全文获取类型
收费全文 | 86476篇 |
免费 | 4817篇 |
国内免费 | 329篇 |
专业分类
林业 | 4184篇 |
农学 | 2932篇 |
基础科学 | 533篇 |
11127篇 | |
综合类 | 15149篇 |
农作物 | 3455篇 |
水产渔业 | 4228篇 |
畜牧兽医 | 43303篇 |
园艺 | 1027篇 |
植物保护 | 5684篇 |
出版年
2021年 | 776篇 |
2020年 | 835篇 |
2019年 | 1022篇 |
2018年 | 1552篇 |
2017年 | 1643篇 |
2016年 | 1470篇 |
2015年 | 1251篇 |
2014年 | 1562篇 |
2013年 | 3529篇 |
2012年 | 2746篇 |
2011年 | 3144篇 |
2010年 | 2080篇 |
2009年 | 2176篇 |
2008年 | 3016篇 |
2007年 | 2870篇 |
2006年 | 2676篇 |
2005年 | 2396篇 |
2004年 | 2296篇 |
2003年 | 2290篇 |
2002年 | 2114篇 |
2001年 | 2624篇 |
2000年 | 2569篇 |
1999年 | 2030篇 |
1998年 | 815篇 |
1997年 | 848篇 |
1996年 | 789篇 |
1995年 | 868篇 |
1994年 | 781篇 |
1992年 | 1495篇 |
1991年 | 1623篇 |
1990年 | 1508篇 |
1989年 | 1550篇 |
1988年 | 1444篇 |
1987年 | 1435篇 |
1986年 | 1464篇 |
1985年 | 1413篇 |
1984年 | 1128篇 |
1983年 | 1018篇 |
1979年 | 1148篇 |
1978年 | 921篇 |
1977年 | 791篇 |
1976年 | 788篇 |
1975年 | 859篇 |
1974年 | 1099篇 |
1973年 | 1034篇 |
1972年 | 1066篇 |
1971年 | 962篇 |
1970年 | 932篇 |
1969年 | 944篇 |
1967年 | 828篇 |
排序方式: 共有10000条查询结果,搜索用时 27 毫秒
991.
992.
OBJECTIVE: To evaluate a technique for preservation of organoleptic tissue characteristics (color, odor, texture, and flexibility) in cadavers used for surgical instruction. STUDY DESIGN: Experimental study. ANIMALS: Forty-three canine cadavers. METHODS: Cadavers were preserved with a modified Larssen solution of the Hospital Cochim, Paris and cryopreservation. Tissue handling qualities were evaluated in surgical laboratory sessions. RESULTS: All cadavers kept texture and tissues consistency, especially skin and muscle, similar to those of live animals. Some skin desquamation and pallor of the mucous membranes occurred with repetitive freeze-thaw cycles. CONCLUSIONS: This preservation technique provides acceptable cadaver quality and tissue handling for use in surgical instruction. CLINICAL RELEVANCE: Preparation of patient cadavers by intravascular injection of modified Larssen solution yielded suitable instructional models for surgical training. 相似文献
993.
Kivaria FM Heuer C Jongejan F Okello-Onen J Rutagwenda T Unger F Boehle W 《The Onderstepoort journal of veterinary research》2004,71(3):189-195
A population-based study was carried out on the Ankole ranching scheme in south-west Uganda with the aim of determining the endemic status of Theileria parva infections. For this purpose, the age-related sero-prevalence of T. parva and the specific calf mortality associated with the parasite were assessed. Blood samples were collected from 931 Ankole calves of up to 12 months of age from 81 randomly selected herds. The relationship between rainfall pattern and whole-body Rhipicephalus appendiculatus counts was determined. The influence of tick control practices on East Coast fever-related calf mortality, and sero-positivity were also determined. A significant (r2 = 0.76, P = 0.000) association between R. appendiculatus counts and rainfall was observed. There was no significant (P > 0.05) association between theileriosis-related calf mortality, sero-positivity and the different tick control practices. Antibody prevalence based on the PIM ELISA was above 70% among calves of 6 months of age in 96% in all the herds. Theileria parva-related calf mortality determined by repeated herd visits and farm records ranged between 0 % and 5.4 %. It was concluded that endemic stability for theileriosis, caused by T. parva, existed in the study area, and that the risk of the occurrence of economically important outbreaks of East Coast fever in indigenous cattle was regarded as minimal under the prevailing conditions. 相似文献
994.
Two 12-week-old Tippler pigeons were evaluated for ocular abnormalities associated with congenital blindness. The pigeons were emaciated and blind. Biomicroscopy and direct and indirect ophthalmoscopy findings of the Tippler pigeons were normal with the exception of partially dilated pupils at rest. Scotopic (blue stimuli) and photopic monocular electroretinograms were extinguished in the blind Tippler pigeons. Histological and electron microscopy studies revealed reduced numbers of rods and cones, and an absence of the double cone complex. The photoreceptor cells' outer segments were absent, and the inner segments were short and broad. The number of cell nuclei in the outer and inner nuclear layers was decreased, and the internal and external plexiform layers were reduced in width. Photoreceptor cell endfeet with developing synaptic ribbons were present in the external plexiform layer. Inflammatory cell and subretinal debris was not seen. The electroretinographic, histopathological, and ultrastructural findings of the blind Tippler pigeons support the diagnosis of a photoreceptor cell dysplasia. 相似文献
995.
Characterisation of three novel canine osteosarcoma cell lines producing high levels of matrix metalloproteinases 总被引:1,自引:0,他引:1
Loukopoulos P O'Brien T Ghoddusi M Mungall BA Robinson WF 《Research in veterinary science》2004,77(2):131-141
Three canine osteosarcoma cell lines were established from spontaneous pelvic and radial osteosarcomas. The cell populations cultured exhibited characteristics of malignancy and consisted of adherent, pleomorphic, mostly large spindle-shaped or polyhedral cells, characterised by the presence of numerous cytoplasmic granules and vacuoles. The main ultrastructural features included the presence of abundant rough endoplasmic reticulum and numerous cytoplasmic vesicles, deposit vacuoles and small cytoplasmic protrusions. Zymography showed that the cell lines produce high levels of MMP-2 and MMP-9, enzymes directly involved in crucial aspects of the metastatic process. Consistent with their osteoblastic lineage and malignant phenotype, all cell lines were immunoreactive to vimentin, osteopontin, PCNA, p53, MMP-2 and MMP-9, while they were negative for cytokeratin, desmin, SMA, Factor VIII, NSE, GFAP, Rb and p21 protein. No retroviral particles or RNA were detected ultrastructurally or with RT-PCR, although the possibility of viral involvement in osteosarcoma cannot be excluded. The new cell lines provide excellent in vitro models that may allow further studies on the pathobiology of canine osteosarcoma to be undertaken. 相似文献
996.
There have been very few clinical trials evaluating therapies for naturally occurring spinal cord injury in dogs and cats. This review describes the methods suitable for evaluating the behavioural recovery of animals with spinal cord injuries, in either a clinical or a laboratory setting. A list of commonly used methods for evaluating behavioural recovery in animals is provided, both in the clinical and laboratory setting; the tests, their limitations and benefits and specific recommendations for their use are also discussed in more depth. 相似文献
997.
Ongör H Cetinkaya B Açik MN Karahan M Bulut H 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2004,51(1):43-45
The present study was carried out to investigate the presence of Chlamydophila abortus, the causative agent of ovine enzootic abortion, in milk samples collected from sheep flocks with and without the history of abortion in Eastern Turkey by means of immunomagnetic separation (IMS) in conjunction with the polymerase chain reaction (PCR). A total number of 201 milk samples collected from 10 flocks with abortion and four flocks without abortion were tested. In the analysis of the milk samples by IMS-PCR, correct amplification was obtained with three (1.5%) samples originating from one flock with abortion. In the digestion of PCR positive products by AluI, restriction profiles observed in all three samples were determined to be the same as C. abortus S26/3. 相似文献
998.
S. Gilbert V. K. Affolter P. Schmidt S. Kosten P. M. Kramme T. L. Gross P. Ihrke P. F. Moore 《Veterinary dermatology》2004,15(Z1):24-24
A previous study described cutaneous lymphocytosis (CL) in 23 cats. The process resembles cutaneous pseudolymphoma in humans, a heterogeneous group of benign reactive proliferations of well‐differentiated lymphocytes in the skin of humans. Morphological and immunophenotypic characteristics do not offer reliable criteria to accurately predict the clinical outcome of feline CL or pseudolymphoma in humans. Presence of clonal cell populations is more consistent with a neoplastic process. In a previous study, feline CL lesions (20 cats) were evaluated for clonality using PCR, and only two cats had monoclonal T‐cell populations. Because false‐negative results may occur, the purpose of this study was to repeat the PCR using a revised primer set based on analysis of additional feline T‐cell receptor γ (TCRγ) sequences. DNA was isolated from 29 skin lesions and six internal organs of 20 cats. DNA integrity was assessed by glyceraldehyde‐3‐phosphate dehydrogenase PCR. Polymerase chain reaction clonality was performed using the revised primer set specific for feline TCRγ, and duplicate samples were evaluated. The PCR products were assessed by heteroduplex analysis. Clonal rearrangement of TCRγ was detected in 14 cats (24 of 35 tissues: 21 of 29 skin lesions and three of six internal organs); eight of these cats are still alive and six were euthanized. Monoclonal populations were seen in three of five cats that had involvement of internal organs. These findings indicate that feline CL is best considered as a slowly progressive process which may be reactive, but often evolves into a low‐grade indolent lymphoma. Funding: George H. Muller Fund for Research in Dermatology. 相似文献
999.
1000.
Our objective was to assess the association of managerial practices, general hygiene and Salmonella infection in Senegalese broiler flocks. Seventy broilers farms were studied from January 2000 to December 2001 around Dakar. A questionnaire was submitted to the farmers and samples of fresh broiler droppings were taken. A 28.6% of the flocks were infected by Salmonella (mainly Hadar and Brancaster serovars). Salmonella infection of the previous flock (OR=6.82) and of day-old chicks (OR=3.73), frequent poultry farmers’ visits (OR=5.38) and keeping sick birds inside the farm (OR=5.32) increased the risk of Salmonella infection. But, using antibiotics on day-old chicks (OR=0.17) and a detergent for cleaning (OR=0.16) decreased the risk. 相似文献