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   11217篇
  免费   648篇
  国内免费   872篇
林业   1541篇
农学   1074篇
基础科学   894篇
  1232篇
综合类   4935篇
农作物   459篇
水产渔业   394篇
畜牧兽医   1435篇
园艺   361篇
植物保护   412篇
  2024年   79篇
  2023年   188篇
  2022年   280篇
  2021年   408篇
  2020年   374篇
  2019年   472篇
  2018年   229篇
  2017年   428篇
  2016年   530篇
  2015年   492篇
  2014年   610篇
  2013年   682篇
  2012年   984篇
  2011年   947篇
  2010年   649篇
  2009年   738篇
  2008年   550篇
  2007年   576篇
  2006年   573篇
  2005年   477篇
  2004年   379篇
  2003年   316篇
  2002年   233篇
  2001年   243篇
  2000年   190篇
  1999年   169篇
  1998年   155篇
  1997年   103篇
  1996年   107篇
  1995年   86篇
  1994年   101篇
  1993年   79篇
  1992年   69篇
  1991年   69篇
  1990年   56篇
  1989年   50篇
  1988年   27篇
  1987年   15篇
  1986年   5篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   6篇
  1981年   3篇
  1980年   3篇
  1978年   1篇
  1956年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
用从自然感染宿主分离的伊氏锥虫原种JG的克隆JGmc1和JGmc5感染免疫活性正常小鼠和免疫抑制小鼠,24h后,以苏拉灭或贝尼尔治疗,两种药物对免疫抑制小鼠的CD100均明显高于免疫活性正常小鼠,由经受一次苏拉灭或贝尼尔治疗未愈的免疫抑制小鼠分离的锥虫,感染免疫活性正常小鼠,再用原来对该克隆感染的免疫活性正常小鼠CD100的苏拉灭或贝尼尔治疗即无效。用免疫溶解试验分别测定一组免疫抑制和免疫活性正确  相似文献   
992.
乌鳢常见疾病及防治   总被引:1,自引:0,他引:1  
调查报道了 1 1种常见乌鳢鱼病的症状和流行情况 ,以及在预防和治疗方面所采取的相应措施。  相似文献   
993.
投入产出法作为一种经济数学方法在水产开发中如何应用尚未见报道。从拟建综合养鱼场的生产目标和最终产品着手,根据各产业间的经济技术联系,通过平衡运算,以确定各类生产的合理规模,使各类生产处于稳定的良性循环之中。  相似文献   
994.
以图像处理系统ERDAS为基础,以TM卫星遥感图像和地面森林资源调查数据为材料,讨论了ER-DAS计算机图像处理的有关过程,研究了如何把遥感图像和森林资源调查数据相结合并从中提取相关信息的方法,建立了遥感图像与GIS资源数据库之间的对应关系。结果表明,该研究方法正确可行,输出图像精度高,可为森林资源管理工作提供重要的遥感基础信息。  相似文献   
995.
本文叙述了自1982年以来由湖南大学土木工程系和机电工厂联合开发研究的微滤机在中国给水净化工程中的应用,该文依据已应用于生活给水、工业用水和工业废水处理的资料,扼要地阐述了微滤机的设备和滤网以及有关微滤机装置的设计原则。  相似文献   
996.
用赤霉酸(GA_3),乙烯利(CPA)、三十烷醇(TRIA)、脱落酸(ABA)、2,4-D 以及6-苄基嘌呤(BA)等激素处理孕穗植株,共处理14份籼稻材料。其中 GA_3和 CPA 对11份材科作了重复试验,证明 GA_3和 CPA 对大部分材料能大幅度提高花培绿苗诱导率,其最适浓度分别为4~7 ppm 和400ppm,但 GA_3、CPA 以及低温预处理,对少数材料的花培诱导有抑制作用。低浓度 TRIA 与 GA_3混合液的处理效果明显优于单独用 GA_3处理的。其它激素除 ABA 有一定作用外,未取得良好效果.  相似文献   
997.
稻螟种群及数量随着水稻熟制和栽培技术的变革,品种更替,治螟药剂的变更,天敌数量的消长,气候的变化而演替。治理策略随着稻螟种群和数量的演替而变化。  相似文献   
998.
Defensin is a small cationic peptide widely distributed in animals and plants. It is an important component of the innate immune defense system of mammals. It has a broad spectrum of antibacterial, antiviral and antifungal activities. Porcine β-defensin-2 (PBD-2) is one of the natural defensins expressed in pigs and has good antibacterial activity in vitro. The purpose of this study is to evaluate the therapeutic effect of PBD-2 in the treatment of Streptococcus suis infection in animals and to provide more insights for evaluating the value of PBD-2 as a therapeutic drug. Firstly, the bactericidal activity of PBD-2 against S. suis clinical isolate SC-19 was measured in vitro, and the cytotoxicity of PBD-2 was tested on mouse-derived macrophages (RAW264.7). Subsequently, C57 female mice aged 4-6 weeks and weighing between 18-22 g infected with S. suis SC-19 were treated with PBD-2 or PBS (n ≥ 6). The survival rate of mice, and the bacteria loads, inflammatory cytokine levels, and pathological changes of tissues were determined. The results showed that PBD-2 (25-200 μg·mL-1) could significantly inhibit the growth of S. suis SC-19 in a concentration-dependent manner (P<0.05). At the same time, PBD-2 had no significant toxic effect on RAW cells (P>0.05). The in vivo study revealed that PBD-2 treatment could effectively reduce the mortality of mice infected with S. suis SC-19. At the same time, PBD-2 treatment significantly reduced bacteria loads in brain, lung, spleen and blood of mice, and decreased the levels of inflammatory cytokines IL-6, IL-12 and TNF-α in mouse sera (P<0.05). At the same time, PBD-2 treatment also significantly alleviated the degree of pathological damages in lung and spleen tissues of mice infected with bacteria (P<0.05). These results indicate that PBD-2 confers great resilience to S. suis in vitro without significant cytotoxicity, while it also exhibits a therapeutic effect on S. suis infection in mice, suggesting that the use of PBD-2 as a therapeutic drug and substitutes for antibiotics is of an excellent prospect.  相似文献   
999.
The objective of this study was to evaluate the safety and efficacy of a purified porcine insulin zinc suspension for treating dogs with uncomplicated diabetes mellitus. Fifty-three dogs were treated for 60 days after an initial dose determination period. The means of the blood glucose concentrations during 12-hour glucose curves and the means of the blood glucose nadir concentrations during 12-hour glucose curves for all dogs were determined before beginning insulin therapy (time 0), at the end of the dose determination period (time 1), 30 days after time 1 (time 2), and 60 days after time 1 (time 3). Presence of polyuria, polydipsia, and ketonuria was determined at each time point. Adequacy of control of hyperglycemia was based on 12-hour blood glucose curves and improvement in clinical variables (results of physical examinations, historic information, polyuria, polydipsia, and ketonuria). Safety was evaluated by questionnaire, performance of physical examination, CBC, serum chemistry profile, and urinalysis. The means of the blood glucose concentrations during 12-hour glucose curves and the means of the blood glucose nadir concentrations during 12-hour glucose curves for all dogs at times 1, 2, and 3 were significantly lower compared with time 0 (P < .0001). There was a reduction in the proportion of dogs with polyuria, polydipsia, and ketonuria of 82, 86, and 80%, respectively. All of the dogs had adequate glycemic control at time 1, 66% at time 2, and 75% at time 3. At time 3, 66% of dogs required insulin injections q12h. Other than hypoglycemia, there were no important adverse effects of insulin administration. The insulin, was safe and efficacious for reducing blood glucose and clinical signs in dogs with diabetes mellitus.  相似文献   
1000.
Downy mildew of pearl millet, caused by Sclerospora graminicola, is a devastating disease, resulting in high economic losses in the semi-arid regions of the world. Recently, induction of host plant resistance using biotic and abiotic inducers are included among disease management practices as an eco-friendly approach. Unsaturated fatty acids are considered as a new generation of plant disease resistance inducers. In the present study, six unsaturated fatty acids, viz. docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), arachidonic acid (AA), linolenic acid, linoleic acid and oleic acid, all originally detected in the zoospores of S. graminicola,were applied to seeds of susceptible cultivars of pearl millet to examine their ability to protect against downy mildew under greenhouse and field conditions. In greenhouse experiments, EPA and AA induced a maximum of 78.6% and 76.5% protection, whereas linoleic acid, DHA and linolenic acid provided up to 66.3%, 61.2% and 24.5% protection, respectively. Oleic acid was not effective in protecting pearl millet (only 5.1% protection). A time interval of four days between treatment of seeds and challenge inoculation was required to obtain optimum protection. Plants raised from treated seeds and challenge inoculated at the tillering and inflorescence stages showed enhanced resistance, resulting in higher grain yield compared to untreated plants of the same cultivar. Chitinase activity was found to be higher in susceptible seedlings of pearl millet after treatment with the fatty acids and pathogen inoculation than in seedlings only inoculated with the pathogen. This indicates that host defence responses are activated and thus that induced resistance is involved in the protection observed. The role of unsaturated fatty acids as activators of resistance against downy mildew in pearl millet is discussed.  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