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   35480篇
  免费   3574篇
  国内免费   2585篇
耳鼻咽喉   216篇
儿科学   488篇
妇产科学   397篇
基础医学   4273篇
口腔科学   656篇
临床医学   4589篇
内科学   5459篇
皮肤病学   321篇
神经病学   1574篇
特种医学   1160篇
外国民族医学   29篇
外科学   3788篇
综合类   6285篇
现状与发展   9篇
一般理论   3篇
预防医学   2574篇
眼科学   933篇
药学   3832篇
  32篇
中国医学   2085篇
肿瘤学   2936篇
  2024年   165篇
  2023年   707篇
  2022年   1687篇
  2021年   2117篇
  2020年   1477篇
  2019年   1257篇
  2018年   1238篇
  2017年   1164篇
  2016年   1072篇
  2015年   1597篇
  2014年   2001篇
  2013年   1832篇
  2012年   2614篇
  2011年   2931篇
  2010年   1828篇
  2009年   1460篇
  2008年   1832篇
  2007年   1888篇
  2006年   1742篇
  2005年   1658篇
  2004年   1170篇
  2003年   1115篇
  2002年   967篇
  2001年   785篇
  2000年   767篇
  1999年   762篇
  1998年   447篇
  1997年   463篇
  1996年   352篇
  1995年   339篇
  1994年   326篇
  1993年   178篇
  1992年   225篇
  1991年   227篇
  1990年   236篇
  1989年   182篇
  1988年   152篇
  1987年   121篇
  1986年   123篇
  1985年   93篇
  1984年   70篇
  1983年   39篇
  1982年   27篇
  1981年   22篇
  1979年   20篇
  1977年   16篇
  1975年   14篇
  1974年   19篇
  1972年   13篇
  1969年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Fused compounds, a unique class of large conjugate structures, have emerged as prime candidates over traditional nitrogen-rich mono-ring or poly-ring materials. Meanwhile, compounds containing catenated nitrogen chains have also attracted attention from scientists due to their high heats of formation. On the other hand, the azoxy [–N Created by potrace 1.16, written by Peter Selinger 2001-2019 N(O)–] moiety has been found to increase density effectively in the molecular structure of compounds. Therefore, combining fused heterocyclic organic skeletons with the azoxy moiety can be regarded as an effective method for increasing the density and heat of formation, which results in substantial increase in detonation properties. Based on the above-mentioned considerations, in this study, a series of new non-hydrogen-containing 5/6/5 fused ring molecules with azoxy moiety structures are designed. Furthermore, their properties as potential high-energy-density materials, including their density, heats of formation, detonation properties, and impact sensitivity, have been extensively evaluated using thermodynamic calculations and density functional theory. Among the investigated compounds, 1,3,8,10-tetranitrodiimidazo[1,5-d:5′,1′-f][1,2,3,4]tetrazine 5-oxide (B), 1,10-dinitrobis([1,2,3]triazolo)[1,5-d:5′,1′-f][1,2,3,4]tetrazine 5-oxide (C) and 2,9-dinitrobis([1,2,4]triazolo)[1,5-d:5′,1′-f][1,2,3,4]tetrazine 5-oxide (D) display remarkable stabilities and are predicted to be high-performance energetic materials due to their high density (>1.94 g cm−3), detonation velocity (>9616 m s−1), and detonation pressure (>41.1 GPa). In addition, our design strategy, which combines the azoxy moiety and fused tricyclic skeleton to construct nitrogen-rich molecular structures with high density and positive heat of formation, is a valuable approach for developing novel high-energy-density materials with excellent performance and stability.

In this work, a series of novel non-hydrogen-containing 5/6/5 fused ring molecules with azoxy moiety were designed, some physicochemical or detonation properties of them were calculated.  相似文献   
992.
Huang  Wei  Chen  Qiang  Zhao  Jianwu  Ma  Wenlong  Zhang  Lei  Yao  Shuxin  Qing  Zhong  Zhi  Liqiang 《Journal of thrombosis and thrombolysis》2021,51(3):617-624
Journal of Thrombosis and Thrombolysis - Deep vein thrombosis (DVT) is the blood clot formed in a vein deep in body, mostly occurred in the lower leg or thigh. Early studies indicate that DVT is a...  相似文献   
993.
BackgroundDealing with chemotherapy-related cardiac dysfunction (CTRCD) remains a significant problem complicated by the difficulty in early detection of cardiotoxicity. Electrocardiogram (ECG) is expected to be the most realistic methodology due to lower cost-performance and non-invasiveness. We investigated the long-term visual fluctuations in the ECG waveforms in patients with chronic doxorubicin (DOX)-induced cardiotoxicity to identify ECG indices for the early detection of cardiotoxicity.MethodsWe conducted a retrospective case series study by reviewing the medical records of 470 consecutive patients with malignant lymphoma who were treated with DOX at our institute between January 2010 and December 2017. Of them, 23 (4.9%) patients developed left ventricular dysfunction and were diagnosed with CTRCD using echocardiography. We assessed the ECG indices on 12-lead ECG recordings before and after treatment in 15 patients; eight patients were excluded due to conduction disturbances or atrial fibrillation.ResultsCTRCD was detected at a median of 475 (interquartile range, IQR: 341–1333) days after initiating chemotherapy. The evaluation of ECG indices preceding CTRCD development was performed 93 (IQR: 52–232) days before the detection of CTRCD. In the stage of CTRCD, the most significant ECG change was T-wave flattening in leads V3–V6 (12 patients, 80%). Additionally, QTa prolongation was observed in leads I and aVL (n = 10, 66%), leads II, III, and aVF (n = 9, 60%), and leads V3–V6 (n = 10, 73%). These ECG changes were not observed before the treatment but were detected mildly in the pre-CTRCD stage, which subsequently worsened in the CTRCD stage.ConclusionsThis study indicated that T-wave changes and QTa prolongation may be useful as an early indicator before the onset of CTRCD in patients with DOX-induced cardiotoxicity.  相似文献   
994.
Huang  Yuxing  Deng  Lisha  Zeng  Lin  Bao  Shanlin  Ye  Kun  Li  Chengxun  Hou  Xiaolin  Yao  Yuan  Li  Dingjun  Xiong  Zhen 《Metabolic brain disease》2021,36(8):2461-2472

Cerebral ischemia/reperfusion (I/R) injury remains a leading cause of death and disability. Long noncoding RNAs (lncRNAs) exert key functions in cerebral I/R injury. Here, we sought to elucidate the mechanism underlying the regulation of H19 in cerebral I/R cell injury. An in vitro model of cerebral I/R injury was created using oxygen–glucose deprivation/reoxygenation (OGD/R). The levels of H19, miR-1306-5p and B cell lymphoma-2 (Bcl-2)-like 13 (BCL2L13) were assessed by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. Cell viability and apoptosis were determined by the Cell Counting-8 Kit (CCK-8) assay and flow cytometry, respectively. The levels of lactate dehydrogenase (LDH) and cytokines were evaluated by enzyme-linked immunosorbent assays (ELISA). Direct relationships among H19, miR-1306-5p and BCL2L13 were verified by dual-luciferase reporter, RNA immunoprecipitation (RIP) and RNA pulldown assays. Our data showed that H19 and BCL2L13 were highly expressed in the cerebral I/R injury rats and OGD/R-triggered SK-N-SH and IMR-32 cells. The knockdown of H19 or BLC2L13 alleviated OGD/R-triggered injury in SK-N-SH and IMR-32 cells. Moreover, H19 silencing protected against OGD/R-triggered cell injury by down-regulating BCL2L13. H19 acted as a sponge of miR-1306-5p and BCL2L13 was a direct target of miR-1306-5p. H19 mediated BCL2L13 expression by sequestering miR-1306-5p. Furthermore, miR-1306-5p was a molecular mediator of H19 function. These results suggested that H19 silencing alleviated OGD/R-triggered I/R injury at least partially depending on the regulation of the miR-1306-5p/BCL2L13 axis.

  相似文献   
995.
目的: 了解河北省结核病耐药疫情及趋势,为制定适合河北省的耐药结核病防治策略提供依据。方法: 采用简单随机抽样的方法抽取河北省14个监测县(区)作为耐药监测点,对2020年监测点的424例培养阳性肺结核患者采用比例法药物敏感性试验(简称“药敏试验”)对异烟肼(INH)、利福平(RFP)、乙胺丁醇(EMB)、链霉素(Sm)、卡那霉素(Km)、氧氟沙星(Ofx)、卷曲霉素(Cm)、丙硫异烟胺(Pto)、对氨基水杨酸钠(PAS)进行耐药性检测。结果: (1)总耐药:初治患者耐INH率最高[9.19%(35/381)],复治患者耐RFP率最高[13.95%(6/43)],总体耐INH率最高[9.43%(40/424)]。(2)单耐药:初治、复治、总体均是单耐RFP率最高[依次为1.84%(7/381)、6.98%(3/43)、2.36%(10/424)]。(3)多耐药:初治患者耐INH+Sm率最高[0.79%(3/381)],复治患者耐INH+Sm、INH+EMB+Sm率最高[均为2.33%(1/43)],总体耐INH+Sm最高[0.94%(4/424)]。(4)耐多药:初治患者耐INH+RFP、 INH+RFP+Km+Ofx率最高[1.31%(5/381)],复治患者耐INH+RFP+EMB率最高[4.65%(2/43)],总体耐INH+RFP、INH+RFP+Km+Ofx率最高[1.18%(5/424)]。总体耐药率为34.20%(145/424),其中初治患者耐药率为33.07%(126/381),复治患者耐药率为44.19%(19/43); 总体耐多药率为5.42%(23/424),其中初治患者耐多药率为5.25%(20/381),复治患者耐多药率为6.98%(3/43)。结论: 河北省2020年结核病耐药形势严峻,要注意一线、二线药物尤其是Km、Ofx的规范使用,从而降低耐药率。  相似文献   
996.
Tocilizumab (TCZ), a biologic that blocks the signal transduction of interleukin-6, has been used for the treatment of various autoimmune diseases. Many of these cases are sometimes complicated by ulcerative colitis (UC). However, the effect of TCZ on UC is unclear. We experienced two cases with concomitant UC that were treated with TCZ, one for Takayasu arteritis (TAK) and the other for relapsing polychondritis (RP). TCZ did not improve UC in either of these cases. TCZ might have adverse effects on the intestinal tract, since interleukin-6 signaling plays an important role in intestinal epithelium maintenance. Treatment with TCZ should therefore be carefully provided in patients complicated with UC.  相似文献   
997.
目的 研究异丙酚在人肝微粒体中的代谢。方法 采用高效液相方法测定孵育液中异丙酚的浓度。研究异丙酚的酶促动力学,推导出药物米氏常数(Km)和最大反应速度(Vmax);并计算体外酶对药物的清除率(CLint)。同时观察不同种类的CYP酶特异性抑制剂对异丙酚代谢的影响。结果 异丙酚在人肝微粒体中Km和Vmax分别为777.43μuM和172.413μM?h ?1?mg ?1?protein,Clint为0.22h?1?mg?1?protein。CYP2B6特异性抑制剂氯吡格雷能够显著抑制异丙酚的代谢,而CYP2C9和CYP2C19特异性抑制剂对异丙酚代谢无显著影响CYP2B6抑制剂能够减少异丙酚的代谢。结论 CYP2B6主要参与异丙酚的代谢, CYP2B6酶抑制剂可能会抑制异丙酚的代谢,造成药物药效或毒性的增加。  相似文献   
998.
目的探讨环状RNA PUM1(circPUM1)对结肠癌细胞增殖、凋亡、迁移、侵袭的影响及其分子机制。方法实时荧光定量聚合酶链反应(qRT-PCR)检测结肠癌组织、癌旁组织中circPUM1、微小RNA-524-5p(miR-524-5p)的表达量。体外培养人结肠癌细胞株SW620,分别将si-NC、si-circPUM1、miR-NC、miR-524-5p mimics、si-circPUM1与anti-miR-NC、si-circPUM1与anti-miR-524-5p转染至SW620细胞。甲基噻唑基四唑(MTT)检测细胞增殖;Transwell小室实验检测细胞迁移、侵袭能力;流式细胞术检测细胞凋亡率;双荧光素酶报告实验验证circPUM1是否能够结合miR-524-5p;蛋白免疫印迹法(Western blotting)检测细胞周期蛋白1(Cyclin D1)、p21、基质金属蛋白酶-2(MMP-2)、基质金属蛋白酶-9(MMP-9)、B淋巴细胞瘤-2(Bcl-2)、B淋巴细胞瘤-2相关蛋白(Bax)表达量。结果结肠癌组织circPUM1的表达水平显著高于癌旁组织(P<0.05),miR-524-5p的表达水平显著降低(P<0.05);干扰circPUM1表达或miR-524-5p过表达后,细胞活力显著降低(P<0.05),迁移细胞数与侵袭细胞数显著减少(P<0.05),细胞凋亡率显著升高(P<0.05),Cyclin D1、MMP-2、MMP-9、Bcl-2蛋白表达显著降低(P<0.05),p21、Bax蛋白表达显著升高(P<0.05);双荧光素酶报告实验证实circPUM1可靶向结合miR-524-5p的作用位点;抑制miR-524-5p表达可减弱干扰circPUM1表达对SW620细胞增殖、凋亡、迁移、侵袭的作用。结论circPUM1可通过海绵吸附miR-524-5p促进结肠癌细胞增殖、迁移、侵袭,抑制细胞凋亡。  相似文献   
999.
目的 调查赤道几内亚Bioko岛恶性疟原虫多药耐药蛋白1(Plasmodium falciparum multidrug resistance protein 1, PfMDR1)、氯喹抗性转运蛋白基因(P. falciparum chloroquine resistant transporter, PfCRT)和Kelch 13基因(P. falciparum Kelch 13, PfK13)多态性,为当地疟疾防控策略制定提供参考。方法 采集2018—2019年赤道几内亚Bioko岛恶性疟原虫感染者外周血样本85份,提取基因组DNA。采用巢式PCR技术扩增PfMDR1、PfCRT和 PfK13基因,对扩增产物进行DNA测序,并对基因序列进行比对。结果 赤道几内亚Bioko岛恶性疟原虫PfK13基因不存在已知与青蒿素抗性相关的突变;PfMDR1基因和PfCRT基因均存在不同比例抗药性突变,其中PfMDR1_N86Y、PfMDR1_Y184F和PfCRT_K76T突变率分别为35.29%(30/85)、72.94%(62/85)和24.71%(21/85)。结论 赤道几内亚Bioko岛恶性疟原虫PfMDR1、PfCRT基因和 PfK13基因均存在不同程度突变。  相似文献   
1000.
目的了解医院多药耐药现状及病原菌耐药性,为预防与控制医院感染提供必要的病原学依据。方法 2012年9月-2013年5月临床住院患者送检的1517份各类标本,采用法国生物梅里埃公司VITEK-32全自动细菌分析系统进行细菌鉴定,药敏试验使用K-B纸片扩散法,以WHONET5.4软件分析数据。结果共分离出1 132株病原菌,标本来源以痰液、分泌物、脓液为主,分别占40.92%、16.40%、12.52%;共检出多药耐药菌567株,其中产ESBLs大肠埃希菌378株占66.67%;产ESBLs克雷伯菌属96株占16.93%;产ESBLs大肠埃希菌对氨苄西林、头孢曲松、头孢呋辛、头孢唑林、哌拉西林耐药率均>97.62%,产ESBLs克雷伯菌属对头孢呋辛、氨苄西林/舒巴坦、阿莫西林/克拉维酸、氨曲南耐药率均为100.00%,耐甲氧西林金黄色葡萄球菌对苯唑西林、头孢唑林、头孢呋辛、环丙沙星、红霉素具有较高的耐药性,多药耐药铜绿假单胞菌、鲍氏不动杆菌对多种抗菌药物显著耐药,而对亚胺培南、美罗培南敏感。结论多药耐药菌医院感染现象日趋严重,应加强病原菌检测和耐药性监测,依据药敏试验结果选用抗菌药物,从而降低医院感染率。  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