全文获取类型
收费全文 | 234篇 |
免费 | 9篇 |
专业分类
林业 | 20篇 |
农学 | 7篇 |
基础科学 | 2篇 |
32篇 | |
综合类 | 66篇 |
农作物 | 12篇 |
水产渔业 | 12篇 |
畜牧兽医 | 70篇 |
园艺 | 7篇 |
植物保护 | 15篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 2篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 3篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1981年 | 2篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1945年 | 2篇 |
1900年 | 1篇 |
1894年 | 1篇 |
1893年 | 2篇 |
1891年 | 1篇 |
1884年 | 1篇 |
排序方式: 共有243条查询结果,搜索用时 15 毫秒
81.
82.
Mumma MJ DiSanti MA Magee-Sauer K Bonev BP Villanueva GL Kawakita H Dello Russo N Gibb EL Blake GA Lyke JE Campbell RD Aycock J Conrad A Hill GM 《Science (New York, N.Y.)》2005,310(5746):270-274
We quantified eight parent volatiles (H2O, C2H6, HCN, CO, CH3OH, H2CO, C2H2, and CH4) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk. 相似文献
83.
The recent development of tunable far-infrared lasers and other high-resolution spectroscopic probes of weakly bound clusters is having a significant impact on our understanding of intermolecular forces and on the complex quantum tunneling dynamics that occur in hydrogen-bonded systems. Far-infrared studies of a variety of interactions are discussed, including several prototypical water-hydrophobe complexes, the water trimer, and the ammonia dimer. Particular attention is paid to the inversion of spectroscopic data to yield detailed intermolecular potential energy surfaces. Investigations of nonpairwise additivity are also described. 相似文献
84.
A hyperprolinemia was discovered, in a new inbred strain of mice, which was equivalent to about a sevenfold elevation above the concentration of proline in the blood of either of the original parental lines, or of 12 other inbred strains with diverse genetic constitution. In addition, mice of this PRO/Re strain exhibited a marked prolinuria, whereas the other 14 inbred strains had no proline detectable in their urine. 相似文献
85.
86.
Polyphosphorylated L-ascorbic Acid: A Stable Form of Vitamin C for Aquaculture Feeds 总被引:1,自引:0,他引:1
Blake F. Grant Paul A. Seib Ming-Long Liao Kenneth E. Corpron 《Journal of the World Aquaculture Society》1989,20(3):143-157
A protected form of vitamin C, L-ascorbyl-2-poly phosphate (APP), was tested for safety and efficacy in fishes. Phosphorylation of the 2-hydroxyl group protected the 2,3-enediol of L-ascorbic acid against oxidation. When APP was added to feed, about 15% of its vitamin C activity was lost during milling and storing 5–7 d at ambient temperature. Stability of APP in pelleted feeds at 25 or 40 C was up to 83 times or 45 times greater than that of ascorbic acid (AA), respectively. In later tests, trout feed mash, steam-pelleted in triplicate, frozen, and shipped on dry ice before analysis, had 46% loss of AA and no apparent loss of APP. With 16% milling loss (highest detected in trout feeds assayed in initial tests) and 22% storage loss after 90 d, conservative APP mix rates were estimated. Mixing 153 g L-ascorbate-equivalent as APP per metric ton of airdry ingredients (153 ppm) would give 128 ppm in the finished feed after steam-pelleting and 100 ppm after 60–90 d storage at 40 C. Low-temperature extrusion of Oregon-Moist salmon feed reduced AA slightly. Ascorbic acid oxidized in frozen storage and while thawing and, after 12 h at room temperature, only trace amounts remained. Ascorbyl-2-polyphosphate at 0.05 to 0.2 times that of equimolar AA in casein-base or practical feeds supported long-term growth and development in rainbow trout and other fishes. Trout feeding trials with practical feeds in actual production regimens documented APP activity at growth rates approaching the maximum for trout farming. Corrected for greater stability, APP antiscorbutic activity appeared to be comparable to that of AA on a molar-equivalent basis. Similarly, apparent equimolar activity was inferred from estimated equilibrium levels of liver, kidney, and whole-body AA and L-ascorbyl-2-sulfate (AS) after prolonged APP use in trout feeds. Fathead minnow growth and reproduction in egg-to-egg life-cycle tests also confirmed APP safety and efficacy as a stabilized source of vitamin C for feeds. None of the typical lesions of scoliosis, malformed gill lamellae, and crenulated opercles, nor conditions of poor health, anorexia, and eventual torpor seen in vitamin C-deficient controls occurred in trout fed APP. No liver pathology was evident in trout fed APP for 252 d at 1.7 to 3.3 times the National Research Council's recommended vitamin C (equivalent) rates. 相似文献
87.
Modern farming has caused considerable declines in UK bumblebee populations, and, while options exist for farmers to increase the quantity of bee-friendly habitat, uptake has been low. Robin Blake explains how existing habitats on farms could be enhanced for the benefit of bumblebees. 相似文献
88.
Brian L. Benham Megan K. Laird Blake B. Ross David H. Vaughan Danny R. Peek 《Water, air, and soil pollution》2007,179(1-4):159-166
A plot-scale, rainfall-simulation study measured edge-of-field pollutant losses from conventional-till, strip-till, and no-till treatments in a burley tobacco production system. The field experiment results show that the conventional-till treatment yielded more total runoff than strip- and no-till treatments. Compared to the conventional-till treatment, both no-till and strip-till reduced the total mass losses of total suspended solids (TSS), total nitrogen (TN), total Kjeldahl nitrogen (TKN), nitrate (NO-N), ammonia (NH3-N), total phosphorus (TP), orthophosphate (PO4-P), and the insecticide chlorpyrifos in runoff. Although statistical analyses indicated that there was no significant difference between the no-till and strip-till practices, the no-till practice consistently yielded less edge-of-field pollutant loss than the strip-till practice. This research reinforces the body of knowledge documenting the effectiveness of conservation-tillage practices in reducing edge-of-field pollutant losses. 相似文献
89.
90.
Alex Taylor William H. Blake Miranda J. Keith-Roach 《Journal of Soils and Sediments》2014,14(11):1886-1893