全文获取类型
收费全文 | 116925篇 |
免费 | 6260篇 |
国内免费 | 122篇 |
专业分类
林业 | 4854篇 |
农学 | 3681篇 |
基础科学 | 831篇 |
13338篇 | |
综合类 | 21917篇 |
农作物 | 4675篇 |
水产渔业 | 5495篇 |
畜牧兽医 | 60085篇 |
园艺 | 1402篇 |
植物保护 | 7029篇 |
出版年
2018年 | 1497篇 |
2017年 | 1613篇 |
2016年 | 1562篇 |
2015年 | 1346篇 |
2014年 | 1515篇 |
2013年 | 4404篇 |
2012年 | 2929篇 |
2011年 | 3626篇 |
2010年 | 2445篇 |
2009年 | 2392篇 |
2008年 | 3647篇 |
2007年 | 3419篇 |
2006年 | 3187篇 |
2005年 | 3052篇 |
2004年 | 3047篇 |
2003年 | 3042篇 |
2002年 | 2910篇 |
2001年 | 3879篇 |
2000年 | 3879篇 |
1999年 | 2929篇 |
1998年 | 1208篇 |
1997年 | 1208篇 |
1995年 | 1369篇 |
1994年 | 1294篇 |
1993年 | 1220篇 |
1992年 | 2626篇 |
1991年 | 2823篇 |
1990年 | 2676篇 |
1989年 | 2710篇 |
1988年 | 2490篇 |
1987年 | 2602篇 |
1986年 | 2672篇 |
1985年 | 2550篇 |
1984年 | 2055篇 |
1983年 | 1892篇 |
1982年 | 1237篇 |
1981年 | 1186篇 |
1980年 | 1090篇 |
1979年 | 1877篇 |
1978年 | 1508篇 |
1977年 | 1208篇 |
1976年 | 1173篇 |
1975年 | 1219篇 |
1974年 | 1576篇 |
1973年 | 1653篇 |
1972年 | 1631篇 |
1971年 | 1567篇 |
1970年 | 1451篇 |
1969年 | 1319篇 |
1967年 | 1136篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
R Korbel 《Tier?rztliche Praxis》1991,19(5):497-507
Ocular diseases in birds are very rarely investigated. Increased keeping of often very expensive caged birds makes it necessary for veterinarians in practice to deal with the problems of ornithoophthalmology. Fundamental physiological and anatomic differences between the mammalian and the avian eye, interspecies variables and general problems in handling do not allow a simple transfer of knowledge of mammal ophthalmology to birds. Therefore, it is necessary to find differentiated, species-orientated solutions in investigation as well as suitable treatments of ocular diseases in birds. An update on ornithoophthalmology is given. 相似文献
102.
A field experiment was conducted during the winter seasons of 1992–93 and 1993–94 at Anand to study the effect of FYM, nitrogen and source of fertilizer on growth and yield of mustard [ Brassica juncea (L.) Czernj & Cosson]. The results showed significant variation in leaf area index (LAI), crop growth rate (CGR), dry matter production and seed yield. The direct effect of farmyard manure (FYM) was conspicuous in improving the growth of mustard. FYM application at 10 tonnes ha−1 significantly increased the LAI, CGR and dry matter accumulation per plant at almost all the stages during first year study (1992–93) and in pooled analysis. Similarly, nitrogen application registered maximum LAI, CGR at 75 kg level and RGR and NAR at 50 kg level at almost all the during both years. Sulphur carrying source (Ammonium sulphate plus single super phosphate) increased all stages growth characters. Maximum dry matter accumulation per plant and seed yield were recorded with highest levels of FYM (20 tonnes ha−1 ), N (75 kg ha−1 ) and source having S. Seed yield was strongly associated with LAI and dry matter accumulation per plant at all the stages. 相似文献
103.
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
104.
105.
R. Zabielski S. G. Pierzynowski 《Journal of animal physiology and animal nutrition》1992,68(3):146-150
Eine Methode zur langfristigen Lymphsammlung aus der jejunalen Lymphbahn bei Schweinen und Schafen Es wird eine Methode zur langfristigen Lymphsammlung im Dünndarmbereich von Schweinen und Schafen vorgestellt. Mit Hilfe eines chirurgischen Eingriffs wurde ein Silikon-Katheder im truncus lymphaticus jejunalis implantiert. Zusätzlich wurde ein zweiter Katheter in die hintere vena cava in Richtung Herz eingesetzt. Beide Katheter wurden sofort miteinander verbunden, um die Wiedereinführung der jejunalen Lymphe in den Blutkreislauf zu gewährleisten. Der negative Druck in der hinteren vena cava im Thoraxteil förderte den Lymphfluß durch das Katheter im truncus lymphaticus jejunalis. Der preprandiale Lymphfluß des Jéjunums betrug bei Schweinen 0,3 ml/h/kg Körpergewicht und stieg postprandial auf 0,78 ml/h/kg an. Beim Schaf betrug der Basiswert 0,75 ml/h/kg. Er stieg nach intraduodenaler Infusion von Rapsöl auf 4,75 ml/h/kg. Eine mechanische Stimulation der intestinalen Receptoren durch 0,9% NaCl-Lösung stimulierte ebenfalls den Lymphfluß. 相似文献
106.
107.
The accumulation of soluble carbohydrates in vegetative parts of sweet sorghum ( Sorghum bicolor (L.) Moench.) represents an intermediate reserve pool for grain filling as well as an irreversible storage up to maturity. In order to study the effect of Sterility on soluble sugar accumulation in vegetative parts, two cytoplasmic male sterile (CMS) lines of sweet sorghum were compared with their corresponding fertile mamtainers for non-structural carbohydrate concentrations in shoots. Plants were harvested at four different physiological stages. The lines showed significant differences in the yield of non-structural carbohydrates. At maturity, the yields of soluble carbohydrates from vegetative parts of the two sterile lines were 93 % and 43 % higher than the yield of the two corresponding fertile lines. At that stage, sucrose represented about 80 % of total soluble carbohydrates and the higher yield of soluble carbohydrates of sterile lines was mainly due to the higher yield of sucrose. This indicates that the yield of extractable carbohydrates, especially sucrose, in vegetative parts of sweet sorghum could be considerably improved by using sterile lines which are utilized in hybrid production. 相似文献
108.
109.
110.