全文获取类型
收费全文 | 8221篇 |
免费 | 504篇 |
国内免费 | 1篇 |
出版年
2023年 | 47篇 |
2022年 | 37篇 |
2021年 | 139篇 |
2020年 | 97篇 |
2019年 | 131篇 |
2018年 | 253篇 |
2017年 | 227篇 |
2016年 | 306篇 |
2015年 | 461篇 |
2014年 | 436篇 |
2013年 | 614篇 |
2012年 | 719篇 |
2011年 | 623篇 |
2010年 | 392篇 |
2009年 | 326篇 |
2008年 | 457篇 |
2007年 | 407篇 |
2006年 | 392篇 |
2005年 | 326篇 |
2004年 | 373篇 |
2003年 | 300篇 |
2002年 | 294篇 |
2001年 | 181篇 |
2000年 | 167篇 |
1999年 | 131篇 |
1998年 | 59篇 |
1997年 | 35篇 |
1996年 | 50篇 |
1995年 | 35篇 |
1994年 | 33篇 |
1993年 | 26篇 |
1992年 | 87篇 |
1991年 | 59篇 |
1990年 | 53篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 40篇 |
1986年 | 37篇 |
1985年 | 39篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1978年 | 12篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 13篇 |
1972年 | 12篇 |
1970年 | 11篇 |
排序方式: 共有8726条查询结果,搜索用时 46 毫秒
991.
Liliana Fernández-Canigia Michael J Dowzicky 《Annals of clinical microbiology and antimicrobials》2012,11(1):1-9
Background
The evolving epidemiology of methicillin resistant Staphylococcus aureus (MRSA) is characterized by the emergence of infections caused by non multiresistant MRSA carrying staphylococcal chromosomal cassette (SCC)mec IV or V in the healthcare settings. A molecular epidemiological analysis of non multiresistant MRSA isolates from four acute general hospitals was performed in Palermo, Italy, during a one year period.Methods
For the purpose of the study, MRSA isolates were defined as non multiresistant when they were susceptible to at least three classes of non ??-lactam antibiotics. Seventy-five isolates were submitted to antimicrobial susceptibility testing, multilocus sequence typing (MLST) and polymerase chain reaction (PCR) for SCCmec, accessory gene regulator (agr) groups, arginine catabolic mobile element (ACME) and Panton Valentine leukocidin (PVL) toxin genes. For epidemiological typing, Multiple-Locus Variable-Number Tandem Repeat Fingerprinting (MLVF) was performed on all isolates and pulsed field gel electrophoresis (PFGE) on ST8 isolates.Results
Non multiresistant MRSA isolates were isolated from all hospitals. Resistances to ciprofloxacin, macrolides and tetracycline were the most prevalent. MLST attributed 46 isolates with ST22, 13 with ST8, eight with ST1, three with ST50 and three with ST398. SCCmec type IV was found in all isolates. PVL was detected in one ST22 isolate. All isolates tested negative for the ACME element. MLVF identified 31 different patterns, some subtype clusters ranging in size between two and 22 isolates. The closely related PFGE patterns of the ST8 isolates differed from USA300.Conclusions
A polyclonal circulation of non multiresistant MRSA along with blurring of boundaries between healthcare associated (HA)-MRSA and community associated (CA)-MRSA appear to be occurring in our epidemiological setting. A better understanding of spread of MRSA with the support of molecular typing can provide invaluable information in the epidemiological, microbiological and clinical fields. 相似文献992.
ABSTRACT: BACKGROUND: Female fertility depends on adequate nutrition and energy reserves, suggesting a correlation between the metabolic reserve and reproductive capacity. Leptin regulates body weight and energy homeostasis. The aim of this study was to investigate whether estradiol or FSH alone has a direct effect on the production of leptin. METHODS: A total of 64 patients submitted to controlled ovarian hyperstimulation with recombinant FSH for assisted reproduction and 20 patients using estradiol valerate for endometrial preparation for oocyte donation treatment were included in the study. All patients used GnRH analogues before starting treatment to achieve pituitary suppression. Blood samples for hormonal measurements were collected before starting and after completing the respective treatments. Data were analyzed statistically by the chi-square test, Student's t-test and Pearson's correlation test. RESULTS: We observed an elevation of serum leptin levels secondary to the increase in estradiol, in the absence of influence of any other ovarian or pituitary hormone. The rising rate of leptin levels was higher in women treated with recombinant FSH, which also had higher levels of estradiol, than in those treated with estradiol valerate. CONCLUSIONS: This study demonstrates a correlation between serum levels of estradiol and leptin, suggesting that estradiol is an important regulator of leptin production and that its effects can be amplified by its association with FSH. 相似文献
993.
Pierce CL Rees JC Fernández FM Barr JR 《Molecular & cellular proteomics : MCP》2012,11(1):M111.012849
A multiple reaction monitoring liquid chromatography method with tandem mass spectrometric detection for quantitation of Staphylococcus aureus via phage amplification detection is described. This phage amplification detection method enables rapid and accurate quantitation of viable S. aureus by detecting an amplified capsid protein from a specific phage. A known amount of metabolically labeled (15)N reference bacteriophage, utilized as the input phage and as the internal standard for quantitation, was spiked into S. aureus samples. Following a 2-h incubation, the sample was subjected to a 3-min rapid trypsin digest and analyzed by high-throughput liquid chromatography tandem mass spectrometric detection targeting peptides unique to both the (15)N (input phage) and (14)N (progeny phage) capsid proteins. Quantitation was achieved by comparing peak areas of target peptides from the metabolically labeled (15)N bacteriophage peptide internal standard with that of the wild-type (14)N peptides that were produced by phage amplification and subsequent digestion when the host bacteria was present. This approach is based on the fact that a labeled species differs from the unlabeled one in terms of its mass but exhibits almost identical chemical properties such as ion yields and retention times. A 6-point calibration curve for S. aureus concentration was constructed with standards ranging from 5.0 × 10(4) colony forming units (CFU) ml(-1) to 2.0 × 10(6) CFU ml(-1), with the (15)N reference phage spiked at a concentration of 1.0 × 10(9) plaque forming units (PFU) ml(-1). Amplification with (15)N bacteriophage coupled with LC-MS/MS detection offers speed (3 h total analysis time), sensitivity (LOD: < 5.0 × 10(4) CFU ml(-1)), accuracy, and precision for quantitation of S. aureus. 相似文献
994.
995.
996.
Blanco M Campos F Rodríguez-Yáñez M Arias S Fernández-Ferro J Gómez-Sánchez JC Castillo J 《PloS one》2012,7(2):e30700
The control of temperature during the acute phase of stroke may be a new therapeutic target that can be applied in all stroke patients, however therapeutic window or timecourse of the temperature effect is not well established. Our aim is to study the association between changes in body temperature in the first 72 hours and outcome in patients with ischemic (IS) and hemorrhagic (ICH) stroke. We prospectively studied 2931 consecutive patients (2468 with IS and 463 with ICH). Temperature was obtained at admission, and at 24, 48 and 72 hours after admission. Temperature was categorized as low (<36°C), normal (36–37°C) and high (>37°C). As the main variable, we studied functional outcome at 3 months determined by modified Rankin Scale.Temperature in stroke patients is higher than in controls, and increases gradually in the first 72 hours after stroke. A positive correlation between temperature and stroke severity determined by NIHSS was found at 24 and 48 hours, but not at admission or 72 hours. In a logistic regression model, high temperature was associated with poor outcome at 24 hours (OR 2.05, 95% CI 1.59–2.64, p<0.0001) and 48 hours (OR 1.93, 95% CI 1.08–2.34, p = 0.007), but not at admission or 72 hours.Temperature increases in patients with stroke in the first 72 hours, with the harmful effect of high temperature occurring in the first 48 hours. The neuroprotective effect of low temperature occurs within the first 24 hours from stroke onset. 相似文献
997.
It is generally assumed that steroid hormones are carried in the blood free and/or bound to plasma proteins. We investigated whether blood cells were also able to bind/carry sex-related hormones: estrone, estradiol, DHEA and testosterone. Wistar male and female rats were fed a cafeteria diet for 30 days, which induced overweight. The rats were fed the standard rat diet for 15 additional days to minimize the immediate effects of excess ingested energy. Controls were always kept on standard diet. After the rats were killed, their blood was used for 1) measuring plasma hormone levels, 2) determining the binding of labeled hormones to washed red blood cells (RBC), 3) incubating whole blood with labeled hormones and determining the distribution of label between plasma and packed cells, discounting the trapped plasma volume, 4) determining free plasma hormone using labeled hormones, both through membrane ultrafiltration and dextran-charcoal removal. The results were computed individually for each rat. Cells retained up to 32% estrone, and down to 10% of testosterone, with marked differences due to sex and diet (the latter only for estrogens, not for DHEA and testosterone). Sex and diet also affected the concentrations of all hormones, with no significant diet effects for estradiol and DHEA, but with considerable interaction between both factors. Binding to RBC was non-specific for all hormones. Estrogen distribution in plasma compartments was affected by sex and diet. In conclusion: a) there is a large non-specific RBC-carried compartment for estrone, estradiol, DHEA and testosterone deeply affected by sex; b) Prior exposure to a cafeteria (hyperlipidic) diet induced hormone distribution changes, affected by sex, which hint at sex-related structural differences in RBC membranes; c) We postulate that the RBC compartment may contribute to maintain free (i.e., fully active) sex hormone levels in a way similar to plasma proteins non-specific binding. 相似文献
998.
999.
Background
Trypanosoma cruzi is the causative agent of Chagas'' Disease. The parasite has a complex population structure, with six major evolutionary lineages, some of which have apparently resulted from ancestral hybridization events. Because there are important biological differences between these lineages, strain typing methods are essential to study the T. cruzi species. Currently, there are a number of typing methods available for T. cruzi, each with its own advantages and disadvantages. However, most of these methods are based on the amplification of a variable number of loci.Methodology/Principal Findings
We present a simple typing assay for T. cruzi, based on the amplification of a single polymorphic locus: the TcSC5D gene. When analyzing sequences from this gene (a putative lathosterol/episterol oxidase) we observed a number of interesting polymorphic sites, including 1 tetra-allelic, and a number of informative tri- and bi-allelic SNPs. Furthermore, some of these SNPs were located within the recognition sequences of two commercially available restriction enzymes. A double digestion with these enzymes generates a unique restriction pattern that allows a simple classification of strains in six major groups, corresponding to DTUs TcI–TcIV, the recently proposed Tcbat lineage, and TcV/TcVI (as a group). Direct sequencing of the amplicon allows the classification of strains into seven groups, including the six currently recognized evolutionary lineages, by analyzing only a few discriminant polymorphic sites.Conclusions/Significance
Based on these findings we propose a simple typing assay for T. cruzi that requires a single PCR amplification followed either by restriction fragment length polymorphism analysis, or direct sequencing. In the panel of strains tested, the sequencing-based method displays equivalent inter-lineage resolution to recent multi- locus sequence typing assays. Due to their simplicity and low cost, the proposed assays represent a good alternative to rapidly screen strain collections, providing the cornerstone for the development of robust typing strategies. 相似文献1000.
Estefania Calvo-álvarez Nestor Adrian Guerrero Raquel álvarez-Velilla Christopher Fernández Prada Jose María Requena Carmen Punzón Miguel ángel Llamas Francisco J. Arévalo Luis Rivas Manuel Fresno Yolanda Pérez-Pertejo Rafael Bala?a-Fouce Rosa M. Reguera 《PLoS neglected tropical diseases》2012,6(11)