全文获取类型
收费全文 | 1550篇 |
免费 | 101篇 |
专业分类
1651篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 24篇 |
2020年 | 16篇 |
2019年 | 34篇 |
2018年 | 36篇 |
2017年 | 38篇 |
2016年 | 47篇 |
2015年 | 55篇 |
2014年 | 62篇 |
2013年 | 90篇 |
2012年 | 108篇 |
2011年 | 105篇 |
2010年 | 78篇 |
2009年 | 43篇 |
2008年 | 72篇 |
2007年 | 68篇 |
2006年 | 75篇 |
2005年 | 63篇 |
2004年 | 53篇 |
2003年 | 57篇 |
2002年 | 70篇 |
2001年 | 20篇 |
2000年 | 10篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 22篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 15篇 |
1968年 | 6篇 |
排序方式: 共有1651条查询结果,搜索用时 0 毫秒
961.
Question: The quantification of functional traits in natural communities can be difficult (e.g. root traits, RGR). Can functional traits measured on pot grown plants be reliably applied to natural communities? Alternatively, can below‐ground plant traits be predicted from above‐ground traits? Location: Southeastern Australia. Methods: We compared 17 shoot, root and whole‐plant morphological traits measured on 14 plant species in a native grassland community to those measured under two different pot conditions: unfertilised and fertilised. Results: The majority of trait values for pot grown plants differed to plants in the field, however, species ranking remained consistent for most leaf traits between the field and the two pot growing conditions. In contrast, species ranking was not consistent for most whole plant traits when comparing field plants to fertilised pot grown plants, providing a caution against the tendency to grow plants in controlled conditions at ‘optimal’ (high) resource levels. Moderate to strong correlations were found between below‐ground and above‐ground plant traits, including between root dry matter content and leaf dry matter content, and between specific root area and specific leaf area. Conclusions: The utility of pot grown plants to quantify traits for field plants is highly dependent on the selection of the growing conditions in the controlled environment. The consistency we observed between above‐ground and below‐ground trait strategies suggests that below‐ground traits may be predictable based on above‐ground traits, reducing the need to quantify root traits on cultured plants. 相似文献
962.
Smetana K Zápotocky M Starková J Trka J 《European journal of histochemistry : EJH》2008,52(3):143-148
The present study was designed to provide more information on nucleoli in apoptotic cells,which were represented in the present study by cultured leukemic myeloblasts (Kasumi-1 cells). The apoptotic process in these cells was produced by trichostatin A (TSA) that is a histone deacetylase inhibitor with strong cytostatic effects. The selected TSA concentration added to cultures facilitated to study apoptotic and not-apoptotic cells in one and the same specimen. The nucleolar diameter and density were determined using computer assisted measurement and densitometry in specimens stained for RNA. In comparison with not-apoptotic cells, in apoptotic cells, nucleolar mean diameter did not change significantly and nucleolar RNA density was also not apparently different. On the other hand, the cytoplasmic RNA density in apoptotic cells was markedly reduced. Thus it seemed to be possible that the transcribed RNA remained "frozen"within the nucleolus but its transport to the cytoplasm decreased or stopped. However, the possibility of the RNA degradation in the cytoplasm of apoptotic cells based on the present study cannot be eliminated. At this occasion it should be added that AgNORs reflecting nucleolar biosynthetic and cell proliferation activity in apoptotic cells decreased in number or disappeared. The presented results also indicated that large nucleoli intensely stained for RNA need not be necessarily related to the high nucleolar biosynthetic or cell proliferation activity and may be also present in apoptotic cells responding to the cytostatic treatment. 相似文献
963.
Verification of reference genes for relative quantification of gene expression by real-time reverse transcription PCR in the pig 总被引:1,自引:0,他引:1
The aim of this study was to develop a set of reliable reference genes for quantification of mRNA expression in the pig. The
mRNA expression stability in pig tissues was studied for 4 genes:EEF1A1, GAPDH, HPRT1 andTOP2B. The level of expression was characterized byCt values for each gene and each tissue. By using the geNorm algorithm, the stability of the reference genes was determined
in the diaphragm, heart, kidney, liver, lungs, longissimus muscle, and spleen. On the basis of this information, suitable
reference genes can be selected for mRNA expression studies in relevant pig tissues. 相似文献
964.
Copley L van der Watt P Wirtz KW Parker MI Leaner VD 《The international journal of biochemistry & cell biology》2008,40(2):227-235
Photolon is a photosensitiser with demonstrated potential as an anti-tumour agent. In this study, an in vitro investigation was performed to determine the mechanism of Photolon-induced cell death. Cell killing was observed in a light-dependent manner and light-activated Photolon resulted in a significant production of reactive oxygen species (ROS), which could be blocked by type I ROS scavengers. Inhibition of ROS production using Trolox prevented Photolon-induced cell death. Light-activated Photolon caused no increase in caspase-3/7 activity, but a rapid increase in lactate dehydrogenase (LDH) release suggesting a loss of membrane integrity and subsequent cell death by necrosis. We conclude that the mechanism of Photolon-induced cell death involves the induction of ROS via a type I mechanism, which is ultimately responsible for cell killing by necrosis. 相似文献
965.
Increased formation of pyridinoline cross-links due to higher telopeptide lysyl hydroxylase levels is a general fibrotic phenomenon. 总被引:5,自引:0,他引:5
Annemarie J van der Slot Anne-Marie Zuurmond Antoon J van den Bogaerdt Magda M W Ulrich Esther Middelkoop Willem Boers H Karel Ronday Jeroen DeGroot Tom W J Huizinga Ruud A Bank 《Matrix biology》2004,23(4):251-257
Fibrosis is characterized by an excessive accumulation of collagen which contains increased levels of pyridinoline cross-links. The occurrence of pyridinolines in the matrix is an important criterion in assessing the irreversibility of fibrosis, which suggests that collagen containing pyridinoline cross-links significantly contributes to the unwanted collagen accumulation. Pyridinoline cross-links are derived from hydroxylated lysine residues located within the collagen telopeptides (hydroxyallysine pathway). Here, we have investigated whether the increase in hydroxyallysine-derived cross-links in fibrotic conditions can be ascribed to an increased expression of one of the lysyl hydroxylases (LH1, LH2 with its splice variants LH2a and LH2b, or LH3) and/or to an increased expression of lysyl oxidase (LOX). In fibroblast cultures of hypertrophic scars, keloid and palmar fascia of Dupuytren's patients, as well as in activated hepatic stellate cells, increased levels of LH2b mRNA expression were observed. Only minor amounts of LH2a were present. In addition, no consistent increase in the mRNA expression levels of LH1, LH3 and LOX could be detected, suggesting that LH2b is responsible for the overhydroxylation of the collagen telopeptides and the concomitant formation of pyridinolines as found in the collagen matrix deposited in long-term cultures by the same fibrotic cells. This is consistent with our previous observation that LH2b is a telopeptide lysyl hydroxylase. We conclude that the increased expression of LH2b, leading to the increased formation of pyridinoline cross-links, is present in a wide variety of fibrotic disorders and thus represents a general fibrotic phenomenon. 相似文献
966.
Chronic inflammation may increase the risk to develop cancer, for instance esophagitis or gastritis may lead to development of esophageal or gastric cancer, respectively. The key molecules attracting leukocytes to local inflammatory sites are chemokines. We here provide a systematic review on the impact of CXC chemokines (binding the receptors CXCR1, CXCR2, CXCR3 and CXCR4) on the transition of chronic inflammation in the upper gastrointestinal tract to neoplasia. CXCR2 ligands, including GRO-α,β,γ/CXCL1,2,3, ENA-78/CXCL5 and IL-8/CXCL8 chemoattract pro-tumoral neutrophils. In addition, angiogenic CXCR2 ligands stimulate the formation of new blood vessels, facilitating tumor progression. The CXCR4 ligand SDF-1/CXCL12 also promotes tumor development by stimulating angiogenesis and by favoring metastasis of CXCR4-positive tumor cells to distant organs producing SDF-1/CXCL12. Furthermore, these angiogenic chemokines also directly enhance tumor cell survival and proliferation. In contrast, the CXCR3 ligands Mig/CXCL9, IP-10/CXCL10 and I-TAC/CXCL11 are angiostatic and attract anti-tumoral T lymphocytes and may therefore mediate tumor growth retardation and regression. Thus, chemokines exert diverging, sometimes dual roles in tumor biology as described for esophageal and gastric cancer. Therefore extensive research is needed to completely unravel the complex chemokine code in specific cancers. Possibly, chemokine-targeted cancer therapy will have to be adapted to the individual's chemokine profile. 相似文献
967.
Bezstarosti Karel Soei Loe Kie Verdouw Pieter D. Lamers Jos M.J. 《Molecular and cellular biochemistry》1997,176(1-2):211-218
Previously we showed in an in situ porcine model that the thiadiazinone derivative [+]EMD 60263, a Ca2+ sensitizer without phosphodiesterase III inhibitory properties, increased contractility more profoundly in stunned than in non-stunned myocardium. This finding was consistent with the observed leftward shifts of the pCa2+/Mg2+-ATPase curves of isolated myofibrils induced by [+]EMD 60263. The aim of the present investigation was to study the possible involvement of protein kinase C in the mechanism of reduced Ca2+ responsiveness of myofilaments during stunning. No differences were observed in the maximal activity of the Ca2+-stimulated Mg2+-ATPase and in the pCa50 of myofibrils isolated from non-stunned and stunned myocardium. After phosphorylation with [gamma-32P]-ATP and excess of purified rat brain protein kinase C, the myofibrils were separated on sodiumdodecylsulphate-polyacrylamide gelectrophoresis and the32 P incorporation counted by the Molecular Imager. Ca2+/phosphatidylserine/sn-1,2 diolein-dependent32 P incorporation catalyzed by excess of purified rat brain protein kinase C in C-protein, TnT and TnI subunits did not show any differences between myofibrils from non-stunned and stunned myocardium. However, protein kinase C-induced phosphorylation of myofibrils isolated from ventricular myocardium of sham-operated pigs resulted in a marked leftward shift of the pCa50 from 6.03 ± 0.04 to 6.44 ± 0.06 (p < 0.05), while porcine heart cyclic AMP-dependent protein kinase-induced phosphorylation resulted in an expected small rightward shift to 5.97, although statistical significance was not reached. Protein kinase C-induced phosphorylation also stimulated (80%) the maximal myofibrillar Mg2+-ATPase activity. [+]EMD 60263 (3 µM) produced a leftward shift of the myofibrillar pCa2+/Mg2+-ATPase curve which was unaffected by prior protein kinase C-induced phosphorylation. In conclusion, the findings with isolated myofibrils from myocardium of anaesthetized open-chest pigs indicate that protein kinase C might be involved in the mechanism of reduced Ca2+ responsiveness of myofilaments in stunned myocardium. However, at this stage no differences could be found between the maximal activity of the Ca2+-stimulated Mg2+-ATPase, the pCa50 and the degree of phosphorylation of myofibrils isolated from stunned and non-stunned myocardium. 相似文献
968.
Epithelial cells can be manipulated to undergo apoptosis depending on the balance between pro-survival and apoptotic signals. We showed that TRAIL-induced apoptosis may be differentially regulated by inhibitors of MEK ERK (U0126) or PI3K/Akt (LY294002) pathway in TRAIL-sensitive (HT-29) and TRAIL-resistant (SW620) human epithelial colon cancer cells. U0126 or LY294002 significantly enhanced TRAIL-induced apoptosis in HT-29 cells, but not in SW620 cells. We report a different regulation of the level of an anti-apoptotic Mcl-1 protein under MEK/ERK or PI3K/Akt pathway inhibition and suggest the mechanisms involved. A special attention was paid to the role of the ERK1/2, Akt, and glycogen synthase kinase 3beta. 相似文献
969.
RYBP-PRC1 complexes mediate H2A ubiquitylation at polycomb target sites independently of PRC2 and H3K27me3 总被引:1,自引:0,他引:1
Tavares L Dimitrova E Oxley D Webster J Poot R Demmers J Bezstarosti K Taylor S Ura H Koide H Wutz A Vidal M Elderkin S Brockdorff N 《Cell》2012,148(4):664-678
Polycomb-repressive complex 1 (PRC1) has a central role in the regulation of heritable gene silencing during differentiation and development. PRC1 recruitment is generally attributed to interaction of the chromodomain of the core protein Polycomb with trimethyl histone H3K27 (H3K27me3), catalyzed by a second complex, PRC2. Unexpectedly we find that RING1B, the catalytic subunit of PRC1, and associated monoubiquitylation of histone H2A are targeted to closely overlapping sites in wild-type and PRC2-deficient mouse embryonic stem cells (mESCs), demonstrating an H3K27me3-independent pathway for recruitment of PRC1 activity. We show that this pathway is mediated by RYBP-PRC1, a complex comprising catalytic subunits of PRC1 and the protein RYBP. RYBP-PRC1 is recruited to target loci in mESCs and is also involved in Xist RNA-mediated silencing, the latter suggesting a wider role in Polycomb silencing. We discuss the implications of these findings for understanding recruitment and function of Polycomb repressors. 相似文献
970.
- 1.
- 1. The reaction of cyanide with cytochrome aa3 in the fully oxidized and reduced states has been studied. In both cases a single molecule of cyanide is bound reversibly per molecule of aa3 (that is, 1 mole cyanide per 2 equivalents of haem a). 相似文献