全文获取类型
收费全文 | 72236篇 |
免费 | 3298篇 |
国内免费 | 34篇 |
专业分类
林业 | 5798篇 |
农学 | 3212篇 |
基础科学 | 449篇 |
10402篇 | |
综合类 | 9115篇 |
农作物 | 3904篇 |
水产渔业 | 5274篇 |
畜牧兽医 | 30351篇 |
园艺 | 1756篇 |
植物保护 | 5307篇 |
出版年
2021年 | 440篇 |
2020年 | 525篇 |
2019年 | 597篇 |
2018年 | 3710篇 |
2017年 | 3693篇 |
2016年 | 2213篇 |
2015年 | 939篇 |
2014年 | 1096篇 |
2013年 | 2272篇 |
2012年 | 2659篇 |
2011年 | 4307篇 |
2010年 | 3473篇 |
2009年 | 2580篇 |
2008年 | 3382篇 |
2007年 | 3561篇 |
2006年 | 1902篇 |
2005年 | 1826篇 |
2004年 | 1836篇 |
2003年 | 1810篇 |
2002年 | 1508篇 |
2001年 | 2091篇 |
2000年 | 2199篇 |
1999年 | 1629篇 |
1998年 | 622篇 |
1997年 | 528篇 |
1996年 | 483篇 |
1995年 | 644篇 |
1994年 | 548篇 |
1993年 | 493篇 |
1992年 | 1197篇 |
1991年 | 1241篇 |
1990年 | 1220篇 |
1989年 | 1145篇 |
1988年 | 1088篇 |
1987年 | 1110篇 |
1986年 | 1053篇 |
1985年 | 986篇 |
1984年 | 821篇 |
1983年 | 704篇 |
1982年 | 427篇 |
1979年 | 646篇 |
1978年 | 510篇 |
1977年 | 459篇 |
1975年 | 459篇 |
1974年 | 532篇 |
1973年 | 517篇 |
1972年 | 547篇 |
1971年 | 465篇 |
1970年 | 436篇 |
1969年 | 483篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
Improvement of both the tensile and impact strength of the same polymeric material has always been a great challenge for the plastic industry. The study focuses on the effect of incorporation of calcium carbonate nanoparticles (0.3 wt% to 15 wt%) into three polypropylene (PP) based matrices viz. PP homopolymer, propylene-ethylene (PP-PE) copolymer and the blend of PP:PP-PE (30:70) to improve their impact behavior without hampering the tensile strength much. A loss in both the tensile and impact properties was observed in PP based nanocomposite. However, PP-PE based nanocomposites showed a significant improvement in impact strength (47 %) at 10 wt% loading with a loss of tensile strength by 22 %. To minimize this loss a blend of PP:PP-PE (30:70) was explored as a matrix. At 10 wt% loading, this matrix showed an improvement of 30 % in impact strength whereas the tensile loss was minimized to 10 %. Further, silane coupling agent which promoted good interfacial adhesion was used for best compositions. The variation of crystalline morphology of the nanocomposites with various formulations was analyzed using differential scanning calorimetry and X-ray diffraction. 相似文献
33.
Alexander Jarryd Ehlers Smith David A. Ehlers Smith Yvette C. Downs Colleen T. 《Landscape Ecology》2019,34(3):537-549
Landscape Ecology - The effects of changing land use, and especially urbanisation, on species and functional diversity are of global concern. Eco-estates are a form of urban housing development... 相似文献
34.
Spyra Marcin Kleemann Janina Cetin Nuket Ipek Vázquez Navarrete Cesar Jesús Albert Christian Palacios-Agundez Igone Ametzaga-Arregi Ibone La Rosa Daniele Rozas-Vásquez Daniel Adem Esmail Blal Picchi Paolo Geneletti Davide König Hannes J. Koo HongMi Kopperoinen Leena Fürst Christine 《Landscape Ecology》2019,34(7):1715-1735
Landscape Ecology - Several case studies investigated the role of ecosystem services in participatory planning processes. However, no systematic study exists that cuts across a large number of... 相似文献
35.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably. 相似文献
36.
37.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus. 相似文献
38.
J A Ellis H Russell J Cavender T R Haven 《Veterinary immunology and immunopathology》1992,34(1-2):35-45
Cattle were immunized with vaccines containing modified-live or inactivated bovine respiratory syncytial virus (BRSV) and serum antibody responses were analyzed. Compared with preinculation values, at Day 14 after two biweekly immunizations with modified-live or inactivated vaccines there were significant increases in BRSV-specific titers in the sera of cattle that received both types of vaccines, as determined by a whole cell ELISA. Using a blocking ELISA and radioimmune precipitation it was determined that there was recognition of the fusion (F) protein by antibodies from cattle that received both types of BRSV antigens: however, virus neutralization assays revealed that only cattle that received modified live virus, either in monovalent or polyvalent vaccines, developed neutralizing antibodies to BRSV after two immunizations. These results indicate that inactivation of BRSV can lead to a dissociation between serological recognition of the F protein and virus neutralization in vaccinated cattle. 相似文献
39.
B Mermer P Hillman R Harris T Krogmann Q Tonelli W Palin P Andersen 《Veterinary immunology and immunopathology》1992,35(1-2):133-141
We have developed an antibody detection enzyme-linked immunosorbent assay (ELISA) for the identification of animals infected by feline immunodeficiency virus (FIV). The ELISA solid-phase antigen consists of recombinant FIV gag proteins expressed in bacteria. The proteins are purified from bacterial lysates as insoluble inclusion bodies. In the case of bacterially expressed p24gag, it is shown that all of the linear, sequential epitopes presented by viral p24 during infection are retained. Purified preparations can be substituted for solid-phase whole virus in the IDEXX PetChektm immunoassay. The antibody ELISA duplicates the sensitivity and specificity of the whole virus based PetChek plate assay. 相似文献
40.
A good correlation exists between specific neutralising antibody titre and protection against challenge with foot-and-mouth disease virus (FMDV) in infected or virus-vaccinated cattle, but not in the case of animals immunised with synthetic FMDV peptides. Therefore, mechanisms other than simple neutralisation are likely to be important in vivo. Antibody affinity may influence the protective capacity of sera from immunised animals and experiments were carried out to measure the functional affinity for synthetic FMDV peptide of sera from guinea pigs and cattle given various synthetic vaccines. In guinea pigs given a single dose of synthetic vaccine, antibody affinity increased with time after immunisation. In cattle, however, administration of a second dose of peptide 21 days after the first markedly retarded the process of affinity maturation. For guinea pig sera of equivalent neutralising activity, those of higher functional affinity had higher protective indices than those of lower functional affinity. Knowledge of the importance of antibody affinity in protection against FMD is important for an improved understanding of the mechanisms of protection and for the design of novel vaccines. 相似文献