全文获取类型
收费全文 | 96870篇 |
免费 | 6066篇 |
国内免费 | 874篇 |
专业分类
林业 | 4574篇 |
农学 | 3101篇 |
基础科学 | 787篇 |
13308篇 | |
综合类 | 17007篇 |
农作物 | 3743篇 |
水产渔业 | 5224篇 |
畜牧兽医 | 48281篇 |
园艺 | 1403篇 |
植物保护 | 6382篇 |
出版年
2021年 | 1080篇 |
2020年 | 1178篇 |
2019年 | 1314篇 |
2018年 | 1935篇 |
2017年 | 2198篇 |
2016年 | 2017篇 |
2015年 | 1831篇 |
2014年 | 2084篇 |
2013年 | 3810篇 |
2012年 | 3953篇 |
2011年 | 4471篇 |
2010年 | 2906篇 |
2009年 | 2728篇 |
2008年 | 3843篇 |
2007年 | 3679篇 |
2006年 | 3282篇 |
2005年 | 3146篇 |
2004年 | 2813篇 |
2003年 | 2851篇 |
2002年 | 2578篇 |
2001年 | 2771篇 |
2000年 | 2823篇 |
1999年 | 2199篇 |
1998年 | 860篇 |
1997年 | 776篇 |
1996年 | 710篇 |
1995年 | 785篇 |
1992年 | 1646篇 |
1991年 | 1823篇 |
1990年 | 1755篇 |
1989年 | 1714篇 |
1988年 | 1586篇 |
1987年 | 1636篇 |
1986年 | 1675篇 |
1985年 | 1499篇 |
1984年 | 1268篇 |
1983年 | 1091篇 |
1982年 | 718篇 |
1979年 | 1157篇 |
1978年 | 919篇 |
1977年 | 761篇 |
1976年 | 758篇 |
1975年 | 792篇 |
1974年 | 1103篇 |
1973年 | 1070篇 |
1972年 | 1050篇 |
1971年 | 974篇 |
1970年 | 876篇 |
1969年 | 837篇 |
1967年 | 726篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
L A Wyant 《Veterinary Clinics of North America: Equine Practice》2001,17(2):297-303
The Internet is a fast-growing technology that allows information (text as well as images) to be shared across the world in an instant. As computer systems, software, and Internet services become less expensive options, the world becomes more experienced and comfortable with these technologies. In the foreseeable future, equine veterinarians are likely to be better educated about diseases and treatments, better connected with specialists for consultations on difficult cases, able to respond to client communications more efficiently, able to accurately educate clients, and able to communicate with colleagues from across the country and the world. Additionally, there is likely to be a time when using the Internet and computers is profitable in all these ways as well as economically. Improving doctor-client relationships and patient care are goals for all veterinarians, and the Internet holds the technology to render these now and in the future. 相似文献
142.
Feline leukemia virus detection by immunohistochemistry and polymerase chain reaction in formalin-fixed, paraffin-embedded tumor tissue from cats with lymphosarcoma. 下载免费PDF全文
M L Jackson D M Haines S M Meric V Misra 《Canadian journal of veterinary research》1993,57(4):269-276
The prevalence of feline leukemia virus (FeLV) antigen and DNA was assessed in formalin-fixed, paraffin-embedded tumor tissues from 70 cats with lymphosarcoma (LSA). Tissue sections were tested for FeLV gp70 antigen using avidinbiotin complex (ABC) immunohistochemistry (IHC); DNA was extracted and purified from the same tissue blocks for polymerase chain reaction (PCR) amplification of a 166 base pair region of the FeLV long terminal repeat (LTR). Results were related to antemortem FeLV enzyme-linked immunosorbent assay (ELISA) for serum p27 antigen, anatomic site of LSA, and patient age. Viral DNA was detected by PCR in 80% of cases and viral antigen by IHC in 57% of cases. Seventeen cases were PCR-positive and IHC-negative; one case was PCR-negative and IHC-positive. Clinical records included FeLV ELISA results for 30 of 70 cats. All 19 ELISA-positive cats were positive by PCR and IHC; of the 11 ELISA-negative cats that were negative by IHC, seven were positive by PCR. When evaluated according to anatomic site, FeLV DNA and antigen were detected less frequently in intestinal LSAs than in multicentric and mediastinal tumors. Lymphosarcoma tissues from cats < 7 yr were several fold more likely to be positive for FeLV antigen by IHC than were tumors from cats > or = 7 yr. However, there was no significant difference in PCR detection of FeLV provirus between LSAs from cats < 7 yr and those > or = 7 yr.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
143.
144.
Donald E. Thrall DVM PHD Margaret C. McEntee DVM† Carol Novotney DVM† Marlene L. Hauck DVM† Rodney L. Page DVM MS† 《Veterinary radiology & ultrasound》1993,34(4):295-300
Eighteen dogs with malignant nasal cavity tumors were treated with radiation therapy, including a boost technique. Three 3:0 Gy boost doses were added to a treatment protocol consisting of sixteen 3.0 Gy daily fractions, bringing the total dose to 57 Gy. This boost technique was implemented without an associated increase in overall treatment time by giving the boost doses on a twice-a-day basis. Boost doses were given during the first half of the radiation therapy period. The treatment was completed as planned in 16 of the 18 dogs; two dogs received lower doses (51 and 54 Gy). Median survival was 177 days, poorer than in some other reported studies of nasal tumor irradiation. Acute effects were unacceptable, with 11 of the 18 dogs developing severe mucositis, desquamation, edema, swelling, and pruritus. The extensive nature of the acute reactions compromised assessment of the effect of the increased radiation dose on the tumor. Although there is justification for assessing more aggressive radiation protocols in canine nasal tumor patients, total doses approximating 60 Gy can not be given as described because of the inability of acutely responding normal tissues to compensate. 相似文献
145.
146.
The insecticide formulation BI 58 EC was tested for teratogenicity in chicken embryos, with particular reference to degradation of the active ingredient (dimethoate) after the treatment of embryonated eggs. The pesticide was diluted in water to a concentration level of 0.8%, and the emulsion was injected into the air space in a volume of 0.1 ml/egg, or hen's eggs were treated by the immersion technique. Residues of dimethoate were measured in the samples on days, 13, 15 and 19 of the incubation of chicken embryos, and morphological examinations were performed simultaneously. Analytical chemistry data indicated a slower degradation of dimethoate in embryos after the immersion of eggs, and cyllosis was remarkable in this group among the sporadic developmental anomalies. The liver tissues of both treated groups exhibited severe fatty infiltration. 相似文献
147.
148.
L Seganti F Superti L Sinibaldi M Marchetti S Bianchi N Orsi 《Comparative immunology, microbiology and infectious diseases》1991,14(3):265-275
Rabies virus is able to infect in vitro a wide range of homeothermic and poikilothermic cells but little is known about its multiplication in arthropod cells. In this research the infection of rabies virus in Aedes pseudoscutellaris cells, a mosquito cell line susceptible to mosquito-borne viruses, was studied. After 60 days of incubation at 26 degrees C up to 70% of infected cells showed the synthesis of both viral nucleocapsid and envelope antigens, although viral yield and cell damage could not be detected. Research performed in order to investigate the role of membrane carbohydrate moieties in rabies virus-mosquito cell interaction suggested the participation of galactose and N-acetylglucosamine whereas sialic acid, known to be a rabies binding site in many homeothermic cell lines, was not involved. 相似文献
149.
P. Merino J.M. Estavillo L.A. Graciolli M. Pinto M. Lacuesta A. Muñoz-Rueda C. Gonzalez-Murua 《Soil Use and Management》2002,18(2):135-141
Abstract. Nitrous oxide (N2 O) is involved in both ozone destruction and global warming. In agricultural soils it is produced by nitrification and denitrification mainly after fertilization. Nitrification inhibitors have been proposed as one of the management tools for the reduction of the potential hazards of fertilizer-derived N2 O. Addition of nitrification inhibitors to fertilizers maintains soil N in ammonium form, thereby gaseous N losses by nitrification and denitrification are less likely to occur and there is increased N utilization by the sward. We present a study aimed to evaluate the effectiveness of the nitrification inhibitor dicyandiamide (DCD) and of the slurry additive Actilith F2 on N2 O emissions following application of calcium ammonium nitrate or cattle slurry to a mixed clover/ryegrass sward in the Basque Country. The results indicate that large differences in N2 O emission occur depending on fertilizer type and the presence or absence of a nitrification inhibitor. There is considerable scope for immediate reduction of emissions by applying DCD with calcium ammonium nitrate or cattle slurry. DCD, applied at 25 kg ha–1 , reduced the amount of N lost as N2 O by 60% and 42% when applied with cattle slurry and calcium ammonium nitrate, respectively. Actilith F2 did not reduce N2 O emissions and it produced a long lasting mineralization of previously immobilized added N. 相似文献
150.