全文获取类型
收费全文 | 319601篇 |
免费 | 18739篇 |
国内免费 | 3858篇 |
专业分类
林业 | 26279篇 |
农学 | 15787篇 |
基础科学 | 4609篇 |
48324篇 | |
综合类 | 49680篇 |
农作物 | 19495篇 |
水产渔业 | 18861篇 |
畜牧兽医 | 123922篇 |
园艺 | 8643篇 |
植物保护 | 26598篇 |
出版年
2022年 | 3178篇 |
2021年 | 4172篇 |
2020年 | 4333篇 |
2019年 | 5150篇 |
2018年 | 5274篇 |
2017年 | 6117篇 |
2016年 | 6074篇 |
2015年 | 6001篇 |
2014年 | 7447篇 |
2013年 | 18388篇 |
2012年 | 9738篇 |
2011年 | 11944篇 |
2010年 | 10220篇 |
2009年 | 10588篇 |
2008年 | 10926篇 |
2007年 | 9799篇 |
2006年 | 9838篇 |
2005年 | 8900篇 |
2004年 | 8048篇 |
2003年 | 7614篇 |
2002年 | 6897篇 |
2001年 | 7759篇 |
2000年 | 7292篇 |
1999年 | 6391篇 |
1998年 | 4307篇 |
1997年 | 4362篇 |
1996年 | 4040篇 |
1995年 | 4684篇 |
1994年 | 4065篇 |
1993年 | 3810篇 |
1992年 | 5099篇 |
1991年 | 5270篇 |
1990年 | 5016篇 |
1989年 | 5055篇 |
1988年 | 4505篇 |
1987年 | 4573篇 |
1986年 | 4608篇 |
1985年 | 4786篇 |
1984年 | 4291篇 |
1983年 | 3978篇 |
1982年 | 3175篇 |
1981年 | 3037篇 |
1980年 | 2980篇 |
1979年 | 3776篇 |
1978年 | 3296篇 |
1977年 | 3060篇 |
1976年 | 2872篇 |
1974年 | 3119篇 |
1973年 | 3148篇 |
1972年 | 2875篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
A. Bhogal A. Bhogal M.A. Shepherd D.J. Hatch L. Brown S.C. Jarvis 《Soil Use and Management》2001,17(3):163-172
Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization. 相似文献
112.
The aim of this study was to assess the PCB pollutionof the South-Western branch of Lake Como by using thezebra mussel (Dreissena polymorpha) as abioindicator since its recent reintroduction. Someenvironmental and physiological variables influencingaccumulation processes of organochlorine compounds inDreissena were investigated because climaticfactors may affect life cycle, reproductive stage andage. PCB levels were highest in the soft tissues ofDreissena close to the industrialized area ofComo (2298 ng g-1 of lipids) and slowly decrease goingnorth, reaching approximately half this value at theclosing section of the lake branch. Nonetheless, thePCB concentrations are well below the dangerous levelsfor the aquatic environment. 相似文献
113.
Margaret C. McEntee DVM Donald E. Thrall DVM PhD 《Veterinary radiology & ultrasound》2001,42(3):221-225
Twenty two dogs with an infiltrative lipoma had computed tomographic (CT) images acquired to evaluate the extent of local disease. Ten dogs had undergone at least one cytoreductive surgical procedure (range = 1-3; median = 2) prior to imaging. Twenty dogs had measurable disease on CT images; 2 dogs had diffuse disease at a previous surgical site that could not be measured. Tumor volume (n = 20) ranged from 20 to 5,632 cm3 (median = 345 cm3; mean = 996 cm3). None of the dogs had evidence of bone involvement on the CT images; 2 of the 22 dogs had tumors that did not come into direct contact with osseous structures. All dogs with measurable disease had evidence of a fat opacity mass with variable degrees of muscle infiltration. Eleven of 22 dogs were given intravenous contrast medium prior to image acquisition and there was not evidence of enhancement of the infiltrative lipoma in any dog. Based on CT images, tumors were classified as well-defined in 9 dogs, moderately well-defined in 4, not well-defined in 3 and a mix of well-defined and not well-defined in 6 dogs. Tumors tended to be less well-defined in regions where the infiltrative lipoma interdigitated with normal body fat. It appears CT imaging allows adequate discrimination of tumor with the caveat that differentiation of normal fat from infiltrative lipoma can be problematic. 相似文献
114.
115.
比格犬人工感染埃立克体病的临床研究 总被引:2,自引:0,他引:2
为了表述比格犬感染埃立克体(Ehrlichia)后的临床表现,用已确证为E.platys和E.canis混合感染的犬血对5条比格犬进行了人工感染,并对临床和血液学变化进行了观察。埃立克体病的潜伏期为6-29天,其后的临床表现为急性发热、眼结膜苍白、厌食、精神沉郁、体重严重减轻、腹泻带血、多处有淤血斑点出现、6-45天内全部死亡。血液学变化显示血红蛋白和白细胞明显减少(P<0.01,P<0.05)。由此可见,比格犬对2种埃立克体(E.canis和E.platys)混合感染的性很高,严重的临床表现与美国学者普遍认为的亚临床状态相左,这可能是中国Gzh981株(E.platys)和Gzh982株(E.casnis)与国外株在毒力上的差异所致。 相似文献
116.
117.
118.
119.
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
120.
马明慧 《农业环境科学学报》2004,(2)