全文获取类型
收费全文 | 132249篇 |
免费 | 7635篇 |
国内免费 | 80篇 |
专业分类
林业 | 6204篇 |
农学 | 4879篇 |
基础科学 | 873篇 |
16828篇 | |
综合类 | 18600篇 |
农作物 | 4849篇 |
水产渔业 | 7176篇 |
畜牧兽医 | 70915篇 |
园艺 | 1717篇 |
植物保护 | 7923篇 |
出版年
2019年 | 1289篇 |
2018年 | 2186篇 |
2017年 | 2471篇 |
2016年 | 2310篇 |
2015年 | 1957篇 |
2014年 | 2377篇 |
2013年 | 5374篇 |
2012年 | 4122篇 |
2011年 | 5006篇 |
2010年 | 3288篇 |
2009年 | 3241篇 |
2008年 | 4778篇 |
2007年 | 4550篇 |
2006年 | 4436篇 |
2005年 | 3904篇 |
2004年 | 3727篇 |
2003年 | 3765篇 |
2002年 | 3457篇 |
2001年 | 4901篇 |
2000年 | 4683篇 |
1999年 | 3715篇 |
1998年 | 1469篇 |
1997年 | 1500篇 |
1996年 | 1320篇 |
1995年 | 1512篇 |
1994年 | 1337篇 |
1993年 | 1315篇 |
1992年 | 2774篇 |
1991年 | 2932篇 |
1990年 | 2922篇 |
1989年 | 2796篇 |
1988年 | 2549篇 |
1987年 | 2563篇 |
1986年 | 2518篇 |
1985年 | 2372篇 |
1984年 | 1946篇 |
1983年 | 1609篇 |
1982年 | 1132篇 |
1979年 | 1703篇 |
1978年 | 1316篇 |
1976年 | 1119篇 |
1975年 | 1206篇 |
1974年 | 1408篇 |
1973年 | 1376篇 |
1972年 | 1345篇 |
1971年 | 1288篇 |
1970年 | 1279篇 |
1969年 | 1214篇 |
1968年 | 1090篇 |
1967年 | 1146篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
992.
993.
Indirect hemagglutination for Eperythrozoon suis detection in experimentally and spontaneously infected swine 总被引:5,自引:0,他引:5
G Baljer K Heinritzi L Wieler 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(6):417-423
Ten splenectomized and non-splenectomized pigs were experimentally infected with E. suis bearing red blood cells in order to determine the antibody response. All animals were monitored for antibody titer by indirect hemagglutination over a period of 80-290 days postinfection. Latent E. suis infection only yielded a detectable antibody titer in one pig. Acutely infected pigs had a titer ranging up to 1:640. Maximum antibody response lasted only 2 months and dropped below the level of detection of our assay within 2 to 3 months. At this time, the clinical symptoms could reappear and antibodies were again detectable. However, no booster effect was observed with this second outbreak. We also determined the antibody frequency in 138 pigs from 16 herds in Southern Germany. Pigs from only 4 out of 6 clinically positive herds had antibody titer against E. suis. 20 out of 78 pigs of the clinical positive herds demonstrated a detectable E. suis antibody titer. In 10 herds that were asymptomatic and presumed uninfected all 80 pigs were serologically negative for E. suis. 相似文献
994.
Comparison of bovine and human platelet deformability, using micropipette elastimetry 总被引:2,自引:0,他引:2
We evaluated the deformability of bovine platelets and contrasted the effects of pharmacologic and thermal perturbations on cytoskeletal structure of human and bovine platelets. Platelets were aspirated into micropipettes (0.7 to 0.8 micron in diameter) by stepwise increments in tension. The resulting lengths of the cell extensions were recorded. The cell extensions aspirated from bovine platelets were shorter than the extensions drawn from human platelets. Disassembly of the circumferential microtubule coil allowed human platelets to pass through the pipette, but the same treatments only slightly increased the deformability of bovine platelets. Alteration of the actin filament cytoskeleton caused increased mechanical fragility of human platelets. In contrast, even the combined use of microtubule and actin filament-disrupting agents only modestly increased the deformability of bovine platelets and did not cause premature fragmentation of the cells. Unusual cytoskeletal structure, absence of an open canalicular system, and disparity in granule size may all contribute to the variance in deformability between the platelets of the 2 species. Reduced cell deformability may impair bovine platelet surface interactions by diminishing the ease of cell spreading and formation of areas of contact between the platelet and other cell surfaces. 相似文献
995.
M Ulbrich C Geissler S M Bassuny F Borowiec M Hoffmann 《Archives of Animal Nutrition》1989,39(6):553-562
In an N balance experiment with male crossbreeding lambs at an age of 3 ... 4 months four different rations were given differing in energy concentration (high greater than 700 EFU cattle/kg DM and low less than 650 EFU cattle/kg DM) and in the energy source (sugar, starch or crude fibre) with crude protein intake being almost equal. The rations contained 2% urea. Microbial protein synthesis in the rumen was assessed according to ROTH and KIRCHGESSNER (1978) (1), RYS et al. (1975) (2) and BICKEL-BAUMANN and LANDIS (1986) (3) on the basis of allantoin excretion in urine. The highest ruminal protein synthesis quotas were 868 ... 921 mg protein N per kg LW0.75 in (2). In (3) 723 ... 766 mg protein N/kg LW0.75 were synthesized. From the 15N labelling of the supplemented urea and the excreted allantoin it could be calculated that 26 ... 40% of the microbial protein resulted from the urea-N of the ration. Despite a high crude protein content of the ration of between 16 and 17% in the DM and a relation of NPN: pure protein of 0.95 the utilization of the NPN in the ration was relatively high but slightly lower than the utilization of pure protein. The variants with higher energy concentration showed as a tendency higher allantoin excretion in spite of slightly lower dry matter intake and a slightly higher NPN utilization than the variants with lower energy concentration. 相似文献
996.
Myenteric ganglioneuritis and encephalomyelitis were diagnosed in an umbrella cockatoo. The cockatoo exhibited clinical signs that were milder than those associated with this syndrome, such as anorexia, muscle wasting, regurgitation, depression, and changes in fecal consistency. The gross lesions also differed from earlier reports in that only the duodenum and proximal jejunum were grossly dilated. Normally the proventriculus and ventriculus are dilated without visible intestinal changes. The histopathological lesions, however, such as perivascular cuffs in the brain stem and muscular mass of the ventriculus and proventriculus, were similar to earlier reports. A virus was suspected, although transmission and isolation of a virus has not occurred in other reports and was not attempted in this case. 相似文献
997.
Polarised light biomicroscopy was used to examine the normal pre-corneal tear film in 21 eyes of 12 pekingese dogs. The purpose of the study was to examine the influence of excessive exophthalmos on the pre-corneal tear film in the dog. The majority of the animals were found to have high levels of ocular surface contamination by particulate material and plaques of viscous mucus. Other abnormalities included surface lipid with an abnormal granular (three dogs) or 'curdled' (two dogs) appearance; excessive thinning of the lipid layer of the tear film; and the presence of dark globular structures in two dogs, which were presumed to be abnormal meibomian lipid. Break up of the tear film was observed in one dog. Grossly, a thread of viscous mucus was frequently observed along the margin of the lower eyelid. It is postulated that this thread forms because of the excessively exophthalmic conformation of the breed, which prevents the normal access of effete mucus and entrapped debris to the lower conjunctival fornix. The combination of the above factors in the pekingese is suggested as the mechanism whereby the tear film has a reduced stability, thus enhancing the risk from factors more usually considered to initiate corneal ulceration in the breed. The possible adverse effects of lid splitting for the mass removal of distichiae in exophthalmic dogs is discussed. 相似文献
998.
Blood bactericidal assay (Pasteurella haemolytica) comparison of morbidity in marketed feeder calves 总被引:2,自引:0,他引:2
An in vitro bactericidal assay that used bovine heparinized blood was investigated for its usefulness in detecting differences in the bactericidal immunity of calves against Pasteurella haemolytica serotype 1 (Ph1). Greater than 90% of killing occurred within 30 minutes. The substitution of fetal calf serum for autologous calf plasma caused loss of bactericidal activity of the blood. Decomplemented calf serum also was low in bactericidal activity. The blood bactericidal assay appears to be opsonin antibody-dependent and complement-dependent. The coefficient of variation (CV) that can be expected with this assay was established by use of a group of 8 calves; within-day CV maximum was 0.9, and between-day CV maximum was 2.1. The blood bactericidal assay was used to evaluate 30 calves under typical market stress from 4 farms in eastern Tennessee. All calves had decreased bactericidal activity, as they moved into a feedyard in Texas. The bactericidal activity was reduced among sick calves, based on the severity of clinical signs. Morbidity was highest during the first 14 days in the feedlot. During this period, healthy calves had a decreased bactericidal index (BI) of 4 points, and calves with clinical signs of bovine respiratory tract disease for 3 days had a decreased BI of 8 points. The average reduction in the BI of calves with clinical signs of bovine respiratory tract disease for 6 or more days was 14 points. 相似文献
999.
S W Dow C R Curtis R L Jones W E Wingfield 《Journal of the American Veterinary Medical Association》1989,195(1):113-117
Of 100 critically ill dogs and cats, 49 (39 dogs, 10 cats) had bacteremia. Gram-negative bacilli were the most common isolates from the bloodstream of dogs with bacteremia (46%), and gram-positive cocci and anaerobic bacteria were isolated from 36% and 31% of positive cultures, respectively; 15% of positive cultures were polymicrobial. In cats, gram-negative bacilli (especially Salmonella enteritidis) and anaerobic bacteria were the most common isolates, and 30% of positive cultures were polymicrobial. Gram-positive cocci were not isolated from the blood-stream of cats. Odds ratios, adjusted for the combined effects of disease status (severe vs nonsevere), results of bacterial culture of blood result (positive vs negative), and species (dog vs cat) were calculated for mortality in animals in the study. In animals with bacteremia, severe disease increased the risk of death 11.6-fold, compared with the risk in animals with nonsevere disease. Bacteremia increased mortality 10-fold in animals with severe disease, compared with mortality in animals with severe disease without bacteremia. Animals with severe disease and bacteremia were 15.6 times more likely to die than were those with nonsevere disease and negative culture results. In animals with nonsevere disease, culture results (positive vs negative) were not related significantly to mortality. Disease status (severe vs nonsevere) in animals without bacteremia also was not significantly related to mortality. There was no significant difference in overall mortality in dogs, compared with that in cats.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
1000.
事实上,变形血原寄生虫和伊氏锥虫是苏拉病的病原体。然而,苏拉病并不仅限于动物中存在。最近,在印度报道人也感染这种流行病,从而确立了它在人畜共患病上的重要地位。这说明,兽医和临床医师在处理疑似苏拉病畜中负有责任。因此,有必要了解此病在疑似病畜中的流行性,进而在不同地区制定针对此病的有效防控方案。然而, 相似文献