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   1233篇
  免费   101篇
  2022年   10篇
  2021年   14篇
  2020年   9篇
  2019年   14篇
  2018年   14篇
  2017年   10篇
  2016年   22篇
  2015年   48篇
  2014年   40篇
  2013年   57篇
  2012年   81篇
  2011年   83篇
  2010年   53篇
  2009年   42篇
  2008年   72篇
  2007年   69篇
  2006年   65篇
  2005年   61篇
  2004年   64篇
  2003年   60篇
  2002年   52篇
  2001年   22篇
  2000年   15篇
  1999年   12篇
  1998年   20篇
  1997年   10篇
  1996年   14篇
  1995年   16篇
  1994年   9篇
  1993年   11篇
  1992年   10篇
  1991年   16篇
  1990年   18篇
  1989年   20篇
  1988年   10篇
  1987年   12篇
  1986年   12篇
  1985年   15篇
  1984年   14篇
  1983年   12篇
  1982年   10篇
  1981年   9篇
  1980年   11篇
  1979年   9篇
  1978年   8篇
  1976年   10篇
  1975年   9篇
  1973年   5篇
  1972年   5篇
  1965年   6篇
排序方式: 共有1334条查询结果,搜索用时 15 毫秒
121.
The Kaiser Permanente Research Program on Genes, Environment, and Health (RPGEH) Genetic Epidemiology Research on Adult Health and Aging (GERA) cohort includes DNA specimens extracted from saliva samples of 110,266 individuals. Because of its relationship to aging, telomere length measurement was considered an important biomarker to develop on these subjects. To assay relative telomere length (TL) on this large cohort over a short time period, we created a novel high throughput robotic system for TL analysis and informatics. Samples were run in triplicate, along with control samples, in a randomized design. As part of quality control, we determined the within-sample variability and employed thresholds for the elimination of outlying measurements. Of 106,902 samples assayed, 105,539 (98.7%) passed all quality control (QC) measures. As expected, TL in general showed a decline with age and a sex difference. While telomeres showed a negative correlation with age up to 75 years, in those older than 75 years, age positively correlated with longer telomeres, indicative of an association of longer telomeres with more years of survival in those older than 75. Furthermore, while females in general had longer telomeres than males, this difference was significant only for those older than age 50. An additional novel finding was that the variance of TL between individuals increased with age. This study establishes reliable assay and analysis methodologies for measurement of TL in large, population-based human studies. The GERA cohort represents the largest currently available such resource, linked to comprehensive electronic health and genotype data for analysis.  相似文献   
122.
123.
A strain of the fungus Cladosporium sp. (RM16) from an egg of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) was assessed as a potential biocontrol agent for this pest. Pathogenicity of the fungus was tested against H. armigera eggs and larvae, cotton aphids (Aphis gossypii Glover; Homoptera: Aphididae), and silverleaf whitefly type B (Bemisia tabaci Gennadius; Hemiptera: Aleyrodidae). The pathogenicity of the fungus to the predatory red and blue beetles (Dicranolaius bellulus Guérin-Méneville; Coleoptera: Melyridae), transverse ladybird beetles (Coccinella transversalis Fabricius; Coleoptera: Coccinellidae), green lacewings (Mallada signatus Schneider; Neuroptera: Chrysopidae) and damsel bugs (Nabis kinbergii Reuter; Hemiptera: Nabidae), was also assessed in the laboratory. Fungus treatment resulted in failure to hatch of up to 64% of H. armigera eggs (compared with 11% in the controls) and mortality of 54% of first instar H. armigera larvae (compared with 5% in the controls). In contrast, it was not pathogenic to later instar H. armigera larvae. Cladosporium RM16 was also efficacious against the sap-sucking insect pests of cotton that were tested. No significant harmful effect of the fungus was found on any of the four beneficial predatory insects assessed in this study. Cladosporium RM16 has the potential as biological control agent to support integrated pest management in cotton farming systems, although this needs intensive study.  相似文献   
124.
In this article, I argue that although cervical cancer is an often stigmatized condition in Brazil, women with cervical cancer in Recife, Brazil, did not simply endure the stigma, they also perpetuated it. I draw on narrative theory and 18 months of ethnographic research in Recife to argue that rather than resisting the stigma associated with their disease, women in Recife used stigma to construct illness narratives that affirmed that they were still held to the same norms and values as the nonill. In turn, those narratives, and the healing narratives constructed along with them, provided women with hope for a future free from cervical cancer and free from the "imperfections" associated with that disease. Thus, women with cervical cancer used stigmatizing narratives both as links back to the "normal" world they inhabited before they became ill, and as bridges forward to the future they hoped to attain.  相似文献   
125.

Background  

The objective of the present study was to isolate and purify the protein fraction(s) of llama seminal plasma responsible for the ovulation-inducing effect of the ejaculate.  相似文献   
126.
The earlier inclusion of children into clinical trials has challenged toxicologists to develop nonclinical strategies to support these trials early in the drug development process, and the routine practise of global development strategies (i.e., concomitant development and filing in multiple geographical regions) adds another complication. Ideally, one would like to develop a stagey that would meet regulatory requirements from all regions. This presentation illustrated the challenges faced in developing a strategy regarding the need to perform a toxicity study in juvenile animals and the design of any necessary study that will receive global regulatory agreement.  相似文献   
127.
Given the pervasiveness of stress and anxiety in our culture it is important to develop and implement interventions that can be easily utilized by large numbers of people that are readily available, inexpensive and have minimal side effects. Two studies explored the effectiveness of a computer-based heart rate variability biofeedback program on reducing anxiety and negative mood in college students. A pilot project (n = 9) of highly anxious students revealed sizable decreases in anxiety and negative mood following utilizing the program for 4 weeks. A second study (n = 35) employing an immediate versus delayed treatment design replicated the results, although the magnitude of the impact was not quite as strong. Despite observing decreases in anxiety, the expected changes in psychophysiological coherence were not observed.  相似文献   
128.
Although statins impart a number of cardiovascular benefits, whether statin therapy during the peri-infarct period improves subsequent myocardial structure and function remains unclear. Thus, we evaluated the effects of atorvastatin on cardiac function, remodeling, fibrosis, and apoptosis after myocardial infarction (MI). Two groups of rats were subjected to permanent coronary occlusion. Group II (n = 14) received oral atorvastatin (10 mg/kg/d) daily for 3 wk before and 4 wk after MI, while group I (n = 12) received equivalent doses of vehicle. Infarct size (Masson''s trichrome-stained sections) was similar in both groups. Compared with group I, echocardiographic left ventricular ejection fraction (LVEF) and fractional area change (FAC) were higher while LV end-diastolic volume (LVEDV) and LV end-systolic and end-diastolic diameters (LVESD and LVEDD) were lower in treated rats. Hemodynamically, atorvastatin-treated rats exhibited significantly higher dP/dtmax, end-systolic elastance (Ees), and preload recruitable stroke work (PRSW) and lower LV end-diastolic pressure (LVEDP). Morphometrically, infarct wall thickness was greater in treated rats. The improvement of LV function by atorvastatin was associated with a decrease in hydroxyproline content and in the number of apoptotic cardiomyocyte nuclei. We conclude that atorvastatin therapy during the peri-infarct period significantly improves LV function and limits adverse LV remodeling following MI independent of a reduction in infarct size. These salubrious effects may be due in part to a decrease in myocardial fibrosis and apoptosis.  相似文献   
129.
The genome of the choanoflagellate Monosiga brevicollis contains at least three genes for the phosphoryl transfer enzyme, arginine kinase (AK; EC 2.7.3.3). Bioinformatic analyses of the deduced amino acid sequences of the proteins coded for by two of these genes showed that one of these AKs is cytoplasmic (denoted AK1) while the other appears to have an N-terminal mitochondrial targeting peptide (denoted AK2). Cloning and expression of the cDNA for AK1 yielded considerable soluble AK activity. Three AK2 constructs were expressed - one corresponding to the full length protein and two corresponding to truncated versions in which the signal peptide had been deleted. Expression of the former construct yielded minimal soluble activity. In contrast, significant AK activity was found in both truncated constructs confirming the importance of removal of the targeting peptide for proper folding and catalytic activity. Both AK1 and AK2 are functional oligomers unlike typical AKs which are monomeric. A phylogenetic analysis showed that these choanoflagellate AKs group more closely with a supercluster consisting of cytoplasmic and mitochondrial CKs and invertebrate AKs that evolved secondarily from a CK-like ancestor. Reaction-diffusion constraints in choanoflagellates are likely mitigated by the presence of AK isoforms which facilitate energy transport in these highly polarized cells.  相似文献   
130.

Purpose

We sought to identify genes of clinical significance to predict survival and the risk for colorectal liver metastasis (CLM), the most common site of metastasis from colorectal cancer (CRC).

Patients and Methods

We profiled gene expression in 31 specimens from primary CRC and 32 unmatched specimens of CLM, and performed Significance Analysis of Microarrays (SAM) to identify genes differentially expressed between these two groups. To characterize the clinical relevance of two highly-ranked differentially-expressed genes, we analyzed the expression of secreted phosphoprotein 1 (SPP1 or osteopontin) and lymphoid enhancer factor-1 (LEF1) by immunohistochemistry using a tissue microarray (TMA) representing an independent set of 154 patients with primary CRC.

Results

Supervised analysis using SAM identified 963 genes with significantly higher expression in CLM compared to primary CRC, with a false discovery rate of <0.5%. TMA analysis showed SPP1 and LEF1 protein overexpression in 60% and 44% of CRC cases, respectively. Subsequent occurrence of CLM was significantly correlated with the overexpression of LEF1 (chi-square p = 0.042), but not SPP1 (p = 0.14). Kaplan Meier analysis revealed significantly worse survival in patients with overexpression of LEF1 (p<0.01), but not SPP1 (p = 0.11). Both univariate and multivariate analyses identified stage (p<0.0001) and LEF1 overexpression (p<0.05) as important prognostic markers, but not tumor grade or SPP1.

Conclusion

Among genes differentially expressed between CLM and primary CRC, we demonstrate overexpression of LEF1 in primary CRC to be a prognostic factor for poor survival and increased risk for liver metastasis.  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