全文获取类型
收费全文 | 38338篇 |
免费 | 2243篇 |
国内免费 | 286篇 |
专业分类
林业 | 1580篇 |
农学 | 1416篇 |
基础科学 | 331篇 |
5509篇 | |
综合类 | 5679篇 |
农作物 | 1488篇 |
水产渔业 | 1807篇 |
畜牧兽医 | 19908篇 |
园艺 | 463篇 |
植物保护 | 2686篇 |
出版年
2021年 | 364篇 |
2020年 | 425篇 |
2019年 | 473篇 |
2018年 | 788篇 |
2017年 | 830篇 |
2016年 | 748篇 |
2015年 | 628篇 |
2014年 | 785篇 |
2013年 | 1833篇 |
2012年 | 1317篇 |
2011年 | 1542篇 |
2010年 | 1059篇 |
2009年 | 1090篇 |
2008年 | 1485篇 |
2007年 | 1335篇 |
2006年 | 1265篇 |
2005年 | 1083篇 |
2004年 | 1039篇 |
2003年 | 1037篇 |
2002年 | 912篇 |
2001年 | 1245篇 |
2000年 | 1231篇 |
1999年 | 930篇 |
1998年 | 389篇 |
1997年 | 419篇 |
1996年 | 341篇 |
1995年 | 394篇 |
1994年 | 342篇 |
1992年 | 659篇 |
1991年 | 785篇 |
1990年 | 687篇 |
1989年 | 720篇 |
1988年 | 663篇 |
1987年 | 624篇 |
1986年 | 670篇 |
1985年 | 595篇 |
1984年 | 462篇 |
1983年 | 414篇 |
1979年 | 553篇 |
1978年 | 432篇 |
1977年 | 360篇 |
1976年 | 365篇 |
1975年 | 397篇 |
1974年 | 461篇 |
1973年 | 475篇 |
1972年 | 449篇 |
1970年 | 367篇 |
1969年 | 402篇 |
1968年 | 357篇 |
1967年 | 360篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Basic studies carried out in India showed that the incubation period of TLCV in plants varied from 8 days in August to 90 days in winter. The acquisition threshold for the whitefly,Bemisia tabaci Gen., was 31 min; it resulted in 3% transmission. An acquisition access of 24 h for a female whitefly on a TLCV source resulted in 30% transmission. A minimum feeding period of 32 min was required by a viruliferous whitefly to cause infection on tomato test plants; this gave 4% transmission. With inoculation access of 24 h on tomato test plants, the transmission rose to 24%. Starving the vector for 1 h pre-acquisition or 1 h pre-inoculation resulted in higher levels of transmission of TLCV: 36 and 40%, respectively, compared with 20% for non-starved whiteflies. Extending the fasting period beyond 1 h resulted in a reduced transmission level. The whiteflies could acquire the virus from the cotyledonary leaves of an infected tomato plant, with a resultant 28% transmission; but infection did not occur when the whiteflies had an inoculation access to such leaves. Higher transmission rates were obtained when the younger leaves on tomato plants were used for acquisition and inoculation. Transmission was 8 and 38% when five whiteflies per plant were allowed 24 h of acquisition access to 11- and 2-month-old virus sources, respectively. After an acquisition access of 24 h to a TLCV source, male and female whiteflies retained their infectivity for 5 and 53 days, respectively. Nymphs can acquire and transmit the virus. When ten whiteflies of each sex were given 24 h of acquisition and of inoculation access, the subsequent transmission rate of males and females was 56 and 86%, respectively. This virus is not transovarially transmitted. Whitefly colonies raised on brinjal were more efficient (70 and 84% transmission in two experiments) than those raised on chilli, cotton, cowpea, tobacco or tomato. 相似文献
63.
64.
65.
Singer N 《Science (New York, N.Y.)》1992,258(5079):32-33
66.
Raskin RE Nipper MN 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1992,21(2):62-67
Frozen sections and imprint smears were used to evaluate the presence and pattern of cytochemical staining reactions in the B- and T-cell regions of lymph nodes from normal dogs and dogs with lymphoma. Staining procedures evaluated included peroxidase (PER), Sudan black B (SBB), naphthol AS-D chloroacetate esterase (CAE), alpha-naphthyl butyrate esterase (NBE), acid phosphatase (ACP), and leukocyte alkaline phosphatase (LAP). In normal lymph nodes, macrophages and some lymphocytes within the interfollicular (T-cell) region and medulla stained positive with ACP and NBE. Smaller numbers of macrophages also occurred sporadically within the germinal follicles. Cells positive for PER, SBB, and CAE were scattered infrequently throughout all regions of the normal lymph node, consistent with granulocytes and mast cells. The LAP stained cells were predominantly and prominently located within the mantle zone of secondary follicles and to a much lesser extent within the germinal centers, compatible with B-cell lymphocytes derived from follicular center cells. Of the 12 dogs with lymphoma, 7 cases (4 immunoblastic, 2 large noncleaved, 1 small noncleaved) stained diffusely positive with LAP, 4 cases (all lymphoblastic) had numerous focally positive lymphocytes using ACP and NBE, and 1 case (immunoblastic) did not stain positive with any of the cytochemical reactions. Cytochemical staining of canine lymph nodes with NBE, ACP, and LAP proved useful in distinguishing between B- or T-cell regions and detecting different cell types of canine lymphoma. 相似文献
67.
Smalheiser N 《Science (New York, N.Y.)》1990,249(4976):1486-1487
68.
N C 《Science (New York, N.Y.)》1990,247(4948):1285
69.
Chalmers GA Nation PN Pritchard J 《The Canadian veterinary journal. La revue veterinaire canadienne》1990,31(4):292-295
Terminal ileitis was diagnosed in three flocks of lambs in different areas of Alberta. Salient clinical features in affected lambs were progressive emaciation with diarrhea, and in some lambs, frequent abdominal stretching. Postmortem findings included thickening of the ileal, and in some animals, the jejunal, cecal and colonic mucosa as a result of mucosal infiltrates of many lymphocytes and fewer plasma cells, eosinophils, globular leukocytes, and neutrophils. Hyperplasia of intestinal lymphoid tissue was prominent in most affected lambs. The cause of the condition is unknown. 相似文献
70.