全文获取类型
收费全文 | 5753篇 |
免费 | 385篇 |
国内免费 | 9篇 |
出版年
2023年 | 39篇 |
2022年 | 48篇 |
2021年 | 208篇 |
2020年 | 95篇 |
2019年 | 120篇 |
2018年 | 162篇 |
2017年 | 133篇 |
2016年 | 208篇 |
2015年 | 272篇 |
2014年 | 322篇 |
2013年 | 402篇 |
2012年 | 473篇 |
2011年 | 506篇 |
2010年 | 280篇 |
2009年 | 199篇 |
2008年 | 300篇 |
2007年 | 247篇 |
2006年 | 229篇 |
2005年 | 207篇 |
2004年 | 198篇 |
2003年 | 159篇 |
2002年 | 136篇 |
2001年 | 96篇 |
2000年 | 83篇 |
1999年 | 88篇 |
1998年 | 33篇 |
1997年 | 24篇 |
1995年 | 33篇 |
1994年 | 26篇 |
1993年 | 35篇 |
1992年 | 48篇 |
1991年 | 59篇 |
1990年 | 40篇 |
1989年 | 48篇 |
1988年 | 33篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 26篇 |
1984年 | 29篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1980年 | 23篇 |
1979年 | 39篇 |
1978年 | 21篇 |
1977年 | 31篇 |
1975年 | 20篇 |
1974年 | 25篇 |
1973年 | 27篇 |
1972年 | 26篇 |
1967年 | 19篇 |
排序方式: 共有6147条查询结果,搜索用时 187 毫秒
81.
Javed Nawab Mohammad Tahir Shah Kifayatullah Khan Roshan Ali 《International journal of phytoremediation》2015,17(9):801-813
Several anthropogenic and natural sources are considered as the primary sources of toxic metals in the environment. The current study investigates the level of heavy metals contamination in the flora associated with serpentine soil along the Mafic and Ultramafic rocks northern-Pakistan. Soil and wild native plant species were collected from chromites mining affected areas and analyzed for heavy metals (Cr, Ni, Fe, Mn, Co, Cu and Zn) using atomic absorption spectrometer (AAS-PEA-700). The heavy metal concentrations were significantly (p < 0.01) higher in mine affected soil as compared to reference soil, however Cr and Ni exceeded maximum allowable limit (250 and 60 mg kg?1, respectively) set by SEPA for soil. Inter-metal correlations between soil, roots and shoots showed that the sources of contamination of heavy metals were mainly associated with chromites mining. All the plant species accumulated significantly higher concentrations of heavy metals as compared to reference plant. The open dumping of mine wastes can create serious problems (food crops and drinking water contamination with heavy metals) for local community of the study area. The native wild plant species (Nepeta cataria, Impatiens bicolor royle, Tegetis minuta) growing on mining affected sites may be used for soil reclamation contaminated with heavy metals. 相似文献
82.
In this study, iron impregnated activated carbon (FeAC) was synthesized following an oxidation and iron impregnation of activated carbon (AC). Both the AC and FeAC were characterized by pHZPC and FTIR spectroscopy. The removal of Methylene Blue (MB) by AC and FeAC was examined under various experimental conditions. The FeAC showed up to 95% (higher than AC) MB removal in the pH range of 7–10. Although the reaction kinetics was pseudo–second order, the overall rate was controlled by a number of processes such as film diffusion, pore diffusion and intraparticle diffusion. The activation energy values for the MB uptake by AC and FeAC (21.79 and 14.82 kJ/mol, respectively) revealed a physisorption process. In the regeneration study, FeAC has shown consistently ≥ 90% MB removal even up to 10 repeated cycles. The reusable characteristic of the spent FeAC improved the practical use of activated carbon and can be a breakthrough for continuous flow system applications where it can work effectively without any significant reduction in its performance. 相似文献
83.
Mahfuzar Rahman Fatema Tuz Jhohura Sabuj Kanti Mistry Tridib Roy Chowdhury Tanveen Ishaque Rasheduzzaman Shah Kaosar Afsana 《PloS one》2015,10(9)
Objectives
A community based approach before, during and after child birth has been proven effective address the burden of maternal, neonatal and child morbidity and mortality in the low and middle income countries. We aimed to examine the overall change in maternal and newborn health outcomes due the “Improved Maternal Newborn and Child Survival” (IMNCS) project, which was implemented by BRAC in rural communities of Bangladesh.Methods
The intervention was implemented in four districts for duration of 5-years, while two districts served as comparison areas. The intervention was delivered by community health workers who were trained on essential maternal, neonatal and child health care services. A baseline survey was conducted in 2008 among 7, 200 women with pregnancy outcome in last year or having a currently alive child of 12–59 months. A follow-up survey was administered in 2012–13 among 4, 800 women of similar characteristics in the same villages.Findings
We observed significant improvements in maternal and essential newborn care in intervention areas over time, especially in health care seeking behaviors. The proportion of births taking place at home declined in the intervention districts from 84.3% at baseline to 71.2% at end line (P<0.001). Proportion of deliveries with skilled attendant was higher in intervention districts (28%) compared to comparison districts (27.4%). The number of deliveries was almost doubled at public sector facility comparing with baseline (P<0.001). Significant improvement was also observed in healthy cord care practice, delayed bathing of the new-born and reduction of infant mortality in intervention districts compared to that of comparison districts.Conclusions
This study demonstrates that community-based efforts offer encouraging evidence and value for combining maternal, neonatal and child health care package. This approach might be considered at larger scale in similar settings with limited resources. 相似文献84.
Camille Lebarbenchon Audrey Jaeger Chris Feare Matthieu Bastien Muriel Dietrich Christine Larose Erwan Lagadec Gérard Rocamora Nirmal Shah Hervé Pascalis Thierry Boulinier Matthieu Le Corre David E. Stallknecht Koussay Dellagi 《PLoS pathogens》2015,11(5)
Ducks and seabirds are natural hosts for influenza A viruses (IAV). On oceanic islands, the ecology of IAV could be affected by the relative diversity, abundance and density of seabirds and ducks. Seabirds are the most abundant and widespread avifauna in the Western Indian Ocean and, in this region, oceanic islands represent major breeding sites for a large diversity of potential IAV host species. Based on serological assays, we assessed the host range of IAV and the virus subtype diversity in terns of the islands of the Western Indian Ocean. We further investigated the spatial variation in virus transmission patterns between islands and identified the origin of circulating viruses using a molecular approach. Our findings indicate that terns represent a major host for IAV on oceanic islands, not only for seabird-related virus subtypes such as H16, but also for those commonly isolated in wild and domestic ducks (H3, H6, H9, H12 subtypes). We also identified strong species-associated variation in virus exposure that may be associated to differences in the ecology and behaviour of terns. We discuss the role of tern migrations in the spread of viruses to and between oceanic islands, in particular for the H2 and H9 IAV subtypes. 相似文献
85.
86.
87.
Sudhir Chandra Joshi Vishal Diwan Ashok J. Tamhankar Rita Joshi Harshada Shah Megha Sharma Ashish Pathak Ragini Macaden Cecilia St?lsby Lundborg 《PloS one》2015,10(5)
Background
Health care or biomedical waste, if not managed properly, can be of high risk to the hospital staff, the patients, the community, public health and the environment, especially in low and middle income settings where proper disposal norms are often not followed. Our aim was to explore perceptions of staff of an Indian rural tertiary care teaching hospital on hospital waste management.Method
A qualitative study was conducted using 10 focus group discussions (FGDs), with different professional groups, cleaning staff, nurses, medical students, doctors and administrators. The FGD guide included the following topics: (i) role of Health Care Waste Management (HCWM) in prevention of health care associated infections, (ii) awareness of and views about HCWM-related guidelines/legislation, (iii) current HCWM practices, (iv) perception and preparedness related to improvements of the current practices, and (v) proper implementation of the available guidelines/legislation. The FGDs were recorded, transcribed verbatim, translated to English (when conducted in Hindi) and analysed using content analysis.Results
Two themes were identified: Theme (A), ‘Challenges in integration of HCWM in organizational practice,’ with the categories (I) Awareness and views about HCWM, (II) Organizational practices regarding HCWM, and (III) Challenges in Implementation of HCWM; and Theme (B), ‘Interventions to improve HCWM,’ with three categories, (I) Educational and motivational interventions, (II) Organizational culture change, and (III) Policy-related interventions.Conclusion
A gap between knowledge and actual practice regarding HCWM was highlighted in the perception of the hospital staff. The participants suggested organizational changes, training and monitoring to address this. The information generated is relevant not merely to the microsystem studied but to other institutions in similar settings. 相似文献88.
The investigation of tissue magnetic susceptibility and the resultant magnetic field offers a new avenue for quantitative tissue characterisation by MRI. One crucial step in mining the phase and field data for relevant tissue information is the correction of externally induced field shifts. This article outlines a multistep approach comprising several methodologies for background field removal. The virtues of B
0 long-range variation detection and compensation of more localised external disturbances are unified in a sequential filter chain. The algorithm is tested by means of a numerical Monte Carlo simulation model and applied to in vivo measurements at 3T and 9.4T as well as to a fixed brain tissue measurement at 9.4T. Further, a comparison to conventional filter types has been undertaken. 相似文献
89.
Sree V. Chintapalli Gaurav Bhardwaj Reema Patel Natasha Shah Randen L. Patterson Damian B. van Rossum Andriy Anishkin Sean H. Adams 《PloS one》2015,10(6)
The mechanism(s) by which fatty acids are sequestered and transported in muscle have not been fully elucidated. A potential key player in this process is the protein myoglobin (Mb). Indeed, there is a catalogue of empirical evidence supporting direct interaction of globins with fatty acid metabolites; however, the binding pocket and regulation of the interaction remains to be established. In this study, we employed a computational strategy to elucidate the structural determinants of fatty acids (palmitic & oleic acid) binding to Mb. Sequence analysis and docking simulations with a horse (Equus caballus) structural Mb reference reveals a fatty acid-binding site in the hydrophobic cleft near the heme region in Mb. Both palmitic acid and oleic acid attain a “U” shaped structure similar to their conformation in pockets of other fatty acid-binding proteins. Specifically, we found that the carboxyl head group of palmitic acid coordinates with the amino group of Lys45, whereas the carboxyl group of oleic acid coordinates with both the amino groups of Lys45 and Lys63. The alkyl tails of both fatty acids are supported by surrounding hydrophobic residues Leu29, Leu32, Phe33, Phe43, Phe46, Val67, Val68 and Ile107. In the saturated palmitic acid, the hydrophobic tail moves freely and occasionally penetrates deeper inside the hydrophobic cleft, making additional contacts with Val28, Leu69, Leu72 and Ile111. Our simulations reveal a dynamic and stable binding pocket in which the oxygen molecule and heme group in Mb are required for additional hydrophobic interactions. Taken together, these findings support a mechanism in which Mb acts as a muscle transporter for fatty acid when it is in the oxygenated state and releases fatty acid when Mb converts to deoxygenated state. 相似文献
90.
Asma Iqbal Mahmoud Labib Darija Muharemagic Syed Sattar Brent R. Dixon Maxim V. Berezovski 《PloS one》2015,10(9)
There are currently no standard methods for the detection of Cryptosporidium spp., or other protozoan parasites, in foods, and existing methods are often inadequate, with low and variable recovery efficiencies. Food testing is difficult due to the low concentrations of parasites, the difficulty in eluting parasites from some foods, the lack of enrichment methods, and the presence of PCR inhibitors. The main objectives of the present study were to obtain DNA aptamers binding to the oocyst wall of C. parvum, and to use the aptamers to detect the presence of this parasite in foods. DNA aptamers were selected against C. parvum oocysts using SELEX (Systematic Evolution of Ligands by EXponential enrichment). Ten rounds of selection led to the discovery of 14 aptamer clones with high affinities for C. parvum oocysts. For detecting parasite-bound aptamers, a simple electrochemical sensor was employed, which used a gold nanoparticle-modified screen-printed carbon electrode. This aptasensor was fabricated by self-assembling a hybrid of a thiolated ssDNA primer and the anti- C. parvum aptamer. Square wave voltammetry was employed to quantitate C. parvum in the range of 150 to 800 oocysts, with a detection limit of approximately 100 oocysts. The high sensitivity and specificity of the developed aptasensor suggests that this novel method is very promising for the detection and identification of C. parvum oocysts on spiked fresh fruits, as compared to conventional methods such as microscopy and PCR. 相似文献