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   1151篇
  免费   48篇
林业   57篇
农学   33篇
基础科学   15篇
  117篇
综合类   169篇
农作物   42篇
水产渔业   38篇
畜牧兽医   622篇
园艺   56篇
植物保护   50篇
  2023年   14篇
  2022年   8篇
  2021年   21篇
  2020年   19篇
  2019年   12篇
  2018年   13篇
  2017年   19篇
  2016年   31篇
  2015年   15篇
  2014年   29篇
  2013年   42篇
  2012年   32篇
  2011年   45篇
  2010年   25篇
  2009年   33篇
  2008年   32篇
  2007年   40篇
  2006年   38篇
  2005年   36篇
  2004年   29篇
  2003年   29篇
  2002年   36篇
  2001年   32篇
  2000年   38篇
  1999年   32篇
  1998年   13篇
  1995年   10篇
  1994年   10篇
  1992年   29篇
  1991年   32篇
  1990年   34篇
  1989年   41篇
  1988年   24篇
  1987年   25篇
  1986年   23篇
  1985年   21篇
  1984年   14篇
  1983年   25篇
  1982年   9篇
  1979年   12篇
  1978年   7篇
  1977年   6篇
  1976年   8篇
  1975年   12篇
  1974年   7篇
  1973年   8篇
  1972年   8篇
  1970年   13篇
  1969年   6篇
  1968年   6篇
排序方式: 共有1199条查询结果,搜索用时 15 毫秒
81.
Persistent dorsal displacement of the soft palate (pDDSP) is a relatively rare equine disorder. This case series reports histories and clinical findings in 8 cases of pDDSP, and outcome after treatment of concurrent epiglottic entrapment (n = 3), laryngeal tie‐forward (n = 6) ± laser staphylectomy (n = 2), and/or sectioning of mucosa ventral to the epiglottis and the hyoepiglotticus muscles (n = 2). Four of 6 horses that underwent tie‐forward ± laser staphylectomy had complete resolution of pDDSP and returned to their previous level of work, as did one horse that had a subepiglottic releasing incision. Correction of concurrent epiglottic entrapment in 3 horses with pDDSP did not result in resolution of pDDSP in any case. Previous laryngeal surgery including laryngoplasty and ventriculocordectomy appear to be risk factors for the development of pDDSP.  相似文献   
82.
83.
BACKGROUND: Gemcitabine has been shown to be effective as a single agent in a variety of tumors including nonHodgkin's lymphoma. Its use in veterinary medicine has been limited and to date this drug has not been used as a first-line therapy in dogs with lymphoma. HYPOTHESIS: Gemcitabine as a single agent may be efficacious in dogs presented for the first time with lymphoma. ANIMALS: Twenty-four dogs with spontaneously occurring lymphoma. METHODS: All dogs were clinically staged and given gemcitabine at 400 mg/m(2) over a 30-minute intravenous infusion weekly for 3 weeks and then given 1 week off treatment before starting a second cycle. RESULTS: A single dose of gemcitabine lowered both neutrophil count (decrease in mean neutrophil count from 10,640 cells/ microL to 3,140 cells/microL) and platelet count (decrease in mean platelet count from 201,290 cells/microL to 139,190 cells/microL) 7 days after administration. Consequently gemcitabine dosage was reduced at the second treatment in 8 of 21 dogs or a dose delay of 1-7 days and a reduction of dosage was used in 7 of 21 dogs. Seven dogs completed the assigned 4-week cycle. Two of these dogs had progressive disease and 5 had stable disease. No objective responses were seen in dogs treated with a second cycle of gemcitabine. CONCLUSIONS AND CLINICAL IMPORTANCE: Gemcitabine administration as a single agent resulted in hematologic toxicity and did not reduce lymphoma burden. If gemcitabine is to be used in veterinary medicine, additional prospective pharmacologic studies should be done to determine the appropriate dosage, regimen, and schedule of use before it can be recommended for use in the treatment of dogs with lymphoma as a single agent.  相似文献   
84.
Two selenium (Se) supplementation trials were conducted in successive years involving a total of 70 red deer calves 3-15 months of age grazing pasture containing 30-57 ppb of Se on a dry matter basis. The trials compared growth rate, whole blood Se and glutathione peroxidase (GSHpx) concentrations of calves which received periodic doses of oral Se or a single injection of barium selenate (equivalent to 50 mg Se) or no Se supplementation. There were no significant weight gain differences between treated and untreated groups in either trial. Whole blood GSHpx levels were strongly correlated with blood Se levels (r = 0.9278) and produced the following regression equation: GSHpx = 0.0155 Se - 2.292. In both years the 3 month old calves had GSHpx levels of 6-9 kU/I which probably derived from maternal transfer of Se. The GSHpx levels in unsupplemented calves declined from these levels to a minimum in winter (group means approximately 2.6) and then progressively rose the following spring and summer. Periodical oral dosing with Se or a single injection of barium selenate significantly elevated blood Se and GSHpx levels throughout the trials.  相似文献   
85.
A randomised double-blind clinical trial of 28 horses was undertaken to evaluate the efficacy of isoxsuprine hydrochloride at four different doses:- 0.0 mg/kg bodyweight (bwt) (placebo), 0.6 mg/kg bwt, 1.2 mg/kg bwt and 1.8 mg/kg bwt for treatment of navicular disease. The results showed that horses treated with isoxsuprine hydrochloride (N = 22) responded significantly with respect to clinical assessment score (P less than 0.01) when compared with the control group (N = 6). Furthermore, there were no dose-related differences in the responses of the horses treated with increasing levels of isoxsuprine. No correlation was found between radiological evidence of the extent of navicular disease and severity of lameness or response to treatment.  相似文献   
86.

Purpose  

The use of only one or a few species—representing an entire taxon—in ecotoxicological standard tests poses risk of underestimating the impact of toxicants on the environment. In earthworm ecotoxicity tests, the species Eisenia fetida or Eisenia andrei are commonly used, and there is evidence that these species respond relatively insensitive towards environmental pollution. With the present study, we wanted to evaluate the risk of underestimating effects of the insecticide imidacloprid in soil organisms by comparing E. fetida with two other earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) regarding their sensitivities towards soil contaminated with this widely used insecticide.  相似文献   
87.
A method is reported for the extraction and analysis of zearalenone in chicken fat, heart muscle, and kidney tissue by using high pressure liquid chromatography (HPLC). Zearalenone is extracted with acetonitrile, cleaned up with hexane, and extracted further with ethyl acetate. Zearalenone is determined by HPLC using a reverse phase radial compression separation system, an ultraviolet absorbance detector, and a mobile phase of acetonitrile-water (60 + 40) (v/v). Recoveries of zearalenone added at levels from 50 to 200 ng/g are in the range 82.6-95.1%.  相似文献   
88.
Fertilization strategies during stock plant and cutting production are linked in terms of cutting nutrient levels and quality. Objectives were to evaluate (1) the effect of stock plant nutrition on tissue nutrient concentration and growth during vegetative propagation and (2) response to fertilizer during propagation for cuttings with 4 different initial tissue nutrient concentrations. ‘Supertunia Royal Velvet’ petunia stock plants were grown under constant fertigation of 0, 50, 100 or 200 mg nitrogen (N).L?1 for 21 days. The 200 mg N.L?1 solution contained 150 nitrate (NO3-N), 50 ammonium (NH4-N), 24 phosphorus (P), 166 potassium (K), 40 calcium (Ca), 20 magnesium (Mg), 0.7 sulfur (S), 1.0 iron (Fe), 0.5 manganese (Mn), 0.5 zinc (Zn), 0.24 copper (Cu), 0.24 boron (B), and 0.1 molybdenum (Mo). Providing a complete fertilizer during propagation of petunia, beginning immediately after sticking of cuttings, reduces the risk of nutrient deficiency. Particularly in situations where fertilizer is not applied early during propagation, stock plants should be managed to ensure unrooted cuttings have adequate nutrient reserves.  相似文献   
89.
The relationship between fine-scale spatial patterns of forage abundance and the feeding patterns of large ungulates is not well known. We compared these patterns for areas grazed in winter by elk and bison in a sagebrush-grassland landscape in northern Yellowstone National Park. At a fine scale, the spatial distribution of mapped feeding stations in 30 m × 30 m sites was found to be random where there were no large patches devoid of vegetation. In areas similar to the mapped sites, the underlying spatial distribution pattern of biomass was also determined to be random. At a broad scale, forage biomass differed among communities across the northern range but forage quality did not. These results suggest that ungulates are feeding randomly within forage patches (fine scale) but may select feeding sites based upon forage abundance at broader, landscape scales. Contrary to what has been suggested in other systems, ungulates were not overmatching at finer scales.  相似文献   
90.
The pathogenic mechanisms of Brucellosis used to adapt to the harsh intracellular environment of the host cell are not fully understood. The present study investigated the in vitro and in vivo characteristics of B. abortus betaine aldehyde dehydrogenase (BetB) (Gene Bank ID: 006932) using a betB deletion mutant constructed from virulent B. abortus 544. In test under stress conditions, including osmotic- and acid stress-resistance, the betB mutant had a lower osmotic-resistance than B. abortus wild-type. In addition, the betB mutant showed higher internalization rates compared to the wild-type strain; however, it also displayed replication failures in HeLa cells and RAW 264.7 macrophages. During internalization, compared to the wild-type strain, the betB mutant was more adherent to the host surface and showed enhanced phosphorylation of protein kinases, two processes that promote phagocytic activity, in host cells. During intracellular trafficking, colocalization of B. abortus-containing phagosomes with LAMP-1 was elevated in betB mutant-infected cells compared to the wild-type cells. In mice, the betB mutant was predominantly cleared from spleens compared to the wild-type strain after 2 weeks post-infection, and the vaccination test with the live betB mutant showed effective protection against challenge infection with the virulent wild-type strain. These findings suggested that the B. abortus betB gene substantially affects the phagocytic pathway in human phagocytes and in host cells in mice. Furthermore, this study highlights the potential use of the B. abortus betB mutant as a live vaccine for the control of brucellosis.  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