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   2254篇
  免费   129篇
  国内免费   10篇
林业   166篇
农学   128篇
基础科学   39篇
  516篇
综合类   168篇
农作物   309篇
水产渔业   210篇
畜牧兽医   483篇
园艺   83篇
植物保护   291篇
  2024年   3篇
  2023年   20篇
  2022年   67篇
  2021年   86篇
  2020年   106篇
  2019年   136篇
  2018年   162篇
  2017年   147篇
  2016年   138篇
  2015年   76篇
  2014年   94篇
  2013年   240篇
  2012年   128篇
  2011年   150篇
  2010年   117篇
  2009年   77篇
  2008年   128篇
  2007年   65篇
  2006年   49篇
  2005年   43篇
  2004年   38篇
  2003年   35篇
  2002年   29篇
  2001年   21篇
  2000年   31篇
  1999年   23篇
  1998年   16篇
  1997年   12篇
  1996年   16篇
  1995年   17篇
  1994年   9篇
  1993年   5篇
  1992年   8篇
  1991年   6篇
  1990年   8篇
  1989年   8篇
  1988年   9篇
  1987年   10篇
  1986年   4篇
  1985年   6篇
  1984年   10篇
  1983年   7篇
  1982年   2篇
  1981年   4篇
  1979年   6篇
  1975年   3篇
  1973年   3篇
  1972年   2篇
  1971年   3篇
  1967年   3篇
排序方式: 共有2393条查询结果,搜索用时 738 毫秒
991.
The objective of this study was to investigate the capability of X-ray imaging in detecting internal infestations caused by the saw-toothed beetle (Oryzaephilus surinamensis L.) in stored dates. Un-infested and infested dates were x-rayed for different life stages (egg, larvae, pupae, and adult) of O. surinamensis. An algorithm was developed to extract 44 features from the X-ray images. Linear discriminant analysis (LDA) was used to discriminate the un-infested and infested dates using extracted features. Overall accuracy of X-ray imaging system was 80% for un-infested and beetle-infested dates. X-ray imaging system yielded around 97% accuracy in detecting internal infestation of dates with an adult beetle while using a pairwise classification method. Further studies are required to investigate the effects of moisture content and hardness of dates in the discrimination between the un-infested and infested dates.  相似文献   
992.
During summer season, increase in the environmental temperature in the subtropical regions of Pakistan is negatively affecting the performance of dairy animals. The study objective was to determine the effect of ambient management (90 days) on productive and physiological performance of lactating Sahiwal cows during hot dry summer season. Fifteen lactating cows during the early lactation stage, having similar parity (3), daily milk production (6.2 l), were randomly allocated to three treatments, 5 cows each, i.e., (1) kept under roof shade only, (2) provision of fans along with roof shade, and (3) provision of roof shade, fans, and sprinklers designated as S, SF, and SFS, respectively. The fans were of 360-rpm capacity and showers were on for 40 min after every 90-min interval from 9:00 to 21:00 h. THI values were 81.1?±?0.7, 80.5?±?0.7, and 77.7?±?0.4 under S, SF, and SFS treatments, respectively. Cows were milked twice daily. Respiration rate (RR) and rectal temperature (RT) data were collected at 14:00 h on daily basis. The daily milk production was significantly higher in cows under SF (7.9?±?1 kg) followed by SFS (6.9?±?1.2 kg) and S (6.1?±?0.9 kg) treatments. The mean RT (101.0?±?0.04 °F) was significantly lower in cows under SFS than that on SF and S treatments and similarly mean RR was also lower (21.2 breaths/min) in cows under SFS followed by SF and S treatments. It is concluded that milk production and physiological performance in Sahiwal cows can be improved by fan-assisted ventilation during hot dry summer in subtropical regions.  相似文献   
993.
994.
ABSTRACT

1. A study was conducted to evaluate the relationship among physical and mechanical properties of the eggshell, as affected by breed and hen’s age.

2. Data on eggshell quality (external characteristics and derived measurements) were obtained from 322 laying hens, from three breeds (Fayoumi, Dandarawi and Hy-Line Brown) during the laying cycle, starting from 38 wks of age for four experimental periods (38, 46, 54 and 62 wks).

3. Eggs obtained from the Fayoumi breed exhibited the highest shell thickness and breaking force. There was a linear improvement in eggshell quality attributes associated with hen’s age up to 54 wks, thereafter a deterioration was found for all breeds.

4. Generally, eggs laid by native breeds (Fayoumi and Dandarawi) had better mechanical properties compared to those produced by the commercial strain (Hy-Line Brown). In addition, the interaction between breed and hen’s age was not significant for any physical property or mechanical attribute. There was a highly significant (P ≤ 0.01) positive correlation between the breaking force and either eggshell toughness or shell thickness, and regression analyses suggested that eggshell toughness was the best predictor for breaking force, followed by shell thickness.  相似文献   
995.

The aim of this study was to clarify the causes of scrotal enlargement in rams and bucks in Qassim region of Saudi Arabia. Enlarged scrotal contents of rams and bucks (n = 153) were examined by visual inspection, palpation, and ultrasonography. Blood samples were obtained and tested for Brucella sp. infection. Clinical and ultrasonographic findings showed that scrotal enlargement was mainly associated with orchitis, peri-orchitis, and epididymitis. Miscellaneous findings were scrotal hernia, scrotal hematoma, and hydrocele. The frequencies of orchitis, peri-orchitis, and epididymitis were 47.4, 21.1, and 14.1% in Awassi rams; 54.5, 21.7, and 8.7% in Najdi rams; 52.3, 20.5, and 9.1% in Ardi bucks; and 50, 16.7, and 16.7% in Damascus bucks, respectively. Orchitis was associated with no-abscess formation (23%), single-abscess formation (15.4%), and multiple-abscesses formation (61.6%). Peri-orchitis was characterized by hard consistency, atrophy of the testes, and extensive connective tissue formation. Epididymitis was observed mainly at the tail of the epididymis (82.4%) but rarely at the head (17.6%). Epididymitis was associated in many cases with abscessation (70.6%). Males with orchitis, peri-orchitis, and epididymitis were positive for Brucella melitensis and Brucella ovis in the frequency of 21.3% and 48.8%, respectively. In conclusion, scrotal enlargement in rams and bucks in Qassim region is caused mainly by inflammation of the testis and/or epididymis and associated tremendously with brucellosis seropositivity.

  相似文献   
996.
Tropical Animal Health and Production - The present study aimed at investigating the percent prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in equines and associated personnel. A...  相似文献   
997.

The study was conducted to evaluate the effect of feeding different levels of sun-dried Ziziphus spina-christi (ZC) leaves on feed intake and live weight gain of local male goats. Twenty-five male local breed of goats at 1 year of age (body weight; BW?=?20.7?±?0.72 kg) were randomly allocated to five treatments and five replications. Treatments were as follows: T1 (grass hay only; control group); T2 (75% grass hay + 25% ZC leaves); T3 (50% grass hay + 50% ZC leaves); T4 (25% grass hay + 75% ZC leaves), and T5 (100% ZC leaves). The study lasted for 90 days. During this period, feed intake, BW change, and average daily gain were evaluated. There was a significant difference in total dry matter intake of goats fed on different levels of ZC leaves compared with the control group. Mixing of the pasture grass hay diet improved (P?<?0.05) goats feed intake from 440 to 592 g/head/day at the minimum proportion of 25% ZC and natural pasture mixture. However, there was no significant difference (P?>?0.05) in feed intake among the supplemented groups (T2–T5) as ZC leaves proportion increased. Goats in the control group and in the 25% ZC treatment diet gained 31.4 and 46.7 g, which was not different (P?>?0.05). The highest average daily BW was gained (P?<?0.05) in goats supplemented with the highest level (100%) of ZC leaves. T5 (100% ZC leaves supplementation) showed a significant increment (P?<?0.05) in body weight gain of goats over other treatments and the control. Feed conversion ratio was increased (P?<?0.05) with increased inclusion level of ZC leaves. Goats on supplemented treatments 1 and 2; treatments 4 and 5 had no significant difference (P?>?0.05) in feed conversion efficiency while there was a significant (P?<?0.05) difference between treatments 2 and 3 diets which had higher (P?<?0.05) feed conversion ratio than the control groups. Generally, the results of the current study showed that supplementation of goats with above 50% level of dried ZC leaves in their diet significantly increased feed intake and body weight gain by improving feed conversion efficiency of goats.

  相似文献   
998.

The aims of the present study were to investigate the prevalence of some virulence genes and also determine the antimicrobial resistance pattern of E. coli isolated from bovine with subclinical mastitis. The milk of 502 cows was collected from 8 dairy herds in the southwest of Iran. Conventional biochemical tests were used for identification of E. coli at the species level. Antimicrobial susceptibility patterns of E. coli isolates were determined by disc agar diffusion method and polymerase chain reaction (PCR) was used for detection of seven virulence genes including f17A, afaE-8, afaD-8, eaeA, cnf1, cnf2, and iucD. Seventy (13.94%) isolates of E. coli were identified in 502 milk samples. The highest rate of resistance was observed against tetracycline (18.6%), while none of the isolates were resistant to streptomycin. Eight (11.5%) out of 70 E. coli isolates carried at least one of the virulence genes. The afaD-8 was the most prevalent gene detected in 5 (7.1%) isolates. The afaE-8, iucD, and eaeA were detected in 3, 3, and 2 isolates respectively. Low prevalence of virulence factors may be indicating that most of the E. coli isolates originated from the commensal flora of cows and enter to the udders via environment contamination with feces.

  相似文献   
999.
Tropical Animal Health and Production - In tropical countries, one of the major threats for diary animal production is climate change. Ambient management interventions are beneficial and are the...  相似文献   
1000.
The aim of the current study was to evaluate the effect of dietary supplementation of Pinus ponderosa leaves ( pine leaves) and α‐tocopherol acetate (vitamin E) powder on male reproductive system, serum metabolites and carcass characteristics of Japanese quails. A total of 360‐day‐old male quails were purchased from the open market and kept at poultry shed for ninety‐four days. After ten days of adaptation, all quails were randomly assigned into 4 groups, control (IC); supplemented with α‐tocopherol acetate (IE) at the rate of 150 mg/L; Pinus ponderosa leaves (IP) at the rate of 150 mg/L; and 70 mg α‐tocopherol acetate and 70 mg Pinus ponderosa leaves (IEP). Pinus ponderosa leaves and α‐tocopherol acetate supplementation had not significantly (p > .05) effected on final body weight gain, feed intake and feed conversion ratio of quails. The high‐density lipoprotein cholesterol (HDLC) and total cholesterol (TC) were significantly (p > .05) affected by IE and IP groups as compared to IC and IEP groups. Triglyceride (TG), glutathione peroxidase (GPx) and superoxide dismutase (SOD) significantly (p < .05) increased in all treatment groups except for the IC group. Aspartate transaminase (AST) significantly (p > .05) decreased in treatment groups as compared to control group. Overall, the mineral levels significantly (p < .05) increased in treatment groups as compared to control. Cloacal gland index values, the quantity of foam production and testis weight were significantly (p < .05) increased in treatment groups. It was concluded that the supplementation of Pinus ponderosa leaves and α‐tocopherol acetate improved the testis weight, foam production, serum antioxidant enzymes and mineral level especially zinc in Japanese quail considered an indicative characteristic of higher sperm production rate and improved sexual activity. Further, higher gametogenesis rate, sperm production or reproductive behaviour including different hormonal level will be analysed in future study.  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