全文获取类型
收费全文 | 5618篇 |
免费 | 340篇 |
国内免费 | 205篇 |
专业分类
林业 | 289篇 |
农学 | 428篇 |
基础科学 | 76篇 |
998篇 | |
综合类 | 802篇 |
农作物 | 367篇 |
水产渔业 | 378篇 |
畜牧兽医 | 2167篇 |
园艺 | 135篇 |
植物保护 | 523篇 |
出版年
2023年 | 33篇 |
2022年 | 53篇 |
2021年 | 97篇 |
2020年 | 86篇 |
2019年 | 103篇 |
2018年 | 131篇 |
2017年 | 156篇 |
2016年 | 159篇 |
2015年 | 125篇 |
2014年 | 157篇 |
2013年 | 252篇 |
2012年 | 280篇 |
2011年 | 312篇 |
2010年 | 257篇 |
2009年 | 234篇 |
2008年 | 314篇 |
2007年 | 293篇 |
2006年 | 249篇 |
2005年 | 241篇 |
2004年 | 214篇 |
2003年 | 270篇 |
2002年 | 334篇 |
2001年 | 325篇 |
2000年 | 195篇 |
1999年 | 148篇 |
1998年 | 40篇 |
1997年 | 45篇 |
1996年 | 37篇 |
1995年 | 48篇 |
1994年 | 45篇 |
1993年 | 37篇 |
1992年 | 47篇 |
1991年 | 40篇 |
1990年 | 54篇 |
1989年 | 51篇 |
1988年 | 34篇 |
1987年 | 39篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 52篇 |
1983年 | 28篇 |
1982年 | 26篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 28篇 |
1977年 | 27篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1972年 | 30篇 |
1971年 | 37篇 |
排序方式: 共有6163条查询结果,搜索用时 15 毫秒
41.
The pupal morphology of the pest species Cameraria ohridella is described and compared with that of the genus Phyllonorycter. The most striking differences are the longer antennal appendages, the absence of a cremaster, the presence of strong lateral thorns on abdominal segments 1–5 and an area without small spines on the same abdominal segments in Cameraria. 相似文献
42.
S. S. De Silva U. S. Amarasinghe & C. Nissanka W. A. D. D. Wijesooriya & M. J. J. Fernando 《Fisheries Management and Ecology》2001,8(1):47-60
Use of geographical information systems (GIS) in inland fisheries has hitherto been essentially restricted to site evaluation for aquaculture development and assessment of limnological changes in time and space in individual water bodies. The present GIS study was conducted on the land-use pattern of the catchments of nine reservoirs in Sri Lanka, for which detailed fishery data, viz. yield, fishing intensity, landing size of major constituent species, together with selected limnological data such as conductivity and chlorophyll- a , were available. Potential statistical relationships (linear, curvilinear, exponential and second-order polynomial) of fish yield ( FY , in kg ha−1 yr−1 ) to different land-use patterns, such as forest cover ( FC , in km2 ) and shrub-land ( SL , in km2 ), either singly, or in combination, and/or the ratio of each land type to reservoir area ( RA in km2 ) and reservoir capacity ( RC in km3 ), were explored. Highly significant relationships were evident between FY to the ratio of SL and/or FC + SL to RA and/or RC . Similarly, the above land-use types to RA and RC ratios were significantly related to limnological features of the reservoirs. The relationships of FY to various parameters obtained in this study were much better correlated than those relationships of FY to limnological and biological parameters used in yield prediction in tropical and temperate lacustrine waters previously. 相似文献
43.
邱德玉 《四川畜牧兽医学院学报》2005,3(4):5-8
文化底蕴越是丰厚的旅游资源,开发价值就越高。正是众多文人贤士游剡访古,使浙东剡溪的历史、文化与自然山水完美地结合在一起,形成了绚丽多彩的剡溪山水文化。文化被认为是旅游业的灵魂,是一种潜在的旅游产品。要提高山水旅游产品的文化品位,必须将山水文化的潜在价值转化为旅游产品。本文对剡溪山水文化旅游资源的开发提出了以下设想:再现“唐诗之路”山水旅游美景,并着重于按唐诗及有关文献、传说等增添新景点,沿江、沿山、于水中进行山水、文化全面开发,形成立体式、全景式的剡中山水文化游道;可开发出文化生态、修学、科考、宗教、节庆等剡溪山水文化旅游产品。 相似文献
44.
45.
Competitive enzyme-linked immunosorbent assay for heartwater using monoclonal antibodies to a Cowdria ruminantium-specific 32-kilodalton protein 总被引:7,自引:0,他引:7
F Jongejan M J Thielemans M De Groot P J van Kooten B A van der Zeijst 《Veterinary microbiology》1991,28(2):199-211
Hybridomas producing monoclonal antibodies (mAb) to Cowdria ruminantium were raised. Four mAbs of the IgG isotype reacted in western blots with a 32-kilodalton Cowdria protein (Cr32), which had previously been shown to be conserved and immunodominant. A fifth mAb of the IgM isotype recognized a 40-kDa Cowdria protein. The latter mAb was negative in an indirect fluorescent antibody test (IFA), whereas the other four were positive. mAb No. 4F10B4 showed the strongest signal in western blots using three different stocks of Cowdria. Immuno-gold labeling of Cowdria organisms in vitro using 4F10B4 showed that Cr32 has surface-exposed antigenic determinants. Using mAb 4F10B4, a competitive ELISA was developed which detected specific Cowdria antibodies in goat, sheep and cattle sera. Antibodies in animal sera competed with binding of mAb 4F10B4 to a crude sonicated Cowdria antigen obtained from infected endothelial cell cultures. The competition ELISA (CELISA) detected antibodies in 55 out of 70 (79%) goats experimentally infected with one of eight different Cowdria stocks. Fourteen out of the 15 sera which were shown negative in the CELISA were also negative in the IFA. Nevertheless, all 15 sera recognized some epitopes of the immunodominant Cowdria-specific 32 kDa protein as judged from their reaction with this protein in western blots. Overall, there was 89% agreement between CELISA and IFA considering all 70 goat sera. Moreover, antibodies were detected in nine out of nine sheep infected with one of three different stocks of Cowdria and in sera from calves experimentally infected by two different strains of heartwater. There were no cross-reactions with Ehrlichia phagocytophila antibodies in goat sera, nor with Anaplasma marginale antibodies in bovine sera. Lack of cross-reactivity and detection of antibodies to eight geographically widely distributed stocks of Cowdria, makes the competition ELISA a promising test for use in heartwater endemic areas. 相似文献
46.
A. Pratelli A. Cavalli G. Normanno M.G. De Palma G. Pastorelli V. Martella C. Buonavoglia 《Zoonoses and public health》2000,47(4):273-276
The results of vaccination trials carried out on pups with maternally derived antibodies (MDA) to canine parvovirus (CPV), using a modified‐live CPV‐2b variant vaccine (29‐97/40 strain), are reported. The vaccine was able to overcome the obstacle of MDA, and to elicit protective immunity in 100% of the pups whose antibody titres were 1:10–1:40, 83% of the pups with titres of 1:80, 57% of the pups with titres of 1:160, and even in 60% of the pups with antibody titres of 1:320. 相似文献
47.
E. Vandermeulen I. van Hoek C. De Sadeleer A. Piepsz H.R. Ham T. Bosmans A. Dobbeleir S. Daminet K. Peremans 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2008,22(2):266-272
Background: Chronic kidney failure is frequently seen in middle-aged and elderly cats. 51 Chromium-ethylene diaminic tetraacetic acid (51 Cr-EDTA) clearance and single blood sample (SBS) method are used in several species to estimate the glomerular filtration rate (GFR).
Hypothesis: The hypothesis of this study was that51 Cr-EDTA clearance could be determined using an SBS method in normal and hyperthyroid cats.
Animals: Forty-six cats were included in this study, with an average age of 9.5 years. Of these cats, 27 had hyperthyroidism; 19 were healthy.
Methods: After IV injection of51 Cr-EDTA (average dose: 4.25 MBq), 7 blood samples were obtained between 5 and 240 minutes. Reference clearance was calculated in mL/min and mL/min/kg body weight, using a 2-compartment model. Optimal time for clearance measurement with SBS was then determined by systematically comparing each individual plasma concentration to the reference multisample clearance.
Results: The average reference plasma clearance of51 Cr-EDTA for all cats was 14.9 mL/min (3.7 mL/min/kg). The clearance in hyperthyroid cats averaged 16.4 mL/min (4.3 mL/min/kg) and in normal cats averaged 10.3 mL/min (2.4 mL/min/kg).
The optimal time for the SBS was 48 minutes after injection of tracer51 Cr-EDTA ( R 2 = 0.9414), giving the following converting equation: clearance = (0.0066 × DV48 minutes ) – 0.9277 (in mL/min).
Conclusions and Clinical Importance: In this study, the single sample51 Cr-EDTA clearance method was used to estimate the global GFR in cats. The method identified differences in clearance between normal and hyperthyroid cats. The optimal time for an SBS was 48 minutes. 相似文献
Hypothesis: The hypothesis of this study was that
Animals: Forty-six cats were included in this study, with an average age of 9.5 years. Of these cats, 27 had hyperthyroidism; 19 were healthy.
Methods: After IV injection of
Results: The average reference plasma clearance of
The optimal time for the SBS was 48 minutes after injection of tracer
Conclusions and Clinical Importance: In this study, the single sample
48.
[目的]比较不同坐果期枣果实品质的差异,为提高枣的精细化管理水平提供科学依据.[方法]挂牌标记枣树的头蓬果、二蓬果、三蓬果,于果实脆熟期末采收.分别测定枣果实物理性状(单果重、果形指数、可食率、含水量、干物质量)和果实内含物含量(可溶性糖、还原糖、淀粉、VC、有机酸、蛋白质),采用TMS-Pro质构仪测定果实质地参数,并进行比较分析.[结果]枣头蓬果、二蓬果、三蓬果的大小、形状和可食部分干物质量均存在显著差异,并依次减小;二蓬果的VC、可溶性蛋白质、可溶性糖、有机酸、淀粉和还原糖含量均高于头蓬果、三蓬果的含量;供试材料不同坐果期枣果实质地各参数间也存在差异.[结论]不同坐果期枣果实品质存在较大差异,头蓬果和二蓬果品质优于三蓬果,采用疏果等措施可提高枣的商品性和经济效益. 相似文献
49.
土壤中硝态氮含量的影响因素研究 总被引:12,自引:0,他引:12
采用田间试验及人工渗滤池试验方法,研究了土壤中硝态氮含量的影响因素。结果表明,影响大田土壤中硝态氮因素很多,程度不一,其中土壤类型决定着硝态氮基础含量,是内因,而施肥及施氮量是影响硝态氮含量最大的外界因素,其次是土壤湿度和氮肥品种,土壤温度对其影响不明显。 相似文献
50.
Olivier M Aggarwal A Allen J Almendras AA Bajorek ES Beasley EM Brady SD Bushard JM Bustos VI Chu A Chung TR De Witte A Denys ME Dominguez R Fang NY Foster BD Freudenberg RW Hadley D Hamilton LR Jeffrey TJ Kelly L Lazzeroni L Levy MR Lewis SC Liu X Lopez FJ Louie B Marquis JP Martinez RA Matsuura MK Misherghi NS Norton JA Olshen A Perkins SM Perou AJ Piercy C Piercy M Qin F Reif T Sheppard K Shokoohi V Smick GA Sun WL Stewart EA Fernando J Tejeda Tran NM Trejo T Vo NT Yan SC Zierten DL Zhao S 《Science (New York, N.Y.)》2001,291(5507):1298-1302
We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases. 相似文献