全文获取类型
收费全文 | 2230篇 |
免费 | 268篇 |
出版年
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 23篇 |
2020年 | 23篇 |
2019年 | 27篇 |
2018年 | 36篇 |
2017年 | 30篇 |
2016年 | 39篇 |
2015年 | 97篇 |
2014年 | 92篇 |
2013年 | 116篇 |
2012年 | 134篇 |
2011年 | 175篇 |
2010年 | 112篇 |
2009年 | 85篇 |
2008年 | 142篇 |
2007年 | 145篇 |
2006年 | 128篇 |
2005年 | 137篇 |
2004年 | 140篇 |
2003年 | 116篇 |
2002年 | 137篇 |
2001年 | 47篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 24篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 21篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 12篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1972年 | 16篇 |
排序方式: 共有2498条查询结果,搜索用时 1 毫秒
71.
Daniel C. B. Jeffery Brandon A. Wyse Muhammad Attiq Rehman Geoffrey W. Brown Zhiying You Roxanne Oshidari Hisao Masai Krassimir Y. Yankulov 《Nucleic acids research》2013,41(18):8475-8488
Position-effect variegation (PEV) phenotypes are characterized by the robust multigenerational repression of a gene located at a certain locus (often called gene silencing) and occasional conversions to fully active state. Consequently, the active state then persists with occasional conversions to the repressed state. These effects are mediated by the establishment and maintenance of heterochromatin or euchromatin structures, respectively. In this study, we have addressed an important but often neglected aspect of PEV: the frequency of conversions at such loci. We have developed a model and have projected various PEV scenarios based on various rates of conversions. We have also enhanced two existing assays for gene silencing in Saccharomyces cerevisiae to measure the rate of switches from repressed to active state and vice versa. We tested the validity of our methodology in Δsir1 cells and in several mutants with defects in gene silencing. The assays have revealed that the histone chaperone Chromatin Assembly Factor I is involved in the control of epigenetic conversions. Together, our model and assays provide a comprehensive methodology for further investigation of epigenetic stability and position effects. 相似文献
72.
Mayank Singh Clayton R. Hunt Raj K. Pandita Rakesh Kumar Chin-Rang Yang Nobuo Horikoshi Robert Bachoo Sara Serag Michael D. Story Jerry W. Shay Simon N. Powell Arun Gupta Jessie Jeffery Shruti Pandita Benjamin P. C. Chen Dorothee Deckbar Markus L?brich Qin Yang Kum Kum Khanna Howard J. Worman Tej K. Pandita 《Molecular and cellular biology》2013,33(16):3390
73.
74.
Lianchun Fan Ibrahim KaduraLara E. Krebs Jeffery L. LarsonDaniel M. Bowden Christopher C. Frye 《Journal of biotechnology》2013
Chinese hamster ovary (CHO) cells have been one of the most widely used host cells for the manufacture of therapeutic recombinant proteins. An effective and efficient clinical cell line development process, which could quickly identify those rare, high-producing cell lines among a large population of low and non-productive cells, is of considerable interest to speed up biological drug development. In the glutamine synthetase (GS)-CHO expression system, selection of top-producing cell lines is based on controlling the balance between the expression level of GS and the concentration of its specific inhibitor, l-methionine sulfoximine (MSX). The combined amount of GS expressed from plasmids that have been introduced through transfection and the endogenous CHO GS gene determine the stringency and efficiency of selection. Previous studies have shown significant improvement in selection stringency by using GS-knockout CHO cells, which eliminate background GS expression from the endogenous GS gene in CHOK1SV cells. To further improve selection stringency, a series of weakened SV40E promoters have been generated and used to modulate plasmid-based GS expression with the intent of manipulating GS-CHO selection, finely adjusting the balance between GS expression and GS inhibitor (MSX) levels. The reduction of SV40E promoter activities have been confirmed by TaqMan RT-PCR and GFP expression profiling. Significant productivity improvements in both bulk culture and individual clonal cell line have been achieved with the combined use of GS-knockout CHOK1SV cells and weakened SV40E promoters driving GS expression in the current cell line generation process. The selection stringency was significantly increased, as indicated by the shift towards higher distribution of producing-cell populations, even with no MSX added into cell culture medium. The potential applications of weakened SV40E promoter and GS-knockout cells in development of targeted integration and transient CHO expression systems are also discussed. 相似文献
75.
The amino acid composition of Nephila clavipes dragline silk fiber was determined by conducting 1H nuclear magnetic resonance (NMR) spectroscopy experiments on acid-hydrolyzed material. N. clavipes dragline silk was found to consist of 43.0 ± 0.6% Gly, 29.3 ± 0.2% Ala, 9.1 ± 0.1% Glx, 4.0 ± 0.1% Leu, 3.3 ± 0.1% Tyr, 3.4 ± 0.2% Ser, 2.7 ± 0.1% Pro, 2.1 ± 0.1% Arg, 1.07 ± 0.05% Asx, 0.96 ± 0.05% Val, 0.48 ± 0.03% Thr, 0.35 ± 0.03% Phe, and 0.28 ± 0.03% Ile. Compared with standard chromatography-based amino acid analysis (AAA), the chemical resolution of NMR allows for an amino acid solution to be characterized without separation and is shown to provide considerably higher precision. This allows for more accurate statistics on the variability of amino acids in spider dragline silk. In general, this 1H NMR AAA technique is applicable to a large range of proteins and peptides for precise composition characterization, especially when the precise content of a minor component is critical and relatively large amounts of sample are available (microgram to milligram quantities). 相似文献
76.
77.
Nayden Chakarov Rudy M. Jonker Martina Boerner Joseph I. Hoffman Oliver Krüger 《Molecular ecology》2013,22(21):5430-5440
Polymorphic genes involved in the conserved molecular signalling of circadian and circannual clocks may play important roles in governing the timing of breeding and dispersal and thereby affect fitness in vertebrates. However, relatively few studies have explored associations between phenological candidate genes and behaviour, and these are somewhat biased towards particular taxonomic groups such as passerine birds and salmonid fish. Consequently, we assayed microsatellite polymorphisms within the exonic and 3′ untranslated regions of the regulatory genes CLOCK, NPAS2, ADCYAP1 and CREB1 in the common buzzard (Buteo buteo), a polymorphic raptor species with three plumage morphs that differ in key life history traits including lifetime reproductive success. In contrast to studies of passerines, CLOCK poly‐glutamine (poly‐Q) was found to be monomorphic in 976 common buzzard nestlings as well as in three other Buteo species. Moreover, none of the candidate genes were significantly associated with fledging dates, although intermediately melanized females were found to lay earlier on average than light or dark morph individuals, and their offspring carried longer ADCYAP1 alleles. In contrast, all three candidate genes explained significant variation in one or more measures of juvenile buzzard dispersal (resighting probability, timing of dispersal and distance dispersed). Our findings contribute towards a broader body of work on the adaptive significance of CLOCK polymorphism, while also building upon previous studies that have documented links between ADCYAP1 variability and the timing of migration. 相似文献
78.
Hifzur Rahman Siddique Aijaz Parray Weixiong Zhong R. Jeffery Karnes Eric J. Bergstralh Shahriar Koochekpour Johng S. Rhim Badrinath R. Konety Mohammad Saleem 《PloS one》2013,8(1)
Background
Lack of reliable predictive biomarkers is a stumbling block in the management of prostate cancer (CaP). Prostate-specific antigen (PSA) widely used in clinics has several caveats as a CaP biomarker. African-American CaP patients have poor prognosis than Caucasians, and notably the serum-PSA does not perform well in this group. Further, some men with low serum-PSA remain unnoticed for CaP until they develop disease. Thus, there is a need to identify a reliable diagnostic and predictive biomarker of CaP. Here, we show that BMI1 stem-cell protein is secretory and could be explored for biomarker use in CaP patients.Methodology/Principal Findings
Semi-quantitative analysis of BMI1 was performed in prostatic tissues of TRAMP (autochthonous transgenic mouse model), human CaP patients, and in cell-based models representing normal and different CaP phenotypes in African-American and Caucasian men, by employing immunohistochemistry, immunoblotting and Slot-blotting. Quantitative analysis of BMI1 and PSA were performed in blood and culture-media of siRNA-transfected and non-transfected cells by employing ELISA. BMI1 protein is (i) secreted by CaP cells, (ii) increased in the apical region of epithelial cells and stromal region in prostatic tumors, and (iii) detected in human blood. BMI1 is detectable in blood of CaP patients in an order of increasing tumor stage, exhibit a positive correlation with serum-PSA and importantly is detectable in patients which exhibit low serum-PSA. The clinical significance of BMI1 as a biomarker could be ascertained from observation that CaP cells secrete this protein in higher levels than cells representative of benign prostatic hyperplasia (BPH).Conclusions/Significance
BMI1 could be developed as a dual bio-marker (serum and biopsy) for the diagnosis and prognosis of CaP in Caucasian and African-American men. Though compelling these data warrant further investigation in a cohort of African-American patients. 相似文献79.
David Freeman Rudy Cedillos Samantha Choyke Zana Lukic Kathleen McGuire Shauna Marvin Andrew M. Burrage Stacey Sudholt Ajay Rana Christopher O'Connor Christopher M. Wiethoff Edward M. Campbell 《PloS one》2013,8(4)
α-synuclein dysregulation is a critical aspect of Parkinson''s disease pathology. Recent studies have observed that α-synuclein aggregates are cytotoxic to cells in culture and that this toxicity can be spread between cells. However, the molecular mechanisms governing this cytotoxicity and spread are poorly characterized. Recent studies of viruses and bacteria, which achieve their cytoplasmic entry by rupturing intracellular vesicles, have utilized the redistribution of galectin proteins as a tool to measure vesicle rupture by these organisms. Using this approach, we demonstrate that α-synuclein aggregates can induce the rupture of lysosomes following their endocytosis in neuronal cell lines. This rupture can be induced by the addition of α-synuclein aggregates directly into cells as well as by cell-to-cell transfer of α-synuclein. We also observe that lysosomal rupture by α-synuclein induces a cathepsin B dependent increase in reactive oxygen species (ROS) in target cells. Finally, we observe that α-synuclein aggregates can induce inflammasome activation in THP-1 cells. Lysosomal rupture is known to induce mitochondrial dysfunction and inflammation, both of which are well established aspects of Parkinson''s disease, thus connecting these aspects of Parkinson''s disease to the propagation of α-synuclein pathology in cells. 相似文献
80.