全文获取类型
收费全文 | 241557篇 |
免费 | 14826篇 |
国内免费 | 650篇 |
专业分类
林业 | 23399篇 |
农学 | 13967篇 |
基础科学 | 2958篇 |
42048篇 | |
综合类 | 19732篇 |
农作物 | 17136篇 |
水产渔业 | 16464篇 |
畜牧兽医 | 91690篇 |
园艺 | 6250篇 |
植物保护 | 23389篇 |
出版年
2021年 | 2451篇 |
2020年 | 2838篇 |
2019年 | 3626篇 |
2018年 | 3943篇 |
2017年 | 4265篇 |
2016年 | 4732篇 |
2015年 | 4271篇 |
2014年 | 5625篇 |
2013年 | 16190篇 |
2012年 | 5934篇 |
2011年 | 7747篇 |
2010年 | 7183篇 |
2009年 | 7816篇 |
2008年 | 7225篇 |
2007年 | 6208篇 |
2006年 | 6943篇 |
2005年 | 6185篇 |
2004年 | 6019篇 |
2003年 | 5755篇 |
2002年 | 5114篇 |
2001年 | 5616篇 |
2000年 | 5350篇 |
1999年 | 5062篇 |
1998年 | 4111篇 |
1997年 | 4147篇 |
1996年 | 3892篇 |
1995年 | 4445篇 |
1994年 | 3882篇 |
1993年 | 3563篇 |
1992年 | 4150篇 |
1991年 | 4225篇 |
1990年 | 4043篇 |
1989年 | 3886篇 |
1988年 | 3478篇 |
1987年 | 3446篇 |
1986年 | 3410篇 |
1985年 | 3725篇 |
1984年 | 3498篇 |
1983年 | 3318篇 |
1982年 | 2761篇 |
1981年 | 2704篇 |
1980年 | 2694篇 |
1979年 | 3038篇 |
1978年 | 2744篇 |
1977年 | 2593篇 |
1976年 | 2433篇 |
1975年 | 2242篇 |
1974年 | 2307篇 |
1973年 | 2329篇 |
1972年 | 2040篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
261.
S. P. Antai P. M. Mbongo 《Plant foods for human nutrition (Dordrecht, Netherlands)》1994,46(4):345-351
Mash prepared from cassava peels was inoculated with eitherSacchromyces cerevisiae orCandida tropicalis and then left to ferment for 7 days. Chemical analysis of the fermented mash showed substantial increase in crude protein content and decrease in carbohydrate content of the mash. The results also revealed slight increases in the ash, fibre and lipid content of the fermented mash. It was further observed that, when the mash was supplemented with inorganic nitrogen sources (urea, ammonium sulfate or sodium nitrate) before commencement of fermentation, the amount of crude protein formed was almost doubled. This enhanced crude protein production was highest in the mash supplemented with urea. Temperature of 30 °C, pH of 5.5 and moisture concentration of 130% were found to be optimum for crude protein formation by the organisms growing on the mash. 相似文献
262.
P I Rekwot E O Oyedipe O O Akerejola A A Voh P M Dawuda 《The British veterinary journal》1989,145(1):85-88
Twenty-one Bunaji (White Fulani, Zebu) and 21 Friesian X Bunaji cross-bred bull calves, approximately 6 months of age, were each divided after weaning into two groups and fed isocaloric rations containing 14.45% (high protein) and 8.51% (low protein) crude protein for 10 months. Serum samples were collected biweekly for 10 months and analysed for serum proteins. Age had no significant effect. The Bunaji had significantly (P less than 0.05) higher total protein, albumin, and alpha 1-globulin than Friesian X Bunaji. While there was no significant difference in body condition score between the two breeds, the Friesian X Bunaji had a significantly (P less than 0.05) higher growth rate. Animals on high protein diets had significantly (P less than 0.05) higher total protein, albumin, alpha 2-globulin, gamma-globulin and total globulin than those on low protein. However, alpha 1-globulin and beta-globulin were not significantly (P greater than 0.05) different for the two treatment groups. 相似文献
263.
Elke Rudloff DVM Dennis T. Crowe DVM Jr. Rebecca Kirby DVM Bobbie Mammato DVM MPH 《Journal of Veterinary Emergency and Critical Care》1996,6(2):103-107
Successful resuscitation of a trauma-induced, suspected tension pneumomediastinum in a dog is presented. The cause was a caudal cervical penetration wound which acted as a one-way valve allowing air to enter, but not exit, the cranial mediastium. Early in the course of hospitalization, respiratory and cardiovascular collapse occurred; an emergent parasternotomy allowed decompression of the mediastinum, and the cradiovascular system immediately responded. The dog made a complete recovery following surgical exploration and removal of contaminated mediastinal tissue. Nine days of intensive care included 24-hour monitoring, oxygen therapy, intravenous crystalloids and colloids, continuous pleural suctioning, nutritional support, antibiotics, and pain control. 相似文献
264.
265.
The Chilean Intermediate Depression to the north of Santiago has experienced a physiognomical transformation from a Prosopis chilensis woodland to an Acacia caven savanna. Today P. chilensis trees are scarce and belong mostly to the larger size classes. By contrast A. caven seems to reproduce frequently and its populations consist of individuals of all size classes. In this paper we document these changes and report the results of tests aimed at determining the causes of these physiognomical changes. We found that livestock, leporids, introduced Mediterranean forbs and agriculture account for differences in seed dispersal and survival of A. caven and P. chilensis, which can explain the documented changes in the Chilean landscape. 相似文献
266.
E. DUVEILLER 《EPPO Bulletin》1994,24(1):135-157
The literature related to bacterial leaf streak of cereals, due to various pathovars of Xanthomonas campestris , is confusing and dispersed. This review presents a synthesis of the knowledge that has been accumulated on the disease in cereals since the early reports on barley and wheat. The aim is to present the current status on geographical distribution of the disease, to explain possible confusions in symptoms, and to show the limited quantitative information available on losses and on host/pathogen interactions. Disease etiology and means of control are also reviewed. The objective is to define the present situation of black chaff in wheat, barley and triticale, and to delineate the major research needs in these crops. Difficulties in controlling bacterial leaf streak arise as a result of limited epidemiological knowledge and of the absence of satisfactory seed treatment permitting the eradication of the bacterium. There is an urgent need for a seed certification scheme and for more information on genetic resistance, with a view to limiting outbreaks of this sporadic but devastating disease. 相似文献
267.
Lyophilised serum offers significant advantages over frozen serum when it comes to shipping such material over long distances. Babesia bigemina and B bovis were cultured in medium supplemented by either frozen-thawed or lyophilised-rehydrated serum. There were no significant differences between the two types of medium in the growth of parasites and percentage of infected cells during subcultivation for 18 days. 相似文献
268.
利用自制的应力-应变试验台,对草莓果实的应力-应变特性和蠕变特性进行了测定与研究,建立了草莓果实应力-应变的数学模型,指出了草莓果实的极限屈服点变动范围。同时对草莓在不同贮藏条件下流变特性的变化规律进行了初步的研究,发现草莓的成熟度、贮藏温度及贮藏时间对果实的硬度、屈服应力均有较显著的影响,建立了屈服应力随时间变化的不同阶段的回归方程,可用于预测在相应贮藏条件下的草莓果实的屈服应力。 相似文献
269.
This paper reviews the radiological features of 50 canine incisive or maxillary tumours and discusses the value of radiological assessment in the diagnosis and staging of these tumours. The 50 tumours examined included 21 sarcomas, 15 carcinomas, three melanomas and an assortment of benign tumours of the oral cavity. There was not any site specificity for the different histological tumour types within the upper dental arcade, although fibrosarcomas had a tendency to be maxillary whereas the squamous cell carcinomas were equally distributed between the incisive and maxillary regions. Seventy-eight per cent of fibrosarcomas, 82 per cent of squamous cell carcinoma and all three melanomas examined showed radiological evidence of bone involvement. Radiographic changes were also seen in the benign tumours. The pattern of growth of tumours correlated with the radiological changes observed. Malignant tumours showed a tendency to irregular or aggressive bone loss whereas bone production predominated in the benign tumours. 相似文献
270.
The objective of these experiments was to examine methods of modifying the fatty acid composition of bovine tissues. In the first experiment, four steers were fitted with duodenal fistulas and were assigned to four diets in a Latin square design. The steers were fed a control diet or the same diet containing 10% high-oleate partially crushed sunflower seeds, serum-coated sunflower seeds, and heat-treated, serum-coated sunflower seeds for 5 d. Samples of digesta and feces were collected on d 5. The inclusion of sunflower seeds (plain or serum-coated) in the diet increased (P less than .05) the digesta concentration of stearate. The percentage of stearate in the digesta and feces was increased (P less than .05) from 51 to 67% and from 64 to 74%, respectively, when steers were fed the untreated sunflower seed. The fecal concentration of oleate was increased (P less than .05) by dietary sunflower seeds in steers that were fed the serum-coated, unheated sunflower seeds. In a second experiment, heifers (four per group) were fed a corn-based control diet or diets containing 10% of high-oleate sunflower oil encapsulated with calcium alginate, either plain, coated with blood meal, or with blood meal integrated into the pellet. After 50 d on treatment, samples of perianal adipose tissue were obtained by biopsy. The fatty acid composition of the adipose tissue was not modified by the inclusion of the encapsulated oleate in the diet. In summary, limited ruminal bypass of sunflower seed oleate was accomplished with sunflower seed but not with encapsulated oleate. 相似文献