全文获取类型
收费全文 | 563篇 |
免费 | 43篇 |
专业分类
林业 | 24篇 |
农学 | 4篇 |
基础科学 | 1篇 |
64篇 | |
综合类 | 57篇 |
农作物 | 19篇 |
水产渔业 | 31篇 |
畜牧兽医 | 369篇 |
园艺 | 17篇 |
植物保护 | 20篇 |
出版年
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 30篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 20篇 |
2017年 | 14篇 |
2016年 | 14篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 25篇 |
2012年 | 41篇 |
2011年 | 60篇 |
2010年 | 28篇 |
2009年 | 11篇 |
2008年 | 41篇 |
2007年 | 33篇 |
2006年 | 37篇 |
2005年 | 34篇 |
2004年 | 30篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有606条查询结果,搜索用时 171 毫秒
61.
62.
This research theorizes a model for unauthorized border crosser (UBC) behavior when crossing the Mexico/U.S. border into Arizona. The manifold model developed here is a modified funneling effect of multiple trails converging together at nodes that separate into multiple exit points. Using hydrological metaphors, we quantify deathsheds into trails by using the remains of UBCs as trail markers and then compare the trails produced from three geostatistical research methods. The results may be used in designing search‐and‐rescue locations. 相似文献
63.
Sonnenberg GF Monticelli LA Alenghat T Fung TC Hutnick NA Kunisawa J Shibata N Grunberg S Sinha R Zahm AM Tardif MR Sathaliyawala T Kubota M Farber DL Collman RG Shaked A Fouser LA Weiner DB Tessier PA Friedman JR Kiyono H Bushman FD Chang KM Artis D 《Science (New York, N.Y.)》2012,336(6086):1321-1325
The mammalian intestinal tract is colonized by trillions of beneficial commensal bacteria that are anatomically restricted to specific niches. However, the mechanisms that regulate anatomical containment remain unclear. Here, we show that interleukin-22 (IL-22)-producing innate lymphoid cells (ILCs) are present in intestinal tissues of healthy mammals. Depletion of ILCs resulted in peripheral dissemination of commensal bacteria and systemic inflammation, which was prevented by administration of IL-22. Disseminating bacteria were identified as Alcaligenes species originating from host lymphoid tissues. Alcaligenes was sufficient to promote systemic inflammation after ILC depletion in mice, and Alcaligenes-specific systemic immune responses were associated with Crohn's disease and progressive hepatitis C virus infection in patients. Collectively, these data indicate that ILCs regulate selective containment of lymphoid-resident bacteria to prevent systemic inflammation associated with chronic diseases. 相似文献
64.
65.
66.
A longitudinal herd-level study was carried out to determine the cumulative incidence of Giardia duodenalis infections in dairy cattle in the New York City Watershed. We also sought to assess the changes in infection pattern of animals diagnosed as shedding Giardia over time, determine risk factors that may be associated with G. duodenalis infections, and identify potentially zoonotic infections. A total of 2109 fecal samples were randomly collected from dairy cattle at 34 farms in the New York City Watershed on a seasonal basis. A total of 504 Giardia-positive samples were identified by zinc sulfate flotation. The overall cumulative incidence of G. duodenalis based on flotation results was 23.9% with 73.8% of all infections occurring in animals under 180 days of age (372/504). The intensity of infection ranged from 2 to 563,200 cysts/gram of feces. Cattle shedding Cryptosporidium spp. oocysts were twice as likely to shed G. duodenalis cysts in comparison to the animals that did not shed oocysts (1.81 95% CI 1.26-2.60 p=0.0012). In the multivariate analysis, only the age of the animal and the presence of dogs on the farm were significantly associated with the likelihood of shedding G. duodenalis. DNA was extracted from positive samples and analyzed by polymerase chain reaction (PCR) of the beta-giardin and triosephosphate isomerase genes of Giardia spp. 304 samples were analyzed by PCR of which 131 were sequenced. 22.1% of sequenced samples were identified as assemblage A and 77.9% were identified as assemblage E. Interestingly, 100% of specimens identified as assemblage A were from calves under 84 days of age indicating that younger cattle are important reservoirs for potentially zoonotic assemblages of G. duodenalis. 相似文献
67.
ABSTRACT: Classical Swine Fever (CSF) is considered an endemic disease in European wild boar populations. In view of the high economic impact of the introduction of the virus into domestic pig units, huge efforts are invested in the preventive control of CSF in wild boar populations. Recent European Community guidelines favour oral mass vaccination against CSF in wild boar populations. The guidelines are explicit on the temporal structure of the vaccination protocol, but little is known about the efficacy of different spatial application schemes, or how they relate to outbreak dynamics.We use a spatially explicit, individual-based wild boar model that represents the ecology of the hosts and the epidemiology of CSF, both on a regional scale and on the level of individual course of infection. We simulate adaptive spatial vaccination schemes accounting for the acute spread of an outbreak while using the temporal vaccination protocol proposed in the Community guidelines.Vaccination was found to be beneficial in a wide range of scenarios. We show that the short-term proactive component of a vaccination strategy is not only as decisive as short-term continuity, but also that it can outcompete alternative practices while being practically feasible. Furthermore, we show that under certain virus-host conditions vaccination might actually contribute to disease persistence in local populations. 相似文献
68.
Stephanie Ann Smith 《Topics in companion animal medicine》2012,27(2):88-94
Thrombosis or thromboembolism are significant concerns in companion animals and can be associated with cardiac, metabolic, neoplastic disease processes or can be one manifestation of inflammatory, infectious, and neoplastic disease conditions. Options for thromboprophylaxis available for clinical use in small animal patients are very limited, with heparin (primarily unfractionated, but more recently low-molecular-weight forms) and aspirin predominating. Controlled studies evaluating the use of these drugs are few, but there is some limited evidence for efficacy in prevention of formation of thrombi. Use of the vitamin K antagonist warfarin has been described, but the narrow therapeutic window has resulted in a high rate of serious adverse events. In human patients, the efficacy of aspirin, heparins, and vitamin K antagonists is well documented in a variety of thrombotic conditions, but there are significant limitations to each of these options. These limitations have prompted the search for new alternatives, some of which are now in wide clinical use in humans. Although the use of some of the drugs discussed here has not yet been described in veterinary patients at risk for thrombosis, many of these agents have been evaluated experimentally in dogs, cats, or both. These new thromboprophylactic agents may soon be beneficial in management of small animal patients at risk for thrombosis. 相似文献
69.
Vicente VA Orélis-Ribeiro R Najafzadeh MJ Sun J Guerra RS Miesch S Ostrensky A Meis JF Klaassen CH de Hoog GS Boeger WA 《Veterinary microbiology》2012,158(1-2):109-122
Lethargic Crab Disease (LCD) caused extensive epizootic mortality of the mangrove land crab Ucides cordatus (Brachyura: Ocypodidae) along the Brazilian coast, mainly in the Northeastern region. The disease was named after the symptoms of slow movement of infected crabs. Causative agents were suspected to be two black yeast-like fungi of the family Herpotrichiellaceae (ascomycete order Chaetothyriales), judged by infected tissue biopsies from moribund U. cordatus. The aim of the present study is to prove that two species are involved in the disease: the recently described black yeast Exophiala cancerae, but also a less virulent, hitherto undescribed fonsecaea-like species, introduced here as the novel species Fonsecaea brasiliensis. Strains were identified by ITS rDNA sequencing, and species borderlines were established by multilocus sequencing and AFLP analysis. Fonsecaea brasiliensis proved to be closely related to the pathogenic species Cladophialophora devriesii which originally was isolated from a systemic infection in a human patient. The virulence of F. brasiliensis is lower than that of E. cancerae, as established by artificial inoculation of mangrove crabs. 相似文献
70.
Labelle AL Whittington JK Breaux CB Labelle P Mitchell MA Zarfoss MK Schmidt SA Hamor RE 《Veterinary ophthalmology》2012,15(1):5-17
Objective: To describe a protocol for the examination of free‐living raptors and report the ophthalmic examination findings of seven raptor species native to central Illinois, namely the barred owl, Cooper’s hawk, eastern screech owl, great horned owl, American kestrel, red‐tailed hawk, and turkey vulture and to determine if the findings relative to visual prognosis affected eligibility for future release. Animals studied: Seventy‐nine free‐living raptors. Procedures: Under manual restraint, complete ophthalmic examination including slit‐lamp biomicroscopy and indirect funduscopy, applanation tonometry, rebound tonometry, ocular morphometrics, B‐mode ultrasound, and electroretinography (ERG) were performed on each bird. Histopathology of enucleated globes was performed after euthanasia or death in selected cases. Results: The examination protocol was easily performed using manual restraint alone on all birds. Ocular lesions were detected in 48.1% of birds, with 47.3% affected unilaterally and 52.6% affected bilaterally. Ocular lesions were considered to be vision threatening in 29.0% of the unilaterally affected birds and 29.0% of the bilaterally affected birds. The most common case outcomes were discharge from hospital to rehabilitation facility (45.6%) followed by euthanasia (43.0%). The presence of an ocular lesion or a vision‐threatening ocular lesion was not significantly associated with outcome. Reference ranges are reported for B‐mode ultrasound, ocular morphometrics, and horizontal corneal diameter in all species. Conclusion: Complete ophthalmic examination can be supplemented by the use of ocular morphometrics, ultrasound, and ERG in the manually restrained raptor. These advanced diagnostic techniques may be useful in developing more objective criteria for evaluating eligibility for release following rehabilitation of free‐living birds of prey. 相似文献