全文获取类型
收费全文 | 675篇 |
免费 | 43篇 |
专业分类
林业 | 26篇 |
农学 | 9篇 |
基础科学 | 2篇 |
48篇 | |
综合类 | 177篇 |
农作物 | 13篇 |
水产渔业 | 25篇 |
畜牧兽医 | 383篇 |
园艺 | 11篇 |
植物保护 | 24篇 |
出版年
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 18篇 |
2010年 | 23篇 |
2009年 | 29篇 |
2008年 | 22篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1972年 | 5篇 |
1971年 | 9篇 |
1970年 | 7篇 |
1969年 | 6篇 |
1968年 | 5篇 |
1967年 | 11篇 |
1966年 | 6篇 |
排序方式: 共有718条查询结果,搜索用时 15 毫秒
71.
Nagata T Ishikawa Y Kinoshita H Kono M Syono Y Fisher RM 《Science (New York, N.Y.)》1970,167(3918):703-704
Magnetic measurements have shown that nondiamagnetic minerals in a lunar crystalline rock of type B are (free Fe(2)+ in paramagnetic pyroxenes) : (antiferromagnetic FeSiO(3)) : (antiferromagnetic FeTiO(3)) : (ferromagnetic iron) = 4.3 : 7 : 20 : 0.08 in weight percentage. The abundance of ferromagnetic Fe in the lunar fines is about 7.5 times its abundance in the crystalline rock. The natural remanent magnetization of the crystalline rock of 7.5 x 10(-6) emu/ g in intensity may not be attributable to its thermoremanent magnetization. 相似文献
72.
J T Blake D E Bailey Y S Lu E J Fisher R Abaza J W Call 《American journal of veterinary research》1969,30(2):171-181
73.
74.
Enzyme-reduced coenzyme binary complexes produce previously unreported shifts in the spectrum of the free coenzyme. These shifts give rise to difference spectra which resemble a general environmental change for reduced diphosphopyridine nucleotide (DPNH) in the glutamic dehydrogenase-DPNH complex, and indicate a more specific enzyme-coenzyme interaction for yeast alcohol dehydrogenase-DPNH, isocitrate dehydrogenase-TPNH, and lactic dehydrogenase-DPNH complexes. 相似文献
75.
76.
77.
78.
P.F. Fisher 《Geoderma》1983,29(2):93-105
The properties of soils associated with the Bronze Age site near the South Lodge of Rushmore Park, Wiltshire, are described. Three primary soil types are identified: rendzinas (Rendolls), argillic brown earths (Hapludalfs) and a brown calcareous earth (Eutrochrept). The mapped distribution of these soil types is related to the archaeological landscape. The argillic brown earths are limited in extent to the deeper soils of the positive (accumulating) lynchets of the field system, whereas rendzinas occupy the negative (eroding) lynchets and the remainder of the fields. The only occurrence of a brown calcareous earth is in a positive lynchet within the enclosure. From the distribution of soil types and analogies with the soils of other prehistoric field systems on the Chalk, it is concluded that the argillic brown earths have formed from a highly calcareous colluvial deposit since abandonment of the field system in the later Bronze Age. Further, the development of this soil type appears to be controlled by lateral throughflow of soil water combined with the re-establishment of a wooded landscape. Formation of the argillic brown earth at this site appears to be more recent than at any other site in southern England for which information has been published. 相似文献
79.
Effects of Restored Stream Buffers on Water Quality in Non-tidal Streams in the Choptank River Basin
Adrienne J. Sutton Thomas R. Fisher Anne B. Gustafson 《Water, air, and soil pollution》2010,208(1-4):101-118
Restoration of riparian buffers is an important component of nutrient reduction strategies in the Chesapeake Bay watershed. In 1998, Maryland adopted a Conservation Reserve Enhancement Program (CREP), which provides financial incentives to take agricultural land out of production to plant streamside vegetation. Between 1998 and 2005, 1–30% of streamside vegetation (average?=?11%), was restored to forest or managed grass in 15 agriculturally dominated sub-basins in the Choptank River basin, a tributary of Chesapeake Bay. Pre-existing forested buffers represented 10–48% of the streamside (average?=?33%), for a total of 12–61% buffered streamsides (average?=?44%). Using multi-year water quality data collected before and after CREP implementation (1986, 2003–2006), we were unable to detect significant effects of CREP on baseflow nutrient concentrations based on the area of restored buffer, the percentage of restored streamside, or the percentage of total riparian buffer in the sub-basins (p?>?0.05). Although CREP increased the average buffered streamside from 33% in the 1990s to 44% by 2005, N and P concentrations have not changed or have increased in some streams over the last 20 years. Reductions may not have occurred for the following reasons: (1) buffer age, width, and connectivity (gaps) between buffers are also important to nutrient reductions; (2) agricultural nutrient inputs may have increased during this period; and (3) riparian buffer restoration was not extensive enough by 2005 to have measurable affects on the stream water quality in these sub-basins. Significant effects of CREP may yet be resolved as the current CREP buffers mature; however, water quality data through 2006 in the Choptank basin do not yet show any significant effects. 相似文献
80.
Kathryn M. Santos Paul R. Fisher Thomas H. Yeager Eric H. Simonne Hannah S. Carter William R. Argo 《Journal of plant nutrition》2013,36(10):1424-1436
Fertilization strategies during stock plant and cutting production are linked in terms of cutting nutrient levels and quality. Objectives were to evaluate (1) the effect of stock plant nutrition on tissue nutrient concentration and growth during vegetative propagation and (2) response to fertilizer during propagation for cuttings with 4 different initial tissue nutrient concentrations. ‘Supertunia Royal Velvet’ petunia stock plants were grown under constant fertigation of 0, 50, 100 or 200 mg nitrogen (N).L?1 for 21 days. The 200 mg N.L?1 solution contained 150 nitrate (NO3-N), 50 ammonium (NH4-N), 24 phosphorus (P), 166 potassium (K), 40 calcium (Ca), 20 magnesium (Mg), 0.7 sulfur (S), 1.0 iron (Fe), 0.5 manganese (Mn), 0.5 zinc (Zn), 0.24 copper (Cu), 0.24 boron (B), and 0.1 molybdenum (Mo). Providing a complete fertilizer during propagation of petunia, beginning immediately after sticking of cuttings, reduces the risk of nutrient deficiency. Particularly in situations where fertilizer is not applied early during propagation, stock plants should be managed to ensure unrooted cuttings have adequate nutrient reserves. 相似文献