全文获取类型
收费全文 | 647篇 |
免费 | 42篇 |
专业分类
林业 | 32篇 |
农学 | 11篇 |
45篇 | |
综合类 | 131篇 |
农作物 | 7篇 |
水产渔业 | 13篇 |
畜牧兽医 | 418篇 |
园艺 | 8篇 |
植物保护 | 24篇 |
出版年
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 39篇 |
2012年 | 16篇 |
2011年 | 28篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 29篇 |
2007年 | 30篇 |
2006年 | 14篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 30篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 16篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1970年 | 9篇 |
1969年 | 5篇 |
排序方式: 共有689条查询结果,搜索用时 31 毫秒
71.
72.
73.
Reed JC 《Science (New York, N.Y.)》2011,334(6059):1075-1076
74.
75.
Seven balloons were launched successfully from Ascension Island in January 1969. The balloons, flown at altitudes of 20 and 24 kilometers, will make possible a detailed analysis of the stratospheric circulation near the equator and will hopefully lead to an understanding of the quasi-biennial stratospheric oscillation in the tropics. 相似文献
76.
77.
Reed AC 《Science (New York, N.Y.)》1930,72(1877):611-620
78.
Gregory SM Davis BK West JA Taxman DJ Matsuzawa S Reed JC Ting JP Damania B 《Science (New York, N.Y.)》2011,331(6015):330-334
The NLR (nucleotide binding and oligomerization, leucine-rich repeat) family of proteins senses microbial infections and activates the inflammasome, a multiprotein complex that promotes microbial clearance. Kaposi's sarcoma-associated herpesvirus (KSHV) is linked to several human malignancies. We found that KSHV Orf63 is a viral homolog of human NLRP1. Orf63 blocked NLRP1-dependent innate immune responses, including caspase-1 activation and processing of interleukins IL-1β and IL-18. KSHV Orf63 interacted with NLRP1, NLRP3, and NOD2. Inhibition of Orf63 expression resulted in increased expression of IL-1β during the KSHV life cycle. Furthermore, inhibition of NLRP1 was necessary for efficient reactivation and generation of progeny virus. The viral homolog subverts the function of cellular NLRs, which suggests that modulation of NLR-mediated innate immunity is important for the lifelong persistence of herpesviruses. 相似文献
79.
The purpose of this study was to find out if an LMA (#1 LMA‐Classic) would provide a better airway than a face mask in spontaneously breathing anesthetized rabbits, and to test if it could be used for mechanically controlled ventilation. Sixteen rabbits (4.1 ± 0.8 kg, mean ± SD) were assigned randomly to three treatment groups; face mask with spontaneous ventilation (FM‐SV; n = 5), LMA with spontaneous ventilation (LMA‐SV; n = 5), and LMA with controlled ventilation (LMA‐CV; n = 6). Rabbits were anesthetized in dorsal recumbency using a circle circuit at constant ET isoflurane (2.3%, Datex airway gas monitor) and constant rectal temperature (38.85 °C) for 2 hours. PaCO2, PaO2, minute volume, tidal volume (Wright's respirometer), and Pe CO2 were measured at 15 minute intervals. Two individuals in the FM‐SV group had PaCO2 >100 mm Hg (>13.3 kPa). One rabbit in the FM‐SV had PaO2 <80 mm Hg (<10.7 kPa). All FM‐SV rabbits showed signs of airway obstruction and two were withdrawn from the study at 45 and 90 minutes, respectively, because of cyanosis. Tidal volume could not be measured in the FM‐SV group. No signs of airway obstructions were observed in either of the LMA groups. Four rabbits in the LMA‐CV group developed gastric tympany, and one of these refluxed after 110 minutes. The significance of differences between the two spontaneously breathing groups and between the two LMA groups were measured using Wilcoxon's rank sum test (with significance assumed at p < 0.05). There were no statistical differences between FM‐SV and LMA‐SV in any variable tested. PaCO2 and Pe ′CO2 were less in the LMA‐CV group than in the LMA‐SV group, while PaO2, tidal volume, and minute volume were all more. We conclude that biologically, the LMA provides a better airway than the face mask during spontaneous breathing and that it can be used for IPPV, but that gastric tympany is likely to occur during IPPV. 相似文献
80.
Solar tracking has been described in several agronomic and wild species, yet variation within a given species has not been reported. To address that issue, photoperiod leaflet reorientation in response to vectorial light was measured in three alfalfa ( Medicago sativa L.) germplasm pools selected from the cultivar Ladak 65. Dark-leaf germplasm responded to all photosynthetic photon flux densities (PPFD) (100 to 700 μmol/m2 /s) with no detectable lag period. Following a 24-h dark treatment only high PPFD (600 to 700μmol/m2 /s) elicited reorientation. Pale-leaf germplasm responded to intermediate (300 to 400 μmol/m2 /s) and high PPFD in a similar manner; however, the low (100-125μmol/m2 /s) PPFD treatment had little effect on reorientation. The 24-h dark treatment decreased reorientation at all PPFD. Small-leaf germplasm responded equally to all PPFD and was not affected by the 24-h dark treatment. The results suggest that available energy levels may influence the reorientation response. Carbonyl cyanide m -chlorophenylhydrazone, an inhibitor of photophosphorylation, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of non-cyclic photosynthetic electron transport, reduced reorientation only in the pale-leaf type. These results suggest that stored energy reserves were adequate to maintain leaflet reorientation in the absence of photosynthesis in all but the pale-leaf germplasm. In that germplasm photosynthetically generated energy may be required to support reorientation. 相似文献