全文获取类型
收费全文 | 219篇 |
免费 | 27篇 |
国内免费 | 1篇 |
专业分类
林业 | 8篇 |
农学 | 1篇 |
25篇 | |
综合类 | 29篇 |
农作物 | 8篇 |
水产渔业 | 26篇 |
畜牧兽医 | 134篇 |
园艺 | 5篇 |
植物保护 | 11篇 |
出版年
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 17篇 |
2007年 | 11篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 7篇 |
1998年 | 2篇 |
1994年 | 1篇 |
排序方式: 共有247条查询结果,搜索用时 31 毫秒
171.
Ryan E. Casey Judith A. Simon Stephanie Atueyi Joel W. Snodgrass Natalie Karouna-Renier Donald W. Sparling 《Water, air, and soil pollution》2007,178(1-4):69-77
Stormwater ponds are an increasingly common feature in urban landscapes. Because these ponds retain runoff and particulate-bound contaminants from impervious surfaces, organisms inhabiting stormwater ponds may be exposed to elevated metal levels in sediments. This study evaluated temporal changes in sediment and macroinvertebrate Cu, Pb and Zn over an eleven-year period with specific attention to land use in pond watersheds. Sediment and invertebrate metal levels were quantified using atomic absorption spectrophotometry (1993 samples) or inductively coupled plasma mass spectrometry (2003–2004 samples). Sediment trace element levels did not significantly change from 1993 to 2003-2004 with the exception of Zn in ponds receiving runoff from highways, which increased from a mean of 32 mg kg?1 in 1993 to 344 mg kg?1 in 2003–2004. Sediment Pb and Cu generally remained below published threshold effects concentrations (TEC) except for two instances of elevated Cu in 2003–2004. Zn remained below the TEC in 1993 but exceeded the TEC in six ponds in 2003–2004. Trace metal body burdens varied among invertebrate groups, and to a lesser extent among land uses, but in both cases this variation was a function of year. In general, trace element body burdens were more similar among invertebrate groups or land use or both during 2003–2004 when compared to levels in 1993. Our results suggest sediment and invertebrate trace metal levels are at steady state in these stormwater management ponds and that risk to organisms inhabiting these ponds does not vary as a function of pond age. 相似文献
172.
A study was undertaken to investigate differences between laboratoryand field pH measurements for precipitation samples collected from 135 weekly precipitation-monitoring sites in the National Trends Network from 12/30/1986 to 12/28/1999. Differences in pH between field and laboratory measurements occurred for 96% of samples collected during this time period. Differences between the two measurements were evaluated for precipitation samples collected before and after January 1994, when modifications to sample-handling protocol and elimination of the contaminating bucket o-ring used in sample shipment occurred. Median hydrogen-ion and pH differences between field and laboratory measurements declined from 3. 9 μeq L-1 or 0. 10 pH units before the 1994 protocol change to 1. 4 μeq L-1 or 0. 04 pH units after the 1994 protocol change. Hydrogen-ion differences between field and laboratory measurements had a high correlation with the sample pH determined in the field. The largest pH differences between the two measurements occurred for high-pH samples (>5. 6), typical of precipitation collected in Western United States; however low-pH samples (<5. 0) displayed the highest variability in hydrogen-ion differences between field and laboratory analyses. Properly screened field pH measurements are a useful alternative to laboratory pH values for trend analysis, particularly before 1994 when laboratory pH values were influenced by sample-collection equipment. 相似文献
173.
Protein kinases play a critical role in cell regulation and their deregulation is a contributing factor in an increasing list of diseases including cancer. Marine sponges have yielded over 70 novel compounds to date that exhibit significant inhibitory activity towards a range of protein kinases. These compounds, which belong to diverse structural classes, are reviewed herein, and ordered based upon the kinase that they inhibit. Relevant synthetic studies on the marine natural product kinase inhibitors have also been included. 相似文献
174.
175.
176.
Sara D. Lawhon Deanna A. Sutton Natalie D. Halbert Jeffrey P. Watkins 《Journal of Equine Veterinary Science》2011,31(12):696-699
Two months following the surgical repair of an acute, open, comminuted, and articular fracture of the left olecranon, a 15-year-old American Saddlebred gelding presented with nonweight-bearing lameness. A fungus cultured from the cubital joint was identified as Scedosporium prolificans by sequencing of the D2 large subunit ribosomal DNA region and subsequently confirmed by phenotypic methods. Therapy with systemic fluconazole, terbinafine and intra-articular voriconazole was attempted, but was unsuccessful. 相似文献
177.
Ward NC Croft KD Puddey IB Hodgson JM 《Journal of agricultural and food chemistry》2004,52(17):5545-5549
Grape seed extract provides a concentrated source of polyphenols, most of which are proanthocyanidins. Polymeric proanthocyanidins are poorly absorbed in the small intestine of humans, and exposure may result from metabolism to phenolic acids by colonic bacteria. Any biological effects of proanthocyanidins may be due to the phenolic acid metabolites. Several phenolic acids have been identified as proanthocyanidin metabolites, but these may be derived from a range of other dietary sources. The aim of this study was to determine if 24-h urinary excretion of specific phenolic acids increased significantly and consistently following regular supplementation with grape seed extract. In a randomized, double-blind placebo-controlled trial, 69 volunteers received grape seed extract (1000 mg/day total polyphenols) or placebo for 6 weeks. Supplementation with grape seed polyphenols resulted in a consistent increase in the excretion of 3-hydroxyphenylpropionic acid (3-HPP, P < 0.001) and 4-O-methylgallic acid (P < 0.001) and a less consistent increase in the excretion of 3-hydroxyphenylacetic acid (P = 0.002). The observed increase in 3-HPP is in line with the suggestion that this compound is a major phenolic acid breakdown product of proanthocyanidin metabolism in vivo. 相似文献
178.
179.
David W. Ramey DVM Natalie Eddington PhD Eugene Thonar PhD Martin Lee PhD 《Journal of Equine Veterinary Science》2002,22(3)
Oral supplements intended for the treatment and prevention of joint-related problems in horses may not contain ingredients at levels that meet label claims. 相似文献