全文获取类型
收费全文 | 129681篇 |
免费 | 7662篇 |
国内免费 | 801篇 |
专业分类
林业 | 5272篇 |
农学 | 4014篇 |
基础科学 | 917篇 |
15177篇 | |
综合类 | 24712篇 |
农作物 | 4678篇 |
水产渔业 | 6005篇 |
畜牧兽医 | 67791篇 |
园艺 | 1726篇 |
植物保护 | 7852篇 |
出版年
2019年 | 1341篇 |
2018年 | 1995篇 |
2017年 | 2203篇 |
2016年 | 1985篇 |
2015年 | 1875篇 |
2014年 | 2107篇 |
2013年 | 5007篇 |
2012年 | 4060篇 |
2011年 | 4940篇 |
2010年 | 3249篇 |
2009年 | 3132篇 |
2008年 | 4484篇 |
2007年 | 4356篇 |
2006年 | 4000篇 |
2005年 | 3755篇 |
2004年 | 3440篇 |
2003年 | 3538篇 |
2002年 | 3351篇 |
2001年 | 3820篇 |
2000年 | 3857篇 |
1999年 | 3031篇 |
1998年 | 1283篇 |
1997年 | 1190篇 |
1995年 | 1263篇 |
1994年 | 1147篇 |
1993年 | 1136篇 |
1992年 | 2478篇 |
1991年 | 2775篇 |
1990年 | 2609篇 |
1989年 | 2586篇 |
1988年 | 2410篇 |
1987年 | 2412篇 |
1986年 | 2491篇 |
1985年 | 2349篇 |
1984年 | 1978篇 |
1983年 | 1741篇 |
1982年 | 1167篇 |
1979年 | 1794篇 |
1978年 | 1423篇 |
1977年 | 1274篇 |
1976年 | 1306篇 |
1975年 | 1367篇 |
1974年 | 1694篇 |
1973年 | 1688篇 |
1972年 | 1625篇 |
1971年 | 1493篇 |
1970年 | 1500篇 |
1969年 | 1420篇 |
1968年 | 1208篇 |
1967年 | 1255篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
J W McBride R E Corstvet D B Paulsen J R McClure F M Enright 《American journal of veterinary research》1992,53(10):1889-1894
Systemic and pulmonary antibody responses of calves to Pasteurella haemolytica were evaluated by measuring immunoglobulin production in blood for 9 days and in pulmonary lavage fluid for 7 days after intrapulmonary inoculation. Clinical signs, pulmonary lesions, pulmonary and systemic inflammatory response, and amount of antigen in lavage fluid were used to evaluate the response of calves to challenge with P haemolytica. The pulmonary response consisted of production of IgG, IgE, and IgM antibodies to P haemolytica antigens and a 17- to 68-fold increase of cells in lavage fluid 8 hours after inoculation, with a gradual decrease toward normal. Antibodies of the IgM isotype to P haemolytica were demonstrated as early as 8 hours through 7 days after inoculation in 3 of 3 calves. Of the anti-P haemolytica isotypes, IgM was found in the highest concentration. In all of the inoculated calves, IgE was found 1 to 2 days after inoculation, and IgG was found in 2 of 3 inoculated calves from day 1 through 7 after inoculation. Detection of IgG correlated with smaller pulmonary lesions. Immunoglobulin A was not detected in lavage fluid. Serum was evaluated for IgG and IgM antibody response to P haemolytica. Specific IgM was detectable 5 days after inoculation, and IgG was detectable 7 days after inoculation. Pasteurella haemolytica antigens were not detected in serum or plasma. A transient increase in neutrophil count was found 8 hours after inoculation, with return to baseline values by 24 hours after inoculation.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
42.
The pyrimidine analog 5-bromodeoxyuridine (BUdR) competes with thymidine for incorporation into DNA. Substitution of BUdR for thymidine does not significantly affect cell viability but does block cell differentiation in many different lineages. BUdR substitution in a mouse myoblast line blocked myogenic differentiation and extinguished the expression of the myogenic determination gene MyoD1. Forced expression of MyoD1 from a transfected expression vector in a BUdR-substituted myoblast overcame the block to differentiation imposed by BUdR. Activation of BUdR-substituted muscle structural genes and apparently normal differentiation were observed in transfected myoblasts. This shows that BUdR blocks myogenesis at the level of a myogenic regulatory gene, possibly MyoD1, not by directly inhibiting the activation of muscle structural genes. It is consistent with the idea that BUdR selectively blocks a class of regulatory genes, each member of which is important for the development of a different cell lineage. 相似文献
43.
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
44.
45.
46.
47.
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
48.
A strain of Yersinia enterocolitica of O serogroup 6,30 isolated from the liver of an aborted ovine fetus was inoculated intravenously into a group of pregnant ewes at about 90 days gestation and produced placentitis with abortion or delivery of infected lambs about 50 days later. Y. enterocolitica of the same serogroup was recovered from the necrotic placental cotyledons and most other fetal tissues and could be isolated from vaginal discharges of the ewes for a least 2 weeks after abortion. Histological changes were consistent with an acute bacterial necrotizing placentitis and systemic infection of the fetus. Subsequent pregnancies in the ewes proceeded to term without evidence of infection. 相似文献
49.
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
50.
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