全文获取类型
收费全文 | 2735篇 |
免费 | 239篇 |
出版年
2022年 | 17篇 |
2021年 | 31篇 |
2019年 | 24篇 |
2018年 | 36篇 |
2017年 | 30篇 |
2016年 | 54篇 |
2015年 | 88篇 |
2014年 | 87篇 |
2013年 | 117篇 |
2012年 | 192篇 |
2011年 | 165篇 |
2010年 | 125篇 |
2009年 | 99篇 |
2008年 | 162篇 |
2007年 | 147篇 |
2006年 | 143篇 |
2005年 | 135篇 |
2004年 | 139篇 |
2003年 | 140篇 |
2002年 | 125篇 |
2001年 | 43篇 |
2000年 | 29篇 |
1999年 | 40篇 |
1998年 | 49篇 |
1997年 | 34篇 |
1996年 | 31篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 26篇 |
1992年 | 46篇 |
1991年 | 31篇 |
1990年 | 34篇 |
1989年 | 24篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1975年 | 18篇 |
1974年 | 18篇 |
1973年 | 13篇 |
1971年 | 13篇 |
1968年 | 14篇 |
排序方式: 共有2974条查询结果,搜索用时 15 毫秒
131.
Masayasu Naito Ursula Hainz Ute E. Burkhardt Buyin Fu Deborah Ahove Kristen E. Stevenson Mohini Rajasagi Baogong Zhu Anselmo Alonso Elizabeth Witten Ken-ichi Matsuoka Donna Neuberg Jonathan S. Duke-Cohan Catherine J. Wu Gordon J. Freeman 《Cancer immunology, immunotherapy : CII》2013,62(2):347-357
CD40L has a well-established role in enhancing the immunostimulatory capacity of normal and malignant B cells, but a formulation suitable for clinical use has not been widely available. Like other TNF family members, in vivo and in vitro activity of CD40L requires a homotrimeric configuration, and growing evidence suggests that bioactivity depends on higher-order clustering of CD40. We generated a novel formulation of human recombinant CD40L (CD40L-Tri) in which the CD40L extracellular domain and a trimerization motif are connected by a long flexible peptide linker. We demonstrate that CD40L-Tri significantly expands normal CD19+ B cells by over 20- to 30-fold over 14 days and induces B cells to become highly immunostimulatory antigen-presenting cells (APCs). Consistent with these results, CD40L-Tri-activated B cells could effectively stimulate antigen-specific T responses (against the influenza M1 peptide) from normal volunteers. In addition, CD40L-Tri could induce malignant B cells to become effective APCs, such that tumor-directed immune responses could be probed. Together, our studies demonstrate the potent immune-stimulatory effects of CD40L-Tri on B cells that enable their expansion of antigen-specific human T cells. The potent bioactivity of CD40L-Tri is related to its ability to self-multimerize, which may be facilitated by its long peptide linker. 相似文献
132.
133.
134.
Protein changes and proteolytic degradation in red and white clover plants subjected to waterlogging
Veselin Stoychev Lyudmila Simova-Stoilova Irina Vaseva Anelia Kostadinova Rosa Nenkova Urs Feller K. Demirevska 《Acta Physiologiae Plantarum》2013,35(6):1925-1932
Red (Trifolium pratense L., cv. “Start”) and white clover varieties (Trifolium repens L., cv. “Debut” and cv. “Haifa”) were waterlogged for 14 days and subsequently recovered for the period of 21 days. Physiological and biochemical responses of the clover varieties were distinctive, which suggested different sensitivity toward flooding. The comparative study of morphological and biochemical parameters such as stem length, leaflet area, dry weight, protein content, protein pattern and proteolytic degradation revealed prominent changes under waterlogging conditions. Protease activity in the stressed plants increased significantly, especially in red clover cv. “Start”, which exhibited eightfold higher azocaseinolytic activity compared to the control. Changes in the protein profiles were detected by SDS-PAGE electrophoresis. The specific response of some proteins (Rubisco, Rubisco-binding protein, Rubisco activase, ClpA and ClpP protease subunits) toward the applied stress was assessed by immunoblotting. The results characterized the red clover cultivar “Start” as the most sensitive toward waterlogging, expressing reduced levels of Rubisco large and small subunits, high content of ClpP protease subunits and increased activity of protease isoforms. 相似文献
135.
Maintenance of the cellular redox balance is crucial for cell survival. An increase in reactive oxygen, nitrogen, or chlorine species can lead to oxidative stress conditions, potentially damaging DNA, lipids, and proteins. Proteins are very sensitive to oxidative modifications, particularly methionine and cysteine residues. The reversibility of some of these oxidative protein modifications makes them ideally suited to take on regulatory roles in protein function. This is especially true for disulfide bond formation, which has the potential to mediate extensive yet fully reversible structural and functional changes, rapidly adjusting the protein''s activity to the prevailing oxidant levels. 相似文献
136.
U Hofmann S Michaelis T Winckler J Wegener KH Feller 《Biosensors & bioelectronics》2013,39(1):156-162
This study presents the time-resolved detection of chemically induced stress upon intracellular signaling cascades by using genetically modified sensor cells based on the human keratinocyte cell line HaCaT. The cells were stably transfected with a HSP72-GFP reporter gene construct to create an optical sensor cell line expressing a stress-inducible reporter protein. The time- and dose-dependent performance of the sensor cells is demonstrated and discussed in comparison to a label-free impedimetric monitoring approach (electric cell-substrate impedance sensing, ECIS). Moreover, a microfluidic platform was established based on μSlidesI(0,4)Luer to allow for a convenient, sterile and incubator-independent time-lapse microscopic observation of the sensor cells. Cell growth was successfully achieved in this microfluidic setup and the cellular response to a cytotoxic substance could be followed in real-time and in a non-invasive, sensitive manner. This study paves the way for the development of micro-total analysis systems that combine optical and impedimetric readouts to enable an overall quantitative characterization of changes in cell metabolism and morphology as a response to toxin exposure. By recording multiple parameters, a detailed discrimination between competing stress- or growth-related mechanisms is possible, thereby presenting an entirely new in vitro alternative to skin irritation tests. 相似文献
137.
Jacob E. Lemieux Sue A. Kyes Thomas D. Otto Avi I. Feller Richard T. Eastman Robert A. Pinches Matthew Berriman Xin‐zhuan Su Chris I. Newbold 《Molecular microbiology》2013,90(3):519-537
Spatial relationships within the eukaryotic nucleus are essential for proper nuclear function. In Plasmodium falciparum, the repositioning of chromosomes has been implicated in the regulation of the expression of genes responsible for antigenic variation, and the formation of a single, peri‐nuclear nucleolus results in the clustering of rDNA. Nevertheless, the precise spatial relationships between chromosomes remain poorly understood, because, until recently, techniques with sufficient resolution have been lacking. Here we have used chromosome conformation capture and second‐generation sequencing to study changes in chromosome folding and spatial positioning that occur during switches in var gene expression. We have generated maps of chromosomal spatial affinities within the P. falciparum nucleus at 25 Kb resolution, revealing a structured nucleolus, an absence of chromosome territories, and confirming previously identified clustering of heterochromatin foci. We show that switches in var gene expression do not appear to involve interaction with a distant enhancer, but do result in local changes at the active locus. These maps reveal the folding properties of malaria chromosomes, validate known physical associations, and characterize the global landscape of spatial interactions. Collectively, our data provide critical information for a better understanding of gene expression regulation and antigenic variation in malaria parasites. 相似文献
138.
Yuben Moodley Vijesh Vaghjiani James Chan Svetlana Baltic Marisa Ryan Jorge Tchongue Chrishan S. Samuel Padma Murthi Ornella Parolini Ursula Manuelpillai 《PloS one》2013,8(8)
Lung diseases are a major cause of global morbidity and mortality that are treated with limited efficacy. Recently stem cell therapies have been shown to effectively treat animal models of lung disease. However, there are limitations to the translation of these cell therapies to clinical disease. Studies have shown that delayed treatment of animal models does not improve outcomes and that the models do not reflect the repeated injury that is present in most lung diseases. We tested the efficacy of amnion mesenchymal stem cells (AM-MSC), bone marrow MSC (BM-MSC) and human amniotic epithelial cells (hAEC) in C57BL/6 mice using a repeat dose bleomycin-induced model of lung injury that better reflects the repeat injury seen in lung diseases. The dual bleomycin dose led to significantly higher levels of inflammation and fibrosis in the mouse lung compared to a single bleomycin dose. Intravenously infused stem cells were present in the lung in similar numbers at days 7 and 21 post cell injection. In addition, stem cell injection resulted in a significant decrease in inflammatory cell infiltrate and a reduction in IL-1 (AM-MSC), IL-6 (AM-MSC, BM-MSC, hAEC) and TNF-α (AM-MSC). The only trophic factor tested that increased following stem cell injection was IL-1RA (AM-MSC). IL-1RA levels may be modulated by GM-CSF produced by AM-MSC. Furthermore, only AM-MSC reduced collagen deposition and increased MMP-9 activity in the lung although there was a reduction of the pro-fibrogenic cytokine TGF-β following BM-MSC, AM-MSC and hAEC treatment. Therefore, AM-MSC may be more effective in reducing injury following delayed injection in the setting of repeated lung injury. 相似文献
139.
Socioeconomic status and anthropometric changes—A meta‐analytic approach from seven German cohorts
下载免费PDF全文
![点击此处可从《Obesity (Silver Spring, Md.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Johannes Haerting Saskia Hartwig Daniel Tiller Daniel Medenwald Susanne Vogt Barbara Thorand Rolf Holle Ursula Bachlechner Heiner Boeing Benedikt Merz Ute Nöthlings Sabrina Schlesinger Sabine Schipf Till Ittermann Nicole Aumann Anja Schienkiewitz Marjolein Haftenberger Karin H. Greiser Jasmine Neamat‐Allah Verena Katzke Alexander Kluttig 《Obesity (Silver Spring, Md.)》2016,24(3):710-718
140.
Farah El Najjar Nicolás Cifuentes-Mu?oz Jing Chen Haining Zhu Ursula J. Buchholz Carole L. Moncman Rebecca Ellis Dutch 《PLoS pathogens》2016,12(9)
Paramyxovirus spread generally involves assembly of individual viral particles which then infect target cells. We show that infection of human bronchial airway cells with human metapneumovirus (HMPV), a recently identified paramyxovirus which causes significant respiratory disease, results in formation of intercellular extensions and extensive networks of branched cell-associated filaments. Formation of these structures is dependent on actin, but not microtubule, polymerization. Interestingly, using a co-culture assay we show that conditions which block regular infection by HMPV particles, including addition of neutralizing antibodies or removal of cell surface heparan sulfate, did not prevent viral spread from infected to new target cells. In contrast, inhibition of actin polymerization or alterations to Rho GTPase signaling pathways significantly decreased cell-to-cell spread. Furthermore, viral proteins and viral RNA were detected in intercellular extensions, suggesting direct transfer of viral genetic material to new target cells. While roles for paramyxovirus matrix and fusion proteins in membrane deformation have been previously demonstrated, we show that the HMPV phosphoprotein extensively co-localized with actin and induced formation of cellular extensions when transiently expressed, supporting a new model in which a paramyxovirus phosphoprotein is a key player in assembly and spread. Our results reveal a novel mechanism for HMPV direct cell-to-cell spread and provide insights into dissemination of respiratory viruses. 相似文献