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   856篇
  免费   94篇
  国内免费   145篇
  1095篇
  2024年   7篇
  2023年   22篇
  2022年   58篇
  2021年   75篇
  2020年   46篇
  2019年   54篇
  2018年   49篇
  2017年   43篇
  2016年   58篇
  2015年   49篇
  2014年   69篇
  2013年   57篇
  2012年   70篇
  2011年   70篇
  2010年   33篇
  2009年   31篇
  2008年   32篇
  2007年   38篇
  2006年   41篇
  2005年   40篇
  2004年   23篇
  2003年   24篇
  2002年   19篇
  2001年   8篇
  2000年   4篇
  1999年   6篇
  1998年   10篇
  1997年   5篇
  1996年   11篇
  1995年   5篇
  1994年   7篇
  1993年   4篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   2篇
  1988年   3篇
  1987年   4篇
  1986年   3篇
  1985年   3篇
  1983年   1篇
  1982年   1篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1965年   1篇
排序方式: 共有1095条查询结果,搜索用时 15 毫秒
161.
The aim of this study was to purify the Chinese Sacbrood Virus Beijing Miyun (BJMY-CSBV) from infected Apis cerana larvae, clone structural protein gene VP1 (named BJMY-CSBV-VP1), and investigate its biological information. The result indicated that the capsid of CSBV is of spherical shape. Gene clone experiment showed that the BJMY-CSBV-VP1 gene sequence comprised 945 bp, encoding 315 amino acids with relative molecular weight of 35.59 kDa and isoelectric point 9.38 pI. Phylogenetic analysis of amino acid sequences showed that the BJMY-CSBV-VP1 and LNDD_2015 were grouped together. Protein secondary structure prediction showed that the gene contained two α-helices, thirteen β-folds, six polypeptide binding sites, and no disulfide bridge. Simultaneously, the BJMY-CSBV-VP1 was ligated to the expression vector pET32a(+) and then transformed into the Escherichia coli BL21 (DE3) for prokaryotic expression. The optimal expression experiment revealed that the protein was found in the inclusion body. The recombinant protein was successfully purified by washing buffer combined with supersonic fragmentation. In this study, we obtained the purified BJMY-CSBV particles, cloned BJMY-CSBV-VP1 gene, investigated the detailed information of the gene by analyzing the sequence, and obtained the purified recombinant protein, which could help for further understanding of the function of the structural protein gene VP1.  相似文献   
162.

Background

The solute carrier (SLC) 7 family genes comprise 14 members and function as cationic amino acid/glycoprotein transporters in many cells, they are essential for the maintenance of amino acid nutrition and survival of tumor cells. This study was conducted to analyze the associations of SLC7 family gene expression with mortality in papillary thyroid carcinoma (PTC).

Methods

Clinical features, somatic mutations, and SLC7 family gene expression data were downloaded from The Cancer Genome Atlas database. Linear regression model analysis was performed to analyze the correlations between SLC7 family gene expression and clinicopathologic features. Kaplan-Meier survival and logistic regression analyses were performed to characterize the associations between gene expression and patients’ overall survival.

Results

Patient mortality was negatively associated with age and tumor size but positively increased cancer stage and absence of thyroiditis in PTC patients. Kaplan-Meier survival analysis indicated that patients with high SLC7A3, SLC7A5, and SLC7A11 expression levels exhibited poorer survival than those with low SLC7A3, SLC7A5, and SLC7A11 expression levels (P?<?0.05 for all cases). Logistic regression analysis showed that SLC7A3, SLC7A5, and SLC7A11 were associated with increased mortality (odds ratio [OR] 8.61, 95% confidence interval [CI] 2.3–55.91; OR 3.87, 95% CI 1.18–17.31; and OR 3.87, 95% CI 1.18–17.31, respectively.

Conclusion

Upregulation of SLC7A3, SLC7A5, and SLC7A11 expression was associated with poor prognosis in PTC patients, and SLC7 gene expression levels are potentially useful prognostic biomarkers.
  相似文献   
163.
In vivo biosensors can recognize and respond to specific cellular stimuli. In recent years, biosensors have been increasingly used in metabolic engineering and synthetic biology, because they can be implemented in synthetic circuits to control the expression of reporter genes in response to specific cellular stimuli, such as a certain metabolite or a change in pH. There are many types of natural sensing devices, which can be generally divided into two main categories: protein-based and nucleic acid-based. Both can be obtained either by directly mining from natural genetic components or by engineering the existing genetic components for novel specificity or improved characteristics. A wide range of new technologies have enabled rapid engineering and discovery of new biosensors, which are paving the way for a new era of biotechnological progress. Here, we review recent advances in the design, optimization, and applications of in vivo biosensors in the field of metabolic engineering and synthetic biology.  相似文献   
164.
In this paper, a nanoscale three-dimensional plasmonic waveguide (TDPW), created by depositing an Ag stripe on a SiO2 layer with an Ag substrate, is introduced and theoretically investigated at visible and telecom wavelengths. By applying the effective index method and finite-difference time-domain numerical simulations, the authors find that the propagation properties of surface plasmon polaritons (SPPs) in the TDPW, including the propagation length and beam width, are mainly decided by the core (the SiO2 layer just under the Ag stripe) itself, due to the much stronger localization of SPPs in the core than in the two side claddings (the SiO2 layer without the covered Ag stripe). And propagating SPPs in the TDPW are strongly confined in the core region, even with a very small waveguide cross section. Furthermore, based on the stronger localization of propagation SPPs in the TDPW, two kinds of bending waveguides, oblique bending and 90° circular bending waveguides, are also investigated. For wavelength of 1550 nm, the 90° circular bending guide with a minimum radius as small as 2.6 μm show nearly zero radiation loss, even with a small waveguide cross section of 70?×?80 nm2. The proposed TDPW is suitable for planar integration and provides a possible way for constructing various nanoscale counterparts of conventional integrated devices such as splitter, resonator, sensor, and optical switch.  相似文献   
165.
Molecular mechanisms governing plant responses to high temperatures   总被引:1,自引:0,他引:1  
The increased prevalence of high temperatures(HTs) around the world is a major global concern, as they dramatically affect agronomic productivity. Upon HT exposure, plants sense the temperature change and initiate cellular and metabolic responses that enable them to adapt to their new environmental conditions.Decoding the mechanisms by which plants cope with HT will facilitate the development of molecular markers to enable the production of plants with improved thermotolerance. In recent decades, genetic, physiological, molecular, and biochemical studies have revealed a number of vital cellular components and processes involved in thermoresponsive growth and the acquisition of thermotolerance in plants. This review summarizes the major mechanisms involved in plant HT responses, with a special focus on recent discoveries related to plant thermosensing, heat stress signaling, and HT-regulated gene expression networks that promote plant adaptation to elevated environmental temperatures.  相似文献   
166.

Background

Despite the availability of multiple treatment strategies, patients with advanced colon carcinoma (CC) have poor prognoses. The aim of this study was to evaluate the efficacy and safety of natural killer (NK) cell therapy in combination with chemotherapy in patients with locally advanced CC.

Methods

We assessed the cytotoxicity of NK cells to CC cells (CCs) and CC stem cells (CSCs) pre-treated with 5-fluorouracil or oxaliplatin in vitro. Then, an open-label cohort study was conducted with locally advanced CC patients who had received radical resection. Patients received either NK cell therapy combined with chemotherapy (NK cell group, 27 patients) or pure chemotherapy (control group, 33 patients). Progression-free survival (PFS), overall survival (OS) and adverse effects were investigated.

Results

Chemotherapy sensitized CCs and CSCs to NK cell cytotoxicity through regulation of NK cell–activating/inhibitory receptor ligands. Poorly differentiated CCs were more susceptible to NK cells than well-differentiated ones. In the cohort study, the 5-year PFS and OS rates in the NK cell group were significantly higher than those in the control group (51.1% versus 35%, P?=?0.044; 72.5% versus 51.6%, P?=?0.037, respectively). Among patients with poorly differentiated carcinomas and low expression of human leukocyte antigen (HLA)-1, the median PFS in the NK cell group versus the control group was 23.5 versus 12.1 months (P?=?0.0475) and 33.1 versus 18.5 months (P?=?0.045), respectively. No significant adverse reactions were reported.

Conclusion

NK cell therapy in combination with chemotherapy in locally advanced CC prevented recurrence and prolonged survival with acceptable adverse effects, especially for poorly differentiated carcinomas.  相似文献   
167.
Precise mitotic spindle assembly is a guarantee of proper chromosome segregation during mitosis. Chromosome instability caused by disturbed mitosis is one of the major features of various types of cancer. JMJD5 has been reported to be involved in epigenetic regulation of gene expression in the nucleus, but little is known about its function in mitotic process. Here we report the unexpected localization and function of JMJD5 in mitotic progression. JMJD5 partially accumulates on mitotic spindles during mitosis, and depletion of JMJD5 results in significant mitotic arrest, spindle assembly defects, and sustained activation of the spindle assembly checkpoint (SAC). Inactivating SAC can efficiently reverse the mitotic arrest caused by JMJD5 depletion. Moreover, JMJD5 is found to interact with tubulin proteins and associate with microtubules during mitosis. JMJD5-depleted cells show a significant reduction of α-tubulin acetylation level on mitotic spindles and fail to generate enough interkinetochore tension to satisfy the SAC. Further, JMJD5 depletion also increases the susceptibility of HeLa cells to the antimicrotubule agent. Taken together, these results suggest that JMJD5 plays an important role in regulating mitotic progression, probably by modulating the stability of spindle microtubules.  相似文献   
168.
169.
It has been demonstrated that matrix metalloproteinase 3 (MMP3) is integrally involved in the neuronal degeneration of the central nervous system by promoting glial activation, neuronal apoptosis and damage to the brain–blood barrier. However, whether MMP3 also contributes to the neuronal degeneration induced by retinal ischemia/reperfusion is still uncertain. In the present study, we detected the cellular localization of MMP3 in adult rat retinae and explored the relationship of its expression with neuronal loss in the ganglion cell layer (GCL) in retinal ischemia/reperfusion. We found that MMP3 was widely expressed in many cells throughout the layers of the rat retinae, including Vertebrate neuron-specific nuclear protein (NeuN)-, parvalbumin-, calbindin-, protein kinase C-α-, glial fibrillary acidic protein-, glutamine synthetase- and CD11b-positive cells. Furthermore, all rats were treated with high intraocular pressure (HIOP) for 1 h (h) and sacrificed at 6 h, 1 day (d), 3 d, and 7 d after HIOP. Compared to the normal control, the expression of both proenzyme MMP3 and active MMP3 were significantly up-regulated after HIOP treatment without alteration of the laminar distribution pattern. Moreover, inhibiting MMP3 ameliorated the loss of NeuN-positive cells in the GCL following HIOP. In summary, our data demonstrates that MMP3 is expressed in multiple types of neurons and glial cells in normal rat retinae. Simultaneously, the up-regulation of its expression and activity are closely involved in neuronal loss in the GCL in retinal ischemia/reperfusion.  相似文献   
170.
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