全文获取类型
收费全文 | 17497篇 |
免费 | 1229篇 |
国内免费 | 413篇 |
专业分类
林业 | 1134篇 |
农学 | 1450篇 |
基础科学 | 355篇 |
2491篇 | |
综合类 | 2711篇 |
农作物 | 735篇 |
水产渔业 | 1145篇 |
畜牧兽医 | 7395篇 |
园艺 | 368篇 |
植物保护 | 1355篇 |
出版年
2023年 | 112篇 |
2022年 | 165篇 |
2021年 | 229篇 |
2020年 | 232篇 |
2019年 | 304篇 |
2018年 | 437篇 |
2017年 | 446篇 |
2016年 | 449篇 |
2015年 | 452篇 |
2014年 | 451篇 |
2013年 | 726篇 |
2012年 | 682篇 |
2011年 | 795篇 |
2010年 | 664篇 |
2009年 | 604篇 |
2008年 | 743篇 |
2007年 | 752篇 |
2006年 | 656篇 |
2005年 | 680篇 |
2004年 | 503篇 |
2003年 | 537篇 |
2002年 | 448篇 |
2001年 | 821篇 |
2000年 | 802篇 |
1999年 | 690篇 |
1998年 | 272篇 |
1997年 | 249篇 |
1996年 | 206篇 |
1995年 | 220篇 |
1994年 | 210篇 |
1993年 | 186篇 |
1992年 | 368篇 |
1991年 | 390篇 |
1990年 | 329篇 |
1989年 | 303篇 |
1988年 | 308篇 |
1987年 | 336篇 |
1986年 | 253篇 |
1985年 | 197篇 |
1984年 | 179篇 |
1983年 | 149篇 |
1982年 | 96篇 |
1981年 | 86篇 |
1980年 | 81篇 |
1979年 | 143篇 |
1978年 | 94篇 |
1977年 | 73篇 |
1975年 | 77篇 |
1974年 | 79篇 |
1969年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
本文旨在研究用干番茄渣(DTP)部分或全部替代大豆、玉米、小麦、麦麸饲料时,对蛋鸡生产性能、蛋品质的影响。将288只试验鸡(27—38周龄)随机分成4组,每组72只.分别为:DTP0(对照组)、DTP50、DTP100、DTP150(每吨饲料中分别含0、50、100、150kg DTP)。与对照组相比.DTP100组使其产蛋量、产蛋总重分别增加2.7%、4.1%.而鸡的体重、蛋重、日消耗饲料量、蛋壳重、蛋壳厚、哈夫单位、蛋黄颜色均与对照组相似。DTP150组使产蛋量、产蛋总重分别降低3.6%、3.0%,但饲料转化率增加2.9%。结果表明.DTP可以作为蛋鸡的饲料原料。 相似文献
43.
D E Granstrom R K Ridley Y Baoan L J Gershwin P M Nesbitt L A Wempe 《American journal of veterinary research》1989,50(4):571-574
Eight bovine hearts with lesions of eosinophilic myositis (EM) and 2 bovine hearts without EM lesions were collected at slaughter. Blood samples from these 10 hearts, and the heart of a newborn calf also were collected. Histologically, Sarcocystis cruzi was identified in the 8 hearts with EM lesions and the 2 hearts without EM lesions, but not in the heart of the newborn calf. Serum was harvested from the 10 blood samples and was used in homologous, modified, passive cutaneous anaphylaxis tests. Antigen was prepared from S cruzi bradyzoites isolated from the 2 hearts without EM lesions. Serum samples from the 8 cattle with EM lesions reacted positively to S cruzi antigen. When heat-inactivated IgE in serum (56 C for 4 hours) was used, all passive cutaneous anaphylaxis responses were considered negative. Using ELISA, serum IgE concentrations from the 10 cattle with and without EM lesions were 2.2 to 9 U/ml. As determined by radial immunodiffusion, IgM concentrations were 80 to 215 mg/dl. Immunoglobulin G concentrations were 420 to 2,050 mg/dl, but most were less than or equal to 1,700 mg/dl. Immunoglobulin A concentrations were 0 to 62 mg/dl; 1 steer with EM lesions had 0 mg/dl. Double-gel immunodiffusion confirmed the presence of Sarcocystis-specific precipitating antibodies. Sera from the 10 cattle with and without EM lesions formed at least 1 precipitin band. 相似文献
44.
The effects of abiotic variables on the response of carnation cultivars to Fusarium oxysporum f.sp. dianthi ( F.o. dianthi ) were examined in experiments conducted under semi-controlled environments. The abiotic variables examined were solar radiation intensity, temperature and growth substrate. Temperature was not controlled, but differed markedly among experiments, thus, its effect was not determined quantitatively. Disease incidence and disease severity varied significantly among the experiments (due mainly to differences in temperature), among the solar radiation treatments and among the cultivars tested. The three-way interaction term (i.e. cultivar × shade treatment × experiment) was highly significant ( P < 0.001) when both disease incidence and disease severity were considered, indicating that no single variable was predominant in determining disease intensity. The effects of the growth substrate on disease progress was examined in plants grown in tuff or in tuff mixed with peat (1 : 1 and 1 : 3) substrates. The growth substrate had a potent effect on disease development in the less susceptible cultivars. Severe epidemics developed in all cultivars when they were grown in the tuff/peat mixture, although some were resistant when grown in tuff alone. These results led to the conclusion that the carnation response to F.o. dianthi is substantially influenced by the environmental conditions of the test. 相似文献
45.
Abstract. In Australia, stubble burning and tillage are two of the major processes responsible for the decline of soil organic carbon concentration in cropped soils, and the resulting soil degradation. However, the relative importance of these two practices in influencing the soil organic carbon concentration and the long-term impact on soil quality and productivity are not clear. The effects of stubble burning as practised by farmers in southeastern Australia were evaluated in two field trials, one of 19 years duration, the other of 5 years. Conventional tillage (three tillage passes) led to greater loss of soil organic carbon than stubble burning. Loss of total soil organic carbon attributed to stubble burning in the 0–10 cm layer was estimated to be 1.75 t C ha−1 over the period of the 19-year trial, equivalent to 29% of that lost due to tillage. In the 5-year trial, no change in soil organic carbon due to stubble burning was detectable. Changes in soil quality associated with stubble burning detected in the longer trial included a reduction in macro-aggregate stability, and increases in pH and exchangeable K+ . Only the latter two were detected in the shorter trial. A higher mean wheat yield (average 0.15 t ha−1 ) following stubble burning was observed in the 19-year trial but not in the 5-year trial. Research to monitor the longer term effects of stubble burning is needed, and to identify conditions where loss of soil organic carbon is minimized. 相似文献
46.
47.
J K Lightner G Y Miller W D Hueston C R Dorn 《Journal of the American Veterinary Medical Association》1988,192(10):1410-1413
Data collected by the National Animal Health Monitoring System in Ohio for a 12-month period during 1986 and 1987 were used to determine the relative magnitude of costs associated with mastitis in the following categories: milk production loss, veterinary services, drugs, producer labor, and "other" factors. The cost of milk loss associated with mastitis that was reported by producers cooperating in the National Animal Health Monitoring System program was compared with estimates based on bulk tank somatic cell counts and individual cow milk somatic cell counts. Using producer-reported estimates, milk loss accounted for about one third of the total cost associated with mastitis. When estimates of milk loss were replaced by estimates based on bulk tank somatic cell counts, milk loss accounted for over 80% of the total cost of mastitis. Estimates of the cost of milk loss based on studies relating milk yield to somatic cell counts differed considerably. Consequently, it was unclear how to best estimate the relative magnitude of the milk loss component of mastitis costs. 相似文献
48.
49.
Mixtures of cymoxanil with mancozeb (Mancur) or with mancozeb plus oxadixyl (Pulsan, Sandocur-M) were effective in controlling either metalaxyl-sensitive (MS) or -resistant (MR) isolates ofPseudoperonospora cubensis on cucumbers (cv. ‘Elem’) in growth chambers. Metalaxyl+mancozeb (Ridomil-MZ) and oxadixyl+mancozeb (SAN-518) mixtures were effective against the metalaxyl-sensitive but less so against the metalaxyl-resistant isolate. Fungicide mixtures were far more effective in controlling either the sensitive or the resistant isolates than were the individual components applied alone, thereby representing significant levels of synergistic interactions. Increased efficacy of mixtures relative to their combined components (synergy factor) was calculated by the Wadley method. Mixtures containing cymoxanil showed high synergy factors against the resistant isolate, whereas Ridomil-MZ and SAN-518 did not evince this phenomenon. We concluded that cymoxanil mixtures might be suitable for the control of downy mildew incited by a metalaxyl-resistant isolate ofP. cubensis. 相似文献
50.
Attempts were made to identify 900 species of staphylococci or micrococci recovered from samples of bovine milk examined for mastitis pathogens. The presence and identity of haemolysins was recorded together with results of disc diffusion antibiotic sensitivity tests. The occurrence of clinical mastitis was also noted and somatic cell counts (SCC) were performed on milk samples which were normal in appearance. Eight hundred and thirty-one coagulase positive staphylococci were obtained, of which 810 were S. aureus and 21 were S. intermedius. Of 65 coagulase negative staphylococci the species of 19 could not be determined by the identification systems used. The remainder were identified as S. hyicus sub sp. hyicus (1), S. hyicus sub sp. chromogenes (19), S. haemolyticus (17), S. hominis (3), S. epidermidis (4), S. capitis (1) and either S. hominis or S. warneri (1). Four other isolates could not clearly be assigned to the genus Staphylococcus or Micrococcus and were designated irregular strains. No micrococci were identified. The presence of alpha, beta, or delta haemolysins occurring singly or in various combinations was identified in 98.3% of coagulase positive staphylococci and in 60% of coagulase negative staphylococci. Epsilon haemolysin was detected in 47.6% of the coagulase negative staphylococci and in 9.5% of S. intermedius. All staphylococci were sensitive to tetracycline (30 microg), novobiocin (1.6 microg), nafcillin (30 microg), methicillin (10 microg) and cephalothin (30 microg) and variable numbers of each species were sensitive to penicillin (2 iu) and streptomycin (10 microg). One non-identified species of coagulase negative staphylococcus was sensitive to erythromycin (0.4 microg) the remaining staphylococci were resistant. Each of the four irregular strains was sensitive to erythromycin and novobiocin. Clinical mastitis was associated with 30.6% of coagulase positive staphylococci, 15.3% of coagulase negative staphylococci, and two of the four irregular strains (50%). Subclinical mastitis as determined by SCC of 500 x 10(3) or greater was associated with 92.7% of coagulase positive and 37.5% of coagulase negative staphylococci. 相似文献