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   21721篇
  免费   2356篇
  国内免费   8338篇
  32415篇
  2024年   208篇
  2023年   592篇
  2022年   1177篇
  2021年   1333篇
  2020年   1172篇
  2019年   1342篇
  2018年   968篇
  2017年   902篇
  2016年   1002篇
  2015年   1377篇
  2014年   1732篇
  2013年   1647篇
  2012年   2263篇
  2011年   1975篇
  2010年   1416篇
  2009年   1478篇
  2008年   1643篇
  2007年   1493篇
  2006年   1412篇
  2005年   1190篇
  2004年   993篇
  2003年   796篇
  2002年   760篇
  2001年   751篇
  2000年   642篇
  1999年   428篇
  1998年   239篇
  1997年   187篇
  1996年   151篇
  1995年   161篇
  1994年   120篇
  1993年   96篇
  1992年   98篇
  1991年   74篇
  1990年   67篇
  1989年   74篇
  1988年   55篇
  1987年   49篇
  1986年   50篇
  1985年   48篇
  1984年   34篇
  1983年   29篇
  1982年   36篇
  1981年   18篇
  1978年   10篇
  1959年   12篇
  1957年   9篇
  1954年   9篇
  1951年   8篇
  1950年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Ponatinib (AP24534) was previously identified as a pan-BCR-ABL inhibitor that potently inhibits the T315I gatekeeper mutant, and has advanced into clinical development for the treatment of refractory or resistant CML. In this study, we explored a novel series of five and six membered monocycles as alternate hinge-binding templates to replace the 6,5-fused imidazopyridazine core of ponatinib. Like ponatinib, these monocycles are tethered to pendant toluanilides via an ethynyl linker. Several compounds in this series displayed excellent in vitro potency against both native BCR-ABL and the T315I mutant. Notably, a subset of inhibitors exhibited desirable PK and were orally active in a mouse model of T315I-driven CML.  相似文献   
992.
Modern humans have occupied almost all possible environments globally since exiting Africa about 100,000 years ago. Both behavioral and biological adaptations have contributed to their success in surviving the rigors of climatic extremes, including cold, strong ultraviolet radiation, and high altitude. Among these environmental stresses, high-altitude hypoxia is the only condition in which traditional technology is incapable of mediating its effects. Inhabiting at >3,000-m high plateau, the Tibetan population provides a widely studied example of high-altitude adaptation. Yet, the genetic mechanisms underpinning long-term survival in this environmental extreme remain unknown. We performed an analysis of genome-wide sequence variations in Tibetans. In combination with the reported data, we identified strong signals of selective sweep in two hypoxia-related genes, EPAS1 and EGLN1. For these two genes, Tibetans show unusually high divergence from the non-Tibetan lowlanders (Han Chinese and Japanese) and possess high frequencies of many linked sequence variations as reflected by the Tibetan-specific haplotypes. Further analysis in seven Tibetan populations (1,334 individuals) indicates the prevalence of selective sweep across the Himalayan region. The observed indicators of natural selection on EPAS1 and EGLN1 suggest that during the long-term occupation of high-altitude areas, the functional sequence variations for acquiring biological adaptation to high-altitude hypoxia have been enriched in Tibetan populations.  相似文献   
993.
Deferoxamine (DFO) is a drug widely used for iron overload treatment to reduce body iron burden. In the present study, it was shown in mouse epidermal JB6 cells that all iron compounds transiently induced extracellular signal-regulated kinases (ERK) phosphorylation, whereas DFO further enhanced ERK phosphorylation over long periods. The ERK phosphorylation by DFO treatment appears to be due to the inhibition of MAPK phosphatases (MKP) by DFO. The combined effects of iron-initiated MAPK activation and DFO-mediated MKP inhibition resulted in a synergistic enhancement on AP-1 activities. The results indicate that the interplay between MAPK and MKP is important in regulating the extent of AP-1 activation. It is known that administration of DFO in iron overload patients often results in allergic responses at the injection sites. The results suggest that this synergistic AP-1 activation might play a role in DFO-induced skin immune responses of iron overload patients.  相似文献   
994.
探讨迷迭香酸对穿透支原体脂蛋白诱导巨噬细胞凋亡的保护作用。方法:以穿透支原体脂蛋白损伤RAW264.7细胞为模型,用MTT法检测细胞存活状况,DNA片断化分析观察穿透支原体脂蛋白对RAW264.7细胞DNA降解的影响,碘化丙啶染色流式细胞术检测细胞凋亡率。结果:7.5mg/L穿透支原体脂蛋白可引起RAW264.7细胞存活率降低,出现细胞凋亡特征性“DNA梯带”,流式细胞术检测细胞出现凋亡亚G1期峰,凋亡率为31.9%;100μmol/L迷迭香酸预处理1小时后可以升高RAW264.7细胞的存活率,凋亡细胞特征性的梯状梯带消失,细胞凋亡亚G1期峰消失,并使RAW264.7细胞的凋亡率下降为7.9%。结论:迷迭香酸有抗穿透支原体脂蛋白诱导RAW264.7细胞凋亡的作用。  相似文献   
995.
蜂毒肽在磷脂膜上取向的高效液相色谱和质谱研究   总被引:1,自引:0,他引:1  
利用脂质体模型系统研究了跨膜电位对蜂毒肽在磷脂磷上取向的影响,采用高效液相色谱与质谱技术相结合方法,分析了蜂毒肽与磷脂膜作用后的胰蛋白酶酶解产物,结果发现,当蜂毒肽分子与没有跨膜电位的脂质体结合后,它的所有酶切位点都能够酶有效切断,当蜂毒肽与带负向膜电全的脂质体结合后,其N端的一个酶切位点被封闭,从而说明跨膜电位造成了蜂毒肽在膜上的重瓣取向。  相似文献   
996.
大口鲇微卫星标记在三个鲇形目鱼类种群间适用性研究   总被引:1,自引:0,他引:1  
研究分析了12对大口鲇(Silurus meriaionalis)微卫星标记引物在兰州鲇(Silurus lanzhouensis)、鲇(Silurus asotus)及革胡子鲇(Clarias fuscus)各群体间通用性。结果表明,大口鲇微卫星标记引物除位点DQ223147、DQ223160扩增无特异性条带,位点DQ223149、DQ223159无多态性外,其余8对在这几种鲇形目鱼类中具有较高的通用性,每个位点等位基因数为2—15个不等;不同重复拷贝类别的位点以富含AC重复单元的等位基因数较多,多态性比较丰富。4个群体平均观测杂合度为0.7571,平均期望杂合度为0.6870,平均多态性信息含量0.6441,均为高度多态,说明这8个位点适用于鲇形目鱼类的遗传学研究。采用Nei’s遗传距离(D)绘制NJ系统发育树,4个群体聚成两大类,兰州鲇与鲇群体先聚类后和大口鲇聚为一大类,革胡子鲇聚为另一大类。8个有效微卫星位点中3个具有特异基因型的稀有等位基因位点(DQ223146、DQ223151与DQ223173),可区分4种鲇形目鱼类,作为其种质鉴定的标记位点。借用已有鲇形目鱼类遗传标记资源,增加同目鱼类遗传连锁图谱上遗传标记的密度,将对今后开展鲇形目鱼类种质资源保护及分子育种奠定坚实基础。    相似文献   
997.
叶片阶段性白化小麦是一种非常特殊的色素突变体。本文对其白色、白绿相嵌及转绿叶片的叶绿体光化活性分别进行了测定。试验表明:(1)白化和白绿相嵌叶片的叶绿体色素合成处于停滞阶段,转绿叶片则处于色素迅速合成阶段;(2)白化、白绿相嵌和转绿叶片叶绿体的激发能传递呈递增趋势;(3)三者对绿体的PSⅡ活性和原初光能转化效率也呈递增趋势;(4)白化叶片叶绿体缺乏PSⅠ和PSⅡ外周天线色素蛋白,白绿相嵌和转绿叶片的类囊体膜多肽组分与正常叶片相近似。  相似文献   
998.
Deferoxamine (DFO) is a drug widely used for iron overload treatment to reduce body iron burden. In the present study, it was shown in mouse epidermal JB6 cells that all iron compounds transiently induced extracellular signal-regulated kinases (ERK) phosphorylation, whereas DFO further enhanced ERK phosphorylation over long periods. The ERK phosphorylation by DFO treatment appears to be due to the inhibition of MAPK phosphatases (MKP) by DFO. The combined effects of iron-initiated MAPK activation and DFO-mediated MKP inhibition resulted in a synergistic enhancement on AP-1 activities. The results indicate that the interplay between MAPK and MKP is important in regulating the extent of AP-1 activation. It is known that administration of DFO in iron overload patients often results in allergic responses at the injection sites. The results suggest that this synergistic AP-1 activation might play a role in DFO-induced skin immune responses of iron overload patients.  相似文献   
999.
Recently, it has been suggested that C2ORF40 is a candidate tumor suppressor gene in breast cancer. However, the mechanism for reduced expression of C2ORF40 and its functional role in breast cancers remain unclear. Here we show that C2ORF40 is frequently silenced in human primary breast cancers and cell lines through promoter hypermethylation. C2ORF40 mRNA level is significantly associated with patient disease-free survival and distant cancer metastasis. Overexpression of C2ORF40 inhibits breast cancer cell proliferation, migration and invasion. By contrast, silencing C2ORF40 expression promotes these biological phenotypes. Bioinformatics and FACS analysis reveal C2ORF40 functions at G2/M phase by downregulation of mitotic genes expression, including UBE2C. Our results suggest that C2ORF40 acts as a tumor suppressor gene in breast cancer pathogenesis and progression and is a candidate prognostic marker for this disease.  相似文献   
1000.
目的:探讨术前访视应用ipad在术前访视中对手术患者心理状态的影响。方法:将300例择期手术患者随机分为对照组(150例)和实验组(150例),对照组采用常规术前访视方案;实验组在此基础上结合ipad展示围术期相关信息,采用焦虑自量表评估两组病人入院时和入手术室时的焦虑状况及血压、心率等指标,并且进行术后并发症和满意度的调查。结果:改良术前访视后焦虑评分、收缩压、舒张压、心率实验组明显低于对照组。结论:术前访视应用ipad可明显减轻手术病人术前的焦虑。  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