全文获取类型
收费全文 | 2914篇 |
免费 | 346篇 |
国内免费 | 425篇 |
出版年
2023年 | 90篇 |
2022年 | 57篇 |
2021年 | 92篇 |
2020年 | 126篇 |
2019年 | 166篇 |
2018年 | 112篇 |
2017年 | 126篇 |
2016年 | 140篇 |
2015年 | 112篇 |
2014年 | 121篇 |
2013年 | 189篇 |
2012年 | 124篇 |
2011年 | 165篇 |
2010年 | 139篇 |
2009年 | 162篇 |
2008年 | 157篇 |
2007年 | 169篇 |
2006年 | 149篇 |
2005年 | 136篇 |
2004年 | 106篇 |
2003年 | 116篇 |
2002年 | 101篇 |
2001年 | 88篇 |
2000年 | 67篇 |
1999年 | 45篇 |
1998年 | 55篇 |
1997年 | 43篇 |
1996年 | 37篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 40篇 |
1992年 | 32篇 |
1991年 | 35篇 |
1990年 | 15篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 28篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 11篇 |
排序方式: 共有3685条查询结果,搜索用时 62 毫秒
991.
V. L. Gavrikov P. Ya. Grabarnik D. Stoyan 《Biometrical journal. Biometrische Zeitschrift》1993,35(4):487-498
In this paper we study relations between trunks and tops of pines in natural Siberian forests. By statistical methods we show that the tops tend to deviate in the direction away from the nearest neighbour tree or from a summary of the trees in a given neighbourhood. In an alternative approach we show that the tops deviate into the direction of the empty space near the trunk position defined by the corresponding Voronoi polygon. 相似文献
992.
Harini Narayanan Lars Behle Martin F. Luna Michael Sokolov Gonzalo Guillén-Gosálbez Massimo Morbidelli Alessandro Butté 《Biotechnology and bioengineering》2020,117(9):2703-2714
In a decade when Industry 4.0 and quality by design are major technology drivers of biopharma, automated and adaptive process monitoring and control are inevitable requirements and model-based solutions are key enablers in fulfilling these goals. Despite strong advancement in process digitalization, in most cases, the generated datasets are not sufficient for relying on purely data-driven methods, whereas the underlying complex bioprocesses are still not completely understood. In this regard, hybrid models are emerging as a timely pragmatic solution to synergistically combine available process data and mechanistic understanding. In this study, we show a novel application of the hybrid-EKF framework, that is, hybrid models coupled with an extended Kalman filter for real-time monitoring, control, and automated decision-making in mammalian cell culture processing. We show that, in the considered application, the predictive monitoring accuracy of such a framework improves by at least 35% when developed with hybrid models with respect to industrial benchmark tools based on PLS models. In addition, we also highlight the advantages of this approach in industrial applications related to conditional process feeding and process monitoring. With regard to the latter, for an industrial use case, we demonstrate that the application of hybrid-EKF as a soft sensor for titer shows a 50% improvement in prediction accuracy compared with state-of-the-art soft sensor tools. 相似文献
993.
PurposeThis study performed the accurate measurements of beam profiles with a new rigid board, which was consistent with the supplied reference beam profiles (RBPs) for clinical Halcyon model.MethodsPercentage depth doses (PDDs), lateral and diagonal dose profiles were measured and compared with RBPs. A water tank was set on the rigid board bridged Halcyon bore without sagging and source-to-surface distance was 90.0 cm. Field sizes were from 2.0 to 28.0 cm squares and depths of lateral and diagonal dose profiles were 1.3, 5.0, 10.0, and 20.0 cm. For the PDD, the depth of maximum dose (dmax), PDD value at depth of 10.0 cm (PDD10), and absolute dose difference (DD) between RBP and measured beam profiles (MBP) were evaluated. For lateral and diagonal dose profiles, DDs for the whole and divided areas (central, shoulder, and extended areas) defined by third derivative, and distance-to-agreement (DTA) in the penumbra area were evaluated.ResultsFor PDDs, the differences of dmax and PDD10 and DD beyond the dmax were within 1.0 mm, 0.3%, and 1.0%, respectively. For lateral and diagonal dose profiles, the DDs reached approximately 5.0% in the whole area because of penumbra area, while the DDs in the central, shoulder, and extended areas were within 1.0%, 2.0%, and 1.0%, respectively. The DTAs in the penumbra area were within 0.8 mm.ConclusionsThe supplied RBPs can be used clinically owing to the good agreement with the accurate MBPs with rigid board. 相似文献
994.
995.
B. Edwin Blaisdell 《Journal of molecular evolution》1985,22(1):69-81
Summary The course of evolutionary change in DNA sequences has been modeled as a Markov process. The Markov process was represented by discrete time matrix methods. The parameters of the Markov transition matrices were estimated by least-squares direct-search optimization of the fit of the calculated divergence matrix to that observed for two aligned sequences. The Markov process corrected for multiple and parallel substitutions of bases at the same site. The method avoided the incorrect assumption of all previously described methods that the divergence between two present-day sequences is twice the divergence of either from the common and unknown ancestral sequence. The three previous methods were shown to be equivalent. The present method also avoided the undesirable assumptions that sequence composition has not changed with time and that the substitution rates in the two descendant lineages were the same. It permitted simultaneous estimation of ancestral sequence composition and, if applicable, of different substitution rates for the two descendant lineages, provided the total number of estimated parameters was less than 16. Properties of the Markov chain were discussed. It was proved for symmetric substitution matrices that all elements of the equilibrium divergence matrix equal 1/16, and that the total difference in the divergence matrix at epoch k equals the total change in the common substitution matrix at epoch 2k for all values of k. It was shown how to resolve an ambiguity in the assignment of two different substitution rates to the two descendant lineages when four or more similar sequences are available. The method was applied to the divergence matrix for codon site 3 for the mouse and rabbit beta-globins. This observed divergence matrix was significantly asymmetric and required at least two different substitution rates. This result could be achieved only by using different asymmetric substitution matrices for the two lineages. 相似文献
996.
For a Gibbs point process of mutually non-intersecting discs a parameter estimation method is suggested. It is applied to a pattern of positions of beadlet anemones, for which, until now, no appropriate Gibbs process model has been found. 相似文献
997.
Robust estimation of density for a two-dimensional point process 总被引:2,自引:0,他引:2
998.
999.
M. Weiss 《Journal of mathematical biology》1982,15(3):305-318
Characterizing the tissue distribution kinetics of drugs by physiological and physico-chemical parameters and using a circulatory model the time course of blood concentration after intravenous injection is predicted for linear pharmacokinetic systems. The interrelationships between the first three (zero to second) moments of the distribution functions of organ transfer times, circulation times and residence times of drug molecules in the body are described. Utilizing literature data the model is applied to the analysis of lidocain kinetics in humans. 相似文献
1000.