全文获取类型
收费全文 | 714篇 |
免费 | 80篇 |
专业分类
林业 | 32篇 |
农学 | 12篇 |
基础科学 | 2篇 |
97篇 | |
综合类 | 87篇 |
农作物 | 37篇 |
水产渔业 | 65篇 |
畜牧兽医 | 385篇 |
园艺 | 26篇 |
植物保护 | 51篇 |
出版年
2023年 | 18篇 |
2022年 | 9篇 |
2021年 | 37篇 |
2020年 | 37篇 |
2019年 | 56篇 |
2018年 | 33篇 |
2017年 | 42篇 |
2016年 | 35篇 |
2015年 | 23篇 |
2014年 | 33篇 |
2013年 | 20篇 |
2012年 | 55篇 |
2011年 | 62篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 39篇 |
2007年 | 45篇 |
2006年 | 38篇 |
2005年 | 34篇 |
2004年 | 14篇 |
2003年 | 17篇 |
2002年 | 17篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 3篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1928年 | 1篇 |
1915年 | 1篇 |
排序方式: 共有794条查询结果,搜索用时 46 毫秒
51.
Nutrition and learning 总被引:2,自引:0,他引:2
52.
53.
Johnson N Carran S Botner J Fontaine K Laxague N Nuetzel P Turnley J Tivnan B 《Science (New York, N.Y.)》2011,333(6038):81-84
In military planning, it is important to be able to estimate not only the number of fatalities but how often attacks that result in fatalities will take place. We uncovered a simple dynamical pattern that may be used to estimate the escalation rate and timing of fatal attacks. The time difference between fatal attacks by insurgent groups within individual provinces in both Afghanistan and Iraq, and by terrorist groups operating worldwide, gives a potent indicator of the later pace of lethal activity. 相似文献
54.
Sanfey AG Rilling JK Aronson JA Nystrom LE Cohen JD 《Science (New York, N.Y.)》2003,300(5626):1755-1758
The nascent field of neuroeconomics seeks to ground economic decision making in the biological substrate of the brain. We used functional magnetic resonance imaging of Ultimatum Game players to investigate neural substrates of cognitive and emotional processes involved in economic decision-making. In this game, two players split a sum of money;one player proposes a division and the other can accept or reject this. We scanned players as they responded to fair and unfair proposals. Unfair offers elicited activity in brain areas related to both emotion (anterior insula) and cognition (dorsolateral prefrontal cortex). Further, significantly heightened activity in anterior insula for rejected unfair offers suggests an important role for emotions in decision-making. 相似文献
55.
Retinoic acid signaling restricts the cardiac progenitor pool 总被引:1,自引:0,他引:1
Organogenesis begins with specification of a progenitor cell population, the size of which provides a foundation for the organ's final dimensions. Here, we present a new mechanism for regulating the number of progenitor cells by limiting their density within a competent region. We demonstrate that retinoic acid signaling restricts cardiac specification in the zebrafish embryo. Reduction of retinoic acid signaling causes formation of an excess of cardiomyocytes, via fate transformations that increase cardiac progenitor density within a multipotential zone. Thus, retinoic acid signaling creates a balance between cardiac and noncardiac identities, thereby refining the dimensions of the cardiac progenitor pool. 相似文献
56.
King MC Marks JH Mandell JB;New York Breast Cancer Study Group 《Science (New York, N.Y.)》2003,302(5645):643-646
Risks of breast and ovarian cancer were determined for Ashkenazi Jewish women with inherited mutations in the tumor suppressor genes BRCA1 and BRCA2. We selected 1008 index cases, regardless of family history of cancer, and carried out molecular analysis across entire families. The lifetime risk of breast cancer among female mutation carriers was 82%, similar to risks in families with many cases. Risks appear to be increasing with time: Breast cancer risk by age 50 among mutation carriers born before 1940 was 24%, but among those born after 1940 it was 67%. Lifetime risks of ovarian cancer were 54% for BRCA1 and 23% for BRCA2 mutation carriers. Physical exercise and lack of obesity in adolescence were associated with significantly delayed breast cancer onset. 相似文献
57.
Treusch S Hamamichi S Goodman JL Matlack KE Chung CY Baru V Shulman JM Parrado A Bevis BJ Valastyan JS Han H Lindhagen-Persson M Reiman EM Evans DA Bennett DA Olofsson A DeJager PL Tanzi RE Caldwell KA Caldwell GA Lindquist S 《Science (New York, N.Y.)》2011,334(6060):1241-1245
Aβ (beta-amyloid peptide) is an important contributor to Alzheimer's disease (AD). We modeled Aβ toxicity in yeast by directing the peptide to the secretory pathway. A genome-wide screen for toxicity modifiers identified the yeast homolog of phosphatidylinositol binding clathrin assembly protein (PICALM) and other endocytic factors connected to AD whose relationship to Aβ was previously unknown. The factors identified in yeast modified Aβ toxicity in glutamatergic neurons of Caenorhabditis elegans and in primary rat cortical neurons. In yeast, Aβ impaired the endocytic trafficking of a plasma membrane receptor, which was ameliorated by endocytic pathway factors identified in the yeast screen. Thus, links between Aβ, endocytosis, and human AD risk factors can be ascertained with yeast as a model system. 相似文献
58.
Chen CH Huang H Ward CM Su JT Schaeffer LV Guo M Hay BA 《Science (New York, N.Y.)》2007,316(5824):597-600
One proposed strategy for controlling the transmission of insect-borne pathogens uses a drive mechanism to ensure the rapid spread of transgenes conferring disease refractoriness throughout wild populations. Here, we report the creation of maternal-effect selfish genetic elements in Drosophila that drive population replacement and are resistant to recombination-mediated dissociation of drive and disease refractoriness functions. These selfish elements use microRNA-mediated silencing of a maternally expressed gene essential for embryogenesis, which is coupled with early zygotic expression of a rescuing transgene. 相似文献
59.
Jessica?S.?VeyseyEmail author Sandra?D.?Mattfeldt Kimberly?J.?Babbitt 《Landscape Ecology》2011,26(5):661-672
The distribution and abundance of species are shaped by local and landscape processes, but the dominant processes may differ
with scale and increasing human disturbance. We investigated population responses of two pool-breeding amphibian species to
differences in local and landscape characteristics in suburbanizing, southeastern New Hampshire, USA. In 2003 and 2004, we
sampled 49 vernal pools for spotted salamander (Ambystoma maculatum) and wood frog (Lithobates sylvaticus) egg masses. Using egg masses as a proxy for breeding-female population size, we examined the relative influence of five
land-use and three isolation variables at two scales (300 and 1000 m) and five wetland variables on egg-mass abundance. For
both species, road density at the landscape scale (1000 m) and hydroperiod most strongly predicted egg-mass abundance, with
abundance decreasing as roads became denser and hydroperiods shortened. Wetland isolation was also an important predictor,
with abundance greatest at more isolated pools, suggesting that both species concentrate at isolated pools when alternative
breeding sites are scarce. Surprisingly, no 300-m parameters were strongly associated with salamander egg-mass abundance,
whereas several landscape parameters were. In suburbanizing areas, it is at least as important to consider landscape-scale
road density as to consider hydroperiod when designing conservation plans for these species. Furthermore, both isolated and
clustered pools provide these species important habitat and may require protection. Finally, the conceptual framework for
spotted-salamander management must be expanded so that spatial configuration at the landscape scale becomes a regular, integrated
component of conservation planning for this species. 相似文献
60.
Ryan EP Heuberger AL Weir TL Barnett B Broeckling CD Prenni JE 《Journal of agricultural and food chemistry》2011,59(5):1862-1870
Emerging evidence supporting chronic disease fighting properties of rice bran has advanced the development of stabilized rice bran for human use as a functional food and dietary supplement. A global and targeted metabolomic investigation of stabilized rice bran fermented with Saccharomyces boulardii was performed in three rice varieties. Metabolites from S. boulardii-fermented rice bran were detected by gas chromatography-mass spectrometry (GC-MS) and assessed for bioactivity compared to nonfermented rice bran in normal and malignant lymphocytes. Global metabolite profiling revealed significant differences in the metabolome that led to discovery of candidate compounds modulated by S. boulardii fermentation. Fermented rice bran extracts from three rice varieties reduced growth of human B lymphomas compared to each variety's nonfermented control and revealed that fermentation differentially altered bioactive compounds. These data support that integration of global and targeted metabolite analysis can be utilized for assessing health properties of rice bran phytochemicals that are enhanced by yeast fermentation and that differ across rice varieties. 相似文献