全文获取类型
收费全文 | 42660篇 |
免费 | 2232篇 |
国内免费 | 1443篇 |
专业分类
46335篇 |
出版年
2023年 | 576篇 |
2022年 | 885篇 |
2021年 | 1097篇 |
2020年 | 1095篇 |
2019年 | 1497篇 |
2018年 | 1524篇 |
2017年 | 917篇 |
2016年 | 1051篇 |
2015年 | 1260篇 |
2014年 | 2550篇 |
2013年 | 3175篇 |
2012年 | 1789篇 |
2011年 | 2576篇 |
2010年 | 1842篇 |
2009年 | 2023篇 |
2008年 | 2211篇 |
2007年 | 2238篇 |
2006年 | 1986篇 |
2005年 | 1767篇 |
2004年 | 1550篇 |
2003年 | 1335篇 |
2002年 | 1211篇 |
2001年 | 759篇 |
2000年 | 694篇 |
1999年 | 705篇 |
1998年 | 699篇 |
1997年 | 580篇 |
1996年 | 534篇 |
1995年 | 510篇 |
1994年 | 473篇 |
1993年 | 414篇 |
1992年 | 354篇 |
1991年 | 323篇 |
1990年 | 274篇 |
1989年 | 234篇 |
1988年 | 206篇 |
1987年 | 196篇 |
1986年 | 171篇 |
1985年 | 273篇 |
1984年 | 465篇 |
1983年 | 389篇 |
1982年 | 365篇 |
1981年 | 278篇 |
1980年 | 250篇 |
1979年 | 202篇 |
1978年 | 151篇 |
1977年 | 147篇 |
1976年 | 127篇 |
1975年 | 102篇 |
1973年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
871.
Chiranjib Banerjee Rajib Bandopadhyay Pratyoosh Shukla 《Indian journal of microbiology》2012,52(4):710-712
A simple agar diffusion method is developed where pure colony of Chlamydomonas sp. CRP7 was isolated from Chlorella sp. CB4 mixtures by passing through agar migration with a light exposure of 6,000 lux for 7 h. The main concept behind it is that Chlamydomonas has flagella and the rhodopsin pigment is attracted towards light. Thus the above two microalgae species can be separated from the mixtures as eye spot serves as a navigator and flagella serves as a propeller for Chlamydomonas spp. Further the genomic DNA was isolated and purified from the above mentioned two species after the separation from the mixtures. PCR amplification was carried out for ITS1, 5.8S and ITS2 regions. The amplified products were sequenced and the sequence analysis confirmed that they belong to Chlamydomonas sp. and Chlorella sp. This is an important augmentation for isolation and separation of microalgae. 相似文献
872.
以人胎肝为材料,通过PT-PCR的方法扩增出人促红细胞生成素受体(hPeoR)的胞外区基因。将获得的或熟体胞外区基因起始密码子改构后克隆原核表达载体pBV220中,进行原核温控诱导表达。表达产物经蛋白N端测序及Western-blot实验证实表达产物是hEpoR胞外区蛋白。利用上罐发酵培养获得的包涵体蛋白经复性纯化后,体外生物学活性检测表明表达产物可特 抑制TF-1细胞在Epo刺激下的生长,证实了 相似文献
873.
874.
Takahashi N Yamada W Masuda K Araki H Tsukamoto Y Galinha A Sautès C Kato K Shimada I 《Glycoconjugate journal》1998,15(9):905-914
N-glycans of a recombinant mouse soluble Fc receptor II (sFcRII) expressed in baby hamster kidney cells were released from glycopeptides by digestion with glycoamidase A (from sweet almond), and the reducing ends of the oligosaccharides were reductively aminated with 2-aminopyridine. The derivatized N-glycans were separated and structurally identified by a three-dimensional high-performance liquid chromatography (HPLC) mapping technique on three kinds of HPLC columns [Takahashi, et al. (1995) Anal. Biochem. 226: 139–46]. Eighteen different major N-glycan structures were identified, of which six were neutral (45%), five mono-sialyl (49%), one di-sialyl (4.6%), five tri-sialyl (1.1%), and one tetra-sialyl (0.3%). All N-glycan structures determined were complex type with fucosylation at the N-acetylglucosamine residue of the reducing end, and N-acetylneuraminic acid, when present, was -(2,3)-linked. The existence of a unique structure containing both N-acetylgalactosamine and -(2,3)-N-acetylneuraminic acid residues at the reducing ends, as below, was confirmed by MALDI-TOF mass spectrometry. 相似文献
875.
Maria-Ioanna Ellina Panagiotis Bouris Alexios J. Aletras Achilleas D. Theocharis Dimitris Kletsas Nikos K. Karamanos 《Biochimica et Biophysica Acta (BBA)/General Subjects》2014
Background
ErbB receptors, EGFR and HER2, have been implicated in the development and progression of colon cancer. Several intracellular pathways are mediated upon activation of EGFR and/or HER2 by EGF. However, there are limited data regarding the EGF-mediated signaling affecting functional cell properties and the expression of extracellular matrix macromolecules implicated in cancer progression.Methods
Functional assays, such as cell proliferation, transwell invasion assay and migration were performed to evaluate the impact of EGFR/HER2 in constitutive and EGF-treated Caco-2 cells. Signaling pathways were evaluated using specific intracellular inhibitors. Western blot was also utilized to examine the phosphorylation levels of ERK1/2. Real time PCR was performed to evaluate gene expression of matrix macromolecules.Results
EGF increases cell proliferation, invasion and migration and importantly, EGF mediates overexpression of EGFR and downregulation of HER2. The EGF–EGFR axis is the main pathway affecting colon cancer's invasive potential, proliferative and migratory ability. Intracellular pathways (PI3K-Akt, MEK1/2-Erk and JAK-STAT) are all implicated in the migratory profile. Notably, MT1- and MT2-MMP as well as TIMP-2 are downregulated, whereas uPA is upregulated via an EGF–EGFR network. The EGF–EGFR axis is also implicated in the expression of syndecan-4 and TIMP-1. However, glypican-1 upregulation by EGF is mainly mediated via HER2.Conclusions and general significance
The obtained data highlight the crucial importance of EGF on the expression of both receptors and on the EGF–EGFR/HER2 signaling network, reveal the distinct roles of EGFR and HER2 on expression of matrix macromolecules and open a new area in designing novel agents in targeting colon cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties. 相似文献876.
877.
大鼠脑突触质膜糖皮质激素受体样抗原的免疫电镜研究 总被引:1,自引:0,他引:1
本文利用ABC金标记法(受体-抗受体中的单克隆抗体-生物素化马抗鼠IgG-金标链霉亲和素),首次在电镜下观察到大鼠脑突触质膜的外表面存在有糖皮质激素受体样抗原,为神经细胞膜上可能存在有糖皮质激素受体提供了形态学依据。 相似文献
878.
B型烟粉虱在四种葫芦科寄主植物上的发育和繁殖 总被引:4,自引:0,他引:4
研究了B型烟粉虱在4种葫芦科寄主植物黄瓜、节瓜、苦瓜和丝瓜上的发育和繁殖特性.结果表明,B型烟粉虱在节瓜上的世代发育历期最短,为19.3 d,在苦瓜上的世代发育历期最长,为29.0 d;世代存活率在黄瓜上最高,为92.85%,在苦瓜上最低,为53.08%;平均单雌产卵量在黄瓜上最多,为187.4粒,苦瓜上最少,为30.0粒;雌成虫寿命以在黄瓜上最长,为25.2 d,在苦瓜上最短,为10.9 d.B型烟粉虱在黄瓜、节瓜、苦瓜和丝瓜上的内禀增长率(rm)分别为0.1453、0.1429、0.0616和0.1055.综合比较4种葫芦科植物,黄瓜是B型烟粉虱的最适宜寄主. 相似文献
879.
Maura Marinozzi Andrea Carotti Roccaldo Sardella Federica Buonerba Federica Ianni Benedetto Natalini Daniela Passeri Giovanni Rizzo Roberto Pellicciari 《Bioorganic & medicinal chemistry》2013,21(13):3780-3789
An asymmetric synthetic strategy was designed for the preparation of the four possible diastereoisomers of 3,6-dimethyl-1-(2-methylphenyl)-4-(4-phenoxyphenyl)-4,8-dihydro-1H-pyrazolo[3,4-e][1,4]thiazepin-7-one, a non-steroidal FXR agonist, we recently discovered following a virtual screening approach. The results obtained from an AlphaScreen assay clearly demonstrated that only the isomer endowed with 4R,6S absolute configuration is responsible for the biological activity. A deep investigation of the different putative binding modes adopted by these enantiomerically pure ligands using computational modeling studies confirmed the enantioselectivity of FXR towards this class of molecules. 相似文献
880.
Jinshan Yang Xiang Luo Xiaojiang Huang Qin Ning Minjie Xie Wei Wang 《Journal of neurochemistry》2014,131(3):383-394
Increasing evidence indicates that the Eph receptors and their ephrin ligands are involved in the regulation of interactions between neurons and astrocytes. Moreover, astrocytic ephrin‐A3 reverse signaling mediated by EphA4 receptors is necessary for controlling the abundance of glial glutamate transporters. However, the role of ephrin‐A3 reverse signaling in astrocytic function and neuronal death under ischemic conditions remains unclear. In the present study, we found that the EphA4 receptor and its ephrin‐A3 ligand, which were distributed in neurons and astrocytes, respectively, in the hippocampus showed a coincident up‐regulation of protein expression in the early stage of ischemia. Application of clustered EphA4 decreased the expressions of astrocytic glutamate transporters together with astrocytic glutamate uptake capacity through activating ephrin‐A3 reverse signaling. In consequence, neuronal loss was aggravated in the CA1 region of the hippocampus accompanied by impaired hippocampus‐dependent spatial memory when clustered EphA4 treatment was administered prior to transient global ischemia. These findings indicate that EphA4‐mediated ephrin‐A3 reverse signaling is a crucial mechanism for astrocytes to control glial glutamate transporters and prevent glutamate excitotoxicity under pathological conditions.