全文获取类型
收费全文 | 210603篇 |
免费 | 13224篇 |
国内免费 | 649篇 |
专业分类
林业 | 22805篇 |
农学 | 13798篇 |
基础科学 | 2927篇 |
40171篇 | |
综合类 | 11956篇 |
农作物 | 16999篇 |
水产渔业 | 15642篇 |
畜牧兽医 | 71594篇 |
园艺 | 6155篇 |
植物保护 | 22429篇 |
出版年
2021年 | 2410篇 |
2020年 | 2794篇 |
2019年 | 3584篇 |
2018年 | 3700篇 |
2017年 | 4060篇 |
2016年 | 4555篇 |
2015年 | 4154篇 |
2014年 | 5504篇 |
2013年 | 16024篇 |
2012年 | 4908篇 |
2011年 | 6529篇 |
2010年 | 6814篇 |
2009年 | 7487篇 |
2008年 | 6030篇 |
2007年 | 4952篇 |
2006年 | 5782篇 |
2005年 | 5002篇 |
2004年 | 4907篇 |
2003年 | 4675篇 |
2002年 | 4024篇 |
2001年 | 4207篇 |
2000年 | 3866篇 |
1999年 | 4009篇 |
1998年 | 3946篇 |
1997年 | 4023篇 |
1996年 | 3758篇 |
1995年 | 4289篇 |
1994年 | 3677篇 |
1993年 | 3364篇 |
1992年 | 3223篇 |
1991年 | 3367篇 |
1990年 | 3070篇 |
1989年 | 3046篇 |
1988年 | 2650篇 |
1987年 | 2680篇 |
1986年 | 2574篇 |
1985年 | 2983篇 |
1984年 | 2937篇 |
1983年 | 2875篇 |
1982年 | 2542篇 |
1981年 | 2507篇 |
1980年 | 2498篇 |
1979年 | 2526篇 |
1978年 | 2363篇 |
1977年 | 2261篇 |
1976年 | 2108篇 |
1975年 | 1877篇 |
1974年 | 1932篇 |
1973年 | 1861篇 |
1971年 | 1628篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
对6头试验公鹿用假台鹿采精,采精前对特制的假阴道以药用凡士林为滑润剂,注水充气,温度为40℃±1℃,以适宜的压力和滑润度,将其安装在人工制做的假台鹿内。拨赶公鹿于采精场诱其爬跨。结果,试验的6头公鹿中有4头能够采精,共22头次,射精量平均每头次1.54ml,精子密度为18.6—37亿/ml,精子活力在0.8以上。93年每头次生产细管冻精106.25支(425支/4头次),是同年电刺激采精法平均64.4支/头次(902支/14头次)的1.65倍,此法既能采到质量高的精液,又比电采法省工、省时、省力、安全,是一种理想的马鹿采精方法。 相似文献
72.
E. G. VLACHOPOULOS 《EPPO Bulletin》1994,24(2):413-415
The major nematode pests of cultivated plants in Greece include root-knot nematodes Meloidogyne spp. (in almost all plants except citrus), cyst-forming nematodes Globodera rostochiensis, G. pallida (in potato), Heterodera avenae (in cereals), Ditylenchus dipsaci (in vegetables and ornamental plants) and Tylenchulus semipenetrans (in citrus). Based on observations made on samples examined at Benaki Phytopathological Institute, it was confirmed that serious infestation of new kiwi orchards with Meloidogyne spp. originated from seedlings infested at the nursery. Also the wide distribution of the nematode Tylenchulus semipenetrans in citrus orchards was mainly attributed to infested seedlings. The above observations led us, in 1985, to the decision to study the nematological fauna of nurseries in Greece. 相似文献
73.
H. Frackowiak 《Anatomia, histologia, embryologia》1989,18(4):342-348
Seventeen lion heads were examined. Their arteries were injected with colored supervinyl-chloride (dissolved in acetone) after which the heads were macerated biologically. The rete mirabile of the maxillary artery was located extracranially and was formed by numerous arteries that arose from the dorsal and medial surfaces of the maxillary artery. The rete released branches (rami retis) which entered the cranial cavity through the orbital fissure where they anastomosed with the intracranial segment of the internal carotid artery. The extracranial portion of the internal carotid was found to be obliterated. Some other arteries leaving the rete anastomosed with the internal ophthalmic artery before it entered the optic canal. The following further arteries left the rete: A. ethmoidalis externa, A. ophthalmica externa, rami musculares and ramus pterygoideus. The rete mirabile of the maxillary artery in the lion provides the principal source of the blood for the brain; it also supplies the orbit. 相似文献
74.
75.
76.
Hypothalamic neurotransmitter concentrations and meat quality in stressed pigs offered excess dietary tryptophan and tyrosine. 总被引:2,自引:0,他引:2
Pale, soft, exudative (PSE) pork occurs, for the most part, from environmental stress on the pig. Amino acid intake may be related to stress susceptibility through hormone and neurotransmitter induction. Two experiments were conducted to determine whether supplementation of 5 g of tryptophan (TRP) or 10 g of tyrosine (TYR) per kilogram of a 14% CP diet would alter the response of pigs to stress as measured by hypothalamic neurotransmitter concentrations and incidence of PSE. Twenty-four (Exp. 1) and 36 (Exp. 2) 92-kg pigs were offered one of three diets: control, TRP-, or TYR-supplemented for 5 d before slaughter. Dietary TRP or TYR supplementation in Exp. 1. doubled (P less than .05) plasma TRP and TYR concentrations, respectively, and increased (P less than .05) 5-hydroxytryptamine, dihydroxyphenyl ethylamine, dihydroxyphenyl acetic acid, and homovanillic acid concentrations in the hypothalamus. Pigs that exhibited stress at slaughter had lower (P less than .05) hypothalamic concentrations of epinephrine, norepinephrine, and 5-hydroxytryptamine. In Exp. 2, pigs were trucked 55 km to a commercial meat packing facility and slaughtered without a rest period. This handling procedure was designed to invoke a high incidence of PSE pork and thus be a strong test of treatments. Supplemental dietary amino acids seemed to alter the frequency distribution of the severity of PSE pork. These data indicate that dietary manipulation of amino acid precursors of neurotransmitters may offer a practical means of reducing stress response in swine. 相似文献
77.
Thyme ( Thymus vulgaris L.) plants were spaced at 15, 30 or 45 cm distances in a clay-loamy soil. They received different levels of nitrogen and phosphorus, besides a constant level of potassium. The results showed, that the wider spacing promoted the growth and production of herb and oil per plant, however dense cultivation significantly increased the yields of herb and oil per unit area. In all cases, the applied fertilization treatments significantly increased the productivity per unit area. Dense cultivation accompanied with higher levels of fertilization proved to be very usefull. The essential oil content was not influenced by either the plant spacing or fertilization treatments applied in this study. 相似文献
78.
Abstract The abundances of Aeromonas salmonicida subsp. salmonicida in the water and in the surface microlayer was studied during the initial phase of a cohabitant infection experiment with Atlantic salmon, Salmo salar L., smolt. Aeromonas salmonicida was detected in the water samples only until the intraperitoneally infected smolt were dead and had been removed. In the lipid rich surface microlayer, A. salmonicida was detected in high concentrations from the day of the first fish mortality and throughout the rest of the experiment. The significance of the high cell surface hydrophobicity is discussed as a possible reason for enrichment of A. salmonicida at the air-water interface. 相似文献
79.
80.
George J. Brewer MD William Schall DVM Robert Dick BS Vilma Yuzbasiyan-Gurkan PhD Michael Thomas DVM George Padgett DVM 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1992,6(1):41-43
Inherited canine copper toxicosis is a serious problem in Bedlington terriers and West Highland White terriers, and may also be a problem in other less-studied breeds. Affected dogs become ill at midlife with progressive and ultimately fatal liver disease. Treatments for removal of copper and prevention of copper accumulation are available, but are most effective if begun before the dog becomes ill. Until recently diagnosis has not been available until the dog is 1 year of age, and then only by an invasive liver biopsy with determination of liver copper concentration. The authors studied the use of 64copper for early diagnosis of canine copper toxicosis. Two procedures were evaluated. The first involved measuring the concentration of 64copper in blood 24 hours after oral administration of the radioisotope. At this time, 64copper was associated primarily with ceruloplasmin secreted into the blood by the liver. This procedure is useful in the diagnosis of the human counterpart, Wilson's disease. However, the authors found it to be nondiscriminatory between affected and unaffected dogs. In contrast, the second procedure, which involved measuring 64copper excreted in stool during 48 hours after an intravenous dose of radioisotope, yielded results that differentiated most affected and unaffected dogs. 相似文献