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   2322篇
  免费   183篇
  国内免费   96篇
林业   224篇
农学   112篇
基础科学   12篇
  119篇
综合类   970篇
农作物   77篇
水产渔业   259篇
畜牧兽医   567篇
园艺   69篇
植物保护   192篇
  2024年   2篇
  2023年   20篇
  2022年   35篇
  2021年   55篇
  2020年   56篇
  2019年   55篇
  2018年   33篇
  2017年   60篇
  2016年   65篇
  2015年   65篇
  2014年   95篇
  2013年   91篇
  2012年   128篇
  2011年   189篇
  2010年   164篇
  2009年   151篇
  2008年   152篇
  2007年   147篇
  2006年   152篇
  2005年   115篇
  2004年   106篇
  2003年   90篇
  2002年   59篇
  2001年   59篇
  2000年   52篇
  1999年   39篇
  1998年   44篇
  1997年   51篇
  1996年   34篇
  1995年   45篇
  1994年   50篇
  1993年   31篇
  1992年   26篇
  1991年   27篇
  1990年   20篇
  1989年   10篇
  1988年   18篇
  1987年   6篇
  1986年   2篇
  1985年   2篇
排序方式: 共有2601条查询结果,搜索用时 29 毫秒
51.
52.
53.
生物超弱发光的光子成像及其检测方法研究   总被引:1,自引:0,他引:1  
任何有生命的物质,人、动物、植物和微生物等都有一种超弱发光,这是生命体本身所固有的一种属性,而且这种超弱发光的强弱与生命活动能力密切相关,新陈代谢愈旺盛,生命活力愈强,则发光也愈强。为此,介绍了生物超弱发光的基本原理和光子成像探测系统的结构,并且对迄今为止生物超弱发光研究的主要实验结果以及超弱发光的主要检测方法进行了归纳总结。  相似文献   
54.
对Bt毒蛋白不同抗性水平棉铃虫品系的生物学研究   总被引:1,自引:0,他引:1  
崔学芬  夏敬源 《棉花学报》2003,15(3):163-165
用对Bt毒蛋白(Cry1Ac)具有一定抗性水平的安阳品系和相对敏感的新疆品系棉铃虫进行Bt毒蛋白(Cry1Ac)的室内毒力测定结果表明,两品系的LC50值分别为8.7645g·L 1和0.2547g·L 1,前者是后者的34.4倍。用转Bt基因抗虫棉中棉所29和常规棉花品种中棉所35蕾期的倒3叶饲养安阳品系和新疆品系棉铃虫的初孵幼虫(孵化后24h),结果表明:两个棉铃虫品系在取食抗虫棉后的累计校正死亡率在1~2d内差异不明显;新疆品系棉铃虫在转Bt基因抗虫棉上发育的最高龄期为4龄,其比率为6.7%;而安阳品系部分棉铃虫能够在转Bt基因抗虫棉上完成生长发育,其4龄幼虫的比率为45.5%,5、6龄幼虫的比率分别为12.6%和3.8%,有1.6%的幼虫能够正常化蛹;用常规棉棉叶饲养的安阳品系和新疆品系棉铃虫各龄幼虫的发育历期差异不显著,而用转Bt基因抗虫棉棉叶饲养的安阳品系棉铃虫幼虫的发育历期与新疆品系虽然差异不显著,但前者的发育历期均短于后者。  相似文献   
55.
J. H. Heering 《Euphytica》1993,74(1-2):143-148
Summary The reproductive biology of Sesbania sesban, S. goetzei and S. keniensis (Leguminosae; Papilionoideae) was studied. Fifty percent flowering was observed at 102 to 153 days after germination for S. sesban accessions; 96 to 146 days for S. goetzei and 131 to 176 days for S. keniensis accessions. Flowers opened in the afternoon and remained fresh for 2–3 days. Bee species including Xylocopa sp., Apis mellifera, Megachile bituberculata and Chalicodoma sp. visited the flowers. Hand pollination experiments showed that all three species were self and cross compatible. The percentage of fully developed seeds was greater in pods formed after cross pollination compared to self pollination. No evidence was found for stigmatic or stylar self incompatibility. Outcrossing is probably the common method of reproduction under natural conditions, although in isolated trees substantial seed set by selfing might occur. Pod production under natural conditions was 34% for S. sesban; 49% for S. goetzei and 39% for S. keniensis. Considerable variation was found in pod production under open pollination between accessions of the same species. Selective abortion was observed within pods, with more mature seeds formed at the distal end of the pod.  相似文献   
56.
Partial self-compatibility in ‘Tombul’ and ‘Montebello’ hazelnuts   总被引:1,自引:0,他引:1  
Summary Self-pollination of hazelnut (Corylus avellana L.) cultivars in 1988 and 1990 revealed the existence of partial self-compatibility in Tombul and Montebello. Percent cluster set in these cultivars averaged 44 and 20%, respectively, but was less than 10% in 8 other cultivars investigated. Percent cluster set from pollination with Segorbe averaged 62 and 41% in 1988 and 1990, respectively. Self-pollination produced 40% fewer nuts per cluster and twice as many blanks as cross-pollination. All cultivars and selections have an active sporophytic incompatibility system.Evaluation of self-compatibility in seedlings from the cross Montebello × Compton revealed that the partial self-compatibility of the maternal parent was transmitted to some of the progeny. Self-pollination resulted in greater than 10% cluster set in two selections, OSU 41.134 and OSU 43.025, in both years, but only in 1988 in OSU 42.089 and Willamette. Three other selections had very low set in both years. Results of incompatible crosses with standard testers were generally in agreement with those of self-pollination, except that the S2 tester induced greater set on 3 genotypes in 1988 and the S1 tester on 2 genotypes in 1990 than self-pollination. The partial self-compatibility of Montebello, OSU 41.134, and OSU 43.025 appears to be due to a failure of their stigmas to prohibit pollen tube growth in incompatible crosses. There is no evidence of a pollen-part mutation in Montebello, nor is there evidence that partial self-compatibility is due to the interaction of S-alleles, as Barcelona, which has the same alleles as these three genotypes, failed to set nuts in all incompatible crosses.  相似文献   
57.
硼对小麦生殖器官形态及解剖结构的影响   总被引:6,自引:0,他引:6  
用溶液培养方法研究硼对小麦生殖器官形态及解剖结构的影响. 结果表明: (1)缺硼严重影响小麦穗的分化, 在一定施硼范围内, 总小穗数和有效小穗数随硼施用量增加而增多; (2)缺硼严重影响小麦雄蕊发育. 无硼(B0处理)条件下, 少数雄蕊不发育, 多数虽发育, 但体积极小, 造孢细胞有丝分裂阶段出现异常, 细胞内有多核现象, 减数分裂  相似文献   
58.
Summary The breeding system of Abelmoschus species is not well known. Although being self-compatibles allogamy reaches 63%. The aim of the study was to place four Abelmoschus species on the log P/O scale devised by Cruden (1977). On this scale P = pollen grains per anther × anthers per flower and O = ovules production. Pollens and ovules productions were therefore assessed for 68 accessions of two cultivated species, A. esculentus and A. caillei, and two wild, A. manihot and A. moschatus. Extreme log P/O values ranged from 1.69 for the variety Clemson Spineliss (A. esculentus) to 2.94 for ORS 278 (A. manihot). Averages of wild species A. moschatus (2.17) and A. manihot (2.19) indicate facultative autogamy. Averages for cultivated species A. esculentus (2.00) and A. caillei (2.05) suggest more autogamy.  相似文献   
59.
本文以分子生物学研究手段为纲 ,从RFLP、RAPD、ITS等方面 ,综述了国内外在棉花黄萎病菌种内划分及致病力分化上的研究状况及最新进展  相似文献   
60.
北沙柳属杨柳科柳属植物,具有萌蘖力强,耐旱、耐盐碱和抗风沙的特点,是中国西北地区固沙造林的主要树种之一,兼具生态效益、经济效益和社会效益。我们综述了国内外近年来北沙柳的相关研究成果包括生长繁殖、生理生态特征、与真菌共生作用、防风固沙、分子生物学及产业化开发与利用,并对未来发展前景做出展望,提出优良种质资源收集、分子定向育种和资源合理开发等建议,旨在为北沙柳的种质资源库管理、资源保护和合理开发应用提供科学依据。  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