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   1355篇
  免费   56篇
  国内免费   5篇
林业   101篇
农学   34篇
基础科学   6篇
  222篇
综合类   115篇
农作物   52篇
水产渔业   87篇
畜牧兽医   583篇
园艺   69篇
植物保护   147篇
  2023年   18篇
  2022年   24篇
  2021年   45篇
  2020年   31篇
  2019年   46篇
  2018年   37篇
  2017年   38篇
  2016年   47篇
  2015年   25篇
  2014年   40篇
  2013年   49篇
  2012年   102篇
  2011年   123篇
  2010年   53篇
  2009年   39篇
  2008年   85篇
  2007年   90篇
  2006年   93篇
  2005年   90篇
  2004年   72篇
  2003年   76篇
  2002年   58篇
  2001年   16篇
  2000年   27篇
  1999年   11篇
  1998年   7篇
  1997年   6篇
  1996年   4篇
  1995年   4篇
  1994年   4篇
  1992年   4篇
  1991年   2篇
  1990年   4篇
  1989年   2篇
  1988年   5篇
  1987年   4篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1980年   3篇
  1979年   2篇
  1978年   6篇
  1976年   2篇
  1975年   2篇
  1974年   1篇
  1968年   1篇
  1966年   1篇
  1960年   1篇
  1950年   1篇
  1924年   1篇
排序方式: 共有1416条查询结果,搜索用时 15 毫秒
951.
To determine the occurrence of potentially human pathogenic microsporidia (Enterocytozoon bieneusi and Encephalitozoon spp.) in wild mice, we examined 289 East-European House Mice (Mus musculus musculus) and West-European House Mice (M. m. domesticus) trapped at 74 localities in an area across the Czech-German border. Microsporidia were detected at 33 localities, in 34% of M. m. musculus and 33% of M. m. domesticus examined specimens. Single-species infection was detected in 23 mice for E. hellem, 42 mice for E. cuniculi and 25 mice for E. bieneusi. No Encephalitozoon intestinalis positive animals were identified. Moreover, co-infections were detected in 6 animals; E. bieneusi co-existed with E. cuniculi or E. hellem in 3 mice. The natural infection of E. hellem has never been recorded in mice before. No differences were found by a statistical analysis of microsporidia occurrence between the House Mouse subspecies. Although the gender-dependent infestation of microsporidia was statistically supported in M. m. musculus, no significant differences were observed when the occurrence of microsporidia was estimated for all males and females irrespective of the House Mouse subspecies. The results of this report document the low host specificity of detected microsporidia species and imply the importance of synanthropic rodents as a potential source of human microsporidial infection.  相似文献   
952.
The effect of dietary vegetable oils differing in fatty acid composition that were infused directly into the duodenum on exocrine pancreatic secretions in pigs has not previously been studied. The objective of the present study was to determine the acute response of the exocrine pancreas to vegetable oils with various fatty acid profiles under prandial conditions. Six growing pigs (BW 13.2 kg) were surgically prepared with pancreatic duct catheters and duodenal reentrant T-cannulas. The animals were fed twice a day (1000 and 1600) a commercial weaner diet at a rate of 2% of BW. Beginning with the morning feeding, olive oil, coconut oil, or saline as a control were infused in boluses every 5 min in total 0.1% of BW over a period of 1 h directly into the duodenum according to a 3 x 3 Latin square design. Pancreatic juice was collected over a period of 4 h, beginning 1 h preprandially (0900) until 3 h postprandially (1300). A time effect was observed after the infusion of olive oil on the volume of secretion, on protein contents and outputs, as well as on lipase contents and outputs and on colipase contents. The infusion of saline and coconut oil changed the runs of the curves for lipase and colipase outputs. No time x treatment interactions were observed regarding volume of secretion, protein contents and outputs, trypsin contents and outputs, and lipase outputs. The runs of the curves for lipase contents were different between the olive oil and saline treatment and between the olive oil and coconut oil treatment. The runs of the curves for the olive oil and saline treatment differed from each other regarding colipase contents. Pooled values of colipase outputs were elevated after coconut oil treatment, and a positive correlation between trypsin and colipase contents was found. Under prandial conditions, the exocrine pancreas responds differently in its acute secretion to different vegetable oils due to the differences in the fatty acid profiles.  相似文献   
953.
Usutu virus (USUV), family Flaviviridae, has been responsible for avian mortality in Austria from 2001 to 2006. The proportion of USUV-positive individuals among the investigated dead birds decreased dramatically after 2004. To test the hypothesis that establishment of herd immunity might be responsible, serological examinations of susceptible wild birds were performed. Blood samples of 442 wild birds of 55 species were collected in 4 consecutive years (2003--2006). In addition, 86 individuals from a birds of prey rehabilitation centre were bled before, at the peak, and after the 2005 USUV transmission season in order to identify titre dynamics and seroconversions. The haemagglutination inhibition test was used for screening and the plaque reduction neutralization test for confirmation. While in the years 2003 and 2004 the proportion of seropositive wild birds was <10%, the percentage of seroreactors raised to >50% in 2005 and 2006. At the birds of prey centre, almost three quarters of the owls and raptors exhibited antibodies before the 2005 transmission season; this percentage dropped to less than half at the peak of USUV transmission and raised again to almost two thirds after the transmission season. These data show a from year to year continuously increasing proportion of seropositive wild birds. The owl and raptor data indicate significant viral exposure in the previous season(s), but also a number of new infections during the current season, despite the presence of antibodies in some of these birds. Herd immunity is a possible explanation for the significant decrease in USUV-associated bird mortalities in Austria during the recent years.  相似文献   
954.
Wildfires in the United States can be destructive to human life and property. The ability to predict fire danger helps reduce the risks associated with wildfires by keeping firefighters on high alert and allowing better preparedness. In the state of Oklahoma, fire is a common occurrence. By looking at past wildfire records and researching the weather conditions under which they burned, we were able to determine the most important weather conditions affecting wildfire size. We looked at 10 different weather variables and found that minimum relative humidity (r = 0.98, P = 0.001), maximum and average wind speed (r = 0.95, P = 0.003; r = 0.95, P = 0.004, respectively), and precipitation (r = 0.88, P = 0.02) were the most important factors relating to wildfire size. Temperature variables did not have significant relationships with wildfire size categories. Additionally, we found that most of the largest wildfires occurred in January and December. This information can be used to adjust and improve current wildfire danger models and predictive abilities. We define conditions under which firefighters should be on high alert with hopes of improving their ability to expediently manage rangeland wildfires.  相似文献   
955.
The infectivity and pathogenicity of Cryptosporidium andersoni (bovine isolate) for neonatal and adult southern multimammate mice (Mastomys coucha) was studied using transmission experiments. C. andersoni isolate used in this study was not infective for BALB/c mice, but experimental infection proved susceptibility of neonatal and adult M. coucha to the infection. The prepatent period was 20-24 days, the patent period varied between 46 and 59 days. No signs of clinical illness or macroscopic findings were detected in infected animals. Cryptosporidium developmental stages were detected only in the glandular part of the stomach of M. coucha in histological sections stained with Wolbach's modification of Giemsa and using immunofluorecence. Histopathological changes were characterized by dilatation and epithelial metaplasia of infected gastric glands without inflammatory response in the lamina propria. Neonatal M. coucha were more susceptible to C. andersoni infection than adults. M. coucha seems to be a useful laboratory model for study of C. andersoni infection.  相似文献   
956.
Bioactive substances including taurine, l-carnitine, polyunsaturated fatty acids, flavonoids and antioxidants were shown to influence the perinatal development of a majority of mammalian systems, nervous, gastrointestinal, immune, etc. A blend of bioactive substances and plants was composed to supplement sow feedstuff, and our study aimed to examine the bone parameters in their offspring. Control sows were fed with a standard diet alone (n = 6). The sows from the supplemented group (n = 6) received the supplementation from the gestation day 80 until the end of lactation. From each sow two piglets were sacrificed, one at 7 d and the second at 28 d of life. The femur and humerus were isolated, bone mineral density and mineral content were determined using dual energy X-ray absorptiometry. Bone maximum strength and elastic force were determined by a three-point bending test. No differences in the body weight were found. At day 7, the bones of piglets from the supplemented group were characterized by higher weight, physical parameters and bone mineral content as compared to control, no difference in length and bone mineral density was observed. At day 28, no differences in humerus parameters were found as well as in femur mineral density and mineral content. However, in relation to the body weight, the weight and physical parameters of femur were higher in the supplemented group as compared to control. In conclusion, the supplementation of sow diet with bioactive substances influenced the development of bones in their offspring.  相似文献   
957.
958.
Amniotic fluid collected from ewes on various days of gestation was examined for the presence of insulin-like growth factor (IGF) binding proteins. IGF-binding proteins with a molecular mass of 40-45 kDa appeared at day 41 of gestation. The level of these major IGF-binding proteins increased during pregnancy and reached a maximum at day 106. Smaller IGF-binding molecules with an approximate molecular mass of 35 kDa and 25 kDa appeared at day 90, also reaching a concentration peak at day 106. The mitogenic activity of sheep amniotic fluid after chromatography on Sephadex G-50 was separated into two peaks. The peak having lower molecular mass corresponded to an elution profile of 125I-IGF-I. The first peak, having higher molecular mass, was eluted immediately after the void volume of column. Electrophoresis and ligand blotting showed that proteins in the first peak had similar properties as IGF-binding proteins.  相似文献   
959.

Objective

To compare volumes for epidural injection calculated on body weight or the length from sacrococcygeal space to occipital crest in dogs.

Study design

Prospective study.

Animals

A total of 431 dogs weighing mean ± standard deviation (range) 24.6 ± 16.1 (1.3–88.0) kg and with vertebral column length 67.6 ± 38.4 (24.8–119.4) cm.

Methods

Dogs were separated into specific weight groups and body condition scores (BCS; 1–5): small (<10 kg), medium 10 to <25 kg), large (25 to <45 kg) and giant (≥45 kg). Calculations for a lumbosacral epidural dose were 0.2 mL kg?1 and for vertebral column length: 0.05 mL cm?1 (<50 cm), 0.07 mL cm–1 (50 to <70 cm), 0.08 mL cm–1 (70 to <80 cm), and 0.11 mL cm–1 (≥80 cm). A split plot anova (p < 0.05) with weight, length and BCS as factors was used.

Results

A significantly larger volume was calculated for length than for weight in small (p < 0.0001–0.0003, BCS 2–5), medium (p < 0.0001–0.0076, BCS 2–5), and large dogs (p ≤ 0.0007–0.0019, BCS 2,3). In large (BCS 4,5) and giant dogs (BCS 2,3), both calculated volumes were similar. In giant dogs (BCS 4,5), a significantly smaller volume was calculated for length (p ≤ 0.0002–0.0165). Regardless of BCS, small (2.18 versus 1.12), medium (3.99 versus 3.16), and large dogs (7.38 versus 6.82) had larger calculated volumes (mL) for length than for weight (p < 0.0001), whereas giant dogs (10.04 versus 10.91) had smaller calculated volumes.

Conclusions

and clinical relevance Mathematically, the epidural volume of injectate varies with the calculation method and is affected by BCS. Small and medium dogs have larger calculated volumes based on length than on weight, and this difference tends to disappear or revert as size increases.  相似文献   
960.
1. Three experiments of 39 d were simultaneously conducted to assess the efficacy of three carbohydrase combinations on performance, apparent nutrient digestibility, intestinal morphology and digestive organ relative weights of chickens fed on a wheat-based diet. 2. Experiment 1 was performed under laboratory conditions, with the birds housed in cages. In experiment 2, the birds were placed in floor pens built in a commercial farm, and raised with their contemporaries at the farm. In experiment 3, broilers were reared under industrial management circumstances in commercial farms. A two-phase feeding programme was used: starter from 1 to 21 d of age and finisher from 22 to 39 d. The basal diet without supplementation (BD) and three enzyme preparations (BDF, BDP and BDR) were evaluated. 3. No differences in growth traits were observed among treatments in experiments 1 and 2. 4. When overall growing period was evaluated, all enzyme combinations improved apparent DM ileal digestibility of feed in the three experiments, but significant differences were only found in experiments 2 and 3. For this same period, an increase in apparent CP ileal digestibility of broiler chickens fed supplemented diets against the control group was found in experiment 3. Moreover, a significant greater apparent ileal fat digestibility in the enzyme treatments compared with the control group was shown when broilers were raised under industrial conditions (experiment 3). 5. Enzyme combinations had no effect on villus heights and crypt depths of broilers in experiment 1, whereas, in experiment 2, a greater villus height was found in BDF and BDP treatments than in control birds. 6. There were no differences in digestive organ relative weights among dietary treatments except for pancreas in experiment 1.  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