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   245篇
  免费   7篇
  国内免费   1篇
林业   30篇
农学   14篇
基础科学   1篇
  34篇
综合类   24篇
农作物   15篇
水产渔业   22篇
畜牧兽医   76篇
园艺   17篇
植物保护   20篇
  2022年   7篇
  2021年   6篇
  2020年   4篇
  2019年   8篇
  2018年   11篇
  2017年   12篇
  2016年   7篇
  2015年   4篇
  2014年   6篇
  2013年   23篇
  2012年   9篇
  2011年   13篇
  2010年   13篇
  2009年   12篇
  2008年   13篇
  2007年   6篇
  2006年   7篇
  2005年   5篇
  2004年   5篇
  2003年   3篇
  2002年   5篇
  2001年   2篇
  2000年   2篇
  1999年   6篇
  1997年   3篇
  1995年   3篇
  1994年   2篇
  1992年   3篇
  1991年   2篇
  1990年   4篇
  1989年   1篇
  1988年   4篇
  1987年   2篇
  1986年   2篇
  1984年   1篇
  1983年   1篇
  1981年   4篇
  1980年   6篇
  1979年   1篇
  1978年   2篇
  1977年   2篇
  1976年   3篇
  1975年   2篇
  1974年   1篇
  1972年   1篇
  1971年   1篇
  1970年   4篇
  1969年   1篇
  1967年   3篇
  1946年   1篇
排序方式: 共有253条查询结果,搜索用时 15 毫秒
81.
比较了天然林和森林采伐区土壤理化性质,评价了森林采伐对土壤的影响。采集了自然林和邻近的采伐林地三个土层(表层、中层和底层)土壤,对其属性进行了调查。森林土壤颗粒大小分布无显著变化。森林表层土和中层土体积密度存在显著差异。林地内表层土和中层土壤pH、表层土有机质和中层土有效磷均显著高于采伐林地的值。两块林地内可交换Na+和阳离子交换能力没有变化。这些结果表明,两块林地内表层和亚表层土壤变化较明显。森林采伐降低土壤理化性质。  相似文献   
82.
Indigenous perennial grasses are widely distributed in the Arabian Peninsula. Their survival under limited rainfall and grazing suggests a potential role as grassland species and for rehabilitation of degraded rangelands. Forage productivity, seed production and water‐use efficiency (WUE) was determined over 2 years for four indigenous grasses: buffel grass (Cenchrus ciliaris L.), dakhna (Coelachyrum piercei Benth.), da’ay (Lasiurus scindicus Henr.) and tuman (Panicum turgidum Forssk.) together with one exotic species, rhodes grass (Chloris gayana Kunth) in the central region of the United Arab Emirates. Three irrigation treatments were used: R1 (1858–6758 m3 ha?1 year?1), R2 (929–3379 m3 ha?1 year?1) and R3 (464–1689 m3 ha?1 year?1). Buffel grass had the highest dry‐matter (DM) yield under all irrigation treatments. The average DM yield of buffel grass was 14·6 and 15·1 t ha?1 in the 2 years which was significantly higher than that for the other grasses with dakhna having the lowest DM yields. The WUE of 0·7 and 0·8 kg DM m?3 in the 2 years for buffel grass was significantly greater than for the other grasses. Buffel grass showed the highest increase in WUE in both years when the irrigation was reduced from treatment R1 to R3. The results suggest that the desert grasses of the Arabian Peninsula, such as buffel grass, could be useful grass species in reducing the use of scarce irrigation water provided that seed production can be increased.  相似文献   
83.
84.
The purpose of this study is to investigate some histochemical reactions in the lining epithelium of the seminiferous tubules and their terminal segment. The material was taken from adult rams killed in the slaughter house. The results showed clear histochemical differences between the seminiferous tubules and the terminal segment. This fact leads to the speculation that the terminal segment has quite different role from that of the seminiferous tubules.  相似文献   
85.
Forty-one, 10-week-old newly weaned goats were randomly allocated into two groups, namely control (n=22) and treated (n=19). Kids in both groups were fed Rhodegrass hay ad libitum that contained < 0.1 mg/kg DM cobalt and 150 g/day of a commercially prepared ruminant concentrate that contained approximately 0.12 mg/kg DM cobalt. This diet provided the minimum daily requirement of cobalt as specified for sheep. The treated goats were supplemented with bi-monthly subcutaneous injections of 2000 microg of hydroxycobalamin. All goats were weighed and blood samples collected monthly for haematological, clinical biochemical and serum vitamin B12 analysis. After a 10-month experimental period the goats were slaughtered. The control animals exhibited significantly (P<0.05) lower weight gains, and had dry scruffy hair coats. In addition, there was a decline in erythrocyte counts, mean haemoglobin, packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration. Controls also exhibited significantly (P<0.05) lower levels of total serum proteins and elevated levels of serum alkaline phosphatase compared to treated goats. Fourteen (63.6%) of the control goats developed pathology consistent with reported field cases of hepatic lipidosis associated with low liver levels of cobalt. Only one (5.3%) of the treated goats developed hepatic lipidosis. Contrary to previous reports that suggested that goats are less sensitive to low levels of dietary cobalt than sheep, it is apparent that this is not the case with Omani goats. This is the first report of the induction of hepatic lipidosis in goats due to feeding low levels of cobalt in their diet.  相似文献   
86.
Twenty young female adult one-humped racing camels (Camelus dromedarius) kept in camps scattered outside Al Ain city and aged between 3- and 6-years-old, died after a short clinical illness. Affected camels were dull, inappetant and pyrexic, with submandibular oedema and enlargement of submandibular lymph nodes. Of 100 camels within the camps, 31 showed clinical signs. At necropsy examination, the liver of dead animals appeared yellowish, enlarged, congested and friable. The main hepatic histological findings were centrolobular necrosis, haemorrhages and cellular vacuolation. Aflatoxins were detected in sera, liver, ruminal contents and in feed ingested by affected animals. Sera of symptomatic and recovered camels also showed increased levels of glutamic oxaloacetic transaminases, glutamic pyruvic transaminases, aspartate transaminases, gamma glutamyl transaminases, glucose, urea nitrogen, phosphorus and total iron. Decreased levels of albumin, calcium, cholesterol and triglycerides were also observed. It was probable that aflatoxicosis was responsible for clinical signs and subsequent death of the camels. The need for suitable and appropriate storage conditions of animal feed to prevent fungal growth and aflatoxin contamination is highlighted.  相似文献   
87.
This report was delineated to study the clinical, bacteriological and therapeutic aspects concerned with acute coliform mastitis in buffaloes. Bacteriological examination of 80 quarter milk samples obtained aseptically from 56 buffaloes with acute mastitis revealed that coliform bacteria was the most common pathogen (45 cases) followed by Staphylococcus aureus (seven cases) then Streptococcus uberis (three cases), and Streptococcus agalactiae (one case). Clinically, hotness, swelling and painful reaction with serous excretion containing clots was recorded in buffaloes with coliform mastitis. The efficacy of ceftiofur was evaluated in the treatment of buffaloes with acute coliform mastitis. Parenteral ceftiofur neither improved clinical signs nor returned milk to pre-infection production level, whereas intramammary ceftiofur and combination of intramammary with parenteral ceftiofur improved the clinical signs in 10/15 and 12/15 buffaloes, respectively. On quarter level, 3/17, 12/17 and 15/21 quarters recovered in groups received parenteral, intramammary and combination therapy, respectively. This study demonstrates that systemic ceftofur is not effective in the treatment of clinical coliform mastitis in buffaloes.  相似文献   
88.

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   
89.
During the production of palm sugar, the palm sap (Arenga pinnata) is heated up to 150 degrees C. Besides the hydrolysis of carbohydrate to generate reducing sugars and degradation of amino acid, many physicochemical changes produced at all these temperatures, having a significant impact on the overall quality of palm sugar. In this study, changes in physico-chemical properties of the palm sap due to heat processing were investigated. Analysis of colour, soluble solid, pH, temperature, sugar and amino acid concentration was determinant. The results showed clearly that the heating process at these high temperatures was necessary to create an environment which was rich in essential precursors for subsequent reactions such as Maillard reaction. Chemical compounds that showed drastic changes in concentration were polar side chain amino acids especially glutamine, asparagine and arginine as well as sucrose and pH value. Other quality characteristics of palm sugar based on colour and soluble solids (Brix) shared an increase in concentration as a function of time.  相似文献   
90.
The leaf extract and its fractions of Peganum harmala L. have shown pronounced mortal effect, decreased percent pupation and adult emergence of the cotton leaf worm, Spodoptera littoralis Boisd. The third instar larvae fed for two days on treated leaves were more susceptible to plant extract and its ethyl acetate and chloroform fractions. The active lowest concentration (5%) of the leaf fractions of P. harmala showed significant effect on the percentage of emerged adult parasitoids, Microplitis rufiventris Kok. GC/MS analysis showed the major constituent in ethyl acetate fraction was (23S) ethylcholest-5-en-3 beta-ol (28.04%) while those of chloroform fraction were hydroxyfuranocoumarin (Bergaptol) (15.68%), piperidinone (12.08%), thymol (11.82%), phosphoric acid, tributyl ester (9.80%) and trimethyl-nonenol (9.66%). The medicinal plant P. harmala could be carefully applied in integrated pest management due to its strong effect on cotton leaf worm pest.  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