全文获取类型
收费全文 | 6405篇 |
免费 | 442篇 |
国内免费 | 4篇 |
出版年
2021年 | 66篇 |
2020年 | 36篇 |
2019年 | 50篇 |
2018年 | 58篇 |
2017年 | 59篇 |
2016年 | 87篇 |
2015年 | 175篇 |
2014年 | 195篇 |
2013年 | 384篇 |
2012年 | 294篇 |
2011年 | 300篇 |
2010年 | 193篇 |
2009年 | 179篇 |
2008年 | 297篇 |
2007年 | 350篇 |
2006年 | 293篇 |
2005年 | 299篇 |
2004年 | 309篇 |
2003年 | 285篇 |
2002年 | 250篇 |
2001年 | 224篇 |
2000年 | 217篇 |
1999年 | 177篇 |
1998年 | 80篇 |
1997年 | 83篇 |
1996年 | 78篇 |
1995年 | 56篇 |
1994年 | 72篇 |
1993年 | 46篇 |
1992年 | 127篇 |
1991年 | 123篇 |
1990年 | 136篇 |
1989年 | 134篇 |
1988年 | 117篇 |
1987年 | 78篇 |
1986年 | 84篇 |
1985年 | 101篇 |
1984年 | 91篇 |
1983年 | 62篇 |
1982年 | 49篇 |
1981年 | 57篇 |
1980年 | 43篇 |
1979年 | 54篇 |
1978年 | 37篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1975年 | 36篇 |
1974年 | 34篇 |
1973年 | 40篇 |
1971年 | 26篇 |
排序方式: 共有6851条查询结果,搜索用时 15 毫秒
991.
Butler MO Imataki O Yamashita Y Tanaka M Ansén S Berezovskaya A Metzler G Milstein MI Mooney MM Murray AP Mano H Nadler LM Hirano N 《PloS one》2012,7(1):e30229
Background
Using in vivo mouse models, the mechanisms of CD4+ T cell help have been intensively investigated. However, a mechanistic analysis of human CD4+ T cell help is largely lacking. Our goal was to elucidate the mechanisms of human CD4+ T cell help of CD8+ T cell proliferation using a novel in vitro model.Methods/Principal Findings
We developed a genetically engineered novel human cell-based artificial APC, aAPC/mOKT3, which expresses a membranous form of the anti-CD3 monoclonal antibody OKT3 as well as other immune accessory molecules. Without requiring the addition of allogeneic feeder cells, aAPC/mOKT3 enabled the expansion of both peripheral and tumor-infiltrating T cells, regardless of HLA-restriction. Stimulation with aAPC/mOKT3 did not expand Foxp3+ regulatory T cells, and expanded tumor infiltrating lymphocytes predominantly secreted Th1-type cytokines, interferon-γ and IL-2. In this aAPC-based system, the presence of autologous CD4+ T cells was associated with significantly improved CD8+ T cell expansion in vitro. The CD4+ T cell derived cytokines IL-2 and IL-21 were necessary but not sufficient for this effect. However, CD4+ T cell help of CD8+ T cell proliferation was partially recapitulated by both adding IL-2/IL-21 and by upregulation of IL-21 receptor on CD8+ T cells.Conclusions
We have developed an in vitro model that advances our understanding of the immunobiology of human CD4+ T cell help of CD8+ T cells. Our data suggests that human CD4+ T cell help can be leveraged to expand CD8+ T cells in vitro. 相似文献992.
Naoto Takahashi Masatomo Miura Stuart A Scott Takenori Niioka Kenichi Sawada 《Journal of hematology & oncology》2012,5(1):1-4
Myelodysplastic syndrome (MDS) is a clonal hematopoietic stem cell disorder of elderly people. Cardiac dysfunction is a marker of grim prognosis in MDS. We evaluated cardiac dysfunction of MDS patients with or without transfusion dependency by tissue doppler echocardiography. We found the average values of ventricular end-systolic and end-diastolic volumes in transfusion dependency MDS group higher than others. These results were strongly correlated to hemoglobin levels. Tissue Doppler Echocardiography should be routinely performed in MDS patients to detect preclinical cardiac alterations and prevent more heart insults in this group of chronic anemic aged patients. 相似文献
993.
Bacillus subtilis is the only bacterium-based host able to clone giant DNA above 1000 kbp. DNA previously handled by this host was limited to that with GC content similar to or lower than that of the B. subtilis genome. To expand the target DNA range to higher GC content, we tried to clone a pTT27 megaplasmid (257 kbp, 69% of G+C) from Thermus thermophilus. To facilitate the reconstruction process, we subcloned pTT27 in a bacterial artificial chromosome (BAC) vector of Escherichia coli. Owing to the ability of BAC to carry around 100 kbp DNA, only 4 clones were needed to cover the pTT27 and conduct step-by-step assembly in the B. subtilis genome. The full length of 257 kbp was reconstructed through 3 intermediary lengths (108, 153, and 226 kbp), despite an unexpected difficulty in the maintenance of DNA >200 kbp. Retrieval of these four pTT27 segments from the B. subtilis genome by genetic transfer to a plasmid pLS20 was attempted. A stable plasmid clone was obtained only for the 108 and 153 kbp intermediates. The B. subtilis genome was demonstrated to accommodate large DNA with a high GC content, but may be restricted to less than 200 kbp by unidentified mechanisms. 相似文献
994.
Tanaka K Arao T Tamura D Aomatsu K Furuta K Matsumoto K Kaneda H Kudo K Fujita Y Kimura H Yanagihara K Yamada Y Okamoto I Nakagawa K Nishio K 《PloS one》2012,7(1):e27922
SRPX2 (Sushi repeat-containing protein, X-linked 2) has recently emerged as a multifunctional protein that is involved in seizure disorders, angiogenesis and cellular adhesion. Here, we analyzed this protein biochemically. SRPX2 protein was secreted with a highly posttranslational modification. Chondroitinase ABC treatment completely decreased the molecular mass of purified SRPX2 protein to its predicted size, whereas heparitinase, keratanase and hyaluroinidase did not. Secreted SRPX2 protein was also detected using an anti-chondroitin sulfate antibody. These results indicate that SRPX2 is a novel chondroitin sulfate proteoglycan (CSPG). Furthermore, a binding assay revealed that hepatocyte growth factor dose-dependently binds to SRPX2 protein, and a ligand-glycosaminoglycans interaction was speculated to be likely in proteoglycans. Regarding its molecular architecture, SRPX2 has sushi repeat modules similar to four other CSPGs/lecticans; however, the molecular architecture of SRPX2 seems to be quite different from that of the lecticans. Taken together, we found that SRPX2 is a novel CSPG that is overexpressed in gastrointestinal cancer cells. Our findings provide key glycobiological insight into SRPX2 in cancer cells and demonstrate that SRPX2 is a new member of the cancer-related proteoglycan family. 相似文献
995.
Moriya K Suzuki M Watanabe Y Takahashi T Aoki Y Uchiyama T Kumaki S Sasahara Y Minegishi M Kure S Tsuchiya S Sugamura K Ishii N 《PloS one》2012,7(6):e37892
Mixed-lineage-leukemia (MLL) fusion oncogenes are intimately involved in acute leukemia and secondary therapy-related acute leukemia. To understand MLL-rearranged leukemia, several murine models for this disease have been established. However, the mouse leukemia derived from mouse hematopoietic stem cells (HSCs) may not be fully comparable with human leukemia. Here we developed a humanized mouse model for human leukemia by transplanting human cord blood-derived HSCs transduced with an MLL-AF10 oncogene into a supra-immunodeficient mouse strain, NOD/Shi-scid, IL-2Rγ(-/-) (NOG) mice. Injection of the MLL-AF10-transduced HSCs into the liver of NOG mice enhanced multilineage hematopoiesis, but did not induce leukemia. Because active mutations in ras genes are often found in MLL-related leukemia, we next transduced the gene for a constitutively active form of K-ras along with the MLL-AF10 oncogene. Eight weeks after transplantation, all the recipient mice had developed acute monoblastic leukemia (the M5 phenotype in French-American-British classification). We thus successfully established a human MLL-rearranged leukemia that was derived in vivo from human HSCs. In addition, since the enforced expression of the mutant K-ras alone was insufficient to induce leukemia, the present model may also be a useful experimental platform for the multi-step leukemogenesis model of human leukemia. 相似文献
996.
997.
Masanori Osawa Nao Hosoda Tamiji Nakanishi Naoyuki Uchida Tomomi Kimura Shunsuke Imai Asako Machiyama Toshiaki Katada Shin-ichi Hoshino Ichio Shimada 《RNA (New York, N.Y.)》2012,18(11):1957-1967
Eukaryotic releasing factor GSPT/eRF3 mediates translation termination-coupled mRNA decay via interaction with a cytosolic poly(A)-binding protein (PABPC1). A region of eRF3 containing two overlapping PAM2 (PABPC1-interacting motif 2) motifs is assumed to bind to the PABC domain of PABPC1, on the poly(A) tail of mRNA. PAM2 motifs are also found in the major deadenylases Caf1–Ccr4 and Pan2–Pan3, whose activities are enhanced upon PABPC1 binding to these motifs. Their deadenylase activities are regulated by eRF3, in which two overlapping PAM2 motifs competitively prevent interaction with PABPC1. However, it is unclear how these overlapping motifs recognize PABC and regulate deadenylase activity in a translation termination-coupled manner. We used a dominant-negative approach to demonstrate that the N-terminal PAM2 motif is critical for eRF3 binding to PABPC1 and that both motifs are required for function. Isothermal titration calorimetry (ITC) and NMR analyses revealed that the interaction is in equilibrium between the two PAM2–PABC complexes, where only one of the two overlapping PAM2 motifs is PABC-bound and the other is PABC-unbound and partially accessible to the other PABC. Based on these results, we proposed a biological role for the overlapping PAM2 motifs in the regulation of deadenylase accessibility to PABPC1 at the 3′ end of poly(A). 相似文献
998.
999.
Takata T Kimura Y Ohnuma Y Kawawaki J Kakiyama Y Tanaka K Kakizuka A 《Journal of structural biology》2012,179(2):93-103
VCP/p97/Cdc48 is a hexameric ring-shaped AAA ATPase that participates in a wide variety of cellular functions. VCP is a very abundant protein in essentially all types of cells and is highly conserved among eukaryotes. To date, 19 different single amino acid-substitutions in VCP have been reported to cause IBMPFD (inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia), an autosomal dominant inherited human disease. Moreover, several similar single amino acid substitutions have been proposed to associate with a rare subclass of familial ALS. The mechanisms by which these mutations contribute to the pathogenesis are unclear. To elucidate potential functional differences between wild-type and pathogenic VCPs, we expressed both VCPs in yeast cdc48 mutants. We observed that all tested pathogenic VCPs suppressed the temperature-sensitive phenotype of cdc48 mutants more efficiently than wild-type VCP. In addition, pathogenic VCPs, but not wild-type VCP, were able to rescue a lethal cdc48 disruption. In yeast, pathogenic VCPs, but not wild-type VCP, formed apparent cytoplasmic foci, and these foci were transported to budding sites by the Myo2/actin-mediated transport machinery. The foci formation of pathogenic VCPs appeared to be associated with their suppression of the temperature-sensitive phenotype of cdc48 mutants. These results support the idea that the pathogenic VCP mutations create dominant gain-of-functions rather than a simple loss of functional VCP. Their unique properties in yeast could provide a convenient drug-screening system for the treatment of these diseases. 相似文献
1000.