全文获取类型
收费全文 | 29665篇 |
免费 | 1486篇 |
国内免费 | 13篇 |
专业分类
林业 | 1117篇 |
农学 | 952篇 |
基础科学 | 191篇 |
4352篇 | |
综合类 | 4780篇 |
农作物 | 1126篇 |
水产渔业 | 1643篇 |
畜牧兽医 | 14676篇 |
园艺 | 374篇 |
植物保护 | 1953篇 |
出版年
2019年 | 338篇 |
2018年 | 506篇 |
2017年 | 589篇 |
2016年 | 561篇 |
2015年 | 400篇 |
2014年 | 543篇 |
2013年 | 1140篇 |
2012年 | 1051篇 |
2011年 | 1278篇 |
2010年 | 871篇 |
2009年 | 812篇 |
2008年 | 1288篇 |
2007年 | 1247篇 |
2006年 | 1180篇 |
2005年 | 1051篇 |
2004年 | 968篇 |
2003年 | 999篇 |
2002年 | 902篇 |
2001年 | 855篇 |
2000年 | 835篇 |
1999年 | 683篇 |
1998年 | 327篇 |
1997年 | 311篇 |
1996年 | 260篇 |
1995年 | 295篇 |
1994年 | 258篇 |
1993年 | 268篇 |
1992年 | 457篇 |
1991年 | 547篇 |
1990年 | 464篇 |
1989年 | 447篇 |
1988年 | 427篇 |
1987年 | 444篇 |
1986年 | 384篇 |
1985年 | 417篇 |
1984年 | 370篇 |
1983年 | 314篇 |
1982年 | 267篇 |
1979年 | 399篇 |
1978年 | 306篇 |
1977年 | 309篇 |
1976年 | 318篇 |
1975年 | 333篇 |
1974年 | 356篇 |
1973年 | 316篇 |
1972年 | 299篇 |
1969年 | 293篇 |
1968年 | 272篇 |
1967年 | 335篇 |
1966年 | 309篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
33.
An account is given of the methodology for fractionation of cock spermatozoa into head and tail fractions by ultrasonication, followed by sucrose density gradient centrifugation. Quantitative estimates of DNA attested to 89.4% purity of the head fraction and low contamination of tails with heads. Recovery of protein and malic dehydrogenase (MDH) activity, following sperm fractionation, averaged 94.3% and 95.7%, respectively. Contamination of the head fraction with tails, as assessed by MDH assay, was only 4.65%, and the purity of the tail fraction was 91%. Intensive succinic dehydrogenase (SDH) activity was histochemically localised in the separated tail fraction and in the tail portion of intact spermatozoa. However, SDH activity was discernible neither in the head fraction nor in the head of intact spermatozoa. 相似文献
34.
The relationship between the levels of CO and airborne Pb was evaluated against conditions of traffic flow, ambient air temperature and the ventilation rates in 3 underground car parks. During the study period significant variations were noted in the levels of the pollutants in each of the car parks which frequently exceeded the proposed Malaysian Air Quality Standard of 0.7 μg m?3Pb and 9 μg L?1 (8 hr average) CO for indoor environs. High correlation coefficient values were obtained between the levels of CO and traffic flow and Pb and traffic flow. High traffic flow also increased the mean air temperature inside the car parks. Reductions in the ventilation rates in the car parks caused an almost two-fold increase in the level of CO and vice versa. A simple mathematical model depicting the CO concentrations in relation to other parameters was formulated. 相似文献
35.
36.
While isotopic techniques have largely superseded traditional markers for the determination of the volume of fluid compartments in vivo, they are not always convenient, especially with diarrhoeic animals. A direct comparison was therefore made in week-old calves between Evans blue and radio-iodinated serum albumin as measures of plasma volume and thiocyanate or 24sodium as measures of extracellular fluid space. The correlation coefficients were excellent (1.00, 0.96; P < 0.001) and the calves had plasma and extracellular fluid volumes of 72 +/- 2 and 438 +/- 2 ml kg-1, respectively. The latter value is, though high, typical of young animals and comparable with other data in calves. 相似文献
37.
38.
39.
T Ishida A Taniguchi S Matsumura T Washizu I Tomoda 《Veterinary immunology and immunopathology》1992,35(1-2):15-22
Eleven feline immunodeficiency virus (FIV) infected asymptomatic carrier (AC) cats were observed for 2 years for development of acquired immunodeficiency syndrome (AIDS). Four of the 11 (36.4%) showed progression of the clinical stage. Persistent generalized lymphadenopathy was noted in three cats as the first sign of illness after the AC phase, while the other showed lymphadenopathy with signs of AIDS-related complex. In all four cats the AIDS-related complex stage lasted for 10 months or longer, and two showed progression of the disease into AIDS. The two cats showing AIDS illnesses died within approximately 1 year after they had developed persistent generalized lymphadenopathy. Pathology confirmed the diagnosis of AIDS characterized by the presence of depletion lesions in the lymphoid organs, and of severe infections of an opportunistic nature. The overall mortality of FIV infected AC cats during a 2 year period was two out of 11 (18.2%). These cats showed decreased concanavalin A mitogen response of peripheral blood mononuclear cells as the disease progressed. 相似文献
40.
Sera from 74,502 cattle from 3087 farms in England and Wales were tested for the presence of antibodies against Hypoderma bovis in the spring of 1988. Twenty-nine positive sera were identified on 18 premises and these animals were treated; an examination of 6030 sera taken from 108 neighbouring herds identified another 17 seropositive animals on 10 farms in Devon, Cornwall, Lancashire, Shropshire and Powys, indicating that these counties still harbour populations of warble fly. 相似文献