全文获取类型
收费全文 | 22069篇 |
免费 | 1004篇 |
国内免费 | 2213篇 |
专业分类
林业 | 1057篇 |
农学 | 1859篇 |
基础科学 | 380篇 |
4913篇 | |
综合类 | 7812篇 |
农作物 | 1468篇 |
水产渔业 | 791篇 |
畜牧兽医 | 4656篇 |
园艺 | 1463篇 |
植物保护 | 887篇 |
出版年
2024年 | 76篇 |
2023年 | 306篇 |
2022年 | 532篇 |
2021年 | 758篇 |
2020年 | 741篇 |
2019年 | 846篇 |
2018年 | 595篇 |
2017年 | 934篇 |
2016年 | 1162篇 |
2015年 | 1031篇 |
2014年 | 1141篇 |
2013年 | 1521篇 |
2012年 | 1701篇 |
2011年 | 1718篇 |
2010年 | 1498篇 |
2009年 | 1499篇 |
2008年 | 1266篇 |
2007年 | 1454篇 |
2006年 | 1219篇 |
2005年 | 874篇 |
2004年 | 708篇 |
2003年 | 578篇 |
2002年 | 417篇 |
2001年 | 342篇 |
2000年 | 360篇 |
1999年 | 289篇 |
1998年 | 200篇 |
1997年 | 212篇 |
1996年 | 218篇 |
1995年 | 171篇 |
1994年 | 126篇 |
1993年 | 142篇 |
1992年 | 130篇 |
1991年 | 103篇 |
1990年 | 92篇 |
1989年 | 80篇 |
1988年 | 63篇 |
1987年 | 45篇 |
1986年 | 37篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1962年 | 4篇 |
1956年 | 9篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
41.
拓扑简化可以为渐进网格带来更好的效果,但目前几乎所有的渐进网格方法都不支持拓扑简化,而且edge collapse和vertex split操作有时会产生非流形.针对这些问题,提出了基于图形旋转系统的渐进网格法.以基于图形旋转系统的数据结构和操作实现了渐进网格,用图形旋转系统的操作集合构建了edge collapse和vertex split操作.在此基础上,通过扩展新操作即可进行任意拓扑变化,从而实现拓扑简化, 相似文献
42.
优质籼型不育系Q2A的选育 总被引:7,自引:3,他引:4
Q2A是重庆市农业科学研究所和重庆市种子公司用金23B×中九B的F2代与58B×Ⅱ-32B的F2代杂交,再用复交F2代与珍汕97A杂交引入野败型胞质育成的一个优质籼型三系不育系,2003年7月通过重庆市科学技术委员会组织的技术鉴定.该不育系异交习性好;可恢性好,配合力强;米质优(12项测试指标中有7项达部颁一级优质米标准,5项达二级标准);苗瘟3级,叶瘟3级,颈瘟7级,对苗瘟和叶瘟表现为中抗,颈瘟感病.其与成恢047配组育成的优质杂交中籼新组合Q优5号米质优,产量高,抗稻瘟病,2003年12月通过重庆市农作物品种审定. 相似文献
43.
试验通过不同浓度的Na2B4O7在改变PDA培养基及棉子壳一木屑培养基的试验,测定了其对毛木耳菌丝生长的影响。结果表明:在200mg/kg浓度下促进作用最为显著,而其浓度超过400 mg/kg时对菌丝有强烈的抑制作用。 相似文献
44.
45.
Two-year field trials with winter wheat cultivars Batis and Toronto were conducted in Southern Bavaria, Germany, to investigate the possible causes of cultivar differences in response to N supply varying in total amount and time of application. Cultivar-related differences in grain yields were observed in treatments with low and medium N supply. High doses of N supply resulted in grain yield adjustment or grain yield advantage for cv. Toronto. The results of this study revealed a consistent, genotypic pattern in response to N fertilization in spite of strong seasonal effects. Systematic modifications in canopy growth rates in response to N supply were of particular relevance and a main factor for differences in tillering intensity resulting in modified stand densities. In the present study, cultivar differences in spike development and interactions with N supply related more to abortion than to initiation processes for number of spikelets and number of flowers per spikelet. High grain density (grains per m2) of cv. Toronto was evident during reproduction stages even under conditions of medium N supply. However, decreased growth rates during the later part of grain filling in combination with low 1000 grain weight, which was barely modified by N fertilization, allowed only partial utilization of this potential. It is assumed that sink limitations were of particular relevance for grain yield development in cv. Toronto, while cv. Batis combined a less intense response to N supply with more stability in the development of grain yield components. 相似文献
46.
本文用离子选择电极法测定了N,N—二甲基膦酸基甘氨酸(NBPG)与银、镉、汞的配合物组成和稳定常数。结果表明,NBPG与Ag~ 、Cd~(2 )、Hg~(2 )均生成组成为1:1的多齿质子型配合物。其lgK_稳值分别为:AgL5.28、CdH_3L3.63、CdH_2L5.16、CdHL7.30、CdL11.56、HgH_3L6.06、HgH_2L7.55、HgHL8.24、HgL12.58。 相似文献
47.
2型猪链球菌的血清学鉴定 总被引:41,自引:0,他引:41
本试验首次证实了2型猪链球菌在我国的存在,采用玻片凝集、琼脂扩散及毛细管沉淀等3项试验,对1990年以来广东某猪场断奶仔猪暴发流行的败血症、脑膜炎及关节炎病猪中分离的15株链球菌进行了血清学鉴定。结果表明:15株链球菌均为2型猪链球菌;用高压法提取抗原进行沉淀反应,其结果比酸热法提取抗原具有简便、敏感、特异性强的特点。 相似文献
48.
INTRODUCTIONIntheworldoftoday,theglobalclimatechangeanditsinfluenceonecologyhavebe-comeaveryimportantproblem,towhichmanyscientists,governnentleadersandordinarypcoplepaycloseattentionI1-'].Inl979,theWorldClimateResearchProgram(WCP)waslaiddowninthefirstworldclimatemeeting.lnl99(),thesecondworldclimatemeetingwasconvcl1edinGencva,andalltl1eexpertsagreedthattheglobalwarmlngwillbeextremelyseriousdisasterthananynatUralcalamityever.Attl1eMectingof"WorldEnvironmentandDevelopment,"holdinBrazil… 相似文献
49.
G. Jager H. Velvis 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(4):467-478
The position of plants withRhizoctonia solani sclerotia (black scurf) on progeny tubers was mapped for an experimental field at Haren where potatoes were grown continuously and in rotation with other crops for five successive years, and for another field at Borgercompagnie with a 12 frequency of potatoes during three potato crops. Initially, the distribution of plants with black scurf on both fields was rather dense and homogeneous. In the following years the distribution became heterogeneous and patchy. The local decline ofR. solani AG 3 (the common potato pathogen) in Haren was apparently caused by an unknown factor selectively suppressingR. solani AG 3, while simultaneouslyR. solani AG 5 increased in mass. This AG 5 type proved to be an inferior competitor of AG 3 on the potato plant in a laboratory experiment. The specificR. solani antagonistVerticillium biguttatum did not play a role. A similar factor could have reduced the formation of black scurf in the experimental field at Borgercompagnie, whereV. biguttatum was also too infrequent to account for the decline.R. solani AG 5 was not present here and could not indicate the presence of a selective factor against AG 3. 相似文献
50.