全文获取类型
收费全文 | 501篇 |
免费 | 26篇 |
国内免费 | 8篇 |
出版年
2023年 | 8篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 11篇 |
2015年 | 14篇 |
2014年 | 17篇 |
2013年 | 24篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 13篇 |
2009年 | 20篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 20篇 |
2005年 | 18篇 |
2004年 | 18篇 |
2003年 | 13篇 |
2002年 | 15篇 |
2001年 | 7篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 7篇 |
1971年 | 6篇 |
排序方式: 共有535条查询结果,搜索用时 31 毫秒
91.
V. R. Prayag S. A. Chiplonkar S. A. Paranjpe 《Biometrical journal. Biometrische Zeitschrift》1995,37(5):565-570
Diet surveys in the science of human nutrition involve longitudinal observations on the same individuals repeated at distinct time points. Consequently a common feature of such surveys is inherent correlation between successive observations. In this paper, an autoregressive model of order 1 is assumed for the successive observations on the same individual in a survey. Further, observations on the same individual in two different surveys are assumed to be correlated. The technique of analysis of variance is modified suitably for this set up and applied to two nutritional surveys carried on army recruits. 相似文献
92.
93.
A. C. Trajstman 《Biometrical journal. Biometrische Zeitschrift》1993,35(1):73-80
There may be experiments where due to misadventure or logistic or ethical reasons final measurements on all experimental units cannot be obtained. If at least 50% of the final measurements have been taken estimates of the lower quantiles and the median can be obtained. For such curtailed experiments it is shown how quantiles, above those that can be estimated directly from the data set, can be estimated indirectly by exploiting a property of symmetric distributions. The performance of the indirect quantile estimator is compared with that of the direct quantile estimator and conditions for the indirect estimator to have smaller variance than the direct estimator are presented. It is also shown how the indirect estimator may be pooled with the direct estimator to obtain an improved estimate of the upper quantiles. When it cannot be assumed that the data come from a symmetric distribution transformations to symmetry may be performed and the indirect estimation technique used on the transformed data; back transformations then yield the estimates of the upper quantiles. 相似文献
94.
To develop further the methods for estimation of NOx absorption by plants supplied with 15 N-labelled fertilizer, we proposed a new calculation method, total N fixed method (TNF), and compared with the 15 N dilution method and the classical mass balance method (MB).
Hydroponically grown soybean plants were supplied with15 N-labelled nitrate and exposed to 200–250 nl l−1 NO2 for 7 d. The proportions of the N derived from NO2 to total N in exposed plants were estimated by the three methods.
The reported rates of NO2 absorption by several plant species, estimated by the 15 N dilution method, were recalculated using the TNF method. The results of the two methods were compared and showed that: (1) The 15 N dilution method overestimated the content of NO2 -N in exposed plants compared with the MB method whilst the TNF method produced estimations of NO2 -N closer to those by the MB method when the plants were supplied with 5 m M nitrate. (2) The differences in estimations between the MB method and either the 15 N dilution method or the TNF method increased with decreasing supply of 15 N-labelled nitrate to roots. 相似文献
Hydroponically grown soybean plants were supplied with
The reported rates of NO
95.
Procedures for deconvolution of pharmacokinetic data are routinely used in the pharmaceutical industry to determine drug release and absorption which is essential in designing optimized drug formulations. Although these procedures are described extensively in the pharmacokinetic literature, they have been studied less from a statistical point of view and variance estimation has not been addressed. We discuss the statistical properties of a numerical procedure for deconvolution. Based on a point‐area deconvolution method we define an estimator for the function that describes the time course of drug release from a drug formulation. Asymptotic distributions are derived and several methods of variance and interval estimation are compared (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
96.
The fidelity of the trajectories obtained from video-based particle tracking determines the success of a variety of biophysical techniques, including in situ single cell particle tracking and in vitro motility assays. However, the image acquisition process is complicated by system noise, which causes positioning error in the trajectories derived from image analysis. Here, we explore the possibility of reducing the positioning error by the application of a Kalman filter, a powerful algorithm to estimate the state of a linear dynamic system from noisy measurements. We show that the optimal Kalman filter parameters can be determined in an appropriate experimental setting, and that the Kalman filter can markedly reduce the positioning error while retaining the intrinsic fluctuations of the dynamic process. We believe the Kalman filter can potentially serve as a powerful tool to infer a trajectory of ultra-high fidelity from noisy images, revealing the details of dynamic cellular processes. 相似文献
97.
ROSALIND MCDOUGALL 《Bioethics》2013,27(1):20-27
This paper argues that doctors' ethical challenges can be usefully conceptualised as role virtue conflicts. The hospital environment requires doctors to be simultaneously good doctors, good team members, good learners and good employees. I articulate a possible set of role virtues for each of these four roles, as a basis for a virtue ethics approach to analysing doctors' ethical challenges. Using one junior doctor's story, I argue that understanding doctors' ethical challenges as role virtue conflicts enables recognition of important moral considerations that are overlooked by other approaches to ethical analysis. 相似文献
98.
99.
100.
PurposeThe aim of this paper is to characterize two different EPID-based solutions for pre-treatment VMAT quality assurance, the 2D portal dosimetry and the 3D projection technique. Their ability to catch the main critical delivery errors was studied.MethodsMeasurements were performed with a linac accelerator equipped with EPID aSi1000, Portal Dose Image Prediction (PDIP), and PerFRACTION softwares. Their performances were studied simulating perturbations of a reference plan through systematic variations in dose values and micromultileaf collimator position. The performance of PDIP, based on 2D forward method, was evaluated calculating gamma passing rate (%GP) between no-error and error-simulated measurements. The impact of errors with PerFRACTION, based on 3D projection technique, was analyzed by calculating the difference between reference and perturbed DVH (%ΔD). Subsequently pre-treatment verification with PerFRACTION was done for 27 patients of different pathologies.ResultsThe sensitivity of PerFRACTION was slightly higher than sensitivity of PDIP, reaching a maximum of 0.9. Specificity was 1 for PerFRACTION and 0.6 for PDIP. The analysis of patients’ DVHs indicated that the mean %ΔD was (1.2 ± 1.9)% for D2%, (0.6 ± 1.7)% for D95% and (−0.0 ± 1.2)% for Dmean of PTV. Regarding OARs, we observed important discrepancies on DVH but that the higher dose variations were in low dose area (<10 Gy).ConclusionsThis study supports the introduction of the new 3D forward projection method for pretreatment QA raising the claim that the visualization of the delivered dose distribution on patient anatomy has major advantages over traditional portal dosimetry QA systems. 相似文献