全文获取类型
收费全文 | 285篇 |
免费 | 9篇 |
专业分类
林业 | 7篇 |
农学 | 29篇 |
99篇 | |
综合类 | 58篇 |
农作物 | 13篇 |
水产渔业 | 14篇 |
畜牧兽医 | 64篇 |
园艺 | 2篇 |
植物保护 | 8篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 20篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 20篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有294条查询结果,搜索用时 343 毫秒
1.
L J Spicer J Klindt F C Buonomo R Maurer J T Yen S E Echternkamp 《Journal of animal science》1992,70(10):3149-3157
Prepubertal gilts of obese (n = 24) or lean (n = 24) genetic lines were injected (s.c.) daily with 0, 2, or 4 mg of porcine somatotropin (pST) for 6 wk starting at 160 d of age to determine whether pST affects follicular function. Blood and ovaries were collected at slaughter 24 h after the last injection. Surface follicles greater than or equal to 1.0 mm in diameter were counted, and pools of follicular fluid (FFL) and granulosa cells were collected from 1.0- to 3.9-mm (small) and 4.0- to 6.9-mm (medium) follicles. Oocytes were collected from small and medium follicles and evaluated for maturational stage and viability. Porcine somatotropin increased (P less than .08) the numbers of small but not the numbers of medium follicles per gilt (P greater than .10). Oocyte maturation and viability were not affected by pST or genetic line. Porcine somatotropin increased (P less than .05) concentrations of insulin-like growth factor I (IGF-I) in serum and FFL of both obese and lean gilts; IGF-I was lower (P less than .01) in lean gilts. Treatment with pST decreased (P less than .05) IGF-II in FFL of lean but not in that of obese gilts. Dose of pST and line had no effect on concentrations of progesterone in FFL of small or medium follicles or on concentrations of estradiol in FFL of small follicles.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
2.
The relationship between the levels of CO and airborne Pb was evaluated against conditions of traffic flow, ambient air temperature and the ventilation rates in 3 underground car parks. During the study period significant variations were noted in the levels of the pollutants in each of the car parks which frequently exceeded the proposed Malaysian Air Quality Standard of 0.7 μg m?3Pb and 9 μg L?1 (8 hr average) CO for indoor environs. High correlation coefficient values were obtained between the levels of CO and traffic flow and Pb and traffic flow. High traffic flow also increased the mean air temperature inside the car parks. Reductions in the ventilation rates in the car parks caused an almost two-fold increase in the level of CO and vice versa. A simple mathematical model depicting the CO concentrations in relation to other parameters was formulated. 相似文献
3.
Previous studies have documented the effectiveness of porcine somatotropin (pST) administered by daily injection in promoting lean tissue growth in lean and obese pigs and the influence of sex and genotype. The present study examined the accretive responses in pigs of different lines and sexes to a slow release formulation of pST (pST-SR). Implants that deliver 2.0 mg of pST/d were implanted in genetically lean and obese barrows and gilts at 65 +/- .7 kg BW (mean +/- SE). Pigs received no, one, or two implants (i.e., doses of 0, 2.0, and 4.0 mg of pST/d). Pigs (four per line x sex x dose) were housed individually and continuously supplied with fresh water and a 19% CP diet containing 1.08% lysine. Pigs were slaughtered on d 0 (four per line x sex) and at the end of the trial (approximately 42 d after implantation) for estimation of initial composition and calculation of accretion rates. Blood samples were collected at d 0, 7, 14, 28, and 42 to measure endocrine and metabolite responses to pST-SR. Sustained-release pST elevated (P < .05) circulating pST throughout the trial with peak concentrations at d 7. On d 7, serum pST concentrations in the pigs given 2.0 mg of pST-SR per day were 16-fold greater than those in control pigs, and in pigs given 4.0 mg of pST-SR per day pST concentrations were 33-fold greater than in controls. Elevated serum pST resulted in increased (P < .05) serum concentrations of insulin-like growth factor (IGF)-I, IGF-II, insulin, and glucose and in reduced (P < .05) concentrations of urea nitrogen and IGF binding protein (IGFBP)-2. Gain was not influenced by pST-SR dose; however, feed consumption was reduced (P < .05) and efficiency of gain was increased (P < .05). Accretion of all body components except cold carcass weight, cecum, and untrimmed Boston butt and ham were changed (P < .05) with pST-SR administration. Heart and stomach were the only components of the carcass and offal whose accretion was not affected by line or sex. Increases in accretion of carcass components (< 75%) induced by sustained-release pST were considerably less than those measured in the organs (liver, 157%; lungs, 748%). The pST-SR treatment resulted in elevated serum concentrations of pST and its mediators and improved efficiency and composition of gain.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
4.
5.
普通小麦和华山新麦草及其属间杂种F_1同工酶分析 总被引:20,自引:0,他引:20
用聚丙烯酰胺凝胶电泳法对普通小麦和华山新麦草及其属间杂种 F_1的三叶期叶片、拔节期叶片、剑叶、幼穗和幼根进行了酯酶同工酶分析。结果表明,不同器官及同一器官的不同发育时期酯酶同工酶酶谱表型有明显差异。普通小麦和华山新麦草就同一器官、同一发育时期相比,酶谱差异较大,佐证了普通小麦和华山新麦草间亲缘关系较远。 相似文献
6.
Development of gilts that conceive early and continue to produce offspring is an objective of swine production. We investigated different patterns of growth on reproductive development and performance of gilts through the first farrowing. At 13 wk of age and 43 kg BW, 286 white crossbred gilts were penned individually and assigned to treatments: Ad lib, ad libitum intake from 13 to 25 wk of age; Control, ad libitum intake from 13 wk of age until 100 kg BW and then 90% of ad libitum intake until 25 wk of age; and Restricted, 74% of ad libitum intake from 13 wk to 25 wk of age. Feed was formulated to restrict energy intake. The study was replicated in three seasons. At 25 wk of age, gilts were moved by treatment to group pens, fed for ad libitum consumption, and estrus detection was initiated. Gilts were inseminated at first estrus, and those recycling were remated. Postmating gilts were fed 1.5x maintenance until 105 to 110 d of pregnancy. Gilts were moved either to the farrowing facility or the abattoir at 105 to 110 d of pregnancy. Those taken to the abattoir were slaughtered and number, weight, and condition of the fetuses were recorded. Gilts moved to the farrowing facility were allowed to farrow, and number, weight, and condition of the piglets were recorded. Daily feed intake during breeding was 3.4 kg/d by Restricted gilts, 2.9 by Control gilts, and 2.7 kg/d by Ad lib gilts. Increased feed intake by Restricted gilts during breeding resulted in compensatory gains that overcame the reduced reproductive performance that resulted from the reduced BW and backfat these gilts carried at the start of breeding. Days to first estrus and pregnancy were not influenced by development period treatment (P < 0.13). Percentage of Ad lib, Control, and Restricted gilts that successfully completed their pregnancies were 61, 74, and 66, respectively (P > 0.19). Total feed fed from 13 wk of age to end of the first pregnancy per gilt assigned did not differ among Ad lib (506 kg) and Control (498 kg) gilts but was less (P < 0.01) in Restricted gilts (451 kg). Number of piglets born per gilt assigned (P > 0.09) and piglets produced per kilogram of feed fed from 13 wk of age to term (P > 0.29) were 6.47 and 0.0134 in Ad lib gilts, 7.26 and 0.0150 in Control gilts, and 6.38 and 0.0149 in Restricted gilts, respectively. Moderate feed restriction, 74% of ad libitum intake, reduced feed consumed from 13 wk of age to end of the first pregnancy with no significant impact on efficiency of piglet production. 相似文献
7.
Cromwell GL Cline TR Crenshaw JD Crenshaw TD Easter RA Ewan RC Hamilton CR Hill GM Lewis AJ Mahan DC Nelssen JL Pettigrew JE Veum TL Yen JT 《Journal of animal science》2000,78(10):2652-2658
A cooperative research study was conducted by members of a regional committee (North Central Regional Committee on Swine Nutrition [NCR-42]) to assess the variability in nutrient composition (DM, CP, Ca, P, Se, NDF, and amino acids) of 14 sources of wheat middlings from 13 states (mostly in the Midwest). A second objective was to assess the analytical variability in nutrient assays among 20 laboratories (labs; 14 experiment station labs and six commercial labs). Wheat middlings were obtained from each participating station's feed mill. The bulk density of the middlings ranged from 289 to 365 g/L. The number of labs that analyzed samples were as follows: DM and CP, 20; Ca, 16; P, 15; Se, 7; NDF, 10; and amino acids, 9. Each lab used its own analytical procedures. The middlings averaged 89.6% DM, 16.2% CP, .12% Ca, .97% P, 36.9% NDF, .53 mg/kg Se, .66% lysine, .19% tryptophan, .54% threonine, .25% methionine, .34% cystine, .50% isoleucine, and .73% valine. As expected, there was considerable variation in nutrient composition among the 14 sources (P < .01), especially for Ca (.08 to .30%) and Se (.05 to 1.07 mg/kg). "Heavy" middlings (high bulk density, >335 g/L), having a greater proportion of flour attached to the bran, were lower in CP, lysine, P, and NDF than "light" middlings (<310 g/L), having cleaner bran, resulting in negative correlations between bulk density and CP (r = -.61), lysine (r = -.59), P (r = -.54), and NDF (r = -.81). Each 1-percentage-point increase in CP in the wheat middlings was associated with .0235 (r2 = .61) and 2.1 (r2 = .39)-percentage-point increases in lysine and NDF, respectively. Lysine content was associated with NDF, CP, and bulk density of wheat middlings (r2 = .88). There was considerable variation among laboratories (P < .01) in analysis of all nutrients. The CV among sources (100 x sigmaS/mean) was greater than among labs (100 x sigmaL/mean) for CP, Ca, P, Se, and NDF, but the CV among labs was greater than that among sources for DM and all of the amino acids except lysine and phenylalanine. 相似文献
8.
Yuri Zharikov David B. Lank Falk Huettmann Russell W. Bradley Nadine Parker Peggy P. -W. Yen Laura A. Mcfarlane-Tranquilla Fred Cooke 《Landscape Ecology》2006,21(1):107-120
We studied habitat selection and breeding success in marked populations of a protected seabird (family Alcidae), the marbled
murrelet (Brachyramphus marmoratus), in a relatively intact and a heavily logged old-growth forest landscape in south-western Canada. Murrelets used old-growth
fragments either proportionately to their size frequency distribution (intact) or they tended to nest in disproportionately
smaller fragments (logged). Multiple regression modelling showed that murrelet distribution could be explained by proximity
of nests to landscape features producing biotic and abiotic edge effects. Streams, steeper slopes and lower elevations were
selected in both landscapes, probably due to good nesting habitat conditions and easier access to nest sites. In the logged
landscape, the murrelets nested closer to recent clearcuts than would be expected. Proximity to the ocean was favoured in
the intact area. The models of habitat selection had satisfactory discriminatory ability in both landscapes. Breeding success
(probability of nest survival to the middle of the chick rearing period), inferred from nest attendance patterns by radio-tagged
parents, was modelled in the logged landscape. Survivorship was greater in areas with recent clearcuts and lower in areas
with much regrowth, i.e. it was positively correlated with recent habitat fragmentation. We conclude that marbled murrelets
can successfully breed in old-growth forests fragmented by logging. 相似文献
9.
10.
Effects of ractopamine on genetically obese and lean pigs 总被引:2,自引:0,他引:2
Twenty-eight genetically obese and 24 lean barrows (65.0 and 68.7 kg average BW, respectively) were allotted within genotype to a 16% CP corn-soybean meal basal diet or this basal diet + 20 ppm ractopamine (a phenethanolamine beta-adrenergic agonist) and allowed ad libitum access to feed for 48 d. Compared to lean pigs, obese pigs had lower ADG, gain to feed ratio, longissimus muscle area, predicted amount of muscle, and weights of trimmed loin and ham, ham lean, heart, spleen, kidney and gastrointestinal tract (P less than .05). Obese pigs also had shorter carcass but higher dressing percentage, backfat thickness, fat depth, fat area, untrimmed loin weight and fasting plasma urea N concentration (P less than .05). Dietary supplementation with 20 ppm ractopamine reduced daily feed intake and improved gain to feed ratio in both lean and obese pigs (P less than .05). Pigs fed ractopamine had shorter carcasses, less fat depth and fat area, smaller weights of stomach and colon plus rectum, but higher dressing percentages, longissimus muscle areas, weights of trimmed Boston butts, picnics and loins, ham lean and predicted amounts of muscle than pigs not fed ractopamine (P less than .05). Supplemental ractopamine had no effect on fasting plasma concentrations of urea N, nonesterified fatty acids, triglyceride or glucose (P greater than .05). No genotype x ractopamine interactions for the criteria described above were detected (P greater than .05). These results suggest that ractopamine will improve the efficiency of feed utilization and carcass leanness in swine with different propensities for body fat deposition. 相似文献