全文获取类型
收费全文 | 20909篇 |
免费 | 1969篇 |
国内免费 | 19篇 |
出版年
2022年 | 119篇 |
2021年 | 280篇 |
2020年 | 137篇 |
2019年 | 218篇 |
2018年 | 278篇 |
2017年 | 211篇 |
2016年 | 393篇 |
2015年 | 695篇 |
2014年 | 773篇 |
2013年 | 975篇 |
2012年 | 1261篇 |
2011年 | 1317篇 |
2010年 | 798篇 |
2009年 | 686篇 |
2008年 | 1020篇 |
2007年 | 1103篇 |
2006年 | 1033篇 |
2005年 | 1020篇 |
2004年 | 1004篇 |
2003年 | 971篇 |
2002年 | 949篇 |
2001年 | 247篇 |
2000年 | 183篇 |
1999年 | 239篇 |
1998年 | 275篇 |
1997年 | 200篇 |
1996年 | 180篇 |
1995年 | 214篇 |
1994年 | 200篇 |
1993年 | 183篇 |
1992年 | 182篇 |
1991年 | 168篇 |
1990年 | 157篇 |
1989年 | 149篇 |
1988年 | 151篇 |
1987年 | 155篇 |
1986年 | 162篇 |
1985年 | 177篇 |
1984年 | 190篇 |
1983年 | 161篇 |
1982年 | 234篇 |
1981年 | 238篇 |
1980年 | 235篇 |
1979年 | 155篇 |
1978年 | 155篇 |
1977年 | 143篇 |
1976年 | 175篇 |
1975年 | 136篇 |
1974年 | 153篇 |
1973年 | 169篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
51.
The enzymatic activity of salivary amylase bound to the surface of several species of oral streptococci was determined by the production of acid from starch and by the degradation of maltotetraose to glucose in a coupled, spectrophotometric assay. Most strains able to bind amylase exhibited functional enzyme on their surface and produced acid from the products of amylolytic degradation. These strains were unable to utilise starch in the absence of salivary amylase. Two strains failed to produce acid from starch, despite the presence of functional salivary amylase, because they could not utilise maltose. Strains that could not bind salivary amylase failed to produce acid from starch. In no case was all the bound salivary amylase active, and two strains of Streptococcus mitis which bound amylase did not exhibit any enzyme activity on their cell surface. The ability to bind amylase may confer a survival advantage on oral bacteria which inhabit hosts that consume diets containing starch. 相似文献
52.
Antimycotic Compounds from the Plant Pathogen Rhizoctonia solani and its Antagonist Trichoderma harzianum 总被引:5,自引:0,他引:5
The soilborne rhizosphere-competent fungal biocontrol agent Trichoderma harzianum isolate Th008 secreted trichodermin (MW = 292) and a small peptide (MW = 876) in culture. These compounds were antagonistic in culture to the mycelial growth of the soilborne fungal pathogen Rhizoctonia solani isolate 2B-12, which is highly virulent to soybean ( Glycine max )seedlings. When 100mg of dried autoclaved mycelial mat of R. solani was added to 200 ml liquid cultures of T. harzianum , the quantity of antimycotic compounds secreted by the latter was 3.5 times greater than that of the antagonist alone. R. solani secreted a coumarin derivative (MW = 313) in liquid culture, which inhibited the mycelial growth of T. harzianum ; however, inhibition of the growth of the antagonist required a greater concentration than that for the antimycotic compounds produced by the antagonist against the pathogen. The inclusion of 100 mg of dried autoclaved mycelial mat of T. harzianum in a 200 ml liquid culture of R. solani did not affect the quantity of the antimycotic compound produced by the pathogen. 相似文献
53.
Global species delimitation and phylogeography of the circumtropical ‘sexy shrimp’ Thor amboinensis reveals a cryptic species complex and secondary contact in the Indo‐West Pacific
下载免费PDF全文
![点击此处可从《Journal of Biogeography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
54.
Christine E. Brown Charles D. Warden Renate Starr Xutao Deng Behnam Badie Yate-Ching Yuan Stephen J. Forman Michael E. Barish 《PloS one》2013,8(10)
A major challenge for successful immunotherapy against glioma is the identification and characterization of validated targets. We have taken a bioinformatics approach towards understanding the biological context of IL-13 receptor α2 (IL13Rα2) expression in brain tumors, and its functional significance for patient survival. Querying multiple gene expression databases, we show that IL13Rα2 expression increases with glioma malignancy grade, and expression for high-grade tumors is bimodal, with approximately 58% of WHO grade IV gliomas over-expressing this receptor. By several measures, IL13Rα2 expression in patient samples and low-passage primary glioma lines most consistently correlates with the expression of signature genes defining mesenchymal subclass tumors and negatively correlates with proneural signature genes as defined by two studies. Positive associations were also noted with proliferative signature genes, whereas no consistent associations were found with either classical or neural signature genes. Probing the potential functional consequences of this mesenchymal association through IPA analysis suggests that IL13Rα2 expression is associated with activation of proinflammatory and immune pathways characteristic of mesenchymal subclass tumors. In addition, survival analyses indicate that IL13Rα2 over-expression is associated with poor patient prognosis, a single gene correlation ranking IL13Rα2 in the top ~1% of total gene expression probes with regard to survival association with WHO IV gliomas. This study better defines the functional consequences of IL13Rα2 expression by demonstrating association with mesenchymal signature gene expression and poor patient prognosis. It thus highlights the utility of IL13Rα2 as a therapeutic target, and helps define patient populations most likely to respond to immunotherapy in present and future clinical trials. 相似文献
55.
56.
57.
Nina Fudge Charles D A Wolfe Christopher McKevitt 《BMJ (Clinical research ed.)》2008,336(7639):313-317
Objectives To understand how the policy of user involvement is interpreted in health service organisations and to identify factors that influence how user involvement is put into practice.Design Ethnographic study using participant observation, interviews, and collection of documentary evidence.Setting A multiagency modernisation programme to improve stroke services in two London boroughs.Participants Service users, National Health Service managers, and clinicians.Results User involvement in the programme was initiated and led by professionals. Professionals determined the areas of service improvement service users could participate in. A wide range of activities were considered “user involvement,” from patient satisfaction surveys to service users delivering peer support. Involvement tended to be most active in the least technical areas and areas with least input from clinicians. Factors that might explain this included organisational structure, the vagueness of the concept of user involvement, the value attributed to service users’ experiential knowledge, and variations in professional and service user understandings of and commitment to involvement. The gains of involvement were harder to identify in terms of impact on services. More evident were the personal gains for those involved: satisfaction of feeling listened to by professionals, social opportunities of meeting others in a similar situation, and increased knowledge about stroke and services available.Conclusions User involvement may not automatically lead to improved service quality. Healthcare professionals and service users understand and practise user involvement in different ways according to individual ideologies, circumstances, and needs. Given the resource implications of undertaking user involvement in service development there is a need for critical debate on the purpose of such involvement as well as better evidence of the benefits claimed for it. 相似文献
58.
59.
60.
Numerous functional ergatoid replacement reproductives were found in one colony of Nasutitermes columbicus in Panama. Their morphology was mainly workerlike, although several imaginal characters such as the compound eyes and variable wing buds were more or less developed. The sex organs were fully mature and the fat body of the females, not of the males, was of the “royal” type. The development of the eyes was not accompanied by the differentiation of the optic lobes of the brain, nor was the presence of wing buds correlated with a development of the wing muscles. 相似文献