全文获取类型
收费全文 | 684篇 |
免费 | 26篇 |
国内免费 | 1篇 |
专业分类
林业 | 17篇 |
农学 | 19篇 |
基础科学 | 2篇 |
97篇 | |
综合类 | 99篇 |
农作物 | 22篇 |
水产渔业 | 18篇 |
畜牧兽医 | 390篇 |
园艺 | 18篇 |
植物保护 | 29篇 |
出版年
2023年 | 11篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 36篇 |
2012年 | 31篇 |
2011年 | 46篇 |
2010年 | 21篇 |
2009年 | 21篇 |
2008年 | 27篇 |
2007年 | 36篇 |
2006年 | 42篇 |
2005年 | 44篇 |
2004年 | 22篇 |
2003年 | 39篇 |
2002年 | 24篇 |
2001年 | 16篇 |
2000年 | 13篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1977年 | 7篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1971年 | 3篇 |
1969年 | 4篇 |
1940年 | 3篇 |
1937年 | 4篇 |
1924年 | 3篇 |
1913年 | 2篇 |
1906年 | 2篇 |
排序方式: 共有711条查询结果,搜索用时 15 毫秒
81.
Production and characterization of a monoclonal antibody against the beta-adrenergic agonist ractopamine 总被引:2,自引:0,他引:2
A monoclonal antibody was generated toward the beta-adrenergic agonist ractopamine hydrochloride ?(1R,3R),(1R, 3S)-4-hydroxy-alpha-[[[3-(4-hydroxyphenyl)-1-methylpropyl]amino]methy l]benzenemethanol hydrochloride?. Ractopamine-glutarate-keyhole limpet hemocyanin (KLH) was used as the antigen for antibody generation in mice. Clone 5G10, secreted antibody with isotype IgG1kappa, was used for the development of an immunoassay. The selected antibody was specific for racemic ractopamine with an IC(50) of 2.69 +/- 0.36 ng/mL (n = 15). Antibody binding toward ractopamine was stereoselective with (1R,3R)-ractopamine having an IC(50) of 0.55 +/- 0.09 ng/mL (n = 3). IC(50) values for the (1S, 3R)-, (1S,3S)-, and (1R,3S)-ractopamine stereoisomers were 2.00 +/- 0.37, 140 +/- 23, and 291+/- 32 ng/mL (n = 3), respectively. Phenethanolamine beta-agonists showed low cross-reactivity. Studies using a series of ractopamine metabolites and ractopamine analogues demonstrated structural requirements for the antibody binding. A free phenolic group on the N-butylphenol moiety was required for high-affinity binding because methoxylated analogues and metabolites glucuronidated at this phenol generally had IC(50) values greater than 200 ng/mL. Ractopamine analogues methoxylated or glucuronidated at the ethanolamine phenol had IC(50) values of 0.7-2.6 ng/mL. Lack of a benzylic hydroxyl group was of less importance to antibody binding than was the correct stereochemical orientation (3R) of ractopamine's N-phenylalkyl group. In conclusion, a highly specific monoclonal antibody to ractopamine hydrochloride was developed that could be of potential utility in screening assays. 相似文献
82.
Trenches excavated across fault scarps on a 13 ka delta surface at Brigham City, Utah, USA, document four types of soil-catena phenomena. First, the relict summit soil is eroded at the scarp crest, and its components incorporated into the accumulating colluvial wedge at the scarp base. Second, the pre-faulting soil weakens laterally as it is traced scarpward beneath the colluvial wedge from a relict position beyond the scarp toe. Third, soils developed on individual colluvial wedges and on the underlying, pre-faulting surface merge downslope to form a cumulative soil profile at the scarp toeslope. Fourth, soil horizons thicken downslope, probably due to the combined affect of more available moisture, water infiltration, and sediment accumulation.Two soil catenas were used to evaluate the applicability of a continuity approach to paleoearthquake dating, by which percentages of total development time represented by each soil at a fault scarp footslope could be estimated. The continuity approach sets total soil development at the scarp footslope, including any buried pre-faulting soil plus the sum development of all colluvial wedge soils corrected by a slope factor (F), equal to total soil development at the scarp summit. Soil development was characterized by Profile Development Index (PDI) and pedogenic clay parameters, using facies models to estimate parent material values for genetically-different colluvial units, and recognizing inherited soil components in colluvial wedges as parent material properties. The F slope factor, used to correct colluvial wedge soils for development attributable to slope position rather than age, was checked by using a nearby fluvial scarp as an independent control. Our soil data, when compared to independent age estimates, imply that rates of soil development have not been constant over the last 13 ka at Brigham City, but rather were considerably higher than average between 13 ka and 8.3 ka. Higher rates are probably due to a relatively high influx of eolian dust during the late Pleistocene to early Holocene following the lowering of Lake Bonneville, a large paleolake in the western USA. These variable rates of soil development preclude using the continuity approach for paleoearthquake dating at Brigham City. However, promising results showing that generally consistent F factors can be calculated for fault and fluvial scarps leave open the possibility that in areas where soil development rates have been relatively constant over the time period in question, the continuity approach may be a broadly applicable method for paleoearthquake dating. 相似文献
83.
Computed tomographic anatomy of the normal canine ethmoid region using both transverse and dorsal imaging plane is described. In the transverse plane, the cribriform plate appears as an irregular heart-shaped to rectangular structure that is generally visualized on no more than one to two contiguous 4-mm slices. In the dorsal plane, the cribriform plate appears as a discrete "V"-shaped structure and can be visualized on four to five contiguous slices. Successful visualization of the cribriform was less dependent on patient positioning for the dorsal plane imaging studies. Computed tomographic findings in four dogs with chronic nasal disease and complete postmortem examination of the ethmoid region indicate that the dorsal imaging plane allows a more accurate assessment of cribriform plate involvement than the transverse imaging plane. 相似文献
84.
85.
The midgut microsomal aldrin epoxidase of variegated cutworm larvae (Peridroma saucia, Hübner) fed bean or peppermint leaves was up to 10 and 45 times more active, respectively, than that of larvae fed a basic control diet. Large increases in oxidase activity and cytochrome P-450 levels also occurred in larvae fed mint plant constituents such as menthol menthone, α-pinene, and β-pinene. Mint-fed larvae were more tolerant of the insecticide, carbaryl, than bean-fed larvae. 相似文献
86.
Michael D. Lucroy DVM MS Jeffrey N. Peck DVM Clifford R. Berry DVM 《Veterinary radiology & ultrasound》2001,42(3):218-220
A 6-year-old neutered male Rottweiler was examined for a progressive right pelvic limb lameness. In radiographs of the right stifle, there was an osteolytic lesion with irregular new bone formation along the cranial aspect of the patella consistent with an aggressive bone lesion. In thoracic radiographs, there were multiple soft tissue nodular opacities throughout the lung fields, consistent with pulmonary metastases. Microscopically, fine needle aspirate samples from the right patella contained pleomorphic spindle cells with cytologic features of osteosarcoma. The presence of pulmonary metastases at the time of initial diagnosis in the dog described herein suggests that osteosarcoma of the patella has the potential for similar aggressive biologic behavior as that seen in dogs with appendicular osteosarcoma. 相似文献
87.
In 8 healthy, awake cows with permanent cannulated ruminal fistulas and carotid artery loops, respiratory mechanics, ventilation, and diaphragmatic electrical activity were studied before and during stepwise insufflation of the rumen with air pressure to 40 mm of Hg. We found that ruminal insufflation increased intraperitoneal, intrapleural, and transdiaphragmatic pressures and decreased lung volume and lung compliance. In individual cows with rumen insufflation there was an increase in pulmonary resistance, but this trend was not significant in the group. Peak expiratory flow rate was increased and peak inspiratory flow rate was unchanged. Inspiratory duration (Ti) decidal volume decreased slightly, breathing frequency decreased markedly, and minute volume decreased. When intraruminal pressure reached 40 mm of Hg, arterial partial pressure of carbon dioxide (PaCO2) increased (P less than 0.01) and that of oxygen (PaO2) decreased (P less than 0,01) and arterial blood pH decreased (P less than 0.02). Diaphragmatic electromyographic activity was increased, but mechanical effectiveness of the diaphragm was reduced at increased intraruminal pressures. 相似文献
88.
L. J. Berry B. I. Osburn J. L. Stott T. Farver B. Heron W. Patton 《Veterinary research communications》1981,5(1):289-293
A mixed breed flock of lambs, consisting of Suffolks, Hampshires, Columbias and Finnish breeds, were vaccinated with binary ethylenimine inactivated bluetongue virus (BTV) serotypes 11, 17 and a mixture of 11 and 17 in aluminum hydroxide. Agar gel precipitin antibodies were used as an indicator of immunity. Sero-conversion of Hampshires and Suffolk lambs was poor at 43% as compared to 84% in the Columbia and Finn lambs. These results indicate a breed difference in immunological response to inactivated BTV vaccine. 相似文献
89.
Roger W. Berry 《Pest management science》1977,8(3):284-290
The toxicity of the synthetic pyrethroid permethrin (NRDC 143) to a range of wood destroying insects has been investigated. In tests using Hylotrupes bajulus, Anobium punctatum, Lyctus brunneus and Reticulitermes santonensis permethrin showed a similar order of toxicity to that of gamma-BHC. Although the toxicity of permethrin to adult A. punctatum was of the same order as that of gamma-BHC, the toxicity to larvae was rather lower. The implications of these results are discussed and it is concluded that, subject to further field evaluation, permethrin could provide an alternative to gamma-BHC and dieldrin in wood preservatives. 相似文献
90.