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   9797篇
  免费   556篇
  国内免费   1019篇
林业   777篇
农学   1000篇
基础科学   174篇
  1334篇
综合类   4099篇
农作物   758篇
水产渔业   892篇
畜牧兽医   1238篇
园艺   398篇
植物保护   702篇
  2024年   24篇
  2023年   137篇
  2022年   184篇
  2021年   234篇
  2020年   219篇
  2019年   280篇
  2018年   207篇
  2017年   342篇
  2016年   456篇
  2015年   383篇
  2014年   338篇
  2013年   494篇
  2012年   764篇
  2011年   540篇
  2010年   518篇
  2009年   534篇
  2008年   558篇
  2007年   716篇
  2006年   656篇
  2005年   552篇
  2004年   468篇
  2003年   336篇
  2002年   292篇
  2001年   254篇
  2000年   224篇
  1999年   182篇
  1998年   184篇
  1997年   180篇
  1996年   143篇
  1995年   146篇
  1994年   94篇
  1993年   137篇
  1992年   130篇
  1991年   91篇
  1990年   82篇
  1989年   70篇
  1988年   56篇
  1987年   30篇
  1986年   68篇
  1985年   30篇
  1984年   13篇
  1983年   5篇
  1982年   3篇
  1981年   3篇
  1980年   4篇
  1979年   3篇
  1976年   2篇
  1975年   2篇
  1956年   2篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
851.
褐潮土长期定位不同施肥制度土壤生产功能演化研究   总被引:16,自引:1,他引:16  
通过14年长期定位试验研究了褐潮土不同施肥制度对土壤生产功能、产量可持续性指数及农学效率的影响。结果表明,N、P为褐潮土作物高产的主要限制因子,14年产量平均,NPK比CK、N、NK、PK分别增产459%、386%、280%、205%(小麦)和154%、108%、87%、78%(玉米);NPK+M(NPK配施厩肥)比NPK平均增产12%,NPK+S(NPK加秸秆)与NPK产量相当。NPK及NPK配施有机肥(包括厩肥和秸秆)处理的小麦、玉米产量可持续性指数高于N、P不均衡施用处理。化肥肥效因作物种类、施肥组合而不同,N肥单施时小麦和玉米N的农学效率降低,而NPK配施时N的农学效率有上升趋势,平均分别为16 kg/kg N(小麦)和14 kg/kg N(玉米);磷肥肥效具有短期的叠加效应,P的农学效率小麦大于玉米,种植10年后P的农学效率最高可达最初的4.5~7倍;K的农学效率在试验进行十年后NK处理平均为负值,同期NPK处理中小麦K的农学效率却急剧增加,K成为作物高产的限制因素;有机肥对小麦和玉米的农学效率分别为21 kg/t和25 kg/t,秸秆对小麦和玉米的农学效率分别为负值和37 kg/t。NPK均衡施肥能提高土壤有机质、全N、全P、速效N、速效P等肥力指标;NPK配施有机肥能加快土壤有机质和N、P、K养分的积累;NPK不均衡施肥导致土壤中此种营养元素的耗竭。  相似文献   
852.
CA贮藏对新鲜石刁柏的影响   总被引:14,自引:0,他引:14  
金同铭 《华北农学报》1992,7(3):117-122
用9种不同的CA条件与低温空气贮藏进行比较,结果证明用CA贮藏法进行石刁柏的贮藏保鲜是可行的。在设定的10个试验区中,当O_2浓度保持在21%的前提下,适当提高CO_2的浓度可提高贮藏效果。以21%O_2,30%CO:_2的贮藏条件保鲜效果较好。当CO_2浓度为0%时,O_2的浓度在1~0%之间保鲜效果最好。在10个试验区中,以空气条件下贮藏效果最差。  相似文献   
853.
用改进的高盐低pH法分离和纯化棉花叶绿体及叶绿体DNA   总被引:2,自引:0,他引:2  
报道了用改进的高盐低pH法分离和纯化棉花叶绿体及叶绿体DNA的实验过程,即先在高盐(离子强度)介质下,通过pH值变换,多次洗涤的方法去除叶绿体表面的静电附着杂质,得到纯净的叶绿体;然后氯仿抽提纯化DNA;最后采用界面针挑法得到高纯度的cpDNA。实验过程中针对棉花的特点,采用PVP排除棉酚和丹宁的干扰,用DIECA抑制酚氧化酶活性,并对实验细节作了较大改进。得到的DNA可满足酶切、PCR等分子生物学分析。  相似文献   
854.
R. Götz  W. Friedt 《Plant Breeding》1993,111(2):125-131
Barley yellow mosaic disease is caused by several viruses, i.e. barley yellow mosaic virus (BaYMV), barley mild mosaic virus (BaMMV) and BaYMV-2. The reaction of different barley germplasms to the barley mosaic viruses was studied in field and greenhouse experiments. The results show a complex situation; some varieties are resistant to all the viruses, while others are resistant to one or two of them only. Crosses between different barley germplasms were earned out in order to test whether genetic diversity of resistance against mosaic viruses does exist, particularly, BaMMV. A total of 45 foreign barley varieties were crossed to German cultivars carrying the resistance gene ym4. In F2 of 27 crosses, no segregation could be detected, leading to the conclusion that the resistance genes of the foreign parents are allelic with ym4 e.g. Ym1 (‘Mokusekko 3’) and Ym2 (‘Mihori Hadaka 3’). A total of 18 crosses segregated in F2 indicating that foreign parents, like ‘Chikurin Ibaraki 1’, ‘Iwate Omugi 1’, and “Anson Barley”, carry resistance genes different from the gene of German cultivars, e.g. ‘Asorbia’ or ‘Franka’. By means of statistical evaluation (Chi2-test), the observed segregation ratios were analyzed in order to obtain significant information on the heredity of resistance. All the resistance genes described here as being different from the gene ym4, act recessively. Most of the exotic varieties seem to carry only one resistance gene. In a few cases, more than one gene may be present.  相似文献   
855.
分子标记辅助选育抗稻白叶枯病的低温敏核不育系3178S   总被引:2,自引:0,他引:2  
本研究以IRBB21为Xa21基因供体,籼型低温敏不育系399S为低温核不育系基因供体,采用杂交和回交方法,逐代用分子标记检测手段,导入广谱抗白叶枯病基因Xa21和低温敏核不育系基因,聚合双亲的有利性状,育成抗白叶枯病的籼型低温敏核不育系3178S,其抗性达到了IRBB21的抗性水平,且保持了399S稳定的育性和双亲的优良经济性状。  相似文献   
856.
本文对GM(1,1)模型参数估计方法进行了改进和简化,据此组建了苏北沿海棉区棉花烂铃病流行趋势超长期预报模型,经1980~1989年回报和1990~1995年预报,棉花烂铃病流行轻、重发生的符合率达100%;1996~2000年预报结果为1998年和2000年为重发生,其余3a为轻发生。这将为棉花烂铃病的研究和防治规划提供科学决策依据,也为GM(1,1)模型能在基层病虫测报站推广应用创造了条件。  相似文献   
857.
The AFLP (amplified fragment length polymorphism) technique has been applied in establishing an extended linkage map of sugar beet. A total of 120 AFLPs were integrated into an existing linkage map based on RFLP markers. Four primer combinations yielded between 19 and 40 polymorphic bands in an F2 population consisting of 94 plants. The AFLP loci were evenly distributed over the nine linkage groups, with the exception of linkage group V where the number of AFLPs was significantly low. The AFLPs were found to be reproducible even against the background of different combinations of Taq DNA polymerases and buffers. However, the quantity of higher molecular weight fragments (>400 bp) was reduced when using plant DNA of poor quality as a template. The results of these experiments are discussed, together with possible applications of AFLPs in sugar beet breeding.  相似文献   
858.
魔芋试管微球茎成熟度对其储藏及萌发率的影响   总被引:2,自引:0,他引:2  
种子在母体植株上的干燥过程是种子完成从发育到萌发的一个重要转换点。魔芋组织培养中诱导试管微球茎过程中,在色泽上有1个明显的变化过程。本实验将这个过程分为3个阶段,对不同采收时期的微球茎进行储藏及萌发研究,结果表明,不同采收期的微球茎,储藏后的萌发率具有较大的差异,而且这种差异与魔芋种具有较大的相关性,这种差异与其保水性能有关。同时对试管微球茎收获度对储藏后萌发率影响的机制进行了初步的探讨。  相似文献   
859.
self-(in)compatibility almond genotypes: A review   总被引:1,自引:0,他引:1  
To compile self-(in)compatibility almond genotypes, a review of 133 commercial cultivars of wide geographical origin was made. The information gathered from own and mainly published work will be useful for both grower's cultivar choice when planting and for breeder's cross design when planning. The almond S genotypes compiled were identified using five different methods: biological (pollination tests in the field and in the laboratory) and molecular (RNases, PCR and sequencing). In most cases, genotypes were assigned after combining more than one technique. Cultivars were classified into three categories: self-incompatible (99), self-compatible (16) and doubtful self-incompatible (18). The database is divided in 9 fields (name, origin, parentage, obtention year (crossing, selection or release), S genotype, technique used, reference, consensus genotype, and cross incompatibility group). A study of the 27 S alleles already identified and their geographical distribution within the cultivated almond is also presented. The study was divided into cultivars of known and unknown parentage and the distribution of S alleles frequencies was uneven among the 133 cultivars. S allele frequencies are related to geographical origin. Some alleles (S 1, S 5, S 7 and S 8) are more frequently observed than the others among cultivars of both known and unknown parentage. In the cultivated almond, the S f allele is only found in the Puglia region, Italy. The S f frequency is three times higher in cultivars released from breeding programmes than in cultivars selected by growers. From the 351 resulting possible genotypes by combination of the 27 S alleles identified only 20 CIG (0-XIX) have been established, which represents a small fraction of the whole genetic diversity of this polymorphic gene in almond.  相似文献   
860.
O. Leoni    S. Cinti    N. Aliano  E. D. Tittonel 《Plant Breeding》2003,122(6):517-520
Crambe abyssinica is becoming a reliable source of industrial oil with good technical characteristics because of its high erucic acid content. The possibility of using the industrial defatted meal of crambe as a feed could further promote the interest in this crop, but is prevented by the high glucosinolate content (70‐150 μmol/g). Therefore the possibility of reducing this parameter by selection was evaluated and a search for a new quick analytical procedure begun. When hydrolysed by myrosinase (thioglucoside glucohydrolase EC 3.2.3.1.), at pH 6.5 or higher, epiprogoitrin, the main glucosinolate in crambe seed (>90% of total glucosinolates), gives (5R)‐5‐vinyl‐1,3‐oxazolidine‐2‐thione quantitatively. The latter can be easily estimated by high‐performance liquid chromatography. This is the background of the proposed analytical procedure that permits rapid analysis of about 100 samples per day using about 25 mg of crambe meal (five seeds) for assay. The method can also be used to select for glucosinolate content in rapeseed and, probably with some adjustment, all crops that have a 2‐hydroxy‐glucosinolate as the main glucosinolate.  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