全文获取类型
收费全文 | 132867篇 |
免费 | 7306篇 |
国内免费 | 99篇 |
专业分类
林业 | 5411篇 |
农学 | 4290篇 |
基础科学 | 840篇 |
17103篇 | |
综合类 | 21509篇 |
农作物 | 5399篇 |
水产渔业 | 6781篇 |
畜牧兽医 | 68100篇 |
园艺 | 1807篇 |
植物保护 | 9032篇 |
出版年
2020年 | 1185篇 |
2019年 | 1386篇 |
2018年 | 2042篇 |
2017年 | 2346篇 |
2016年 | 2113篇 |
2015年 | 1752篇 |
2014年 | 2233篇 |
2013年 | 5305篇 |
2012年 | 4135篇 |
2011年 | 5126篇 |
2010年 | 3268篇 |
2009年 | 3410篇 |
2008年 | 4998篇 |
2007年 | 4692篇 |
2006年 | 4377篇 |
2005年 | 4108篇 |
2004年 | 3873篇 |
2003年 | 3986篇 |
2002年 | 3562篇 |
2001年 | 4162篇 |
2000年 | 4258篇 |
1999年 | 3375篇 |
1998年 | 1485篇 |
1997年 | 1390篇 |
1996年 | 1295篇 |
1995年 | 1537篇 |
1994年 | 1365篇 |
1993年 | 1235篇 |
1992年 | 2584篇 |
1991年 | 2702篇 |
1990年 | 2595篇 |
1989年 | 2615篇 |
1988年 | 2371篇 |
1987年 | 2348篇 |
1986年 | 2428篇 |
1985年 | 2342篇 |
1984年 | 1883篇 |
1983年 | 1678篇 |
1982年 | 1149篇 |
1979年 | 1748篇 |
1978年 | 1399篇 |
1977年 | 1151篇 |
1976年 | 1213篇 |
1975年 | 1292篇 |
1974年 | 1501篇 |
1973年 | 1514篇 |
1972年 | 1406篇 |
1971年 | 1304篇 |
1970年 | 1251篇 |
1969年 | 1284篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Sunflower cake (SC), horse bean (HB), and alfalfa meal (AM) were treated with rising doses of formaldehyde (F) from 0.0, 0.2 ... 2.0 g F per 100 g crude protein. We have followed the differences of crude protein solubility, its degradability and disappearance of dry matter in the rumen as well as the amount of reversible bonded F from the F dose. With AM it was found a significant influence of ADF on the degradability and on the amount of acid-labile bonded F and/or on the decrease of N solubility. From the total N content the share of soluble nitrogen decreased in SC by 31%, HB by 24%, and in AM only by 12.5%. With the increase of the F dose its protective effect on proteins against the degradability mainly in SC and HB also rose significantly. The degradability of AM protein was influenced more by the incubation time than by the effect of treatment. The degradability of the SC proteins fell from 95% with untreated to 27% treated with the maximum dose. With AM it fell slowly from 84% to 74% by the determination coefficient R2 = 0.77. It was observed a marked decrease in HB only from the dose of 1.28% F. The changes in dry matter disappearance were similar to the changes in crude protein degradability and to the changes of solubility in SC and AM. The in situ method proved very suitable for the determination of the extent of degradability of the feed proteins in the rumen. 相似文献
962.
A neonatal foal with signs of rectal bleeding was diagnosed with an intraluminal rectal mass and intussusception on surgical exploration of the abdomen. Histologically, the mass consisted of cystic spaces lined by simple columnar epithelium with numerous goblet cells and was surrounded by thin bands of smooth muscle in a myxomatous stroma. Although the mass shared similarities with retrorectal cystic hamartoma (tailgut cyst) and juvenile polyps, described in human medicine, location and histologic findings were not entirely consistent with either condition. 相似文献
963.
Perennial ryegrass is the primary forage component of ruminant diets in New Zealand. It is persistent and palatable, and immature ryegrass has a high nutritive value (NV). However, seedhead development substantially lowers its feeding value (FV) as fibre concentration increases, the rate and extent of digestibility decreases, and voluntary intake declines. Ryegrass pastures are susceptible to accumulation of endophytic and saprophytic fungi in dead material at the base of the sward, especially when mature and laxly grazed. Feeding forage legumes to ruminants grazing grass-dominant pastures will improve animal performance and lessen the reliance on a single species to meet all nutritional requirements. The FV of forage is a function of intake and NV, measured by chemical analyses and animal feeding trials. Performance of individual animals grazing forages is usually limited by energy intake because structural fibre can slow digestion and clearance from the rumen and because of competition between individuals for available feed. The use of metabolisable energy (ME) content of forage to signify FV can give a reasonable indication of animal performance, but it should be used in conjunction with chemical analyses to improve the accuracy of predictions. The relationship between FV, pasture production, animal performance and profitability is complex. The importance of skilled management to maintain pasture quality and optimise animal performance under inconsistent climatic conditions should not be underestimated. Acceptable animal performance with minimal veterinary intervention requires good nutrition, but the genetic potential of livestock in New Zealand cannot be met solely by grazing pasture, especially when a high utilisation of pasture is required to maintain quality and profitability. Producers are responding to industry demands to reduce the seasonality in supply of milk and meat by changing lambing and calving dates, and extending lactation length in dairy cows. Social changes include adoption of once-daily milking in the dairy industry. Some changes have necessitated increased use of supplements and others can be met by feeding forages with a higher FV than ryegrass, all of which require an improved knowledge of feed quality. This information is available through rapid and inexpensive near infrared spectroscopy (NIRS) analysis, enabling animal nutritional needs to be balanced by appropriate nutrient supply. It is essential that producers continue to improve animal welfare, limit excessive use of fertilisers and meet the demands of overseas consumers. Good nutrition, with an increased use of legumes and other forages to complement ryegrass pastures, will enable these objectives to be achieved. 相似文献
964.
Chwalibog A Tauson AH Thorbek G 《Journal of animal physiology and animal nutrition》2004,88(3-4):101-112
Energy metabolism and substrate oxidation was measured in 12 growing pigs by means of indirect calorimetry and nutrient balances. The measurements were carried out during 5 days of feeding followed by 4 days of starvation and 5 days of re-feeding. During the feeding period, dietary carbohydrates were the main energy source, sufficient to cover energy requirements without oxidation of fat. Starvation reduced the total heat production and affected the oxidation pattern by reducing protein oxidation and shifting from carbohydrate to fat oxidation. On the second day of starvation, the main energy source was body fat and there was no oxidation of carbohydrate. On the second day of re-feeding, the heat production reached the same level as during the feeding period. Also, during the second day of re-feeding, the pattern of nutrient oxidation was similar to the feeding period with oxidation of carbohydrate providing 90% and oxidation of protein providing 10% of the total heat production. There was no fat oxidation. The results demonstrated that the growing pigs were able to re-establish oxidative patterns already 2 days after re-alimentation. 相似文献
965.
966.
Characterisation of three novel canine osteosarcoma cell lines producing high levels of matrix metalloproteinases 总被引:1,自引:0,他引:1
Loukopoulos P O'Brien T Ghoddusi M Mungall BA Robinson WF 《Research in veterinary science》2004,77(2):131-141
Three canine osteosarcoma cell lines were established from spontaneous pelvic and radial osteosarcomas. The cell populations cultured exhibited characteristics of malignancy and consisted of adherent, pleomorphic, mostly large spindle-shaped or polyhedral cells, characterised by the presence of numerous cytoplasmic granules and vacuoles. The main ultrastructural features included the presence of abundant rough endoplasmic reticulum and numerous cytoplasmic vesicles, deposit vacuoles and small cytoplasmic protrusions. Zymography showed that the cell lines produce high levels of MMP-2 and MMP-9, enzymes directly involved in crucial aspects of the metastatic process. Consistent with their osteoblastic lineage and malignant phenotype, all cell lines were immunoreactive to vimentin, osteopontin, PCNA, p53, MMP-2 and MMP-9, while they were negative for cytokeratin, desmin, SMA, Factor VIII, NSE, GFAP, Rb and p21 protein. No retroviral particles or RNA were detected ultrastructurally or with RT-PCR, although the possibility of viral involvement in osteosarcoma cannot be excluded. The new cell lines provide excellent in vitro models that may allow further studies on the pathobiology of canine osteosarcoma to be undertaken. 相似文献
967.
Variety of traits important in diagnostics and epidemiology of pathogenic microorganisms may change due to antibiotics. Movement ability, that is characteristic for every serovar except from Salmonella Gallinarum-Pullorum, is important to salmonellas. In own experiments using semi-fluid MSRV medium, it was found that a decrease in salmonella sensibility to selected antibiotics and chemiotherapeutics due to passage might lead to weakening of its movement ability. Movement ability of all strains (S. Enteritidis, S. Dublin, S. Typhimurium) after passage with amoxycillin, neomycin, colistin and enrofloxacin became weakened as compared to results achieved before passage. The strongest inhibition of movement ability was most often observed in strains after passage on medium with colistin. It seems to be associated with the action mechanism of the antibiotic. Colistin injuries cellular membranes, where flagella (active motoric organ of Salmonella) are anchored. Appearance of drug-resistance as a result of passage at the presence of antibiotics may cause variability of biochemical properties of Salmonella rods and leads to weakening of movement ability of ciliated Salmonella. 相似文献
968.
Kaleczyc J Pidsudko Z Franke-Radowiecka A Sienkiewicz W Majewski M Lakomy M Timmermans JP 《Polish journal of veterinary sciences》2004,7(3):199-201
The present study investigated the chemical coding of neurons in the celiac-superior mesenteric ganglion complex supplying the normal (n=4) and inflamed (n=4) ileum (chemically-induced inflammation) in juvenile pigs using retrograde tracing combined with immunohistochemistry. Ileum-projecting neurons (IPN) were predominantly distributed in the left and right superior mesenteric pools of the ganglion. The majority of them were adrenergic (tyrosine hydroxylase-positive) and also contained neuropeptide Y, somatostatin or galanin. No clear-cut differences in the distribution and chemical coding of IPN were found between normal and inflamed pigs. However, in the inflamed group, the density of peptidergic, IPN-associated nerve fibres was higher than that found in the control group. 相似文献
969.
There have been very few clinical trials evaluating therapies for naturally occurring spinal cord injury in dogs and cats. This review describes the methods suitable for evaluating the behavioural recovery of animals with spinal cord injuries, in either a clinical or a laboratory setting. A list of commonly used methods for evaluating behavioural recovery in animals is provided, both in the clinical and laboratory setting; the tests, their limitations and benefits and specific recommendations for their use are also discussed in more depth. 相似文献
970.
Since the only registrated anti-ectoparasiticum for horses (foxim) is no longer available in The Netherlands, some cases of amitraz intoxication of the horse have occurred. In this article the literature concerning amitraz intoxications and experiments will be discussed and some cases will be described. 相似文献