全文获取类型
收费全文 | 383篇 |
免费 | 13篇 |
专业分类
林业 | 7篇 |
农学 | 2篇 |
基础科学 | 1篇 |
40篇 | |
综合类 | 47篇 |
农作物 | 17篇 |
水产渔业 | 9篇 |
畜牧兽医 | 267篇 |
园艺 | 2篇 |
植物保护 | 4篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 19篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 17篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 3篇 |
1966年 | 1篇 |
1947年 | 1篇 |
1884年 | 1篇 |
排序方式: 共有396条查询结果,搜索用时 15 毫秒
91.
92.
M. G. Solomon J. D. Fitzgerald 《The Journal of Horticultural Science and Biotechnology》2013,88(5):535-537
The effects of fenoxycarb, an insect growth regulator, on predatory anthocorids, were tested in comparison with the broad-spectrum insecticide deltamethrin, in pear orchard trials. The results confirmed the effectiveness of fenoxycarb against pear sucker, Cacop- sylla pyricola and revealed no damaging effects on larval or adult anthocorids (mainly Anthocoris nemoralis). Deltamethrin reduced numbers of both C. pyricola and anthocorids, allowing a resurgence of C. pyricola later in the season. Fenoxycarb is shown to be suitable for use in integrated pest management programmes in pear. 相似文献
93.
J Cernicharo B Lefloch P Cox D Cesarsky C Esteban F Yusef-Zadeh DI Mendez J Acosta-Pulido Garcia Lopez RJ A Heras 《Science (New York, N.Y.)》1998,282(5388):462-465
The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula. 相似文献
94.
PO Wennberg TF Hanisco L Jaegle DJ Jacob EJ Hintsa EJ Lanzendorf JG Anderson R Gao ER Keim SG Donnelly LAD Negro DW Fahey SA McKeen RJ Salawitch CR Webster RD May RL Herman MH Proffitt JJ Margitan EL Atlas SM Schauffler F Flocke CT McElroy TP Bui 《Science (New York, N.Y.)》1998,279(5347):49-53
The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected. 相似文献
95.
A previously unknown solid phase of H2O has been identified by its peculiar growth patterns, distinct pressure-temperature melting relations, and vibrational Raman spectra. Morphologies of ice crystals and their pressure-temperature melting relations were directly observed in a hydrothermal diamond-anvil cell for H2O bulk densities between 1203 and 1257 kilograms per cubic meter at temperatures between -10 degrees and 50 degreesC. Under these conditions, four different ice forms were observed to melt: two stable phases, ice V and ice VI, and two metastable phases, ice IV and the new ice phase. The Raman spectra and crystal morphology are consistent with a disordered anisotropic structure with some similarities to ice VI. 相似文献
96.
97.
Yearling ewes (n = 32) were used in a 2x2x2 factorial experiment to determine effects of breed (Targhee vs. Suffolk), energy intake (1x vs. 3x NEm requirements, and physiological status (nonpregnant, nonlactating vs. lactating) on serum GH, insulin, NEFA, glucose, and blood urea nitrogen (BUN) concentrations. Blood collections were made in two periods that began 21 and 32 d after ewes lambed. Lactating ewes had more GH peaks (P<.10), higher (P<.01) mean GH concentration, and greater (P<.01) area under the GH curve (AUC) than nonlactating ewes. The AUC was greater (P<.01) in ewes fed 1x NEm than in ewes fed 3x NEm. Energy intake had no effect on serum GH before feeding (P>.23) when evaluated within physiological statuses. After feeding, GH concentrations were greater (P<.10) for ewes fed 1x NEm than for those fed 3x NEm. Insulin and glucose did not differ (P>.23) between energy intake levels. Insulin and glucose were greater (P<.001) in nonlactating than in lactating ewes when evaluated within breed. Lactating and Targhee ewes fed 1x NEm had greater (P<.001) NEFA concentration than nonlactating and Targhee ewes fed 3x NEm, respectively. Ewes fed 3x NEm and Targhee ewes had greater (P<.005) BUN concentrations than ewes fed 1x NEm and Suffolk ewes, respectively. Physiological status seems to play a more important role in the regulation of GH than does energy intake. Higher BUN concentrations in Targhee than in Suffolk ewes demonstrates one metabolic event that distinguishes a breed's adaptation to the environment in which it originated. 相似文献
98.
Eric D. H. Durieux Thomas B. Farver Patrick S. Fitzgerald Kai J. Eder David J. Ostrach 《Fish physiology and biochemistry》2011,37(1):21-29
Acetylcholinesterase (AChE) activity is one of the most common biomarkers of neurotoxicity used in aquatic organisms. However,
compared to its extensive use as biomarker, the effects of natural factors on AChE activity remain unclear especially in estuarine
fishes. The aim of this study was to evaluate the effects of natural factors on AChE activity of striped bass (Morone saxatilis) juveniles. Brain AChE activity was measured in YOY (Young-Of-Year) individuals collected monthly from August 2007 to January
2008 at 12 different sites in the San Francisco Estuary system. The spatio-temporal variability of AChE was analyzed relative
to water temperature and salinity as well as fish size. AChE activity was highly positively correlated with water temperature
and to a lesser extent negatively with fish size while no relationship was detected with salinity. Taking into account these
natural factors when using AChE as a biomarker will help to determine and understand the effects of neurotoxic contaminants
on fish in estuarine systems. 相似文献
99.
100.