全文获取类型
收费全文 | 48936篇 |
免费 | 2926篇 |
国内免费 | 285篇 |
专业分类
林业 | 2472篇 |
农学 | 1815篇 |
基础科学 | 374篇 |
7713篇 | |
综合类 | 5998篇 |
农作物 | 1911篇 |
水产渔业 | 2744篇 |
畜牧兽医 | 24743篇 |
园艺 | 618篇 |
植物保护 | 3759篇 |
出版年
2021年 | 588篇 |
2020年 | 637篇 |
2019年 | 617篇 |
2018年 | 1223篇 |
2017年 | 1327篇 |
2016年 | 1208篇 |
2015年 | 976篇 |
2014年 | 1220篇 |
2013年 | 2431篇 |
2012年 | 2047篇 |
2011年 | 2168篇 |
2010年 | 1406篇 |
2009年 | 1419篇 |
2008年 | 2011篇 |
2007年 | 1814篇 |
2006年 | 1653篇 |
2005年 | 1503篇 |
2004年 | 1388篇 |
2003年 | 1363篇 |
2002年 | 1186篇 |
2001年 | 1477篇 |
2000年 | 1456篇 |
1999年 | 1131篇 |
1998年 | 438篇 |
1997年 | 455篇 |
1996年 | 391篇 |
1995年 | 423篇 |
1992年 | 789篇 |
1991年 | 891篇 |
1990年 | 790篇 |
1989年 | 847篇 |
1988年 | 774篇 |
1987年 | 743篇 |
1986年 | 777篇 |
1985年 | 693篇 |
1984年 | 542篇 |
1983年 | 486篇 |
1979年 | 653篇 |
1978年 | 523篇 |
1977年 | 439篇 |
1976年 | 417篇 |
1975年 | 441篇 |
1974年 | 555篇 |
1973年 | 542篇 |
1972年 | 535篇 |
1971年 | 423篇 |
1970年 | 392篇 |
1969年 | 432篇 |
1968年 | 381篇 |
1967年 | 387篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
The utilization of dietary lysine for protein synthesis is affected by the digestibility of protein-bound lysine, by its intestinal resorption and by its oxidative catabolism. The approach chosen in this paper enables a comparison of the cumulative effect of these processes on the utilization of free and protein-bound lysine, respectively. The principle of the approach is based on a quantification of the expiration of 14C-labelled carbon dioxide after an oral administration of a diet, which contains L-(U-14C)-lysine either as a free amino acid or bound to yeast proteins. During an adaptation phase cockerels of the Japanese quail received a diet based mainly on ground wheat and wheat gluten. This diet was supplemented either with yeast proteins or with a mixture of L-amino acids which simulates the composition of the yeast proteins. In the main experiment the expiration of labelled carbon dioxide was measured during 240 minutes after the administration of the corresponding labelled diets. Just before treatment the animals were either in the postprandial phase or in a state of slight hunger. The maximum of expiration of labelled carbon dioxide occurred around the 60th minute after administration of the corresponding labelled diets. The cumulative expiration of labelled carbon dioxide, expressed in per cent of the radioactive dose used, amounts to 15.5% and 14.3% for free and protein-bound lysine, respectively. The utilization of both forms of lysine in the Japanese quail is lower than in broilers. 相似文献
33.
34.
2 groups of 20 cocks each were selected at random from non-dwarf White Leghorn (28 weeks post-hatch) and dwarf Krishna-J (38 weeks post-hatch) genotypes. The treated groups comprised 10 White Leghorn and 10 Krishna-J cocks. The remaining birds served as controls. 8 weeks prior to furazolidone treatment, semen was collected from both control groups at regular 4-day intervals, for 4 weeks. Cocks of the treated groups of both genotypes were administered furazolidone (0.14 g/bird/day) for 7 consecutive days. Semen was collected from all cocks at regular 4-day intervals for 4 weeks. Semen from the cocks of the same group was pooled. The pooled ejaculate volume and sperm density did not differ significantly in the 2 genotypes. The semen output as well as sperm density increased along with progressive attainment of sexual maturity. Furazolidone treatment caused significant reduction in semen volume as well as sperm concentration in either genotype. 相似文献
35.
Abstract. Experiments were started in 1967 to investigate the effects of soil mixing on fen peat soil. Peaty topsoil was mixed with mineral subsoil to a maximum depth of 80 cm at two sites, one with a clay subsoil, the other sand. Mixing was done on a commercial scale with a range of implements. After initial increases, yields of arable crops on both mixed soils were subsequently similar to those on unmixed soil. Residual herbicide activity was enhanced on mixed soils, and evidence of peat conservation was obtained at one site. The practice has not been taken up commercially because of the high capital cost of mixing and lack of serious problems which had been predicted following peat wastage. 相似文献
36.
37.
38.
39.
Do Thi Thanh HUONG Vidya JAYASANKAR Safiah JASMANI Hisako SAIDO-SAKANAKA Andrew J. WIGGINTON Marcy N. WILDER 《Fisheries Science》2004,70(3):518-520
40.