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   416篇
  免费   18篇
林业   9篇
农学   33篇
  60篇
综合类   28篇
农作物   26篇
水产渔业   27篇
畜牧兽医   242篇
植物保护   9篇
  2023年   3篇
  2022年   3篇
  2021年   5篇
  2019年   4篇
  2018年   4篇
  2017年   10篇
  2016年   3篇
  2015年   10篇
  2014年   9篇
  2013年   18篇
  2012年   29篇
  2011年   22篇
  2010年   16篇
  2009年   19篇
  2008年   30篇
  2007年   21篇
  2006年   15篇
  2005年   17篇
  2004年   17篇
  2003年   14篇
  2002年   18篇
  2001年   14篇
  2000年   10篇
  1999年   13篇
  1998年   2篇
  1996年   2篇
  1994年   3篇
  1993年   7篇
  1992年   5篇
  1991年   8篇
  1990年   10篇
  1989年   6篇
  1988年   7篇
  1987年   5篇
  1986年   8篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1981年   3篇
  1979年   2篇
  1978年   4篇
  1975年   4篇
  1974年   2篇
  1973年   5篇
  1972年   4篇
  1968年   2篇
  1967年   2篇
  1966年   2篇
  1936年   2篇
  1925年   1篇
排序方式: 共有434条查询结果,搜索用时 125 毫秒
51.
The immunoreactivity of constitutive endothelial nitric oxide synthase (eNOS) was studied in the trigeminal ganglia (TG) of a crotaline snake, Trimeresurus flavoviridis. eNOS immunoreactivity was found in TG neurons of different sizes. The percentage of eNOS-positive TG neurons was significantly higher in the mandibular division than in the infrared-related divisions, the maxillary division and ophthalmic ganglion (p<0.001). These findings suggest that eNOS in the TG of crotaline snakes is involved in constitutive neurotransmission in the TG, and is minimally involved in processing in the infrared-sensory system.  相似文献   
52.
Expression of osteopontin (OPN) was investigated in the spinal cords of rats with clip compression injury. Western blot analysis demonstrated that OPN protein increased significantly in the spinal cord during the early stages after injury. The increased expression of OPN was partially paralleled by that of proliferating cell nuclear antigen (PCNA). Immunohistochemical staining showed that OPN was expressed in proliferating activated microglia/macrophages in core lesions and in some astrocytes at the periphery of lesions. These results indicate that expression of OPN protein increases mainly in activated microglia/macrophages after spinal cord injury, suggesting that OPN is related to cell proliferation during the early stages after injury, probably leading to tissue remodeling.  相似文献   
53.
An active compound that inhibits cancer cells was isolated from the fruit of Prunus mume, and its structure and in vitro activities were characterized. The n-hexane fraction obtained from methanol extracts exhibited the strongest inhibitory effect on the growth of cancer cells. From the n-hexane fraction, a new compound named B-1 was purified through preparative thin-layer chromatography, ODS column chromatography, and reverse phase high-performance liquid chromatography and its structure was analyzed by fast atom bombardment mass spectrometry and 1H and 13C NMR. The molecular formula of B-1 was C19H22O6 {2-hydroxy-1-[(7-hydroxy-2-oxo-2H-chromen-6-yl)methyl]-2-methylpropyl-(2Z)-3-methyl-but-e-enoate:prunate}, and the IC50 value was in the range of 39-58 microg/mL in descending order of the cancer cell lines Hep-2, SW-156, HEC-1-B, and SK-OV-3. B-1 exhibited 81-96% inhibition at a concentration level of 100 microg/mL against all cells, based on an 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. However, B-1 showed little effect against normal cells with only 23% or less growth inhibition at 100 microg/mL. Thus, B-1 has a highly specific inhibitory effect against cancer cells but little effect against normal cells. When the cancer cell lines Hep-2 and SK-OV-3 were incubated with B-1 for 72 h, most of the tested cells suffered strong growth inhibition. The compound has the potential to be developed as a nutraceutical.  相似文献   
54.
Naive and memory CD4+ T cell survival controlled by clonal abundance   总被引:1,自引:0,他引:1  
Immunity to a plethora of microbes depends on a diverse repertoire of na?ve lymphocytes and the production of long-lived memory cells. We present evidence here that low clonal abundance in a polyclonal repertoire favors the survival and activation of na?ve CD4(+) T cells as well as the survival of their memory cell progeny. The inverse relation between clonal frequency and survival suggests that intraclonal competition could help maintain an optimally diverse repertoire of T cells and an optimal environment for the generation of long-lived memory cells.  相似文献   
55.
The expression pattern of CD44 was studied in the rat testis following ischemia/reperfusion (I/R) injury to elucidate the possible role of the CD44 adhesion molecule in acute experimental testicular torsion. Western blot analysis showed that CD44 expression began to increase significantly 24 hr after reperfusion, compared with the normal control; the increased expression persisted until 96 hr after I/R. Immunohistochemistry showed that, in the normal testis, CD44 was constitutively expressed mainly in ED2-positive resident macrophages in the interstitial space. After I/R, the majority of inflammatory cells in the interstitial space surrounding the damaged tubules were ED1-positive macrophages that were CD44-positive. These findings suggest that the significant increase in CD44 expression that occurs during the delayed phase after reperfusion originates from infiltrating macrophages possibly in anticipation of the migration and adhesion of additional macrophages into the affected testis.  相似文献   
56.
OBJECTIVE: To evaluate whether a synthetic analogue of feline facial pheromone (FFP) calms cats before, and reduces struggling during intravenous catheterization. DESIGN: Block-randomized, 'blinded' clinical trial. ANIMALS: Seventy-seven healthy cats presented for elective surgery. PROCEDURE: Cats given glycopyrrolate and oxymorphone were assigned to one of four treatments: acepromazine and exposure to FFP (aceFFP); acepromazine and exposure to a placebo (acePlac); exposure to FFP only (FFP) and exposure to placebo only (Plac). The behaviour of cats was recorded on videotape for evaluation by assessors unaware of treatment group. Cats' veins were then catheterized by veterinary students unaware of the study protocol. Based on each cat's response to catheterization, the student independently decided whether intramuscular ketamine was required. RESULTS: Cats in the aceFFP group appeared to be calmer than acePlac cats on the basis of head position and their location in the cage (suggesting benefit from FFP among cats receiving acepromazine) but appeared to be less sedated. Cats in the aceFFP group also appeared to be calmer than FFP cats on the basis of head position and location in the cage. Feline facial pheromone cats were also calmer than Plac cats when compared using body and leg position. Exposure to FFP did not significantly reduce struggling at catheterization, nevertheless, the students were able to catheterize the veins in all cats. CONCLUSION AND CLINICAL RELEVANCE: There were no detrimental behavioural effects associated with either FFP or acepromazine. The FFP had additional calming effects in cats given acepromazine and, to a lesser degree, helped to calm cats that were not given acepromazine. Feline facial pheromone helps to calm cats in unfamiliar surroundings.  相似文献   
57.
58.
Avian pathogenic Escherichia coli (APEC) cause colibacillosis, a disease which is responsible for significant losses in poultry. Control of colibacillosis is problematic due to the restricted availability of relevant antimicrobial agents and to the frequent failure of vaccines to protect against the diverse range of APEC serogroups causing disease in birds. Previously, we reported that the increased serum survival gene (iss) is strongly associated with APEC strains, but not with fecal commensal E. coli in birds, making iss and the outer membrane protein it encodes (Iss) candidate targets for colibacillosis control procedures. Preliminary studies in birds showed that their immunization with Iss fusion proteins protected against challenge with two of the more-commonly occurring APEC serogroups (O2 and O78). Here, the potential of an Iss-based vaccine was further examined by assessing its effectiveness against an additional and widely occurring APEC serogroup (O1) and its ability to evoke both a serum and mucosal antibody response in immunized birds. In addition, tissues of selected birds were subjected to histopathologic examination in an effort to better characterize the protective response afforded by immunization with this vaccine. Iss fusion proteins were administered intramuscularly to four groups of 2-wk-old broiler chickens. At 2 wk postimmunization, chickens were challenged with APEC strains of the O1, O2, or O78 serogroups. One week after challenge, chickens were euthanatized, necropsied, any lesions consistent with colibacillosis were scored, and tissues from these birds were taken aseptically. Sera were collected pre-immunization, postimmunization, and post-challenge, and antibody titers to Iss were determined by enzyme-linked immunosorbent assay (ELISA). Also, air sac washings were collected to determine the mucosal antibody response to Iss by ELISA. During the observation period following challenge, 3/12 nonimmunized chickens, 1/12 chickens immunized with 10 microg of GST-Iss, and 1/12 chickens immunized with 50 microg of GST-Iss died when challenged with the O78 strain. No other deaths occurred. Immunized chickens produced a serum and mucosal antibody response to Iss and had significantly lower lesion scores than nonimmunized chickens following challenge, regardless of the challenge strain. This study expands on our previous report of the value of Iss as an immunoprotective antigen and demonstrates that immunization with Iss can provide significant protection of chickens against challenge with three different E. coli strains.  相似文献   
59.
A 6-year-old ShihTzu presented with tonic-clonic cluster seizure. T2-weighted magnetic resonance (MR) images showed bilateral diffuse hyperintense lesions at the cerebral cortex with enlarged sulci. Computed tomography revealed a portosystemic shunt (PSS) and azygos continuation. Based on the clinical signs, blood examinations and diagnostic images, the dog was diagnosed with hepatic encephalopathy secondary to PSS. The neurologic signs were gradually improved after medical therapy for hyperammonemia. This is the first report of hyperintensity of the cerebral cortex on T2-weighted MR images associated with acute hepatic encephalopathy in a dog.  相似文献   
60.
The effect of by‐products of oriental medicinal plants (OMP; T1) containing 0.03% herb extracts (T2) or 0.1% aminolevulinic acid (T3) on the production performance of swine during the finishing period and on its meat quality were investigated. No significant differences were found in the weight gain, feed intake and feed conversion rate among the tested groups (P > 0.05). But the treated group showed higher (P < 0.05) moisture and ash and lower protein than the control group. The T3 group showed a lower meat cholesterol content (38.42 mg/100 g) compared to the other groups (P < 0.05). The vitamin E content of the muscle in the treated groups was higher compared to the control group. No antibiotic content was detected in all treated and control samples. The values of the volatile basic nitrogen (VBN) and thiobarbituric acid reactive substance (TBARS) of the treated groups were significantly lower (P < 0.01) than the control group. The treated groups had significantly better (P < 0.05) sensory‐test scores for color, flavor, off‐flavor and total acceptability compared to the control group.  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