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   12553篇
  免费   959篇
林业   1253篇
农学   475篇
基础科学   63篇
  2894篇
综合类   810篇
农作物   521篇
水产渔业   962篇
畜牧兽医   5031篇
园艺   342篇
植物保护   1161篇
  2023年   104篇
  2022年   141篇
  2021年   263篇
  2020年   256篇
  2019年   196篇
  2018年   590篇
  2017年   554篇
  2016年   524篇
  2015年   412篇
  2014年   479篇
  2013年   733篇
  2012年   965篇
  2011年   909篇
  2010年   514篇
  2009年   415篇
  2008年   798篇
  2007年   733篇
  2006年   600篇
  2005年   615篇
  2004年   568篇
  2003年   527篇
  2002年   427篇
  2001年   297篇
  2000年   278篇
  1999年   246篇
  1998年   86篇
  1997年   68篇
  1996年   50篇
  1995年   70篇
  1994年   45篇
  1993年   44篇
  1992年   85篇
  1991年   74篇
  1990年   65篇
  1989年   66篇
  1988年   61篇
  1987年   49篇
  1986年   48篇
  1985年   48篇
  1984年   43篇
  1983年   36篇
  1979年   37篇
  1974年   26篇
  1973年   21篇
  1972年   22篇
  1971年   23篇
  1970年   27篇
  1969年   25篇
  1968年   25篇
  1967年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
We measured the potential impact of articles representing the International Symposium on Veterinary Epidemiology and Economics (ISVEE) plenary-session presentations in subsequent published literature. Between July 1, 2004 and November 9, 2004, we searched the Web of Science for citations in the scientific literature to all 99 plenary-session articles published in the proceedings of the previous nine ISVEEs (or in journal special issues dedicated to the ISVEE plenary articles). We used a 4-year window around the publication of each of the ISVEE proceedings. We located 187 citations for 37 (of the 99) articles. We infer that the ISVEE proceedings represent an important resource for veterinary epidemiology.  相似文献   
132.
The aim of this trial was to assess the effect that calcium gluconate priming of 468 broilers has on the antibacterial activity of a standard dose of enrofloxacin. Hence, a series of oral pharmacokinetic studies were carried out in four groups of broilers medicated individually through an oral cannula as follows: group A, medicated only with enrofloxacin 10mg/kg; group B, receiving immediately one after the other, calcium gluconate (200mg/kg) and enrofloxacin 10mg/kg; group C, dosed first with calcium gluconate (200mg/kg) and 1h later enrofloxacin (10mg/kg); and group D, dosed first with calcium gluconate (200mg/kg) and 2h later enrofloxacin (10mg/kg). Broilers were bled at different times after the dose of enrofloxacin and antibacterial activity, measured as concentration of enrofloxacin, was measured by an agar diffusion assay. Results revealed that group D the greatest values of maximum serum concentration (Cs(max)), area under the concentration vs. time curve (AUC) and area under the moment curve (AUMC). These values were statistically higher than the corresponding ones derived from groups A, B and C (P<0.05). Taking Cs(max) and AUC values of group A as reference baseline, an increase of 24% and 50%, respectively, was obtained in group D. Group B had the lowest Cs(max), AUC, AUMC and elimination half life (T(1/2)beta) and these values were statistically different from groups A, C and D (P<0.05). The T(1/2)beta was statistically longer in groups C and D as compared with A and B, and the former groups were also different between each other (P<0.05). These results show that if calcium gluconate is first dosed to broilers and 2h later enrofloxacin is administered (as in group D), a more pronounced antibacterial activity of enrofloxacin can be obtained. A challenge of this sequential dosing scheme in a field trial may reveal its clinical value.  相似文献   
133.
134.
135.

BACKGROUND

Ecballium elaterium (common name: squirting cucumber) is an emerging weed problem in hedgerow or superintensive olive groves under no tillage. It colonizes the inter-row area infesting the natural or sown cover crops, and is considered a hard-to-control weed. Research in other woody crops has shown E. elaterium has a patchy distribution, which makes this weed susceptible to design a site-specific control strategy only addressed to E. elaterium patches. Therefore, the aim of this work was to develop a methodology based on the analysis of imagery acquired with an uncrewed aerial vehicle (UAV) to detect and map E. elaterium infestations in hedgerow olive orchards.

RESULTS

The study was conducted in two superintensive olive orchards, and the images were taken using a UAV equipped with an RGB sensor. Flights were conducted on two dates: in May, when there were various weeds infesting the orchard, and in September, when E. elaterium was the only infesting weed. UAV-orthomosaics in the first scenario were classified using random forest models, and the orthomosaics from September with E. elaterium as the only weed, were analyzed using an unsupervised algorithm. In both cases, the overall accuracies were over 0.85, and the producer's accuracies for E. elaterium ranged between 0.74 and 1.00.

CONCLUSION

These results allow the design of a site-specific and efficient herbicide control protocol which would represent a step forward in sustainable weed management. The development of these algorithms in free and open-source software fosters their application in small and medium farms. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   
136.
Journal of Plant Diseases and Protection - Tobacco (Nicotiana tabacum L.) is one of the major nonfood crops in the Southern of Brazil. During 2019/2020 and 2020/2021 crop seasons, Root Knot...  相似文献   
137.

BACKGROUND

Amaranthus palmeri is an aggressive annual weed native to the United States, which has become invasive in some European countries. Populations resistant to acetolactate synthase (ALS) inhibitors have been recorded in Spain and Italy, but the evolutionary origin of the resistance traits remains unknown. Bioassays were conducted to identify cross-resistance to ALS inhibitors and a haplotype-based genetic approach was used to elucidate the origin and distribution of resistance in both countries.

RESULTS

Amaranthus palmeri populations were resistant to thifensulfuron-methyl and imazamox, and the 574-Leu mutant ALS allele was found to be the main cause of resistance among them. In two Spanish populations, 376-Glu and 197-Thr mutant ALS alleles were also found. The haplotype analyses revealed the presence of two and four distinct 574-Leu mutant haplotypes in the Italian and Spanish populations, respectively. None was common to both countries, but some mutant haplotypes were shared between geographically close populations or between populations more than 100 km apart. Wide genetic diversity was found in two very close Spanish populations.

CONCLUSION

ALS-resistant A. palmeri populations were introduced to Italy and Spain from outside Europe. Populations from both countries have different evolutionary histories and originate from independent introduction events. ALS resistance then spread over short and long distances by seed dispersal. The higher number and genetic diversity among mutant haplotypes from the Spanish populations indicated recurrent invasions. The implementation of control tactics to limit seed dispersal and the establishment of A. palmeri is recommended in both countries. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   
138.
Surveillance of hepatitis E virus (HEV) in risk groups is an important strategy to monitor its circulation pattern and to timely detect changes thereof. The aims of this cross-sectional study were to estimate the prevalence of HEV infections in pigs and humans from different regions of the country, to identify risk factors for increasing anti-HEV IgG prevalence and to characterize HEV strains. The presence of anti-HEV antibodies was assessed by commercial ELISA in serum samples from the general population, farm and slaughterhouse employees, as well as pigs sampled in the three regions of Cuba from February to September 2016. Overall, individuals with occupational exposure to swine or swine products (70/248, 28.2%) were 4 times more likely to be seropositive compared to the general population (25/285, 8.7%; OR: 4.18; p < .001). Within the risk group, risk factors included age, number of years working in a professional activity with direct exposure to swine, geographic region and distance between residence and closest professional swine setting, while wearing gloves had a protective effect. Prevalence of total anti-HEV antibodies in swine was 88.2% (165/187) and HEV RNA was detected by real-time RT-PCR in 9.2% (16/173) swine stools. All HEV strains sequenced clustered within genotype 3. Some strains clearly belonged to subtype 3a, while another group of strains was related with subtypes 3b and 3 k but partial HEV sequences did not allow unequivocal subtype assignment. These findings suggest that the high HEV exposure in Cuban individuals with swine-related occupations could be due to enzootic HEV in certain regions, direct contact with infectious animals or their products as well as environmental contamination.  相似文献   
139.
Medial glenohumeral ligament injury is commonly reported during medial shoulder joint instability in dogs. Arthroscopy is considered the gold standard procedure, but it is invasive and requires distension of the joint. Ultrasonographic examination of the medial glenohumeral ligament has been studied as a possible, less invasive alternative to arthroscopy however it has not been considered a useful method of assessment due to the interference of the probe with the pectoral muscles. The aims of this prospective analytical randomized pilot study were to develop a standardized ultrasound protocol for visualizing the canine medial glenohumeral ligament and to compare goniometry and ultrasound findings in cadaver dogs with versus without transection of the medial glenohumeral ligament. Nine adult Beagle cadavers (18 shoulders) were used. The first six shoulders were used in a preliminary study to describe an ultrasound technique to identify the medial glenohumeral ligament. Arthroscopy was performed on the remaining 12 shoulders, with six randomly selected medial glenohumeral ligaments from these shoulders, transected during the procedure. Ultrasound examination was performed after each arthroscopic procedure by an ultrasonographer blinded to the patient group. Four medial glenohumeral ligaments (67%) were correctly identified during the preliminary study. Ultrasonographic examination failed to diagnose the transection of all six medial glenohumeral ligaments in the second part of the study. No difference was observed in the ligament thickness between the dogs with and without a transected medial glenohumeral ligament. Dogs with a transected medial glenohumeral ligament had a wider articular space compared to dogs without a transected ligament (P < 0.001), and an articular space wider than 8.2 mm was discriminatory of a transected medial glenohumeral ligament in all the shoulders. In conclusion, the medial glenohumeral ligament could be identified with a medial ultrasonographic approach of the shoulder and a wider articular space can be a sign of a medial shoulder joint instability. Further studies are needed to confirm these preliminary findings in living dogs, with and without shoulder instability.  相似文献   
140.
The objective of this retrospective study was to assess the effect of receiving a single (n = 50,285) or double (n = 4392) artificial insemination (AI), 12 h apart, within a timed artificial insemination protocol on pregnancy per AI (P/AI) in nulliparous heifers (inseminated with either sex-sorted or conventional semen) and pluriparous Holstein cows in a commercial dairy herd. Also, this study aimed to investigate the relationship between temperature-humidity index (THI) and time of the first AI and fertility. Fertility of cows receiving two AI with normothermia (THI <68) was higher (p < .05) than cows receiving a single AI (42.9% vs. 36.4%). P/AI of cows receiving two AI with severe heat stress (THI >85) was higher (p < .05) than cows receiving a single AI (21.0% vs. 12.6%). Regardless of heat stress conditions, applying the first AI in the morning increased (p < .05) P/AI in cows with double AI than in cows whose first AI occurred in the afternoon (38.4 vs. 33.3%). With moderate heat stress, and sexed-sorted semen, P/AI to timed AI was higher (65.0 vs. 51.9%; p < .05) in heifers receiving double AI than those serviced once. It was concluded that double AI, 12 h apart, enhanced fertility at timed AI than herd mates with a single AI, particularly with heat stress at breeding.  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