全文获取类型
收费全文 | 88915篇 |
免费 | 5483篇 |
国内免费 | 817篇 |
专业分类
林业 | 3605篇 |
农学 | 2859篇 |
基础科学 | 741篇 |
11046篇 | |
综合类 | 16883篇 |
农作物 | 3383篇 |
水产渔业 | 4273篇 |
畜牧兽医 | 45670篇 |
园艺 | 1226篇 |
植物保护 | 5529篇 |
出版年
2021年 | 941篇 |
2020年 | 1013篇 |
2019年 | 1244篇 |
2018年 | 1561篇 |
2017年 | 1791篇 |
2016年 | 1618篇 |
2015年 | 1499篇 |
2014年 | 1724篇 |
2013年 | 3299篇 |
2012年 | 3252篇 |
2011年 | 3874篇 |
2010年 | 2494篇 |
2009年 | 2408篇 |
2008年 | 3428篇 |
2007年 | 3295篇 |
2006年 | 2953篇 |
2005年 | 2855篇 |
2004年 | 2568篇 |
2003年 | 2597篇 |
2002年 | 2474篇 |
2001年 | 2687篇 |
2000年 | 2722篇 |
1999年 | 2086篇 |
1998年 | 831篇 |
1997年 | 752篇 |
1996年 | 696篇 |
1995年 | 784篇 |
1993年 | 696篇 |
1992年 | 1593篇 |
1991年 | 1762篇 |
1990年 | 1691篇 |
1989年 | 1641篇 |
1988年 | 1520篇 |
1987年 | 1566篇 |
1986年 | 1610篇 |
1985年 | 1446篇 |
1984年 | 1219篇 |
1983年 | 1048篇 |
1982年 | 699篇 |
1979年 | 1090篇 |
1978年 | 849篇 |
1976年 | 727篇 |
1975年 | 763篇 |
1974年 | 1023篇 |
1973年 | 1004篇 |
1972年 | 974篇 |
1971年 | 896篇 |
1970年 | 873篇 |
1969年 | 818篇 |
1967年 | 712篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
W L?scher 《DTW. Deutsche tier?rztliche Wochenschrift》1992,99(2):51-54
The article considers the attractions and dangers of homeopathic therapy from the view of a pharmacologist. Homeopathic drugs may exert pharmacodynamic (but also toxic) effects at low dilutions (D0-D6), but there is no scientific proof for specific effects of higher dilutions except for substances with a high toxic potential. Most homeopathic drugs have no reasonable basis for clinical use but, in case of toxic compounds, especially those with carcinogenic or allergic potential, homeopathy may bear risks for the animal and, because of residues in food animals, also for humans. Thus, homeopathic treatment should not be used when effective conventional treatments are available, and the use of homeopathic drugs with toxic potential should be avoided. 相似文献
32.
33.
34.
Twelve different mating types among the Hampshire and Landrace breeds were used to determine direct, maternal, heterosis, and recombination effects for performance and carcass traits. Mating types used were two purebred, two F1, two F2, two F3, and four backcross. Carcass data were collected on 238 barrows and 262 gilts over four replications. Traits measured were length (LENG), 10th rib off midline backfat (BF10), longissimus muscle area (LMA), and dressing percentage (DRS%). Average backfat (AVBF) was calculated as the mean of three midline fat depths measured opposite the first rib, last rib, and last lumbar vertebra. The model used to evaluate the carcass traits included main effects of mating type, farrowing season, and sex and included slaughter weight as a covariate. The performance traits of ADG, feed efficiency (FE), daily feed consumption (DFC), lean gain per day (LNGN), and lean efficiency (LNEF) were measured on a pen basis. Comparisons of reciprocal F1 crosses showed that carcasses from pigs sired by Hampshire boars were leaner and had more LMA than those sired by Landrace boars. Heterosis percentages were significant for AVBF (7.2%; P less than .01), BF10 (8.8%; P less than .01), DRS% (1.5%; P less than .01), ADG (11.5%; P less than .01), DFC (10.2%; P less than .01), LNGN (10.6%; P less than .01), and LNEF (6.0%; P less than .05). Epistatic recombination losses in the offspring were significant for LENG (3.6 cm; P less than .05) and approached significance for BF10 (6.1 mm; P less than .10). 相似文献
35.
L. AUDIGÉ 《Australian veterinary journal》1992,69(11):268-271
Blood samples were collected from 91 rusa deer (Cervus timorensis russa), immediately after being shot. Serum mean biochemical values from shot deer are presented for blood urea nitrogen, creatinine, creatine kinase, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, total protein, albumin, calcium, and phosphorus. Mean total protein and albumin increased with age. There was an age-associated increase of gamma globulins. Mean creatine kinase activity and creatinine, albumin and phosphorus concentrations were higher in stags than in hinds. Pregnant hinds had lower mean creatine kinase activity and phosphorus and higher mean alanine aminotransferase and total protein than non-pregnant hinds. Mean calcium concentration increased when deer were agitated before bleeding. 相似文献
36.
Little is known about the effect of fertilization on the N uptake of sunflowers. A 42 factorial trial with 0, 60, 120 and 180 kg N ha−1 and 0, 15, 30 and 45 kg P ha−1 was conducted over three years. The N content and concentration of leaves, stems and capitula were determined at three growth stages. High N levels increased the N content and concentration of all plant parts at all growth stages sharply. High P levels increased the N content of all plant components through better growth. P has an inconsistent effect on N concentration but tended to decrease it. After flowering the crop assimilated 20 to 25 % of the total N. This implies that N applied can still be applied and utilized by the crop at a late stage. This should be substantiated by further research. 相似文献
37.
A survey on coccidial infections in goats from central Spain was carried out. Fifty-five goat farms from 28 localities belonging to the three bioclimatic subregions of the area were visited. Individual samples (702) were obtained from the rectum of 130 young (under 1 year of age) and adult (572 over 1 year of age) goats. Coproscopical analyses showed a 100% prevalence and a moderate average intensity (7606.48 +/- 17918.78 Eimeria oocysts per gram of faeces), although wide variations were seen among herds and among individuals within each goat flock. Statistical analysis showed a strong age-related reduction in oocysts output in goats up to 4 years of age. The intensity of coccidial infections (young and adult goats, herds) was independent of the prevailing bioclimatic conditions. Heavier infections in young goats were found in bigger herds, whereas adult goats from these same big flocks (over 300 animals) showed the lowest oocyst output. Under our conditions, neither the female restocking rate nor the age structure seemed to play a significant role in the intensity of the Eimeria infections. 相似文献
38.
39.
M T Zavy P E Juniewicz W A Phillips D L VonTungeln 《American journal of veterinary research》1992,53(4):551-557
The productivity and well-being of animals can be substantially affected by stress. This is particularly true in the case of beef calves that are subjected to a multitude of stressors over a short period during the first year of life. Perhaps the most often studied stress-responsive variable has been blood corticosteroid concentrations. Factors such as age, gender, genetics, and degree of prior experience, can influence how an animal perceives and responds to a given stressor. Few studies have tried to control these variables, and accordingly, many conflicting results have been published regarding the impact of various stressors on cortisol response. We measured baseline plasma cortisol concentration over a 44-day study in Bos indicus and Bos taurus calves. Plasma cortisol values in Bos indicus calves were higher (32.60 +/- 0.66 ng/ml) than values in calves of Bos taurus (25.81 +/- 0.76) breeding. A precipitous decrease in cortisol concentration was observed 7 days after transport stress in all calves. Baseline cortisol concentration did not provide any indication of the intensity of the various stressors. However, significant differences were readily observed after ACTH administration. On the basis of cortisol secretion, stresses of transport and weaning were similar and were the most stressful to calves, regardless of genotype. 相似文献
40.
Abstract. The effect of Medicago arborea on erosion on a burnt area was studied in experimental plots near Valencia, Spain, between 1989 and 1992. Its growth and development was studied, and its effect was compared with the natural vegetation (matorral) and bare soil. Medicago decreased soil loss by 41.7% and runoff by 25.7% compared with bare soil. However, under natural vegetation soil loss was 27.5% less than under Medicago. 相似文献