全文获取类型
收费全文 | 319篇 |
免费 | 13篇 |
国内免费 | 5篇 |
专业分类
林业 | 11篇 |
农学 | 6篇 |
29篇 | |
综合类 | 62篇 |
农作物 | 3篇 |
水产渔业 | 19篇 |
畜牧兽医 | 190篇 |
园艺 | 4篇 |
植物保护 | 13篇 |
出版年
2019年 | 4篇 |
2018年 | 4篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 19篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 3篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 7篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1968年 | 2篇 |
1963年 | 3篇 |
1962年 | 2篇 |
1961年 | 3篇 |
1958年 | 11篇 |
1957年 | 7篇 |
1956年 | 7篇 |
1955年 | 5篇 |
1954年 | 6篇 |
1953年 | 8篇 |
1948年 | 4篇 |
1946年 | 3篇 |
排序方式: 共有337条查询结果,搜索用时 62 毫秒
11.
Amounts of total and extractable major nutrients have been measuredin soils under a variety of tree plantations at three sitesin Lowland Britain. The measurements repeat a study performedat these sites 23 years previously. Comparisons are made betweentotal stocks of litter and soil nitrogen, phosphorus, potassiumand calcium under broadleaved and coniferous trees planted oncontrasted lowland soils. Accumulation is shown under some conifersbut few broadleaves except for alder, under which progressiveincreases in nitrogen are suggested. Nutrient stocks are shownto be related to growth rate. The results reported also lendsome support to the view that the effects of different treespecies on development of soil properties are less significant,when viewed over a whole rotation, than measurements made earlyin the rotation, especially in the canopy closure to first thinningperiod, would suggest. 相似文献
12.
Abstract. Chinese catfish, Clarias fuscus (Lacepède), within three size ranges were evaluated for growth, survival and feed conversion ratios (FCR). A 4 × 3 factorial design was used during year-long trials which included four temperatures (20,25,30 and 35 °C) and three feeding rates with commercially formulated salmon/trout feed. Specific growth rates of juvenile fish (1–60g) were highest, ranging from 1–64% body weight/day at 20°C (2%/day feed rate), to 4–94%/day at 25°C (6%/day feed rate). Specific growth rates of sub-adult fish (60–150g) averaged 0–65%/day, with no significant difference between temperature-feed rate treatments. Specific growth rates of adult fish (>150g) were lowest, averaging 0–30%/day for grouped feed rate treatments at 25°C, and 0–16%/day at 30°C. Most mortalities occurred during the juvenile stage, with survival ranging from 0% at 35°C(2% feed rate) to 96% at 30°C(6% feed rate). Survival was 95–100% with sub-adults and adults. FCR were 1 to 4 with juveniles, 2 to 12 with sub-adults, and 3 to 22 with adults. These trials suggest that optimal growth and FCRs were obtained at 25°C; with feed rates of 6%/day with juveniles, 2%/day with sub-adults, and 1%/day with adult fish. Final yields at 25 and 30°C indicate that even though growth and FCR are optimal at 25°C, survival was greater at 30°C, which compensated for reduced growth performance at this temperature. Yields at 25 and 30°C were almost double those at 20°C. 相似文献
13.
14.
15.
HUI-CHU LIN DVM MS Diplomate ACVA AUBREY N. BAIRD DVM MS Diplomate ACVS DAVID G. PUGH DVM MS Diplomate ACT DAVID E. ANDERSON DVM MS Diplomate ACVS EARL M. GAUGHAN DVM MS Diplomate ACVS 《Veterinary surgery : VS》1997,26(5):444-450
Objective— To study the combined effects of intra-abdominal CO2 insufflation with changes in body position during laparoscopy in xylazine-ketamine-halothane anesthetized llamas. Study Design— Prospective, controlled study. Animals— Nine castrated, male llamas weighing 114 ± 23 kg, 3 to 13 years old. Methods— Three llamas (preliminary study [PS] group) were used to study the effect of right lateral, dorsal, and left lateral recumbency on gas exchange and acid-base status. The other six (experimental study [ES] group) were used to study the combined effects of changes in body position and CO2 insufflation to an intraabdominal pressure of 10 to 12 mm Hg. Heart rate, respiratory rate, and indirect arterial blood pressures (systolic [SAP], mean [MAP], and diastolic [DAP]) were recorded every 5 minutes during anesthesia. Arterial blood gases (PaO2 and PaCO2) and acid-base status (pHa and HCO3) were measured immediately after induction of anesthesia and before each change of position. Results— In the PS group, significant decreases in SAP, MAP and PaCO2 and increases in PaO2 and pHa were observed when the llamas were turned from right lateral to dorsal recumbency. Values for HCO-3 were lower than the postinduction values, but they remained unaffected by the changes in position. In the ES group, values for MAP were significantly lower when the llamas were placed in dorsal and left lateral recumbency than those observed during right lateral recumbency. Arterial O2 tension during right lateral recumbency was lower but returned to preinsufflation values when the llamas were placed in the dorsal position. All llamas recovered uneventfully within 30 minutes after termination of anesthesia. Conclusions— Insufflation of CO2 and changing body position induce minor and transient changes in cardiovascular and respiratory function. Clinical Relevance— Laparoscopy with mild intra-abdominal CO2 insufflation (10 to 12 mm Hg) can be used safely in spontaneously breathing llamas anesthetized with xylazine, ketamine, and halothane. 相似文献
16.
17.
Temperatures above those normally present in larval sites of certain mosquitoes (for example, Aedes stimulans) cause larvae of potential males to be feminized in all degrees. Certain combinations of temperatures will affect these larvae so that an abnormal pair of genital appendages consistently appears in addition to the usual pair. These appendages appear to be masculine and are presumed to come from imaginal discs that are latent in present-day Diptera. 相似文献
18.
19.
20.