全文获取类型
收费全文 | 79038篇 |
免费 | 6562篇 |
国内免费 | 4873篇 |
专业分类
90473篇 |
出版年
2024年 | 138篇 |
2023年 | 901篇 |
2022年 | 2078篇 |
2021年 | 3607篇 |
2020年 | 2331篇 |
2019年 | 2843篇 |
2018年 | 2882篇 |
2017年 | 2037篇 |
2016年 | 2876篇 |
2015年 | 4599篇 |
2014年 | 5304篇 |
2013年 | 5975篇 |
2012年 | 6919篇 |
2011年 | 6367篇 |
2010年 | 3827篇 |
2009年 | 3385篇 |
2008年 | 4124篇 |
2007年 | 3671篇 |
2006年 | 3178篇 |
2005年 | 2686篇 |
2004年 | 2280篇 |
2003年 | 1982篇 |
2002年 | 1733篇 |
2001年 | 1563篇 |
2000年 | 1568篇 |
1999年 | 1448篇 |
1998年 | 851篇 |
1997年 | 798篇 |
1996年 | 808篇 |
1995年 | 736篇 |
1994年 | 687篇 |
1993年 | 530篇 |
1992年 | 818篇 |
1991年 | 658篇 |
1990年 | 601篇 |
1989年 | 533篇 |
1988年 | 421篇 |
1987年 | 362篇 |
1986年 | 336篇 |
1985年 | 299篇 |
1984年 | 221篇 |
1983年 | 199篇 |
1982年 | 112篇 |
1981年 | 118篇 |
1980年 | 86篇 |
1979年 | 147篇 |
1978年 | 84篇 |
1977年 | 95篇 |
1975年 | 111篇 |
1974年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
An acidic microenvironment induces disruption of adherens junctions (AJs) of hepatoma cells. This study investigated the impact of an acidic extracellular pH (pHe) on p120-catenin (p120-ctn) serine phosphorylation. pH 6.6 treatment increased intracellular calcium levels, activated protein kinase C (PKC)α and PKCδ, and decreased serine phosphorylation of p120-ctn. Further knockdown of PKCα and δ by small interference RNA (siRNA) prevented the pH 6.6-induced downregulation of p120-ctn at AJ and the serine dephosphorylation of p120-ctn. Moreover, PP2 pretreatment and siRNA of c-Src abrogated the pH 6.6-induced PKCδ activation. Together, the c-Src-PKCδ cascade and PKCα regulate the acidic pHe-induced AJ disruption. 相似文献
992.
993.
While sulfur dioxide (SO2) has been previously known for its toxicological effects, it is now known to be produced endogenously in mammals from sulfur-containing amino acid l-cysteine. l-cysteine is catalyzed by cysteine dioxygenase (CDO) to l-cysteinesulfinate, which converts to β-sulfinylpyruvate through transamination by aspartate aminotransferase (AAT), and finally spontaneously decomposes to pyruvate and SO2. The present study explored endogenous SO2 production, and AAT and CDO distribution in different rat tissue. SO2 content was highest in stomach, followed by tissues in the right ventricle, left ventricle, cerebral gray matter, pancreas, lung, cerebral white matter, renal medulla, spleen, renal cortex and liver. AAT activity and AAT1 mRNA expression were highest in the left ventricle, while AAT1 protein expression was highest in the right ventricle. AAT2 and CDO mRNA expressions were both highest in liver tissue. AAT2 protein expression was highest in the renal medulla, but CDO protein expression was highest in liver tissue. In all tissues, AAT1 and AAT2 were mainly distributed in the cytoplasm rather than the nucleus. These observed differences among tissues endogenously generating SO2 and associated enzymes are important in implicating the discovery of SO2 as a novel endogenous signaling molecule. 相似文献
994.
目的研究大鼠局灶性脑缺血再灌注损伤后神经元和星形胶质细胞表达量的动态演变及各自cyclin D1的表达差异。方法建立大鼠大脑中动脉阻塞(MCAO)再灌注模型,随机分为再灌注后1d组,3d组,7d组,14d组和假手术组,应用流式细胞术检测各组再灌注后不同时间点神经元和星形胶质细胞数量变化及各自cyclin D1的表达。结果缺血侧梗死边缘区皮质星形胶质细胞的表达增加,而神经元的表达下降,与假手术组比较有明显差异(P〈0.05);神经元和星形胶质细胞中各自cyclin D1的表达在再灌注7d、14d后表达上调,且星形胶质细胞中的cyclinD1增加更明显,与假手术组比较有统计学差异(P〈0.05)。结论大鼠脑缺血再灌注后,缺血侧梗死边缘区皮质星形胶质细胞和神经元的cyclinD1表达均有不同程度的上调,星形胶质细胞的cyclin D1表达上调比神经元的更为显著。 相似文献
995.
996.
997.
Xin Chen Jian Zhang Ji-Hua Liu Bo-Yang Yu 《Journal of Molecular Catalysis .B, Enzymatic》2008,54(3-4):72-75
The regioselective glycosylation of three isomers of hydroxybenzoic acids was observed in Panax ginseng hairy root cultures. p-Hydroxybenzoic acid (1) and m-hydroxybenzoic acid (2) were converted into their corresponding glycosides (1a and 2a) and glycosyl esters (1b and 2b) while no metabolite of o-hydroxybenzoic acid (3) was detected. A new compound, m-hydroxybenzoic acid β-d-xylopyranosyl (1 → 6)-β-d-glycopyranosyl ester (2c) was identified as a biotransformation product of 2. Further time-course studies of the biotransformation reactions showed that the glycosides were major products in the latter stage. The addition of carbohydrates or antioxidants increased glycosyl esters formation. 相似文献
998.
The behavior of Na/K pump currents when exposed to an oscillating electric field is studied by computer simulation. The pump
current from a single pump molecule was sketched based on previous experimental results. The oscillating electric field is
designed as a symmetric, dichotomous waveform varying the membrane potential from −30 to −150 mV around the membrane resting
potential of −90 mV. Based on experimental results from skeletal muscle fibers, the energy needed to overcome the electrochemical
potentials for the Na and K-transports are calculated in response to the field’s two half-cycles. We found that a specially
designed oscillating electric field can eventually synchronize the pump molecules so that all the individual pumps run at
the same pumping rate and phase as the field oscillation. They extrude Na ions during the positive half-cycle and pump in
K ions during the negative half-cycle. The field can force the two ion-transports into the corresponding half-cycles, respectively,
but cannot determine their detailed positions. In other words, the oscillating electric field can synchronize pumps in terms
of their pumping loops but not at a specific step in the loop. These results are consistent with our experimental results
in measurement of the pump currents. 相似文献
999.
1000.
脑中风是严重危害我国中老年人身体健康的主要疾病之一,对中风相关基因单核苷酸多态性位点在人群中分布情况的研究将有助于深入认识中风发病机制及提高防治能力。该研究用寡核苷酸芯片方法检测了8个多态性位点与中风易感性之间的关联。结果发现:寡核苷酸芯片技术作为一种很好的基因分型方法,具有高通量、平行性、微量化、自动化和快速灵敏等的特点,适用于大规模基因分型平台的建立;实验初步发现与中风易感性相关的有血管紧张素原(AGT)基因M235T(OR=3.437,CI=1.211,9.709),载脂蛋白E(APOE)基因cys158arg (OR=9.434,1.686-83.3),亚甲基四氢叶酸还原酶(MTHFR)基因C677T(OR=2.591,1.002-6.711),血管紧张素ⅡⅠ型受体(AT1R)基因A1166C(OR=0.213,0.057-0.799)。 相似文献