全文获取类型
收费全文 | 64889篇 |
免费 | 3017篇 |
国内免费 | 46篇 |
专业分类
林业 | 2638篇 |
农学 | 1690篇 |
基础科学 | 437篇 |
6451篇 | |
综合类 | 15062篇 |
农作物 | 2519篇 |
水产渔业 | 2468篇 |
畜牧兽医 | 32410篇 |
园艺 | 703篇 |
植物保护 | 3574篇 |
出版年
2018年 | 565篇 |
2017年 | 604篇 |
2016年 | 581篇 |
2014年 | 610篇 |
2013年 | 1994篇 |
2012年 | 1340篇 |
2011年 | 1612篇 |
2010年 | 1017篇 |
2009年 | 968篇 |
2008年 | 1569篇 |
2007年 | 1541篇 |
2006年 | 1511篇 |
2005年 | 1515篇 |
2004年 | 1473篇 |
2003年 | 1525篇 |
2002年 | 1465篇 |
2001年 | 1534篇 |
2000年 | 1516篇 |
1999年 | 1234篇 |
1997年 | 552篇 |
1995年 | 609篇 |
1994年 | 582篇 |
1993年 | 578篇 |
1992年 | 1324篇 |
1991年 | 1412篇 |
1990年 | 1470篇 |
1989年 | 1506篇 |
1988年 | 1419篇 |
1987年 | 1369篇 |
1986年 | 1410篇 |
1985年 | 1382篇 |
1984年 | 1162篇 |
1983年 | 1018篇 |
1982年 | 728篇 |
1981年 | 692篇 |
1980年 | 651篇 |
1979年 | 1140篇 |
1978年 | 922篇 |
1977年 | 830篇 |
1976年 | 772篇 |
1975年 | 866篇 |
1974年 | 1134篇 |
1973年 | 1068篇 |
1972年 | 1135篇 |
1971年 | 1091篇 |
1970年 | 1030篇 |
1969年 | 885篇 |
1968年 | 719篇 |
1967年 | 851篇 |
1966年 | 699篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Modell W 《Science (New York, N.Y.)》1939,89(2311):349-350
44.
Glock WS 《Science (New York, N.Y.)》1922,56(1452):484-485
45.
46.
Karen E. Bateman DVM MSc Pamela A. Catton Paul W. Pennock Stephen A. Kruth 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(4):267-272
Eighteen dogs with malignant melanoma of the oral cavity were treated with high-dose per fraction (0–7–21) radiation therapy. Eight hundred cGy was administered on days 0, 7, and 21 for a total dose of 2,400 cGy in 3 weeks. Of 17 dogs evaluated, 9 (53%) had a complete remission and 5 (30%) achieved a partial remission with an overall response rate of 83%. Local failure occurred in 2 of the 9 dogs where a complete response was initially observed. One dog died of intercurrent disease, and one died of metastatic disease without evidence of local recurrence. Five dogs are alive and free of disease 9 to nineteen months from the initiation of therapy. The 0–7–21 protocol was well-tolerated, and acute radiation reactions were low-grade and limited to the skin. The results of this study demonstrate that oral melanomas in dogs are responsive to radiation. 0–7–21 radiation therapy offers a viable alternative to radical excision, especially when tumor volume or location would require cosmetically or functionally debilitating surgery. 相似文献
47.
48.
This study describes the epidemiological features of bovine spongiform encephalopathy (BSE) in Northern Ireland where the first case occurred in November 1988. They were very similar to those observed in Great Britain except that the annual incidence of BSE in 1990 in Northern Ireland, 2.3 confirmed cases per 10,000 adult cows, was approximately one 10th of that in Great Britain. The findings were also consistent with the current hypothesis that affected cattle had been exposed to a scrapie-like agent via cattle feedstuffs containing ruminant-derived protein. However, a preliminary investigation of the potential sources of infection for cattle in Northern Ireland did not provide any conclusive evidence. 相似文献
49.
X M Zhang W Herbst H Lange-Herbst T Schliesser 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(10):765-770
1,268 sera collected from slaughtered pigs in Hassia (FRG) from 1986 to 1988 were tested for antibodies against porcine and human influenza A virus strains using the single radial haemolysis test (SRHT). Antibodies against the porcine strains (subtype H1N1) A/Swine/Arnsberg/1/81, A/Swine/Iowa/15/30 and A/New Jersey/7/76 were detected in 411 (32.4%), 318 (25.1%) and 304 (24.0%) of sera, respectively. Up to 1988 a slight increase (10%) in the seroprevalence to A/Swine/Arnsberg/1/81 was noticed, whereas the results obtained with the other strains showed little variation. Antibodies against the human H1N1 strain A/Singapore/6/86 were only found in sera collected 1987 and 1988 in rates of 1.6% and 3.0%. Serological indication of infections with the human H3N2 strains A/Victoria/1/75, A/Hong Kong/1/68 and A/Philippines/2/82 could be shown in 286 (22.6%), 178 (14.4%) and 135 (10.6%) of the serum samples. Within the three year period the rate of sera positive for antibodies against A/Philippines/2/82 increased from 6.5% to 23.0%, whereas no variation in the rates were found using the other H3N2 strains. Antibodies simultaneously against porcine (H1N1) and human (H3N2) virus strains were detected in 9.9% of all sera tested. 相似文献
50.
Linear functions of body weight and condition score at weaning and 18 mo of age were used to predict the mature weight (A) and maturing rate (k) parameters of an asymptotic growth model of Angus cows at the Subtropical Agricultural Research Station, Brooksville, FL. From 1981 through 1988 a heavy-mature-weight line (Line A) and a rapid-maturing line (Line K) were selected based on predicted A and k values. Linear contrasts (A-K) of least squares means for weight at fixed ages indicated that the weight difference between lines increased from birth to maturity during the period of the study. Animals from Line A were heavier (P less than .01) at all ages. A negative response in maternal ability, relative to increased growth potential of their calves, seems to have occurred in the cows of Line A. Mature weight was reached at approximately 4.5 yr of age in Line K and at approximately 5.5 yr in Line A. Brody's three-parameter and Richards' four-parameter functions were fitted to 2,855 quarterly weights of cows, from birth to 6.5 yr of age, to estimate the average growth curve for each line. Brody's model gave better estimates of weights from 18 mo to maturity, but the asymptotic residual mean squares were slightly higher because early weights were overestimated. Linear and nonlinear regression analyses of weight-age data and comparisons of degree of maturity at different premature ages showed differences in the growth patterns of the two lines selected for early predicted values of A and k. 相似文献