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   302篇
  免费   8篇
  国内免费   1篇
林业   25篇
农学   34篇
基础科学   2篇
  74篇
综合类   20篇
农作物   20篇
水产渔业   21篇
畜牧兽医   23篇
园艺   10篇
植物保护   82篇
  2023年   3篇
  2022年   6篇
  2021年   8篇
  2020年   11篇
  2019年   12篇
  2018年   7篇
  2017年   9篇
  2016年   14篇
  2015年   11篇
  2014年   9篇
  2013年   23篇
  2012年   11篇
  2011年   17篇
  2010年   15篇
  2009年   13篇
  2008年   23篇
  2007年   17篇
  2006年   11篇
  2005年   12篇
  2004年   3篇
  2003年   10篇
  2002年   4篇
  2001年   3篇
  2000年   12篇
  1999年   2篇
  1998年   6篇
  1997年   2篇
  1996年   4篇
  1995年   3篇
  1994年   1篇
  1992年   1篇
  1991年   2篇
  1990年   3篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1977年   2篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1971年   2篇
  1969年   2篇
  1967年   1篇
排序方式: 共有311条查询结果,搜索用时 0 毫秒
251.
We studied genetic variation in Puccinia psidii, a newly introduced rust fungus in Hawaii, using microsatellite markers. All 36 Hawaiian P. psidii isolates analyzed had the same genotype at 11 microsatellite loci, while three genotypes were identified among four isolates from Florida and 11 genotypes among 18 isolates from Brazil. One of the isolates from Florida had 95% similarity to the Hawaiian isolates. We conclude that the genetically homogeneous P. psidii isolates in Hawaii might have derived from the same strain originally introduced into the Islands and are closely related to one of the strains found in Florida.  相似文献   
252.
Coniothyrium minitans, marketed as Contans, has become a standard management tool against Sclerotinia sclerotiorum in a variety of crops, including winter lettuce. However, it has been ineffective against lettuce drop caused by S. minor. The interactions between C. minitans and S minor were investigated to determine the most susceptible stage in culture to attack by C. minitans, and to determine its consistency on S minor isolates belonging to four major mycelial compatibility groups (MCGs). Four isolates of S. minor MCG 1 and 5 each from MCGs 2 and 3 and one from MCG 4 were treated in culture at purely mycelial, a few immature sclerotial, and fully mature sclerotial phases with a conidial suspension of C. minitans. Sclerotia from all treatments were harvested after 4 weeks, air dried, weighed, and plated on potato dextrose agar for recovery of C. minitans. S. minor formed the fewest sclerotia in plates that received C. minitans at the mycelial stage; C. minitans was recovered from nearly all sclerotia from this treatment and sclerotial mortality was total. However, the response of MCGs was inconsistent and variable. Field experiments to determine the efficacy of C. minitans relative to the registered fungicide, Endura, on lettuce drop incidence and soil inoculum dynamics were conducted from 2006 to 2009. All Contans treatments had significantly lower numbers of sclerotia than Endura and unsprayed control treatments, and drop incidence was as low as in Endura-treated plots (P > 0.05). Although the lower levels of lettuce drop in Contans treatments were correlated with significantly lower levels of sclerotia, the lower levels of lettuce drop, despite the presence of higher inoculum in the Endura treatment, was attributable to the prevention of infection by S. minor. A useful approach to sustained lettuce drop management is to employ Contans to lower the number of sclerotia in soil and to apply Endura to prevent S. minor infection within a cropping season.  相似文献   
253.
Journal of Plant Diseases and Protection - Barley shoot fly (Delia flavibasis) is one of the destructive insect pests of barley (Hordeum vulgare L.) at seedling stage. Resistance to barley shoot...  相似文献   
254.
Severe mosaic accompanied by leaf and fruit deformation symptoms was observed on banana plants growing in three banana farms of Uttar Pradesh, India. The disease incidence was approximately 18–25% at these locations during the three successive years from 2005 to 2007. The occurrence of Cucumber mosaic virus (CMV) was initially detected by bioassay, electron microscopic observations, Western blot immunoassay and RT-PCR. For molecular identification of virus, the RNA 1a, RNA 2b and RNA 3 genomic fragments were amplified by RT-PCR and sequenced. The sequence analysis of these genomic fragments revealed its highest identities and close relationships with Indian strains of CMV of subgroup IB; therefore, virus associated with the mosaic disease of banana was identified as an isolate of CMV of subgroup IB. In the limited reports existing from India, which provided preliminary serological or only coat protein-based identification of CMV infecting banana but the comprehensive studies were lacking. In the present communication, we present a detailed biological, serological and molecular characterization of CMV-Banana for the first time from India.  相似文献   
255.
Saflufenacil is a new herbicide on the market and its effectiveness on horseweed, several populations of which have evolved resistance to glyphosate, is not clear. In this research, the effect of adjuvants on the control of horseweed with saflufenacil in the field, the effect of the interaction between glyphosate and saflufenacil on glyphosate‐resistant and glyphosate‐susceptible horseweed and the patterns of uptake and translocation of glyphosate applied alone and in combination with saflufenacil in horseweed were evaluated. The addition of methylated seed oil to saflufenacil provided the best control of horseweed, with crop oil concentrate being intermediate in effect and non‐ionic surfactant ranking as the least‐effective adjuvant. The interaction between glyphosate and saflufenacil was additive with regards to the control of glyposate‐resistant horseweed. The glyphosate‐susceptible horseweed population absorbed 6–13% more 14C‐glyphosate than the glyphosate‐resistant population. The addition of saflufenacil reduced 14C‐glyphosate translocation in both the glyphosate‐resistant and the glyphosate‐susceptible horseweed populations by at least 6%; however, due to the exceptional efficacy of saflufenacil, these reductions did not reduce the level of control. Saflufenacil holds great potential as an alternative control option for glyphosate‐resistant horseweed and is a valuable tool in the management of resistant weeds.  相似文献   
256.
The present study evaluated the effect of supplementation of retinol in the vitrification solution on the viability, apoptosis and development-related gene expression in vitrified buffalo preantral follicles. Preantral follicles isolated from cortical slices of ovaries were randomly assigned into three groups: Group1—Control fresh preantral follicles; Group 2—Vitrification treatment (Vitrification solution 1 (VS1) –TCM-199 + 25 mM HEPES + Foetal bovine serum (FBS) 10%, Ethylene glycol (EG): 10%, Dimethyl sulphoxide (DMSO): 10%, Sucrose-0.3 M for 4 min; VS2- TCM-199 + 25 mM HEPES + FBS10%, EG:25%, DMSO: 25%, Sucrose:0.3 M for 45 s); Group3—vitrification treatment +5 μM of Retinol. Preantral follicles were placed in corresponding vitrification medium and plunged into liquid nitrogen (−196°C). After a week, the follicles were thawed and analysed for follicular viability and gene expression. There was no significant difference in the viability rates among the Group 1(Fresh preantral follicles) (91.46 ± 2.39%), Group 2 (89.59 ± 2.46%) and Group 3 (87.19 ± 4.05%). There was a significantly (p < .05) higher mRNA expression of BCL2L1, GDF-9 and BMP-15 in the vitrification + retinol group compared with the control group. There was a significantly (p < .05) higher expression of Caspase-3 and Annexin-5 in the vitrification group and Vitrification + retinol group compared with control group of follicles. It is concluded that the supplementation of 5 μM of Retinol in Vitrification solution was an efficient vitrification procedure for the vitrification of buffalo preantral follicles.  相似文献   
257.

The present research work entitled “Correlation of testicular ultrasonography, testicular biometry, serum testosterone levels and seminal attributes in pre- and post-pubertal age for breeding soundness evaluation in Osmanabadi bucks” was undertaken in 18 healthy Osmanabadi bucks from the Instructional Livestock Farm Complex, Bombay Veterinary College, Mumbai, Maharashtra. The body weight (kg), scrotal circumference (cm) and testicular biometry (cm) of post-weaning 18 Osmanabadi male kids was recorded every 15 days from weaning, i.e., 120?±?10 days along with serum testosterone (ng/ml) by radioimmunoassay method at monthly intervals for the next 6 months. Semen was collected six times on the seventh month onward during post-pubertal age at 15-day interval from 18 bucks. The semen was evaluated for macroscopic and microscopic tests. The body weight increased from 14.45?±?0.67 to 19.57?±?0.70 kg from four to nine and a half months of age. The average daily body weight gain was 31.27 g. Maximum body weight gain was 01.19?±?0.16 kg from 5 to 6 followed by 01.15?±?0.16 kg from 4 to 5 months of age. The scrotal circumference increased from 17.22?±?0.56 to 19.03?±?0.55 cm from four to nine and a half months of age with maximum increased between 4 and 5 followed by 6 and 7 months of age. The testicular length, width and thickness of right and left testicles were recorded by ultrasonography method. There was increase in mean right and left testicular length, width and thickness from 5.25?±?0.19 to 5.84?±?0.18 and 5.49?±?0.21 to 6.16?±?0.20; 2.99?±?0.12 to 3.32?±?0.12 and 3.10?±?0.13 to 3.44?±?0.12 and 2.97?±?0.12 to 3.16?±?0.12 and 3.06?±?0.12 to 3.31?±?0.11 cm, respectively by ultrasonography, between four to nine and a half months of age. Testicular length, width and thickness gain was at maximum in 5 to 6 months of age. Left testicular length was more than the right testis. Before puberty, there was sudden gain in body weight, testicular length and width. However, scrotal circumference showed significant increase after puberty. Body weight had highest correlation with ultrasonographic left testicular thickness (r?=?1) followed by scrotal circumference, ultrasonographic right and left testicular width, left testicular length, right testicular length and thickness and least by right testicular thickness (r?=?0.95). The semen was thin to thick in consistency and average semen density was 3.10?±?0.05. Average semen volume was 0.81?±?0.02 ml, mass activity, initial motility, live and dead sperm count, abnormal sperm count and sperm concentration were 3.45?±?0.13, 76.16?±?1.16 and 75.16?±?1.28% and 24.84?±?1.28, 12.30?±?0.50% and 2631.04?±?45.74 million/ml, respectively in 18 bucks in six collection at 15 days. There was significant rise in semen volume, mass activity, initial motility and concentration at 8.5 months and live count, density at 9 months of age which indicates the age of sexual maturity is 8.5 to 9 months in Osmanabadi bucks. The body weight had highest positive correlation with mass activity (r?=?98) followed by initial motility, live sperm count and total sperm concentration, semen volume (r?=?76). The scrotal circumference had highest positive correlation with initial motility (r?=?98) followed by live sperm count, total sperm count, mass activity, semen volume (r?=?86). On the other hand, body weight and scrotal circumference were negatively correlated with abnormal and dead sperm count. The mean testosterone concentration increased from 0.02?±?0.004 to 5.75?±?0.80 ng/ml between four and half to nine and half months of age, respectively. There was significant rise (p?<?0.01) up to 1.38?±?0.28 ng/ ml at 6.5 months, i.e., age of puberty and up to 5.75?±?0.80 ng/ml at 9.5 months, i.e., age of sexual maturity. Testosterone had highest positive correlation with testicular length followed by testicular width, length, body weight and scrotal circumference, mass activity, live sperm count, initial motility, while it had highest negative correlation with dead and abnormal sperm count. From the present research work, it was concluded that the scrotal circumference, testicular length, width and thickness increased with increasing body weight. Before puberty, there was sudden gain in body weight, testicular length and width. However, scrotal circumference increased significantly at post-pubertal age. So testicular length, body weight, testicular width in pre pubertal age and scrotal circumference post-pubertal age can be used as indicator for selection of Osmanabadi bucks for breeding purpose. On the other hand, the semen parameters should consider only after 8.5 to 9 months of age for selection of Osmanabadi bucks for breeding.

  相似文献   
258.
The karyotypes of three shrew species (Mammalia, Soricomorpha, Soricidae) from Nepal were examined for the first time. Based on the karyotypes and overall differences in skull size, the current Episoriculus caudatus appeared to include two distinct species: the larger E. caudatus and the smaller Episoriculus sacratus. Episoriculus sacratus has three subspecies, E. s. soluensis in Nepal and Sikkim, E. s. umbrinus in Assam, Myanmar and the Yunnan Province of China, and E. s. sacratus in the Sichuan Province of China. Soriculus nigrescens had a diploid chromosome number (2n) and fundamental number (FN), including two X chromosomes, of 64 and 92, respectively, consisting of 11 metacentric or submetacentric, two subtelocentric and 18 acrocentric pairs of autosomes, a metacentric X and an acrocentric Y chromosome. Episoriculus sacratus soluensis had 2n = 74 and FN = 126, consisting of 12 metacentric or submetacentric, 13 subtelocentric and 11 acrocentric pairs of autosomes, a submetacentric X and an acrocentric Y chromosome. Episoriculus caudatus had 2n = 60 and FN = 118, consisting of 19 metacentric or submetacentric, nine subtelocentric and one acrocentric pair of autosomes, a subtelocentric X and an acrocentric Y chromosome. The karyotypes of these three species are characterized by their large 2n and FN values compared with other Soricidae.  相似文献   
259.
The isolation and spectral data of di-(2-ethyl) hexyl phthalate (1) from Cassia auriculata leaves are reported.  相似文献   
260.
A mixed population of equine cyathostomin (Nematoda, Strongyloidea) infective third stage larvae (L3) was cultured in vitro using a cell-free medium. Some L3 were cultured immediately after Baermann collection from fecal cultures, while others were kept in water at 4 °C for 7 days before initiating the in vitro cultures. Cultures were examined daily for viability. At days 2, 7, 14 and 21 larvae were collected for identification of developmental stage and morphological changes, using both light and scanning electron microscopy. Larvae were classified as early L3 (EL3), developing L3 (DL3), late L3 (LL3) and fourth stage larvae (L4) on the basis of morphological features. Viability remained high throughout the entire study period in cultures of both non-refrigerated (84.7%) and refrigerated (77.4%) larvae. However, viability of the non-refrigerated was significantly greater from 7 through 21 days of culture. Significant differences were also observed in the percentage of DL3 between the non-refrigerated and refrigerated larval cultures by day 7. The highest percentage of DL3 larvae (22.5%) was reached at the end of study in those larvae that were not previously refrigerated. The data suggests that prior refrigeration decreases viability and slows L3 development. At day 21 LL3 larvae were only a small percentage of the DL3: 6.9 and 5% in non-refrigerated and refrigerated cultures, respectively. Few of these larvae freed themselves from the L3 cuticle and moulted to L4 stage. Characteristics of individual species in vitro developmental patterns were determined by the molecular identification of individual larvae in pools of larvae randomly collected at days 0 and 21. Seven species (Coronocyclus coronatus, Cylicostephanus goldi, Cylicostephanus longibursatus, Cyathostomum catinatum, Cylicocyclus nassatus, Cylicocyclus ashworthi, Petrovinema poculatum) were identified in the day 0 pool. The greatest tendency to develop in vitro was shown by the genus Cylicostephanus with the species C. goldi and C. longibursatus that developed to the LL3-L4 stages. C. nassatus, C. ashworthi and C. coronatus did not progress in their development beyond the EL3 stage, while no apparent signs of development were registered for C. catinatum.  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