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   20032篇
  免费   1726篇
  国内免费   712篇
耳鼻咽喉   262篇
儿科学   477篇
妇产科学   368篇
基础医学   2807篇
口腔科学   334篇
临床医学   2380篇
内科学   3740篇
皮肤病学   241篇
神经病学   1383篇
特种医学   580篇
外国民族医学   9篇
外科学   2143篇
综合类   1619篇
一般理论   7篇
预防医学   1497篇
眼科学   470篇
药学   1734篇
  10篇
中国医学   586篇
肿瘤学   1823篇
  2023年   266篇
  2022年   530篇
  2021年   905篇
  2020年   637篇
  2019年   700篇
  2018年   714篇
  2017年   572篇
  2016年   544篇
  2015年   778篇
  2014年   976篇
  2013年   1079篇
  2012年   1479篇
  2011年   1482篇
  2010年   897篇
  2009年   766篇
  2008年   1025篇
  2007年   1082篇
  2006年   987篇
  2005年   943篇
  2004年   764篇
  2003年   711篇
  2002年   630篇
  2001年   346篇
  2000年   371篇
  1999年   409篇
  1998年   231篇
  1997年   253篇
  1996年   220篇
  1995年   171篇
  1994年   171篇
  1993年   123篇
  1992年   172篇
  1991年   133篇
  1990年   129篇
  1989年   117篇
  1988年   104篇
  1987年   110篇
  1986年   92篇
  1985年   69篇
  1984年   63篇
  1983年   77篇
  1982年   39篇
  1981年   36篇
  1979年   35篇
  1978年   30篇
  1977年   29篇
  1976年   36篇
  1974年   35篇
  1970年   32篇
  1969年   31篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
Angiogenesis,the formation of new bloodvessels,is necessary for the growth of tumors andtheir metastasis.TNP- 470 is a synthetic analogueof fumagillin and has stronger antiangiogenic  ac-tivity and less side- effects than fumagillin.Thiscompound has been reported to suppress the prolif-eration and metastasis of various kinds of tu-mors[1] . Using nude mice xenografts of ACHN hu-man renal cell carcinoma ( RCC) ,the presentstudyattempted to examine the action of TNP- 470 ongrowth,metastasi…  相似文献   
42.
目的 对兔心肌缺血的模型制备方法进行改进 ,并探讨其在 MRI诊断研究中的价值。方法 分别采用高位结扎左冠状动脉前降支 (L AD)和同时低位结扎 L AD及左冠状动脉旋支 (L Cx)建立兔心肌梗塞模型 ,并在术后行 MRI检查 ,对取材后心肌标本行氯化三苯四氮唑 (TTC)及病理检查。结果  1L AD组 2 0 % (5 / 2 5 )发生心室颤动导致死亡 ,L AD +L Cx组无一例发生室颤死亡。 2 L AD组 EKG改变明显者占 5 6 % (14 / 2 5 ) ,其中 2 1.4 3% (3/14 )在即刻就有 EKG明显改变 ,并在 30分钟后恢复正常 ;EKG改变不明显者占 4 4 % (11/ 2 5 ) ;L AD +L Cx组 10 0 %有 EKG明显改变 ,且 30分钟后亦无明显恢复。 3L AD组心肌梗塞范围较小 ,并均限于左室前壁 ,室间隔前部损害 ;而 L AD+L Cx组心肌梗塞范围较大 ,且累及左室前壁及侧壁 ,无一例有室间隔前部损害。4 L AD组中有 30 % (6 / 2 0 )不能显示小灶缺血局部心肌运动降低 ,16 .6 7% (3/ 18)无法分辨早期小梗塞灶的 MRI信号变化 ;而 L AD+L Cx组均能显示缺血局部心肌运动降低及梗塞灶早期的 MRI信号变化。结论 低位结扎兔心 L AD+L Cx,手术死亡率低 ,EKG改变明显 ,梗塞面积较大 ,是 MRI研究中一种较理想的心肌缺血动物模型制备方法。  相似文献   
43.
OBJECTIVE: To quantify accurately the rate of adverse reactions after the preschool (fifth) dose of adsorbed diphtheria toxoid-pertussis vaccine-tetanus toxoid (DPT) vaccine and to test the hypothesis that large local reactions are attributable to the diphtheria toxoid. DESIGN: Double-blind randomized controlled trial. SETTING: Suburban community public health unit. PARTICIPANTS: Healthy children 4 to 5 years of age with a history of having received four doses of adsorbed DPT vaccine. INTERVENTIONS: Subjects were given either the standard DPT vaccine (with 25 Lf units of diphtheria toxoid) or a modified DPT vaccine (with 10 Lf units of diphtheria toxoid). They were assessed 24 hours later by a nurse. Serum samples obtained before vaccination were tested for diphtheria and tetanus antitoxin levels by means of neutralization assay and enzyme-linked immunosorbent assay. MAIN OUTCOME MEASURES: Rates of large local reactions (an area of redness or swelling or both of 5 cm or greater) 24 hours after vaccination in the two groups. Relation between serum antitoxin levels before vaccination and the rate of large local reactions in each group. RESULTS: Of the 250 subjects enrolled 124 received the standard vaccine and 126 the modified one. Large local reactions occurred in 71% of the subjects receiving the standard vaccine and 52% of those receiving the modified one (p less than 0.01). In the former group large erythematous reactions occurred significantly more often in those with an elevated prevaccination diphtheria antitoxin level than in those without an elevated level; no relation was found between such reactions and the prevaccination tetanus antitoxin level. Reduced arm movement was evident in 45% of the children in the two groups. Few had systemic adverse reactions. CONCLUSIONS: Large local reactions occur frequently after the preschool administration of the DPT vaccine. These reactions are uncomfortable but not serious. They result in part from the large amount of diphtheria toxoid in the standard DPT vaccine.  相似文献   
44.
OBJECTIVE: To determine physical activity patterns in chronic hemodialysis patients with a specific emphasis on the difference between dialysis and nondialysis days. Design A cross-sectional single-center study. SETTING: Vanderbilt University Outpatient Dialysis Unit. PATIENTS: Twenty current chronic hemodialysis patients: 10 male, 10 female; 15 black, 5 white; mean age, 50.1 +/- 9.9 years; height, 164.5 +/- 10.9 cm; weight, 82.5 +/- 15.4 kg; length on dialysis, 57.3 +/- 45.3 months. METHODS: Minute-by-minute physical activity was assessed over a 7-day period using a triaxial accelerometer, which consists of raw numbers or counts calculated by the 3 axes of the accelerometer (PA counts). PA counts were extrapolated on a daily and hourly basis. Physical functioning tests included: sit-to-stand, 6-minute walk, and 1-repetition maximal leg press exercise. Laboratory values for serum concentrations of albumin, prealbumin, C-reactive protein, and cholesterol were also collected. MAIN OUTCOME MEASURE: PA counts. RESULTS: Total PA counts were significantly lower on dialysis days when compared with nondialysis days (128,279 +/- 74,009 versus 168,744 +/- 95,168, respectively, P = .025). The average PA counts during the 4-hour dialysis time period were significantly lower on dialysis days when compared with nondialysis days (3,086 +/- 3,749 versus 11,070 +/- 7,695, respectively, P = .001). At postdialysis hours 1 and 2, PA counts on dialysis days were significantly higher than on nondialysis days (11,410 +/- 5,340 versus 9,082 +/- 6,646, P = .008, and 14,048 +/- 9,728 versus 8,662 +/- 6,433, P = .016, respectively). By postdialysis hour 4, PA counts on dialysis days had significantly decreased when compared with nondialysis days (6,068 +/- 6,268 versus 10,512 +/- 7,420 PA counts, P = .01, respectively). From postdialysis hours 5 to 20, there was no significant difference in PA counts between dialysis and nondialysis days. CONCLUSION: This study shows that physical activity is lower on dialysis days when compared with nondialysis days, and this decrease is caused by the lack of activity during the 4-hour hemodialysis procedure. New behavior modification strategies involving physical activity, both during hemodialysis and on nondialysis days, must be examined in this patient population.  相似文献   
45.
46.
P-glycoprotein (Pgp) is a plasma membrane protein that was first characterised in multidrug resistant cell lines. The occurrence of Pgp in clinical tumors has been widely studied. Recent investigations have begun to focus on the relationship between Pgp detection in tumors and treatment outcome. In several types of tumors, detection of Pgp correlates with poor response to chemotherapy and shorter survival. P-glycoprotein overexpression often occurs upon relapse from chemotherapy but may also occur at the time of diagnosis. Studies of experimental rat liver carcinogenesis have shown that Pgp expression increases in late stages of carcinogenesis, suggesting that Pgp may be involved in tumor progression. While some of the Pgp isoforms are known to transport hydrophobic chemotherapeutic drugs out of tumor cells, the biologic effects of Pgp overexpression in tumor cells are not fully understood, because the spectrum of substrates for Pgp-mediated transport has not been determined. In the rat liver carcinoma model, strong expression of Pgp is associated with a highly vascular stroma, suggesting that Pgp in tumor cells may affect the connective tissue stroma. The regulation of Pgp appears to be complex, and little is known about how it is up-regulated during carcinogenesis. Further studies of the role of Pgp in malignancy may contribute to our understanding of molecular mechanisms which underlie tumor progression.  相似文献   
47.
将SRSV/3T3细胞DNA转染NIH/3T3细胞,转染后17d,实验组出现18个集落,对照组出现4个集落。将实验组集落细胞接种于3只BALB/C裸鼠皮下,全部长成纤维肉瘤。将SRSV/3T3细胞DNA用EcoRI和BamHI酶切电泳,分别应用5种癌基因(v-myc、KJ-ras、v-src、v-sis和e-fos)作Southern印迹和分子杂交。发现SRSV/3T3细胞DNA的BamHI酶切片段与c-fos探针杂交后,在2.2~3.0 kb处出现阳性杂交带。应用c-fos单抗检测转化细胞,细胞核内呈阳性反应。表明SRSV/3T3细胞DNA含有fos样转化基因,在转化细胞内有此基因的过度表达。  相似文献   
48.
Ischaemia-reperfusion injury (IRI) is of obvious relevance in situations where there is an interruption of blood supply to the gut, as in vascular surgery, or in the construction of free intestinal grafts. It is now appreciated that IRI also underlies the gut dysfunction that occurs in early shock, sepsis, and trauma. The events that occur during IRI are complex. However, recent advances in cellular biology have started to unravel these underlying processes. The aim of this review is to provide an outline of current knowledge on the mechanisms and consequences of IRI. Initially, IRI appears to be mediated by reactive oxygen metabolites and, at a later stage, by the priming and activation of polymorphonuclear neutrophils (PMN). Ischaemia-reperfusion injury can diminish the barrier function of the gut, and can promote an increase in the leakage of molecules (intestinal permeability) or the passage of microbes across the wall of the bowel (bacterial trans-location). Ischaemia-reperfusion injury to the gut can result in the generation of molecules that may also harm distant tissues.  相似文献   
49.
50.
动态观察了乙醇摄入对小鼠肝功能及磺胺嘧啶(SD)代谢动力学的影响。结果表明,每天以25g/kg乙醇摄入2周,SGST活性明显升高,随着摄入时间的延长,在一定时间范围内呈进行性增高,同时,SALT活性也与乙醇摄入时间呈明显正相关,提示长期乙醇摄入对肝脏的不利影响。乙醇对肝匀浆中GST和苯胺羟化酶活性呈双重作用,早期具有诱导酶活性的作用,但诱导的时间和强度不同,后期则可抑制酶的活性。SD在小鼠体内的代谢符合二房室模型,乙醇对SD的代谢具有双相作用,早期使SD代谢加速,后期则使代谢延缓,表明乙醇对代谢SD的N乙酰化酶可能具有酶促酶抑双重作用。  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