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   883篇
  免费   43篇
  国内免费   2篇
林业   76篇
农学   66篇
基础科学   15篇
  254篇
综合类   51篇
农作物   102篇
水产渔业   70篇
畜牧兽医   213篇
园艺   16篇
植物保护   65篇
  2023年   16篇
  2022年   21篇
  2021年   29篇
  2020年   47篇
  2019年   50篇
  2018年   52篇
  2017年   60篇
  2016年   53篇
  2015年   23篇
  2014年   37篇
  2013年   99篇
  2012年   56篇
  2011年   60篇
  2010年   40篇
  2009年   36篇
  2008年   34篇
  2007年   22篇
  2006年   16篇
  2005年   12篇
  2004年   11篇
  2003年   13篇
  2002年   15篇
  2001年   15篇
  2000年   15篇
  1999年   8篇
  1998年   6篇
  1997年   4篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   7篇
  1990年   7篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1986年   3篇
  1985年   4篇
  1980年   5篇
  1978年   2篇
  1977年   2篇
  1975年   1篇
  1973年   1篇
  1971年   2篇
  1970年   1篇
  1968年   1篇
  1960年   1篇
  1959年   3篇
  1957年   2篇
排序方式: 共有928条查询结果,搜索用时 15 毫秒
81.
The present study was conducted to screen Kashmir valley sheep with history of prolificacy for the presence of FecB mutation. Forced polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) and single strand conformation polymorphism (SSCP) techniques were employed to detect any polymorphism present in bone morphogenetic protein receptor type 1B (BMPR1B) gene. Further, it was aimed at introgressing the FecB mutation into nonprolific noncarrier sheep. A 140-bp fragment of BMPR1B gene was amplified from isolated genomic DNA and subjected to forced RFLP with restriction enzyme AvaII. Three different RFLP patterns were identified. SSCP analysis showed one-to-one correspondence with RFLP patterns. Sequencing of the samples showing different patterns revealed that the wild (+) and mutant (B) alleles were different by a single nucleotide substitution in the form of A109G from wild to mutant allele. It led to change in amino acid from Glutamine (Q) to Arginine (R) from wild to mutant allele. The mutation was only detected in NARI-Suwarna and their crosses; all Kashmir valley sheep with prolific history lacked it. The + allele was abundant in the studied population. The FecB mutation was introgressed in nonprolific noncarrier sheep by crossing ewes with NARI-Suwarna rams possessing the mutation. First generation crossing produced heterozygous (B+) progeny. Some of the F1 heterozygous ewes gave birth to twins when mated to unrelated NARI-Suwarna rams. It showed that FecB mutation was successfully expressing in those crosses.  相似文献   
82.
A survey was carried in North Khorasan Province, Iran in 2010–2011, designed to identify Theileria spp. infections of both sheep and ticks. The tick species were also examined. Ninety sheep from different flocks were clinically examined, and blood samples and ixodid ticks were collected. Light microscopy of blood smears revealed Theileria spp. infection in 37 (41.1 %), while 74 (82.2 %) of blood samples were positive using semi-nested PCR. Theileria ovis, Theileria lestoquardi, and mixed infection were detected in 63/90 (70 %), 5/90 (5.5 %), and 6/90 (6.6 %) of samples, respectively. Of the 434 ticks that were collected, the most prevalent species was Rhipicephalus turanicus (69.3 %) followed by Hyalomma marginatum turanicum (18.4 %), Dermacentor marginatus (6.4 %), and Rhipicephalus bursa (5.7 %). The ticks were separated into 42 tick pools, and the salivary glands were dissected out in 0.85 % (w/v) saline under a stereomicroscope and examined using semi-nested PCR. Three pools of H. marginatum turanicum salivary glands were infected with T. ovis and T. lestoquardi, and one pool of R. turanicus was infected with T. ovis. Based on these results, it is concluded that the prevalence of T. ovis is higher than T. lestoquardi and that H. marginatum turanicum and R. turanicus are likely vectors of T. lestoquardi and T. ovis in this area.  相似文献   
83.
The anthelmintic potentials of the aqueous and methanol extracts of Euphorbia helioscopia were investigated. In folklore medicine, E. helioscopia (Euphorbiaceae) is used in the treatment of various gastrointestinal ailments and diseases. A worm motility inhibition (WMI) assay and egg hatch assay (EHA) were used for in vitro assessment, and a faecal egg count reduction (FECR) assay was used for an in vivo study. The in vitro study revealed anthelmintic effects of crude methanolic extracts of E. helioscopia on live Haemonchus contortus worms as evident from their paralysis and/or death at 8h after exposure, different concentrations (12.5mgml(-1), 25mgml(-1) and 50mgml(-1)) of aqueous and methanolic extracts were used against H. contortus which exhibited dose-dependent anthelmintic effects on H. contortus. Aqueous and methanolic extracts of aerial parts (stem, leaves and flowers) of E. helioscopia were found to have very low percent inhibitory egg hatching as compared to levamisole. It is concluded that the entire plant of E. helioscopia possesses significant anthelmintic activity and could be a potential alternative for treating cases of helminth infections in ruminants.  相似文献   
84.
Various plants are well known for their insecticidal activity and their use was maintained for millennia throughout all the agricultural regions of the world. In a current context, the use of Botanical insecticides represents one of the best alternatives to chemicals for the development of environmental-friendly strategies for stored grain pest control. Datura alba Nees is a plant found extensively in the warmer regions of the world and it is used as a medicinal plant. This study aims to assess the contact toxicity and the trans-generational effect of D.?alba leaf extract (DLE) against two important insect pests on stored rice, Trogoderma granarium and Sitophilus oryzae, under laboratory conditions. Filter papers were soaked in three DLE concentration solutions and in two control treatments: water and acetone. The survivor specimens (F0) were transferred to a new untreated feeding substrate and the population build up of the two following generations (F1 and F2) were counted after 30 and 60?days, respectively. The highest DLE concentration (2.5?%) induced the significantly highest mortality with 33.5 and 45?% mortality in T.?granarium and S.?oryzae after 7?days of exposure, respectively. The DLE long-term effect toward both tested species was also proved by the high demographic decrease in the F2 generations, when compared to control groups. This study is the first step toward establishing a scientific basis for the effective application of D.?alba plant materials as biorational tools to control stored grain pests.  相似文献   
85.
Glanders is a highly infectious and zoonotic disease of solipeds caused by Burkholderia mallei. Progressive loss of efficiency and fatal outcome resulted in massive economic losses, which forced veterinary authorities throughout the world to implement disease control measures; these measures included mass testing using the complement fixation test and/or malleinization, and the culling of positives. This led to the eradication of glanders from Western Europe and North America in the 1950s. However, in the last decade, the number of outbreaks in Asia and South America increased steadily, and glanders regained the status of a re-emerging transboundary disease. Pakistan has been an endemic country for the past 120 years, but concise data on the presence of disease are not available. A total of 533 serum samples were collected from draught equines, a suspected risk group for glanders, from various districts of Punjab in Pakistan. The complement fixation test and the highly sensitive Western blot technique were used for serodiagnosis. No animal (horse, mule, and donkey) was found to be positive for infection. Glanders seems to be restricted to remote, sporadic pockets of endemicity and may cause outbreaks after being introduced into naive populations by (asymptomatic) shedders.  相似文献   
86.
保护性耕作下西南旱三熟农田土壤水分动态及产量效应   总被引:1,自引:0,他引:1  
以西南地区麦/玉/薯三熟制种植模式为研究对象,研究了不同保护性耕作模式下旱地土壤水分动态变化、水分利用效率、作物产量和经济效应。结果表明,不同保护性耕作对整个农田生态系统产量和水分利用效率具有显著影响。秸秆覆盖(TS)、地膜覆盖(TM)、秸秆覆盖+地膜覆盖(TSM)和垄作+秸秆覆盖+地膜覆盖(RSM)能改善7,10月份0—60cm土层土壤含水量及贮水量,而垄作(R)、垄作+秸秆覆盖(RS)和垄作+地膜覆盖(RM)的作用不明显。与平作(CK)相比,RSM,RM,RS,TSM,TM,TS和R分别使系统增产10.52%,6.11%,6.77%,4.59%,5.12%,3.15%,1.24%。这些处理对水分利用效率和降水利用效率的增幅分别为1.26%~11.08%,1.27%~10.57%。研究结果说明,从WUE、降水利用效率、产量效应、经济效益这4个方面来看,垄作+秸秆覆盖+地膜覆盖耕作模式综合效益最佳。  相似文献   
87.
The creamy colour of many wheat-based end-products is conferred by endogenous lutein. During post-harvest storage of grain, free lutein may be converted in part to potentially more stable lutein mono- and di-fatty acid esters. This study investigates the synthesis of lutein esters and stability of free lutein and lutein esters over a wide range of temperatures in grain of a high lutein bread wheat, Triticum aestivum L. line DM5685*B12 and a durum, Triticum durum L cv Kamilaroi. Disappearance of free lutein and lutein esterification followed first order reaction rates. The maximum rate of lutein esterification was at ≈80 °C, however, the optimum temperature for maximum synthesis with minimum degradation was between 30 °C and 60 °C. No ester synthesis was observed at temperatures higher than 120 °C. The data are consistent with an enzyme participating in the esterification reaction. Lutein esters were found to be more stable than free lutein with a longer shelf life at 60 °C whilst at temperatures ≤40 °C, lutein degradation was minimal. This study provides new information on lutein ester formation and lutein stability that should be useful to grain handlers and food manufacturers seeking to optimise retention of lutein for the benefit of consumers.  相似文献   
88.
The present study was conducted to compare the effects of xenogenic bovine fetal demineralized bone matrix (DBM), commercial DBM, omentum, omentum-calf fetal DBM, cortical autograft and xenogenic cartilage powder on the healing of tibial defects in a dog model to determine the best material for bone healing. Seven male adult mongrel dogs, weighing 26.2 ± 2.5 kg, were used in this study. Seven holes with a diameter of 4-mm were created and then filled with several biomaterials. Radiographs were taken postoperatively on day 1 and weeks 2, 4, 6, 8. The operated tibias were removed on the 56th postoperative day and histopathologically evaluated. On postoperative days 14, 42 and 56, the lesions of the control group were significantly inferior to those in the other group (p < 0.05). On the 28th postoperative day, the autograft group was significantly superior to the control and omentum groups (p < 0.05). Moreover, calf fetal DBM was significantly superior to the control group. There was no significant difference between the histopathological sections of all groups. Overall, the omentum and omentum-DBM groups were superior to the control group, but inferior to the autograft, commercial-DBM, calf fetal DBM and calf fetal cartilage groups.  相似文献   
89.
Present study was undertaken to study the prevalence of β-haemolytic streptococci in equine of northern temperate region of Jammu and Kashmir, India. One hundred and forty one samples were collected in duplicate from nasopharyngeal tract of diseased (53) and apparently healthy equine (88) for isolation and direct PCR. A total of 77 isolates of streptococci were recovered from 141 samples with an overall prevalence rate of 54.60%. Out of these 77 isolates, 52 were from diseased and 25 from apparently healthy animals. Of the 77 isolates, 4 were identified as Streptococcus equi subsp. equi, 56 as S. equi subsp. zooepidemicus and 17 as S. dysgalactiae subsp. equisimilis. Thus the overall prevalence of S. equi subsp. equi, S. equi subsp. zooepidemicus and S. dysgalactiae subsp. equisimilis was 2.83, 39.71 and 12.05% respectively. The sensitivity of the PCR for the detection of S. equi species was found higher when attempted from direct swab samples.  相似文献   
90.
The present study was primarily carried out to trace the behavioral, physiological, and adrenal changes during the first stage of labor in cases of dystocia, either in parturient buffalo heifers or cows, and their clinical significance. Of the 118 investigated buffalo herds, 40 cows (dystocia = 20 and eutocia = 20) and 40 heifers (dystocia = 20 and eutocia = 20) were used in this study. Cows approaching actual birth were transferred to a calving box with straw bedding. Behavior of the studied animals was recorded from the time that the animal was moved to the calving box until the emergence of the fetal limbs in the vulval lips. If no progress in parturition was observed within two hours after the rupture of fetal sacs (end of the first stage), these cases were considered as suffering dystocia. As the fetal limbs emerged from the birth canal, animals were examined clinically to determine their average pulse and respiratory rates as well as body temperature. Blood samples were collected to determine the cow/heifers cortisol level. Results of the present study indicated that dystocia was accompanied by disturbed physiological status and cortisol levels. Practical monitoring system of parturient animals, through observing behavioral, physiological, and adrenal aspects during calving, should be regarded to expect dystocia and provide help for the animal in the appropriate time.  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