全文获取类型
收费全文 | 470篇 |
免费 | 42篇 |
专业分类
林业 | 19篇 |
农学 | 1篇 |
基础科学 | 1篇 |
36篇 | |
综合类 | 62篇 |
农作物 | 5篇 |
水产渔业 | 13篇 |
畜牧兽医 | 341篇 |
园艺 | 14篇 |
植物保护 | 20篇 |
出版年
2023年 | 3篇 |
2021年 | 6篇 |
2020年 | 20篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 29篇 |
2012年 | 15篇 |
2011年 | 9篇 |
2010年 | 15篇 |
2009年 | 23篇 |
2008年 | 21篇 |
2007年 | 11篇 |
2006年 | 19篇 |
2005年 | 23篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 16篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有512条查询结果,搜索用时 750 毫秒
71.
72.
73.
Single‐voxel and multi‐voxel spectroscopy yield comparable results in the normal juvenile canine brain when using 3 Tesla magnetic resonance imaging
下载免费PDF全文
![点击此处可从《Veterinary radiology & ultrasound》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alison M. Lee Michaela J. Beasley Emerald D. Barrett Judy R. James Jennifer M. Gambino 《Veterinary radiology & ultrasound》2018,59(5):577-586
Conventional magnetic resonance imaging (MRI) characteristics of canine brain diseases are often nonspecific. Single‐ and multi‐voxel spectroscopy techniques allow quantification of chemical biomarkers for tissues of interest and may help to improve diagnostic specificity. However, published information is currently lacking for the in vivo performance of these two techniques in dogs. The aim of this prospective, methods comparison study was to compare the performance of single‐ and multi‐voxel spectroscopy in the brains of eight healthy, juvenile dogs using 3 Tesla MRI. Ipsilateral regions of single‐ and multi‐voxel spectroscopy were performed in symmetric regions of interest of each brain in the parietal (n = 3), thalamic (n = 2), and piriform lobes (n = 3). In vivo single‐voxel spectroscopy and multi‐voxel spectroscopy metabolite ratios from the same size and multi‐voxel spectroscopy ratios from different sized regions of interest were compared. No significant difference was seen between single‐voxel spectroscopy and multi‐voxel spectroscopy metabolite ratios for any lobe when regions of interest were similar in size and shape. Significant lobar single‐voxel spectroscopy and multi‐voxel spectroscopy differences were seen between the parietal lobe and thalamus (P = 0.047) for the choline to N‐acetyl aspartase ratios when large multi‐voxel spectroscopy regions of interest were compared to very small multi‐voxel spectroscopy regions of interest within the same lobe; and for the N‐acetyl aspartase to creatine ratios in all lobes when single‐voxel spectroscopy was compared to combined (pooled) multi‐voxel spectroscopy datasets. Findings from this preliminary study indicated that single‐ and multi‐voxel spectroscopy techniques using 3T MRI yield comparable results for similar sized regions of interest in the normal canine brain. Findings also supported using the contralateral side as an internal control for dogs with brain lesions. 相似文献
74.
High field magnetic resonance imaging contributes to diagnosis of equine distal tarsus and proximal metatarsus lesions: 103 horses
下载免费PDF全文
![点击此处可从《Veterinary radiology & ultrasound》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Myra F. Barrett Kurt T. Selberg Sherry A. Johnson Jake Hersman David D. Frisbie 《Veterinary radiology & ultrasound》2018,59(5):587-596
Injury of the distal tarsus and proximal metatarsus commonly causes lameness. Magnetic resonance imaging (MRI) allows concurrent assessment of both the distal tarsal joints and suspensory ligament origin, and aids identification of lesions that may otherwise go undetected by other modalities. In this retrospective observational study, the medical records of a veterinary imaging center were searched for MRI exams of the distal tarsus and proximal metatarsus for the years 2012 through 2014. Studies for 125 limbs of 103 horses were identified and retrospectively evaluated by two board‐certified veterinary radiologists. Soft tissue and osseous changes were characterized and graded by degree of severity. The patients’ signalment, lameness severity, and results of diagnostic analgesia were recorded. Osteoarthritic changes of the distal intertarsal and tarsometatarsal joints were the most common findings. Other findings included bone marrow lesions, degenerative changes of the small cuboidal bones, subchondral cystic lesions, and intertarsal desmopathy. Suspensory ligament desmopathy was found in 53% of limbs. Fourty‐seven percent of limbs that responded to analgesia of the proximal suspensory ligament had more severe lesions in the distal tarsus. Bone marrow lesions of the third tarsal bone were the only MRI finding that correlated with grade of lameness in patients for which lameness grade was reported. The grade of lameness has a poor correlation with the severity of lesions found on MRI. The findings support the use of MRI for simultaneous evaluation of the proximal metatarsus and distal tarsus, particularly given the difficulty of lesion localization with diagnostic analgesia. 相似文献
75.
76.
77.
V Aksyuk FF Balakirev GS Boebinger PL Gammel RC Haddon DJ Bishop 《Science (New York, N.Y.)》1998,280(5364):720-722
A silicon micromechanical magnetometer was constructed and successfully used in 60-tesla pulsed magnetic fields of less than 100-millisecond duration. The device is small, inexpensive to fabricate, and easy to use. It features a fast mechanical response (up to 50,000 hertz) and extremely high sensitivity yet is relatively robust against electrical and mechanical noise. Quantum oscillations in the magnetization of a 1-microgram sample of an organic superconductor, kappa-[bis(ethylenedithio)tetrathiafulvalene]2Cu(NCS)2, have been observed with this device. 相似文献
78.
WC Feldman BL Barraclough S Maurice RC Elphic DJ Lawrence DR Thomsen AB Binder 《Science (New York, N.Y.)》1998,281(5382):1489-1493
Global maps of thermal and fast neutron fluxes from the moon suggest three end-member compositional units. A high thermal and low fast neutron flux unit correlates with the lunar highlands and is consistent with feldspathic rocks. The South Pole-Aitken basin and a strip that surrounds the nearside maria have intermediate thermal and fast neutron flux levels, consistent with more mafic rocks. There appears to be a smooth transition between the most mafic and feldspathic compositions, which correspond to low and high surface altitudes, respectively. The maria show low thermal and high fast neutron fluxes, consistent with basaltic rocks. 相似文献
79.
RA Periana DJ Taube S Gamble H Taube T Satoh H Fujii 《Science (New York, N.Y.)》1998,280(5363):560-564
Platinum catalysts are reported for the direct, low-temperature, oxidative conversion of methane to a methanol derivative at greater than 70 percent one-pass yield based on methane. The catalysts are platinum complexes derived from the bidiazine ligand family that are stable, active, and selective for the oxidation of a carbon-hydrogen bond of methane to produce methyl esters. Mechanistic studies show that platinum(II) is the most active oxidation state of platinum for reaction with methane, and are consistent with reaction proceeding through carbon-hydrogen bond activation of methane to generate a platinum-methyl intermediate that is oxidized to generate the methyl ester product. 相似文献
80.
RC Elphic DJ Lawrence WC Feldman BL Barraclough S Maurice AB Binder PG Lucey 《Science (New York, N.Y.)》1998,281(5382):1493-1496
The Lunar Prospector neutron spectrometer data correlate well with iron and titanium abundances obtained through analysis of Clementine spectral reflectance data. With the iron and titanium dependence removed, the neutron spectrometer data also reveal regions with enhanced amounts of gadolinium and samarium, incompatible rare earth elements that are enriched in the final phases of magma crystallization. These regions are found mainly around the ramparts of the Imbrium impact basin but not around the other basins, including the much larger and deeper South Pole-Aitken basin. This result confirms the compositional uniqueness of the surface and interior of the Imbrium region. 相似文献