全文获取类型
收费全文 | 1886篇 |
免费 | 80篇 |
国内免费 | 1篇 |
专业分类
1967篇 |
出版年
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 8篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 34篇 |
2015年 | 66篇 |
2014年 | 70篇 |
2013年 | 102篇 |
2012年 | 95篇 |
2011年 | 101篇 |
2010年 | 63篇 |
2009年 | 66篇 |
2008年 | 115篇 |
2007年 | 107篇 |
2006年 | 124篇 |
2005年 | 109篇 |
2004年 | 118篇 |
2003年 | 110篇 |
2002年 | 109篇 |
2001年 | 31篇 |
2000年 | 29篇 |
1999年 | 33篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 18篇 |
1995年 | 30篇 |
1994年 | 10篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 20篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1935年 | 6篇 |
1934年 | 5篇 |
1931年 | 7篇 |
排序方式: 共有1967条查询结果,搜索用时 15 毫秒
81.
Aim: Ultraviolet (UV) mutagenesis was carried out to obtain mutant strains of Cupriavidus necator that could produce ( R )-3-hydroxybutyric acid [( R )-3-HB] in the culture supernatant.
Methods and Results: C. necator (formerly known as Ralstonia eutropha ) was subjected to UV radiation to generate mutants that are capable of producing ( R )-3-HB in the culture supernatant. Results indicated that UV mutagen disrupted the phbB ( phbB knock-out) and thus, promoted production of ( R )-3-HB in mutant strains. Inclusion of acetoacetate esters (carbonyl compounds) in the culture broth led to increased production of ( R )-3-HB. Thus, acetoacetyl-CoA (an intermediate of the PHB synthetic pathway) might have been converted to acetoacetate, which in the presence of ( R )-3-HB dehydrogenase and NADPH/NADP+ , resulted in extracellular production of ( R )-3-HB.
Conclusions: UV mutagenesis proved to be a satisfactory method in generating interesting mutants for extracellular production of ( R )-3-HB. Extracellular production of ( R )-3-HB upon addition of acetoacetate esters would suggest a likely ( R )-3-HB biosynthetic pathway in C. necator .
Significance and Impact of the Study: Mutants obtained in this study are very useful for production of ( R )-3-HB. For the first time, the production of ( R )-3-HB by C. necator via acetoacetate is reported. 相似文献
Methods and Results: C. necator (formerly known as Ralstonia eutropha ) was subjected to UV radiation to generate mutants that are capable of producing ( R )-3-HB in the culture supernatant. Results indicated that UV mutagen disrupted the phbB ( phbB knock-out) and thus, promoted production of ( R )-3-HB in mutant strains. Inclusion of acetoacetate esters (carbonyl compounds) in the culture broth led to increased production of ( R )-3-HB. Thus, acetoacetyl-CoA (an intermediate of the PHB synthetic pathway) might have been converted to acetoacetate, which in the presence of ( R )-3-HB dehydrogenase and NADPH/NADP
Conclusions: UV mutagenesis proved to be a satisfactory method in generating interesting mutants for extracellular production of ( R )-3-HB. Extracellular production of ( R )-3-HB upon addition of acetoacetate esters would suggest a likely ( R )-3-HB biosynthetic pathway in C. necator .
Significance and Impact of the Study: Mutants obtained in this study are very useful for production of ( R )-3-HB. For the first time, the production of ( R )-3-HB by C. necator via acetoacetate is reported. 相似文献
82.
Takashi Yazawa Yoshitaka Imamichi Koh‐ichi Yuhki Junsuke Uwada Daisuke Mikami Masayuki Shimada Kaoru Miyamoto Takeshi Kitano Satoru Takahashi Toshio Sekiguchi Nobuo Suzuki Md. Rafiqul Islam Khan Fumitaka Ushikubi Akihiro Umezawa Takanobu Taniguchi 《Molecular reproduction and development》2019,86(7):786-797
83.
Mari Kawamura Tadashi Yamamoto Keisuke Yamashiro Shinsuke Kochi Chiaki Yoshihara‐Hirata Hidetaka Ideguchi Hiroaki Aoyagi Kazuhiro Omori Shogo Takashiba 《Journal of cellular and molecular medicine》2019,23(2):1211-1223
The recruitment of tissue‐resident stem cells is important for wound regeneration. Periodontal ligament cells (PDL cells) are heterogeneous cell populations with stemness features that migrate into wound sites to regenerate periodontal fibres and neighbouring hard tissues. Cell migration is regulated by the local microenvironment, coordinated by growth factors and the extracellular matrix (ECM). Integrin‐mediated cell adhesion to the ECM provides essential signals for migration. We hypothesized that PDL cell migration could be enhanced by selective expression of integrins. The migration of primary cultured PDL cells was induced by platelet‐derived growth factor‐BB (PDGF‐BB). The effects of blocking specific integrins on migration and ECM adhesion were investigated based on the integrin expression profiles observed during migration. Up‐regulation of integrins α3, α5, and fibronectin was identified at distinct localizations in migrating PDL cells. Treatment with anti‐integrin α5 antibodies inhibited PDL cell migration. Treatment with anti‐integrin α3, α3‐blocking peptide, and α3 siRNA significantly enhanced cell migration, comparable to treatment with PDGF‐BB. Furthermore, integrin α3 inhibition preferentially enhanced adhesion to fibronectin via integrin α5. These findings indicate that PDL cell migration is reciprocally regulated by integrin α3‐mediated inhibition and α5‐mediated promotion. Thus, targeting integrin expression is a possible therapeutic strategy for periodontal regeneration. 相似文献
84.
85.
86.
Singlet oxygen, generated during photosynthesis, is a strong oxidant that can, potentially, damage various molecules of biological importance. We investigated the effects in vivo of singlet oxygen on the photodamage to photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC 6803. Increases in intracellular concentrations of singlet oxygen, caused by the presence of photosensitizers, such as rose bengal and ethyl eosin, stimulated the apparent photodamage to PSII. However, actual photodamage to PSII, as assessed in the presence of chloramphenicol, was unaffected by the production of singlet oxygen. These observations suggest that singlet oxygen produced by added photosensitizers acts by inhibiting the repair of photodamaged PSII. Labeling of proteins in vivo revealed that singlet oxygen inhibited the synthesis of proteins de novo and, in particular, the synthesis of the D1 protein. Northern blotting analysis indicated that the accumulation of psbA mRNAs, which encode the D1 protein, was unaffected by the production of singlet oxygen. Subcellular localization of polysomes with bound psbA mRNAs suggested that the primary target of singlet oxygen might be the elongation step of translation. 相似文献
87.
Furuhata S Ando K Oki M Aoki K Ohnishi S Aoyagi K Sasaki H Sakamoto H Yoshida T Ohnami S 《Molecular and cellular biochemistry》2007,298(1-2):125-138
Among the many tissue stem or progenitor cells recently being unveiled, endothelial progenitor cells (EPCs) have attracted
particular attention, not only because of their cardinal role in vascular biology and embryology but also because of their
potential use in the therapeutic development of a variety of postnatal diseases, including cardiovascular and peripheral vascular
disorders and cancer. The aim of this study is to provide some basic and comprehensive information on gene expression of EPCs
to characterize the cells in molecular terms. Here, we focus on EPCs derived from CD34-positive mononuclear cells of human
umbilical cord blood. The EPCs were purified and expanded in culture and analyzed by a high-density oligonucleotide microarray
and real-time RT-PCR analysis. We identified 169 up-regulated and 107 down-regulated genes in the EPCs compared with three
differentiated endothelial cells of human umbilical vein endothelial cells (HUVEC), human lung microvascular endothelial cells
(LMEC) and human aortic endothelial cells (AoEC). It is expected that the obtained list include key genes which are critical
for EPC function and survival and thus potential targets of EPC recognition in vivo and therapeutic modulation of vasculogenesis
in cancer as well as other diseases, in which de novo vasculogenesis plays a crucial role. For instance, the list includes
Syk and galectin-3, which encode protein tyrosine kinase and β-galactoside-binding protein, respectively, and are expressed higher in EPCs than
the three control endothelial cells. In situ hybridization showed that the genes were expressed in isolated cells in the fetal
liver at E11.5 and E14.5 of mouse development. 相似文献
88.
A rapid analysis method of strongly acidic amino acids and related compounds by a simple modification of an existing amino acid analyzer is presented. In this method, an anion-exchanger column (2.6 X 150 mm) packed with Hitachi 3013-N resin was developed with 0.2 M citric acid. Complete separation of phosphothreonine, phosphoserine, phosphotyrosine, cysteic acid, homocysteic acid, and glutathionesulfonic acid was achieved within 35 min, with no regeneration of the column being required. Tyrosine-O-sulfate was analyzed by the same column using 2 M sodium acetate buffer, pH 5.5. Performic acid oxidation of a variety of proteins and direct analysis of the products by this system successfully detected cysteine, homocysteine, and/or glutathione bound to proteins through disulfide bonds. This suggest the potential use of the method for analysis of the states of protein thiol groups, especially those of clinically significant mutant proteins where mutation of arginine to cysteine is rather frequently recognized. 相似文献
89.
90.
Rintaro Moroi Katsuya Endo Yoshitaka Kinouchi Hisashi Shiga Yoichi Kakuta Masatake Kuroha Yoshitake Kanazawa Yosuke Shimodaira Takahiko Horiuchi Seiichi Takahashi Tooru Shimosegawa 《Immunogenetics》2013,65(4):265-271
An association between FCGR3A-158 V/F polymorphism and biological responses to infliximab has been reported in Crohn’s disease (CD) in Western countries. However, little is known about the mechanism by which gene polymorphism affects the responses to infliximab. The aims of this study were to confirm the association in Japanese CD patients and to reveal the effect of gene polymorphism on biological responses to infliximab. Japanese CD patients were examined retrospectively at weeks 8 and 30. Clinical and biological responses were assessed by the Crohn’s disease activity index and C-reactive protein levels, respectively. The infliximab-binding affinity of natural killer (NK) cells from FCGR3A-158 V/V, V/F and F/F donors was examined. Infliximab-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) activities were also determined using transmembrane TNF-α-expressing Jurkat T cells as target cells and peripheral blood mononuclear cells (PBMCs) from V/V, V/F and F/F donors as effector cells. Biological responses at week 8 were statistically higher in V/V patients, whereas no significant differences were observed in either clinical responses at weeks 8 and 30 or biological responses at week 30 among the three genotypes. NK cells and PBMCs from V/V patients also showed higher infliximab-binding affinity and infliximab-mediated ADCC activity, respectively. Our results suggest that FCGR3A-158 polymorphism is a predicting factor of biological responses to infliximab in the early phases. FCGR3A-158 polymorphism was also found to affect the infliximab-binding affinity of NK cells and infliximab-mediated ADCC activity in vitro, suggesting that an effect on ADCC activity influences biological responses to infliximab in CD patients. 相似文献