全文获取类型
收费全文 | 9419篇 |
免费 | 447篇 |
国内免费 | 14篇 |
专业分类
林业 | 611篇 |
农学 | 230篇 |
基础科学 | 84篇 |
1595篇 | |
综合类 | 1648篇 |
农作物 | 361篇 |
水产渔业 | 828篇 |
畜牧兽医 | 3468篇 |
园艺 | 281篇 |
植物保护 | 774篇 |
出版年
2023年 | 60篇 |
2022年 | 76篇 |
2021年 | 155篇 |
2020年 | 216篇 |
2019年 | 214篇 |
2018年 | 208篇 |
2017年 | 221篇 |
2016年 | 213篇 |
2015年 | 185篇 |
2014年 | 254篇 |
2013年 | 452篇 |
2012年 | 551篇 |
2011年 | 712篇 |
2010年 | 371篇 |
2009年 | 355篇 |
2008年 | 641篇 |
2007年 | 632篇 |
2006年 | 599篇 |
2005年 | 580篇 |
2004年 | 614篇 |
2003年 | 572篇 |
2002年 | 505篇 |
2001年 | 103篇 |
2000年 | 90篇 |
1999年 | 94篇 |
1998年 | 84篇 |
1997年 | 73篇 |
1996年 | 67篇 |
1995年 | 63篇 |
1994年 | 63篇 |
1993年 | 53篇 |
1992年 | 65篇 |
1991年 | 52篇 |
1990年 | 61篇 |
1989年 | 53篇 |
1988年 | 58篇 |
1987年 | 56篇 |
1986年 | 37篇 |
1985年 | 33篇 |
1984年 | 39篇 |
1983年 | 40篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 28篇 |
1979年 | 25篇 |
1978年 | 21篇 |
1977年 | 15篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 17篇 |
排序方式: 共有9880条查询结果,搜索用时 46 毫秒
11.
David Lipsitz DVM Robin E. Levitski DVM Wayne L. Berry BVSc MMedVet 《Veterinary radiology & ultrasound》2001,42(1):14-19
Three dogs with multilobular osteochondrosarcoma of the skull were evaluated using magnetic resonance (MR) imaging. Spin echo T1, T2, proton weighted and post contrast T1W images were obtained with a 1.5 Tesla magnet. The MR imaging findings were similar in all three dogs with mixed signal intensities in the T1W, T2W and proton weighted images and fairly large areas of contrast enhancement in the post contrast T1W images. The extent of brain and soft tissue involvement were well delineated and provided useful information concerning surgical planning. MR imaging provided a useful method of evaluating dogs with skull tumors. 相似文献
12.
Effect of age on absorption and immune responses to weaning or introduction of novel dietary antigens in pigs 总被引:14,自引:0,他引:14
Pigs weaned at three weeks old absorb food protein antigens from the intestine. The amount of antigen absorbed declines over the next three weeks, and this decline is associated with an increasing level of serum antibody to the fed proteins. There was no difference in the rate of immune elimination of intravenously injected antigen in fed and unfed controls. The reduction of serum antigen is thus likely to reflect reduced absorption, possibly mediated by locally produced antibody. Pigs weaned at 10 weeks old also absorbed antigens and produced an antibody response when introduced to soya; and after three weeks of feeding soya the absorption of antigen was substantially reduced. This latter exclusion was specific for soya as a second novel protein (ovalbumin) was absorbed when introduced to the diet at this time. At six months, pigs no longer absorbed soya proteins when they were introduced to the diet. Furthermore, pigs of this age had serum 'antibody' to soya and other proteins such as keyhole limpet haemocyanin to which they had never been exposed. 相似文献
13.
David A. Detweiler David S. Biller DVM James J. Hoskinson DVM Kenneth R. Harkin DVM 《Veterinary radiology & ultrasound》2001,42(2):108-112
Canine dysautonomia is an idiopathic condition resulting in loss of autonomic nervous system function. Recently, the prevalence of dogs diagnosed with dysautonomia in the mid-western United States has increased. In this study the medical records and radiographic findings in 24 dogs with dysautonomia were reviewed. A diagnosis of dysautonomia was made in 17 (71%) of the dogs in this study by postmortem examination, the remaining 7 (29%) dogs were diagnosed pharmacologically. The radiographic findings supportive of dysautonomia include aspiration pneumonia, megaesophagus, or a distended stomach, small bowel, or urinary bladder. In some instances, the disease radiographically mimicked other disorders of the gastrointestinal tract, including mechanical obstruction. 相似文献
14.
Marie Engel David W. Hird Tim E. Carpenter Martin Wierup 《Preventive veterinary medicine》1995,24(4):245-252
A cohort of 53 swine seronegative to Aujeszky's disease virus (ADV) was monitored in a 1 year study of a chronically infected commercial Swedish weaner pig producing herd. Serum samples were acquired from all 134 adult swine and analyzed by enzyme-linked immmunosorbent assay (ELISA). Animals testing negative, along with introduced replacement gilts, were followed serologically every second month. Movements of animals were recorded for 319 days and exposure to seropositive animals was calculated for each seronegative pig in the cohort. The accumulated daily pig contact between the 53 ADV-non-infected swine and 43 infected swine was 35 660 days and the median number of days in contact for the non-infected swine with infected was 222. Despite the frequent contact with seropositive pigs, no seronegative animals seroconverted during the first 11 months of observation. Forty-six of 53 pigs seroconverted after a clinical outbreak during the twelfth month of observation. 相似文献
15.
Susan J. Holcombe VMD MS Alicia L. Bertone DVM PhD David S. Biller DVM Valerie Haider DVM 《Veterinary radiology & ultrasound》1995,36(2):119-125
The purpose of this study was to define normal gross anatomic structures in the equine stifle with magnetic resonance images. Magnetic resonance (MR) images were made in sagittal, 15° supinated, transverse, and dorsal planes of two equine stifles. The MR images were scrutinized by comparing MR images to dissection specimens and frozen cross sections of stifle joints. Sagittal and 15° supinated images were the most valuable in assessing articular cartilage, subchondral bone, and soft tissue structures within the joint. Cranial and caudal cruciate ligaments, medial and lateral menisci, meniscotibial and meniscofemoral ligaments, long digital extensor tendon, and patellar ligaments were easily evaluated. MR images provided substantially more gross anatomical information than the currently available imaging modalities. 相似文献
16.
17.
18.
Newby TJ Stokes CR Huntley J Evans P Bourne FJ 《Veterinary immunology and immunopathology》1979,1(1):37-47
The immune response of pigs fed 200 mg per day of dinitrophenylated bovine gamma globulin has been evaluated in terms of the antibody and lymphocyte responses and of the induction of tolerance and immune exclusion. Although dosing for ten days resulted in a small IgA response as indicated by splenic plaque forming cells, serum antibody could only be detected when dosing was continued for 42 days. secretory antibody was detected at any time. Antigen feeding for two weeks rendered the animals hyporesponsive to subsequent parenteral antigenic challenge but had little effect upon their ability to exclude an oral dose of antigen from the circulation. 相似文献
19.
The concentration of electrical energy usage in alternating-current motor drives presents an opportunity for substantial conservation. Emerging advances in power semiconductor transistor systems will support a major commerical effort to this end. An alternating-current synthesizer for this purpose may soon be available. The synthesizer produces electricial power of variable and programmable frequency, voltage, and wave form so that performance can be optimized. This technology provides the additional opportunity for fundamental improvements in electrical distribution and usage systems in the longer term. Power processing with semiconductor a-c motor controls is expected to become widespread in the near future. 相似文献
20.
The systemic fungicides furalaxyl, metalaxyl and ofurace, 1 Ofurace is the proposed BSI and ISO common name for α-(2-chloro-N-2,6-xylylacetamido)-γ-butyrolactone. used to control diseases caused by phycomycetes, were extremely active in vitro against Pythium ultimum, Phytophthora nicotianae and Phytophthora palmivora. Sporangia production was reduced more than mycelial growth but germination of sporangia and zoospores was relatively unaffected. Less than 1% of the metalaxyl or furalaxyl, present in media at the ED50 for hyphal growth, was firmly absorbed by Phyt. palmivora mycelium; uptake was against a concentration gradient and was characterised by a rapid accumulation followed by a more gradual release. Respiration and wall synthesis were not inhibited, whilst membrane permeability was unaffected. Lipid patterns were altered but these changes were probably of secondary importance. The fungicides inhibited protein and nucleic acid synthesis; RNA production was particularly affected. There was some evidence of a reduction in nuclear division. The primary effect of furalaxyl and metalaxyl probably involves impaired biosynthesis of RNA so that mitosis is inhibited; ofurace may act in the same way. 相似文献