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   3142篇
  免费   157篇
  国内免费   13篇
林业   235篇
农学   172篇
基础科学   51篇
  662篇
综合类   217篇
农作物   398篇
水产渔业   308篇
畜牧兽医   811篇
园艺   98篇
植物保护   360篇
  2023年   33篇
  2022年   107篇
  2021年   131篇
  2020年   157篇
  2019年   174篇
  2018年   182篇
  2017年   173篇
  2016年   176篇
  2015年   115篇
  2014年   132篇
  2013年   307篇
  2012年   180篇
  2011年   216篇
  2010年   146篇
  2009年   89篇
  2008年   173篇
  2007年   104篇
  2006年   72篇
  2005年   64篇
  2004年   65篇
  2003年   58篇
  2002年   45篇
  2001年   27篇
  2000年   38篇
  1999年   26篇
  1998年   17篇
  1997年   16篇
  1996年   23篇
  1995年   17篇
  1994年   10篇
  1993年   10篇
  1992年   10篇
  1991年   16篇
  1990年   15篇
  1989年   18篇
  1988年   11篇
  1987年   15篇
  1986年   10篇
  1985年   14篇
  1984年   15篇
  1983年   10篇
  1981年   10篇
  1979年   10篇
  1975年   10篇
  1973年   7篇
  1972年   6篇
  1971年   8篇
  1970年   5篇
  1969年   5篇
  1967年   5篇
排序方式: 共有3312条查询结果,搜索用时 15 毫秒
991.
A field study was performed to assess the drug residue level in edible tissues after a therapeutic application of the synthetic glucocorticoids dexamethasone and flumethasone. Three diseased calves were injected intramuscularly with a commercial batch of dexamethasone esters and slaughtered 72 h after treatment. Another three calves were injected intramuscularly with an aqueous flumethasone preparation and slaughtered 24 h later. Residues of synthetic glucocorticoids in liver, muscle, kidney, and urine were assessed by competitive enzyme immunoassay. All dexamethasone concentrations exceeded the maximal residue level of 0.75 microg/kg in muscle and kidney and 2 microg/kg in the liver. The presence of both dexamethasone and flumethasone in the liver was confirmed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). These results indicate that liver tissue provides a suitable matrix to monitor the presence of illegal residues of synthetic glucocorticoids in slaughtered animals.  相似文献   
992.
R. C. Sharma    E. Duveiller    F. Ahmed    B. Arun    D. Bhandari    M. R. Bhatta    R. Chand    P. C. P. Chaurasiya    D. B. Gharti    M. H. Hossain    A. K. Joshi    B. N. Mahto    P. K. Malaker    M. A. Reza    M. Rahman    M. A. Samad    M. A. Shaheed    A. B. Siddique    A. K. Singh    K. P. Singh    R. N. Singh  S. P. Singh 《Plant Breeding》2004,123(6):520-524
Helminthosporium leaf blight (HLB) is the most important disease constraint to wheat (Triticum aestivum L.) cultivation in the eastern Gangetic Plains of South Asia. A Helminthosporium Monitoring Nursery (HMN) including potential adapted and exotic sources of HLB resistance was developed in Bangladesh, India and Nepal to assess the stability of genetic resistance across locations. The 8th, 9th and 10th HMN assessed the HLB resistance and agronomic traits of 17 wheat genotypes across 20 environments of Bangladesh, India and Nepal in the 1999‐2000, 2000‐2001 and 2001‐2002 cropping seasons, respectively. The area under the disease progress curve (AUDPC) for HLB, grain yield, thousand‐kernel weight (TKW), days to heading, days to maturity, and plant height were examined. The 17 genotypes showed a range of variability for disease and agronomic characters. Disease severity (AUDPC) differed in the 3 years and showed the highest values in 2002. The increase in AUDPC in 2002 caused the lowest grain yield, with an average 18% reduction due to HLB. A few genotypes (SW 89‐5422, Yangmai‐6 and Ning 8201) appeared to have stable HLB resistance across environments. However, most of the higher‐yielding genotypes, except BL 1883, were unstable. The results suggest that careful selection of HLB resistance with acceptable grain yield, TKW and plant height may be possible using the wheat genotypes included in the HMN.  相似文献   
993.
Summary Four newly detected accessions of wild barley (Hordeum vulgare ssp. spontaneum) resistant to powdery mildew caused by Blumeria graminis f. sp. hordei were studied with the aim of finding the number of genes/loci conferring the resistance of individual accessions, the type of inheritance of the genes and their relationships to the Mla locus. F2 populations after crosses between the winter variety ‘Tiffany’ and four wild barley accessions and use of microsatellite DNA markers were focused on the identification of individual resistance genes/loci by means of their chromosomal locations. In PI466495, one locus conferring powdery mildew resistance was identified in highly significant linkage with the marker Bmac0213. This location is consistent with the known locus Mla on chromosome 1HS. In the other three accessions the resistance was determined by two independent loci. In PI466197, PI466297 and PI466461, one locus was identified on chromosome 1HS and three new loci were revealed on chromosomes 2HS (highly significant linkage with Bmac0134), 7HS (highly significant linkage with Bmag0021) and 7HL (significant linkage with EBmac0755). Our prospective aim is identification of further linked DNA markers and the exact location of the resistance genes on the barley chromosomes.  相似文献   
994.
Mehmet Ali Sudupak 《Euphytica》2004,135(2):229-238
Intra and inter-species ISSR variation and use of ISSR markers in determination of genetic relationship were investigated in an accession collection representing twoperennial and six annual Cicerspecies. Screening of Ciceraccessions with SSR primers revealed highly reproducible amplicon profiles with relatively high multiplex ratios. Many of the primers generated amplicon profiles with which not only the differences among species can readily be identified, but also polymorphisms within species could be detected more efficiently. PCR products at 150 gel positions detected using six SSR primers in Cicer accessions were treated as dominant DNA markers and utilized to compute the distances among accessions and species. Cluster analysis of accessions and species revealed groupings that corroborate our previous studies of relationships based on allozyme and AFLP analysis. Consistent with the AFLP analysis carried out in the same accession collection, ISSR-based groupings indicated that perennial C. incisumis genetically close to the annuals of the second crossability group (C. pinnatifidum,C. bijugum, C. judaicum) while C. reticulatum is the closest wild species to the cultivated chickpea. ISSR-based variation estimates were relatively higher when compared to previous estimates computed from RAPD and AFLP data. Technically, ISSR analysis combines the PCR-based targeting of microsatellite-associated polymorphisms with no prior sequence requirement and stringent PCR conditions. Similarly, when compared to AFLP analysis, it is less technically demanding allowing to survey polymorphic loci in the genome. Thus, ISSR-PCR technology is a reliable, fast, and cost-effective marker system that can be used to study genetic variation and genetic relationships in the genusCicer. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
995.
‘Ogura radish’, a cytoplasmic genetic male sterile line, was crossed with four local and three Japanese cultivars to identify maintainer lines. Out of seven F1 families, one cross involving a local cultivar, Aushi, produced 100% male sterile (MS) progeny. The crosses involving the other two local cultivars, Tangail Local and Kuni, produced about 90% MS progeny, indicating the presence of maintainer gene(s) for male sterility. The fourth local cultivar, Tasaki, produced 100% male fertile (MF) progeny. All three exotic cultivars appeared to possess the chromosomal gene(s) for controlling the male sterility. In BC1, BC2 and BC3 generations, segregation of MS plants were more frequent when ‘Aushi’ was used as recurrent parent. The expression of male sterility was not affected by seasonal influences. Thus the local cultivar ‘Aushi’ may be used as maintainer line for ‘Ogura radish’. To produce hybrid seed, ‘Tasaki’ can be used as pollinator line as it exhibit high heterosis with ‘Aushi’. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
996.
For studying genetic diversity caused byselection for adaptation and end-use, 17microsatellites (SSR), representative ofthe barley genome, were used in 26 barley(Hordeum vulgare L.) accessions andcultivars in Tunisia. Theaccessions/cultivars originate fromdifferent geographic regions and are ofdifferent end-use. For the 15 polymorphicSSR, the mean number of alleles per locuswas 3.6 and the average polymorphisminformation content was 0.45. Clusteranalysis based on SSR data and onmorphological data clearly differentiatethe genotypes according to their type(local landraces vs. varieties), row-numberand end-use. The correlation between bothdiversity measures was highly significant(r = 0.25, p<10-5) and thecorrespondence between the clustering basedon SSR and morphological data wasrelatively good. Our results show the largegenetic diversity of the Tunisian barleycultivars and the association of thisdiversity with adaptation traits.  相似文献   
997.
S. M. Ali  B. Sharma  M. J. Ambrose 《Euphytica》1993,73(1-2):115-126
The economic importance and current progress made in studies of the host-parasite relationship and identification of sources of resistance and breeding strategies of some important biotic diseases of pea are reviewed in this paper. The root rot complex caused by Rhizoctonia solani, Fusarium solani, Aphanomyces euteiches, Pythium ultimum and Fusarium oxysporum f. sp. pisi, race 1 and 2 has been reported from all commercial pea growing areas of the world. Adequate sources of resistance have been identified and there has been impressive success in the control of the Fusarium wilt pathogen following the introduction of wilt-resistant cultivars. Leaf and stem diseases of pea caused by the Ascochyta complex, Peronospora viciae and Erysiphe pisi are prevalent in most temperate pea growing regions of the world. Several sources of resistance are available, some of which are surprisingly durable. The biochemical genetic parameters of phenolic content used for assaying resistance to Erysiphe pisi offers an alternative method of evaluating breeding material. Wild relatives of pea (Pisum fulvum and P. humile) are valuable additional sources of genetic variation and provide good sources of resistance to pests and diseases. In temperate rainfed pea growing areas of southern Australia, pea seed yield is more closely related to dry matter production than harvest index. Tall and leafy cultivars proved more productive than afila types.  相似文献   
998.
Tropical Animal Health and Production - This study aimed to investigate the interactive effect of dietary threonine (i.e., 100, 110, and 120%) and low and high dietary potassium (i.e., 0.85 and...  相似文献   
999.
Tropical Animal Health and Production - Separation of autosomal and sex-linked direct additive genetic effects has significant role in sheep breeding programs. Hence, this study was conducted to...  相似文献   
1000.

Bovine uterine torsion refers to the rotation of the gravid uterus around its longitudinal axis. It is the dominant cause of dystocia in buffaloes. A total of two hundred and seventeen dystocia’s Egyptian buffaloes were examined, and another twenty were apparently normal at the full term (healthy pregnant group). From the dystocia’s buffaloes, twenty-three percentage (n = 50) was uterine torsion after gynecology inspection at presentation (Ut group) and 5 days after the manual correction (Utc group). The buffaloes with uterine torsion exhibited loss of appetite, constipation, colic, and straining. The incidence of torsion was mostly at first parity that accounting for 50% of cases. Regarding to the pregnancy stage, torsion mostly occurred at full term, where it primarily occurred in buffaloes at 3 years of age. Right-sided torsion ensued in 90% of all cases. The survival rate of the pregnant buffaloes was 90% (45 buffaloes), and 10% (5 buffaloes) was directed to the culling. Regarding to the fetal survival outcome, 30% of fetuses was survived where the other 70% was died. The hematological results denoted leucocytosis in Ut and Utc groups that attributed to neutrophilia, monocytosis, and eosinophilia. Biochemical assessments were denoted an augments in the levels of serum AST, LDH, CPK, creatinine, blood urea nitrogen, progesterone, cortisol, MDA, NO, TAC, blood lactate (bLac), TNF-α, and IL-6. Where there were a non significant fluctuations in the ALT, GGT, calcium, and phosphorus levels in the torsion cases. The significant declines in 17-β-oestradiol, total proteins, albumin, magnesium, and GSH levels in the dams suffering from Ut were observed. The robust elevations in AST (156 ± 3.47) and bLac (16.12 ± 0.18) with severe hypomagnesaemia (2.69 ± 0.15) were evident in 10% of the torsion cases that directed to the culling. This can conclude that robust elevations in AST and bLac with severe hypomagnesaemia are factors denoting a poor prognosis for uterine torsion in the buffaloes.

  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