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   2619篇
  免费   163篇
  国内免费   114篇
林业   21篇
农学   480篇
基础科学   45篇
  254篇
综合类   935篇
农作物   160篇
水产渔业   150篇
畜牧兽医   481篇
园艺   175篇
植物保护   195篇
  2024年   7篇
  2023年   40篇
  2022年   71篇
  2021年   90篇
  2020年   112篇
  2019年   112篇
  2018年   81篇
  2017年   117篇
  2016年   133篇
  2015年   109篇
  2014年   136篇
  2013年   156篇
  2012年   157篇
  2011年   169篇
  2010年   119篇
  2009年   115篇
  2008年   108篇
  2007年   113篇
  2006年   95篇
  2005年   100篇
  2004年   56篇
  2003年   75篇
  2002年   58篇
  2001年   42篇
  2000年   46篇
  1999年   43篇
  1998年   31篇
  1997年   44篇
  1996年   30篇
  1995年   41篇
  1994年   26篇
  1993年   31篇
  1992年   31篇
  1991年   27篇
  1990年   21篇
  1989年   30篇
  1988年   20篇
  1987年   18篇
  1986年   22篇
  1985年   11篇
  1984年   15篇
  1982年   4篇
  1981年   4篇
  1980年   6篇
  1979年   3篇
  1978年   3篇
  1977年   8篇
  1976年   3篇
  1975年   3篇
  1955年   1篇
排序方式: 共有2896条查询结果,搜索用时 265 毫秒
61.
QUANTITATIVE CONTRAST ULTRASOUND ANALYSIS OF RENAL PERFUSION IN NORMAL DOGS   总被引:1,自引:1,他引:1  
Eight normal dogs with no evidence of renal disease, weighing between 8 and 25 kg were imaged using contrast harmonic ultrasound after injection of a microbubble contrast medium. All dogs received three separate bolus injections of 0.05 ml of commercial contrast medium (Definity). Time/mean pixel value (MPV) curves were generated for selected regions in the cortex and medulla of the left kidney in each dog. Upslope, downslope, baseline, peak intensity, and time to peak were calculated for each zone. For a bolus injection, within the renal cortex (averaging all subjects) the upslope was 7.4 +/- 1.5 MPV/s, downslope was -0.4 +/- .2 MPV/s, baseline was 66.8 +/- 9.3 MPV, peak was 103.6 +/- 8.2 MPV, time to peak (from injection) was 12.8 +/- 5.3 s and from time of contrast medium reaching the kidney was 5.1 +/- 2.0 s. Within the renal medulla (averaging all subjects), upslope was 2.8 +/- 1.7 MPV/s, downslope was -0.3 +/- .2 MPV/s, baseline was 39.3 +/- 6.0 MPV, peak was 65.2 +/- 14.3 MPV, time to peak from injection was 20.9 +/- 6.4 s and from time of contrast reaching the kidney was 11.6 +/- 4.1 s. These baseline data may prove useful in the evaluation of dogs with diffuse disease or vascular compromise.  相似文献   
62.
The purpose of this study was to investigate the association between renal hypoechoic subcapsular thickening observed ultrasonographically and the presence of renal lymphosarcoma in cats. The ultrasonography database was retrospectively searched for cats that underwent ultrasound examination and ultrasound guided needle renal aspirate, renal biopsy, or necropsy. One radiologist unaware of the final diagnosis evaluated the images for the presence of hypoechoic subcapsular thickening and other abnormal findings. Fifty-four cats met the inclusion criteria. Hypoechoic subcapsular thickening was found in 21 cats of which 17 had lymphosarcoma; the remaining four cats had a different diagnosis. Eleven out of 33 cats without hypoechoic subcapsular thickening were positive for lymphosarcoma, and the rest had a different diagnosis. There was a significant association between hypoechoic subcapsular thickening and renal lymphosarcoma (P = 0.001). The positive predictive value of hypoechoic subcapsular thickening for lymphosarcoma was 80.9% and the negative predictive value was 66.7%. The sensitivity and specificity of hypoechoic subcapsular thickening for the diagnosis of renal lymphosarcoma were 60.7% and 84.6%, respectively. The results of this study indicate that the presence of hypoechoic subcapsular thickening in feline kidneys is associated with renal lymphosarcoma.  相似文献   
63.
The lipids metabolism of tomato and bean plants during biological control of wilt pathogens (Fusarium oxysporum f.sp.lycopersici andF. oxysporum f.sp.phaseoli, respectively) byBacillus subtilis was investigated. The interaction of wilt pathogens with both tomato and bean caused an imbalance and drastic reduction in total lipids, triacylglycerol, sterol and all phospholipd fractions except phosphatidic acid. The application of a formulated biocontrol agent,B. subtilis, eliminated the detrimental effect of both wilt pathogens and consequently prevented catabolism of lipid fractions in both tomato and bean. Moreover, the changes in the lipid fractions as a sensitive monitor for biocontrol of wilt diseases suggest a positive correlation between the application ofB. subtilis and improvement in the host metabolism towards anabolism. http://www.phytoparasitica.org posting Sept. 20, 2006.  相似文献   
64.
A case of renal tubular carcinoma with bone metaplasia is reported in a 20-year-old male, mixed breed horse having a history of weight loss and hematuria. This report includes the clinical signs, macroscopic and microscopic lesions, and the immunohistochemical findings of this neoplasm.  相似文献   
65.
Three dead dogs were brought to the College of Veterinary Medicine, Kyungpook National University for study. Clinically, all the dogs showed emaciation, anorexia, depression, hemorrhagic vomiting and diarrhea for 7~10 days before death. All the clinical signs were first noted for about one month after feeding the dogs with commercial diets. At necropsy, all 3 dogs had severe renal damage with the same green-yellowish colored nephroliths in the renal pelvis. They also showed systemic hemorrhage and calcification of several organs, which might have been induced by uremia. Microscopically, necrosis, calcification and calculi were detected in the renal tubules, and especially in the proximal convoluted tubules and collecting ducts of the kidney. These findings were supportive of a mycotoxic effect, and especially on their kidneys. However, the precise cause of the toxic effect in these cases of canine renal failure could not be determined.  相似文献   
66.
磺胺类药物对猪肾脏损害的病理学观察   总被引:1,自引:0,他引:1  
对14例含有磺胺结晶的猪肾脏用10%中性福尔马林固定,常规石蜡切片技术切片染色,对肾脏进行组织病理学观察。结果显示,皮质区肾小管上皮细胞肿胀变性、髄质区肾小管破坏较为严重,大部分肾小管、集合管上皮细胞脱落、变性坏死,并引起梗阻性肾病,同时,肾小球囊腔扩张、血管球萎缩。结果证实,超剂量或长期使用磺胺类药物会严重损害肾实质,导致肾功能下降甚至肾衰竭。  相似文献   
67.
Ascochyta blight causes significant yield loss in pulse crops worldwide. Integrated disease management is essential to take advantage of cultivars with partial resistance to this disease. The most effective practices, established by decades of research, use a combination of disease-free seed, destruction or avoidance of inoculum sources, manipulation of sowing dates, seed and foliar fungicides, and cultivars with improved resistance. An understanding of the pathosystems and the inter-relationship between host, pathogen and the environment is essential to be able to make correct decisions for disease control without compromising the agronomic or economic ideal. For individual pathosystems, some components of the integrated management principles may need to be given greater consideration than others. For instance, destruction of infested residue may be incompatible with no or minimum tillage practices, or rotation intervals may need to be extended in environments that slow the speed of residue decomposition. For ascochyta-susceptible chickpeas the use of disease-free seed, or seed treatments, is crucial as seed-borne infection is highly effective as primary inoculum and epidemics develop rapidly from foci in favourable conditions. Implemented fungicide strategies differ according to cultivar resistance and the control efficacy of fungicides, and the effectiveness of genetic resistance varies according to seasonal conditions. Studies are being undertaken to develop advanced decision support tools to assist growers in making more informed decisions regarding fungicide and agronomic practices for disease control.  相似文献   
68.
矮生长豇豆的生育与产量形成   总被引:7,自引:1,他引:6  
对春播和秋播矮生长豇豆的生长动态,叶面积形成与效能,结荚与豆荚产量形成特性等进行研究,结果表明,春播矮生长豇豆植株和各个器官的生长动态均呈S形曲线变化。秋播矮生长豇豆虽然无抽蔓期,但其生长动态与春播基本相同,而且植株生长和叶面积都较大,单株结荚稍多,但产量无明显差异。净同化率(NAR)在营养生长过程较高,生殖生长过程较低。本文还讨论了矮生与蔓生长豇豆生育与产量形成的差异。  相似文献   
69.
AC10大豆是以75-23-1-5-15品系经激光红宝石辐照,选衣出75-54红品系,以之为父本,以西德青豆SogleenOgden为线本进行有性杂交,再用红宝石2500V辐射选能而成,具早熟、高产、优质等特点,667m^2产量154.47kg,比对照八个月爆增产30.66%。  相似文献   
70.
南方菜豆花叶病毒(SBMV)主要有2株系:菜豆株系(SBMV-B)和豇豆株系(SBMV-C),血清学方法不能予以区分。根据已报道的核酸序列设计了2对特异引物,进行RT-PCR扩增并克隆到载体Bluescript中,序列测定予以证实后利用随机引物法合成放射性cDNA探针,再进行体外转译合成地高辛UTP标记的RNA探针。2种探针均可分别特异地检测Northernblot膜上的SBMV-B和SBMV-C。RNA探针检测SBMV-B和SBMV-C灵敏度分别为:0.1μg和0.01μg。  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