全文获取类型
收费全文 | 2642篇 |
免费 | 288篇 |
国内免费 | 160篇 |
出版年
2024年 | 7篇 |
2023年 | 56篇 |
2022年 | 50篇 |
2021年 | 90篇 |
2020年 | 103篇 |
2019年 | 123篇 |
2018年 | 108篇 |
2017年 | 114篇 |
2016年 | 97篇 |
2015年 | 114篇 |
2014年 | 160篇 |
2013年 | 192篇 |
2012年 | 95篇 |
2011年 | 121篇 |
2010年 | 96篇 |
2009年 | 140篇 |
2008年 | 145篇 |
2007年 | 154篇 |
2006年 | 112篇 |
2005年 | 91篇 |
2004年 | 96篇 |
2003年 | 93篇 |
2002年 | 64篇 |
2001年 | 64篇 |
2000年 | 56篇 |
1999年 | 59篇 |
1998年 | 39篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 28篇 |
1992年 | 35篇 |
1991年 | 21篇 |
1990年 | 30篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有3090条查询结果,搜索用时 15 毫秒
1.
《Revista espa?ola de geriatría y gerontología》2020,55(1):11-17
Background and objectiveThe aim of this study was to determine the clinical and functional outcomes of patients discharged to nursing homes after a hip fracture.MethodsThe study included all patients admitted to a group of nursing homes after a hip fracture in 2016. A geriatric assessment protocol was applied, and patients were treated with a specific protocol for 90 days. They were assessed for nutritional status (Mini-Nutritional Assessment and Body Mass Index), pain (Visual Analogue Scale, and the PAINAD Scale), the presence of pressure ulcers, blood test (D vitamin, haemoglobin, proteins), and functional status (Barthel index and Functional Assessment Categories).ResultsOut of a total of 175 patients, 116 (75%) met the inclusion criteria. The mean age was 84.9 years old (±6.7 SD), and 91 (78.4%) were women. At admission, 73.8% of 65 residents had anaemia, 76.7% hypovitaminosis D, 88% malnutrition or «at risk of malnutrition», and 15.3% had pressure ulcers. After 90 days, the moderate-severe functional status (Barthel index < 60) was reduced from 90.4 to 39.6%, dependence due to gait from 97.3 to 36.1%, and moderate-severe pain from 88.9 to 14.4%. Most of the pressure ulcers healed (94.4%).ConclusionsPatients admitted to nursing homes after a hip fracture had poor clinical and functional status. This study shows that after 90 days from admission these patients had positive outcomes in terms of functionality, gait, pain control, and pressure ulcers healing. 相似文献
2.
Musculoskeletal modeling allows for analysis of individual muscles in various situations. However, current techniques to realistically simulate muscle response when significant amounts of intentional coactivation is required are inadequate. This would include stiffening the neck or spine through muscle coactivation in preparation for perturbations or impacts. Muscle coactivation has been modeled previously in the neck and spine using optimization techniques that seek to maximize the joint stiffness by maximizing total muscle activation or muscle force. These approaches have not sought to replicate human response, but rather to explore the possible effects of active muscle. Coactivation remains a challenging feature to include in musculoskeletal models, and may be improved by extracting optimization objective functions from experimental data. However, the components of such an objective function must be known before fitting to experimental data. This study explores the effect of components in several objective functions, in order to recommend components to be used for fitting to experimental data. Four novel approaches to modeling coactivation through optimization techniques are presented, two of which produce greater levels of stiffness than previous techniques. Simulations were performed using OpenSim and MATLAB cooperatively. Results show that maximizing the moment generated by a particular muscle appears analogous to maximizing joint stiffness. The approach of optimizing for maximum moment generated by individual muscles may be a good candidate for developing objective functions that accurately simulate muscle coactivation in complex joints. This new approach will be the focus of future studies with human subjects. 相似文献
3.
《Current biology : CB》2020,30(13):2433-2445.e3
Media player
4.
The genetic diversity of a clonal sedge (Tertraria capillaris) was assessed using isozyme analysis of 11 loci. Of 29 enzyme systems tested, eight were selected which gave interpretable bands with consistently good resolution. Though seedlings of the species are rarely observed in nature, isozyme analysis showed that for the study transects containing 100 sample plants, the majority of plants at the site were sexually rather than clonally derived. Young plants generated from embryos grown in vitro from excised seeds showed a high level of genetic diversity which could account for the genetic diversity measured in the parent population. In terms of restoration of the species, 85% of the assessed genetic diversity at the study site could be retained if 25 T. capillaris plants were taken at random. The study illustrates how genetic assessment coupled with tissue culture methods provides a feasible model for the recovery of most of the assessed local genetic diversity of a clonal species. 相似文献
5.
Saldanha Bay,South Africa: recovery of Gracilaria verrucosa (Gracilariales,Rhodophyta) 总被引:2,自引:2,他引:0
Since World War II the greater Saldanha Bay lagoon system, South Africa, has been an important Gracilaria producer. Two agar factories, built in the 1960's, used Gracilaria from Saldanha Bay as their raw material. In the early 1970's the industry was destroyed as a result of dredging and marine construction operations to establish a harbor in the bay for loading ore. These environmental changes destroyed stocks and prevented the previously significant beachings of the seaweed from occurring. After a few years of no or very low commercial production, the resource slowly started to recover. The size of Gracilaria drifts increased over the following eight years to approximately one-third of the original output. This trend seems to continue. Although the stocks and resultant drifts are unlikely to recover fully to their original quantity, current production is already sufficient to ensure re-establishment of a seaweed industry in Saldanha Bay. This could have considerable socio-economic impact on the area. 相似文献
6.
Malika Virah-Sawmy Katherine J. Willis Lindsey Gillson 《Global Ecology and Biogeography》2009,18(1):98-110
Aim Coastal biodiversity hotspots are globally threatened by sea‐level rise. As such it is important to understand how ecosystems resist, respond and adapt to sea‐level rise. Using pollen, geochemistry, charcoal and diatom records in conjunction with previously published palaeoclimatic records, we investigated the mechanism, interactions and ecosystem response and resilience of Madagascar's littoral forest to late Holocene sea‐level rise. Location Sediment sequences were collected along the south‐east coast of Madagascar in two adjacent habitats in Mandena; the highly diverse littoral forest fragment and species‐poor Erica‐matrix. Methods We used a multi‐proxy approach to investigate the relative influence of environmental changes on the littoral ecosystem. We reconstructed past vegetation and fire dynamics over the past 6500 years at two sites in the littoral forest using fossil pollen and macrofossil charcoal contained in sedimentary sequences. Alongside these records we reconstructed past marine transgressions from the same sedimentary sequences using geochemical analyses, and a salinity and drought index through the analysis of fossil diatoms. Results Our findings indicated that it was the synergistic effect of sea‐level rise coupled with rainfall deficits that triggered a threshold event with a switch from two types of littoral forest (an open Uapaca forest and a closed littoral forest fragment) to an Erica–Myrica heath/grassland occurring in approximately less than 100 years. Resilience to sea‐level rise differed in the two adjacent habitats, suggesting that the littoral forest fragment was more resilient to the impacts of sea‐level change and aridity than the open Uapaca woodland. Conclusions We demonstrated that the littoral ecosystem was influenced by late Holocene sea‐level rise and climatic desiccation. While climate change‐integrated conservation strategies address the effects of climate change on species distribution and dispersal, our work suggests that more attention should be paid to the impacts of interactive climatic variables that affect ecosystem thresholds. 相似文献
7.
Christian Alvarez Glaucia Gon?alves Barbosa Raquel de Vasconcellos Carvalhaes de Oliveira Bernardina Penarrieta Morales Bodo Wanke Márcia dos Santos Lazéra 《Memórias do Instituto Oswaldo Cruz》2013,108(1):126-129
In this study, we evaluated several techniques for the detection of the yeast form of Cryptococcus in decaying wood and measured the viability of these fungi in environmental samples stored in the laboratory. Samples were collected from a tree known to be positive for Cryptococcus and were each inoculated on 10 Niger seed agar (NSA) plates. The conventional technique (CT) yielded a greater number of positive samples and indicated a higher fungal density [in colony forming units per gram of wood (CFU.g-1) ] compared to the humid swab technique (ST). However, the difference in positive and false negative results between the CT-ST was not significant. The threshold of detection for the CT was 0.05.103 CFU.g-1, while the threshold for the ST was greater than 0.1.103 CFU-1. No colonies were recovered using the dry swab technique. We also determined the viability of Cryptococcus in wood samples stored for 45 days at 25ºC using the CT and ST and found that samples not only continued to yield a positive response, but also exhibited an increase in CFU.g-1, suggesting that Cryptococcus is able to grow in stored environmental samples. The ST.1, in which samples collected with swabs were immediately plated on NSA medium, was more efficient and less laborious than either the CT or ST and required approximately 10 min to perform; however, additional studies are needed to validate this technique. 相似文献
8.
9.
10.
Senescence is a progressive biological process expressed in behavioural, morphological, physiological, biochemical and cellular age-related changes. Age-associated alterations in activity are regularly found in insects when examining whole-organism senescence over the adult lifespan. In addition, overall stress resistance usually decreases with senescence. In the present study, we measured the critical thermal minimum (CTmin) and the subsequent recovery period over the lifespan of the sub-Antarctic wingless fly, Anatalanta aptera. Experiments were conducted on males and females in seven age groups: newly emerged, 1.5-, 5-, 7-, 13-, 15- and 18-month-old adults. Surprisingly, CTmin decreased significantly with ageing in A. aptera, from −3.8 ± 0.5°C just after the emergence to −5.6 ± 0.7°C in the 18-month-old flies. The subsequent recovery period remained similar between the seven groups tested. Our unexpected results contradict the previous data collected in other insects. We have demonstrated for the first time that ageing may improve rather than impair locomotor activity during unfavourable thermal conditions. It raises questions and challenges the literature dealing with ageing. These fascinating results also question the underpinning mechanisms involved in the improvement of the thermal performance with ageing in A. aptera. 相似文献