全文获取类型
收费全文 | 189991篇 |
免费 | 11001篇 |
国内免费 | 693篇 |
专业分类
林业 | 7936篇 |
农学 | 6310篇 |
基础科学 | 1418篇 |
23945篇 | |
综合类 | 31789篇 |
农作物 | 7153篇 |
水产渔业 | 9411篇 |
畜牧兽医 | 98847篇 |
园艺 | 2668篇 |
植物保护 | 12208篇 |
出版年
2020年 | 1707篇 |
2019年 | 2059篇 |
2018年 | 2997篇 |
2017年 | 3401篇 |
2016年 | 3076篇 |
2015年 | 2790篇 |
2014年 | 3331篇 |
2013年 | 7584篇 |
2012年 | 6120篇 |
2011年 | 7348篇 |
2010年 | 5038篇 |
2009年 | 4939篇 |
2008年 | 7019篇 |
2007年 | 6795篇 |
2006年 | 6275篇 |
2005年 | 5802篇 |
2004年 | 5444篇 |
2003年 | 5555篇 |
2002年 | 5130篇 |
2001年 | 6116篇 |
2000年 | 6051篇 |
1999年 | 4877篇 |
1998年 | 1963篇 |
1997年 | 1904篇 |
1996年 | 1781篇 |
1995年 | 2055篇 |
1994年 | 1778篇 |
1993年 | 1802篇 |
1992年 | 3713篇 |
1991年 | 4006篇 |
1990年 | 3929篇 |
1989年 | 3920篇 |
1988年 | 3604篇 |
1987年 | 3633篇 |
1986年 | 3631篇 |
1985年 | 3366篇 |
1984年 | 2801篇 |
1983年 | 2435篇 |
1982年 | 1640篇 |
1979年 | 2429篇 |
1978年 | 1921篇 |
1977年 | 1654篇 |
1976年 | 1658篇 |
1975年 | 1721篇 |
1974年 | 2120篇 |
1973年 | 2181篇 |
1972年 | 2120篇 |
1971年 | 1885篇 |
1970年 | 1919篇 |
1969年 | 1775篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
321.
322.
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
323.
Abstract. Information on land resources and the capacity of land to support agricultural production is a prerequisite for the formation of sound agricultural policies. This paper summarizes Canadian experiences in developing national and regional land evaluation systems. Potential users expected the system to estimate the degree to which changes in biophysical and socio-economic conditions would alter options for land use and production, and to provide a context for more detailed analysis.
A broad-scale land evaluation system was designed to serve the needs identified by representative user groups. Two prototype systems were developed from available information to test the major features of the system design. Neither prototype was complete; one was national in extent and capable of addressing issues of national and provincial importance, the other covered a sub-provincial area but allowed for more detailed evaluation of the effects of soil modifying processes. A full range of applications was demonstrated using one or other of the prototype systems. As a result of this project, the broad-scale land evaluation system design was improved and verified, ongoing research and data collection activities were adjusted to ensure that they meet the needs of a macroscale land evaluation system, and approaches were developed to overcome problems of land evaluation system development. 相似文献
A broad-scale land evaluation system was designed to serve the needs identified by representative user groups. Two prototype systems were developed from available information to test the major features of the system design. Neither prototype was complete; one was national in extent and capable of addressing issues of national and provincial importance, the other covered a sub-provincial area but allowed for more detailed evaluation of the effects of soil modifying processes. A full range of applications was demonstrated using one or other of the prototype systems. As a result of this project, the broad-scale land evaluation system design was improved and verified, ongoing research and data collection activities were adjusted to ensure that they meet the needs of a macroscale land evaluation system, and approaches were developed to overcome problems of land evaluation system development. 相似文献
324.
J Tetens S A Barker M Waguespack G Hosgood 《Canadian journal of veterinary research》2001,65(2):133-135
The objectives were to use high performance liquid chromatography (HPLC) to validate an established method for adenine nucleotide separation in equine colonic mucosal tissue, to determine the inherent variability in the tissue and extraction method, and to determine the stability of ATP, ADP, and AMP in the tissue with time. Equine colonic mucosal tissue obtained from a single horse was immediately submersed in liquid nitrogen, and stored at -70 degrees C. Samples were lyophilized, extracted, and separated by HPLC. The limit of quantitation was 0.05 microg/mL. The coefficient of variation for the instrument was less than 10% for all nucleotides measured. When the tissue was not homogenized prior to sampling, there were significant differences in adenine nucleotide content between samples. However, when the tissue was homogenized prior to analysis, these differences were no longer significant. There was no significant decrease in ATP, ADP, or AMP content over a 54-day analysis period. 相似文献
325.
326.
Transmission of porcine reproductive and respiratory syndrome virus from persistently infected sows to contact controls. 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M D Bierk S A Dee K D Rossow S Otake J E Collins T W Molitor 《Canadian journal of veterinary research》2001,65(4):261-266
The objective of this study was to determine if porcine reproductive and respiratory syndrome virus (PRRSV) could persist in non-pregnant sows and if persistently infected sows could transmit virus to naive contact controls. Twelve PRRSV-naive, non-pregnant sows (index sows) were infected with a field isolate of PRRSV and housed in individual isolation rooms for 42 to 56 days postinfection. Following this period, 1 naive contact sow was placed in each room divided by a gate allowing nose-to-nose contact with a single index sow. Index sows were not viremic at the time of contact sow entry. Virus nucleic acid was detected by polymerase chain reaction, and infectious virus was detected by virus isolation in sera from 3 of the 12 contact sows at 49, 56, and 86 days postinfection. All 3 infected contacts developed PRRSV antibodies. Virus nucleic acid was detected in tissues of all of the 12 index sows at 72 or 86 days postinfection. Nucleic acid sequencing indicated that representative samples from index and infected contacts were homologous (> 99%) to the PRRSV used to infect index sows at the onset of the study. This study demonstrates that PRRSV can persist in sows and that persistently infected sows can transmit virus to naive contact animals. 相似文献
327.
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
328.
329.
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
330.