全文获取类型
收费全文 | 232056篇 |
免费 | 12731篇 |
国内免费 | 148篇 |
专业分类
林业 | 9389篇 |
农学 | 7427篇 |
基础科学 | 1537篇 |
28626篇 | |
综合类 | 38123篇 |
农作物 | 8793篇 |
水产渔业 | 11787篇 |
畜牧兽医 | 120208篇 |
园艺 | 3082篇 |
植物保护 | 15963篇 |
出版年
2019年 | 2096篇 |
2018年 | 3241篇 |
2017年 | 3557篇 |
2016年 | 3346篇 |
2015年 | 2869篇 |
2014年 | 3555篇 |
2013年 | 9174篇 |
2012年 | 6462篇 |
2011年 | 7980篇 |
2010年 | 5269篇 |
2009年 | 5267篇 |
2008年 | 7869篇 |
2007年 | 7535篇 |
2006年 | 7204篇 |
2005年 | 6606篇 |
2004年 | 6500篇 |
2003年 | 6539篇 |
2002年 | 6172篇 |
2001年 | 7442篇 |
2000年 | 7209篇 |
1999年 | 5845篇 |
1998年 | 2376篇 |
1997年 | 2413篇 |
1996年 | 2213篇 |
1995年 | 2676篇 |
1994年 | 2395篇 |
1993年 | 2358篇 |
1992年 | 4772篇 |
1991年 | 4998篇 |
1990年 | 5066篇 |
1989年 | 5077篇 |
1988年 | 4651篇 |
1987年 | 4716篇 |
1986年 | 4730篇 |
1985年 | 4553篇 |
1984年 | 3798篇 |
1983年 | 3376篇 |
1982年 | 2341篇 |
1981年 | 2163篇 |
1979年 | 3372篇 |
1978年 | 2762篇 |
1977年 | 2388篇 |
1976年 | 2222篇 |
1975年 | 2361篇 |
1974年 | 2983篇 |
1973年 | 3049篇 |
1972年 | 2942篇 |
1971年 | 2589篇 |
1970年 | 2574篇 |
1969年 | 2410篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
G W De Lisle D M Collins H F Huchzermeyer 《The Onderstepoort journal of veterinary research》1992,59(2):163-165
Restriction endonuclease analysis and DNA hybridization revealed five ovine strains of Mycobacterium paratuberculosis from South Africa had identical DNA patterns to an ovine strain from Canada. Genetically this strain type has features in common with the two major groups of M. paratuberculosis. 相似文献
43.
Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%. 相似文献
44.
T Nishita M Sakomoto T Ikeda H Amasaki M Shino 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(10):1147-1149
Salivary or secreted carbonic anhydrase (CA), which constitutes a new class of CA, designated CA-VI, was isolated. Swine CA-VI purified from swine saliva by inhibitor-affinity chromatography and ion exchange chromatography had a specific activity of 5,468 units/mg. The molecular weight was 250,000, as determined by gel filtration under non-denaturing conditions, and the subunit molecular weight was found to be 37,000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that swine CA-VI consists of 7 subunits. The treatment of the enzyme with endo-N-acetylglucosaminidase F reduced its subunit molecular weight from 37,000 to 35,000 and 32,000. We raised a rabbit antibody against purfied swine CA-VI. Double immunodiffusion showed that anti-swine CA-VI serum reacted with swine CA-VI and swine saliva, but not with hemolysate (containing CA-I and CA-Il) or muscle extracts (containing CA-III). The concentration of CA-VI in swine saliva, measured using single radial immunodiffusion, was 0.027 +/- 0.017 mg/mg total protein. 相似文献
45.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils. 相似文献
46.
A shrubby plant, abundant in east Kenya, Gynandropsis gynandra (L.) Brig., was shown to exhibit repellent and acaricidal properties to larvae, nymphs and adult Rhipicephalus appendiculatus and Amblyomma variegatum ticks. All stages of ticks avoided the leaves of the plant and a high percentage of the ticks which were continuously exposed to its leaves died; surviving ticks were weak and inactive but regained activity when exposed to fresh air. The effectiveness of the plant's leaves as a repellent and acaricide was most pronounced on nymphs and least pronounced on adults. Field investigations indicated that ticks were not found up to 2-5 m from the plant in areas where the plant was predominant. The potential of using the plant for tick control within an integrated tick management system in the resource-poor farming context in Africa was highlighted. 相似文献
47.
A strain of Yersinia enterocolitica of O serogroup 6,30 isolated from the liver of an aborted ovine fetus was inoculated intravenously into a group of pregnant ewes at about 90 days gestation and produced placentitis with abortion or delivery of infected lambs about 50 days later. Y. enterocolitica of the same serogroup was recovered from the necrotic placental cotyledons and most other fetal tissues and could be isolated from vaginal discharges of the ewes for a least 2 weeks after abortion. Histological changes were consistent with an acute bacterial necrotizing placentitis and systemic infection of the fetus. Subsequent pregnancies in the ewes proceeded to term without evidence of infection. 相似文献
48.
Three in vitro assays to detect benzimidazole resistance, namely, the egg-hatch assay, tubulin-binding assay, and a larval-development assay, were evaluated by estimating the level of benzimidazole resistance in three field isolates of Haemonchus contortus compared with a susceptible reference strain. Comparisons were also made with estimates of benzimidazole resistance of the three field strains obtained from an in vivo controlled anthelmintic efficacy test. All three in vitro tests showed similar, consistent results which also suggested greater sensitivity than the in vivo assay. These results indicate that selection of an in vitro technique to determine benzimidazole resistance should therefore be based on considerations other than precision, such as technical expertise, availability of equipment, cost and speed in which diagnosis is required. 相似文献
49.
Classical “high-lysine” sorghum lines are characterized by smaller seeds than average, due to a decrease in prolamin synthesis and a subsequent decrease in yield. To exploit the natural variation in lysine content and to identify ecotypes with a seed lysine content higher than average, characterized by plump seeds, a method was developed based on root-growth inhibition of seeds growing on a medium containing aminoethylcysteine (AEC), a lysine analogue. By using a collection of sorghum mutants and ecotypes a correlation coefficient of 0.926 between root length and lysine content was established. This method, which uses the root length of plants growing on aec to indicate which lines have a potential elevated lysine content, can be applied for the screening of sorghum germplasm. Since this is a non-destructive method it can also be used at the individual seed level, for example for screening progenies of regenerated plants from in vitro culture to exploit the somaclonal variation. 相似文献
50.
Little is known about the effect of fertilization on the N uptake of sunflowers. A 42 factorial trial with 0, 60, 120 and 180 kg N ha−1 and 0, 15, 30 and 45 kg P ha−1 was conducted over three years. The N content and concentration of leaves, stems and capitula were determined at three growth stages. High N levels increased the N content and concentration of all plant parts at all growth stages sharply. High P levels increased the N content of all plant components through better growth. P has an inconsistent effect on N concentration but tended to decrease it. After flowering the crop assimilated 20 to 25 % of the total N. This implies that N applied can still be applied and utilized by the crop at a late stage. This should be substantiated by further research. 相似文献