全文获取类型
收费全文 | 102288篇 |
免费 | 5866篇 |
国内免费 | 314篇 |
专业分类
林业 | 4548篇 |
农学 | 3642篇 |
基础科学 | 758篇 |
13227篇 | |
综合类 | 16306篇 |
农作物 | 3889篇 |
水产渔业 | 5113篇 |
畜牧兽医 | 52729篇 |
园艺 | 1299篇 |
植物保护 | 6957篇 |
出版年
2019年 | 964篇 |
2018年 | 1676篇 |
2017年 | 1799篇 |
2016年 | 1646篇 |
2015年 | 1405篇 |
2014年 | 1782篇 |
2013年 | 4156篇 |
2012年 | 3075篇 |
2011年 | 3683篇 |
2010年 | 2549篇 |
2009年 | 2617篇 |
2008年 | 3735篇 |
2007年 | 3402篇 |
2006年 | 3311篇 |
2005年 | 2965篇 |
2004年 | 3013篇 |
2003年 | 2979篇 |
2002年 | 2760篇 |
2001年 | 3370篇 |
2000年 | 3343篇 |
1999年 | 2641篇 |
1998年 | 1216篇 |
1997年 | 1163篇 |
1996年 | 1061篇 |
1995年 | 1187篇 |
1994年 | 1129篇 |
1993年 | 990篇 |
1992年 | 2069篇 |
1991年 | 2197篇 |
1990年 | 2227篇 |
1989年 | 2113篇 |
1988年 | 1963篇 |
1987年 | 1853篇 |
1986年 | 1942篇 |
1985年 | 1789篇 |
1984年 | 1509篇 |
1983年 | 1370篇 |
1979年 | 1485篇 |
1978年 | 1178篇 |
1977年 | 1032篇 |
1976年 | 997篇 |
1975年 | 1053篇 |
1974年 | 1171篇 |
1973年 | 1252篇 |
1972年 | 1197篇 |
1971年 | 1042篇 |
1970年 | 1060篇 |
1969年 | 1093篇 |
1967年 | 960篇 |
1966年 | 918篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
61.
62.
63.
R W Morgan J Gelb C S Schreurs D Lütticken J K Rosenberger P J Sondermeijer 《Avian diseases》1992,36(4):858-870
Recombinant strains of herpesvirus of turkeys (HVT) were constructed that contain either the fusion protein gene or the hemagglutinin-neuraminidase gene of Newcastle disease virus (NDV) inserted into a nonessential gene of HVT. Expression of the NDV antigens was regulated from a strong promoter element derived from the Rous sarcoma virus long terminal repeat. Recombinant HVT strains were stable and fully infectious in cell culture and in chickens. Chickens receiving a single intra-abdominal inoculation at 1 day of age with recombinant HVT expressing the NDV fusion protein had an immunological response and were protected (> 90%) against lethal intramuscular challenge at 28 days of age with the neurotropic velogenic NDV strain Texas GB. Recombinant HVT expressing the NDV hemagglutinin-neuraminidase provided partial protection (47%) against the same challenge. Chickens vaccinated with recombinant HVT vaccines had low levels of protection against NDV replication in the trachea when challenged ocularly. Recombinant HVT vaccines and the parent HVT strain provided similar levels of protection to chickens challenged with the very virulent RB1B strain of Marek's disease virus, indicating that insertion of foreign sequences into the HVT genome did not compromise the ability of HVT to protect against Marek's disease. 相似文献
64.
Summary. A weed management strategy for the control of Rottboellia cochinchinensis (Lour.) W.D. Clayton in maize, based on reducing the level of spikelet germination from the seedbank and reducing the intensity of weed-crop interference, was conducted over two seasons. The management practices evaluated included chemical control (atrazine, metolachlor, pendimethalin, EPTC), cultural control (straw mulch), mechanical control (inter-row cultivation) and biological control (living mulch). The results indicated that the various management practices had no effect on the growth and development of the crop but significantly affected the weed. The pendimethalin (1°5 kg a.i. ha−1 ) and inter-row cultivation (14 and 28 days after planting) treatments gave satisfactory control of the weed in the crop over the duration of the critical period of weed competition. All other treatments were ineffective. All management practices made significant contributions to the weed seedbank, thus ensuring the predominance of the weed. 相似文献
65.
A Pyrenophora teleomorph was recently found on barley stubble in South Africa. Single-ascospore isolates, mated on water agar containing sterile pieces of barley stubble, produced the teleomorph within 12 months of incubation at 15°C in the dark. Based on morphological characteristics and symptom expression on barley plants, the teleomorph is ascribed to P. japonica (anamorph Drechslera tuberosa ). This is the first report describing the occurrence of the teleomorph of D. tuberosa in South Africa. 相似文献
66.
R. N. White 《The Journal of small animal practice》1995,36(4):151-158
The surgical repair of tracheal collapse in 25 dogs is described. The initial presenting signs included coughing, dyspnoea, gagging, retching, exercise intolerance, cyanosis and collapse. Diagnosis was based upon the clinical signs, plain radiography and tracheal endoscopy. The collapse was corrected by the application of a number of extraluminal polypropylene prosthetic rings applied to the affected trachea. Additionally, a left arytenoid lateralisation was also performed. The perioperative complication rate was approximately 4 per cent, while the success rate was 75 per cent. The technique reduces the likelihood of catastrophic postoperative complications associated with iatrogenic laryngeal paralysis which is a possible complication of placement of extraluminal tracheal support devices. 相似文献
67.
A device for determining the sorptivity of soil aggregates 总被引:2,自引:0,他引:2
A device that infiltrated water over a small circular surface area having a radius ranging between 1.45 mm and 2.5 mm was used to measure the sorptivity of initially air-dry aggregates of size greater than 20 mm. The small infiltration area caused the water uptake to be dominated by capillarity that allowed the use of a simple formula to obtain the sorptivity from the steady-state flow rate that occurred very early after the start of imbibition. The results of measurements of sorptivity made on a fine sand agreed with those obtained from measurements on one-dimensional water infiltration into columns of the sand. Sorptivity measurements on stabilized aggregates of a clay soil and on air-dried field aggregates of a clay soil were easily made. The simplicity and rapidity of the method allowed measurements to be conveniently replicated. 相似文献
68.
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
69.
70.
The therapeutic activity of diminazene aceturate, difluoromethylornithine (DFMO) and a combination of the two agents was investigated in experimental Trypanosoma brucei brucei infections in mongrel dogs. The criteria used in the assessment of the trypanocidal effect of these compounds included the examination of the blood for the parasite, as well as clinical and haematological changes at intervals following treatment. Diminazene aceturate (7 mg/kg intramuscularly), DFMO (300 mg/kg/day orally in three divided doses for six days) and the combination of diminazene aceturate (7 mg/kg intramuscularly) and DFMO (300 mg/kg/day orally for six days) produced an intermittent aparasitemia in the dogs. Relapse infection occurred in all the three groups, but the period of aparasitemia produced by the combination of the agents was longest. The packed cell volume, haemoglobin concentration and red cell count values decreased after the dogs were inoculated with the parasite. The values improved slightly following the treatments with the agents or their combination. The total white blood cell counts in the infected dogs indicated leucocytosis, but this improved with drug treatment. 相似文献