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   941篇
  免费   64篇
  国内免费   1篇
  1006篇
  2023年   2篇
  2022年   5篇
  2021年   18篇
  2020年   6篇
  2019年   11篇
  2018年   13篇
  2017年   12篇
  2016年   20篇
  2015年   43篇
  2014年   45篇
  2013年   61篇
  2012年   78篇
  2011年   81篇
  2010年   52篇
  2009年   36篇
  2008年   72篇
  2007年   74篇
  2006年   71篇
  2005年   70篇
  2004年   67篇
  2003年   44篇
  2002年   42篇
  2001年   10篇
  2000年   3篇
  1999年   3篇
  1998年   9篇
  1997年   8篇
  1996年   6篇
  1995年   3篇
  1994年   5篇
  1993年   8篇
  1992年   2篇
  1991年   5篇
  1990年   8篇
  1989年   5篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1981年   1篇
  1974年   1篇
  1970年   1篇
排序方式: 共有1006条查询结果,搜索用时 125 毫秒
41.

Background

Carotid sinus syndrome (CSS) can cause prodromal symptoms of syncope such as dizziness and nausea. Patients with end-stage cancer lose self-efficacy associated with reduced activities of daily life (ADL). Herein, we report a case of end-stage cancer in which self-efficacy was enhanced as the patient gained self-control of prodromal symptoms of syncope.

Case presentation

A 70-year-old patient with end-stage esophageal cancer and enlarged supraclavicular lymph nodes developed CSS. The CSS was a mixed type with both bradycardia and decreased blood pressure, accompanied by prodromal symptoms prior to syncope episodes. The patient incidentally discovered that he could decrease the duration of symptoms by contracting the muscles in his hands and legs. By applying this coping method at the onset of prodromal symptoms, he was also able to reduce the severity and duration of symptoms, which resulted in enhanced self-efficacy. As a result, the frequency of prodromal symptoms also decreased even though ADL improved.

Conclusion

This patient was diagnosed with vasoinhibitory-predominant mixed-type CSS. The coping method the patient developed seemed to avoid the onset of abrupt blood pressure decrease via peripheral vascular constriction action. Achievement of adequate coping such as self-control of prodromal symptoms enabled our patient to improve his self-efficacy even at the end stages of cancer. This case of enhanced self-efficacy could possibly illustrate a placebo effect for prevention of recurrence.
  相似文献   
42.
ATP drives the conformational change of the group II chaperonin from the open lid substrate-binding conformation to the closed lid conformation to encapsulate an unfolded protein in the central cavity. The detailed mechanism of this conformational change remains unknown. To elucidate the intra-ring cooperative action of subunits for the conformational change, we constructed Thermococcus chaperonin complexes containing mutant subunits in an ordered manner and examined their folding and conformational change abilities. Chaperonin complexes containing wild-type subunits and mutant subunits with impaired ATP-dependent conformational change ability or ATP hydrolysis activity, one by one, exhibited high protein refolding ability. The effects of the mutant subunits correlate with the number and order in the ring. In contrast, the use of a mutant lacking helical protrusion severely affected the function. Interestingly, these mutant chaperonin complexes also exhibited ATP-dependent conformational changes as demonstrated by small angle x-ray scattering, protease digestion, and changes in fluorescence of the fluorophore attached to the tip of the helical protrusion. However, their conformational change is likely to be transient. They captured denatured proteins even in the presence of ATP, whereas addition of ATP impaired the ability of the wild-type chaperonin to protect citrate synthase from thermal aggregation. These results suggest that ATP binding/hydrolysis causes the independent conformational change of the subunit, and further conformational change for the complete closure of the lid is induced and stabilized by the interaction between helical protrusions.  相似文献   
43.

Background

Despite the marked increase of diverticulosis, its risk factors have not been adequately elucidated. We therefore aim to identify significantly associated factors with diverticulosis. We also aim to investigate the present state of diverticulosis in Japan.

Methods

We reviewed the medical records from 1990 to 2010 that included the data of consecutive 62,503 asymptomatic colonoscopy examinees from the general population in Japan. Most recent 3,327 examinees were analyzed with 16 background factors.

Results

Among the 62,503 subjects (47,325 men and 15,178 women; 52.1 ± 9.2 years old), diverticulosis was detected in 11,771 subjects (18.8%; 10,023 men and 1,748 women). The incidences of diverticulosis in 1990-2000 and 2001-2010 were respectively 13.0% (3,771 of 29,071) and 23.9% (8,000 of 33,432): the latter was much higher than the former in all age groups and for both genders. Considering the anatomical locations of colorectal diverticula, left-sided ones have markedly increased with age but not significantly changed with times. Univariate analyses of the 3,327 subjects showed significant association of diverticulosis with four basic factors (age, sex, body mass index, blood pressure), three life style-related factor (smoking, drinking, severe weight increase in adulthood), and two blood test values (triglyceride, HbA1c). The multiple logistic analysis calculating standardized coefficients (β) and odds ratio (OR) demonstrated that age (β = 0.217-0.674, OR = 1.24-1.96), male gender (β = 0.185, OR = 1.20), smoking (β = 0.142-0.200, OR = 1.15-1.22), severe weight increase in adulthood (β = 0.153, OR = 1.17), HbA1c (β = 0.136, OR = 1.15), drinking (β = 0.109, OR = 1.11), and serum triglyceride (β = 0.098, OR = 1.10) showed significantly positive association with diverticulosis whereas body mass index and blood pressure did not.

Conclusions

The large-scale data of asymptomatic colonoscopy examinees from the general population from 1990 to 2010 indicated that the prevalence of diverticulosis is still increasing in Japan. Age, male gender, smoking, severe weight increase in adulthood, serum HbA1c, drinking, and serum triglyceride showed significant positive association with diverticulosis.  相似文献   
44.
The use of combinations of Bacillus thuringiensis (Bt) toxins with diverse modes of action for insect pest control has been proposed as the most efficient strategy to increase target range and delay the onset of insect resistance. Considering that most cases of cross-resistance to Bt toxins in laboratory-selected insect colonies are due to alteration of common toxin binding sites, independent modes of action can be defined as toxins sharing limited or no binding sites in brush border membrane vesicles (BBMV) prepared from the target insect larvae. In this paper, we report on the specific binding of Cry2Ae toxin to binding sites on BBMV from larvae of the three most commercially relevant heliothine species, Heliothis virescens, Helicoverpa zea, and Helicoverpa armigera. Using chromatographic purification under reducing conditions before labeling, we detected specific binding of radiolabeled Cry2Ae, which allowed us to perform competition assays using Cry1Ab, Cry1Ac, Cry1Fa, Vip3A, Cry2Ae, and Cry2Ab toxins as competitors. In these assays, Cry2Ae binding sites were shared with Cry2Ab but not with the tested Cry1 or Vip3A toxins. Our data support the use of Cry2Ae toxin in combination with Cry1 or Vip3A toxins in strategies to increase target range and delay the onset of heliothine resistance.  相似文献   
45.
First generation of insect-protected transgenic corn (Bt-corn) was based on the expression of Cry1Ab or Cry1Fa proteins. Currently, the trend is the combination of two or more genes expressing proteins that bind to different targets. In addition to broadening the spectrum of action, this strategy helps to delay the evolution of resistance in exposed insect populations. One of such examples is the combination of Cry1A.105 with Cry1Fa and Cry2Ab to control O. nubilalis and S. frugiperda. Cry1A.105 is a chimeric protein with domains I and II and the C-terminal half of the protein from Cry1Ac, and domain III almost identical to Cry1Fa. The aim of the present study was to determine whether the chimeric Cry1A.105 has shared binding sites either with Cry1A proteins, with Cry1Fa, or with both, in O. nubilalis and in S. frugiperda. Brush-border membrane vesicles (BBMV) from last instar larval midguts were used in competition binding assays with 125I-labeled Cry1A.105, Cry1Ab, and Cry1Fa, and unlabeled Cry1A.105, Cry1Aa, Cry1Ab, Cry1Ac, Cry1Fa, Cry2Ab and Cry2Ae. The results showed that Cry1A.105, Cry1Ab, Cry1Ac and Cry1Fa competed with high affinity for the same binding sites in both insect species. However, Cry2Ab and Cry2Ae did not compete for the binding sites of Cry1 proteins. Therefore, according to our results, the development of cross-resistance among Cry1Ab/Ac, Cry1A.105, and Cry1Fa proteins is possible in these two insect species if the alteration of shared binding sites occurs. Conversely, cross-resistance between these proteins and Cry2A proteins is very unlikely in such case.  相似文献   
46.

Background

Intralymphatic tumors in the extratumoral area are considered to represent the preceding phase of lymph node metastasis. The aim of this study was to clarify the biological properties of intralymphatic tumors susceptible to the development of lymph node metastasis, with special reference to the expression of cancer initiating/stem cell (CIC/CSC) related markers in cancer cells and the number of infiltrating stromal cells.

Material and Methods

Primary lung adenocarcinomas with lymphatic permeation in the extratumoral area were retrospectively examined (n = 107). We examined the expression levels of CIC/CSC related markers including ALDH1, OCT4, NANOG, SOX2 and Caveolin-1 in the intralymphatic cancer cells to evaluate their relationship to lymph node metastasis. Moreover, the number of infiltrating stromal cells expressing CD34, α-smooth muscle actin, and CD204 were also evaluated.

Results

Among the intralymphatic tissues, low ALDH1 expression in cancer cells, high SOX2 expression in cancer cells, and a high number of CD204(+) macrophages were independent predictive factors for lymph node metastasis (P = 0.004, P = 0.008, and P = 0.028, respectively). Among these factors, only low ALDH1 expression in cancer cells was significantly correlated with the farther spreading of lymph node metastasis (mediastinal lymph node, pathological N2) (P = 0.046) and the metastatic lymph node ratio (metastatic/resected) (P = 0.028). On the other hand, in the primary tumors, ALDH1 expression in the cancer cells was not associated with lymph node metastasis. Intralymphatic cancer cells expressing low ALDH1 levels exhibited lower E-cadherin expression levels than cancer cells with high levels of ALDH1 expression (P = 0.015).

Conclusions

Intralymphatic cancer cells expressing low levels of ALDH1 and infiltrating macrophages expressing CD204 have a critical impact on lymph node metastasis. Our study also highlighted the significance of evaluating the biological properties of intralymphatic tumors for tumor metastasis.  相似文献   
47.
Skin pigmentation is one of the most variable phenotypic traits in humans. A non-synonymous substitution (rs1426654) in the third exon of SLC24A5 accounts for lighter skin in Europeans but not in East Asians. A previous genome-wide association study carried out in a heterogeneous sample of UK immigrants of South Asian descent suggested that this gene also contributes significantly to skin pigmentation variation among South Asians. In the present study, we have quantitatively assessed skin pigmentation for a largely homogeneous cohort of 1228 individuals from the Southern region of the Indian subcontinent. Our data confirm significant association of rs1426654 SNP with skin pigmentation, explaining about 27% of total phenotypic variation in the cohort studied. Our extensive survey of the polymorphism in 1573 individuals from 54 ethnic populations across the Indian subcontinent reveals wide presence of the derived-A allele, although the frequencies vary substantially among populations. We also show that the geospatial pattern of this allele is complex, but most importantly, reflects strong influence of language, geography and demographic history of the populations. Sequencing 11.74 kb of SLC24A5 in 95 individuals worldwide reveals that the rs1426654-A alleles in South Asian and West Eurasian populations are monophyletic and occur on the background of a common haplotype that is characterized by low genetic diversity. We date the coalescence of the light skin associated allele at 22–28 KYA. Both our sequence and genome-wide genotype data confirm that this gene has been a target for positive selection among Europeans. However, the latter also shows additional evidence of selection in populations of the Middle East, Central Asia, Pakistan and North India but not in South India.  相似文献   
48.
Ectopic gene expression, or the gain-of-function approach, has the advantage that once the function of a gene is known the gene can be transferred to many different plants by transformation. We previously reported a method, called FOX hunting, that involves ectopic expression of Arabidopsis full-length cDNAs in Arabidopsis to systematically generate gain-of-function mutants. This technology is most beneficial for generating a heterologous gene resource for analysis of useful plant gene functions. As an initial model we generated more than 23 000 independent Arabidopsis transgenic lines that expressed rice fl-cDNAs (Rice FOX Arabidopsis lines). The short generation time and rapid and efficient transformation frequency of Arabidopsis enabled the functions of the rice genes to be analyzed rapidly. We screened rice FOX Arabidopsis lines for alterations in morphology, photosynthesis, element accumulation, pigment accumulation, hormone profiles, secondary metabolites, pathogen resistance, salt tolerance, UV signaling, high light tolerance, and heat stress tolerance. Some of the mutant phenotypes displayed by rice FOX Arabidopsis lines resulted from the expression of rice genes that had no homologs in Arabidopsis . This result demonstrated that rice fl-cDNAs could be used to introduce new gene functions in Arabidopsis. Furthermore, these findings showed that rice gene function could be analyzed by employing Arabidopsis as a heterologous host. This technology provides a framework for the analysis of plant gene function in a heterologous host and of plant improvement by using heterologous gene resources.  相似文献   
49.
The significance of cyclooxygenase-2 (COX-2) expression in ovarian cancer has been discussed. In this study, we found increased expression of COX-1 mRNA and protein in three out of 10 ovarian cancer cell lines. Prostaglandin E 2 (PGE2) production was elevated in these three cell lines, but not in other seven cell lines. COX-2 protein was not detected in any of the cell lines. Cytosolic prostaglandin E synthase (cPGES) mRNA and protein were detected in all 10 cell lines. Membrane-associated PGES-1 (mPGES-1) was detected in some of the ovarian cell lines, but its presence did not correspond with PGE2 production. In contrast, mPGES-2 mRNA and protein were detected in all 10 cell lines. A nonselective COX inhibitor (indometacin) and a selective COX-1 inhibitor (SC-560) strongly inhibited PGE2 production by the three cell lines, while selective COX-2 inhibitors (NS-398 and rofecoxib) did not inhibit PGE2 production. In addition, increased expression of COX-1, not COX-2 protein was observed in the mass of ovarian cancer tissues from 22 patients when compared with that in normal tissue. These findings suggest that COX-1 might be a major enzyme regulating PGE2 production in ovarian cancer cells.  相似文献   
50.
In plants, Ca2+, phosphatidylinositol phosphates (PtdInsPs) and inositol phosphates are major components of intracellular signaling. Several kinds of proteins and enzymes, such as calmodulin (CaM), protein kinase, protein phosphatase, and the Ca2+ channel, mediate the signaling. Two new Ca2+-binding proteins were identified from Arabidopsis thaliana and named PCaP1 and PCaP2 [plasma membrane (PM)-associated Ca2+(cation)-binding protein 1 and 2]. PCaP1 has an intrinsically disordered region in the central and C-terminal parts. The PCaP1 gene is expressed in most tissues and the PCaP2 gene is expressed predominantly in root hairs and pollen tubes. We recently demonstrated that these proteins are N-myristoylated, stably anchored in the PM, and are bound with phosphatidylinositol phosphates, especially PtdInsP2s. Here we propose a model for the switching mechanism of Ca2+-signaling mediated by PtdInsPs. Ca2+ forms a complex with CaM (Ca2+-CaM) when there is an increase in the cytosol free Ca2+. The binding of PCaPs with Ca2+-CaM causes PCaPs to release PtdInsPs. Until the release of PtdInsPs, the signaling is kept in the resting state.Key words: calcium signal, calmodulin, inositol phosphate, intrinsically disordered protein, myristoylation, phosphatidylinositol phosphate, plasma membrane  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