首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   102181篇
  免费   6123篇
  国内免费   635篇
林业   3898篇
农学   3098篇
基础科学   811篇
  12684篇
综合类   19195篇
农作物   3789篇
水产渔业   4828篇
畜牧兽医   53086篇
园艺   1354篇
植物保护   6196篇
  2020年   924篇
  2019年   1164篇
  2018年   1641篇
  2017年   1944篇
  2016年   1716篇
  2015年   1566篇
  2014年   1821篇
  2013年   3671篇
  2012年   3457篇
  2011年   4168篇
  2010年   2828篇
  2009年   2693篇
  2008年   3850篇
  2007年   3673篇
  2006年   3288篇
  2005年   3137篇
  2004年   2789篇
  2003年   2886篇
  2002年   2687篇
  2001年   3118篇
  2000年   3160篇
  1999年   2444篇
  1998年   1019篇
  1997年   948篇
  1995年   967篇
  1992年   1892篇
  1991年   2148篇
  1990年   2000篇
  1989年   1924篇
  1988年   1803篇
  1987年   1865篇
  1986年   1875篇
  1985年   1722篇
  1984年   1474篇
  1983年   1251篇
  1982年   890篇
  1979年   1383篇
  1978年   1095篇
  1977年   924篇
  1976年   959篇
  1975年   1017篇
  1974年   1280篇
  1973年   1238篇
  1972年   1197篇
  1971年   1093篇
  1970年   1038篇
  1969年   1047篇
  1968年   884篇
  1967年   993篇
  1966年   930篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Summary The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the complement fixation test, DOT-ELISA, Western immunoblot and rapid card agglutination test. Dried blood on Whatman filter paper no. 1 was eluted in PBS 0·05% Tween 20 giving an initial dilution of 1∶10. The reactivity of the eluted samples in both DOT-ELISA and Western immunoblotting were similar to those obtained with the corresponding straight serum sample dilutions. Filter paper samples gave lower reactivity in the remaining tests when compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at temperatures ranging between 15·5 and 24°C and those kept refrigerated. Storage at 15·5 to 24°C did not significantly affect reactivity for up to six months. Eluates from filter papers stored for six months at 15·5 to 24°C continued to give similar reactivity as those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the rapid card agglutination test. It is concluded that collecting blood on filter papers is a suitable technique for large scale seroepidemiological studies on anaplasmosis and offers many advantages in developing countries where transport and cold chain facilities are a major constraint.
Resumen Se estudió la efectividad de muestras de sangre colectadas en papel filtro, en comparación con las correspondientes muestras convencionales du suero, en el diagnóstico de anaplasmosis bovina, utilizando fijación de complemento, DOT-ELISA, Western, immunoblot y la prueba rápida de la tarjeta. La sangre seca en papel Whatman No 1 fue removida con PBS 0·05% entre 20, dando una dilución inicial de 1∶10. La reactividad de las muestras removidas de papel filtro, en la prueba de DOT-ELISA y Western immunoblotting, fueron similares a la obtenida con la correspondiente muestra de suero. Las muestras de papel filtro reaccionaron menos en las otras pruebas, cuando se compararon con las correspondients muestras du suero. No hubo diferencia significativa en la reactividad entre los lavados del papel filtro guardados a temperaturas entre 15·5 y 24°C y aquellos guardados en refrigeración. El almacenaje entre 15·5 y 24°C, no afectó la reactividad hastas seis meses. Los lavados de papel filtro guardados por seis meses entre 15·5 y 24°C, dieron la misma reactividad como los lavados frescos, en la prueba DOT-ELISA y Western blot, lo mismo que en la prueba de aglutinación rápida de tarjeta. Se concluye, qu la colección de sangre en papel filtro, es una buena técnica para estudios epidemiológicos de cierta magnitud, sobre anaplasmosis, ofreciendo ventajas considerables en paises en desarrollo en donde las cadenas de frío son deficientes.

Résumé La fiabilité du sang récolté sur papier filtre comparée à celle des prélèvements conventionnels de sérum pour le diagnostic de l'anaplasmose a été étudiée à l'aide des tests suivants: fixation du complément, ELISA, immunoblot de Western, test rapide d'agglutination sur carte. Du sang séché sur papier filtre Whatman No 1 a fait l'object d'une élution dans une solution de PBS à 0,05 p. 100 (Tween 20) pour donner une dilution de base au dilution de base au 1∶10. Le réactivité des échantillons, autant avec le test ELISA que l'immunoblot Western, a été identique à celle obtenue par dilution directe de sérums homologue. Les échantillons sur papier filtre ont donné une réactivité plus faible pour les autres tests, comparée à celle des échantillons de sérum semblables. Aucune différence significative n'a été décelée quant à leur réactivité les éluats provenant de papiers filtres stockés à des températures comprises entre 15,5 et 24°C at ceux conservés au réfrigérateur. Le stockage entre 15,5 et 24°C n'a pas non plus affecté la réactivité de fa?on significative; les éluats conservés à partir des papiers filtres, à cette même température durant 6 mois, ont montré des réactions identiques que ceux provenant de papiers filtres fra?chement préparés, à la fois avec le test ELISA, celui de Western Blot et le test d'agglutination rapide sur carte. On peut conclure que la collecte du sang sur papier filtre est une technique adaptée à l'étude épidémiologique de l'anaplasmose à grande échelle. Elle offre de nombreux avantages dans les pays en développement où offre de nombreux avantages dans les pays en développement où les moyens de transports et la cha?ne du froid constituent des contraintes majeures.
  相似文献   
92.
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   
93.
94.
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   
95.
Ultrasonography and MRI have become valuable tools for imaging of tendon injuries. The current study examines the histopathologic basis for the imaging abnormalities. Five injured equine forelimbs and two normal contralateral limbs were studied with high resolution real time ultrasound and MRI. Histologic sections were made and correlated with the diagnostic images. All lesions were readily seen by both modalities. Lesions characterized by hemorrhage, edma, and cellular infiltration were sonolucent on ultrasound and bright on MRI images. MRI returned to normal as fibrogenesis ensued. Ultrasound images remained abnormal until fibrillar reallgnment occured with completion of the healing process. High resolution real time ultrasound and MRI both accurately reflect the tissue abnormalities in acute tendon injuries. The injured horse does appear to be an effective model for correlative imaging studies of tendon injuries.  相似文献   
96.
The conventional culture method was compared to coagglutination for detection of Actinobacillus (Haemophilus) pleuropneumoniae in 425 sets of pig lungs. Sera from the same animals were evaluated for antibodies to A. pleuropneumoniae by the complement fixation (CF) test. All samples were collected at 2 packing plants in Iowa. In 2 nonvaccinated herds with no history of respiratory disease, the difference between standard culture results and coagglutination was highly significant (P less than 0.001). None of the 57 pigs in this group were positive for A. pleuropneumoniae by conventional culture, but 7 were positive by the coagglutination test. There were 15 animals with CF titers between 1:8 and 1:32. Animals from 6 herds vaccinated for A. pleuropneumoniae and without recent respiratory problems were evaluated. One out of 118 animals tested was positive for A. pleuropneumoniae by standard culture as compared to 9 positive by coagglutination. The difference in positive results between culture and coagglutination was highly significant (P less than 0.001). Twenty-eight animals had CF titers to A. pleuropneumoniae (1:4 to greater than or equal to 1:128). Two hundred fifty lungs and sera samples were collected from 7 herds which had recently experienced varying degrees of respiratory disease. Thirty-nine lungs were positive for A. pleuropneumoniae by culture and 182 were positive by coagglutination. The number of positives detected by coagglutination was significantly different (P less than 0.001) from the number positive by culture. There were 172 animals with antibody titers ranging from suspect to greater than or equal to 1:128. There were significantly fewer positive animals detected by standard culture than with the CF test (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
97.
98.
A genetically engineered Eimeria tenella antigen (GX3262), produced as a fusion protein with beta-galactosidase and identified with a monoclonal antibody, induced partial but significant protection in young broiler chickens against experimental E. tenella and Eimeria acervulina infections. The antigen appears to share a T-helper cell epitope with the parasite as evidenced by (a) booster inoculation with either the recombinant antigen or with a small number of live oocysts enhanced the protective immunity in GX3262 primed chickens, and (b) ability of the antigen to induce in vitro stimulation of T-cells from chickens immunized with antigen or parasite. These observations suggest the feasibility of a single vaccination of 1 or 2-day-old broilers with GX3262 to induce an acceptable degree of protective immunity. The implications of the observations reported here are far reaching in terms of a practical coccidiosis vaccine for poultry, and show for the first time that 1-day-old broiler chickens can be efficiently vaccinated with a recombinant antigen against one or more species of Eimeria.  相似文献   
99.
100.
Data from 321 spring-calving cows (mean calving date March 27) were used to assess the effects of body condition, live weight, cow age (from 4 to 13 yr), and breed (237 Hereford x Friesians and 84 Blue-Greys) and time of calving on the proportion of cows that became pregnant, the number of days from the start of mating to pregnancy, and calving interval. Mating started at turn-out to pasture in mid-May and lasted 9 to 10 wk. Body condition at calving and breed were the most significant animal factors affecting reproductive performance. Cows calving in higher body condition had shorter (P less than .001) calving intervals (11.2 d per unit of body condition at calving). Blue-Grey cows became pregnant in a higher proportion (90%) and calving interval was shorter (364 d) than in Hereford x Friesians (83%; 374 d). Body condition at the start of mating was less important and body condition at the end of mating had no effect. Live weight at calving and changes in live weight from calving to the start of mating and during the mating period had no significant effect. The proportion of cows becoming pregnant decreased significantly with age in Hereford x Friesian cows older than 7 yr. The variance in calving interval accounted for by calving date, body condition at calving, breed, and age was 42%.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号