全文获取类型
收费全文 | 8177篇 |
免费 | 725篇 |
国内免费 | 1篇 |
专业分类
8903篇 |
出版年
2023年 | 35篇 |
2022年 | 91篇 |
2021年 | 164篇 |
2020年 | 100篇 |
2019年 | 119篇 |
2018年 | 167篇 |
2017年 | 124篇 |
2016年 | 266篇 |
2015年 | 449篇 |
2014年 | 497篇 |
2013年 | 539篇 |
2012年 | 703篇 |
2011年 | 758篇 |
2010年 | 515篇 |
2009年 | 396篇 |
2008年 | 560篇 |
2007年 | 530篇 |
2006年 | 478篇 |
2005年 | 456篇 |
2004年 | 435篇 |
2003年 | 365篇 |
2002年 | 396篇 |
2001年 | 84篇 |
2000年 | 53篇 |
1999年 | 77篇 |
1998年 | 92篇 |
1997年 | 63篇 |
1996年 | 49篇 |
1995年 | 24篇 |
1994年 | 31篇 |
1993年 | 29篇 |
1992年 | 27篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1967年 | 8篇 |
排序方式: 共有8903条查询结果,搜索用时 15 毫秒
91.
Muhl Marco Berger Markus Finkbeiner Matthias 《The International Journal of Life Cycle Assessment》2019,24(9):1701-1714
The International Journal of Life Cycle Assessment - Weighting as an optional step in life cycle impact assessment (LCIA) has recently gained momentum through increased policy requirements in the... 相似文献
92.
Elgar Susanne Quabius Silke Tribius Alessa Heinrichs Dirk Haaser Andr Kühnel Martin Laudien Florian Hoppe Robert Mlynski Petra Ambrosch Markus Hoffmann 《Translational oncology》2021,14(2)
Previous studies describe a correlation between HPV-positivity and non-smoking in TSCC; p16INK4A-expression as surrogate-marker for HPV-DNA/RNA-positivity is discussed controversially. In the present study, these parameters are assessed prospectively. HPV-status of sputum and tonsillar-swabs was analyzed to determine their validity as surrogate-marker for tissue-HPV-status.TSCC- (n = 52) and non-neoplastic tonsillar tissue (n = 163) were analyzed. HPV-DNA- and HPV-RNA-status of total sputum, cellular fraction and supernatants, tonsillar-swabs and -tissue was determined by (RT)-PCR. Immunohistochemistry determined p16INK4A-expression.23/163 (14.2%) non-neoplastic tonsils were HPV-DNA-positive; five patients (3 HPV16, 2 HPV11) had active HPV-infections (HPV-RNA-positive), in all biomaterials. 140/163 (85.9%) patients were either HPV-DNA-positive or HPV-DNA-negative in all samples. 21/52 (40.4%) TSCC-tonsils were HPV-DNA-positive; 17 patients were HPV-RNA-positive (14 HPV16; 4 HPV18). 40/52 (76.9%) TSCC-patients were congruent in all biomaterials. p16INK4A-expression alone would have misclassified the HPV-status of 14/52 (26.2%) TSCC-patients.This prospective study confirms the discrepancy between HPV-status and p16INK4A-expression and the significant correlation between non-smoking and HPV-DNA-positivity. HPV-sputum- and/or swab-results do not consistently match tissue-results, possibly having (detrimental) consequences if those were used to assess tissue-HPV-status. In the 5 patients with active HPV infection in the non-neoplasitic tonsils, tonsillectomy likely prevented subsequent development of TSCC. 相似文献
93.
Wan Yun Ho Jer-Cherng Chang Kenneth Lim Amaury Cazenave-Gassiot Aivi T. Nguyen Juat Chin Foo Sneha Muralidharan Ashley Viera-Ortiz Sarah J.M. Ong Jin Hui Hor Ira Agrawal Shawn Hoon Olubankole Aladesuyi Arogundade Maria J. Rodriguez Su Min Lim Seung Hyun Kim John Ravits Shi-Yan Ng Markus R. Wenk Edward B. Lee Greg Tucker-Kellogg Shuo-Chien Ling 《The Journal of cell biology》2021,220(9)
94.
Novel rhizobox design to assess rhizosphere characteristics at high spatial resolution 总被引:1,自引:1,他引:1
Wenzel Walter W. Wieshammer Gottfried Fitz Walter J. Puschenreiter Markus 《Plant and Soil》2001,237(1):37-45
Available tools to study rhizosphere characteristics at a sub-mm spatial resolution suffer from a number of shortfalls, including geometrically and physiologically ill-defined root layers containing soil or other growth medium. Such designs may result in over- or underestimation of root-induced changes in the rhizosphere. We present a novel rhizobox design that overcomes these shortfalls. Plants are pre-grown in a soil–root compartment with an opening slit at the bottom. As plants reach the targeted physiological stage, this compartment is transferred on top of a rhizosphere soil compartment attached to a vertical root-only compartment. The latter is made up of a membrane (pore size 7 m to restrict root hair growth into the rhizosphere compartment or 30 m to restrict only root growth) and a transparent acrylic window which is gently pressed against the membrane and rhizosphere soil compartment using an adjustable screw. This design allows roots to penetrate from the upper soil–root compartment through the slit into the root-only compartment. Root growth and distribution can be monitored through the acrylic window using digital camera equipment. Upon termination of the experiment, the rhizosphere compartment is removed and frozen prior to separation of sub-mm soil layers using microtome techniques. In a test experiment, canola (Brassica napus L. cv. Sprinter) developed a fairly dense root monolayer within 8 days. Using measurement of soil characteristics at 0.5–1-mm increments across the rhizosphere we demonstrate that the proposed rhizobox design is yielding reproducible data. Due to exudation of LMWOC, we found a statistically significant increase of DOC towards the root plane, whereas more stable soil characteristics were not affected by root activity. Limitations and further extensions of this rhizobox design, including the use of micro suction cups and microsensors for pH and redox potential to measure spatial and temporal changes in a non-destructive manner are discussed along with potential applications such as validation of rhizosphere models. 相似文献
95.
Alpha interferon (IFN-alpha) and pegylated IFN-alpha (pegIFN-alpha) are used for the treatment of chronic hepatitis B (CHB). Unfortunately, only a minority of patients can be cured. The mechanisms responsible for hepatitis B virus (HBV) resistance to pegIFN-alpha treatment are not known. pegIFN-alpha is also used to treat patients with chronic hepatitis C (CHC). As with chronic hepatitis B, many patients with chronic hepatitis C cannot be cured. In CHC, IFN-alpha signaling has been found to be inhibited by an upregulation of protein phosphatase 2A (PP2A). PP2A inhibits protein arginine methyltransferase 1 (PRMT1), the enzyme that catalyzes the methylation of the important IFN-alpha signal transducer STAT1. Hypomethylated STAT1 is less active because it is bound by its inhibitor, PIAS1. In the present work, we investigated whether similar molecular mechanisms are also responsible for the IFN-alpha resistance found in many patients with chronic hepatitis B. We analyzed the expression of PP2A, the enzymatic activity of PRMT1 (methylation assays), the phosphorylation and methylation of STAT1, the association of STAT1 with PIAS1 (via coimmunoprecipitation assays), the binding of activated STAT1 to interferon-stimulated response elements (via electrophoretic mobility shift assays), and the induction of interferon target genes (via real-time RT-PCR) in human hepatoma cells expressing HBV proteins as well as in liver biopsies from patients with chronic hepatitis B and from controls. We found an increased expression of PP2A and an inhibition of IFN-alpha signaling in cells expressing HBV proteins and in liver biopsies of patients with CHB. The molecular mechanisms involved are similar to those found in chronic hepatitis C. 相似文献
96.
Cho YW Hong T Hong S Guo H Yu H Kim D Guszczynski T Dressler GR Copeland TD Kalkum M Ge K 《The Journal of biological chemistry》2007,282(28):20395-20406
PTIP, a protein with tandem BRCT domains, has been implicated in DNA damage response. However, its normal cellular functions remain unclear. Here we show that while ectopically expressed PTIP is capable of interacting with DNA damage response proteins including 53BP1, endogenous PTIP, and a novel protein PA1 are both components of a Set1-like histone methyltransferase (HMT) complex that also contains ASH2L, RBBP5, WDR5, hDPY-30, NCOA6, SET domain-containing HMTs MLL3 and MLL4, and substoichiometric amount of JmjC domain-containing putative histone demethylase UTX. PTIP complex carries robust HMT activity and specifically methylates lysine 4 (K4) on histone H3. Furthermore, PA1 binds PTIP directly and requires PTIP for interaction with the rest of the complex. Moreover, we show that hDPY-30 binds ASH2L directly. The evolutionarily conserved hDPY-30, ASH2L, RBBP5, and WDR5 likely constitute a subcomplex that is shared by all human Set1-like HMT complexes. In contrast, PTIP, PA1, and UTX specifically associate with the PTIP complex. Thus, in cells without DNA damage agent treatment, the endogenous PTIP associates with a Set1-like HMT complex of unique subunit composition. As histone H3 K4 methylation associates with active genes, our study suggests a potential role of PTIP in the regulation of gene expression. 相似文献
97.
98.
Veselov D Langhans M Hartung W Aloni R Feussner I Götz C Veselova S Schlomski S Dickler C Bächmann K Ullrich CI 《Planta》2003,216(3):512-522
The development of Agrobacterium tumefaciens-induced plant tumors primarily depends on the excessive production of auxin and cytokinin by enzymes encoded on T-DNA genes integrated into the plant genome. The aim of the present study was to investigate the involvement of additional phytohormone signals in the vascularization required for rapid tumor proliferation. In stem tumors of Ricinus communis L., free auxin and zeatin riboside concentrations increased within 2 weeks to 15-fold the concentrations in control stem tissue. Auxin and cytokinin immunolocalization revealed the highest concentrations within and around tumor vascular bundles with concentration gradients. The time-course of changes in free auxin concentration in roots was inversely correlated with that in the tumors. The high ethylene emission induced by increased auxin- and cytokinin correlated with a 36-fold accumulation of abscisic acid in tumors. Ethylene emitted from tumors and exogenously applied ethylene caused an increase in abscisic acid concentrations also in the host leaves, with a diminution in leaf water vapor conductance. Jasmonic acid concentration reached a maximum already within the first week of bacterial infection. A wound effect could be excluded. The results demonstrate the concerted interaction of a cascade of transiently induced, non-T-DNA-encoded phytohormones jasmonic acid, ethylene and abscisic acid with T-DNA-encoded auxin and zeatin riboside plus trans-zeatin, all of which are required for successful plant tumor vascularization and development together with inhibition of host plant growth. 相似文献
99.
We applied the cDNA differential display technique (DDT) in a DNA-repair deficient cell model to isolate genes involved in dysregulation of cell proliferation and development of cancer. The comparative analysis of mRNA expression patterns of human diploid fibroblasts from Fanconi's amemia (FA) and normal phenotype led to the identification of a novel cDNA CO9. Northern blot analysis reveals that CO9 is significantly upregulated in FA fibroblasts but downregulated or absent in fibroblasts from normal donors. CO9 was also highly expressed in FA B-cells of complementation group A and in Raji cells. However, CO9 is not expressed in FA complementation groups B, C, D and E. The full-length cDNA is 840 bp long and contains an open reading frame of 216 bp (72 amino acids), which encodes for a 7.6-kDa protein. The lengths of the 5′ and 3′ untranslated region are 165 and 459 bp, respectively. The N-terminal and C-terminal nucleotide sequence of CO9 shows homology to a putative human l-3-phosphoserine phosphatase identified recently (HSPSPASE, EMBL Accession No. Y10275) but lacks a 476-bp stretch in the open reading frame. The loss of nucleotides within the open reading frame introduces a new termination codon in the CO9 cDNA along with a novel COOH terminus resulting in a new protein product. Database chromosome mapping localized CO9 to chromosome 7q 11.2. We hypothesize that CO9 represents a novel protein being a partial homologue to the l-3-phosphoserine phosphatase but with a different regulatory cell function. 相似文献
100.
Monoclonal antibodies binding to different domains of nucleolin have been used to localize nucleolin in tissue culture cells ofXenopus laevis.The monoclonal antibody b6-6E7 binds to an epitope in the N-terminal domain, which contains arrays of phosphorylation consensus sites. This monoclonal antibody binds to nucleolin of oocytes and of eggs with high affinity. In contrast, the monoclonal antibody Nu-1H6 binds poorly to the modified forms of nucleolin arising during meiosis and mitosis. In interphase cells, monoclonal antibody b6-6E7 preferentially stains the periphery of the nucleoli, where most of the rRNA accumulates. Staining by monoclonal antibody Nu-1H6 complements this pattern by staining mainly the center of the nucleoli. The epitope of monoclonal antibody Nu-1H6 is within the central domain of nucleolin, which contains the first two RNA binding domains. RNase treatment of cells results in loss of nucleolin from nucleoli. In mitotic cells, both monoclonal antibodies decorate the surface of condensing chromosomes in prophase. The periphery of the condensed chromosomes in metaphase and anaphase is preferentially stained by monoclonal antibody b6-6E7. 相似文献