全文获取类型
收费全文 | 2086篇 |
免费 | 127篇 |
国内免费 | 4篇 |
专业分类
2217篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 32篇 |
2021年 | 53篇 |
2020年 | 41篇 |
2019年 | 40篇 |
2018年 | 50篇 |
2017年 | 52篇 |
2016年 | 73篇 |
2015年 | 89篇 |
2014年 | 136篇 |
2013年 | 168篇 |
2012年 | 167篇 |
2011年 | 206篇 |
2010年 | 127篇 |
2009年 | 106篇 |
2008年 | 131篇 |
2007年 | 138篇 |
2006年 | 119篇 |
2005年 | 94篇 |
2004年 | 79篇 |
2003年 | 60篇 |
2002年 | 84篇 |
2001年 | 16篇 |
2000年 | 5篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2217条查询结果,搜索用时 15 毫秒
61.
Biological Trace Element Research - Vanadium (V) has not been elucidated as an essential mineral in ruminants, though in lower organisms and rat model, its role is well known as insulin—a... 相似文献
62.
Plant Molecular Biology - The design and use of existing VIGS vectors for revealing monocot gene functions are described and potential new vectors are discussed, which may expand their repertoire.... 相似文献
63.
Amyotrophic lateral sclerosis (ALS), a progressive motor-neurone disease, affects individuals usually aged between 50 and 70 years. C21orf2, recently identified as the new ALS susceptibility gene, harbours rare missense mutations that cause this fatal disease. We used bioinformatics and molecular modelling approaches to study specific ALS-associated mutations in C21orf2. Both native and mutant structures of the protein obtained from homology modelling were analysed in detail to gain insights into the potential impact of these mutations on the protein structure and its function. Our analyses reveal that more than 75% of the mutations are likely to be deleterious. These effects seem to carry through to mouse C21orf2 as well, indicating that mouse would make a viable animal model to study this ALS gene in detail. 相似文献
64.
65.
Luciana de Brito Vargas Marcia H Beltrame Brenda Ho Wesley M Marin Ravi Dandekar Gonzalo Montero-Martín Marcelo A Fernndez-Via A Magdalena Hurtado Kim R Hill Luiza T Tsuneto Mara H Hutz Francisco M Salzano Maria Luiza Petzl-Erler Jill A Hollenbach Danillo G Augusto 《Molecular biology and evolution》2022,39(1)
The killer-cell immunoglobulin-like receptors (KIR) recognize human leukocyte antigen (HLA) molecules to regulate the cytotoxic and inflammatory responses of natural killer cells. KIR genes are encoded by a rapidly evolving gene family on chromosome 19 and present an unusual variation of presence and absence of genes and high allelic diversity. Although many studies have associated KIR polymorphism with susceptibility to several diseases over the last decades, the high-resolution allele-level haplotypes have only recently started to be described in populations. Here, we use a highly innovative custom next-generation sequencing method that provides a state-of-art characterization of KIR and HLA diversity in 706 individuals from eight unique South American populations: five Amerindian populations from Brazil (three Guarani and two Kaingang); one Amerindian population from Paraguay (Aché); and two urban populations from Southern Brazil (European and Japanese descendants from Curitiba). For the first time, we describe complete high-resolution KIR haplotypes in South American populations, exploring copy number, linkage disequilibrium, and KIR–HLA interactions. We show that all Amerindians analyzed to date exhibit the lowest numbers of KIR–HLA interactions among all described worldwide populations, and that 83–97% of their KIR–HLA interactions rely on a few HLA-C molecules. Using multiple approaches, we found signatures of strong purifying selection on the KIR centromeric region, which codes for the strongest NK cell educator receptors, possibly driven by the limited HLA diversity in these populations. Our study expands the current knowledge of KIR genetic diversity in populations to understand KIR–HLA coevolution and its impact on human health and survival. 相似文献
66.
67.
Hoti SL Vasuki V Lizotte MW Patra KP Ravi G Vanamail P Manonmani A Sabesan S Krishnamoorthy K Williams SA 《Bulletin of entomological research》2001,91(2):87-92
An Hha 1 based polymerase chain reaction (PCR) assay developed for the detection of Brugia malayi, the causative agent of Brugian lymphatic filariasis, was evaluated for its sensitivity in the laboratory and for its usefulness in measuring changes in transmission of the disease in the field. Laboratory studies showed that the new assay was highly sensitive in comparison with the standard dissection and microscopy technique. The assay can detect as little as 4 pg of parasite DNA or a single microfilaria in pools of up to 100 mosquitoes. The optimum pool size for convenience was found to be 50 mosquitoes per pool. The efficacy of PCR assay was evaluated in filariasis control programmes in operation in endemic areas of Kerala State, South India. The infection rates obtained by the Hha I PCR assay and the conventional dissection and microscopy technique were 1.2% and 1.7% respectively in operational areas and 8.3% and 4.4% respectively, in check areas, which were not significantly different (P < 0.05). Thus, the Hha I PCR assay was found to be as sensitive as the conventional technique and hence it can be used as a new epidemiological tool for assessing parasite infection in field-collected mosquitoes. 相似文献
68.
Nancy L. Wilczynski R. Brian Haynes John N. Lavis Ravi Ramkissoonsingh Alexandra E. Arnold-Oatley The HSR Hedges Team 《CMAJ》2004,171(10):1179-1185
Background
Evidence from health services research (HSR) is currently thinly spread through many journals, making it difficult for health services researchers, managers and policy-makers to find research on clinical practice guidelines and the appropriateness, process, outcomes, cost and economics of health care services. We undertook to develop and test search terms to retrieve from the MEDLINE database HSR articles meeting minimum quality standards.Methods
The retrieval performance of 7445 methodologic search terms and phrases in MEDLINE (the test) were compared with a hand search of the literature (the gold standard) for each issue of 68 journal titles for the year 2000 (a total of 25 936 articles). We determined sensitivity, specificity and precision (the positive predictive value) of the MEDLINE search strategies.Results
A majority of the articles that were classified as outcome assessment, but fewer than half of those in the other categories, were considered methodologically acceptable (no methodologic criteria were applied for cost studies). Combining individual search terms to maximize sensitivity, while keeping specificity at 50% or more, led to sensitivities in the range of 88.1% to 100% for several categories (specificities ranged from 52.9% to 97.4%). When terms were combined to maximize specificity while keeping sensitivity at 50% or more, specificities of 88.8% to 99.8% were achieved. When terms were combined to maximize sensitivity and specificity while minimizing the differences between the 2 measurements, most strategies for HSR categories achieved sensitivity and specificity of at least 80%.Interpretation
Sensitive and specific search strategies were validated for retrieval of HSR literature from MEDLINE. These strategies have been made available for public use by the US National Library of Medicine at www.nlm.nih.gov/nichsr/hedges/search.html.With the increasing emphasis on “using evidence” and “value for money” in health services, it is essential that researchers, clinicians, health system managers and public policy-makers be able to retrieve relevant, high-quality reports of health services research (HSR). Efficiently retrieved research evidence can aid in decision-making about which services to provide and in the resource allocation decisions to support those services, reducing the need for arbitrary decisions and aiding collaboration with clinicians and consumers.1 MEDLINE is a huge and expanding bibliographic resource that is freely available to all with Internet access. Yet the volume of the literature often overwhelms both clinicians and health system decision-makers.2,3 End-users of MEDLINE and other large bibliographic databases have difficulty executing precise searches2,3 and are often unaware of what kind of information to seek, where to find it3,4 and how to judge its quality.3HSR has been defined as the scientific study of the effect of health care delivery; the organization and management of health care access, quality, cost and financing; and the evaluation of the impact of health services and technology (Allmang NA, Koonce TY. Health services research topic searches. Bethesda [MD]: National Library of Medicine; 2000. Unpublished report). More recently, HSR has been defined as the multidisciplinary field of scientific investigation that studies how social factors, financing systems, organizational structures and processes, health technologies and personal behaviours affect access to health care, the quality and cost of health care and, ultimately, health and well-being.5 HSR articles constitute only a tiny fraction of the MEDLINE database and are spread through a large number of journals; hence, MEDLINE searching is challenging. Conversely, journal browsing is impractical as a means of retrieving all relevant studies for a given question or staying abreast of the literature. Our aim was to develop methodologic search filters for MEDLINE to enable end-users to efficiently retrieve articles of relevance to clinical practice guidelines (CPGs) and the appropriateness, process, outcomes, cost and economics of health services. 相似文献69.
Three deoxypreussomerins, palmarumycins CP1, JC1 and JC2, have been isolated from a collection of the stems of Jatropha curcas. The second and third compounds are antibacterial constituents which were characterized from spectral evidence. The X-ray crystallographic structure of palmarumycin JC1 was also studied. Deoxypreussomerins have been obtained here from a plant source in appreciable quantities. 相似文献
70.
Medicinal herbs used in indigenous medicines for the management of diabetes mellitus contain both organic and inorganic constituents.
Some of these inorganic trace elements possess antidiabetic properties, which accounts for the activity of medicinal herbs.
The aim of this study was to analyze the inorganic trace elements present in Eugenia jambolana seeds and to evaluate the hypoglycemic activity of the inorganic part of E. jambolana seeds on streptozotocin-induced diabetes. The seeds of E. jambolana seeds were reduced to ash and the inorganic elements present were assayed. The hypoglycemic efficacy of the inorganic part
was tested by the glucose tolerance test on streptozotocin-induced diabetes. Elements such as zinc, chromium, vanadium, potassium,
and sodium, possessing hypoglycemic activity, were present in the seed. The E. jambolana seed ashtreated diabetic rats exhibited normoglycemia and better glucose tolerance. The conclusion that the inorganic constituents
might play a important role in the antidiabetic nature E. jambolana seeds was reached. 相似文献