全文获取类型
收费全文 | 2461篇 |
免费 | 405篇 |
国内免费 | 2篇 |
出版年
2015年 | 45篇 |
2014年 | 66篇 |
2013年 | 68篇 |
2012年 | 98篇 |
2011年 | 93篇 |
2010年 | 64篇 |
2009年 | 43篇 |
2008年 | 93篇 |
2007年 | 91篇 |
2006年 | 61篇 |
2005年 | 74篇 |
2004年 | 79篇 |
2003年 | 78篇 |
2002年 | 78篇 |
2001年 | 83篇 |
2000年 | 66篇 |
1999年 | 59篇 |
1998年 | 39篇 |
1997年 | 29篇 |
1996年 | 37篇 |
1995年 | 27篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 55篇 |
1991年 | 76篇 |
1990年 | 56篇 |
1989年 | 70篇 |
1988年 | 52篇 |
1987年 | 55篇 |
1986年 | 54篇 |
1985年 | 55篇 |
1984年 | 64篇 |
1983年 | 43篇 |
1982年 | 41篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1979年 | 60篇 |
1978年 | 40篇 |
1977年 | 54篇 |
1976年 | 32篇 |
1975年 | 42篇 |
1974年 | 40篇 |
1973年 | 47篇 |
1972年 | 46篇 |
1971年 | 31篇 |
1970年 | 35篇 |
1969年 | 30篇 |
1968年 | 24篇 |
1967年 | 23篇 |
1966年 | 31篇 |
排序方式: 共有2868条查询结果,搜索用时 177 毫秒
181.
The present study investigated the association of mothers' marriage and changes in young adolescents' cognitive and socioemotional development and changes in family processes. Analyses employed longitudinal data from the Three-City Study to track maternal partnerships for 860 low-income adolescents (10–14 years-old in Wave 1) across a 16 month period. No short-term benefits or risks emerged for youth when mothers entered marriage, with few changes in family or maternal functioning linked with marriage formation as well. In contrast, adolescents in stably married families experienced improved academic, behavioral, and psychological well-being compared to youth in stable cohabiting or single-parent families. Stable marriage was similarly linked to improvements across multiple domains of home and mothers' functioning. These patterns were not moderated by the male partner's identity (biological father or stepfather). Results support the benefits of stable marriage on youth development, but suggest that policies supporting movements into new marriages may not result in improved adolescent or family functioning, at least in the short term. 相似文献
182.
A. Joan Levine Alberto Salvan Glenn Talaska Mark F. Boeniger Anthony Suruda Paul A. Schulte 《Biomarkers》2013,18(2):135-138
Epithelial-cell micronuclei (MN) are potentially useful markers of occupational exposure to genotoxicants. With intermittent exposures, cells sampled either before or after a specific time interval, reflecting the time it takes for damaged cells to become available at the epithelial surface, are unlikely to be exposure-related. It may then be important to conduct an exposure-window analysis, with the goal of identifying the relevant exposures.We re-analysed individual exposure data from a previous study (Suruda et al. 1993) of MN formation in 22 male mortuary science students exposed to formaldehyde during a 90-day embalming class. We conducted an exposurewindow analysis and compared the results with those obtained with 90-day cumulative exposure. The window widths varied between 7 and 25 days, in 1 day increments, assuming a constant 7-day cell-cycle. We assessed the fit (likelihood-ratio test) of a linear regression model, regressing the change in buccal MN prevalence on formaldehyde exposure, using both asymptotic and non-asymptotic methods. Exposures defined from 7-15 to 7-18 days before specimen collection provided a slightly better fit than the 90-day cumulative exposure, with a doubling of the regression coefficient for the exposure effect (for the 7-16-days window LR = 5.32, p = 0.032, coefficient = 0.088 MN per 1000 cells per ppm-hr; 95% CI = 0.014, 0.16; for the 90-day cumulative exposure LR = 4.44, p = 0.048, coefficient = 0.045 MN per 1000 cells per ppm-hr, 95% CI = 0.0038, 0.086). Although hampered by the small number of subjects, these results reinforce the potential importance of exposure timing. 相似文献
183.
Adam C. Levine Richard M. Munyaneza Justin Glavis-Bloom Vanessa Redditt Hannah C. Cockrell Bantu Kalimba Valentin Kabemba Juvenal Musavuli Mathias Gakwerere Jean Paul de Charles Umurungi Sachita P. Shah Peter C. Drobac 《PloS one》2013,8(12)
Objective
To investigate the accuracy of three clinical scales for predicting severe disease (severe dehydration or death) in children with diarrhea in a resource-limited setting.Methods
Participants included 178 children admitted to three Rwandan hospitals with diarrhea. A local physician or nurse assessed each child on arrival using the World Health Organization (WHO) severe dehydration scale and the Centers for Disease Control (CDC) scale. Children were weighed on arrival and daily until they achieved a stable weight, with a 10% increase between admission weight and stable weight considered severe dehydration. The Clinical Dehydration Scale was then constructed post-hoc using the data collected for the other two scales. Receiver Operator Characteristic (ROC) curves were constructed for each scale compared to the composite outcome of severe dehydration or death.Results
The WHO severe dehydration scale, CDC scale, and Clinical Dehydration Scale had areas under the ROC curves (AUCs) of 0.72 (95% CI 0.60, 0.85), 0.73 (95% CI 0.62, 0.84), and 0.80 (95% CI 0.71, 0.89), respectively, in the full cohort. Only the Clinical Dehydration Scale was a significant predictor of severe disease when used in infants, with an AUC of 0.77 (95% CI 0.61, 0.93), and when used by nurses, with an AUC of 0.78 (95% CI 0.63, 0.93).Conclusions
While all three scales were moderate predictors of severe disease in children with diarrhea, scale accuracy varied based on provider training and age of the child. Future research should focus on developing or validating clinical tools that can be used accurately by nurses and other less-skilled providers to assess all children with diarrhea in resource-limited settings. 相似文献184.
In eukaryotic cells short-lived proteins are degraded in a specific process by the ubiquitin-proteasome system (UPS), whereas long-lived proteins and damaged organelles are degraded by macroautophagy (hereafter referred to as autophagy). A growing body of evidence now suggests that autophagy is important for clearance of protein aggregates that form in cells as a consequence of ageing, oxidative stress, alterations that elevate the amounts of certain aggregation-prone proteins or expression of aggregating mutant variants of specific proteins. Autophagy is generally considered to be a non-specific, bulk degradation process. However, a recent study suggests that p62/SQSTM1 may link the recognition of polyubiquitinated protein aggregates to the autophagy machinery.1 This protein is able to polymerize via its N-terminal PB1 domain and to recognize polyubiquitin via its C-terminal UBA domain. It can also recruit the autophagosomal protein LC3 and co-localizes with many types of polyubiquitinated protein aggregates.1 Here we discuss possible implications of these findings and raise some questions for further investigation. 相似文献
185.
Gabriel A. Koepp Chinmay U. Manohar Shelly K. McCrady‐Spitzer Avner Ben‐Ner Darla J. Hamann Carlisle F. Runge James A. Levine 《Obesity (Silver Spring, Md.)》2013,21(4):705-711
Objective: Sedentariness is associated with weight gain and obesity. A treadmill desk is the combination of a standing desk and a treadmill that allow employees to work while walking at low speed. Design and Methods: The hypothesis was that a 1‐year intervention with treadmill desks is associated with an increase in employee daily physical activity (summation of all activity per minute) and a decrease in daily sedentary time (zero activity). Employees (n = 36; 25 women, 11 men) with sedentary jobs (87 ± 27 kg, BMI 29 ± 7 kg/m2, n = 10 Lean BMI < 25 kg/m2, n = 15 Overweight 25 < BMI < 30 kg/m2, n = 11 Obese BMI > 30 kg/m2) volunteered to have their traditional desk replaced with a treadmill desk to promote physical activity for 1 year. Results: Daily physical activity (using accelerometers), work performance, body composition, and blood variables were measured at Baseline and 6 and 12 months after the treadmill desk intervention. Subjects who used the treadmill desk increased daily physical activity from baseline 3,353 ± 1,802 activity units (AU)/day to, at 6 months, 4,460 ± 2,376 AU/day (P < 0.001), and at 12 months, 4,205 ± 2,238 AU/day (P < 0.001). Access to the treadmill desks was associated with significant decreases in daily sedentary time (zero activity) from at baseline 1,020 ± 75 min/day to, at 6 months, 929 ± 84 min/day (P < 0.001), and at 12 months, 978 ± 95 min/day (P < 0.001). For the whole group, weight loss averaged 1.4 ± 3.3 kg (P < 0.05). Weight loss for obese subjects was 2.3 ± 3.5 kg (P < 0.03). Access to the treadmill desks was associated with increased daily physical activity compared to traditional chair‐based desks; their deployment was not associated with altered performance. For the 36 participants, fat mass did not change significantly, however, those who lost weight (n = 22) lost 3.4 ± 5.4 kg (P < 0.001) of fat mass. Weight loss was greatest in people with obesity. Conclusions: Access to treadmill desks may improve the health of office workers without affecting work performance. 相似文献
186.
Gary G. Bennett Dori M. Steinberg Michele G. Lanpher Sandy Askew Ilana B. Lane Erica L. Levine Melody S. Goodman Perry B. Foley 《PloS one》2013,8(8)
Objective
Offering calories on restaurant websites might be particularly important for consumer meal planning, but the availability of and ease of accessing this information are unknown.Methods
We assessed websites for the top 100 U.S. chain restaurants to determine the availability of and ease of access to calorie information as well as website design characteristics. We also examined potential predictors of calorie availability and ease of access.Results
Eighty-two percent of restaurants provided calorie information on their websites; 25% presented calories on a mobile-formatted website. On average, calories could be accessed in 2.35±0.99 clicks. About half of sites (51.2%) linked to calorie information via the homepage. Fewer than half had a separate section identifying healthful options (46.3%), or utilized interactive meal planning tools (35.4%). Quick service/fast casual, larger restaurants, and those with less expensive entrées and lower revenue were more likely to make calorie information available. There were no predictors of ease of access.Conclusion
Calorie information is both available and largely accessible on the websites of America’s leading restaurants. It is unclear whether consumer behavior is affected by the variability in the presentation of calorie information. 相似文献187.
H. B. Levine 《Ethnic and racial studies》2013,36(2):323-344
Modern social life is sometimes characterized as ‘post‐traditional’, an environment where personal identity is continually reconstructed. Concepts of ethnic identity on the other hand usually evoke some notion of tradition, continuity with the past, and intersubjectivity. This article discusses the personal accounts of Jewishness given by a sample of New Zealanders with ‘mixed’ (Jewish and gentile) backgrounds. It explores and analyses their use of themes that come from both modernity and Jewish tradition and defines the different types of identification implicit in their accounts. Particular attention is paid to how these kinds of identification are transmitted, because the literature (on both Jewishness and ethnicity in general) contains debates about the persistence of different expressions of identity. I conclude that a substantial dispersal of Jewish identity has occurred in New Zealand which apparently contradictory theoretical positions are useful in explaining. This suggests that a more holistic perspective is required to account adequately for the diversity of ethnic identity in contemporary society. 相似文献
188.
Peter Kivisto I.C. Jarvie J. Milton Yinger Marc V. Levine Robert Paine 《Ethnic and racial studies》2013,36(1):167-177
Andrew Hacker, TWO NATIONS: BLACK AND WHITE, SEPARATE, HOSTILE, UNEQUAL, New York: Charles Scribner's Sons, 1992, vii + 257 pp., $24.95. Catherine Silk and John Silk, RACISM AND ANTI‐RACISM IN AMERICAN POPULAR CULTURE, Manchester: Manchester University Press, 1990, x + 186 pp., £27.50. Therese Daniels and Jane Gerson (eds), THE COLOUR BLACK, BLACK IMAGES IN BRITISH TELEVISION, London: BFI Publishing, 1989, 160 pp., £4.95 (paper). Jim Pines and Paul Willemen (eds), QUESTIONS OF THIRD CINEMA, London: BFI Publishing, 1989, x + 246 pp., £7.95 (paper). David R. Roediger, THE WAGES OF WHITENESS: RACE AND THE MAKING OF THE AMERICAN WORKING CLASS, London: Verso, 1991, 191 pp., £12.95 (paper). William Cohen, AT FREEDOM'S EDGE: BLACK MOBILITY AND THE SOUTHERN WHITE QUEST FOR RACIAL CONTROL, 1861–1915, Baton Rouge: Louisiana State University Press, 1991, 340 pp., $42.50. Robert L. Cooper, LANGUAGE PLANNING AND SOCIAL CHANGE, Cambridge: Cambridge University Press, 1990, 216 pp., £27.50, £9.95 (paper). Emmanual Sivan and Menachem Friedman (eds), RELIGIOUS RADICALISM AND POLITICS IN THE MIDDLE EAST, Albany: State University of New York Press, 1990, 244 pp., n.p. Eliezer Ben‐Rafael and Stephen Sharot, ETHNICITY, RELIGION, AND CLASS IN ISRAELI SOCIETY, Cambridge: Cambridge University Press, 1991, 287 pp., £32.50. 相似文献
189.
Catherine E.M. Hogwood Andrew S. Tait Nadejda Koloteva‐Levine Daniel G. Bracewell C. Mark Smales 《Biotechnology and bioengineering》2013,110(1):240-251
Recombinant protein products such as monoclonal antibodies (mAbs) for use in the clinic must be clear of host cell impurities such as host cell protein (HCP), DNA/RNA, and high molecular weight immunogenic aggregates. Despite the need to remove and monitor HCPs, the nature, and fate of these during downstream processing (DSP) remains poorly characterized. We have applied a proteomic approach to investigate the dynamics and fate of HCPs in the supernatant of a mAb producing cell line during early DSP including centrifugation, depth filtration, and protein A capture chromatography. The primary clarification technique selected was shown to influence the HCP profile that entered subsequent downstream steps. MabSelect protein A chromatography removed the majority of contaminating proteins, however using 2D‐PAGE we could visualize not only the antibody species in the eluate (heavy and light chain) but also contaminant HCPs. These data showed that the choice of secondary clarification impacts upon the HCP profile post‐protein A chromatography as differences arose in both the presence and abundance of specific HCPs when depth filters were compared. A number of intracellularly located HCPs were identified in protein A elution fractions from a Null cell line culture supernatant including the chaperone Bip/GRP78, heat shock proteins, and the enzyme enolase. We demonstrate that the selection of early DSP steps influences the resulting HCP profile and that 2D‐PAGE can be used for monitoring and identification of HCPs post‐protein A chromatography. This approach could be used to screen cell lines or hosts to select those with reduced HCP profiles, or to identify HCPs that are problematic and difficult to remove so that cell‐engineering approaches can be applied to reduced, or eliminate, such HCPs. Biotechnol. Bioeng. 2013; 110: 240–251. © 2012 Wiley Periodicals, Inc. 相似文献
190.
G. C. H. Yang, K. Fried and P. H. Levine Detection of medullary thyroid microcarcinoma using ultrasound‐guided fine needle aspiration cytology Objective: Compared with incidental papillary thyroid microcarcinoma (microPTC), incidental medullary thyroid microcarcinoma (microMTC) is clinically more significant. The objective of the present study was to summarize our experience in detecting microMTCs. Methods: From 1995 to 2011, there were 10 825 thyroid fine needle aspirates (FNAs) guided using high‐resolution ultrasound with on‐site preparation and evaluation by a cytopathologist. Of the 140 microcarcinomas detected, 132 were microPTCs and eight were microMTCs, which are the subject of the present study. Results: All eight cases were incidentalomas and none of the five women and three men, age 37–70 years, had a family history of MTC. One patient had two FNAs at an interval of 10 months, two had a single lymph node metastasis and one had a 0.1‐cm tumour nodule near the main tumour. Four of five plasmacytoid cell microMCTs had irregular borders; two round cell and one rectangular cell tumours had smooth borders. In contrast, 17 larger MTCs diagnosed in the same period included seven plasmacytoid, four giant cell and six spindle cell types. All five plasmacytoid microMTCs were correctly diagnosed on FNA, but the round cell and rectangular cell tumours were undercalled as follicular lesions. Sampling of colloid from adjacent follicles was noted in microMTCs. Two were diagnosed on histology following recommended surgery and one was diagnosed on recommended repeat FNA. Conclusions: US‐guided FNA of thyroid lesions is a powerful tool in the detection of microMTCs, provided that cytopathologists are alerted to the pitfalls described in the present study. 相似文献