全文获取类型
收费全文 | 135641篇 |
免费 | 7787篇 |
国内免费 | 70篇 |
专业分类
林业 | 5576篇 |
农学 | 4644篇 |
基础科学 | 862篇 |
17488篇 | |
综合类 | 18959篇 |
农作物 | 5087篇 |
水产渔业 | 7089篇 |
畜牧兽医 | 72970篇 |
园艺 | 1798篇 |
植物保护 | 9025篇 |
出版年
2020年 | 1171篇 |
2019年 | 1410篇 |
2018年 | 2229篇 |
2017年 | 2489篇 |
2016年 | 2295篇 |
2015年 | 1999篇 |
2014年 | 2451篇 |
2013年 | 5731篇 |
2012年 | 4350篇 |
2011年 | 5164篇 |
2010年 | 3502篇 |
2009年 | 3548篇 |
2008年 | 5152篇 |
2007年 | 4970篇 |
2006年 | 4644篇 |
2005年 | 4263篇 |
2004年 | 4108篇 |
2003年 | 4175篇 |
2002年 | 3808篇 |
2001年 | 4774篇 |
2000年 | 4641篇 |
1999年 | 3747篇 |
1998年 | 1471篇 |
1997年 | 1452篇 |
1996年 | 1341篇 |
1995年 | 1600篇 |
1994年 | 1328篇 |
1993年 | 1359篇 |
1992年 | 2762篇 |
1991年 | 2901篇 |
1990年 | 2866篇 |
1989年 | 2897篇 |
1988年 | 2610篇 |
1987年 | 2592篇 |
1986年 | 2539篇 |
1985年 | 2400篇 |
1984年 | 1956篇 |
1983年 | 1715篇 |
1982年 | 1154篇 |
1979年 | 1649篇 |
1978年 | 1284篇 |
1977年 | 1135篇 |
1976年 | 1100篇 |
1975年 | 1164篇 |
1974年 | 1357篇 |
1973年 | 1448篇 |
1972年 | 1378篇 |
1971年 | 1195篇 |
1970年 | 1247篇 |
1969年 | 1146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Braden KW Blanton JR Montgomery JL van Santen E Allen VG Miller MF 《Journal of animal science》2007,85(3):754-768
Two hundred crossbred cattle (Bos indicus x Bos taurus) were supplemented with 2% Tasco (Ascophyllum nodosum) in a commercial finishing facility to evaluate marbling score, USDA quality grade, sensory traits, and retail display shelf life. Treatment animals (n = 100) received a steam-rolled corn (Zea mays)-based diet containing 2% Tasco meal (DM basis), for 14 d beginning at d 45 of the finishing period and again 14 d before slaughter. Control animals (n = 100) received a steam-rolled corn (Zea mays)-based diet without Tasco at identical feeding periods. Carcasses from Tasco-fed cattle exhibited greater marbling scores (P = 0.003) than controls. There were no treatment effects (P > 0.05) on sensory, shear, or purge attributes of striploin or inside round steaks with the exception of inside round steaks from Tasco animals having a greater initial tenderness (P = 0.03) and lower off-flavor score (P = 0.002) than control steaks. The LM samples from Tasco-fed cattle had a greater percentage of ether extractable fat (P = 0.001) and lower percentage of protein (P = 0.001) than controls. Inside round samples from treated animals exhibited a greater percentage of moisture (P = 0.03) than control steaks. Visual lean color of striploin steaks was not affected by Tasco supplementation (P = 0.26); however, steaks from Tasco-treated animals were more uniform and had less discoloration and browning than those from controls (P = 0.005, 0.04, and 0.05, respectively). Inside round visual scores and instrument values reflected similar treatment responses (P < 0.05), with a majority of the effects on muscle redness (CIE a*, hue angle) and measures of discoloration. Tasco steaks were generally more red and less discolored during extended postmortem aging and retail exposure (P < 0.05). The results from this study indicate that short-term supplementation of 2% Tasco meal in feedlot cattle increases carcass quality and prolonged retail shelf life. 相似文献
992.
993.
Veterinary public health (VPH) issues have received increased attention over the last few years as a result of the rising threat of emerging zoonoses (i.e., those due to globalized trade in animal and animal products and to changes in livestock production systems and the environment). The international dimension of VPH is gradually becoming recognized, and there is a growing need for veterinarians with experience in this field. In order to familiarize (future) veterinarians with the international dimension of VPH, the Department of Public Health and Food Safety of the Faculty of Veterinary Medicine, Utrecht University, has been organizing a course in Veterinary Public Health and Animal Production for over the last 10 years. This course has been intended for Dutch as well as foreign final-year veterinary students and recent veterinary graduates. By bringing together participants from different countries, the course reinforces the international dimension of the issues addressed through the exchange of experiences by the participants themselves. The present article provides information about this course on Veterinary Public Health (VPH): it discusses logistics, didactical approaches, the course program, and the use of information and communication technology (ICT). Special attention is given to the intercultural aspects of higher education, all of which play an important role in the efficient exchange of knowledge between lecturers and students. International courses are an important tool to enable participants to interact in a multicultural environment and address issues that demand international cooperation and a global public health focus. 相似文献
994.
Canine monocytic ehrlichiosis (CME) is a tick-borne disease caused by the rickettsia Ehrlichia canis. Ocular lesions are a common feature of the disease and can be present in all stages. The purpose of this retrospective study was to determine the prevalence, type and response to treatment of ocular lesions associated with monocytic ehrlichiosis in 46 affected dogs presented to the Autonomous University of Barcelona-Veterinary Teaching Hospital (UAB-VTH) from January 2000 to December 2002. Dogs were included in the study only if they had a positive serologic test for E. canis and information about the clinical outcome was available. Eighteen breeds were represented, with the German Shepherd dog (n = 6) being the most common. There were 25 intact and three castrated males, and 16 intact and two neutered females. Twenty dogs (43.4%) were between 5 and 10 years old. Seventeen dogs (37% of all cases of monocytic ehrlichiosis diagnosed during the study period) had ocular signs, and 11 dogs (64.7% of the ocular cases) had only ocular lesions without apparent systemic signs. Exudative retinal detachment was the most common ocular manifestation; other prevalent findings included anterior exudative uveitis and optic neuritis. Five of the 17 cases with ocular lesions (29.4%) had ocular bleeding disorders (hyphema or retinal hemorrhages). All the dogs with ocular disease presented with bilateral signs. Dogs with posterior segment disease had titers against E. canis that were > or = 1 : 320, while lower titers were noted in dogs with anterior exudative uveitis. Two dogs presented with chronic autoimmune panuveitis after ehrlichiosis treatment. Canine ehrlichiosis should be considered in the differential diagnosis of exudative retinal detachment and anterior uveal inflammatory lesions. 相似文献
995.
996.
997.
Monoclonal antibodies identify phenotypically and functionally distinct cell types in the bovine lymphoid system 总被引:16,自引:0,他引:16
P A Lalor W I Morrison B M Goddeeris R M Jack S J Black 《Veterinary immunology and immunopathology》1986,13(1-2):121-140
Monoclonal antibodies were produced against bovine lymphoid cells. The reactivities of the antibodies for membrane determinants were examined on both cell suspensions and cryostat tissue sections prepared from bovine blood, thymus, spleen and lymph nodes. The antibodies were putatively grouped into sets which reacted with monomorphic and polymorphic determinants associated with bovine class I and class II major histocompatibility complex (MHC) antigens (MAbs P12 and P3, and R1 and P2 respectively), or associated with differentiation antigens expressed on T cells and monocytes (MAb P5) or exclusively on monocytes (MAb P8). The antibodies were used to identify the surface phenotypes of cells which stimulate (R1+ P5+ P8+) and proliferate (R1- P5+ P8-) in the bovine mixed leukocyte cultures, and cells which proliferate in response to the mitogen, concanavalin A (R1- P5+). 相似文献
998.
R M Roberts 《The Veterinary record》1986,118(18):505-507
Of 1140 vaginal mucus agglutination tests (VMAT) on specimens obtained in 1971-72 from 663 dairy cows in seven herds infected with brucellosis, 97 were positive. When the VMAT was positive one or more serological tests were also positive. Of the 97 corresponding serum agglutination tests 80 sera had titres of more than 533 international units. Only 69.8 per cent of VMAT from serologically positive cows were positive. No evidence was found of non-specific agglutinins in vaginal mucus and positive VMAT reactions appeared to be specific for field infection. Three cows showed evidence of local agglutinins in the vagina. Hence herd testing by VMAT has no advantage over tests of blood serum but the test could be an aid in establishing whether individual cattle are infected. 相似文献
999.
The efficiency of utilization of feed energy as digestible, metabolizable and net energy is similar in pregnant and lactating sows irrespective of the stage of these physiological conditions. This efficiency with the value of about 71% resembles the one found in the growing and fattening pigs, which enables us to use, for this category of animals, the same system offered evaluation and of the energy requirements based on fat nutritive units. The maintenance energy requirement expressed in ME varies from 467 kJ/kg 0.75 in pregnant sows to 512 kJ/kg 0.75 in lactating sows, for the suckling piglets having intermediary value of 498 kJ/kg 0.75. The efficiency of utilization of diets protein for maintenance and for synthesis is also similar for these categories of pigs, varying from 71% in lactating sows to 75-76% in pregnant sows. In suckling piglets we had recorded an efficiency of DCP utilization which varies parabolically with size of the ingesta and therefore with that of weight gain. The DCP maintenance requirement expressed in g N dig./kg 0.75 varies within narrow limits between 0.345 g N in suckling piglets 0.380 g N in pregnant sows; In lactating sows we have detected an intermediary value of 0.355 g N. Based on these experimental data and also using recent experimental results obtained by Schiemann and Beyer (1984) regarding the energy and N content of the foetuses, of the organs of reproductions and of milk, we could calculate the energy and protein requirements. These requirements when compared with the values used in our country show us higher values of energy in pregnant and lactating sows and lower values of protein for the same categories, including the piglets, where we have also found lower values for the energy too. 相似文献
1000.
Luminol-dependent chemiluminescence of peripheral blood lymphocytes from dogs stimulated with concanavalin A (Con A) or phytohemagglutinin P (PHA) was measured with a Pico-Lite luminometer. 10 microliter of luminol gave optimal quantum yield from 1 X 10(6) lymphocytes sensitized with either 80 micrograms Con A or 160 micrograms PHA. Addition of superoxide dismutase did not influence the course of chemiluminescence. Whereas catalase produced 41% increase in quantum yield, mannitol caused a 51% inhibition of chemiluminescence. Lymphocytes exposed to varying doses of short term x-irradiation or lymphocytes isolated from dogs kept under continuous exposure through a gamma irradiation source showed dose-related depression of chemiluminescence. Membrane factors may be involved in lymphocyte stimulation to chemiluminescence as pulse experiments with Con A and PHA revealed. It is proposed that chemiluminescence measurements may be useful in monitoring early events in lymphocyte stimulation by antigens and mitogens. 相似文献