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   58712篇
  免费   3298篇
  国内免费   37篇
林业   3050篇
农学   2213篇
基础科学   351篇
  7424篇
综合类   6817篇
农作物   2099篇
水产渔业   3186篇
畜牧兽医   32888篇
园艺   724篇
植物保护   3295篇
  2019年   496篇
  2018年   955篇
  2017年   1035篇
  2016年   1007篇
  2015年   865篇
  2014年   1011篇
  2013年   2320篇
  2012年   1804篇
  2011年   2197篇
  2010年   1436篇
  2009年   1368篇
  2008年   2030篇
  2007年   2040篇
  2006年   1933篇
  2005年   1788篇
  2004年   1681篇
  2003年   1666篇
  2002年   1537篇
  2001年   2332篇
  2000年   2186篇
  1999年   1722篇
  1998年   684篇
  1997年   623篇
  1996年   601篇
  1995年   671篇
  1994年   572篇
  1993年   558篇
  1992年   1262篇
  1991年   1397篇
  1990年   1450篇
  1989年   1331篇
  1988年   1243篇
  1987年   1230篇
  1986年   1167篇
  1985年   1104篇
  1984年   917篇
  1983年   723篇
  1982年   524篇
  1979年   792篇
  1978年   616篇
  1977年   469篇
  1976年   524篇
  1975年   502篇
  1974年   624篇
  1973年   605篇
  1972年   633篇
  1971年   601篇
  1970年   588篇
  1969年   537篇
  1967年   497篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
1. To improve the influence of variation of ME intake, an experiment was carried out using equalised feeding to investigate the comparative effects on protein and energy utilisation in chicks of diets containing medium chain triglyceride (MCT) and long chain triglyceride (LCT). Experimental diets were given at 3 different food intakes, namely, 100, 120 or 147 g/bird/10 d. The diets contained MCT or LCT on an isoenergetic basis. Maize oil and caprylic acid triglyceride respectively, were used as LCT and MCT sources.

2. Body weight gain and food efficiency of chicks significantly increased with the supplement of dietary MCT compared with dietary LCT at all food intakes. Protein retention and the efficiency of protein utilisation (protein retained/protein intake) at all food intakes also significantly increased with dietary MCT, while body fat and fat retention were significantly reduced. Chicks fed the LCT‐supple‐mented diet, on the other hand, had a lower protein retention, but significantly higher fat retention. The value for energy retention and the efficiency of energy utilisation (energy retained/ME intake) were not significantly different between MCT‐ and LCT‐supplemented diets.

3. It was concluded that supplementing MCT to the chick diet would improve body weight gain and protein utilisation while regulating fat deposition compared to the LCT supplemented diet, under equalised feeding conditions.  相似文献   

992.
A total of 578 slaughter pigs from 2 Danish conventional farrow-to-finish operations (Herds a and B) were followed from an age of 14 days to slaughter. Pigs were weighed at 3 weeks intervals and at slaughter and extended post mortem examination of the plucks was done. Regression models with second and third order interaction terms demonstrated that Mycoplasma-like pneumonia, complicated pneumonia, anterio-ventral pleuritis, pericarditis, fissures and atrophic rhinitis, separately and through interactions with other lesions, significantly reduced mean daily gains during specific intervals of the growth period in 2 conventional swine herds. It is likely that the periods of reduced growth reflect the times when the diseases were in the acute and early recovery stages. Maximum estimated reductions in daily gains associated with the combined lesions were 82 grams and 283 grams during the interval 120-140 days in Herds A and B, respectively. Although dorso-caudal pleuritis and parietal pleuritis had minor negative effects during 2 intervals neither had a significant adverse effect on total growth rate in either herd (Paisley et al. 1993). R2 values for the regression models were less than 0.27 showing that the lesions present at slaughter explained less than 27% of the variation in herd mean daily gains during any interval.  相似文献   
993.
Local anaesthetic techniques and diagnostic imaging tools are currently used in conjunction with thorough physical and lameness examinations to diagnose sacroiliac disease (SID) in the horse. The deep and inaccessible location of the sacroiliac joint (SIJ), however, often renders diagnostic imaging modalities, such as radiography, nuclear scintigraphy and ultrasonography, unreliable in identifying sacroiliac problems. The equine clinician therefore often has to rely on positive results of local anaesthetic techniques to confirm a diagnosis of SID. Regional infiltration techniques have been described but result in a diffuse distribution of large volumes of local anaesthetic solution throughout the entire lumbosacroiliac region, which is nonspecific to the SIJ and has the potential to produce false positive results. Several periarticular injection approaches to the SIJ have recently been described. A combination of periarticular SIJ injections with the use of modest amounts of local anaesthetic solution provides increased SIJ specificity, but may lead to false negative results in cases where the pain originates from surrounding soft tissues. This article clarifies terminology related to sacroiliac injections, reviews current injection techniques, highlights the advantages and disadvantages of each approach, and investigates injectate volume considerations.  相似文献   
994.
Tuberculosis infections caused by Mycobacterium (M.) pinnipedii in a South American sea lion, Bactrian camel, and Malayan tapirs kept in two zoological gardens spanning a time period of 5 years are reported. The zoos were linked by the transfer of one tapir. Conventional bacteriological and molecular methods were applied to detect the pathogen. Spoligotyping and MIRU/VNTR-typing performed to assess the genetic similarity revealed identical molecular characteristics of the isolates from all animals involved. Anti-tuberculosis antibodies were detected using ELISA and a recently developed serological rapid test. The study shows that: (i) using molecular methods, the assessment of the genetic relationship of infectious agents helps to confirm the routes of infection, and that (ii) immunological tests may help to detect tuberculosis infections ante mortem more reliably and early. This would prevent the transfer of tuberculosis by asymptomatic animals.  相似文献   
995.
Structural polypeptides of two plaque-purified variant isolates of fowlpox virus differing in plaque morphology and size were examined by Coomassie blue-staining and immunoblot analysis of purified virions. A total of 30 structural polypeptides were observed, ranging in molecular weight from 14,100 to 122,600. A late polypeptide of 36,400 molecular weight was quite prominent in the small-plaque clone but absent in the large-plaque clone. Two other polypeptides, of 33,700 and 34,800 molecular weight, were present in virions from large-plaque virus and cell lysates of both clones but were absent in the small-plaque virions. These differences were observed whether the viruses were grown in chorioallantoic membrane or in chicken embryo fibroblast cultures. No difference was observed between the growth curves of the two virus clones. Differences observed in the polypeptides of the two viruses may be due to changes in the less conserved regions of viral DNA and may be used for differentiation of virus isolates.  相似文献   
996.
The immunoprophylactic capacity of specific immune plasma was evaluated in pony foals infected experimentally with Rhodococcus equi. Immune plasma, produced by repeated parenteral administration of viable R. equi to adult horses, was harvested and frozen. Group I (six control foals) and Group II (six principal foals) received lactated Ringers solution and immune plasma respectively at three and five days of age. R. equi were aerosolised into a caudal lung lobe of all foals at seven days of age. Clinical signs, haematological alterations, immune responses, thoracic radiographs and technetium99m pulmonary perfusion scans were monitored. All foals were destroyed and complete post mortem examinations performed. All foals developed pneumonia as evidenced by clinical, radiographic and perfusion alterations, but the survival rate of principal foals was significantly (P less than 0.01) greater than that of control foals. Five control foals developed terminal disease, whereas all principal foals recovered. There was no significant (P greater than 0.05) difference in temperature response, or peripheral blood leucocyte, neutrophil or fibrinogen concentrations between groups. ELISA values for R. equi antibody were significantly (P less than 0.001) greater in principal foals following treatment, but there was no significant (P greater than 0.05) difference in IgG or IgM concentrations between groups. Results of the haemolysis inhibition assay indicated that equi factor neutralising antibodies were transferred by immune plasma to the principal foals. Post mortem examinations of five control foals destroyed at approximately three weeks post infection because of terminal disease, revealed severe pyogranulomatous pneumonia. One control and all principal foals were either free of lesions or had resolving lesions and/or minimal scar formation at three months post infection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
997.
Detection and survival of group A rotavirus in a piggery   总被引:1,自引:0,他引:1  
Samples of dust, faeces and effluent were collected from a piggery and examined for group A rotavirus, using a commercial ELISA test, electron microscopy and inoculation of MA-104 cells. Rotavirus antigen was demonstrated in samples collected from farrowing and weaner rooms but not from fattener and sow houses. Rotavirus antigen was also detected in samples collected from a weaner room which had been free of piglets for three months. A cytopathic porcine rotavirus (British isolate SW20/21) was kept at room temperature for four months; it survived with titres reduced by 2 log10. These observations suggest that the environment of commercial piggeries is an important source of rotaviral infection for young piglets.  相似文献   
998.
Mandibular condylectomy was effective in improving mastication and stopping weight loss in a horse. The horse had a history of intermittent purulent drainage from a facial wound and unilateral ankylosis of the temporomandibular joint.  相似文献   
999.
A study was performed in five identical outdoor production units in the same geographic area using growing-finishing pigs of similar genetic makeup, age, diet and feed management. The severity of tail-biting (TS) was scored 1-4. The average group prevalence of bitten tails at slaughter on different farms was between 14.1+/-2.1% and 20.1+/-3.0% (P<0.05). The odds of a barrow being bitten were 2.9 times higher than those for a gilt. The most frequently recorded score of bitten tails was TS3, indicating moderate wounds with low grade infection. The prevalence of bitten barrows was positively correlated with the percentage of gilts in a group (r = 0.54, P<0.001). Pigs with zero TS score had no significantly higher weights at slaughter compared to pigs with a score of TS1. As the TS increased from 1 to 4, weights decreased (TS 1 to TS 2 to 4, P<0.05). TS 3 and 4 were positively (P<0.001) associated with subsequent carcass condemnation. We concluded that outdoor rearing does not prevent tail-biting.  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