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   15923篇
  免费   1006篇
  国内免费   1373篇
林业   1190篇
农学   1056篇
基础科学   815篇
  1815篇
综合类   7292篇
农作物   1042篇
水产渔业   663篇
畜牧兽医   2550篇
园艺   1138篇
植物保护   741篇
  2024年   104篇
  2023年   295篇
  2022年   714篇
  2021年   732篇
  2020年   648篇
  2019年   708篇
  2018年   452篇
  2017年   802篇
  2016年   542篇
  2015年   806篇
  2014年   817篇
  2013年   971篇
  2012年   1288篇
  2011年   1355篇
  2010年   1247篇
  2009年   1095篇
  2008年   1023篇
  2007年   939篇
  2006年   808篇
  2005年   689篇
  2004年   426篇
  2003年   270篇
  2002年   302篇
  2001年   284篇
  2000年   251篇
  1999年   115篇
  1998年   68篇
  1997年   41篇
  1996年   49篇
  1995年   46篇
  1994年   45篇
  1993年   41篇
  1992年   38篇
  1991年   31篇
  1990年   22篇
  1989年   25篇
  1988年   26篇
  1987年   24篇
  1986年   18篇
  1985年   8篇
  1984年   13篇
  1979年   5篇
  1974年   9篇
  1973年   5篇
  1972年   8篇
  1971年   5篇
  1970年   8篇
  1962年   5篇
  1956年   6篇
  1904年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
柿广翅蜡蝉在某些柑桔产区新上升为主要害虫。我们于1986年7月间在宜昌柑桔产区对其卵块分布图式进行了调查,通过10组资料分析,得如下结果:(1)由比较频次法测得卵块在桔园呈负二项或截尾负二项分布。(2)由聚集强度测定方法测得卵块在桔园呈聚集分布图式,其分布的基本成份是疏松的个体群,个体群的分布是聚集的,个体内的分布是随机的。(3)由 IwaoM~*指标法求得个体群大小为1~3株(10组资料平均为1.7株)桔树所占面积。(4)由 Blackich 的λ值测得,卵块密度大于6的9组资料其聚集是由于卵块自身聚集行为习性造成(由成虫产卵行为决定),或某些环境因子作用引起。而有一组密度为2.4的资料,其聚集可能完全由于某些环境条件的作用而引起。  相似文献   
953.
It has been shown that zearalenone disrupts early pregnancy in swine without altering intrauterine content of estradiol 17 beta or progesterone, embryo migration, or estradiol-17 beta synthesis by blastocysts. However, serum concentrations of progesterone were reduced 2 to 3 weeks after mating in gilts that ingested zearalenone. Therefore, progesterone was administered to gilts during early pregnancy to determine whether it could counteract the detrimental actions of zearalenone on embryonic development. Thirty-two crossbred gilts (Hampshire x Chester White x Yorkshire x Duroc) were assigned randomly to a 2 x 2 factorial arrangement of treatments: zearalenone (Z); zearalenone plus progesterone (ZP); progesterone (P); or control (C). From postmating days 4 to 15, Z- and ZP-treated gilts were fed 1 mg of Z/kg of body weight, and P-treated and C gilts were fed ethanol as vehicle in a corn-soybean diet. On postmating days 3 to 15, P- and ZP-treated gilts were injected IM with 100 mg of progesterone, and C and Z-treated gilts were injected with progesterone carrier (15% ethanol, 15% benzyl alcohol, 70% propylene glycol). Blood was collected from gilts by puncture of the jugular vein daily from days 3 to 15, on alternate days from days 17 to 31, and then twice weekly until the end of the experiment. Fetal development was assessed in Z- and ZP-treated gilts on postmating day 47.6 +/- 2.9 by cesarean section and in P-treated and C gilts at slaughter on postmating days 51.2 +/- 3.2. Serum concentrations of progesterone in P-treated gilts were greater on days 7 to 8, 10 to 15, 17, and 19 than in C gilts. Serum concentrations of progesterone were greater on days 8, 10, and 12 in ZP-treated than in C gilts. However, serum concentrations of progesterone were lower in ZP-treated gilts than in C gilts on postmating days 19 to 31.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
954.
AIM: Inflammatory responses play an important role in the post- percutaneous transluminal coronary angioplasty (PTCA) restenosis and has been demonstrated occuring immediately after PTCA. Interleukin-6(IL-6) and tumor necrosis factor-α(TNF-α) are the main inflammatory cytokines. We try to compare the changes in interleukin-6(IL-6) and TNF-α after PTCA in the patients with and without collateral circulation to probe into the pathogenesis of early inflammatory response. METHODS: The extent of myocardial ischemia induced by balloon inflation was quantified by a scoring system referring to the Leaman coronary score. The IL-6、TNF-α levels of coronary heart disease group and control group before and after PTCA are calculated. RESULTS: The concentrations of IL-6 and TNF-α were (9.592±1.847) ng/L and (26.959±1.967) ng/L, respectively, and were significantly increased 4 hours after PTCA. CONCLUSION: IL-6 and TNF-α are sensitive indicators of the early inflammatory response after PTCA. Ischemia scores reflected the extent of ischemia reperfusion injury during PTCA. Collateral circulation decreased the early inflammatory response after PTCA.  相似文献   
955.
家鸡蛋壳组织结构的扫描电镜观察   总被引:4,自引:1,他引:3  
用扫描电子显微技术对家鸡蛋壳结构进行研究的结果,进一步直观形象地丰富了我们在这个领域的知识。  相似文献   
956.
957.
The available literature on necrotic enteritis in broiler chickens is reviewed.

The records of three poultry diagnostic laboratories in Ontario were examined for the years 1969, 1970 and 1971. During this period 855 (7.7%) of 11,076 consignments of broiler chickens examined were diagnosed as necrotic enteritis. The condition was most common in broilers at three weeks of age, with 66% of all cases occurring in chickens between two and four and one half weeks. The disease occurred throughout the year but it was most common during July, August, September and October. Necrotic enteritis often occurred more than once per year on a farm.

  相似文献   
958.
959.
960.
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