全文获取类型
收费全文 | 2409篇 |
免费 | 192篇 |
国内免费 | 1篇 |
专业分类
2602篇 |
出版年
2023年 | 7篇 |
2022年 | 22篇 |
2021年 | 45篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 41篇 |
2017年 | 29篇 |
2016年 | 75篇 |
2015年 | 125篇 |
2014年 | 131篇 |
2013年 | 170篇 |
2012年 | 225篇 |
2011年 | 219篇 |
2010年 | 138篇 |
2009年 | 121篇 |
2008年 | 153篇 |
2007年 | 163篇 |
2006年 | 126篇 |
2005年 | 132篇 |
2004年 | 122篇 |
2003年 | 107篇 |
2002年 | 102篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 15篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有2602条查询结果,搜索用时 15 毫秒
61.
Brian Huntley Judy R. M. Allen Yvonne C. Collingham Thomas Hickler Adrian M. Lister Joy Singarayer Anthony J. Stuart Martin T. Sykes Paul J. Valdes 《PloS one》2013,8(4)
Whereas fossil evidence indicates extensive treeless vegetation and diverse grazing megafauna in Europe and northern Asia during the last glacial, experiments combining vegetation models and climate models have to-date simulated widespread persistence of trees. Resolving this conflict is key to understanding both last glacial ecosystems and extinction of most of the mega-herbivores. Using a dynamic vegetation model (DVM) we explored the implications of the differing climatic conditions generated by a general circulation model (GCM) in “normal” and “hosing” experiments. Whilst the former approximate interstadial conditions, the latter, designed to mimic Heinrich Events, approximate stadial conditions. The “hosing” experiments gave simulated European vegetation much closer in composition to that inferred from fossil evidence than did the “normal” experiments. Given the short duration of interstadials, and the rate at which forest cover expanded during the late-glacial and early Holocene, our results demonstrate the importance of millennial variability in determining the character of last glacial ecosystems. 相似文献
62.
Jasper van der Slegt Lijckle van der Laan Eelco J. Veen Yvonne Hendriks Jannie Romme Jan Kluytmans 《PloS one》2013,8(8)
Background
Surgical site infections (SSI’s) are associated with severe morbidity, mortality and increased health care costs in vascular surgery.Objective
To implement a bundle of care in vascular surgery and measure the effects on the overall and deep-SSI’s rates.Design
Prospective, quasi-experimental, cohort study.Methods
A prospective surveillance for SSI’s after vascular surgery was performed in the Amphia hospital in Breda, from 2009 through 2011. A bundle developed by the Dutch hospital patient safety program (DHPSP) was introduced in 2009. The elements of the bundle were (1) perioperative normothermia, (2) hair removal before surgery, (3) the use of perioperative antibiotic prophylaxis and (4) discipline in the operating room. Bundle compliance was measured every 3 months in a random sample of surgical procedures and this was used for feedback.Results
Bundle compliance improved significantly from an average of 10% in 2009 to 60% in 2011. In total, 720 vascular procedures were performed during the study period and 75 (10.4%) SSI were observed. Deep SSI occurred in 25 (3.5%) patients. Patients with SSI’s (28,5±29.3 vs 10.8±11.3, p<0.001) and deep-SSI’s (48.3±39.4 vs 11.4±11.8, p<0.001) had a significantly longer length of hospital stay after surgery than patients without an infection. A significantly higher mortality was observed in patients who developed a deep SSI (Adjusted OR: 2.96, 95% confidence interval 1.32–6.63). Multivariate analysis showed a significant and independent decrease of the SSI-rate over time that paralleled the introduction of the bundle. The SSI-rate was 51% lower in 2011 compared to 2009.Conclusion
The implementation of the bundle was associated with improved compliance over time and a 51% reduction of the SSI-rate in vascular procedures. The bundle did not require expensive or potentially harmful interventions and is therefore an important tool to improve patient safety and reduce SSI’s in patients undergoing vascular surgery. 相似文献63.
Yvonne Dzierma Frank G. Nuesken Jochen Fleckenstein Stephanie Kremp Norbert P. Licht Christian Ruebe 《PloS one》2013,8(1)
Respiratory motion during percutaneous radiotherapy can be considered based on respiration-correlated computed tomography (4DCT). However, most treatment planning systems perform the dose calculation based on a single primary CT data set, even though cine mode displays may allow for a visualisation of the complete breathing cycle. This might create the mistaken impression that the dose distribution were independent of tumour motion. We present a movie visualisation technique with the aim to direct attention to the fact that the dose distribution migrates to some degree with the tumour and discuss consequences for gated treatment, IMRT plans and flattening-filter-free beams. This is a feasibility test for a visualisation of tumour and isodose motion. Ten respiratory phases are distinguished on the CT, and the dose distribution from a stationary IMRT plan is calculated on each phase, to be integrated into a movie of tumour and dose motion during breathing. For one example patient out of the sample of five lesions, the plan is compared with a gated treatment plan with respect to tumour coverage and lung sparing. The interplay-effect for small segments in the IMRT plan is estimated. While the high dose rate, together with the cone-shaped beam profile, makes the use of flattening-filter-free beams more problematic for conformal and IMRT treatment, it can be the option of choice if gated treatment is preferred. The different effects of respiratory motion, dose build-up and beam properties (segments and flatness) for gated vs. un-gated treatment can best be considered if planning is performed on the full 4DCT data set, which may be an incentive for future developments of treatment planning systems. 相似文献
64.
65.
Ezrin and HNRNP expression correlate with increased virus release rate and early onset of virus‐induced apoptosis of MDCK suspension cells 下载免费PDF全文
Sabine Kluge Yvonne Genzel Kim Laus Anja Serve Antje Pflugmacher Britta Peschel Erdmann Rapp Udo Reichl 《Biotechnology journal》2016,11(10):1332-1342
With the aim to adapt high‐yield adherent cell lines to suspension growth, Madin Darby canine kidney (MDCK) suspension cells were developed recently that achieved comparable influenza virus yields despite an early induction of apoptosis compared to the parental adherent cell line. For both cell lines, a comprehensive study under comparable infection conditions is performed comprising information on: time course of viral infection, antiviral state of cells, virus‐induced apoptosis, and virus‐induced cellular protein expression for early and late infection with influenza A/PuertoRico/8/34 H1N1. The proteomic analysis is performed with 2D differential gel electrophoreses followed by mass spectrometry. Based on flow cytometric data and on the differential expression of various stress and apoptosis‐related proteins, the earlier onset of virus‐induced apoptosis is confirmed for suspension cells. Surprisingly, the data indicated an increased virus release rate for suspension cells. These observations correlate with an increased expression of the apical marker protein ezrin, known to play a role in influenza‐induced cytoskeletal rearrangement, and the differential expression of heterogeneous nuclear ribonucleoproteins, known to bind actively influenza viral proteins and play a central role in regulating gene expression. Based on these findings, additional studies towards the design of MDCK suspension cells with further increase in influenza virus yields will be performed. 相似文献
66.
Obesity and Age‐Related Changes in Markers of Oxidative Stress and Inflammation Across Four Generations 下载免费PDF全文
67.
Human pluripotent stem cells (hPSCs) represent a platform to study human development in vitro under both normal and disease conditions. Researchers can direct the differentiation of hPSCs into the cell type of interest by manipulating the culture conditions to recapitulate signals seen during development. One such cell type is the melanocyte, a pigment-producing cell of neural crest (NC) origin responsible for protecting the skin against UV irradiation. This protocol presents an extension of a currently available in vitro Neural Crest differentiation protocol from hPSCs to further differentiate NC into fully pigmented melanocytes. Melanocyte precursors can be enriched from the Neural Crest protocol via a timed exposure to activators of WNT, BMP, and EDN3 signaling under dual-SMAD-inhibition conditions. The resultant melanocyte precursors are then purified and matured into fully pigmented melanocytes by culture in a selective medium. The resultant melanocytes are fully pigmented and stain appropriately for proteins characteristic of mature melanocytes. 相似文献
68.
Introduction
There is limited research on Autism Spectrum Disorders (ASD) in females. Although the empathy construct has been examined thoroughly in autism, little attention has been paid to empathy in adult women with this condition or to gender differences within the disorder.Objective
Self-reported empathy in adult women with ASD was examined and compared to that of typically developed men and women as well as to men with this condition.Methods
Online databases were searched for articles investigating self-reported empathy among adult women with ASD. Only six studies comparing women to men were identified.Results
All studies found women with an ASD to report lower levels of empathy than typically developed women, and typically developed men, but similar levels to men with this condition.Conclusion
The self-reported empathic ability of women diagnosed with ASD resembles that of their male counterparts most closely; they show a hypermasculinisation in empathy. This is particularly surprising considering the large gender difference in empathy in the general population.Discussion
One of the limitations of this review is that the current diagnostic criteria for ASD are oriented towards male-specific behaviour and fail to integrate gender specific characteristics. Hence, women diagnosed with ASD are likely to be at the male end of the continuum. The suggested hypermasculinisation of women on the spectrum, as evident from this review, may therefore be exaggerated due to a selection bias. 相似文献69.
Charlotte G. W. Seijger Gea Drost Joram M. Posma Baziel G. M. van Engelen Yvonne F. Heijdra 《PloS one》2016,11(3)
Background
In this large observational study population of 105 myotonic dystrophy type 1 (DM1) patients, we investigate whether bodyweight is a contributor of total lung capacity (TLC) independent of the impaired inspiratory muscle strength.Methods
Body composition was assessed using the combination of body mass index (BMI) and fat-free mass index. Pulmonary function tests and respiratory muscle strength measurements were performed on the same day. Patients were stratified into normal (BMI < 25 kg/m2) and overweight (BMI ≥ 25 kg/m2) groups. Multiple linear regression was used to find significant contributors for TLC.Results
Overweight was present in 59% of patients, and body composition was abnormal in almost all patients. In overweight patients, TLC was significantly (p = 2.40×10−3) decreased, compared with normal-weight patients, while inspiratory muscle strength was similar in both groups. The decrease in TLC in overweight patients was mainly due to a decrease in expiratory reserve volume (ERV) further illustrated by a highly significant (p = 1.33×10−10) correlation between BMI and ERV. Multiple linear regression showed that TLC can be predicted using only BMI and the forced inspiratory volume in 1 second, as these were the only significant contributors.Conclusions
This study shows that, in DM1 patients, overweight further reduces lung volumes, as does impaired inspiratory muscle strength. Additionally, body composition is abnormal in almost all DM1 patients. 相似文献70.
Yvonne Schaffler Etzel Cardeña Sophie Reijman Daniela Haluza 《Culture, medicine and psychiatry》2016,40(1):74-99
Recent studies in African contexts have revealed a strong association between spirit possession and severe trauma, with inclusion into a possession cult serving at times a therapeutic function. Research on spirit possession in the Dominican Republic has so far not included quantitative studies of trauma and dissociation. This study evaluated demographic variables, somatoform dissociative symptoms, and potentially traumatizing events in the Dominican Republic with a group of Vodou practitioners that either do or do not experience spirit possession. Inter-group comparisons revealed that in contrast to non-possessed participants (n = 38), those experiencing spirit possession (n = 47) reported greater somatoform dissociation, more problems with sleep, and previous exposure to mortal danger such as assaults, accidents, or diseases. The two groups did not differ significantly in other types of trauma. The best predictor variable for group classification was somatoform dissociation, although those items could also reflect the experience of followers during a possession episode. A factor analysis across variables resulted in three factors: having to take responsibility early on in life and taking on a professional spiritual role; traumatic events and pain; and distress/dissociation. In comparison with the non-possessed individuals, the possessed ones did not seem to overall have a remarkably more severe story of trauma and seemed to derive economic gains from possession practice. 相似文献