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   4543篇
  免费   326篇
  国内免费   1篇
  2023年   20篇
  2022年   49篇
  2021年   88篇
  2020年   58篇
  2019年   64篇
  2018年   94篇
  2017年   88篇
  2016年   155篇
  2015年   201篇
  2014年   222篇
  2013年   311篇
  2012年   369篇
  2011年   352篇
  2010年   225篇
  2009年   193篇
  2008年   287篇
  2007年   301篇
  2006年   262篇
  2005年   248篇
  2004年   211篇
  2003年   190篇
  2002年   196篇
  2001年   42篇
  2000年   21篇
  1999年   39篇
  1998年   63篇
  1997年   25篇
  1996年   37篇
  1995年   45篇
  1994年   23篇
  1993年   39篇
  1992年   26篇
  1991年   22篇
  1990年   15篇
  1989年   8篇
  1988年   12篇
  1987年   21篇
  1986年   15篇
  1985年   16篇
  1984年   15篇
  1983年   15篇
  1982年   14篇
  1981年   17篇
  1980年   17篇
  1977年   10篇
  1976年   12篇
  1975年   16篇
  1974年   10篇
  1973年   10篇
  1972年   11篇
排序方式: 共有4870条查询结果,搜索用时 15 毫秒
151.
In a clinical setting it seems to be normal these days that a relevant proportion or even the majority of different bacterial species has already one or more acquired antibiotic resistances. Unfortunately, the overuse of antibiotics for livestock breeding and medicine has also altered the wild-type resistance profiles of many bacterial species in different environmental settings. As a matter of fact, getting in contact with resistant bacteria is no longer restricted to hospitals. Beside food and food production, the aquatic environment might also play an important role as reservoir and carrier. The aim of this study was the assessment of the resistance patterns of Escherichia coli and Klebsiella spp. out of surface water without prior enrichment and under non-selective culture conditions (for antibiotic resistance). In addition, the presence of clinically important extended spectrum beta lactamase (ESBL) and carbapenmase harboring Enterobacteriaceae should be investigated. During Joint Danube Survey 3 (2013), water samples were taken over the total course of the River Danube. Resistance testing was performed for 21 different antibiotics. Samples were additionally screened for ESBL or carbapenmase harboring Enterobacteriaceae. 39% of all isolated Escherichia coli and 15% of all Klebsiella spp. from the river Danube had at least one acquired resistance. Resistance was found against all tested antibiotics except tigecycline. Taking a look on the whole stretch of the River Danube the proportion of multiresistances did not differ significantly. In total, 35 ESBL harboring Enterobacteriaceae, 17 Escherichia coli, 13 Klebsiella pneumoniae and five Enterobacter spp. were isolated. One Klebsiella pneumoniae harboring NMD-1 carbapenmases and two Enterobacteriaceae with KPC-2 could be identified. Human generated antibiotic resistance is very common in E. coli and Klebsiella spp. in the River Danube. Even isolates with resistance patterns normally associated with intensive care units are present.  相似文献   
152.
153.
Staphylococcus epidermidis is the most common cause of device-associated infections. It has been shown that active and passive immunization in an animal model against protein SesC significantly reduces S. epidermidis biofilm-associated infections. In order to elucidate its role, knock-out of sesC or isolation of S. epidermidis sesC-negative mutants were attempted, however, without success. As an alternative strategy, sesC was introduced into Staphylococcus aureus 8325–4 and its isogenic icaADBC and srtA mutants, into the clinical methicillin-sensitive S. aureus isolate MSSA4 and the MRSA S. aureus isolate BH1CC, which all lack sesC. Transformation of these strains with sesC i) changed the biofilm phenotype of strains 8325–4 and MSSA4 from PIA-dependent to proteinaceous even though PIA synthesis was not affected, ii) converted the non-biofilm-forming strain 8325–4 ica::tet to a proteinaceous biofilm-forming strain, iii) impaired PIA-dependent biofilm formation by 8325–4 srtA::tet, iv) had no impact on protein-mediated biofilm formation of BH1CC and v) increased in vivo catheter and organ colonization by strain 8325–4. Furthermore, treatment with anti-SesC antibodies significantly reduced in vitro biofilm formation and in vivo colonization by these transformants expressing sesC. These findings strongly suggest that SesC is involved in S. epidermidis attachment to and subsequent biofilm formation on a substrate.  相似文献   
154.

Objective

To present current guidelines regarding treatment of mastocytosis in pregnancy on the example of observed patients.

Design

Case control national study.

Setting

Polish Center of the European Competence Network on Mastocytosis (ECNM).

Population or Sample

23 singleton spontaneous pregnancies in 17 women diagnosed with mastocytosis in years 1999–2014, before becoming pregnant.

Methods

Prospective analysis outcomes of pregnancies and deliveries.

Main Outcome Measures

Survey developed in cooperation with the Spanish Instituto de Estudios de Mastocitosis de Castilla-La Mancha (CLMast), Hospital Virgen del Valle, Toledo, Red Espańola de Mastocitosis (REMA), Spain.

Results

All 23 pregnancies resulted from natural conception. Obstetrical complications recorded in the first trimester included spontaneous miscarriage (5 pregnancies). Four patients delivered preterm, including one delivery due to preeclampsia at 26 weeks which resulted with neonate death due to extreme prematurity. Five women delivered via cesarean: four due to obstetrical indications and one due to mastocytosis, during which no anesthesia related complications were recorded. Of patients delivering vaginally, two received extradural anesthesia, three required oxytocin infusion due to uterine hypotonia. No labor complications were recorded. In one woman with pregnancy-induced hypertension, early puerperium was complicated by the presence of persistent arterial hypertension. One neonate was born with the signs of cutaneous mastocytosis. Another neonate was diagnosed with Patau syndrome. Four women were treated for mastocytosis prior to conception and continued therapy after becoming pregnant. One patient was put on medications in the first trimester due to worsening of her symptoms. Pregnancy exerted only a slight effect on the intensity and frequency of mastocytosis-related symptoms observed. Worsening of the disease-related symptoms was documented in only four patients (23%). None of the patients showed the signs of anaphylaxis, either before becoming pregnant, or during pregnancy and puerperium.

Conclusions

There is no contraindication to pregnancy when mastocystosis-related pathologies are under appropriate medical control.  相似文献   
155.
There are very few reports that describe the mutational landscape of cervical cancer, one of the leading cancers in Indian women. The aim of the present study was to investigate the somatic mutations that occur in cervical cancer. Whole exome sequencing of 10 treatment naïve tumour biopsies with matched blood samples, from a cohort of Indian patients with locally advanced disease, was performed. The data revealed missense mutations across 1282 genes, out of 1831 genes harbouring somatic mutations. These missense mutations (nonsynonymous + stop-gained) when compared with pre-existing mutations in the COSMIC database showed that 272 mutations in 250 genes were already reported although from cancers other than cervical cancer. More than 1000 novel somatic variations were obtained in matched tumour samples. Pathways / genes that are frequently mutated in various other cancers were found to be mutated in cervical cancers. A significant enrichment of somatic mutations in the MAPK pathway was observed, some of which could be potentially targetable. This is the first report of whole exome sequencing of well annotated cervical cancer samples from Indian women and helps identify trends in mutation profiles that are found in an Indian cohort of cervical cancer.  相似文献   
156.

Background

The human T-Cell Lymphotropic Virus Type 1 (HTLV-1) is a retrovirus associated with neurological alterations; individuals with HTLV-1 infection may develop HTLV-1 associated myelopathy / tropical spastic paraparesis (HAM/TSP). Frequent neurological complaints include foot numbness and leg weakness. In this study, we compared the distribution of the body weight on different areas of the foot in HTLV-1 patients with HAM/TSP, asymptomatic HTLV-1 patients, and healthy individuals.

Methodology

We studied 36 HTLV-1 infected patients, who were divided in two groups of 18 patients each based on whether or not they had been diagnosed with HAM/TSP, and 17 control subjects. The evaluation included an interview on the patient’s clinical history and examinations of the patient’s reflexes, foot skin tactile sensitivity, and risk of falling. The pressure distribution on different areas of the foot was measured with baropodometry, using a pressure platform, while the patients had their eyes open or closed.

Main Findings

The prevalence of neurological disturbances—altered reflexes and skin tactile sensitivity and increased risk of falling—was higher in HTLV-1 HAM/TSP patients than in HTLV-1 asymptomatic patients. The medium and maximum pressure values were higher in the forefoot than in the midfoot and hindfoot in both HTLV-1 groups. In addition, the pressure on the hindfoot was lower in HAM/TSP patients compared to control subjects.

Conclusions

The neurological disturbances associated with HTLV-1 infection gradually worsened from HTLV-1 asymptomatic patients to HAM/TSP patients. Baropodometry is a valuable tool to establish the extent of neurological damage in patients suffering from HTLV-1 infection.  相似文献   
157.
158.
159.
The ability to analyze the distribution of topoisomers in a plasmid DNA sample is important when evaluating the quality of preparations intended for gene therapy and DNA vaccination or when performing biochemical studies on the action of topoisomerases and gyrases. Here, we describe the separation of supercoiled (sc) and open circular (oc) topoisomers by multimodal chromatography. A medium modified with the ligand N-benzyl-N-methyl ethanolamine and an elution scheme with increasing NaCl concentration are used to accomplish the baseline separation of sc and oc plasmid. The utility of the method is demonstrated by quantitating topoisomers in a purified plasmid sample.  相似文献   
160.
Grape quality for winemaking depends on sugar accumulation and metabolism in berries. Abscisic acid (ABA) and gibberellins (GAs) have been reported to control sugar allocation in economically important crops, although the mechanisms involved are still unknown. The present study tested if ABA and gibberellin A3 (GA3) enhance carbon allocation in fruits of grapevines by modifying phloem loading, phloem area and expression of sugar transporters in leaves and berries. Pot‐grown Vitis vinifera cv. Malbec plants were sprayed with ABA and GA3 solutions. The amount of soluble sugars in leaves and berries related to photosynthesis were examined at three points of berry growth: pre‐veraison, full veraison and post‐veraison. Starch levels and amylase activity in leaves, gene expression of sugar transporters in leaves and berries and phloem anatomy were examined at full veraison. Accumulation of glucose and fructose in berries was hastened in ABA‐treated plants at the stage of full veraison, which was correlated with enhancement of Vitis vinifera HEXOSE TRANSPORTER 2 (VvHT2) and Vitis vinifera HEXOSE TRANSPORTER 6 (VvHT6) gene expression, increases of phloem area and sucrose content in leaves. On the other hand, GA3 increased the quantity of photoassimilates delivered to the stem thus increasing xylem growth. In conclusion, stimulation of sugar transport by ABA and GA3 to berries and stems, respectively, was due to build‐up of non‐structural carbohydrates in leaves, modifications in phloem tissue and modulation in gene expression of sugar transporters.  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