首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   241848篇
  免费   14555篇
  国内免费   672篇
林业   23549篇
农学   14026篇
基础科学   2965篇
  42176篇
综合类   20728篇
农作物   17267篇
水产渔业   16675篇
畜牧兽医   89531篇
园艺   6362篇
植物保护   23796篇
  2021年   2494篇
  2020年   2896篇
  2019年   3683篇
  2018年   3982篇
  2017年   4304篇
  2016年   4783篇
  2015年   4332篇
  2014年   5701篇
  2013年   16326篇
  2012年   6047篇
  2011年   7994篇
  2010年   7296篇
  2009年   7890篇
  2008年   7315篇
  2007年   6336篇
  2006年   7023篇
  2005年   6252篇
  2004年   6174篇
  2003年   5979篇
  2002年   5269篇
  2001年   5301篇
  2000年   4939篇
  1999年   4850篇
  1998年   4093篇
  1997年   4151篇
  1996年   3891篇
  1995年   4460篇
  1994年   3839篇
  1993年   3533篇
  1992年   3952篇
  1991年   4160篇
  1990年   3789篇
  1989年   3800篇
  1988年   3345篇
  1987年   3350篇
  1986年   3303篇
  1985年   3675篇
  1984年   3459篇
  1983年   3302篇
  1982年   2767篇
  1981年   2696篇
  1980年   2697篇
  1979年   2987篇
  1978年   2711篇
  1977年   2562篇
  1976年   2414篇
  1975年   2220篇
  1974年   2354篇
  1973年   2274篇
  1972年   1997篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
A toxic dose of selenium administered by IM injection to a 3-year-old Chihuahua resulted in pulmonary edema and death. The compound had been dispensed to the owner inadvertently in combination with a vitamin E preparation. Vitamin and mineral products often are considered safe for use in megadoses by the uninformed public. The potential danger of selenium overdosage should not be underestimated.  相似文献   
102.
103.
Ovine-derived fibroblasts were used to validate an insulin-like growth factor I (IGF-I) membrane-receptor binding assay system. Competitive binding using fibroblasts revealed that half-maximal inhibition of 125I-IGF-I binding by IGF-I was 2.3 nM. SDS-polyacrylamide gel electrophoresis analysis of specific protein-associated 125I-IGF-I was consistent with the migration of 125I-IGF-I-labeled Type I IGF receptor alpha-subunits at Mr 133,000 daltons. Further, the efficiency of two cell solubilization methods was examined and time-dependent binding equilibrium was determined for the membrane assay system. Satellite cell-derived myotubes were subsequently isolated from primary satellite cell cultures established from the semimembranosus muscles of high and low efficiency-of-gain (EOG) Targhee rams, and IGF-I receptor dynamics were measured. A membrane competitive binding study revealed that half-maximal inhibition of 125I-IGF-I binding was achieved by 1-ng IGF-I for low, and 10-ng IGF-I for high, EOG myotube membrane preparations. Kd values were similar between the high EOG (4.78 nM) and low EOG (2.95 nM) groups; however, receptor concentrations (Bmax) appeared to differ between groups. High EOG membrane receptor Bmax was 3.88 pmole/micrograms protein (19.87 pmole/micrograms DNA), whereas low EOG membrane receptor Bmax was 1.22 pmole/micrograms protein (9.28 pmole/micrograms DNA). These preliminary findings support the hypothesis that genetic selection for EOG results in altered satellite cell responsiveness to IGF-I.  相似文献   
104.
105.
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   
106.
107.
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   
108.
109.
Seedling ryegrass and oat plants in various proportions were exposed to oviposition by frit fly in the laboratory. The growth stage of the ryegrass ranged from single-leaved (unattractive as oviposition sites) to three-leaved (almost immune to serious damage). Oat plants attracted most oviposition and their inclusion usually reduced oviposition on ryegrass, by up to 90%. Where the frit fly population density was so high that potential oviposition exceeded the availability of oviposition sites, inclusion of oats did not reduce the number of eggs laid on ryegrass.
This approach does not, therefore, show promise of a reliable control method against severe primary attack in the field, but is potentially useful over an important range of population densities at which further control measures might otherwise be required. The inclusion of oats would also provide an early warning of damage.  相似文献   
110.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号