首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1273篇
  免费   46篇
  国内免费   1篇
  2021年   11篇
  2020年   8篇
  2019年   12篇
  2018年   10篇
  2017年   16篇
  2016年   15篇
  2015年   39篇
  2014年   39篇
  2013年   79篇
  2012年   69篇
  2011年   44篇
  2010年   41篇
  2009年   52篇
  2008年   48篇
  2007年   62篇
  2006年   58篇
  2005年   45篇
  2004年   58篇
  2003年   60篇
  2002年   69篇
  2001年   31篇
  2000年   40篇
  1999年   33篇
  1998年   15篇
  1997年   14篇
  1996年   15篇
  1994年   13篇
  1993年   6篇
  1992年   23篇
  1991年   22篇
  1990年   21篇
  1989年   16篇
  1988年   16篇
  1987年   20篇
  1986年   8篇
  1985年   12篇
  1984年   9篇
  1983年   11篇
  1982年   11篇
  1981年   7篇
  1980年   16篇
  1979年   10篇
  1978年   6篇
  1977年   7篇
  1976年   17篇
  1975年   12篇
  1974年   15篇
  1973年   8篇
  1972年   10篇
  1970年   9篇
排序方式: 共有1320条查询结果,搜索用时 15 毫秒
991.
992.

Purpose

Nurses and other healthcare workers frequently experience belief conflict, one of the most important, new stress-related problems in both academic and clinical fields.

Methods

In this study, using a sample of 1,683 nursing practitioners, we developed The Assessment of Belief Conflict in Relationship-14 (ABCR-14), a new scale that assesses belief conflict in the healthcare field. Standard psychometric procedures were used to develop and test the scale, including a qualitative framework concept and item-pool development, item reduction, and scale development. We analyzed the psychometric properties of ABCR-14 according to entropy, polyserial correlation coefficient, exploratory factor analysis, confirmatory factor analysis, average variance extracted, Cronbach’s alpha, Pearson product-moment correlation coefficient, and multidimensional item response theory (MIRT).

Results

The results of the analysis supported a three-factor model consisting of 14 items. The validity and reliability of ABCR-14 was suggested by evidence from high construct validity, structural validity, hypothesis testing, internal consistency reliability, and concurrent validity. The result of the MIRT offered strong support for good item response of item slope parameters and difficulty parameters. However, the ABCR-14 Likert scale might need to be explored from the MIRT point of view. Yet, as mentioned above, there is sufficient evidence to support that ABCR-14 has high validity and reliability.

Conclusion

The ABCR-14 demonstrates good psychometric properties for nursing belief conflict. Further studies are recommended to confirm its application in clinical practice.  相似文献   
993.

Background & Aims

Osteopontin (OPN) is a matricellular protein that upregulates during pathogenesis of hepatic fibrosis. The present study was aimed to evaluate whether serum OPN could be used as a biomarker to assess the degree of hepatic fibrosis in patients with hepatitis C virus (HCV) infection.

Methods

Needle biopsy was performed on HCV patients and scored as zero fibrosis (F0), mild fibrosis (F1), moderate fibrosis (F2), severe fibrosis (F3) and liver cirrhosis (F4) based on Masson’s trichrome and α-smooth muscle actin (α-SMA) staining. Serum OPN levels were measured using ELISA and correlated with the degree of fibrosis. Furthermore, the OPN values were correlated and evaluated with platelets count, serum hyaluronic acid (HA), and collagen type IV and subjected to receiver operating characteristic (ROC) curve analysis.

Results

Serum OPN levels were remarkably increased from F0 through F4 in a progressive manner and the differences were significant (P < 0.001) between each group. The data were highly correlated with the degree of hepatic fibrosis. The ROC curve analysis depicted that serum OPN is an independent risk factor and an excellent biomarker and a prognostic index in HCV patients.

Conclusions

The results of the present study indicate that serum OPN levels reflect the degree of hepatic fibrosis and could be used as a biomarker to assess the stage of fibrosis in HCV patients which would help to reduce the number of liver biopsies. Furthermore, serum OPN serves as a prognostic index towards the progression of hepatic fibrosis to cirrhosis and hepatocellular carcinoma.  相似文献   
994.
Glycoprotein nonmelanoma protein B (GPNMB, alias osteoactivin), a type I transmembrane glycoprotein, is cleaved by extracellular proteases, resulting in release of an extracellular fragment (ECF). GPNMB is widely expressed by neurons within the CNS, including the hippocampus; however, its function in the brain remains unknown. Here, we investigated the role of GPNMB in memory and learning by using transgenic (Tg) mice over‐expressing GPNMB (Tg mice on a BDF‐1 background) and ECF‐treated mice. In the hippocampus of both wild‐type and Tg mice, GPNMB was highly expressed in neurons and astrocytes. Tg mice exhibited memory improvements in two types of learning tasks but were impaired in a passive‐avoidance test. In Tg mice, the hippocampus displayed increased levels of the α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate receptor subunit GluA1. Intracerebroventricular administration of ECF (50 ng) to Institute of Cancer Research (ICR) mice also improved memory in a passive‐avoidance test and increased hippocampal GluA1 levels 24 h after treatment. In Tg mice and ECF (0.25 μg/mL)‐treated hippocampal slices, long‐term potentiation was promoted. These findings suggest that GPNMB may be a novel target for research on higher order brain functions.

  相似文献   

995.
Ameloblastin, the most abundant nonamelogenin enamel matrix protein, plays a role in ameloblast differentiation. Here, we found that ameloblastin was expressed in osteosarcoma cells; to explore the potential functions of ameloblastin in osteoblasts, we investigated whether this protein is involved in osteogenic differentiation and bone formation on the premise that CD63, a member of the transmembrane-4 glycoprotein superfamily, interacts with integrins in the presence of ameloblastin. Ameloblastin bound to CD63 and promoted CD63 binding to integrin β1. The interaction between CD63 and integrin β1 induced Src kinase inactivation via the binding of CD63 to Src. The reduction of Src activity and osteogenic differentiation mediated by ameloblastin were abrogated by treatment with anti-CD63 antibody and overexpression of constitutively active Src, respectively. Therefore, our results suggest that ameloblastin is expressed in osteoblasts and functions as a promoting factor for osteogenic differentiation via a novel pathway through the interaction between CD63 and integrin β1.  相似文献   
996.
Acquired cystic disease (ACD)-associated renal cell carcinoma (RCC) is a recently established entity. In this article, we introduce the general view of this new entity. Macroscopically, the disease exclusively occurs in ACD and may arise as a dominant mass or non-dominant masses. Histologically, the tumor is characterized by a microcystic pattern, neoplastic cells with an eosinophilic or oncocytic cytoplasm and frequent intratumoral oxalate crystal deposition. Prominent nucleoli of tumor cells are often observed. Immunohistochemically, neoplastic cells are generally positive for AMACR but negative for cytokeratin 7. Ultrastructurally, neoplastic cells contain abundant mitochondria in the cytoplasm. Genetically, the gain of chromosomes 3, 7, 17 and abnormality of the sex chromosome were frequently observed in several studies. In conclusion, ACD-associated RCC may be widely recognized as a distinct entity in the near future because this tumor is morphologically and genetically different from other renal tumor entities that have been previously established.  相似文献   
997.
The chloroplast genome of the highly neutral-lipid-producing marine pennate diatom Fistulifera sp. strain JPCC DA0580 was fully sequenced using high-throughput pyrosequencing. The general features and gene content were compared with three other complete diatom chloroplast genomes. The chloroplast genome is 134,918 bp with an inverted repeat of 13,330 bp and is slightly larger than the other diatom chloroplast genomes due to several low gene-density regions lacking similarity to the other diatom chloroplast genomes. Protein-coding genes were nearly identical to those from Phaeodactylum tricornutum. On the other hand, we found unique sequence variations in genes of photosystem II which differ from the consensus in other diatom chloroplasts. Furthermore, five functional unknown ORFs and a putative serine recombinase gene, serC2, are located in the low gene-density regions. SerC2 was also identified in the plasmids of another pennate diatom, Cylindrotheca fusiformis, and in the plastid genome of the diatom endosymbiont of Kryptoperidinium foliaceum. Exogenous plasmids might have been incorporated into the chloroplast genome of Fistulifera sp. by lateral gene transfer. Chloroplast genome sequencing analysis of this novel diatom provides many important insights into diatom evolution.  相似文献   
998.
Human interleukin-11 (hIL-11) is a pleiotropic cytokine administered to patients with low platelet counts. From a structural point of view hIL-11 belongs to the long-helix cytokine superfamily, which is characterized by a conserved core motif consisting of four α-helices. We have investigated the region of hIL-11 that does not belong to the α-helical bundle motif, and that for the purpose of brevity we have termed "non-core region." The primary sequence of the interleukin was altered at various locations within the non-core region by introducing glycosylation sites. Functional consequences of these modifications were examined in cell-based as well as biophysical assays. Overall, the data indicated that the non-core region modulates the function of hIL-11 in two ways. First, the majority of muteins displayed enhanced cell-stimulatory properties (superagonist behavior) in a glycosylation-dependent manner, suggesting that the non-core region is biologically designed to limit the full potential of hIL-11. Second, specific modification of a predicted mini α-helix led to cytokine inactivation, demonstrating that this putative structural element belongs to site III engaging a second copy of cell-receptor gp130. These findings have unveiled new and unexpected elements modulating the biological activity of hIL-11, which may be exploited to develop more versatile medications based on this important cytokine.  相似文献   
999.
Plant production of methanol (MeOH) is a poorly understood aspect of metabolism, and understanding MeOH production in plants is crucial for modeling MeOH emissions. Here, we have examined the source of MeOH emissions from mature and immature leaves and whether pectin methylesterase (PME) activity is a good predictor of MeOH emission. We also investigated the significance of below-ground MeOH production for mature leaf emissions. We present measurements of MeOH emission, PME activity, and MeOH concentration in mature and immature tissues of tomato (Lycopersicon esculentum). We also present stable carbon isotopic signatures of MeOH emission and the pectin methoxyl pool. Our results suggest that below-ground MeOH production was not the dominant contributor to daytime MeOH emissions from mature and immature leaves. Stable carbon isotopic signatures of mature and immature leaf MeOH were similar, suggesting that they were derived from the same pathway. Foliar PME activity was related to MeOH flux, but unexplained variance suggested PME activity could not predict emissions. The data show that MeOH production and emission are complex and cannot be predicted using PME activity alone. We hypothesize that substrate limitation of MeOH synthesis and MeOH catabolism may be important regulators of MeOH emission.  相似文献   
1000.
Neutral glycosphingolipids containing one to six sugars in their oligosaccharide chains have been isolated from cysts of the brine shrimp Artemia franciscana. The structures of these glycolipids were identified by methylation analysis, partial acid hydrolysis, gas-liquid chromatography, combined gas-liquid chromatography-mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and proton nuclear magnetic resonance spectroscopy to be Glcβ1-Cer, Manβ1-4Glcβ1-Cer, Fucα1-3Manβ1-4Glcβ1-Cer, GlcNAcβ1-3Manβ1-4Glcβ1-Cer, GlcNAcα1-2Fucα1-3Manβ1-4Glcβ1-Cer, GalNAcβ1-4GlcNAcβ1-3Manβ1-4Glcβ1-Cer, GalNAcβ1-4(Fucα1-3)GlcNAcβ1-3Manβ1-4Glcβ1-Cer (CPS), and GalNAcβ1-4(GlcNAcα1-2Fucα1-3)GlcNAcβ1-3Manβ1-4Glcβ1-Cer (CHS). Two glycosphingolipids, CPS and CHS, were characterized as novel structures. Because Artemia contains a certain series of glycosphingolipids (-Fucα3Manβ4GlcβCer), which differ from the core sugar sequences reported thus far, we tentatively designated the glycosphingolipids characterized as nonarthro-series ones. Furthermore, CHS exhibited a hybrid structure of arthro-series and nonarthro-series sugar chain. Two novel glycosphingolipids were characterized from the brine shrimp Artemia franciscana; one was composed of arthrotetraose and a branching fucose attached to N-acetylglucosamine residue, and the other was composed of CPS with an additional N-acetylglucosamine residue attached to the branching fucose.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号