全文获取类型
收费全文 | 38196篇 |
免费 | 2241篇 |
国内免费 | 285篇 |
专业分类
林业 | 1576篇 |
农学 | 1412篇 |
基础科学 | 324篇 |
5482篇 | |
综合类 | 5651篇 |
农作物 | 1487篇 |
水产渔业 | 1797篇 |
畜牧兽医 | 19864篇 |
园艺 | 456篇 |
植物保护 | 2673篇 |
出版年
2021年 | 363篇 |
2020年 | 423篇 |
2019年 | 469篇 |
2018年 | 785篇 |
2017年 | 829篇 |
2016年 | 748篇 |
2015年 | 627篇 |
2014年 | 783篇 |
2013年 | 1828篇 |
2012年 | 1311篇 |
2011年 | 1527篇 |
2010年 | 1057篇 |
2009年 | 1089篇 |
2008年 | 1476篇 |
2007年 | 1327篇 |
2006年 | 1253篇 |
2005年 | 1079篇 |
2004年 | 1036篇 |
2003年 | 1029篇 |
2002年 | 910篇 |
2001年 | 1245篇 |
2000年 | 1230篇 |
1999年 | 927篇 |
1998年 | 387篇 |
1997年 | 418篇 |
1996年 | 341篇 |
1995年 | 391篇 |
1994年 | 341篇 |
1992年 | 656篇 |
1991年 | 780篇 |
1990年 | 685篇 |
1989年 | 720篇 |
1988年 | 661篇 |
1987年 | 623篇 |
1986年 | 666篇 |
1985年 | 591篇 |
1984年 | 462篇 |
1983年 | 412篇 |
1979年 | 553篇 |
1978年 | 431篇 |
1977年 | 359篇 |
1976年 | 365篇 |
1975年 | 396篇 |
1974年 | 459篇 |
1973年 | 474篇 |
1972年 | 447篇 |
1970年 | 366篇 |
1969年 | 400篇 |
1968年 | 357篇 |
1967年 | 359篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Sampling of the benthic fauna showed that dredging operations produced relatively short-term effects on invertebrate population levels. The behaviour of the animals was immediately affected, the differences between species were noted and the implications of dredging at different times of year are discussed. 相似文献
102.
Grass silage made in late May from S24 perennial ryegrass was offered to twelve Ayrshire cows in a 16-week feeding experiment. The silage had a DM content of 25.3%, a pH of 3.91, and contained 16.8% CP and 68.4% digestible organic matter in the DM. The silage was fed ad libitum and was the sole feed in the control treatment. In the other three treatments the silage was supplemented with a cube offered at rates of 0.8, 1.4 and 2.0 kg per 10 kg milk. The cube contained 82.2% groundnut, plus molasses and minerals, and had 37.9% CP in the DM. The daily intake of silage DM was 11.4 kg per cow on average over the four treatments which did not differ significantly. The mean daily milk yields were 14.8 kg per cow in the control treatment, and 16.5, 18.2 and 18.4 kg in the 0.8, 1.4 and 2.0 kg supplement treatments respectively. The SNF, CP and lactose contents of the milk were Wghest on the 1.4 kg supplement treatment. It is concluded that with a high digestibility silage, there is little evidence to support the feeding of more than 1.4 kg of high-protein cubes per 10 kg milk in the declining phase of lactation. 相似文献
103.
104.
The lignin content of 50 samples of five grasses of known in vivo digestibility were determined by the methods of Armitage, van Soest and two modifications of the van Soest technique. The error in predicting DM digestibility varied from ±3.1 for tbe Armitage metbod to ±5.0 for the van Soest method. This error compares nnfavourably witb ±2.1 previonsly obtained on tbe same samples with the in vitro technique of Tilley and Terry. 相似文献
105.
106.
The distribution of leaf area and light intensity within wheat crops differing in row direction, row spacing and rate of sowing is described. Regardless of the manner of planting, 75% of the total leaf area was found within a band 31/2 in. wide, centred on the centre of the row. Light penetration within crops spaced at 14 in. was greater than within those spaced at 7 in. Light penetration within rows running N.–S. was more uniform and higher, particularly around noon, than within rows running E.-W. Within N.-S. rows the position midway between rows received the highest amount of light, but light decreased on either side until it was least beneath the rows. Within E.-W. rows at 14 in. spacing, maximum light was recorded at 101/2 in. on the southern side of a row, decreasing progressively as the row was approached. 相似文献
107.
Significant deviations from the ratios expected, according to the single dominant gene hypothesis for resistance to Fusarium wilt, were found in crosses involving several susceptible and resistant tomato lines. The susceptible class was the deficient one in F2 and F3 populations, as well as in backcrosses in which the heterozygotic resistant F1 served as the male parent. The reciprocal backcross, with the F1 as the female and the homozygous susceptible as the male, gave segregations better approximating or consistent with the single gene hypothesis. Reciprocal F1 and F2 generations did not give any evidence of cytoplasmic effects.The results were interpreted assuming preferential fertilization of ovules by pollen grains carrying the dominant I allele for resistance.The practical implications of the phenomenon of preferential fertilization in breeding for Fusarium resistance are discussed. 相似文献
108.
J. N. Köstler 《Forstwissenschaftliches Centralblatt》1962,81(1-2):62-63
Ohne Zusammenfassung 相似文献
109.
110.