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   2267篇
  免费   311篇
  国内免费   15篇
  2023年   40篇
  2022年   38篇
  2021年   93篇
  2020年   90篇
  2019年   72篇
  2018年   67篇
  2017年   78篇
  2016年   65篇
  2015年   76篇
  2014年   107篇
  2013年   211篇
  2012年   83篇
  2011年   125篇
  2010年   97篇
  2009年   83篇
  2008年   86篇
  2007年   109篇
  2006年   86篇
  2005年   60篇
  2004年   66篇
  2003年   57篇
  2002年   48篇
  2001年   34篇
  2000年   31篇
  1999年   40篇
  1998年   44篇
  1997年   28篇
  1996年   24篇
  1995年   36篇
  1994年   35篇
  1993年   34篇
  1992年   41篇
  1991年   30篇
  1990年   26篇
  1989年   25篇
  1988年   19篇
  1987年   16篇
  1986年   11篇
  1985年   32篇
  1984年   38篇
  1983年   44篇
  1982年   30篇
  1981年   24篇
  1980年   17篇
  1979年   13篇
  1978年   21篇
  1977年   10篇
  1976年   10篇
  1975年   8篇
  1972年   14篇
排序方式: 共有2593条查询结果,搜索用时 15 毫秒
1.
The mixing performance of gastric contents during digestion is expected to have a major role on the rate and final bioavailability of nutrients within the body. The aim of this study was to characterize the ability of the human stomach to advect gastric contents with different rheological properties. The flow behavior of two Newtonian fluids (10−3 Pa s, 1 Pa s) and a pseudoplastic solution (K=0.223 Pa s0.59) during gastric digestion were numerically characterized within a simplified 3D model of the stomach geometry and motility during the process (ANSYS-FLUENT). The advective performances of each of these gastric flows were determined by analyzing the spatial distribution and temporal history of their stretching abilities (Lagrangian analysis). Results illustrate the limited influence that large retropulsive and vortex structures have on the overall dynamics of gastric flows. Even within the distal region, more than 50% of the flow experienced velocity and shear values lower than 10% of their respective maximums. While chaotic, gastric advection was always relatively poor (with Lyapunov exponents an order of magnitude lower than those of a laminar stirred tank). Contrary to expectations, gastric rheology had only a minor role on the advective properties of the flow (particularly within the distal region). As viscosity increased above 1 St, the role of fluid viscosity became largely negligible. By characterizing the fluid dynamic and mixing conditions that develop during digestion, this work will inform the design of novel in vitro systems of enhanced biomechanical performance and facilitate a more accurate diagnosis of gastric digestion processes.  相似文献   
2.

Purpose

To explore how the use of a laser needle-knife affects vertebroarterial morphology and protein expression of PI-3K, AKT and VEGF in the carotid artery of a rabbit model of cervical spondylotic arteriopathy (CSA), and to determine its primary treatment mechanism.

Methods

The CSA rabbit model consisted of 30 rabbits with CSA that were randomly divided into a model group (n?=?10), an acupuncture group (n?=?10) and a laser needle-knife group (n?=?10) plus a further 10 wild type rabbits placed into a normal group. Rabbits in the acupuncture group were treated by needling the Fengchi (GB 20) and Jiaji (EX-B2) acupoints, while those in the laser needle-knife group were treated with a laser needle-knife on the Jiaji (EX-B2) near the spinous process of the fifth cervical vertebra, the rabbit in both groups immobilized during treatment. Rabbits in the other two groups received no treatment, but were immobilized for a similar duration. The morphology of the right vertebral artery and the distribution of pore size before and after treatment were compared using BET and SEM, and the protein expression of PI-3K, AKT and VEGF in the carotid artery of the four groups measured using Western blot analysis.

Results

The pore diameter and specific surface area of the right vertebral artery increased after treatment, as did the number of micropores. Compared with the normal group, the protein expression of PI-3K, AKT and VEGF in the carotid artery of the model group was significantly lower (P?<?0.05), while that of the laser needle-knife group was significantly higher (P?<?0.05 and P?<?0.01). In addition, rabbits from the acupuncture and laser needle-knife groups demonstrated significantly higher levels of protein expression of PI-3K and VEGF in the carotid artery compared with the model group (P?<?0.05 and P?<?0.01).

Conclusions

By promoting micrangium hyperplasia within the vertebral artery of rabbits with CSA, treatment with a laser needle-knife modified the protein expression of PI-3K, AKT and VEGF, suggesting that laser needle-knife therapy possibly treats CSA though these signaling pathways.  相似文献   
3.
4.
The pollution of environment by toxic chemicals is a global and chronic problem. Human health risk due to exposure to chemical pollutants is constantly increasing. Pesticides form major toxic chemicals in environment. Scientifically, there is an obviously correlation between the exposure to pesticides and appearance of many diseases. Currently, the significance of natural products for health and medicine has been formidable. The present study investigated the effect of grapeseed oil in male rats exposed to diazinon. The experimental rats were divided into five groups. The rats of the first group were served as control. The experimental animals of the second group were exposed to diazinon (DZN). The animals of the third group were supplemented with grapeseed oil and treated with DZN. The rats of the fourth group were supplemented with grapeseed oil. The experimental rats of the fifth group were supplemented with corn oil. Hematobiochemical and histopathological evaluations were chosen as indicators of DZN toxicity and protective role of grapeseed oil. In rats exposed only to DZN, the levels of serum glucose, triglycerides, cholesterol, low density lipoprotein cholesterol, very low density lipoprotein cholesterol, creatinine, urea nitrogen, uric acid, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, creatine kinase and lactate dehydrogenase were statistically increased, while the level of serum total protein was significantly decreased. Moreover, the histopathological evaluations of the liver, kidney and testis showed that DZN causes several severe alterations. Pretreatment with grapeseed oil exhibited a protective role against DZN toxicity which confirmed by the inhibition of hematobiochemical and histopathological changes due to DZN exposure. Additionally, the present study suggests that the effect of grapeseed oil supplementation against DZN toxicity may be attributed to the antioxidant role of its constituents.  相似文献   
5.
目的了解全自动血型鉴定系统用于检测ABO血型和Rh(D)血型的效果。方法采用深圳爱康AK03A型数字血型仪对北海市中心血站2010年5月—2011年12月无偿献血者20702份样本进行ABO血型和Rh(D)血型鉴定,并与手工试管法进行对比验证。结果发现正反定型不一致的有75例,ABO初筛血型错误的36例,Rh(D)阴性的53例。结论全自动血型鉴定系统检测血型快捷、方便、高效,能降低检测人员的工作强度,但判读结果时需要与手工试管法结合进行验证,才能得出正确的结果。  相似文献   
6.
脑胶质瘤在成人原发脑肿瘤中居首位,目前的治疗手段疗效较差,手术切除后复发率高,而化疗药物不能有效的穿透血脑屏障并聚集在肿瘤部位。纳米材料作为载药体为其治疗开辟了新的思路,纳米材料在保持药物稳定性,增加其血液循环时间方面有明显优势。但目前纳米材料还存在着一些亟待解决的问题,如穿透血脑屏障(BBB)、准确靶向于脑胶质瘤细胞等。本文简略论述了纳米材料载药的特性及优势,重点就目前纳米材料载药所面临的问题进行综述,总结了纳米药物穿透血脑屏障的多种策略及纳米药物靶向于脑胶质瘤的不同方式,并详细讨论了目前纳米材料载药多重靶向策略,对其未来的发展进行展望。  相似文献   
7.
Praziquantel (PZQ) is an acylated quinoline-pyrazine originally developed for veterinary application but now one of the most used anti-helminthic drugs for treatment of certain trematodes and cestodes in both human and other animals. The present study investigated the mutagenic and physiological responses in the juveniles of African catfish, Clarias gariepinus following short term exposure to praziquantel. Based on the 53.52 mg/l 96 h LC50 of PZQ obtained, two sublethal concentrations of 5.35 and 10.70 mg/l of the drug were selected and fish were exposed to these concentrations and control for 15 days. Micronuclei induction in the peripheral blood of PZQ-exposed fish was highest on day 10 but the fish morphological parameters were not affected. The packed cell volume (PCV) was significantly reduced (p < 0.05) from day 5 while red blood cells (RBC) and hemoglobin (Hb) significantly declined (p < 0.05) on day 15. Macrocytic anemia was observed on day 1 of study and thereafter microcytic anemia developed on day 5 of study. The white blood cell (WBC) was significantly (p < 0.05) elevated from day 10 of exposure while values of mean cellular volume (MCV), mean cellular hemoglobin (MCH) and mean cellular hemoglobin concentration (MCHC) were not significantly different (p > 0.05) from the control. Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and glucose levels significantly increased while protein reduced (p < 0.05) throughout the exposure period but a mixed trend was observed in the leukocyte differentials. PZQ should be used with caution as sublethal exposure elicited micronucleus induction and alterations of hematological and biochemical parameters in the fish.  相似文献   
8.
The intertidal wormSipunculus nudus was exposed to various temperatures for an analysis of the integrated changes in energy and acid-base status. Animals were incubated in sea water or maintained for up to 8 days at 4 and 0°C while dwelling in the sediment. Cannulation of the animals prior to experimentation allowed the analysis of blood gas parameters ( , and pH). fell to 0 torr within 8 days at 0°C. A simultaneous reduction of ventilatory activity was derived from measurements of the pattern of coelomic fluid pressure changes associated with ventilatory movements. The increase in and an onset of anaerobic metabolism, indicated by the accumulation of end products like acetate and propionate both in the coelomic fluid and the body wall musculature, led to the development of a progressive acidosis and a deviation from the alphastat regulation of intracellular pH seen in unburied animals. The drop in intracellular pH together with the depletion of the adenylates and the phosphagen, phospho-l-arginine, reflect a significant decrease in the Gibb's free-energy change of ATP hydrolysis. These changes are interpreted to indicate lethal cold injuries, because recovery was not possible when the animals were returned to 12°C after more than 2 days of exposure to 0°C. A low critical temperature indicating the onset of cold-induced anaerobiosis is concluded to exist below 4°C owing to the insufficient response of the ventilatory system to the developing hypoxia.  相似文献   
9.
目的:探讨复方丹参滴丸联合阿司匹林治疗冠心病患者的疗效及其对血脂水平的影响。方法:选取2015年1月至2016年1月我院收治的冠心病患者86例,按照随机数字表法将其分为对照组和实验组,各43例,两组均给予常规治疗,对照组在常规治疗基础上联用阿司匹林,实验组在常规治疗基础上联用阿司匹林和复方丹参滴丸。治疗8周后,对比两组患者临床疗效、甘油三酯(TG)、总胆固醇(TC)、低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)水平;并对比两组患者的不良反应发生情况。结果:实验组总有效率为86.05%,显著高于对照组的37.21%(P0.05);治疗8周后,实验组TC、TG以及LDL-C较治疗前下降,HDL-C较治疗前升高,差异均有统计学意义(P0.05);治疗8周后,实验组患者血脂TC、TG、LHL均较对照组降低,HDL较对照组升高(P0.05)。治疗期间,实验组不良反应发生率为4.65%,对照组为6.98%,两组患者不良反应发生率无统计学差异(P0.05)。结论:冠心病患者采用复方丹参滴丸联合阿司匹林治疗具有较好的疗效,并能有效改善患者血脂水平,且安全性较高,具备临床推广价值。  相似文献   
10.
目的:探讨短期胰岛素泵强化治疗对2型糖尿病患者血脂血糖代谢的影响。方法:选取76例2型糖尿病患者,按给药方式不同分为两组,对照组(38例)给予门冬胰岛素常规治疗,观察组(38例)给予胰岛素泵强化治疗,依据两组治疗前后的血糖、血脂指标变化及治疗前、治疗后1周、2周的ADL量表评分评价短期胰岛素泵强化治疗对2型糖尿病患者血脂血糖代谢的影响。结果:治疗后,两组患者的空腹血糖(FPG)、糖化血红蛋白(Hb Alc)、总胆固醇(TC)、甘油三酯(TG)、低密度脂蛋白胆固醇(LDL-C)水平均较治疗前显著降低,高密度脂蛋白胆固醇(HDL-C)水平均明显升高,且观察组FPG、Hb Alc、TC、TG、LDL-C水平均明显低于对照组,HDL-C水平显著高于对照组(P0.05)。治疗后1周、2周,两组ADL评分均较治疗前明显提高,且观察组显著高于对照组(P0.05)。结论:短期胰岛素泵强化治疗能显著改善2型糖尿病患者的血糖血脂代谢紊乱,并提高患者的日常生活能力。  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