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   19356篇
  免费   1962篇
  国内免费   141篇
  21459篇
  2022年   228篇
  2021年   344篇
  2020年   281篇
  2019年   336篇
  2018年   452篇
  2017年   338篇
  2016年   628篇
  2015年   925篇
  2014年   1033篇
  2013年   1185篇
  2012年   1477篇
  2011年   1358篇
  2010年   920篇
  2009年   774篇
  2008年   1079篇
  2007年   980篇
  2006年   915篇
  2005年   798篇
  2004年   823篇
  2003年   670篇
  2002年   620篇
  2001年   361篇
  2000年   330篇
  1999年   283篇
  1998年   169篇
  1997年   158篇
  1996年   132篇
  1995年   122篇
  1994年   140篇
  1993年   121篇
  1992年   196篇
  1991年   208篇
  1990年   186篇
  1989年   200篇
  1988年   178篇
  1987年   163篇
  1986年   157篇
  1985年   142篇
  1984年   127篇
  1983年   102篇
  1982年   100篇
  1981年   105篇
  1980年   94篇
  1979年   106篇
  1978年   110篇
  1976年   91篇
  1975年   100篇
  1974年   96篇
  1973年   90篇
  1972年   77篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
141.

Background

The post-resuscitation phase after out-of-hospital cardiac arrest (OHCA) is characterised by a systemic inflammatory response (e.g., severe sepsis), for which the immature granulocyte count is a diagnostic marker. In this study we evaluated the prognostic significance of the delta neutrophil index (DNI), which is the difference in leukocyte subfractions as assessed by an automated blood cell analyser, for early mortality after OHCA.

Materials and Methods

OHCA records from the emergency department cardiac arrest registry were retrospectively analysed. Patients who survived at least 24 h after return of spontaneous circulation were included in the analysis. We evaluated mortality and cerebral performance category scores at 30 days.

Results

A total of 83 patients with OHCA were included in the study. Our results showed that DNI >8.4% on day 1 (hazard ratio [HR], 3.227; 95% CI, 1.485–6.967; p = 0.001) and DNI >10.5% on day 2 (HR, 3.292; 95% CI, 1.662–6.519; p<0.001) were associated with increased 30-day mortality in patients with OHCA. Additionally, DNI >8.4% on day 1 (HR, 2.718; 95% CI, 1.508–4.899; p<0.001) and DNI >10.5% on day 2 (HR, 1.709; 95% CI, 1.051–2.778; p = 0.02) were associated with worse neurologic outcomes 30 days after OHCA.

Conclusion

A higher DNI is a promising prognostic marker for 30-day mortality and neurologic outcomes after OHCA. Our findings indicate that patients with elevated DNI values after OHCA might be closely monitored so that appropriate treatment strategies can be implemented.  相似文献   
142.
Hypoglycemia can cause rapid and severe brain damage. We studied the impact of hypoglycemic brain damage in the insulin-induced hypoglycemic rats. Thirty male rats were divided into normal blood sugar control group (group A), the blank group (group B), and the experimental group which was further divided into four groups according to the level of blood glucose reperfusion i.e., blood glucose ≤3 mmol/L (Group C), ≤6 mmol/L (Group D), ≤9 mmol/L (Group E), and >9 mmol/L (Group F). Each groups had five rats. TUNEL and FJB staining were used to observe the apoptosis and necrosis in the rat hippocampus CA1 and DG regions and transmission electron microscopy for ultra-structures. We observed that neuronal apoptosis and necrosis of group A and B were not obvious. The apoptotic and necrotic neuron cell densities in the hippocampus CA1 and DG regions were moderately detected in group C, D, and E, while we found it maximum in group F. No significant difference was found in apoptotic and necrotic neuron cell density in the hippocampus CA1 and DG regions in group A and B. Apoptotic and necrotic cell density was significantly increased in all experimental groups as compared to the control group. Moreover, the apoptotic and necrotic cell density was significantly higher in group F than other experimental groups (group C, D, and E). However, apoptosis and necrosis in hippocampus CA1 and DG regions was not differed significantly among groups C, D, and E. All results were well supported by transmission electron microscopy. In conclusion, under the condition of the same blood glucose level, the degree of brain damage related to the blood glucose level with hypoglycemia and rapid blood glucose increased after hypoglycemia could cause more significant brain damage.  相似文献   
143.
A dye reduction method was developed for estimating total aerobic and/or psychrotrophic bacterial counts in ground beef. The method is based on color changes in indicator disks placed on the meat surface.  相似文献   
144.
Objective : To examine lifestyle factors associated with metabolic syndrome (MetS) and to explore the relationships between MetS and non‐traditional cardiovascular disease risk factors [adiponectin, leptin, C‐reactive protein (CRP), interleukin‐6 (IL‐6), and serum amyloid A (SAA)] in an isolated Aboriginal Canadian community. Research Methods and Procedures : Data were obtained from 360 non‐diabetic adults participating in a population‐based study of Aboriginal Canadians. Fasting samples were drawn for glucose, insulin, lipids, adiponectin, leptin, CRP, IL‐6, and SAA. Percentage body fat was measured using bioelectrical impedance analysis. Past year physical activity and fitness level were assessed. MetS was diagnosed according to the criteria of the National Cholesterol Education Program, the World Health Organization, and the International Diabetes Federation. Results : The results showed that older age, higher percentage body fat, and lower fitness levels were associated with increased odds of MetS regardless of MetS definition and subject gender. Past year physical activity was independently related with the World Health Organization‐MetS in male subjects. Subjects with MetS had significantly higher leptin, CRP, IL‐6, and SAA levels and lower adiponectin levels; however, only adiponectin remained significantly low after adjustment for age and percentage body fat. Discussion : The study showed that higher percentage body fat and lower physical activity and fitness were associated with a higher prevalence of MetS in this Aboriginal community and that hypoadiponectinemia was independently associated with MetS.  相似文献   
145.
Expression of a polyubiquitin promoter isolated from Gladiolus   总被引:2,自引:0,他引:2  
Joung YH  Kamo K 《Plant cell reports》2006,25(10):1081-1088
A polyubiquitin promoter (GUBQ1) including its 5′UTR and intron was isolated from the floral monocot Gladiolus because high levels of expression could not be obtained using publicly available promoters isolated from either cereals or dicots. Sequencing of the promoter revealed highly conserved 5′ and 3′ intron splicing sites for the 1.234 kb intron. The coding sequence of the first two ubiquitin genes showed the highest homology (87 and 86%, respectively) to the ubiquitin genes of Nicotiana tabacum and Oryza sativa RUBQ2. Transient expression following gene gun bombardment showed that relative levels of GUS activity with the GUBQ1 promoter were comparable to the CaMV 35S promoter in gladiolus, tobacco, rose, rice, and the floral monocot freesia. The highest levels of GUS expression with GUBQ1 were attained with Gladiolus. The full-length GUBQ1 promoter including 5′UTR and intron were necessary for maximum GUS expression in Gladiolus. The relative GUS activity for the promoter only was 9%, and the activity for the promoter with 5′UTR and 399 bp of the full-length 1.234 kb intron was 41%. Arabidopsis plants transformed with uidA under GUBQ1 showed moderate GUS expression throughout young leaves and in the vasculature of older leaves. The highest levels of transient GUS expression in Gladiolus have been achieved using the GUBQ1 promoter. This promoter should be useful for genetic engineering of disease resistance in Gladiolus, rose, and freesia, where high levels of gene expression are important.  相似文献   
146.
Rapid development of next generation sequencing (NGS) technologies in recent years has made whole genome sequencing of bacterial genomes widely accessible. However, it is often unnecessary or not feasible to sequence the whole genome for most applications of genetic analyses in bacteria. Selectively capturing defined genomic regions followed by NGS analysis could be a promising approach for high-resolution molecular typing of a large set of strains. In this study, we describe a novel and straightforward PCR-based target-capturing method, hairpin-primed multiplex amplification (HPMA), which allows for simultaneous amplification of numerous target genes. To test the feasibility of NGS-based strain typing using HPMA, 20 target gene sequences were simultaneously amplified with barcode tagging in each of 41 Salmonella strains. The amplicons were then pooled and analyzed by 454 pyrosequencing. Analysis of the sequence data, as an extension of multilocus sequence typing (MLST), demonstrated the utility and potential of this novel typing method, MLST-seq, as a high-resolution strain typing method. With the rapidly increasing sequencing capacity of NGS, MLST-seq or its variations using different target enrichment methods can be expected to become a high-resolution typing method in the near future for high-throughput analysis of a large collection of bacterial strains.  相似文献   
147.
Peramine is an insect-feeding deterrent produced by Epichloë species in symbiotic association with C3 grasses. The perA gene responsible for peramine synthesis encodes a two-module nonribosomal peptide synthetase. Alleles of perA are found in most Epichloë species; however, peramine is not produced by many perA-containing Epichloë isolates. The genetic basis of these peramine-negative chemotypes is often unknown. Using PCR and DNA sequencing, we analyzed the perA genes from 72 Epichloë isolates and identified causative mutations of perA null alleles. We found nonfunctional perA-ΔR* alleles, which contain a transposon-associated deletion of the perA region encoding the C-terminal reductase domain, are widespread within the Epichloë genus and represent a prevalent mutation found in nonhybrid species. Disparate phylogenies of adjacent A2 and T2 domains indicated that the deletion of the reductase domain (R*) likely occurred once and early in the evolution of the genus, and subsequently there have been several recombinations between those domains. A number of novel point, deletion, and insertion mutations responsible for abolishing peramine production in full-length perA alleles were also identified. The regions encoding the first and second adenylation domains (A1 and A2, respectively) were common sites for such mutations. Using this information, a method was developed to predict peramine chemotypes by combining PCR product size polymorphism analysis with sequencing of the perA adenylation domains.  相似文献   
148.
149.
Structural insights into the clathrin coat   总被引:2,自引:0,他引:2  
Clathrin is a cytoplasmic protein best known for its role in endocytosis and intracellular trafficking. The diverse nature of clathrin has recently become apparent, with strong evidence available suggesting roles in both chromosome segregation and reassembly of the Golgi apparatus during mitosis. Clathrin functions as a heterohexamer, adopting a three-legged triskelion structure of three clathrin light chains and three heavy chains. During endocytosis clathrin forms a supportive network about the invaginating membrane, interacting with itself and numerous adapter proteins. Advances in the field of structural biology have led us to a greater understanding of clathrin in its assembled state, the clathrin lattice. Combining techniques such as X-ray crystallography, NMR, and cryo-electron microscopy has allowed us to piece together the intricate nature of clathrin-coated vesicles and the interactions of clathrin with its many binding partners. In this review I outline the roles of clathrin within the cell and the recent structural advances that have improved our understanding of clathrin-clathrin and clathrin-protein interactions.  相似文献   
150.
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