全文获取类型
收费全文 | 78836篇 |
免费 | 4256篇 |
国内免费 | 93篇 |
专业分类
林业 | 3187篇 |
农学 | 2043篇 |
基础科学 | 461篇 |
8566篇 | |
综合类 | 15395篇 |
农作物 | 3133篇 |
水产渔业 | 3426篇 |
畜牧兽医 | 41684篇 |
园艺 | 844篇 |
植物保护 | 4446篇 |
出版年
2019年 | 720篇 |
2018年 | 1094篇 |
2017年 | 1216篇 |
2016年 | 1050篇 |
2015年 | 905篇 |
2014年 | 1192篇 |
2013年 | 2622篇 |
2012年 | 2114篇 |
2011年 | 2570篇 |
2010年 | 1615篇 |
2009年 | 1730篇 |
2008年 | 2596篇 |
2007年 | 2405篇 |
2006年 | 2287篇 |
2005年 | 2135篇 |
2004年 | 2077篇 |
2003年 | 2136篇 |
2002年 | 1922篇 |
2001年 | 2385篇 |
2000年 | 2438篇 |
1999年 | 1869篇 |
1998年 | 719篇 |
1997年 | 712篇 |
1996年 | 711篇 |
1995年 | 805篇 |
1993年 | 740篇 |
1992年 | 1553篇 |
1991年 | 1750篇 |
1990年 | 1634篇 |
1989年 | 1646篇 |
1988年 | 1472篇 |
1987年 | 1534篇 |
1986年 | 1596篇 |
1985年 | 1547篇 |
1984年 | 1184篇 |
1983年 | 1057篇 |
1982年 | 704篇 |
1979年 | 1152篇 |
1978年 | 894篇 |
1977年 | 755篇 |
1975年 | 774篇 |
1974年 | 1024篇 |
1973年 | 1024篇 |
1972年 | 1043篇 |
1971年 | 993篇 |
1970年 | 987篇 |
1969年 | 903篇 |
1968年 | 810篇 |
1967年 | 799篇 |
1966年 | 732篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
111.
The conformation of the urethra, the position of the bladder neck and the distance between the external urethral orifice and the cranial pubic brim were compared in 30 continent and 30 incontinent bitches with incompetence of the urethral sphincter mechanism, using the measurements made from vagino-urethrograms. The bladder neck was significantly (P less than 0.001) further caudal in incontinent dogs than in continent dogs. Its position was not affected by neutering and could not be explained by the degree of urethral curvature. The distance from the external urethral orifice to the cranial pubic brim was correlated (P less than 0.001) with bodyweight but was not significantly different in the continent and incontinent bitches. In neutered animals, the distance between the cranial pubic brim and the external urethral orifice was significantly (P less than 0.05) shorter than in entire animals. 相似文献
112.
The capability of field-collected American dog ticks, Dermacentor variabilis, to infect horses with Ehrlichia risticii, causative agent of Potomac horse fever (PHF), was examined by allowing adult ticks collected from horse farms with a history of PHF to feed on susceptible horses. More than 500 male and female ticks attached and fed on 3 test horses; however, no clinical or serologic evidence of PHF was observed in treated or control horses. All horses were challenge exposed with E risticii-infective blood by inoculation at 60 to 65 days after ticks fed, and all developed clinical PHF with subsequent seroconversion. The data, therefore, indicated that adult D variabilis, a common parasite of horses on Maryland premises where PHF is enzootic, may not serve as a vector of E risticii. 相似文献
113.
114.
Effects of green pruning on growth and stem shape of Eucalyptus nitens (Deane and Maiden) Maiden 总被引:2,自引:0,他引:2
An experiment was established in two high quality Eucalyptus nitens Deane and Maiden (Maiden) plantations in Tasmania. At the start of the experiment the trees were three years old and the plantations were on the point of canopy closure. Selected trees were pruned to remove 0, 50% or 70% of the lower green crown length, and each was surrounded by eight unpruned trees. The 50% treatment had no impact on height or diameter increment in the two years following treatment, but removal of 70% of the lower crown length resulted in significant decreases in both height and diameter increment. There were no changes in the height of 50%-pruned trees relative to the height of surrounding unpruned trees (relative height), and it was concluded that dominance would not be affected by this treatment. The relative height of 70%-pruned trees was less at one site, and this treatment may result in loss of dominance. Stem taper was generally unaffected by either pruning treatment. Changes in stem form were restricted to trees in the 70% pruning treatment and were only transient. It was concluded that removal of 50% of the lower green crown length is an appropriate level of pruning for the species provided that growth rates are rapid and pruning is timed to coincide with canopy closure. Since dominance was unaffected by this level of pruning, thinning at the time of pruning is unnecessary. It may be possible to minimise the impact on growth of higher levels of pruning by thinning at the time of pruning. 相似文献
115.
REASON FOR PERFORMING STUDY: The effectiveness and best method to perform a partial arytenoidectomy in racehorses is unclear. This study was performed to evaluate the success of and complications that can occur after a unilateral partial arytenoidectomy with primary mucosal closure in Thoroughbred racehorses. HYPOTHESIS: Partial arytenoidectomy is an effective surgical procedure to return Thoroughbred racehorses, afflicted by arytenoid chondropathy or a failed laryngoplasty, to preoperative levels of performance. METHODS: Seventy-six Thoroughbred racehorses admitted to the New Bolton Centre between 1992 and 2006 were assessed. Information was obtained from the medical records about the horse, laryngeal abnormalities, surgery and other findings during hospitalisation. Racing information was evaluated relative to those independent variables by an analysis of variance with a level of significance of P<0.05. RESULTS: Arytenoid chondropathy was the presenting complaint in 54 horses and failed laryngoplasty in 22 horses. Thirteen horses (17%) underwent a second surgery for laser excision of intralaryngeal granulation tissue at the arytenoidectomy site. Seventy-three horses were discharged from the hospital and racing outcome was evaluated. Sixty horses (82%) raced after surgery and 46 horses (63%) raced 5 or more times after surgery. The median time from surgery to the first start was 6 months. The average earnings/start was not significantly different before and after surgery. There was no association between earnings after surgery and age, gender, location of lesion, type of lesion, duration of tracheal intubation or undergoing a second surgery. CONCLUSIONS AND POTENTIAL RELEVANCE: A Thoroughbred racehorse is likely to race after a unilateral partial arytenoidectomy with primary mucosal closure and return to a preoperative level of performance. 相似文献
116.
Cockram MS Kent JE Goddard PJ Waran NK Jackson RE Mcgilp IM Southall EL Amory JR Mcconnell TI O'Riordan T Wilkins BS 《Veterinary journal (London, England : 1997)》2000,159(2):139-146
The effect of a novel lairage environment on the ability of sheep to recover from 16 h of transport was investigated. Sheep were transported from grass paddocks to either novel outside paddocks or inside pens, and housed groups were transported to either familiar or novel inside pens. During transport, sheep from outside paddocks lay down less than those from inside pens. In sheep transported to inside pens, those from outside paddocks spent more time lying and spent less time eating; hay and water intakes during the first 12 h post-transport were lower than those previously kept inside. There was no obvious effect of a novel environment post-transport on blood biochemistry, suggesting that the lower post-transport feed and water intakes in a novel environment did not have a significant effect on the ability of the sheep to recover from the feed and water deprivation associated with transport. 相似文献
117.
Lakritz J Tyler JW Hostetler DE Marsh AE Weaver DM Holle JM Steevens BJ Denbigh JL 《American journal of veterinary research》2000,61(9):1021-1025
OBJECTIVE: To determine the effects of pasteurization of colostrum on serum lactoferrin concentration and neutrophil oxidative function by comparing values from calves given pasteurized (76 C, 15 minutes) colostrum versus calves given fresh frozen colostrum. ANIMALS: 8 Holstein bull calves were used to study the effects of pasteurization of colostrum on the absorption of lactoferrin and neutrophil oxidative burst. Three additional calves were used to study the effect of exogenous lactoferrin on neutrophil oxidative burst. METHODS: Calves were fed fresh frozen or heat pasteurized colostrum (76 C for 15 minutes) via esophageal feeder within 4 hours of birth. Neutrophils were isolated from whole blood samples. Neutrophil oxidative burst was induced by phorbol ester (300 ng/ml) stimulation of cells (1 X 10(6) cells) at 37 C. Serum lactoferrin concentrations were compared, using immunoblot analysis. Serum IgG concentrations were determined by radial immunoassay. Comparisons were made between the use of the 2 types of colostrum in calves by measuring subsequent serum IgG and lactoferrin concentrations and neutrophil superoxide production. RESULTS: Serum IgG and lactoferrin concentrations increased more in calves receiving fresh frozen colostrum. Neutrophil superoxide production was higher in neutrophils prepared from calves receiving fresh frozen colostrum. Colostral lactoferrin addition to neutrophil incubations resulted in increased oxidative burst. CONCLUSIONS AND CLINICAL RELEVANCE: Compared with calves given fresh frozen colostrum, calves given pasteurized colostrum had decreased serum IgG and lactoferrin concentrations and neutrophil superoxide production 24 hours after administration. These results suggest that pasteurizing bovine colostrum at 76 C for 15 minutes has substantial effects on passive transfer of proteins and neutrophil function. 相似文献
118.
Chase-Topping ME Gunn G Strachan WD Edwards SA Smith WJ Hillman K Stefopoulou SN Thomson JR 《Veterinary journal (London, England : 1997)》2007,173(2):353-360
The objective of this study was to investigate epidemiological risk factors for porcine non-specific colitis (NSC). Forty-seven Scottish pig farms, with and without a clinical history of diarrhoea during the growing period (15-40 kg), were selected. The study included farm visits, clinical inspection of pigs, completion of farm management questionnaires, pathological tests into the cause of the diarrhoea and analysis of the non-starch polysaccharide (NSP) content of feeds. The results from 17 farms designated as NSC and 10 control farms suggest dietary associations with NSC. Farms with NSC fed diets with significantly higher levels of NSPs, especially containing the sugars glucose, arabinose and xylose. Few management factors were identified, although the high prevalence of infectious colitis reduced the power of the study. 相似文献
119.
Medical records of six cats diagnosed with lumbosacral intervertebral disk disease were reviewed. Clinical signs included reluctance to jump, low tail carriage, elimination outside the litter box, reluctance to ambulate, pelvic-limb paresis, urinary incontinence, and constipation. All cats had lumbosacral hyperpathia on palpation. Computed tomography in four cats revealed evidence of extradural spinal cord compression at the seventh lumbar (L(7)) to first sacral (S(1)) vertebral interspace. Compression was confirmed via myelography in three of these four cats, with confirmation in the fourth cat at the time of decompressive laminectomy. Each of the six cats underwent dorsal decompressive laminectomy at the L(7) to S(1) interspace. Postoperative clinical follow-up lasted 3 to 35 months, with most cats having excellent outcomes. 相似文献
120.
Bread-making quality indices (dough strength and dough mixing stability) in relation to flour protein content, glutenin/gliadin ratio, and high-molecular-weight (HMW) subunits of glutenin have been investigated in Triticum aestivum progenies during a three year agronomic trial. Dough strength (W) proved to be a fairly stable characteristic, slightly but positively correlated with flour protein content. High could be associated with a high glutenin/gliadin ratio as well as with the presence of specific HMW. subunits of glutenin, while high protein content tended to favour a balanced dough tenacity-extensibility ratio (P/L = 0.4—0.6). Satisfactory values of dough-mixing stability were frequently observed in association with good expression of W showing that the two quality traits may coexist without much difficulty in the same genotype. From the plant breeding standpoint the data suggest feasible to obtain high dough strength by concentrating in a genotype the HMW subunits of glutenin known to have a beneficial effect on W. However, very high W may present unfavourable P/L ratios. This possibility is enhanced when the flour has a low protein content which often occurs in high yielding genotypes. 相似文献