全文获取类型
收费全文 | 1782篇 |
免费 | 96篇 |
国内免费 | 4篇 |
专业分类
林业 | 80篇 |
农学 | 37篇 |
基础科学 | 10篇 |
259篇 | |
综合类 | 326篇 |
农作物 | 86篇 |
水产渔业 | 117篇 |
畜牧兽医 | 716篇 |
园艺 | 43篇 |
植物保护 | 208篇 |
出版年
2023年 | 11篇 |
2022年 | 17篇 |
2021年 | 36篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 28篇 |
2016年 | 34篇 |
2015年 | 32篇 |
2014年 | 38篇 |
2013年 | 58篇 |
2012年 | 75篇 |
2011年 | 108篇 |
2010年 | 56篇 |
2009年 | 55篇 |
2008年 | 85篇 |
2007年 | 112篇 |
2006年 | 120篇 |
2005年 | 85篇 |
2004年 | 97篇 |
2003年 | 86篇 |
2002年 | 87篇 |
2001年 | 21篇 |
2000年 | 34篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 23篇 |
1994年 | 14篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 11篇 |
1970年 | 8篇 |
排序方式: 共有1882条查询结果,搜索用时 93 毫秒
31.
Alan FRANZLUEBBERS Derek HUNT Gary TELFORD Shabtai BITTMAN Quirine KETTERINGS 《农业科学与工程前沿(英文版)》2021,8(1):81-96
32.
33.
Anne H. Beaudreau Eric J. Ward Richard E. Brenner Andrew O. Shelton Jordan T. Watson Jennifer C. Womack Sean C. Anderson Alan C. Haynie Kristin N. Marshall Benjamin C. Williams 《Fish and Fisheries》2019,20(4):601-619
Heterogeneity in human responses and decision‐making can contribute to the resilience of social–ecological systems in the face of environmental, political and economic pressures. In fishery systems worldwide, the ability of harvesters to maintain a diverse portfolio of fishing strategies is important for building adaptive capacity. We used a case‐study approach to examine the complexity of factors that inhibit or promote diversification in fisheries of Alaska, one of the major fishing regions of the world. Through a combination of harvest records and literature review, we explored shifts in participation and portfolio diversity in Alaskan fisheries over three decades. The four case‐studies examined the responses of fishers, fleets and communities to multiple, intersecting pressures, including biological declines, market and price dynamics, fishery privatization and the 1989 Exxon Valdez oil spill. These cases illustrate how stressors acting at multiple scales can encourage or constrain opportunities for diversification, and that these opportunities may be spread inequitably across participants. Overall, we found evidence for reduced participation and increasing specialization in Alaskan commercial fisheries. While numerous factors explain these trends, policies like individual quota systems and the increasing cost of entry into fisheries are forcing consolidation at local to regional scales. A portfolio approach to managing fisheries that reduces barriers to diversification and includes broad representation of resource users and communities in management may help to maintain opportunity and choice for fishers. 相似文献
34.
Parker M Pollnitz AP Cozzolino D Francis IL Herderich MJ 《Journal of agricultural and food chemistry》2007,55(15):5948-5955
35.
36.
Paige E Boyle Michael D Richardson Mary C Savin Douglas E Karcher Daniel A Potter 《Pest management science》2019,75(8):2071-2078
Earthworm activity is beneficial in most natural and agricultural systems, but excessive earthworm casting is a problem on sports fields worldwide. Expulsion of soil‐rich earthworm fecal matter, or casts, as mounds of soil on the turf canopy can muddy the surface, reduce photosynthesis, and lead to thinning, weed invasion and surface softening. Casts affect ball roll on sports fields, cause fouling of maintenance equipment, and dull mower blades. Build‐up of cast material on reel mower units can affect height and quality of cut. Casting activity is dependent on environmental conditions such as soil texture, temperature, moisture, pH, and organic matter. Response to environmental conditions varies by species. Management options are limited, because no pesticides are specifically labeled for earthworm control at this time, and cultural control methods such as soil modification, turfgrass clipping removal, and sand topdressing have limited and inconsistent efficacy. Products containing plant‐derived saponins and irritants show promise for earthworm management. Pest management practices to mitigate excessive earthworm casting will likely need to be species‐specific, but limited knowledge of earthworm identification by end‐users further inhibits the efficacy of control measures. © 2019 Society of Chemical Industry 相似文献
37.
Transformation of the nitrogen cycle: recent trends, questions, and potential solutions 总被引:12,自引:0,他引:12
Galloway JN Townsend AR Erisman JW Bekunda M Cai Z Freney JR Martinelli LA Seitzinger SP Sutton MA 《Science (New York, N.Y.)》2008,320(5878):889-892
Humans continue to transform the global nitrogen cycle at a record pace, reflecting an increased combustion of fossil fuels, growing demand for nitrogen in agriculture and industry, and pervasive inefficiencies in its use. Much anthropogenic nitrogen is lost to air, water, and land to cause a cascade of environmental and human health problems. Simultaneously, food production in some parts of the world is nitrogen-deficient, highlighting inequities in the distribution of nitrogen-containing fertilizers. Optimizing the need for a key human resource while minimizing its negative consequences requires an integrated interdisciplinary approach and the development of strategies to decrease nitrogen-containing waste. 相似文献
38.
Benjamin J. Ahern Dean W. Richardson Raymond C. Boston Thomas P. Schaer 《Veterinary surgery : VS》2010,39(5):588-593
Objective: To determine the rate of postoperative infection (POI) for internal fixation repaired equine long bone fractures and arthrodeses and identify associated risk factors. Study Design: Case series. Animals: Horses (n=192) with fracture repair of the third metacarpal and metatarsal bones, radius, ulna, humerus, tibia, and femur, or arthrodesis with internal fixation. Methods: Medical records (1990–2006) were reviewed for signalment, anatomic location, fracture classification and method of repair, technique and surgical duration, bacterial species isolated, postoperative care, onset of POI, and outcome. Results: Of 192 horses (171 [89%] closed, 21 [11%] open fractures), 157 (82%) were discharged from the hospital. Infection occurred in 53 (28% horses), of which 31 (59%) were discharged. Repairs without POI were 7.25 times more likely to be discharged from the hospital. Closed fractures were 4.23 times more likely to remain uninfected and 4.59 times more likely to be discharged from the hospital compared with open fractures. Closed reduction and internal fixation was associated with a 2.5‐fold reduction in rate of POI and a 5.9 times greater chance for discharge from the hospital compared with open reduction and internal fixation. Females had a strong trend for increased POI when compared with colts and stallion but not geldings. Conclusions: Overall rate of POI was 28%. Fracture classification, method of repair, gender, and surgical duration were significant risk factors. 相似文献
39.
Leif Sundheim Alan R. Poplawsky Albert H. Ellingboe 《Physiological and Molecular Plant Pathology》1988,33(3)
Two chitinase encoding EcoRI fragments from the enteric soil bacterium Serratia marcescens were cloned. From a genomic library of 5686 transductants, 21 expressed chitinase activity as indicated by clearing of a chitin-containing medium. The chitinase encoding clones could be divided into two groups. Four had an 18kb EcoRI fragment and 17 had a 9·4 kb EcoRI fragment. In Southern hybridization experiments the 18kb fragment showed no homology to the 9·4 kb fragment and restriction enzyme maps indicated no similarity. Triparental mating with fluorescent Pseudomonas spp. yielded transconjugants that expressed chitinase activity, inhibited growth of Fusarium oxysporum f. sp. redolens germ tubes and reduced disease of radish caused by the same fungus. 相似文献
40.
Alan Noble 《Pest management science》1988,23(3):259-265
A test for the identity of specific phenoxy ester herbicides was required. Work with packed column and capillary GLC showed that the retention times could be used to identify major ester components. An esterification method with acetyl chloride produced a mean yield of 98% with a range of phenoxy acids and alcohols. This method could be used to produce standards for the specific quantitative analysis of esters in formulations. 相似文献