全文获取类型
收费全文 | 60303篇 |
免费 | 3417篇 |
国内免费 | 36篇 |
专业分类
林业 | 2425篇 |
农学 | 1851篇 |
基础科学 | 301篇 |
6616篇 | |
综合类 | 10220篇 |
农作物 | 2087篇 |
水产渔业 | 2798篇 |
畜牧兽医 | 33009篇 |
园艺 | 705篇 |
植物保护 | 3744篇 |
出版年
2018年 | 895篇 |
2017年 | 912篇 |
2016年 | 808篇 |
2015年 | 773篇 |
2014年 | 839篇 |
2013年 | 2575篇 |
2012年 | 1669篇 |
2011年 | 2019篇 |
2010年 | 1269篇 |
2009年 | 1250篇 |
2008年 | 1879篇 |
2007年 | 1846篇 |
2006年 | 1727篇 |
2005年 | 1580篇 |
2004年 | 1501篇 |
2003年 | 1543篇 |
2002年 | 1470篇 |
2001年 | 1809篇 |
2000年 | 1783篇 |
1999年 | 1462篇 |
1998年 | 620篇 |
1997年 | 606篇 |
1996年 | 546篇 |
1995年 | 641篇 |
1994年 | 600篇 |
1993年 | 571篇 |
1992年 | 1221篇 |
1991年 | 1369篇 |
1990年 | 1258篇 |
1989年 | 1265篇 |
1988年 | 1163篇 |
1987年 | 1136篇 |
1986年 | 1194篇 |
1985年 | 1194篇 |
1984年 | 960篇 |
1983年 | 900篇 |
1982年 | 582篇 |
1979年 | 891篇 |
1978年 | 701篇 |
1977年 | 694篇 |
1976年 | 711篇 |
1975年 | 714篇 |
1974年 | 866篇 |
1973年 | 842篇 |
1972年 | 812篇 |
1971年 | 727篇 |
1970年 | 769篇 |
1969年 | 733篇 |
1968年 | 650篇 |
1967年 | 656篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
Oidtmann B Schaefers N Cerenius L Söderhäll K Hoffmann RW 《Veterinary microbiology》2004,100(3-4):269-282
A diagnostic procedure, based on a polymerase chain reaction method (PCR) was developed to detect infection of crayfish with the Oomycete Aphanomyces astaci. A set of oligonucleotide primers was designed to specifically amplify A. astaci DNA in the ITS region surrounding the 5.8S rDNA gene. The PCR amplifies a 115 bp amplicon. The specificity of the primers was demonstrated by testing on 27 A. astaci strains and against 20 non-A. astaci Oomycetes and 5 fungal species. Most of the non-A. astaci Oomycete or fungal species included in the study are either known parasites of freshwater crayfish cuticle or can be found in their natural environment. Specificity was also tested against crayfish tissue and some known parasites and bacteria infecting crayfish.
A protocol for the extraction of A. astaci DNA from infected crayfish tissue was developed. The optimised method allows the detection of two genome equivalents of purified A. astaci genomic DNA.
The method was tested on noble crayfish (Astacus astacus), artificially infected with A. astaci. Detection of A. astaci was possible at the very first time of sampling, which was 2 days after the beginning of spore exposure. 相似文献
133.
Two experiments were performed to determine the endocrine and ovarian changes in medroxyprogesterone acetate (MAP)-primed ewes after ram introduction. Experiment 1 was performed during the mid-breeding season with 71 ewes primed with an intravaginal MAP sponge for 12 days. While the control (C) ewes (n = 35) were in permanent contact with rams, the ram effect (RE) ewes (n = 36) were isolated for 34 days prior to contact with rams. At sponge withdrawal, all ewes were joined with eight sexually experienced marking Corriedale rams and estrus was recorded over the next 4 days. The ovaries were observed by laparoscopy 4-6 days after estrus. Four weeks later, pregnancy was determined by transrectal ultrasonography. In eight ewes from each group, ovaries were ultrasonographically scanned; FSH, LH, and estradiol-17beta were measured every 12 hours until ovulation or 96 hours after estrus. The response to the rams was not affected by the fact that ewes had been kept or not in close contact with males before teasing. No differences were found in FSH, LH, estradiol-17beta concentrations, growth of the ovulatory follicle, onset of estrus, ovulation rate, or pregnancy rate. Experiment 2 was performed with 14 ewes during the nonbreeding season. Ewes were isolated from rams for 1 month, and received a 6-day MAP priming. Ovaries were ultrasonographically scanned every 12 hours, and FSH, LH, estradiol-17beta, and progesterone were measured. Ewes that ovulated and came into estrus had higher FSH and estradiol-17beta levels before introduction of the rams than did ewes that had a silent ovulation. The endocrine pattern of the induced follicular phase of ewes that came into estrus was more similar to a normal follicular phase, than in ewes that had a silent ovulation. The follicle that finally ovulated tended to emerge earlier and in a more synchronized fashion in those ewes that did come into estrus. All ewes that ovulated had an LH surge and reached higher maximum FSH levels than ewes that did not ovulate, none of which had an LH surge. We conclude that (a) the effect of ram introduction in cyclic ewes treated with MAP may vary depending on the time of the breeding season at which teasing is performed; (b) patterns of FSH, and estradiol-17beta concentrations, as indicators of activity of the reproductive axis, may be used to classify depth of anestrus; and (c) the endocrine pattern of the induced follicular phase, which is related to the depth of anestrus, may be reflected in the behavioral responses to MAP priming and the ram effect. 相似文献
134.
Estimation of genetic parameters among reproductive and growth traits in yearling heifers 总被引:1,自引:0,他引:1
Growth and reproductive data were obtained on 779 beef heifers at the San Juan Basin Research Center, Hesperus, Co. Genetic parameters were estimated for age of puberty (AOP), age of first calving (AOC), julian day of first calving (DOC), julian day of second calving (DOSC), birth weight, weaning weight, yearling weight, and average daily gain from weaning to yearling and to cycling weights. The least squares model included birth year, age of dam and breed as fixed effects, sire/breed as a random variable, and day of birth and percent inbreeding as covariates. Day of birth was not included in the analyses of AOC, DOC or DOSC. Paternal half-sib estimates of heritability were: AOP, .10 +/- .17; AOC, .01 +/- .12; DOC, .09 +/- .13 and DOSC, .36 +/- .18. Genetic and phenotypic correlations were generally favorable, but genetic correlations were variable with large standard errors. Inbreeding had a detrimental effect on reproductive traits, and a seasonal effect was present for AOP. 相似文献
135.
J Kirpensteijn R B Fingland C P Godshalk 《Journal of the American Veterinary Medical Association》1992,200(1):95-96
A 14-month-old Arabian colt was admitted for treatment of an articular fracture of the supraglenoid tubercle of the right forelimb. Successful repair was achieved by use of three 5.5-mm cortical screws placed in lag fashion across the fracture line. In other reports of supraglenoid tubercle fractures in horses, investigators have preferred conservative management or surgical removal of the fragment, because of limited success with internal fixation. Use of three 5.5-mm screws placed in lag fashion may offer an alternative method of treatment in selected cases of supraglenoid tubercle fractures. 相似文献
136.
137.
138.
139.
B C Barr M L Anderson P C Blanchard B M Daft H Kinde P A Conrad 《The Veterinary record》1990,126(5):120-121
140.
A R Irizarry-Rovira L Kaufman J A Christian S R Reberg S B Adams D B DeNicola W Rivers J F Hawkins 《Journal of veterinary diagnostic investigation》2000,12(2):180-183
A 4-year-old female donkey residing in an open field in Indiana was admitted for evaluation of facial lesions of 2 years duration. Cytologic and histologic examination of exudate and tissue from the lesions revealed a pyogranulomatous inflammatory reaction with numerous yeasts. Sporothrix schenckii was suspected to be the infectious agent; however, multiple culture attempts did not provide positive identification of the organism. Serologic examination supported infection with S. schenckii. A specific direct immunofluorescent antibody test performed on paraffin-embedded tissue sections confirmed the organism as S. schenckii. Clinical signs resolved after appropriate iodide therapy. 相似文献