全文获取类型
收费全文 | 201325篇 |
免费 | 13301篇 |
国内免费 | 719篇 |
专业分类
林业 | 22695篇 |
农学 | 13886篇 |
基础科学 | 2956篇 |
39531篇 | |
综合类 | 9705篇 |
农作物 | 16941篇 |
水产渔业 | 15381篇 |
畜牧兽医 | 65929篇 |
园艺 | 6142篇 |
植物保护 | 22179篇 |
出版年
2021年 | 2410篇 |
2020年 | 2797篇 |
2019年 | 3583篇 |
2018年 | 3575篇 |
2017年 | 3933篇 |
2016年 | 4511篇 |
2015年 | 4141篇 |
2014年 | 5490篇 |
2013年 | 16027篇 |
2012年 | 4691篇 |
2011年 | 6190篇 |
2010年 | 6685篇 |
2009年 | 7389篇 |
2008年 | 5701篇 |
2007年 | 4636篇 |
2006年 | 5546篇 |
2005年 | 4766篇 |
2004年 | 4651篇 |
2003年 | 4431篇 |
2002年 | 3820篇 |
2001年 | 3877篇 |
2000年 | 3550篇 |
1999年 | 3798篇 |
1998年 | 3928篇 |
1997年 | 4002篇 |
1996年 | 3741篇 |
1995年 | 4256篇 |
1994年 | 3636篇 |
1993年 | 3333篇 |
1992年 | 3041篇 |
1991年 | 3172篇 |
1990年 | 2857篇 |
1989年 | 2831篇 |
1988年 | 2451篇 |
1987年 | 2507篇 |
1986年 | 2369篇 |
1985年 | 2809篇 |
1984年 | 2813篇 |
1983年 | 2752篇 |
1982年 | 2475篇 |
1981年 | 2444篇 |
1980年 | 2446篇 |
1979年 | 2365篇 |
1978年 | 2255篇 |
1977年 | 2173篇 |
1976年 | 2022篇 |
1975年 | 1759篇 |
1974年 | 1757篇 |
1973年 | 1696篇 |
1971年 | 1457篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
G. L. RICHARDSON dvm T. R. O'BRIEN dvm PhD Diplomateacvr J. R. PASCOE bvsc D. M. MEAGHER dvm PhD Dipiomateacvs 《Veterinary surgery : VS》1986,15(2):156-160
The medical records of 38 horses with puncture wounds of the navicular bursa were reviewed. Only 12 horses had a satisfactory outcome (breeding or riding). Of the remaining 26 horses, 19 were euthanized, five were sold due to persistent severe lameness, one died, and one was lost to long-term follow-up. Different combinations of conservative management prior to surgical debridement and drainage of the navicular bursa were unsuccessful in resolving the condition. Horses that were treated surgically within 1 week of the injury and had a hind leg affected had the best chance of a satisfactory outcome. Additional wound debridement was necessary in 15 horses after initial surgical treatment. The most common complications encountered were navicular bone osteomyelitis and sepsis of the deep digital flexor tendon. Thirteen of 14 horses that had rupture of the deep digital flexor tendon and subluxation of the distal interphalangeal joint had an unsatisfactory outcome. One mare subsequently developed ankylosis of the distal interphalangeal joint and was a useful brood mare. Two horses that had biaxial palmar digital neurectomy because of persistent lameness were later euthanized because of navicular bone fracture and rupture of the deep digital flexor tendon. Results from limited numbers of bacterial cultures and antibiotic sensitivities suggest that penicillin and an aminoglycoside antibiotic should be used as initial antibiotic therapy. Immediate surgical debridement and appropriate antibiotic treatment are recommended as the minimum therapy for penetrating wounds of the navicular bursa in horses. 相似文献
72.
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints. 相似文献
73.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment. 相似文献
74.
Praveen C. Verma Debasis Chakrabarty Satya Narayan Jena Devesh K. Mishra Pradhyumna K. Singh Samir V. Sawant Rakesh Tuli 《Industrial Crops and Products》2009,29(2-3):581-589
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species. 相似文献
75.
76.
邹琳娜 《农业工程技术:农产品加工》2006,(9):15-16
植物健康综合管理系统(IpHM)在保证根系健康生长方面确实起到了作用。这就对种植者提出了挑战。植物营养调节、水分管理、根/冠生长管理的成败取决于是否有健康的根系和成分配比适当的栽培基质。[编者按] 相似文献
77.
78.
Detection of a broad range of potato viruses in a single assay by mechanical inoculation of herbaceous test plants 总被引:1,自引:0,他引:1
To optimize mechanical inoculation of test plants as part of the regulated post-entry quarantine testing of stolon- and tuber-forming Solanum spp. (including potato), nine test plant species have been screened for their ability to detect 22 potato-infecting viruses. These included all the common mechanically transmissible potato viruses and most of the viruses found in potato incidentally. The symptoms observed after mechanical inoculation are shown for each combination of test plant species and virus. Under given conditions, Nicotiana occidentalis -P1 and Nicotiana hesperis -67A were found to detect reliably 20 and 18 out of 22 viruses respectively. These and former results on the seed-transmissible viruses and Andean potato mottle virus demonstrate that these Nicotiana species are very suitable for post-entry quarantine testing. Addition of either Chenopodium amaranticolor or Chenopodium quinoa to these two species may slightly extend the range of viruses. Therefore, using C. amaranticolor / C. quinoa , N. hesperis -67A and N. occidentalis -P1 for the biological screening of imported Solanum spp. will improve both the efficiency and the quality of post-entry quarantine testing. 相似文献
79.
80.
Abstract The potential utility of pelvic fin rays as ageing structures was evaluated for southern US muskellunge Esox masquinongy Mitchill populations by comparing age estimates among three readers and against cleithrum estimates, and by comparing observed length changes of tagged fish with changes predicted from growth equations based on pelvic fin ray age estimates. Mean coefficient of variation in age estimates among all readers and between the two readers with prior ageing experience was 17.8% and 5.6%, respectively. Exact and within 1-year agreement rates between pelvic fin rays and cleithra were 76% and 100%, respectively. Mean (± 2 SE) estimated absolute error between observed and predicted length changes for 13 tagged muskellunge was 30 ± 14 mm. This evaluation indicated that pelvic fin rays may prove to be a useful, non-lethal method for ageing muskellunge in southern US waters. Validation studies are still needed to ensure that growth rings form consistently throughout fish's life span. 相似文献