全文获取类型
收费全文 | 546篇 |
免费 | 39篇 |
专业分类
林业 | 7篇 |
农学 | 7篇 |
基础科学 | 2篇 |
42篇 | |
综合类 | 32篇 |
农作物 | 7篇 |
水产渔业 | 9篇 |
畜牧兽医 | 471篇 |
园艺 | 3篇 |
植物保护 | 5篇 |
出版年
2023年 | 8篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 20篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 20篇 |
2013年 | 24篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 27篇 |
2009年 | 22篇 |
2008年 | 34篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 9篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有585条查询结果,搜索用时 31 毫秒
1.
A. Bhogal A. Bhogal M.A. Shepherd D.J. Hatch L. Brown S.C. Jarvis 《Soil Use and Management》2001,17(3):163-172
Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization. 相似文献
2.
T. D. G. Watson † D. Gaffhey C. T. Mooney† H. Thompson‡ C. J. Packard J. Shepherd 《The Journal of small animal practice》1992,33(5):207-212
Hyperchylomicronaemia was identified in a four-week-old Siamese kitten with lethargy, in-appetence, hindlimb ataxia and profound anaemia. The kitten was euthanased and at necropsy a thrombus was found occluding the caudal aorta. Two littermates later presented with lethargy, inappetence and hypertriglyceri-daemia which resolved after being weaned on to a low fat diet. A similar condition was subsequently diagnosed in a kitten born to the same sire but a different queen. The expression of hyperchylomicronaemia in two related litters was suggestive of an inherited, familial defect in the function of lipoprotein lipase (LPL). The activity of this enzyme was reduced in all three parents, the two recovered cases and two related, but apparently unaffected kittens, compared with a control group of unrelated cats belonging to the breeder. This reduction in activity was not attributable to defective activation of LPL by its serum cofactor apolipoprotein C-II or the presence in plasma of a factor that inhibited LPL. The gene that codes for LPL was examined by restriction fragment length polymorphism analysis using a human LPL cDNA probe. The results showed that the cat has a similar, but not identical, LPL gene to man. However, there were no differences in the restriction fragment patterns obtained from affected, unaffected and control animals. 相似文献
3.
Precise localization of the needle tip during CT-guided percutaneous biopsy is considered to be a key element of a successful procedure. To ensure accuracy, the true needle tip must be differentiated from a false or simulated tip which appears when the CT slice encompasses only the shaft of an angled needle. By obtaining images of an aspiration biopsy needle inserted vertically into a phantom and then incrementally tilting the gantry, the authors were able to compare the characteristic features of the true tip to the simulated tip. The true tip was abrupt and distinct and had an adjacent flame-like low density artifact. The simulated tip was indistinct and tapered, yet still produced the adjacent artifact. We concluded that the shape and distinctness of the end portion of the needle itself, rather than the attendant artifact, were the most reliable criteria for accurate needle tip identification. 相似文献
4.
Piper L. Wall DVM PhD DACVECC ; Maisha M. Rudison BS ; Tatjana Lazic DVM Dean H. Reidesel DVM PhD 《Journal of Veterinary Emergency and Critical Care》2002,12(1):1-8
Objective: To establish baseline values for descending thoracic aortic blood flow parameters as determined with a transesophageal combined M‐mode and pulsed Doppler ultrasound‐based monitoring method. Design: Preliminary observational study. Setting: University small animal teaching hospital. Animals: The study population consisted of anesthetized canine patients undergoing nonemergent surgeries. Prospectively set criteria for inclusion were adequate body size for placement of the esophageal probe and a nonemergent reason for surgery. The criterion for exclusion was recent trauma. Interventions: Placement of the transesophageal probe. Measurements and main results: Data was collected during 15 surgeries. Data from three dogs was excluded from data analysis (two recently hit by motor vehicles, one recently having undergone a total hip replacement). Each parameter was stable across time within each individual dog. The ranges of the descending thoracic aortic parameters across the 12 nonemergent cases were as follows: blood flow, 0.038–0.085 L min?1 kg?1; blood flow per beat, 0.31–0.84 mL kg?1; blood acceleration, 6–29 m s2?1; blood peak velocity, 38–105 m s?1; left ventricular ejection time interval 331–492 ms; and diameter, 0.30–0.93 mm kg?1. Conclusions: The range of descending thoracic aortic blood flow parameters encountered in this small group of dogs during nonemergent surgeries was broad; however, each parameter was quite stable across time with little change occurring in any dog during monitoring. 相似文献
5.
PETER MUIR BVSc MVetClinStud PhD MACVSC MRCVS MARK D. MARKEL DVM PhD Diplomate ACVS JOHN J. BOGDANSKE BS KENNETH A. JOHNSON MVSC PHD FACVSc Diplomate ACVS 《Veterinary surgery : VS》1995,24(1):15-24
Dual-energy x-ray absorptiometry was used to measure bone mineral density of four regions in healed femora of nine dogs after fracture fixation with a leg-lengthening plate. Six to 85 months (mean, 46 months) after surgery, the bone mineral density of healed femora was not significantly different from the contralateral uninjured femora ( P >.05; power = 0.8 at Δ= 15%). Radio-lucencies around the proximal screws, apparently associated with screw loosening, were seen on radiographic views of the healed femora of three dogs. In one of these dogs, one screw in the proximal metaphysis had broken. Force-plate analysis of gait was also performed on dogs at the time of bone mineral density measurement. Peak vertical force was decreased in the pelvic limb with the healed fracture compared with the contralateral unoperated limb ( P < 0.05). Clinically apparent lameness in three dogs did not appear to be associated with altered bone mineral density and may have been caused by hip osteoarthritis, a nondisplaced hairline diaphyseal fracture, and screw loosening in conjunction with extensive post-traumatic soft tissue injury. 相似文献
6.
T D Watson L Burns C J Packard J Shepherd 《American journal of veterinary research》1992,53(5):771-775
Affinity chromatography on heparin sepharose was used to identify 2 lipolytic enzymes in heparinized plasma from horses. One enzyme was typical of hepatic triglyceride lipase (HTGL), because it was resistant to inactivation by high concentrations of NaCl, and it did not require the addition of serum for activity. The other enzyme was identified as lipoprotein lipase (LPL), because of its inactivation at NaCl concentrations in excess of 0.2M, and its dependency on addition of serum as a source of apolipoprotein C-II activator. The enzymes were purified by 347-(HTGL) and 442- (LPL) fold, with yields of 54 and 58%, respectively. The partially purified enzymes were used to design incubation conditions that gave optimal activities for each enzyme in vitro. A selective assay was then developed for direct measurement of LPL and HTGL activities in heparinized plasma from horses. Analysis of HTGL took advantage of the almost complete inactivation of LPL when serum cofactor was excluded from the assay at the NaCl concentration that gave optimal HTGL activity. Prior incubation of heparinized plasma with sodium dodecyl sulfate to inhibit HTGL was necessary for measurement of LPL, because HTGL retained 67% of its activity at the NaCl concentration required for optimal LPL activity. Activity of each enzyme was measured in heparinized plasma from 12 Shetland ponies. The mean activity +/- SD for LPL was 3.22 +/- 1.04 mumol of fatty acids/ml of heparinized plasma/h (mumol of FA/ml/h. The mean activity for HTGL was 4.9 +/- 1.56 mumol of FA/ml/h. The performance of the assay was assessed by replicate analysis of pools of each enzyme with high and low activities.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
7.
George J. Brewer MD William Schall DVM Robert Dick BS Vilma Yuzbasiyan-Gurkan PhD Michael Thomas DVM George Padgett DVM 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1992,6(1):41-43
Inherited canine copper toxicosis is a serious problem in Bedlington terriers and West Highland White terriers, and may also be a problem in other less-studied breeds. Affected dogs become ill at midlife with progressive and ultimately fatal liver disease. Treatments for removal of copper and prevention of copper accumulation are available, but are most effective if begun before the dog becomes ill. Until recently diagnosis has not been available until the dog is 1 year of age, and then only by an invasive liver biopsy with determination of liver copper concentration. The authors studied the use of 64copper for early diagnosis of canine copper toxicosis. Two procedures were evaluated. The first involved measuring the concentration of 64copper in blood 24 hours after oral administration of the radioisotope. At this time, 64copper was associated primarily with ceruloplasmin secreted into the blood by the liver. This procedure is useful in the diagnosis of the human counterpart, Wilson's disease. However, the authors found it to be nondiscriminatory between affected and unaffected dogs. In contrast, the second procedure, which involved measuring 64copper excreted in stool during 48 hours after an intravenous dose of radioisotope, yielded results that differentiated most affected and unaffected dogs. 相似文献
8.
M.L. Castor BS R.E. Wooley DVM PhD E.B. Shotts PhD J. Brown DVM PhD J.B. Payeur DVM PhD 《Journal of Equine Veterinary Science》1989,9(5)
During an outbreak of equine salmonellosis in a veterinary teaching hospital 20 Salmonella isolates were cultured from sick horses (13 isolates) or from the hospital environment (7 isolates). Three serotypes were isolated from the environment including: S. give, S. newportand S. agona. The serotypes isolated from horses included: S. give, S. newport and S. anatum. Examination of antibiotic profiles, presence of plasmids, production of bacteriocins and hemagglutination of erythrocytes implied a common origin for the equine and environmental isolates. 相似文献
9.
K.A. Jarvis Ph.D M.J. Woliner BS E.P. Steffey VMD PhD 《Veterinary anaesthesia and analgesia》1992,19(1):41-45
The accuracy of thermodilution for measuring flow rates of 10–40 L/min was evaluated using a commercially available thermodilution cardiac output computer in an in vitro model. Water (36.5–37.5°C) was directed through a mixing chamber via a constant flow pump. Thermodilution estimates of flow using four different volumes (10, 20, 30, 40 ml) of iced water injectate were compared to simultaneous measurements of timed samples of effluent from the mixing chamber. Injectate volume had a significant impact on the accuracy of thermodilution estimation (p < 0.05). Thermodilution overestimated measured flow when 10 and 20 ml of injectate were used to determine flow rates < 20 L/min but underestimated flow when injectate volumes of 30 and 40 ml were used, or when measured flow was > 25 L/min. The discrepancy between thermodilution flow and measured flow increased as rate of fluid flow increased. 相似文献
10.
L.S. Faudskar DVM M. R. Raffe DVM MS D. A. Randall BS D. R. Bing BS RRT 《Journal of Veterinary Emergency and Critical Care》1997,7(1):49-58
A laboratory evaluation was performed to evaluate the performance characteristics of a new veterinary ventilator. The ventilator studied was configured according to manufacturer's directions and attached to a test lung via a pneumotachograph and differential pressure transducer interfaced to a pulmonary mechanics analyzer system. Constant resistance (R=10 cm H2 O/L/sec) and compliance (C=3 ml/cm H2 O) factors were maintained for all trials. The ventilator operated at the manufacturer's preprogrammed parameters. In the first trial, body weight was the only variable. In the second trial, an endotracheal tube was placed in series between the ventilator's breathing circuit and the pneumotachograph. Body weights from 1–20 kgs were evaluated. Mean values for respiratory rate (RR), minute ventilation (VE), inspiratory time (Ti), peak inspiratory pressure (PIP), and peak inspiratory flow (Fpki) displayed on the ventilator control panel; tidal volume (VT), calculated from the displayed minute volume, and identical parameters measured by the pulmonary mechanics system at each body weight, were compared using a two factor analysis of variance. Significant differences (P< 0.05) were found between mean displayed and measured values for RR, PIP, and Fpki. 相似文献