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   203378篇
  免费   13320篇
  国内免费   648篇
林业   22652篇
农学   13789篇
基础科学   2925篇
  39470篇
综合类   9982篇
农作物   16881篇
水产渔业   15435篇
畜牧兽医   67857篇
园艺   6137篇
植物保护   22218篇
  2021年   2374篇
  2020年   2775篇
  2019年   3573篇
  2018年   3582篇
  2017年   3932篇
  2016年   4504篇
  2015年   4125篇
  2014年   5487篇
  2013年   16011篇
  2012年   4718篇
  2011年   6242篇
  2010年   6674篇
  2009年   7384篇
  2008年   5779篇
  2007年   4724篇
  2006年   5602篇
  2005年   4847篇
  2004年   4751篇
  2003年   4532篇
  2002年   3898篇
  2001年   3997篇
  2000年   3664篇
  1999年   3890篇
  1998年   3931篇
  1997年   3994篇
  1996年   3734篇
  1995年   4262篇
  1994年   3636篇
  1993年   3340篇
  1992年   3117篇
  1991年   3243篇
  1990年   2940篇
  1989年   2920篇
  1988年   2513篇
  1987年   2584篇
  1986年   2434篇
  1985年   2873篇
  1984年   2870篇
  1983年   2787篇
  1982年   2493篇
  1981年   2458篇
  1980年   2456篇
  1979年   2405篇
  1978年   2289篇
  1977年   2214篇
  1976年   2035篇
  1975年   1808篇
  1974年   1827篇
  1973年   1754篇
  1971年   1481篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
141.
糖槭叶枯病 Phyllosticta negundinis病菌孢子放散开始期和高峰期与每年的温、湿度变化有关。病害发生严重程度与降雨量关系密切 ,降雨早且量大时病害严重。病菌以分生孢子器和分生孢子在病叶上越冬 ,通过气流传播成为翌年初侵染源。喷洒 70 %甲基托布津可湿性粉剂 10 0 0倍液和 75%百菌清可湿性粉剂 80 0倍液均能收到较好的效果  相似文献   
142.
143.
144.
Lactate Kinetics in veterinary Critical Care: A Review   总被引:3,自引:0,他引:3  
Elevation in blood lactate concentration, with or without accompanying metabolic acidosis, is a hallmark finding in patients with circulatory compromise, and is also consistently noted in other conditions affecting critically ill or injured individuals. Little is reported in a veterinary literature regarding lactate measurement in the emergency and critical care setting, despite impressive reports of the clinical usefulness of lactate measurement in people. The purpose of this article is to review lactate kinetics and the clinical utility of lactate measurement. Limitations to lactate evaluation will also be discussed.  相似文献   
145.
Results are given of a survey on the occurrence of pathotypes (races) of Synchytrium endobioticum (potato wart) in both parts of re-unified Germany. An assortment of six differential cultivars appears to be sufficient to distinguish between the seven presently important German wart pathotypes. A total of ten pathotypes was recorded. Two West and two East German pathotypes seem to be identical, based on the results obtained with presently available cultivars. In contrast to pathotype 1 (common race) which prior to 1945 was distributed over the whole German territory, the 'new' pathotypes seem to prefer the central and south German mountain areas.  相似文献   
146.
合成了14个含有 N-莰-2-基的磷酰胺和硫代磷酰胺类化合物,用红外、核磁及元素分析确定其结构,并探讨了~(31)Pδ值的规律性变化。初步生物试验表明,磷酰胺类化合物对水稻发芽具有明显的抑制作用,其中化合物Ⅱ1的活性大于对照药剂抗倒胺但低于多效唑。  相似文献   
147.
148.
149.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.  相似文献   
150.
Ovarian follicular dynamics and embryo yield were studied during 2 different FSH regimens for superovulation of cattle. Twenty heifers were given intramuscular injections of FSH (total of 35 mg NIH) either once daily for 3 days (Group 3×1) or twice daily for 4 days (Group 4×2). At 72 h after the first FSH injection, each animal was injected with 0.75 mg cloprostenol. Inseminations were performed at 12 h and 24 h after the onset of heat. Transrectal ultrasonography was performed on the day of the first FSH injection, the day of cloprostenol injection, the day of insemination and finally on the day of embryo recovery (day 6 or 7 after heat). The numbers of small (2–4 mm), medium (5–9 mm) and large (>10 mm) size follicles were recorded. The total number of corpora lutea, eggs and transferable embryos were recorded on the day of embryo recovery. No differences were found between the 2 groups in either of the parameters studied (p>0.05). It can be concluded that treatment with this FSH preparation once daily for 3 days gives a folliculogenic and superovulatory response similar to a treatment regimen where it is given twice daily for 4 days.  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