全文获取类型
收费全文 | 1060篇 |
免费 | 143篇 |
国内免费 | 692篇 |
专业分类
1895篇 |
出版年
2024年 | 20篇 |
2023年 | 32篇 |
2022年 | 60篇 |
2021年 | 60篇 |
2020年 | 67篇 |
2019年 | 71篇 |
2018年 | 52篇 |
2017年 | 52篇 |
2016年 | 53篇 |
2015年 | 67篇 |
2014年 | 105篇 |
2013年 | 116篇 |
2012年 | 124篇 |
2011年 | 127篇 |
2010年 | 99篇 |
2009年 | 105篇 |
2008年 | 122篇 |
2007年 | 106篇 |
2006年 | 75篇 |
2005年 | 65篇 |
2004年 | 64篇 |
2003年 | 33篇 |
2002年 | 42篇 |
2001年 | 49篇 |
2000年 | 45篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有1895条查询结果,搜索用时 15 毫秒
121.
122.
Yu Xin Chen Shen Mengwei Tang Zitao Guo Yi Shi Zhenghua Gu Jun Shao Liang Zhang 《The Journal of biological chemistry》2022,298(3)
N-demethylases have been reported to remove the methyl groups on primary or secondary amines, which could further affect the properties and functions of biomacromolecules or chemical compounds; however, the substrate scope and the robustness of N-demethylases have not been systematically investigated. Here we report the recreation of natural evolution in key microdomains of the Thermomicrobium roseum sarcosine oxidase (TrSOX), an N-demethylase with marked stability (melting temperature over 100 °C) and enantioselectivity, for enhanced substrate scope and catalytic efficiency on -C-N- bonds. We obtained the structure of TrSOX by crystallization and X-ray diffraction (XRD) for the initial framework. The natural evolution in the nonconserved residues of key microdomains—including the catalytic loop, coenzyme pocket, substrate pocket, and entrance site—was then identified using ancestral sequence reconstruction (ASR), and the substitutions that accrued during natural evolution were recreated by site-directed mutagenesis. The single and double substitution variants catalyzed the N-demethylation of N-methyl-L-amino acids up to 1800- and 6000-fold faster than the wild type, respectively. Additionally, these single substitution variants catalyzed the terminal N-demethylation of non-amino-acid compounds and the oxidation of the main chain -C-N- bond to a -C=N- bond in the nitrogen-containing heterocycle. Notably, these variants retained the enantioselectivity and stability of the initial framework. We conclude that the variants of TrSOX are of great potential use in N-methyl enantiomer resolution, main-chain Schiff base synthesis, and alkaloid modification or degradation. 相似文献
123.
为了探究ASFV E248R蛋白调控cGAS-STING信号通路的机制,利用双荧光素酶报告系统验证ASFV E248R蛋白够剂量依赖性地抑制cGAS-STING和HT-DNA诱导的IFN-β的产生。通过相对定量PCR技术验证,过表达E248R抑制IFNB1、RANTES、IL-6和TNF-αβ基因的转录水平。免疫共沉淀和激光共聚焦试验结果表明,E248R与STING相互作用。通过蛋白印迹试验证实,过表达E248R可抑制STING的表达。研究表明ASFV E248R蛋白通过抑制STING的表达拮抗天然免疫应答。该结果将扩展对ASF免疫逃逸的认知,为疫苗的研制提供新的思路。 相似文献
124.
本文用5种动物的370例心脏,对右心室条束作了比较解剖学观察。狗右心室条束的出现率为97%,兔64%,牛52%,猪38%,羊25%。牛、猪、羊和兔的右心室条事多附着室间隔和室前壁之间,狗的条束多附着前乳头肌或室间隔和前壁之间。动物的右心室要束可分暗红色条束和乳白色条束,暗红色条束主要由心肌纤维构成,条不周边的结缔组织中含有不细胞;乳白色条束主要由结缔组织和位于中央的呸细胞构成,心肌纤维少或缺如。心 相似文献
125.
反义寡核苷酸药物癌泰得的定性分析方法研究 总被引:3,自引:0,他引:3
癌泰得 (ACTCACTCAGGCCTCAGACT)为端粒酶表达抑制活性反义寡核苷酸 .为了探讨其定性检测手段 ,通过阴离子交换高效液相色谱和毛细管凝胶电泳分析方法 ,确定了该硫代寡核苷酸以及与其有关的短序列和部分未被硫代类似物的保留时间 ,并分析了不同混合物样品 .结果表明 ,阴离子交换高效液相色谱对硫代寡核苷酸骨架上的差异非常敏感 ,可很好地分离长度相同的硫代和未完全硫代类似物 ,并且随未被硫代磷酸基数目增加 ,保留时间依次缩短 .阴离子交换高效液相色谱对硫代寡核苷酸的长度不敏感 ,不能分离相差一个碱基的硫代寡核苷酸 .毛细管凝胶电泳可很好地分离长度相差一个碱基的硫代寡核苷酸 ,不能分离同长硫代和部分硫代寡核苷酸 .高效液相色谱结合毛细管凝胶电泳可有效地确定癌泰得的纯度和修饰程度 . 相似文献
126.
Propagation of potato tubers in a nutrient mist bioreactor 总被引:1,自引:0,他引:1
Zhenlong Hao Fan Ouyang Yuxuan Geng Xiangdong Deng Zanmin Hu Zhenghua Chen 《Biotechnology Techniques》1998,12(8):641-644
The newly designed nutrient mist bioreactor provided an environment supporting multiple-layer culture. In vitro tubers of potato (Solanum tuberosum L.) were induced and cultured in this bioreactor by using two culture methods. The percentage of the inocula eventually forming tubers in a two-step method was 98% with only 54% being formed in a one-step method. The two-step method improved the efficiency of tuber induction, expedited and synchronized the tuberization. © Rapid Science Ltd. 1998 相似文献
127.
外源基因直接转移技术之评价 总被引:2,自引:0,他引:2
外源基因直接转移技术有PEG法、电击法、基因枪法、微注射法、脂质体法、生殖细胞转化法等.本文对它们进行了比较分析,指出它们各自的优缺点,并提出生殖细胞转化法是一种值得探索和应用的转化方法 相似文献
128.
Ji-Feng Feng Xiao-Fei Gao Ying-yan Pu Geoffrey Burnstock Zhenghua Xiang Cheng He 《Purinergic signalling》2015,11(3):361-369
Recruitment of oligodendrocyte precursor cells (OPCs) to the lesions is the most important event for remyelination after central nervous system (CNS) injury or in demyelinating diseases. However, the underlying molecular mechanism is not fully understood. In the present study, we found high concentrations of ATP could increase the number of migrating OPCs in vitro, while after pretreatment with oxidized ATP (a P2X7 receptor antagonist), the promotive effect was attenuated. The promotive effect of 2′(3′)-O-(4-benzoylbenzoyl) adenosine 5′-triphosphate (BzATP) (a P2X7 receptor agonist) was more potent than ATP. After incubation with BzATP, the activity of Fyn, one member of the Src family of kinases, was enhanced. Moreover, the interaction between P2X7 and Fyn was identified by co-immunoprecipitation. After blocking the activity of Fyn or down-regulating the expression of Fyn, the migration of OPCs induced by BzATP was inhibited. These data indicate that P2X7 receptors/Fyn may mediate ATP-induced OPC migration under pathological conditions.
Electronic supplementary material
The online version of this article (doi:10.1007/s11302-015-9458-3) contains supplementary material, which is available to authorized users. 相似文献129.
Qiang Yu Zhengqing Zhao Jihu Sun Wei Guo Jiqiang Fu Geoffrey Burnstock Cheng He Zhenghua Xiang 《Histochemistry and cell biology》2010,133(2):177-188
Expression of P2X4 and P2X6 receptor subunits in the gastrointestinal tract of the rat was studied with double-labeling fluorescence immunohistochemistry. The results showed that P2X6 receptors were expressed widely in the submucosal and myenteric plexuses. In the myenteric plexus, P2X6 receptors were expressed mainly in large size neurons which resembled Dogiel type II neurons. These P2X6 receptor-immunoreactive (ir) neurons also expressed calbindin 28K, calretinin and neuronal nuclei (NeuN), proteins that are markers of intrinsic sensory neurons. In the submucosal plexus, all the calbindin 28K, calretinin and NeuN-ir cells were immunoreactive for P2X6 receptors. P2X6 receptors do not form homomultimers, but rather heteromultimers with either P2X2 or P2X4 receptors. P2X4 receptors were not expressed in neurons, but were expressed in macrophages of the rat gastrointestinal tract. These data indicate that P2X6 receptors are mainly expressed on intrinsic sensory neurons and that ATP, via P2X6 receptors probably in heteromeric combination with P2X2 receptors, may be involved in regulating the physiological functions of these neurons. 相似文献
130.
缬沙坦联合硝苯地平缓释片治疗老年性高血压的临床效果观察 总被引:1,自引:0,他引:1
目的:探讨缬沙坦联合硝苯地平缓释片治疗老年性高血压的临床效果.方法:选择确诊为原发性高血压门诊及住院老年患者170例,52例患者采用缬沙坦治疗,分为A组;56例患者采用硝苯地平缓释片治疗,分为B组;62例患者采用缬沙坦联合硝苯地平缓释片治疗,分为C组.治疗6周后,比较各组临床效果及治疗前后收缩压(SBP)和舒张压(DBP)变化的差值.结果:联合用药治疗效果及控制血压效果好于单一用药效果.结论:缬沙坦联合硝笨地平缓释片治疗老年性高血压安全有效,临床效果好于单一用药效果. 相似文献