全文获取类型
收费全文 | 693篇 |
免费 | 72篇 |
专业分类
765篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 21篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 24篇 |
2015年 | 34篇 |
2014年 | 39篇 |
2013年 | 42篇 |
2012年 | 55篇 |
2011年 | 42篇 |
2010年 | 39篇 |
2009年 | 23篇 |
2008年 | 41篇 |
2007年 | 29篇 |
2006年 | 38篇 |
2005年 | 23篇 |
2004年 | 28篇 |
2003年 | 29篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1986年 | 9篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1967年 | 2篇 |
1962年 | 2篇 |
1959年 | 4篇 |
1954年 | 2篇 |
1953年 | 2篇 |
排序方式: 共有765条查询结果,搜索用时 0 毫秒
41.
Clara K. Chow Daniel J. Corsi Karen Lock Manisha Madhavan Pam Mackie Wei Li Sun Yi Yang Wang Sumathi Swaminathan Patricio Lopez-Jaramillo Diego Gomez-Arbelaez álvaro Avezum Scott A. Lear Gilles Dagenais Koon Teo Martin McKee Salim Yusuf 《PloS one》2014,9(11)
Background
Previous research has shown that environments with features that encourage walking are associated with increased physical activity. Existing methods to assess the built environment using geographical information systems (GIS) data, direct audit or large surveys of the residents face constraints, such as data availability and comparability, when used to study communities in countries in diverse parts of the world. The aim of this study was to develop a method to evaluate features of the built environment of communities using a standard set of photos. In this report we describe the method of photo collection, photo analysis instrument development and inter-rater reliability of the instrument.Methods/Principal Findings
A minimum of 5 photos were taken per community in 86 communities in 5 countries according to a standard set of instructions from a designated central point of each community by researchers at each site. A standard pro forma derived from reviewing existing instruments to assess the built environment was developed and used to score the characteristics of each community. Photo sets from each community were assessed independently by three observers in the central research office according to the pro forma and the inter-rater reliability was compared by intra-class correlation (ICC). Overall 87% (53 of 60) items had an ICC of ≥0.70, 7% (4 of 60) had an ICC between 0.60 and 0.70 and 5% (3 of 60) items had an ICC ≤0.50.Conclusions/Significance
Analysis of photos using a standardized protocol as described in this study offers a means to obtain reliable and reproducible information on the built environment in communities in very diverse locations around the world. The collection of the photographic data required minimal training and the analysis demonstrated high reliability for the majority of items of interest. 相似文献42.
Chinnapaka Somaiah Atul Kumar Darilang Mawrie Amit Sharma Suraj Dasharath Patil Jina Bhattacharyya Rajaram Swaminathan Bithiah Grace Jaganathan 《PloS one》2015,10(12)
Mesenchymal stem cells (MSC) can differentiate into several cell types and are desirable candidates for cell therapy and tissue engineering. However, due to poor cell survival, proliferation and differentiation in the patient, the therapy outcomes have not been satisfactory. Although several studies have been done to understand the conditions that promote proliferation, differentiation and migration of MSC in vitro and in vivo, still there is no clear understanding on the effect of non-cellular bio molecules. Of the many factors that influence the cell behavior, the immediate cell microenvironment plays a major role. In this context, we studied the effect of extracellular matrix (ECM) proteins in controlling cell survival, proliferation, migration and directed MSC differentiation. We found that collagen promoted cell proliferation, cell survival under stress and promoted high cell adhesion to the cell culture surface. Increased osteogenic differentiation accompanied by high active RHOA (Ras homology gene family member A) levels was exhibited by MSC cultured on collagen. In conclusion, our study shows that collagen will be a suitable matrix for large scale production of MSC with high survival rate and to obtain high osteogenic differentiation for therapy. 相似文献
43.
Justin M. Gifford Won Byoung Chae Kankshita Swaminathan Stephen P. Moose John A. Juvik 《Global Change Biology Bioenergy》2015,7(4):797-810
In light of rising energy costs, lignocellulosic ethanol has been identified as a renewable alternative to petroleum-based transportation fuels. In an attempt to reach government mandated ethanol production levels, potential plant biofeedstock candidates have been investigated, and cold-tolerant, perennial accessions within the C4 grass genus Miscanthus have been identified as leading contenders in the Midwestern US. To facilitate the development of improved cultivars through marker-assisted breeding, a quantitative trait locus (QTL) study was conducted on a full-sib, F1 mapping population segregating for flowering time, height, leaf width, and yield using a genetic map consisting of 846 segregating SNP and SSR markers. This was a 3 year study investigating the genetic architecture underlying traits important to biomass production in a population of 221 progeny from a cross between M. sinensis ‘Grosse Fountaine’ and M. sinensis ‘Undine’ established in the spring of 2010; 72 QTLs with LOD scores above the genome-wide, permuted threshold equivalent to a P-value of 0.05 were identified across 13 traits. Of the 36 QTLs identified in 2011, 22 were detected again the following year. Both the use of spring emergence and vigor rating as a covariate to account for variation related to differences in establishment increased the power to detect QTLs in the 2 year establishment period. Finally, a dry period in the middle of the 2012 growing season suggested that yield declines were due to a decrease in tiller diameter. 相似文献
44.
Biofiltration for treating VOCs: an overview 总被引:1,自引:0,他引:1
Swaminathan Detchanamurthy Peter Alan Gostomski 《Reviews in Environmental Science and Biotechnology》2012,11(3):231-241
In this paper we present a review of Biofiltration, one of the air pollution control technologies (APCT) used to treat volatile organic compounds (VOCs) effectively. It also talks about the history of biofiltration, and also proposes few ideas for the future developments in the biofiltration research pertaining to VOC control. Moreover, the paper also discusses about various important physical, chemical and biological factors which affect the performance of a biofilter both directly and indirectly. This paper will be handier for those who are new to the field of biofiltration research for VOC treatment. 相似文献
45.
Bin Ma Kevin M. Guckian Edward Yin-Shiang Lin Wen-Cherng Lee Daniel Scott Gnanasambandam Kumaravel Timothy L. Macdonald Kevin R. Lynch Cheryl Black Sowmya Chollate Kyungmin Hahm Gregg Hetu Ping Jin Yi Luo Ellen Rohde Anthony Rossomando Robert Scannevin Joy Wang Chunhua Yang 《Bioorganic & medicinal chemistry letters》2010,20(7):2264-2269
Modifying FTY720, an immunosuppressant modulator, led to a new series of well phosphorylated tetralin analogs as potent S1P1 receptor agonists. The stereochemistry effect of tetralin ring was probed, and (?)-(R)-2-amino-2-((S)-6-octyl-1,2,3,4-tetrahydronaphthalen-2-yl)propan-1-ol was identified as a good SphK2 substrate and potent S1P1 agonist with good oral bioavailability. 相似文献
46.
Nilufer Rahmioglu Toby Andrew Lynn Cherkas Gabriela Surdulescu Ramasamyiyer Swaminathan Tim Spector Kourosh R. Ahmadi 《PloS one》2009,4(2)
Background
The liver function test (LFT) is among the most commonly used clinical investigations to assess hepatic function, severity of liver diseases and the effect of therapies, as well as to detect drug-induced liver injury (DILI).Aims
To determine the relative contribution of genetic and environmental factors as well as test and quantify the effects of sex, age, BMI and alcohol consumption to variation in liver function test proteins - including alanine amino transaminase (ALT), Albumin, gamma glutamyl transpeptidase (GGT), total bilirubin, total protein, total globulin, aspartate transaminase (AST), and alkaline phosphotase (ALP) - using the classical twin model.Methods
Blood samples were collected from a total of 5380 twin pairs from the TwinsUK registry. We measured the expression levels of major proteins associated with the LFT, calculated BMI from measured weight and height and questionnaires were completed for alcohol consumption by the twins. The relative contribution of genetic and environmental factors to variation in the LFT proteins was assessed and quantified using a variance components model fitting approach.Results
Our results show that (1) variation in all the LFTs has a significant heritable basis (h2 ranging from 20% to 77%); (2) other than GGT, the LFTs are all affected to some extent by common environmental factors (c2 ranging from 24% to 54%); and (3) a small but significant proportion of the variation in the LFTs was due to confounding effects of age, sex, BMI, and alcohol use.Conclusions
Variation in the LFT proteins is under significant genetic and common environmental control although sex, alcohol use, age and BMI also contribute significantly to inter-individual variation in the LFT proteins. Understanding the underlying genetic contribution of liver function tests may help the interpretation of their results and explain wide variation among individuals. 相似文献47.
Sophia Vijay Soumya Swaminathan Preetish Vaidyanathan Aleyamma Thomas L. S. Chauhan Prahlad Kumar Sonali Chiddarwar Beena Thomas Puneet K. Dewan 《PloS one》2009,4(11)
Background
Provider-initiated HIV testing and counselling (PITC) is internationally recommended for tuberculosis (TB) patients, but the feasibility, effectiveness, and impact of this policy on the TB programme in India are unknown. We evaluated PITC of TB patients across two districts in India considered to have generalized HIV epidemics, Tiruchirappalli (population 2.5 million) and Mysore (population 2.8 million).Methodology/Principal Findings
Starting June 2007, healthcare providers in both districts were instructed to ascertain HIV status for all TB patients, and refer those with unknown HIV status to the nearest Integrated Counselling and Testing Centre (ICTC)—often in the same facility—for counselling and voluntary HIV testing. All TB patients registered from June 2007 to March 2008 were followed prospectively. Field investigators assessed PITC practices and abstracted data from routine TB programme records and HIV counselling registers to determine the proportion of TB patients appropriately evaluated for HIV infection. Patient records were traced to determine the efficiency of referral links to HIV care and antiretroviral treatment (ART). Between July 2007 and March 2008, 5299 TB patients were registered in both study districts. Of the 4701 with unknown HIV status at the time of TB treatment initiation, 3368 (72%) were referred to an ICTC, and 3111 (66%) were newly tested for HIV. PITC implementation resulted in the ascertainment of HIV status for 3709/5299 (70%) of TB patients, and detected 200 cases with previously undiagnosed HIV infection. Overall, 468 (8.8%) of all registered TB patients were HIV-infected; 177 (37%) were documented to have also received any ART.Conclusions
With implementation of PITC in India, HIV status was successfully ascertained for 70% of TB patients. Previously undiagnosed HIV-infection was detected in 6.4% of those TB patients newly tested, enabling referral for life-saving anti-retroviral treatment. ART uptake, however, was poor, suggesting that PITC implementation should include measures to strengthen and support ART referral, evaluation, and initiation. 相似文献48.
Lauren M. Uhler Nagalingeswaran Kumarasamy Kenneth H. Mayer Anjali Saxena Elena Losina Malaisamy Muniyandi Adam W. Stoler Zhigang Lu Rochelle P. Walensky Timothy P. Flanigan Melissa A. Bender Kenneth A. Freedberg Soumya Swaminathan for the CEPAC International investigators 《PloS one》2010,5(9)
Background
Indian guidelines recommend routine referral for HIV testing of all tuberculosis (TB) patients in the nine states with the highest HIV prevalence, and selective referral for testing elsewhere. We assessed the clinical impact and cost-effectiveness of alternative HIV testing referral strategies among TB patients in India.Methods and Findings
We utilized a computer model of HIV and TB disease to project outcomes for patients with active TB in India. We compared life expectancy, cost, and cost-effectiveness for three HIV testing referral strategies: 1) selective referral for HIV testing of those with increased HIV risk, 2) routine referral of patients in the nine highest HIV prevalence states with selective referral elsewhere (current standard), and 3) routine referral of all patients for HIV testing. TB-related data were from the World Health Organization. HIV prevalence among TB patients was 9.0% in the highest prevalence states, 2.9% in the other states, and 4.9% overall. The selective referral strategy, beginning from age 33.50 years, had a projected discounted life expectancy of 16.88 years and a mean lifetime HIV/TB treatment cost of US$100. The current standard increased mean life expectancy to 16.90 years with additional per-person cost of US$10; the incremental cost-effectiveness ratio was US$650/year of life saved (YLS) compared to selective referral. Routine referral of all patients for HIV testing increased life expectancy to 16.91 years, with an incremental cost-effectiveness ratio of US$730/YLS compared to the current standard. For HIV-infected patients cured of TB, receiving antiretroviral therapy increased survival from 4.71 to 13.87 years. Results were most sensitive to the HIV prevalence and the cost of second-line antiretroviral therapy.Conclusions
Referral of all patients with active TB in India for HIV testing will be both effective and cost-effective. While effective implementation of this strategy would require investment, routine, voluntary HIV testing of TB patients in India should be recommended. 相似文献49.
Clostridium botulinum neurotoxins are zinc endopeptidase proteins responsible for cleaving specific peptide bonds of proteins of neuroexocytosis apparatus. The ability of drugs to interfere with toxin's catalytic activity is being evaluated with zinc chelators and metalloprotease inhibitors. It is important to develop effective pharmacological treatment for the intact holotoxin before the catalytic domain separates and enters the cytosol. We present here evidence for a novel mechanism of an inhibitor binding to the holotoxin and for the chelation of zinc from our structural studies on Clostridium botulinum neurotoxin type B in complex with a potential metalloprotease inhibitor, bis(5-amidino-2-benzimidazolyl)methane, and provide snapshots of the reaction as it progresses. The binding and inhibition mechanism of this inhibitor to the neurotoxin seems to be unique for intact botulinum neurotoxins. The environment of the active site rearranges in the presence of the inhibitor, and the zinc ion is gradually removed from the active site and transported to a different site in the protein, probably causing loss of catalytic activity. 相似文献
50.
A novel, cost effective and time saving technique for primary cell culture from gills and kidney using fish serum has been developed. Single cell suspension of gills and kidney of Clarias gariepinus was obtained by trypsinization. Minimum essential medium supplemented with 10% fish serum in place of 10% foetal calf serum and 20% fish muscle extract, yielded confluent monolayer on 6th and 8th day in gill and kidney tissue respectively at 28 degrees C. Fish serum can be successfully used as media supplement for cultivation and maintenance of primary cell culture from fishes. 相似文献