity caused by corneal oedema. Congenital hyposomatotropism and possible secondary hypothyroidism were diagnosed on the basis of fasting serum levels of insulin-like growth factor-1 and thyroxine levels, respectively. These endocrinopathies are rare in the cat and have not been reported to cause ocular signs. The cat died during investigation of these diseases, and histopathological examination of the eyes showed significantly reduced corneal endothelial cell density and number of corneal epithelial cell layers when compared with age-matched healthy control corneas. These changes were implicated in the development of the corneal oedema.  相似文献   
996.
当病原微生物侵入胃肠道乃至动物机体细胞时,动物往往会表现出一系列的疾病病症。目前已经确定,某种病原菌侵入机体引起肠道疾病的首要的必需步骤为黏附于肠壁细胞之上。肠道疾病的第二个发展阶段为病原菌在肠道的增殖。  相似文献   
997.
Eleutheroside B (EB) is a phenylpropanoid glycoside with anti‐inflammatory properties, neuroprotective abilities, immunomodulatory effects, antinociceptive effects, and regulation of blood glucose. The aim of this study was to investigate the effects of EB on the barrier function in the intestinal porcine epithelial cells J2 (IPEC‐J2). The IPEC‐J2 cells were inoculated into 96‐well plates at a density of 5 × 103 cells per well for 100% confluence. The cells were cultured in the presence of EB at concentrations of 0, 0.05, 0.10, and 0.20 mg/ml for 48 hr. Then, 0.10 mg/ml was selected as the suitable concentration for the estimation of transepithelial electric resistance (TEER) value, alkaline phosphatase activity, proinflammatory cytokines mRNA expression, tight junction mRNA and protein expression. The results of this study indicated that the supplementation of EB in IPEC‐J2 cells decreased cellular membrane permeability and mRNA expression of proinflammatory cytokines, including interleukin‐6 (IL‐6), interferon‐γ (INF‐γ), and tumour necrosis factor‐α (TNF‐α). The supplementation of EB in IPEC‐J2 cells increased tight junction protein expression and anti‐inflammatory cytokines, interleukin 10 (IL‐10) and transforming growth factor beta (TGF‐β). In addition, the western blotting and real‐time quantitative polymerase chain reaction (RT‐qPCR) results indicated that EB significantly (p < 0.05) increased the mRNA and protein expression of intestinal tight junction proteins, Claudin‐3, Occludin, and Zonula Occludins protein‐1 (ZO‐1). Therefore, dietary supplementation of EB may increase intestinal barrier function, tight junction protein expression, anti‐inflammatory cytokines, and decrease proinflammatory cytokines synthesis in IPEC‐J2 cells.  相似文献   
998.
Summary

The impact of day and night temperatures on pot chrysanthemum (cultivars ‘Covington’ and ‘Irvine’) was assessed by exposing cuttings, stuck in weeks 39, 44, and 49, to different temperature regimes in short-days. Glasshouse heating set-points of 12°, 15°, 18°, and 21°C, were used during the day, with venting at 2°C above these set-points. Night temperatures were then automatically manipulated to ensure that all of the treatments achieved similar mean diurnal temperatures. Plants were grown according to commercial practice and the experiment was repeated over 2 years. Increasing the day temperature from approx. 19°C to 21°C, and compensating by reducing the night temperature, did not have a significant impact on flowering time, although plant height was increased. This suggests that a temperature integration strategy which involves higher vent temperatures, and exploiting solar gain to give higher than normal day temperatures, should have minimal impact on crop scheduling. However, lowering the day-time temperature to approx. 16°C, and compensating with a warmer night, delayed flowering by up to 2 weeks. Therefore, a strategy whereby, in Winter, more heat is added at night under a thermally-efficient blackout screen may result in flowering delays. Transfers between the temperature regimes showed that the flowering delays were proportional to the amount of time spent in a low day-time temperature regime. Plants flowered at the same time, irrespective of whether they were transferred on a 1-, 2-, or 4-week cycle.  相似文献   
999.
1000.
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