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   5786篇
  免费   248篇
  国内免费   15篇
林业   418篇
农学   243篇
基础科学   40篇
  695篇
综合类   628篇
农作物   226篇
水产渔业   228篇
畜牧兽医   3138篇
园艺   51篇
植物保护   382篇
  2020年   48篇
  2019年   55篇
  2018年   77篇
  2017年   111篇
  2016年   99篇
  2015年   65篇
  2014年   91篇
  2013年   215篇
  2012年   178篇
  2011年   195篇
  2010年   129篇
  2009年   127篇
  2008年   239篇
  2007年   223篇
  2006年   195篇
  2005年   212篇
  2004年   189篇
  2003年   189篇
  2002年   187篇
  2001年   206篇
  2000年   200篇
  1999年   186篇
  1998年   54篇
  1997年   73篇
  1996年   68篇
  1995年   58篇
  1994年   47篇
  1993年   63篇
  1992年   128篇
  1991年   136篇
  1990年   135篇
  1989年   138篇
  1988年   108篇
  1987年   122篇
  1986年   103篇
  1985年   97篇
  1984年   93篇
  1983年   67篇
  1979年   81篇
  1978年   63篇
  1977年   73篇
  1976年   46篇
  1975年   69篇
  1974年   85篇
  1973年   74篇
  1972年   75篇
  1971年   56篇
  1970年   70篇
  1969年   51篇
  1968年   44篇
排序方式: 共有6049条查询结果,搜索用时 15 毫秒
21.
Efficacy of fenbendazole, at doses of 7.5 and 10.0 mg/kg of body weight, against inhibited early 4th-stage larvae of Ostertagia ostertagi and other nematodes of the abomasum and intestinal tract, was investigated in naturally infected yearling heifers in late May 1982. In Louisiana, this is near the end of the period (March to May) in which maximal numbers of inhibition-prone larvae are acquired. The mean numbers of O ostertagi in 10 untreated control cattle were: adults, 4,880; developing 4th-stage larvae, 12,546; and inhibited early 4th-stage larvae, 167,931. At the 7.5 mg/kg dose level (10% liquid suspension) in 10 cattle, percentage reduction of O ostertagi in comparison with controls was: adults, 95.7%; developing 4th stages, 91.1%; and inhibited 4th stage, 55.0%. Percentage reductions of other genera were as follows: abomasum--Trichostrongylus axei, 99.6%; Haemonchus sp, 95.1%; intestinal tract--Cooperia spp, 97.8%; Trichostrongylus colubriformis, 100.0%; and Oesophagostomum radiatum 4th stage and adults, 100.0%. At the 10.0 mg/kg dose (10% liquid suspension) in 11 cattle, the percentage reduction of O ostertagi in comparison with controls was: adults, 98.6%; developing 4th stages, 92.9%; and inhibited 4th stage, 80.0%. Percentage reductions of other genera were: abomasum--T axei, 99.9%; Haemonchus sp, 98.8%; intestinal tract--Cooperia spp, 99.3%; T colubriformis, 100.0%; and Oes radiatum 4th stage and adults, 100.0%. Variability of efficacy against inhibited larvae was observed, particularly at the 7.5 mg/kg dose; at this dose, 7 of the 10 heifers in the group yielded in excess of 54,000 surviving larvae.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
22.
This paper describes the ultrasonographic appearance, location and size of the spleen in 50 healthy commercial milk cows destined for slaughter. The intercostal spaces of the left thoracic wall were scanned with a 3.5 MHz linear transducer. In each intercostal space, the appearance of the splenic parenchyma, the dorsal and ventral margins and the distance between them, and the diameter of the splenic vessels were recorded. The spleen was seen in intercostal spaces 7-12. It was 2.0-5.0 cm thick, and tapered ventrally. The splenic capsule appeared as an echogenic line. The splenic parenchyma consisted of numerous small regularly spaced echoes, and vessels within the parenchyma appeared as anechoic round to oval or elongated images. The long axis was oblique, running caudodorsal to cranioventral. The distance from the dorsal margin of the spleen to the midline of the back was greatest in the 7th intercostal space (60.9+/-6.81) and smallest in the 12th intercostal space (12.7+/-2.85 cm). The extent of the spleen was greatest in the 8th intercostal space (24.9+/-10.77 cm) and smallest in the 12th intercostal space (9.5+/-5.38 cm). The mean diameter of the splenic vessels ranged from 0.66+/-0.28 to 0.90+/-0.65 cm, depending on the intercostal space scanned. Ultrasonography of the spleen in healthy cows provides information that can be used as a reference when examining cattle with suspected splenic disease.  相似文献   
23.
Domestic environmental pollution resulting from urban livestock farming was investigated in Makurdi using parasitological techniques. The test tube flotation technique was used for the parasitological analysis of animal faecal matter and soil samples collected from residential premises. Ectoparasitic fauna of dogs, goats, sheep and cattle cohabiting with humans within the same residential compound were also collected and identified. The hand-picking and body brushing methods were employed to search for ticks, fleas, lice and mites. Of the 150 soil samples examined, 55 (36.7 %) were positive for 1 or more eggs of helminth parasites. There was no significant difference in the distribution of eggs in the soil samples from the 3 areas sampled (Chi2 = 0.046, df = 2, P > 0.05). Ascaris species were the dominant parasite eggs found. Of the 180 faecal samples examined, 107 (59.4 %) were positive for 1 or more eggs of helminth parasites. Chi-square analysis showed no significant difference in the level of infection of different animal faeces sampled (Chi2 = 5.74, df = 4, P > 0.05). Ascaris species were again the dominating helminth parasite eggs found. There was also no significant difference in the prevalence of helminth eggs in the animal faecal samples from the 3 areas sampled (Chi2 = 5.99, df = 4, P > 0.05). A total of 1908 ectoparasites was recovered (ticks: 32.80 %; lice: 22.43 %; fleas: 22.06 % and mite: 22.69 %). There was no significant difference in infestation animals between sexes (Chi2 = 0.10, df = 4, P > 0.05). The predominant genus encountered for ticks were Amblyomma, while Linognathus (43.90 %), Ctenocephalides (97.38 %) and Sarcoptes (58.89 %) were most predominant for lice, fleas and mites respectively. The public health implications of the findings, especially as these relate to the increasing incidence and prevalence of zoonotic infections, are discussed.  相似文献   
24.
Despite aggressive pre- or postoperative treatment, feline fibrosarcomas have a high relapse rate. In this study, a new treatment option based on immune stimulation by intra-tumoral delivery of three feline cytokine genes was performed. The objective of this phase-I dose-escalation study was to determine a safe dose for further evaluation in a subsequent phase-II trial. Twenty-five client-owned cats with clinical diagnosis of fibrosarcoma - primary tumours as well as recurrences - entered the study. Four increasing doses of plasmids coding for feIL-2, feIFN-gamma or feGM-CSF, respectively, were previously defined. In groups I, II, III and IV these doses were 15, 50, 150 and 450 microg per plasmid and a corresponding amount of magnetic nanoparticles. Two preoperative intra-tumoral injections of the magnetic DNA solution were followed by magnetofection. A group of four control cats received only surgical treatment. Side effects were registered and graded according to the VCOG-CTCAE scale and correlated to treatment. Statistical analyses included one-way anova, post hoc and Kruskal-Wallis tests. ELISA tests detecting plasma feIFN-gamma and plasma feGM-CSF were performed. One cat out of group IV (450 microg per plasmid) showed adverse events probably related to gene delivery. As these side effects were self-limiting and occurred only in one of eight cats in group IV, this dose was determined to be well tolerable. Altogether six cats developed local recurrences during a 1-year observation period. Four of these cats had been treated with dose IV. Regarding these observations, a subsequent phase-II trial including a representative amount of cats should be tested for the efficacy of dose IV as well as dose III.  相似文献   
25.
26.
Certain circulatory and respiratory values were measured in horses in the standing, lateral, and supine positions. Twelve adult horses were kept in the standing position under the influence of glycerol guiacolate. Alterations in position to lateral and dorsal recumbencies were achieved without any further drug administration. The changes from the standing to the lateral position decreased the arterial oxygen tension, but left the arterial carbon dioxide tension unchanged. There was no statistically significant effect of body position on respiratory flow rates or volumes. The shift from the lateral position to the supine position had no statistically significant effect on any of the measured values. It is assumed that the change from the standing to the lateral position results in an increase in ventilation of the uppermost parts of the lung. The perfusion inequalities are due mainly to the effect of gravity of the pulmonary circulation which may result in a decrease in arterial oxygen tension.  相似文献   
27.
28.
29.
A phenomenon of inhibition among Salmonella organisms colonizing the gut of young animals can be demonstrated which is important in connection with immunization using live Salmonella vaccines. For practical utilization of this inhibition phenomenon, research into its specificity is very important. In vitro broth culture and animal experiments have shown inhibition to be genus-specific, i.e. there is no inhibition between strains of different genera of Enterobacteriaceae in most cases. The strongest inhibition occurs between isogenic (identical genotype) strains (strain-specific inhibition). This applies to Salmonella and other genera of Enterobacteriaceae. There was a close correlation between the degree of the inhibitory effect and the genetic relatedness of the strains, as has been demonstrated in Salmonella strains of different epidemiological classification. The inhibitory capacity was most pronounced among closely related strains. Clonal strains of Salmonella Enteritidis phage type 4 fully inhibited caecal colonization by Salmonella Enteritidis phage type 4 strains in 65% of the combinations tested in chicks. In broth culture experiments, the share of combinations with complete inhibition was above 90%. A significant inhibitory competence of a selected strongly inhibitory Salmonella Enteritidis phage type 4 strain against the majority of Salmonella Enteritidis field isolates can be expected. However, Salmonella Enteritidis strains of all phase types showed almost no inhibitory competence against other Salmonella serotypes.  相似文献   
30.
A study was conducted to determine the variations in physical characters and immunocompetence among scavenging local chicken ecotypes in Tanzania. Eighty-four adult scavenging local chickens from four eco-climatic regions of Tanzania were studied. Measurements of adult body weight, body length, shank length and egg weight and observations of plumage colour and pattern, earlobe colour, skin colour and the shape of the comb were conducted. The antibody response to sheep red blood cells, serum haemolytic complement and the cutaneous response to phytohaemagglutinin-P were assessed. Five ecotypes were identified and named Mbeya, Morogoro-medium, Ching'wekwe, Kuchi and Singamagazi. Singamagazi and Kuchi were significantly heavier, with longer shanks and heavier eggs than the other ecotypes. The average adult body weight for males ranged from 1621 g (Mbeya) to 2915 g (Singamagazi). Average female weights ranged from 1108 g (Morogoro-medium) to 2020 g (Singamagazi). Mean egg weights ranged from 37.65 g (Ching'wekwe) to 45.61 (Singamagazi). The Kuchi had mostly rose and walnut combs, while the other ecotypes were mostly single combed. In each ecotype there were chickens with a high or low antibody response to red blood cells, but there was a significant difference between the ecotypes.  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