全文获取类型
收费全文 | 148832篇 |
免费 | 7824篇 |
国内免费 | 84篇 |
专业分类
林业 | 6214篇 |
农学 | 4366篇 |
基础科学 | 933篇 |
16665篇 | |
综合类 | 28320篇 |
农作物 | 5713篇 |
水产渔业 | 6747篇 |
畜牧兽医 | 77104篇 |
园艺 | 1766篇 |
植物保护 | 8912篇 |
出版年
2018年 | 1857篇 |
2017年 | 1982篇 |
2016年 | 1858篇 |
2015年 | 1669篇 |
2014年 | 1890篇 |
2013年 | 5639篇 |
2012年 | 3756篇 |
2011年 | 4622篇 |
2010年 | 3014篇 |
2009年 | 2965篇 |
2008年 | 4552篇 |
2007年 | 4271篇 |
2006年 | 4018篇 |
2005年 | 3785篇 |
2004年 | 3825篇 |
2003年 | 3810篇 |
2002年 | 3693篇 |
2001年 | 4501篇 |
2000年 | 4523篇 |
1999年 | 3483篇 |
1998年 | 1501篇 |
1997年 | 1514篇 |
1995年 | 1717篇 |
1994年 | 1586篇 |
1993年 | 1535篇 |
1992年 | 3163篇 |
1991年 | 3439篇 |
1990年 | 3330篇 |
1989年 | 3385篇 |
1988年 | 3084篇 |
1987年 | 3083篇 |
1986年 | 3276篇 |
1985年 | 3191篇 |
1984年 | 2598篇 |
1983年 | 2419篇 |
1982年 | 1573篇 |
1981年 | 1500篇 |
1979年 | 2370篇 |
1978年 | 1941篇 |
1977年 | 1654篇 |
1976年 | 1641篇 |
1975年 | 1688篇 |
1974年 | 2155篇 |
1973年 | 2185篇 |
1972年 | 2145篇 |
1971年 | 2024篇 |
1970年 | 1946篇 |
1969年 | 1793篇 |
1968年 | 1500篇 |
1967年 | 1570篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
J O Britt A Z Nagy E B Howard 《Journal of the American Veterinary Medical Association》1979,175(9):921-923
Acute viral hepatitis was diagnosed in five California sea lions (Zalophus californianus) stranded along the Los Angeles coast. Light microscopy revealed large nuclear inclusion bodies in hepatocytes. Electron microscopy provided evidence that these inclusion bodies were composed of adenovirus-like virions. Attempts to grow the virus in cell culture systems were unsuccessful. 相似文献
942.
943.
944.
B. R. Blakley 《The Canadian veterinary journal. La revue veterinaire canadienne》1979,20(12):358-360
The data on health problems from visual livestock inspection at an auction mart in Saskatchewan during a two year period were tabulated for swine, cattle and calves. The major conditions seen in swine were underweight animals, infectious diseases or congenital abnormalities. Infectious diseases such as Hypoderma spp. infestations, ringworm or eye infections were the primary troubles in older cattle. Young calves demonstrated a predominance of congenital (herniation) and infectious (enteritis or navel infection) diseases. 相似文献
945.
946.
947.
Birth difficulty and poor lamb vigour are significant causes of perinatal lamb mortality. In this study we investigated whether sheep breeds differing in appearance, muscularity and selection history also had differences in dystocia and lamb vigour, and considered some of the factors that may contribute to the variation in these traits. Data were collected at birth from a total of 3252 lambs of two terminal sire breeds selected for lean growth (Suffolk [S], n = 500 and Texel [T], n = 1207), from a Hill breed (Scottish Blackface [B], n = 610), which has been mainly selected for hardiness, and a crossbred (Mule × T [M], n = 935) representing a maternal line. For each lamb the degree of assistance at delivery, lamb presentation, amount of assistance to achieve successful sucking, sex, litter size and birth weight were recorded. T lambs required the most, and B and M lambs the least assistance at birth, S lambs were intermediate (% lambs assisted: T = 55.7, S = 30.7, B = 22.7, M = 24.9, P < 0.001). T and S lambs were equally likely to be malpresented at birth (29% of births) and more likely to be malpresented than B or M lambs (20%; P < 0.001). In T and S breeds lambs requiring veterinary assistance at delivery were mainly heavy and singleton lambs, whereas in B and M breeds these were exclusively low birth weight lambs in multiple litters. Although heavier lambs needed greater birth assistance, T lambs were lighter than S and M lambs, but heavier than B lambs (birth weight (kg): S = 4.66, M = 4.56, T = 4.32, B = 3.67, P < 0.001). S lambs were more likely to require assistance with sucking than other breeds, and T lambs also required more assistance than B or M lambs (% lambs assisted to suck: S = 56.0, T = 31.6, M = 19.8, B = 18.4, P < 0.001). Heavier lambs were more likely to suck unaided than lighter lambs (P < 0.001). The data suggest that the two terminal sire breeds, selected narrowly for greater productivity (muscle growth and conformation), are more likely to experience birth difficulty and poorer lamb vigour than the breed selected for hardiness, or the cross breed. Whether these effects arise as a consequence of genetic selection (e.g. for specific lamb conformation), or as a result of management practices to achieve selection goals (e.g. increased intervention at lambing) is unknown. Specific actions to improve birth difficulty and lamb vigour, such as including these traits in the selection index, would be beneficial in improving the welfare of ewes and lambs of the terminal sire breeds. 相似文献
948.
Blood from calves infected with Theileria annulata and T parva was freed from host cell elements and the piroplasms liberated from the red cells by ammonium chloride lysis. Lysates of the purified piroplasms and control host cell material were examined electrophoretically for several enzymes. Zymograms stained for glucose phosphate isomerase showed distinct differences between the host cell enzyme pattern and parasite enzyme patterns. The isoenzyme pattern of T annulata piroplasms differed from the isoenzyme pattern of T parva piroplasms. 相似文献
949.
While both Brucella abortus and Yersinia enterocolitica IX have O antigens in common, they differ significantly with respect to motility. Thus Br abortus is always non-motile while Y enterocolitica is motile when grown at room temperature. The presence of yersinia H agglutinins in serum can be shown to be evidence of previous exposure to Y enterocolitica. These agglutinins are not generated by brucella infection. A rapid H agglutination test will serve to provide this differentiation without interference from cross-reacting O antigens. 相似文献
950.
Glanzmann thrombasthenia (GT) is characterized by a defect of platelet aggregation. This autosomal recessive genetic disorder is caused by an abnormality of the platelet glycoprotein receptors alpha IIb or beta III. Recently, we identified a horse with clinical and pathological features of GT. The aim of this study was to describe this case of GT at the molecular level. A point mutation from G to C in exon 2 of ITGA2B causing a substitution of the expected amino acid arginine 72 (Arg(72)) by a proline (Pro(72)) was encountered. This amino acid change may result in abnormal structural conformations that yield an inactive alpha IIb subunit. The genomic DNA analysis showed that this horse was homozygous for the missense mutation. 相似文献