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   170946篇
  免费   12134篇
  国内免费   4064篇
耳鼻咽喉   2695篇
儿科学   2501篇
妇产科学   2391篇
基础医学   25872篇
口腔科学   4000篇
临床医学   17561篇
内科学   29683篇
皮肤病学   4533篇
神经病学   12911篇
特种医学   9069篇
外国民族医学   21篇
外科学   21362篇
综合类   6737篇
现状与发展   16篇
一般理论   32篇
预防医学   9381篇
眼科学   4318篇
药学   15889篇
  38篇
中国医学   3743篇
肿瘤学   14391篇
  2024年   197篇
  2023年   1366篇
  2022年   3678篇
  2021年   7017篇
  2020年   4078篇
  2019年   4701篇
  2018年   5414篇
  2017年   4563篇
  2016年   5377篇
  2015年   7584篇
  2014年   8941篇
  2013年   9859篇
  2012年   14576篇
  2011年   14456篇
  2010年   8472篇
  2009年   7133篇
  2008年   9888篇
  2007年   9498篇
  2006年   8728篇
  2005年   8123篇
  2004年   6756篇
  2003年   5960篇
  2002年   5124篇
  2001年   3995篇
  2000年   3718篇
  1999年   3170篇
  1998年   1488篇
  1997年   1245篇
  1996年   963篇
  1995年   855篇
  1994年   756篇
  1993年   545篇
  1992年   1092篇
  1991年   955篇
  1990年   890篇
  1989年   783篇
  1988年   674篇
  1987年   642篇
  1986年   488篇
  1985年   481篇
  1984年   342篇
  1983年   260篇
  1982年   159篇
  1981年   202篇
  1980年   153篇
  1979年   259篇
  1978年   185篇
  1976年   164篇
  1974年   167篇
  1973年   142篇
排序方式: 共有10000条查询结果,搜索用时 193 毫秒
981.
The present study was performed to determine whether the effects induced by GABA(B) receptor-acting drugs would be related with the alteration in GABA(B) receptor expression in the hippocampus using Mongolian gerbil, a genetic epilepsy model. The distribution patterns of both GABA(B) receptor 1A/B and GABA(B)receptor 2 immunoreactivities were similarly detected in the hippocampi of normal and seizure-prone gerbils. Following baclofen (GABA(B) receptor agonist) or phaclofen (GABA(B) receptor antagonist) treatment, GABA(B) receptor immunoreactivities were decreased or increased by dose-dependent manners, respectively. Vigabatrin (GABA transaminase inhibitor) or 3-mercaptopropionic acid (GAD inhibitor) treatment did not affect GABA(B) receptor expressions. These findings suggest that GABA(B) receptor expression in the gerbil hippocampus may be altered by baclofen or phaclofen treatment.  相似文献   
982.
Background:  The definition of allergic rhinitis and the classification of its severity and treatment have advanced in recent years following the publication of the Allergic Rhinitis and its Impact of Asthma (ARIA) document. The ARIA and the European Academy of Allergology and Clinical Immunology (ARIA/EAACI) have published a set of recommendations that outline the pharmacological and clinical criteria to be met by medications commonly used in the treatment of allergic rhinitis.
Methods:  An international group of experts met to assess the profile of the antihistamine, desloratadine, under the ARIA/EAACI criteria. Data on desloratadine were collected from peer-reviewed clinical studies and review articles, which were corroborated and augmented by comprehensive public access documents from the European Medicines Evaluation Agency (EMEA).
Results and conclusion:  Based on this systematic review, it was concluded that the efficacy, safety and pharmacology of desloratadine broadly meet the ARIA/EAACI criteria for antihistamines.  相似文献   
983.
CT三维重建在侧颅底的应用研究   总被引:6,自引:0,他引:6  
目的 探讨CT三维重建在侧颅底的应用价值。方法 15例健康成人在Picker5000全身CT机上行连续轴位扫描,将扫描获得的原始数据输入Voxel Q图像后处理工作站,采用表面阴影法(surface shaded display,SSD)进行三维重建。结果 侧颅底CT三维重建能清楚显示正常侧颅底孔、裂和重要的骨性标志。重建的结构可整体显示或切割后单独显示,两均可在三维空间绕任意轴旋转任意角度。结论 三维CT能立体而直观的显示侧颅底骨性结构,有利于侧颅底外科手术方案的设计。  相似文献   
984.
The marginal zone macrophages of the spleen are implicated in the clearance of polysaccharides, but underlying mechanisms need to be pinpointed. SIGN-R1 is one of five recently identified mouse genes that are homologous to human DC-SIGN and encode a single, external, C-terminal C-type lectin domain. We find that a polyclonal antibody to a specific SIGN-R1 peptide reacts primarily and strongly with a subset of macrophages in the marginal zone of spleen and lymph node medulla. In both sites, SIGN-R1 exists primarily in an aggregated form, resistant to dissociation into monomers upon boiling in SDS under reducing conditions. Upon transfection into three different cell lines, high-mol.-wt forms bearing SIGN-R1 are expressed, as well as reactivity with ER-TR9, a mAb previously described to react selectively with marginal zone macrophages. SIGN-R1-expressing macrophages preferentially sequester dextrans following i.v. injection. Likewise, when phagocytic cells are enriched from spleen and tested in culture, dextran is selectively endocytosed by a subset of very large SIGN-R1(+) cells representing approximately 5% of total released macrophages. Uptake of FITC-dextran by these macrophages in vivo and in vitro is blocked by ER-TR9 and polyclonal anti-SIGN-R1 antibodies. Following transfection with SIGN-R1, cell lines become competent to endocytose dextrans. The dextran localizes primarily to compartments lacking transferrin receptor and the LAMP-1 CD107a panlysosomal antigen. Therefore, SIGN-R1 mediates the uptake of dextran polysaccharides, and it is predominantly expressed in the macrophages of the splenic marginal zone and lymph node medulla.  相似文献   
985.
Applications of the pulsatile flow versatile ECLS: in vivo studies   总被引:3,自引:0,他引:3  
INTRODUCTION: T-PLS (Twin-Pulse Life Support) is the first commercial pulsatile ECLS (Extra Corporeal Life Support) device (1). The dual sac structure of T-PLS can effectively reduce high membrane oxygenator inlet pressure and hemolysis. To verify both the use of T-PLS for ECLS and the advantages of T-PLS, we tested various models. METHOD AND RESULTS: In the partial CPB (cardio pulmonary bypass) model (swine), T-PLS (N = 6), and Biopump (N = 2), a single pulsatile pump (N = 2), were compared. In the case of single pulsatile flow, during pump systole, pressure increased to 700 - 800 mmHg at the inlet port of the membrane oxygenator. fHb, a hemolysis measurement value, was about 80 mg/dL at 3 hours. On the contrary, because of T-PLS's dual sac system, the pressure of T-PLS had a maximum value of about 250 mmHg and fHb was similar to that of the commercial centrifugal pumps. In the total CPB model (bovine, N = 6), the heart was stopped via cardioplegia (Kcl). T-PLS flow was maintained at 3.0-4.5 L/min. T-PLS functioned like a natural heart, having a pulse pressure of 26-43 mmHg and a pulse rate of 40-60 bpm (beats per minute). In the emergency case model (canine, N = 6), T-PLS was started 10 minutes after cardiac arrest from electronic shock. In spite of cardiac arrest for a period of 40 minutes, the heart was recovered after defibrillation. In the ARDS (Acute Respiratory Distress Syndrome) model (canine, N = 6), minimal ventilator parameters were set: tidal volume 130 ml, respiration rate = bpm, FiO2 = 10%. Three hours after starting T-PLS, PO2 of the carotid artery blood (after 2 hours: 195 +/- 89.4; after 3 hours: 258 +/- 99.3 mmHg) was above half the value of the femoral artery but was within normal range. CONCLUSION: It is suggested that a portable pulsatile ECLS like T-PLS may be used as a CPB device and as an alternative CPR (cardiopulmonary resuscitation) device in the case of cardiac arrest. Due to the pulsatile flow, oxygenated blood is delivered to the patient without overloading the ARDS patients heart.  相似文献   
986.
A series of 20 hepatocellular carcinomas and 8 intrahepatic cholangiocarcinomas was screened from the Korean population for microsatellite alterations, including a loss of heterozygosity and replication errors using nine microsatellite markers containing several genes. The microsatellite results and our previous comparative genomic hybridization results of two tumors were compared at each locus, and the correlations between these and clinicopathologic variables were examined. The most characteristic findings were found at 13q. Replication errors were prevalent at D13S160 (13q21.2 approximately q31) and D13S292(13q12). The incidence of loss of heterozygosity, however, was higher at D13S153 (13q14.1 approximately q14.3) and D13S265(13q31 approximately q32). In contrast, there were higher deletion frequencies observed in hepatocellular carcinoma (HCC) and higher amplification frequencies observed in intrahepatic cholangiocarcinoma at 13q in our previous comparative genomic hybridization (CGH) study. Higher frequencies of replication errors were observed at D16S408 (13q12 approximately q21) and D16S504(13q23 approximately q24) in the HCC. This study found that significant differences in the patterns of genetic instability of microsatellites were dependent on the chromosomal loci. It is believed that certain genes at altered CGH regions, which are relevant to the development and/or progression of these cancers, are activated by different mutation mechanisms.  相似文献   
987.
Carcinoma of the cervix is typically treated with a combination of intracavitary brachytherapy and external beam radiation. The external beam dose is delivered with whole pelvis fields followed by split fields that protect midline organs at risk (bladder and rectum) while treating the parametria. Three approaches have been developed to shield midline structures: a simple rectangular block, a block customized to a single brachytherapy isodose line, and a step wedge filter constructed to conform to multiple brachytherapy isodose lines. A customized step wedge filter has the potential to produce a more homogeneous dose distribution but has not achieved widespread use due to labor intensive construction. We have developed a simple, novel method to produce a custom midline step wedge using dynamic multileaf collimation (dMLC). A comparison of film measurements in a phantom with the dose calculated by a commercial treatment planning system demonstrated agreement within 3% or 3 mm. The technique requires delivery times comparable to conventional techniques.  相似文献   
988.
Phosphatidylinositol 3-kinase (PI3K) is critical player in cell proliferation and survival. The effects of LY294002 and wortmannin, inhibitors of PI3K, on nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression in lipoploysaccharide (LPS)-induced Raw 264.7 cells were investigated. Significant inhibition of LPS-induced protein kinase B (PKB, Akt) phosphorylation occurred at 25 microM LY294002 or 0.5 microM wortmannin. At the same concentrations, LY294002, but not wortmannin, significantly inhibited NO production and iNOS expression. LY303511, an inactive analogue of LY294002, also inhibited NO production and iNOS expression. In addition, LY294002 and LY303511 significantly inhibited the DNA binding activity of NF-kappaB and NF-kappaB dependent reporter gene expression. These results suggest that LY294002 inhibits iNOS expression at least in part via inhibition of NF-kappaB activation, independent of PI3K.  相似文献   
989.
990.
The sequestration of chemokines on the surface of microvascular endothelium is an early event in the selective recruitment of leukocytes. The sequestration and presentation of chemokines must be tightly controlled to confine the extravasation of leukocytes and to prevent uncontrolled inflammation. We investigated whether soluble molecules released under physiological conditions could control chemokine immobilization on cell surfaces and function as regulatory chemokine binding molecules. We determined that human serum contains a molecule that suppresses RANTES (CCL5) binding to endothelial cells, PBMC and CHO cells. Using platelet-rich and platelet-free plasma, serum from patients with thrombocytopenia, and purified platelets, we identified platelets as the source of the chemokine-binding molecule and further identified it as chondroitin sulfate A. In contrast to platelet-derived fully-sulfated chondroitin sulfate A, low-sulfated chondroitin sulfate A present in plasma was almost inactive. Under physiological flow conditions chondroitin sulfate A was found to block RANTES-mediated firm adhesion of monocytes to endothelial cells. It also prevented RANTES-mediated influx of calcium in CCR5-transfected CHO cells while internalization of CCR5 was only marginally reduced. Taken together, chondroitin sulfate A released from platelets appears to act as an important regulatory molecule for cellular responses to chemokines.  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