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   88752篇
  免费   5412篇
  国内免费   41篇
林业   3026篇
农学   2745篇
基础科学   529篇
  10122篇
综合类   16477篇
农作物   3677篇
水产渔业   4370篇
畜牧兽医   46434篇
园艺   1109篇
植物保护   5716篇
  2019年   838篇
  2018年   1220篇
  2017年   1419篇
  2016年   1325篇
  2015年   1172篇
  2014年   1397篇
  2013年   3514篇
  2012年   2616篇
  2011年   3115篇
  2010年   2021篇
  2009年   1981篇
  2008年   2997篇
  2007年   2906篇
  2006年   2741篇
  2005年   2589篇
  2004年   2445篇
  2003年   2460篇
  2002年   2346篇
  2001年   2951篇
  2000年   2840篇
  1999年   2305篇
  1998年   987篇
  1997年   899篇
  1996年   801篇
  1995年   973篇
  1994年   867篇
  1993年   864篇
  1992年   1843篇
  1991年   1848篇
  1990年   1786篇
  1989年   1841篇
  1988年   1590篇
  1987年   1703篇
  1986年   1759篇
  1985年   1689篇
  1984年   1326篇
  1983年   1192篇
  1982年   852篇
  1981年   729篇
  1979年   1129篇
  1978年   910篇
  1977年   791篇
  1976年   744篇
  1975年   814篇
  1974年   1006篇
  1973年   1053篇
  1972年   1009篇
  1971年   963篇
  1970年   911篇
  1969年   823篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Introduction:  Mycobacterial cell wall‐DNA complex (MCC) is a bifunctional anticancer agent that induces cancer cell apoptosis and stimulates cytokine synthesis by immune cells. Intravesical MCC is currently being evaluated in humans with high‐grade urinary bladder cancer. Evaluation of MCC in dogs with transitional cell carcinoma (TCC) will allow mechanistic studies in a natural animal model of TCC, and a potentially beneficial therapy for dogs with this cancer. In this study, we have determined the anticancer activity of MCC against canine TCC cells in vitro .
Methods:  Canine TCC cells (K9TCC cell line) were incubated with MCC (0.05–100 μg/ml, 0.5–72 hours). Cellular proliferation was measured by MTT reduction. Cell cycle was analyzed by flow cytometry with propidium iodide. Apoptosis was identified by flow cytometry using anti‐active‐caspase‐3/PE and anti‐cleaved‐PARP/FITC antibodies. Apoptosis‐inducing activity of 100 μg/ml MCC in combination with piroxicam (0.1–1.0 uM) was evaluated.
Results:  MCC inhibited K9TCC cell proliferation in a concentration‐dependent manner (maximal activity – 45% at 100 μg/ml MCC) in association with the presence of activated caspase‐3 and cleaved PARP. Inhibition of proliferation and apoptosis‐inducing activities of MCC were independent of cell cycle phase. A thirty‐minute exposure of MCC was sufficient for optimal activity. Piroxicam (0.5 uM) enhanced apoptosis‐inducing activity of MCC.
Conclusions:  MCC induces apoptosis in K9TCC cells. This activity is potentiated by piroxicam. Following positive results in vitro , in vivo studies have been initiated. One dog, treated to date, has had a minor reduction in tumor volume following the first course of treatment with no treatment‐related toxicity.  相似文献   
992.
Waldenström Macroglobulinemia is a low‐grade immunosecretory disorder associated with lymphoid tumours, which is rarely reported in veterinary medicine. In this study, we describe two clinical cases of this rare syndrome in dogs, each characterized by a different onset and clinical course. In one case, a hyperacute onset and aggressive behaviour of the neoplasm was observed. Absolute serum viscosity (SV) was retrospectively evaluated in order to explain clinical findings. Rotational viscosimetry showed good precision in measuring SV. Both dogs had SV values higher than a control groups of healthy dogs although only one subject developed hyperviscosity symptoms and complications. At high paraprotein concentrations, a slight reduction of the M‐component was associated with a marked decrease in SV. Thus, this work suggests that SV assessment is a relevant tool for managing monoclonal gammopathies, whose usefulness should be further confirmed in larger cohorts of dogs.  相似文献   
993.
994.
Several investigators have suggested that the blood-vessel system in the equine periodontal ligament does not only serve nutritional needs, but also specific functional needs, e.g. in terms of a shock absorbing system. In order to supplement the previous data, corrosion casts of the periodontal blood vessels were studied with special attention to the spatial arrangement and connections of the vessels. The heads of eight warm-blooded horses (age 2.5–23 years, seven female, one male), which had been killed for medical reasons, were dissected. The arteria alveolaris inferior and the a. infraorbitalis were perfused with 100 ml Heparin (20 000 IU) followed by 100 ml tap water. After storage at 4°C for 24–96 h, 10–200 ml methacrylate resin (BiodurTM E20) were injected by use of a cartridge pistol for approx. 1 h. After polymerization for 24 h at 60°C, the jaws were frozen and cut with a steel band saw in a horizontal, sagittal or transversal plane to obtain segments that exposed the periodontal space. The specimens were macerated in detergent at 60°C until the soft tissues had vanished. Care was taken to keep the periodontal vessels complete and in topographical integrity. The vascular casts were mesoscopically examined by use of a dissection microscope (magnification 5.8×–40×). The blood vessels in the periodontal space connected with vessels in three other sites:
  • (1)

    occlusal – with the blood vessels of the gingiva;

      相似文献   
995.
The purpose of this study was to investigate the response of horses to confinement and isolation in a stable (indoor individual housing) for the first time using behavioral indices, heart rate, and salivary cortisol concentration. Six naive 2-year-old Australian Stock Horse fillies were examined at 4-hour intervals over 24 hours in an outdoor group paddock followed by 24 hours in indoor individual housing. Behavioral observations and scores and heart rates were recorded and saliva samples were taken at each interval. During stabling, all horses became agitated and demonstrated increased vocalization and movement. Behavioral scores were significantly higher in the indoor individual housing (P < .001). No significant difference in heart rates between the two environments was detected. Mean salivary cortisol did not increase significantly (2 ng/mL ± 1.4 ng/mL in outdoor group paddock vs 2.5 mL ± 1.2 ng/mL in indoor individual housing). No diurnal rhythm in salivary cortisol was evident in either the outdoor group paddock or indoor individual housing. The results of this study highlight that a combination of behavioral and physiological measures allow better understanding of stress, where one measurement may be misleading. First time stabling of horses elicited marked behavioral responses indicative of stress that were not reflected in increased heart rates or salivary cortisol concentrations. The lack of a diurnal cortisol rhythm and the comparatively high basal cortisol concentrations found in the outdoor group paddock environment may imply that the fillies were already stressed; therefore, stabling did not cause further aberrations detectable by salivary cortisol analysis.  相似文献   
996.
The growth performance and endocrine responses of male weaner pigs (3 to 8 weeks of age) was evaluated in two different environments (clean and dirty) and housing (single or groups of 10 pigs/pen) conditions. The dirty environment contained significantly elevated ammonia, carbon dioxide and dust levels compared with the clean environment. Pigs grew faster and consumed more feed in the clean environment and this was associated with reduced plasma cortisol concentrations compared with pigs in the dirty environment. Pigs housed in groups in the dirty environment had increased β-endorphin and decreased IGF-I concentrations compared to group housed pigs in the clean environment. Feed conversion efficiency did not differ due to environment or group housing. Plasma concentration of cortisol, β-endorphin, IGF-I and IGF-II did not differ between single and group housed pigs. Activity of the hypothalamic-pituitary-adrenal (HPA) axis was greater in response to environmental conditions than group housing, and this was associated with reduced growth in weaner pigs.  相似文献   
997.
The effect of true milk use in the diet of Spanish Brown Swiss male calves on animal performance, carcass and meat quality, and fatty acids composition was studied. In experiment 1, the effect of milk intake [ad libitum continuous (ADLIB) feed vs. restricted 0.7 during 75 days followed by ad libitum feed (RESTR)] and slaughter endpoint (225 kg vs. 5 month) were studied. In experiment 2, ad libitum concentrate feeding [grain-fed (GF)] was compared with milk supplementation until slaughter [milk-fed (MF)] in calves slaughtered at 345 kg. As regards to milk intake, carcass weight and degree of fatness were higher in the ADLIB group (P<0.05). The RESTR group revealed a higher percentage of saturated fatty acids (P<0.05). In experiment 2, the MF group exhibited a higher fat percentage (P<0.05), lower press and cooking losses (P<0.05), and higher scores for tenderness and juiciness (P<0.05) than the GF group. The percentage of saturated fatty acids was higher in the MF group (P<0.05). The results suggest that true milk use in veal production could be an advantageous alternative in terms on production costs, animal performance, and carcass and meat quality.  相似文献   
998.
Ophthalmic emergencies are common presenting complaints in an emergency room. Most ophthalmic emergencies can be treated and stabilized until an ophthalmologist can be consulted. Most ocular emergencies involve loss of vision, compromised globe integrity, or severe ocular pain. Delay in treating true emergencies may result ina blind eye or loss of an eye. This article discusses the clinical signs,diagnosis, and treatment as well as the prognosis of some of the more common ophthalmic emergencies.  相似文献   
999.
Lactation in the mare is associated with changes in the release of metabolic as well as reproductive hormones. Plasma glucose concentration is constantly reduced in lactating compared with non-lactating mares. Several metabolic signals have been proposed to link nutrition and somatic metabolism with reproductive function. The following experiment was performed to study the effect of acute hypoglycaemia on the release of insulin-like growth factor-1 (IGF-1) and luteinizing hormone (LH) in cyclic mares. Different doses of insulin (0.1 and 0.2 IU/kg body weight) were given to induce a decrease in plasma glucose concentration, as existent in lactating mares. All horses treated with insulin developed a hypoglycaemia over a time period of nearly 10 h. The IGF-1 and LH were analysed before and after insulin administration. At no point of time, a significant difference between the two insulin treatments and the control treatment was observed. Therefore, the hypoglycaemic horse is apparently able to provide the brain with sufficient glucose. Short-term hypoglycaemia does not affect the hypothalamo-pituitary-ovarian axis, and concentrations of IGF-1 and LH remained stable during insulin-induced hypoglycaemia. An acute change in plasma glucose concentration is thus not or at least not the only metabolic signal that links nutrition and somatic metabolism with reproductive function in the horse mare.  相似文献   
1000.
Burkholderia mallei causes glanders or farcy in solipeds, a disease that must be reported to the OIE (Office International des Epizooties, Paris, France). The number of reported outbreaks has increased steadily during the last decade. Serodiagnosis is hampered by the considerable number of false‐positives and ‐negatives of the internationally prescribed tests. The major problem leading to low sensitivity and specificity of complement fixation test (CFT) and enzyme‐linked immunosorbent assay (ELISA) has been linked to the test antigens currently used, i.e. crude preparations of whole cells. Future perspectives for the development and evaluation of serological test kits using well‐characterized single antigens are discussed in the light of recent molecular research on B. mallei and the closely related saprozoonotic agent B. pseudomallei.  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