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   14057篇
  免费   1066篇
  国内免费   72篇
林业   626篇
农学   824篇
基础科学   125篇
  1999篇
综合类   1666篇
农作物   495篇
水产渔业   1042篇
畜牧兽医   7023篇
园艺   228篇
植物保护   1167篇
  2023年   90篇
  2021年   88篇
  2020年   122篇
  2019年   204篇
  2018年   374篇
  2017年   345篇
  2016年   334篇
  2015年   306篇
  2014年   327篇
  2013年   571篇
  2012年   477篇
  2011年   568篇
  2010年   462篇
  2009年   420篇
  2008年   554篇
  2007年   577篇
  2006年   471篇
  2005年   520篇
  2004年   407篇
  2003年   446篇
  2002年   358篇
  2001年   759篇
  2000年   721篇
  1999年   590篇
  1998年   171篇
  1997年   164篇
  1996年   126篇
  1995年   150篇
  1994年   156篇
  1993年   120篇
  1992年   321篇
  1991年   346篇
  1990年   291篇
  1989年   266篇
  1988年   271篇
  1987年   319篇
  1986年   245篇
  1985年   193篇
  1984年   170篇
  1983年   147篇
  1982年   94篇
  1981年   83篇
  1980年   79篇
  1979年   141篇
  1978年   94篇
  1977年   73篇
  1975年   77篇
  1974年   79篇
  1971年   69篇
  1969年   70篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Objective-To evaluate adverse effects and survival times in dogs with osteosarcoma that received a single SC infusion of carboplatin as adjunctive chemotherapeutic treatment following limb amputation or limb-sparing surgery. Design-Retrospective case series. Animals-17 client-owned dogs with spontaneously occurring osteosarcoma. Procedures-Medical records of dogs that underwent limb amputation or limb-sparing surgery followed by a single continuous SC infusion of carboplatin (total dose, 300 mg/m(2) infused over 3, 5, or 7 days) were evaluated. Signalment, tumor location, type of surgery (amputation or limb-sparing), duration of carboplatin infusion, results of hematologic and serum biochemical analyses, and adverse effects were recorded. Kaplan-Meier survival analysis was performed. Results-Median survival time for all dogs was 365 days. Nine dogs had adverse bone marrow-related (hematologic) effects, 1 had adverse gastrointestinal effects, and 7 had infections at the surgical site. No significant differences were detected in survival times of dogs grouped according to tumor location, type of surgery, duration of carboplatin infusion, or development of postoperative infection. Conclusions and Clinical Relevance-Median survival time and adverse effects in dogs with osteosarcoma that received a single SC infusion of carboplatin over a 3-, 5-, or 7-day period as adjunctive treatment following limb amputation or limb-sparing surgery were comparable to those of previously reported chemotherapy protocols requiring IV drug administration over several weeks. Further investigation is needed to evaluate the efficacy of this protocol as adjunctive treatment for osteosarcoma and other tumors in dogs.  相似文献   
982.
983.
Four experiments were conducted to evaluate the nutrient contributions and physiological health benefits of spray-dried egg (SDE) containing only unfertilized eggs as a protein source in nursery pig diets. In all experiments, all diets were formulated to the same ME and Lys content, and each pen within a block (by BW) housed the same number of barrows and gilts. In Exp. 1 and 2 (168 and 140 pigs, respectively; 5 kg BW; 16 d old; 14 replicates/experiment), conducted at a university farm, treatments were with or without 5% SDE in a nursery control diet, which included antibiotics and zinc oxide. Pigs were fed for 10 d after weaning to measure ADG, ADFI, and G:F. The SDE increased (P < 0.05) ADG (Exp. 1: 243 vs. 204 g/d; Exp. 2: 204 vs. 181 g/d) and ADFI (Exp. 1: 236 vs. 204 g/d; Exp. 2: 263 vs. 253 g/d) compared with the control diet but did not affect G:F. In Exp. 3 (1,008 pigs; 5.2 kg BW; 20 d old; 12 replicates/treatment), conducted at a commercial farm, treatments were in a factorial arrangement of with or without SDE and high or low spray-dried plasma (SDP) in nursery diets, which included antibiotics and zinc oxide. Pigs were fed for 6 wk using a 4-phase feeding program (phases of 1, 1, 2, and 2 wk, respectively) with declining diet complexity to measure ADG, ADFI, G:F, removal rate (mortality plus morbidity), and frequency of medical treatments per pen and day (MED). The diets with the SDE increased (P < 0.05) ADFI during phase 1 only (180 vs. 164 g/d) compared with the diets without the SDE but did not affect growth performance during any other phases. The diets with SDE reduced MED during phase 1 (0.75% vs. 1.35%; P < 0.05) and the overall period (0.84% vs. 1.01%; P = 0.062) compared with the diets without the SDE but did not affect removal rate. In Exp. 4 (160 pigs; 6.7 kg BW; 21 d old; 10 replicates/treatment), conducted at a university farm to determine whether SDE can replace SDP, treatments were in a factorial arrangement of with or without SDP or SDE in nursery diets, which excluded antibiotics and zinc oxide. Pigs were fed for 6 wk using the same schedule used in Exp. 3 to measure ADG, ADFI, and G:F. The diets with SDE increased (P < 0.05) ADFI during phase 1 only (195 vs. 161 g/d) compared with the diets without SDE but did not affect growth performance during any other periods. In conclusion, SDE can be an efficacious protein and energy source in nursery pig diets and improves health and, in some instances, increases growth rate.  相似文献   
984.
The present study investigated the effect of inclusion of multi-microbe probiotic product on growth performance, apparent digestibility of nutrients, cecal microbiota and small intestinal morphology in broilers. Four hundred days-old Ross chicks were randomly allotted to five treatments on the basis of body weight (BW). Each treatment had four replicates of 20 chicks in each. Experimental diets were fed in two phases, starter (day 0-21) and finisher (day 22-35). Dietary treatments were; basal diet without any antimicrobial (NC), basal diet added with 20 mg Avilamycin/kg of diet (PC), 10(7) cfu multi-microbe probiotic/kg of diet (P1), 10(8) cfu multi-microbe probiotic/kg of diet (P2), and 10(9) cfu multi-microbe probiotic/kg of diet (P3). Overall BW gain and feed conversion ratio were better (p < 0.05) for treatments PC, P2 and P3 compared with NC and P1, with P1 being better (p < 0.05) than NC. Overall feed intake in treatments PC, P1, P2 and P3 were greater (p < 0.05) than NC. Apparent digestibility of dry matter and crude protein were greater (p < 0.05) in treatments PC, P2 and P3 compared with NC, with P1 being intermediate and not different form NC, PC, P2 and P3. At d 21 and 35, treatments PC, P1, P2 and P3 showed lower (p < 0.05) cecal Clostridium and Coliforms count in relation to NC. Moreover, cecal Clostridium (d 21) and Coliforms (d 21 and 35) count were lower (p < 0.05) in treatment PC in relation to P1; with P2 and P3 being intermediate and not different from PC. However, there was no effect of dietary treatments on cecal total anaerobic bacteria and Bifidobacterium spp. count. The villus height of duodenum in treatment PC was greater (p < 0.05) than NC, with P1, P2 and P3 being intermediate. Villus height of ileum in treatment PC was greater (p < 0.05) than in treatments P1 and NC, whereas it remained comparable among treatments PC, P2 and P3. Villus height to crypt depth ratio of ileum was greater (p < 0.05) for treatment PC, P2 and P3 compared with that in P1 and NC. It is concluded that multi-microbe probiotic inclusion at 10(8) and 10(9) cfu/kg diet had beneficial effects on broilers growth performance, apparent digestibility of nutrients and intestinal morphology and can be used as replacement to antibiotics growth promoter in broiler nutrition.  相似文献   
985.
986.
987.
Toxic and protective constituents in pet foods   总被引:1,自引:0,他引:1  
An analytical survey of mutagens, nitrosamines, polychlorinated biphenyls, toxic elements, and gamma-emission, as well as the toxicologically protective constituents zinc, selenium, and vitamin C, in 48 pet foods was conducted. Aside from high concentrations of fluoride and iodide in some samples and the expectedly higher concentrations of mercury and selenium in certain cat foods containing fish, the samples were notably free of the other toxic constituents. Direct-acting and promutagens and nitrosamines were not detectable in any of the samples. gamma-Emission was very low in all of the foods. Polychlorinated biphenyls were only detected in one cat food.  相似文献   
988.
Hybridoma cell lines secreting monoclonal antibody (MCA) to avian leukosis virus (ALV) structural proteins p27 and p19 have been established. In an indirect enzyme-linked immunosorbent assay (ELISA), MCA 6AL20 (IgG1 isotype) reacted with RPL-40 (ALV subgroup A), avian myeloblastosis virus (AMV) (a mixture of subgroups A and B), Rous-associated virus (RAV)-2 (subgroup B), and Carr-Zilber strain of Rous sarcoma virus (CZ-RSV) (subgroup D) but not with Prague strain of RSV (PrC-RSV) (subgroup C) or the endogenous virus RAV-0 (subgroup E). MCA 6AL22 reacted as above and also reacted marginally with PrC-RSV. Both MCAs immunoprecipitated p19 from 35S-methionine-labeled chicken embryo fibroblasts (CEFs) infected with RPL-40 or RAV-1, but not from CEFs infected with RAV-0, thus identifying the viral structural protein p19 as a polypeptide with subgroup-specific epitopes. Both MCAs can be used to differentiate RPL-40 from RAV-0 infection either in an indirect antibody ELISA or by immunoprecipitation. A third MCA, 6AL42 (IgG2a isotype), reacted with the above viruses of subgroups A, B, C, and D at an antibody titer up to 1000-fold higher than with subgroup E RAV-0 virus in indirect ELISAs. MCA 6AL42 immunoprecipitated p27 from cells infected with RPL-40, RAV-1, or RAV-0. These MCAs are potentially useful in developing immunological tests for differentiation of ALV strains.  相似文献   
989.
The effects of concurrent cage contamination with Salmonella typhimurium and Eimeria tenella on the establishment of salmonella infection in day-old chickens were investigated. Chickens were divided into five groups: uninfected recipient birds placed in a cage contaminated by donor birds infected with E. tenella and S. typhimurium; E. tenella-infected recipients placed in a cage contaminated by S. typhimurium-infected donors; uninfected recipients placed in a cage contaminated by S. typhimurium-infected donors; E. tenella-infected recipients placed in a cage contaminated by uninfected donors; and uninfected recipients placed in a cage contaminated by uninfected donors. Three identical trials were conducted. Recipient birds were necropsied 4, 7, and 11 days after caging. In the cage where donor birds infected with both organisms had been reared, S. typhimurium counts in feces and number of feces positive for S. typhimurium were significantly (P less than 0.05) greater than those in the other cages on days 0, 4, and 7 after caging. Moreover, in this cage, more chicks died, counts of S. typhimurium in cecal contents were greater, and more birds were positive for S. typhimurium than in the other groups. This suggests that S. typhimurium infection in day-old chickens is enhanced in cages contaminated with E. tenella and S. typhimurium compared with infection in cages contaminated with S. typhimurium alone.  相似文献   
990.
Day-old domesticated Muscovy ducklings (Cairina moshata) were given the trichothecene mycotoxins T-2 toxin or diacetoxyscirpenol at 0.25, 0.5, or 1 micrograms/g of feed for 7 days. All concentrations of both toxins caused characteristic dose-related lesions on the roof of the oral cavity of the birds. Muscovy ducklings showed these signs in a shorter time (less than 16 hours in some cases) and at a lower feed concentration of these trichothecenes than did other avian species in similar studies.  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