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   166729篇
  免费   12195篇
  国内免费   4972篇
耳鼻咽喉   2009篇
儿科学   3593篇
妇产科学   4509篇
基础医学   22845篇
口腔科学   4450篇
临床医学   14654篇
内科学   27904篇
皮肤病学   2968篇
神经病学   10282篇
特种医学   5934篇
外国民族医学   17篇
外科学   22151篇
综合类   15653篇
现状与发展   12篇
一般理论   34篇
预防医学   12611篇
眼科学   3748篇
药学   15421篇
  48篇
中国医学   4511篇
肿瘤学   10542篇
  2022年   1814篇
  2021年   2852篇
  2020年   2194篇
  2019年   2365篇
  2018年   3010篇
  2017年   2667篇
  2016年   2588篇
  2015年   3467篇
  2014年   4425篇
  2013年   5240篇
  2012年   7416篇
  2011年   8138篇
  2010年   5701篇
  2009年   5040篇
  2008年   6678篇
  2007年   6768篇
  2006年   6544篇
  2005年   5674篇
  2004年   5150篇
  2003年   4915篇
  2002年   4541篇
  2001年   8040篇
  2000年   7896篇
  1999年   6336篇
  1998年   2232篇
  1997年   1751篇
  1996年   1223篇
  1995年   1115篇
  1994年   1019篇
  1992年   3828篇
  1991年   3930篇
  1990年   3628篇
  1989年   3614篇
  1988年   3484篇
  1987年   3315篇
  1986年   3130篇
  1985年   3003篇
  1984年   2072篇
  1983年   1803篇
  1979年   1914篇
  1978年   1189篇
  1977年   993篇
  1975年   1197篇
  1974年   1366篇
  1973年   1413篇
  1972年   1357篇
  1971年   1250篇
  1970年   1140篇
  1969年   1124篇
  1968年   1029篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
The role of non-complement-activating alloantibodies in humoral graft rejection is unclear. We hypothesized that the non-complement-activating alloantibodies synergistically activate complement in combination with complement-activating antibodies. B10.A hearts were transplanted into immunoglobulin knock out (Ig-KO) mice reconstituted with monoclonal antibodies to MHC class I antigens. In allografts of unreconstituted Ig-KO recipients, no C4d was detected. Similarly, reconstitution with IgG1 or low dose IgG2b alloantibodies did not induce C4d deposition. However, mice administered with a low dose of IgG2b combined with IgG1 had heavy linear deposits of C4d on vascular endothelium. C4d deposits correlated with decreased graft survival. To replicate this synergy in vitro, mononuclear cells from B10.A mice were incubated with antibodies to MHC class I antigens followed by incubation in normal mouse serum. Flow cytometry revealed that both IgG2a and IgG2b synergized with IgG1 to deposit C4d. This synergy was significantly decreased in mouse serum deficient in mannose binding lectin (MBL) and in serum deficient in C1q. Reconstitution of MBL-A/C knock out (MBL-KO) serum with C1q-knock out (C1q-KO) serum reestablished the synergistic activity. This suggests a novel role for non-complement-activating alloantibodies and MBL in humoral rejection.  相似文献   
992.
BACKGROUND: Epidemiologic studies reveal that posttraumatic stress disorder (PTSD) is highly comorbid with both conduct disorder and major depression in men. The genetic and environmental etiology of this comorbidity has not been examined. METHODS: Data were analyzed from 6744 middle-aged male-male monozygotic and dizygotic twins from the Vietnam Era Twin Registry. Conduct disorder, major depression, and PTSD were assessed via telephone interview using the Diagnostic Interview Schedule for the DSM-III-R in 1992. Structural equation modeling was used to estimate additive genetic, shared environmental, and individual-specific environmental effects common and specific to conduct disorder, major depression, and PTSD. RESULTS: The association between conduct disorder and PTSD was explained primarily by common shared environmental influences; these explained 10% (95% confidence interval: 6%-17%) of the variance in PTSD. The association between major depression and PTSD was largely explained by common genetic influences; these explained 19% (95% confidence interval: 11%-26%) of the variance in PTSD. CONCLUSIONS: Our findings suggest that different etiologic mechanisms explain the association of conduct disorder and major depression with PTSD in male veterans. If replicated in other populations, results suggest research aimed at identifying specific genetic and environmental factors that influence PTSD may benefit from starting with those that have been more consistently and strongly associated with major depression and conduct disorder.  相似文献   
993.
Excitation functions were measured by the stacked-foil technique for (nat)Rb(alpha,xn)(87m,87m+g,88)Y and (nat)Sr(alpha,xn)(86,88,89)Zr reactions from their respective thresholds up to 26 MeV. The samples for irradiation were prepared by sedimentation and pellet pressing techniques. The measured data were compared with those available in the literature. From the excitation functions, integral yields of the products were calculated. The suitable energy ranges for the production of (87)Y and (88)Y via (nat)Rb(alpha,xn) processes and of (89)Zr via the (nat)Sr(alpha,xn) process are E(alpha)=26-->20 MeV, E(alpha)=26-->5 MeV and E(alpha)=20-->8.5 MeV, respectively. The respective yields amount to 8.2, 0.08 and 0.9 MBq/microA h. Production of (88)Y is feasible if a waiting time of about 2 months is allowed to let the impurities decay out. Also, (87)Y can be produced with a relatively low impurity of (88)Y. The yields of both (88)Y and (87)Y via the present routes are, however, appreciably lower than those via the (nat)Sr(p,xn) processes. There is a possibility to produce (89)Zr via the alpha-particle irradiation of (nat)Sr. The yield is rather low but would be considerably increased if enriched (86)Sr would be used as target material. The radionuclidic impurity levels in all the three products are discussed.  相似文献   
994.
Three-dimensional imaging for the quantification of myocardial motion is a key step in the evaluation of cardiac disease. A tagged magnetic resonance imaging method that automatically tracks myocardial displacement in three dimensions is presented. Unlike other techniques, this method tracks both in-plane and through-plane motion from a single image plane without affecting the duration of image acquisition. A small z-encoding gradient is subsequently added to the refocusing lobe of the slice-selection gradient pulse in a slice following CSPAMM acquisition. An opposite polarity z-encoding gradient is added to the orthogonal tag direction. The additional z-gradients encode the instantaneous through plane position of the slice. The vertical and horizontal tags are used to resolve in-plane motion, while the added z-gradients is used to resolve through-plane motion. Postprocessing automatically decodes the acquired data and tracks the three-dimensional displacement of every material point within the image plane for each cine frame. Experiments include both a phantom and in vivo human validation. These studies demonstrate that the simultaneous extraction of both in-plane and through-plane displacements and pathlines from tagged images is achievable. This capability should open up new avenues for the automatic quantification of cardiac motion and strain for scientific and clinical purposes.  相似文献   
995.
提高毛发移植的覆盖率   总被引:4,自引:2,他引:2  
目的探讨显微外科技术自体毛发移植的特点和方法,提高毛发移植成活的覆盖率。方法在较低温度(20°C)环境下,采用边切边缝方法取耳后或枕后毛发,在显微镜下分离成保留周围少量脂肪组织的毛囊族或单株,按需要移植部位不同进行不同的毛囊族或单株并套插的显微外科技术移植共31例。结果31例移植毛发后随访21例,随访时间6~38个月,移植后的毛发能基本覆盖无毛发区的皮肤和瘢痕,移植覆盖率较原来的移植方法提高33%,且外形自然,效果稳定。结论显微外科技术自体毛囊族状(微株小株)或单株移植,具有操作快、损伤小、低温保湿等特点,能较好地保留毛囊周围少量脂肪,在孔与孔的皮肤间隙内再用毛发移植针植入单株毛坯的“套插”移植,更有助于增加毛发覆盖率。  相似文献   
996.
Objective The aim of this study was to evaluate of adilty of two acute renal failure-specific scoring systenms (the classification by Bellome et al and the AKIN criteria) for predicting hospital mortality after cardiac surgery in adult patients. Methods Between October 1 st 2006 to Decemjber 31 st 2006, 509 adult patients who ungerwent coronary artery bypass grafting (CABG) and/ or valve operation were enrolled in this study. The medical data collection included gender, age, types of operation, perioperative he- modynamic parameters, urine output, biochemical parameters and outcome. Renal function was assessed daily according to the classi- ficatinn by Bellomo and the AKIN criteria, respectively. As references, Acure Physiology and Chronic Health Evaluation(APACHE) Ⅱ and Sepsis-related Organ Failure Assessment (SOFA) score were also calculated. Resuits Three hundred and forty-one patients were male (67.0%), and 168 were female (33.0%), mean age was (56.2±12.0) years old. Tnree hundred and nine patieats un- derwent CABG, 182 underwent valve operation and 18 underwent CABG plus valve operation, Mean duration of ventilation support was (20.4±17.7) houra, and the ICU stay was (1.4±1.0) days. Postoperative hospital stay was (13.8±9.1) days. According to the classification by Bellomo., the highest in-hospital mortality was 52.9% in ARFS group. Mahiplicatinn of in-hospital morality rate was abserved (X2 for trend, P<0.01) in 0.4% (non-ARF), 1.2% (stage 1), 12.0% (stal~ 2) and 32.4% (stage 3) of pa- tients based on the AKIN criteria. By applying the area under the receiver operating characteristic ourve, the classification by Bellomo and the AKIN criteria had good discriminative power. Furthering, multivariate logistic regression analysis verified that the Odds Ratio of the AKIN criteria was 5.478 (P =0.028, 95% Confidence Interval 1.027- 24.856), after adjusting for gender and age. Con- clusion Analytical data confinned good discriminative power of both the AKIN criteria and the classification by Bellomo for predicting hospital mortality of adult postoperative patient with ARF.  相似文献   
997.
OBJECTIVE: The purpose of this investigation was to test a modified telescopic anastomosis in large muscular arteries. MATERIAL AND METHODS: The right carotid arteries in 30 sheep (average weight 57+/-5.7 kg) were transected and anastomosed end to end using two guided sutures and compared with a control group (10 sheeps) using two external sutures (Lauritzen method). RESULTS: The mean time to complete the anastomosis (4.5 min) and hemostasis (4.3 min) in the experimental group was less than the control group (17.3 min for anastomosis and 6.4 min for hemostasis) (P<0.05). In addition, the total amount of blood loss during the modified anastomosis was significantly lower than Lauritzen method (3.8 versus 8 ml). In both experimental and control groups the scanning electron microscopy (SEM) at 90th day post-operation revealed a continuous smooth layer of endothelial cells covering the anastomotic junction. CONCLUSIONS: Anastomosis with two guided sutures is easy and faster to perform and could be applicable to an acutely transected vessel.  相似文献   
998.
胃肠道恶性肿瘤围手术期肠内免疫营养的临床研究   总被引:3,自引:0,他引:3  
目的评价肠内免疫营养对胃肠道恶性肿瘤术后免疫功能、炎症反应、营养状态、并发症的影响,探讨I临床推广应用的理论依据。方法将90例胃肠道恶性肿瘤随机分为免疫营养组、普通营养组和对照组,术前5天和术后1、8天分别检测多项指标。结果(1)术后免疫营养组免疫指标明显高于另两组;(2)术后免疫营养组的炎性指标明显低于另两组;(3)术后免疫营养组的前白蛋白明显高于另两组;(4)术后免疫营养组的并发症明显低于另两组。结论围手术期肠内免疫营养可在术后早期提高病人的免疫功能,减轻术后应激反应,降低术后并发症的发生率,并缩短平均住院时间。  相似文献   
999.
1000.
The impacts of caffeic acid (3,4‐dihydroxycinnamic acid, CA) on the pharmacokinetics of levodopa (L‐dopa) were studied in rabbits. A single dose of 5/1.25 mg·kg?1 l ‐dopa/carbidopa was administered alone or was co‐administered with three different doses of caffeic acid (2.5, 5, and 10 mg·kg?1), or a single dose of 5 mg·kg?1 caffeic acid was administered alone via an intramuscular route to six rabbits each in a crossover treatment protocol. Plasma levels of l ‐dopa, 3‐O‐methyldopa (3‐OMD), caffeic acid, and ferulic acid were determined and subsequently used to calculate their pharmacokinetic parameters. The results indicated that caffeic acid administered at a dose of 10 mg·kg?1 decreased about 22% of the peripheral formation of 3‐OMD and about 31% of the Cmax of 3‐OMD. In addition, the metabolic ratios (MR, AUC of 3‐OMD/AUC of L‐dopa) decreased by about 22%. Results also indicated that caffeic acid significantly decreased the proportion of 3‐OMD (p < 0.05). In contrast, the parameters of neither caffeic acid nor ferulic acid were significantly affected by l ‐dopa/carbidopa. In conclusion, caffeic acid at a dose of 10 mg·kg?1 can significantly affect the COMT metabolic pathway of L‐dopa. Copyright © 2009 John Wiley & Sons, Ltd.  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