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   868篇
  免费   67篇
  2023年   2篇
  2022年   11篇
  2021年   22篇
  2020年   11篇
  2019年   17篇
  2018年   26篇
  2017年   17篇
  2016年   23篇
  2015年   46篇
  2014年   45篇
  2013年   62篇
  2012年   83篇
  2011年   72篇
  2010年   52篇
  2009年   34篇
  2008年   61篇
  2007年   49篇
  2006年   41篇
  2005年   57篇
  2004年   36篇
  2003年   31篇
  2002年   32篇
  2001年   9篇
  2000年   3篇
  1999年   4篇
  1998年   4篇
  1997年   8篇
  1996年   2篇
  1995年   4篇
  1994年   5篇
  1993年   4篇
  1992年   5篇
  1991年   5篇
  1990年   4篇
  1989年   7篇
  1988年   2篇
  1987年   3篇
  1983年   3篇
  1979年   4篇
  1978年   2篇
  1976年   3篇
  1973年   3篇
  1959年   2篇
  1942年   1篇
  1941年   1篇
  1940年   2篇
  1939年   1篇
  1936年   1篇
  1933年   1篇
  1927年   1篇
排序方式: 共有935条查询结果,搜索用时 15 毫秒
131.
The coordination of the ligands bis(pyrazol-1-yl)acetate (bpza) and bis(3,5-dimethylpyrazol-1-yl)acetate (bdmpza) to rhenium(VII) was investigated. The compounds [(bpza)ReO3] and [(bdmpza)ReO3] were synthesised by reaction of bpza and bdmpza with perrhenic acid with the loss of one water molecule. The new complex [(bdmpza)ReO3] was characterised by single-crystal X-ray analysis. It has a monomeric structure with a distorted octahedron for the [N,N,O]ReO3 central core.  相似文献   
132.
Objective: The aim of the study was to assess the uptake of dental services by the old and very old population within the scope of the Berlin Aging Study (Berliner Altersstudie BASE ). Design: A multi‐disciplinary structured interview was performed on 928 subjects, aged from 70 to 103 years of whom 516 persons volunteered to take part in a 14‐session intensive protocol. Six representative study groups were matched for age and gender. Subjects were asked to recall the timing of their most recent dental visit. Data were validated by sending for dental records and compared with all study participants from the multi‐disciplinary intake assessment. Data were related to age group, dental state, dementia and education. Results: Reported last contact with dental services ranged from 2 weeks to 52 years (median 18 months) with a higher time lapse in the study groups aged 85 and older. Dentate subjects had seen their dentist more recently than edentate subjects. Higher education correlated with an increased dental utilisation. Subjective memory on the time lapse since the last dental appointment coincided in 13% of the subjects with available dental records (n=84), was misjudged between one and six months in 55%, and by more than six months in the remainder. Moderately or severely demented subjects who remembered their last dental appointment (n=48 of 70) showed no consistently different utilisation to healthy or mildly demented studs participants. Conclusion: Edentate old and very old subjects show the least frequent utilisation of dental services. Data on motivation and barriers to care are needed to develop strategies to improve the use of dental services and thus promote oral health in late life.  相似文献   
133.
134.
This study aimed at the identification of genetic variations in the myostatin (MSTN) gene and testing their effects on carcass quality traits. We comparatively sequenced Giant Grey (GG) and New Zealand White (NZW) rabbits that were founders of a cross‐bred population. Alignment of our sequence data with the GenBank sequence of the rabbit MSTN gene (Ensembl Gene ID ENSOCUG00000012663) identified three single nucleotide polymorphisms (SNPs). The two novel SNPs (c.?125T>C, c.373+234G>A) and one known SNP (c.747+34C>T) were subsequently analysed for linkage with carcass composition traits in 363 F2 animals of the cross GG × NZW. Significant linkage was found between c.373+234G>A and nine carcass composition traits (< 0.05). No significant effects were found for c.?125T>C and c.747+34C>T. Because the linked SNP is located in intron 1 and no genetic variation was found in the coding region, further investigations are necessary to understand the functional effect of the c.373+234G>A variant on the variability of the traits.  相似文献   
135.
Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system (CNS). Neither the antigenic target(s) nor the cell population(s) responsible for CNS tissue destruction in MS have been fully defined. The objective of this study was to simultaneously determine the antigen (Ag)-specificity and phenotype of un-manipulated intrathecal CD4+ and CD8+ T cells of patients with relapsing-remitting and progressive MS compared to subjects with other inflammatory neurological diseases. We applied a novel Ag-recognition assay based on co-cultures of freshly obtained cerebrospinal fluid T cells and autologous dendritic cells pre-loaded with complex candidate Ag''s. We observed comparably low T cell responses to complex auto-Ag''s including human myelin, brain homogenate, and cell lysates of apoptotically modified oligodendroglial and neuronal cells in all cohorts and both compartments. Conversely, we detected a strong intrathecal enrichment of Epstein-Barr virus- and human herpes virus 6-specific (but not cytomegalovirus-specific) reactivities of the Th1-phenotype throughout all patients. Qualitatively, the intrathecal enrichment of herpes virus reactivities was more pronounced in MS patients. This enrichment was completely reversed by long-term treatment with the IL-2 modulating antibody daclizumab, which strongly inhibits MS disease activity. Finally, we observed a striking discrepancy between diminished intrathecal T cell proliferation and enhanced cytokine production of herpes virus-specific T cells among progressive MS patients, consistent with the phenotype of terminally differentiated cells. The data suggest that intrathecal administration of novel therapeutic agents targeting immune cells outside of the proliferation cycle may be necessary to effectively eliminate intrathecal inflammation in progressive MS.  相似文献   
136.
Selection of clonally propagated chrysanthemums is mostly performed on F1 hybrids using phenotypic characteristics without the use of molecular information. We applied 448 amplified fragment length polymorphism markers to a set of 81 accessions, mainly from the European gene pool, covering the different horticultural types (cut, pot and garden varieties) and originating from the most important European chrysanthemum breeders. The average pairwise genetic similarity of 0.69 was moderate to rather high. Neighbour-joining clustering resulted in no grouping of the accessions, either by their common origin or their horticultural type, or by similarities in important phenotypic characteristics. The structure of the dendrogram could not be supported by bootstrap analysis. Furthermore, network analysis using SplitsTree, principal coordinate analysis via DARwin or analysis of the population with structure did not differentiate reliable and invariable clusters. Therefore, we tested the marker saturation by plotting the mean coefficient of variation for every pairwise similarity of the bootstrap analysis against the different numbers of markers. We showed that the number of markers is sufficient for a precise estimate of genetic similarity and that the lack of bootstrap support is not due to a low genetic diversity or a lack of marker information, but most likely resulted from the breeding history of the cultivars, involving repeated backcrosses and the exchange of genotypes between breeders.  相似文献   
137.
The human sulfatase family has 17 members, 13 of which have been characterized biochemically. These enzymes specifically hydrolyze sulfate esters in glycosaminoglycans, sulfolipids, or steroid sulfates, thereby playing key roles in cellular degradation, cell signaling, and hormone regulation. The loss of sulfatase activity has been linked to severe pathophysiological conditions such as lysosomal storage disorders, developmental abnormalities, or cancer. A novel member of this family, arylsulfatase K (ARSK), was identified bioinformatically through its conserved sulfatase signature sequence directing posttranslational generation of the catalytic formylglycine residue in sulfatases. However, overall sequence identity of ARSK with other human sulfatases is low (18–22%). Here we demonstrate that ARSK indeed shows desulfation activity toward arylsulfate pseudosubstrates. When expressed in human cells, ARSK was detected as a 68-kDa glycoprotein carrying at least four N-glycans of both the complex and high-mannose type. Purified ARSK turned over p-nitrocatechol and p-nitrophenyl sulfate. This activity was dependent on cysteine 80, which was verified to undergo conversion to formylglycine. Kinetic parameters were similar to those of several lysosomal sulfatases involved in degradation of sulfated glycosaminoglycans. An acidic pH optimum (∼4.6) and colocalization with LAMP1 verified lysosomal functioning of ARSK. Further, it carries mannose 6-phosphate, indicating lysosomal sorting via mannose 6-phosphate receptors. ARSK mRNA expression was found in all tissues tested, suggesting a ubiquitous physiological substrate and a so far non-classified lysosomal storage disorder in the case of ARSK deficiency, as shown before for all other lysosomal sulfatases.  相似文献   
138.
Summary In light of previous data, which suggested thatAc-like sequences might have undergone a significant radiation in the recent past, I examined the copy number ofAc-like sequences in representatives of all theZea taxa, both maize and teosinte. The maize and teosinte samples contained approximately equal numbers ofAc-like sequences. FewAc-like sequences were in unmethylated regions of DNA. Unmethylated elements were distributed randomly among both maize and teosinte lines. The appearance in a line of a discrete band resulting from digestion with one methylation-sensitive restriction enzyme was correlated with the appearance of discrete bands with other methylation-sensitive bands. This suggests that individualAc-like elements are occasionally demethylated in many sites. No unmethylated element having restriction fragments of the lengths predicted from the publishedAc sequence was seen in the approximately 326 elements examined.  相似文献   
139.

Objective

The objective was to evaluate the 25(OH) vitamin D (25(OH)D) status of patients with juvenile idiopathic arthritis (JIA) and determine whether the 25(OH)D level is associated with disease activity and the course of JIA.

Methods

Patients ≤?16?years of age with recently diagnosed JIA (<?12?months) were enrolled in the inception cohort of patients with newly diagnosed JIA (ICON), an ongoing prospective observational, controlled multicenter study started in 2010. Clinical and laboratory parameters were ascertained quarterly during the first year and half-yearly thereafter.Of the 954 enrolled patients, 360 patients with two blood samples taken during the first 2?years after inclusion and with follow up of 3?years were selected. The serum 25(OH)D levels were determined and compared with those of subjects from the general population after matching for age, sex, migration status and the month of blood-drawing.

Results

Nearly half of the patients had a deficient 25(OH)D level (<?20?ng/ml) in the first serum sample and a quarter had a deficient level in both samples. Disease activity and the risk of developing JIA-associated uveitis were inversely correlated with the 25(OH)D level (β?=???0.20, 95% CI ??0.37; 0.03, hazard ratio 0.95, 95% CI 0.91; 0.99, respectively).

Conclusion

In this study, 25(OH)D deficiency was common and associated with higher disease activity and risk of developing JIA-associated uveitis. Further studies are needed to substantiate these results and determine whether correcting 25(OH)D deficiency is beneficial in JIA.
  相似文献   
140.
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