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   134278篇
  免费   7368篇
  国内免费   93篇
林业   5477篇
农学   4322篇
基础科学   847篇
  17295篇
综合类   21826篇
农作物   5486篇
水产渔业   6811篇
畜牧兽医   68807篇
园艺   1822篇
植物保护   9046篇
  2020年   1196篇
  2019年   1394篇
  2018年   2057篇
  2017年   2346篇
  2016年   2125篇
  2015年   1762篇
  2014年   2257篇
  2013年   5347篇
  2012年   4192篇
  2011年   5173篇
  2010年   3290篇
  2009年   3455篇
  2008年   5059篇
  2007年   4775篇
  2006年   4456篇
  2005年   4171篇
  2004年   3923篇
  2003年   4050篇
  2002年   3623篇
  2001年   4179篇
  2000年   4295篇
  1999年   3394篇
  1998年   1498篇
  1997年   1405篇
  1996年   1300篇
  1995年   1554篇
  1994年   1380篇
  1993年   1249篇
  1992年   2606篇
  1991年   2719篇
  1990年   2621篇
  1989年   2636篇
  1988年   2386篇
  1987年   2362篇
  1986年   2440篇
  1985年   2354篇
  1984年   1903篇
  1983年   1693篇
  1982年   1168篇
  1979年   1761篇
  1978年   1416篇
  1977年   1166篇
  1976年   1222篇
  1975年   1310篇
  1974年   1519篇
  1973年   1535篇
  1972年   1423篇
  1971年   1312篇
  1970年   1276篇
  1969年   1297篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
Colostrum-deprived, neonatal, 2 days old pigs were inoculated with the attenuated HT-/SK or the virulent 90HS strain of porcine parvovirus (PPV) by the oral or subcutaneous route and sacrificed 2, 4 or 6 days after inoculation. Then, comparison was made on viral multiplication in pigs between the two strains. Pigs inoculated with the HT-/SK strain showed no detectable viremia or HI antibody responses against PPV within 6 days after inoculation. Only in pigs inoculated by the subcutaneous route, a small amount of virus was recovered from the spleen, liver, or mesenteric lymph nodes. These viruses were distinguished from the parental virulent 90HS strain, as examined for rct maker in vitro. When pigs were inoculated with the virulent 90HS strain, viremia appeared in all of them 1 day after inoculation and continued for up to the sacrificed day. Moreover, a considerable amount of virus was also detected from all tissues, including brain, lung, liver, spleen, pancreas, small intestine, and lymph node tissues, in all pigs tested. HI antibodies were first detected 6 days after inoculation.  相似文献   
992.
The effects of resistant starch (RS) intake on nutrient digestibility, microbial fermentation products, faecal IgA, faecal pH, and histological features of the intestinal mucosa of old dogs were evaluated. The same formulation was extruded in two different conditions: one to obtain elevated starch cooking degree with low RS content (0.21%) and the other lower starch cooking with high RS content (1.46%). Eight geriatric Beagles (11.5 ± 0.38 years old) were fed each diet for 61 days in a crossover design. Food intake, nutrient digestibility, fermentation products, faecal pH, and faecal IgA were examined via variance analysis. Histological results of intestinal biopsies were assessed via Wilcoxon test for paired data. The morphometric characteristics of large intestine crypts were evaluated via paired t tests (p < .05). Protein, fat, and energy digestibilities were higher for the low‐RS diet (p < .05). Dogs receiving the high‐RS diet had lower faecal pH and higher values for propionate, butyrate, total volatile fatty acids, and lactate (p < .05). No differences between diets were found in the histological parameters of the gut mucosa, and only a tendency for deeper crypts in the descending colon was observed for dogs fed the high‐RS diet (p = .083). The intake of a corn‐based kibble diet manufactured with coarse ground raw material and low starch gelatinization to obtain 1.4% of RS affected microbial fermentation products and faecal pH and tended to increase crypt depth in the descending colon of old dogs.  相似文献   
993.
A case of unilateral spastic paresis in a Poll Hereford heifer is described. The heifer could not actively flex the right stifle or hock and the toe just contacted the ground. There was cranial distortion and collapse of the distal tibial epiphysis and remodelling of the articular surfaces within the stifle and hock. There was moderately severe muscle atrophy, but a primary peripheral or central neuropathological lesion could not be found.  相似文献   
994.
995.
A haematological disorder in a dog characterised by a massive leucocytosis, mainly composed of eosinophils and their precursors is reported here. The normal composition of cells in the bone marrow was displaced in favour of the eosinophils and their precursors. No apparent cause for the pronounced eosinophilia could be determined by clinical, haematological, clinical-chemical, radiological or pathological examinations. A diagnosis of eosinophilic leukaemoid reaction was suggested as the criteria for the diagnosis of eosinophilic leukaemia in the dog but this was not firmly established.  相似文献   
996.
997.
A machine is described for experimental application of herbicides in volumes of spray liquid in the range 5–20 I/ha and at a uniform drop size. Uniformity of distribution is comparable to that from a conventional small-plot sprayer working under optimal conditions. The machine was used to apply 2,4-D ester, barban and tri-allate. Subsequent biological assessments revealed no major loss of effectiveness in weed control when compared with applications in 165 or 200 I/ha sprayed through hydraulic fan nozzles as in contemporary field practice. Essais préliminaires au champ avec l'ester du 2,4-D, le barbane et le triallate appliqués en pulvérisation avec un volume de 5 à 20 l/ha Un appareil est décrit pour l'application expérimental d'herbicides en pulvérisation avec un volume de liquide alla de 5 à 20 I/ha et une taille uniforme de gouttes. L'uniformité de la distribution est comparable à celle d'un pulvérisateur pour petites parcelles travaillant dans des conditions optimales. L'appareil a été utilisé pour appliquer du 2.4-D ester, du barbane et du triallate. Des essais biologiques effectués & la suite des traitements ont montré qu'il n'y avait pas de perte importante d'efficacité herbicide par comparaison avec des traitements appliqués avec 165 ou 200 1/ha en utilisant les buses S fente en usage dans la pratique actuelle des traitements au champ. Vorläufige Feldversuche mit 2,4-D Ester, Barban und Triallat mit Brühemengen von 5–20 l/ha Es wird ein GerSt beschrieben mit dem versuchsmässig Herbizide mit Brühemengen zwischen 5 und 20 1/ha bei gleichbleibender Tropfengrösse ausgebracht werden können. Die Gleichmässigkeit der Verteilung lässt sich mit der eines unter optimalen Bedingungen arbeitenden Parzellenspritz-geräts vergleichen. Mit diesem Gerät wurden 2,4-D Ester, Barban und Triallat ausgebracht. Die darauffotgende bio-logische Früfung zeigte keinen wesentlichen Verlust in der Wirksamkeit der Unkrautbekämpfung, verglichen mit den gegenwärtig üblichen Verfahren mit 163 oder 200 l/ha und Flachstrahldüsen.  相似文献   
998.
Conjunctival fungal flora in horses, cattle, dogs, and cats   总被引:4,自引:0,他引:4  
Conjunctival swab specimens were obtained from both eyes of 43 horses, 25 cows, 50 dogs, and 25 cats without keratitis or other ophthalmologic problems. Fungi were isolated from 95% of the horses, 100% of the cows, 22% of the dogs, and 40% of the cats. Aspergillus spp were isolated from 56% of the horses, 12% of the cows, 8% of the cats, and none of the dogs. Penicillium spp and Cladosporium spp were isolated ubiquitously. Collectively, 28 species from 209 isolants were identified.  相似文献   
999.
We examined whether mutation of the platelet‐derived growth factor receptor protein tyrosine kinase (PDGFR)‐α and PDGFR‐β genes contributes to their overexpression in canine vascular tumours. Genomic sequences of trans‐ or juxtamembrane regions of PDGFR‐α and PDGFR‐β were analysed with immunohistochemical staining and polymerase chain reaction‐direct sequencing using DNA from paraffin‐embedded neoplastic tissues of 27 hemangiosarcomas (HSAs) and 20 hemangiomas (HAs). Immunohistochemically, 75% of the HA cases were positive for PDGFR‐α and almost most of the HA cases were negative for PDGFR‐β. Of the HSA cases, 55.6% were negative for PDGFR‐α and 63% were strongly positive for PDGFR‐β. Among the HA cases, 1 missense mutation was detected in PDGFR‐α exon 18 and 1 in PDGFR‐β exon 17. Two HSA cases had missense mutations in exon 14 and 1 in exon 17 of PDGFR‐β. Thus, genomic mutation of trans‐ or juxtamembrane regions of PDGFRs was not the main mechanism driving the activation of receptors in HSA and HA.  相似文献   
1000.
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