全文获取类型
收费全文 | 2425篇 |
免费 | 317篇 |
国内免费 | 61篇 |
专业分类
化学 | 898篇 |
晶体学 | 1篇 |
力学 | 83篇 |
综合类 | 83篇 |
数学 | 942篇 |
物理学 | 796篇 |
出版年
2024年 | 12篇 |
2023年 | 126篇 |
2022年 | 283篇 |
2021年 | 440篇 |
2020年 | 258篇 |
2019年 | 177篇 |
2018年 | 147篇 |
2017年 | 141篇 |
2016年 | 155篇 |
2015年 | 96篇 |
2014年 | 114篇 |
2013年 | 175篇 |
2012年 | 69篇 |
2011年 | 81篇 |
2010年 | 70篇 |
2009年 | 62篇 |
2008年 | 57篇 |
2007年 | 64篇 |
2006年 | 38篇 |
2005年 | 33篇 |
2004年 | 28篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 8篇 |
1995年 | 14篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 10篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1959年 | 5篇 |
排序方式: 共有2803条查询结果,搜索用时 31 毫秒
61.
《Biomedical chromatography : BMC》2017,31(9)
Paralytic shellfish toxins (PSTs), including gonyautoxins and saxitoxins, are produced by multiple species of microalgae and dinoflagellates, and are bioaccumulated by shellfish and other animals. Human exposure to PSTs typically occurs through ingestion of recreationally harvested contaminated shellfish and results in nonspecific symptomology. Confirmation of exposure to PSTs has often relied on the measurement of saxitoxin, the most toxic congener; however, gonyautoxins (GTXs), the sulfated carbamate derivatives of saxitoxin, may be present in shellfish at higher concentrations. To improve identification of PST exposures, our group has developed an online solid phase extraction hydrophilic interaction liquid chromatography method to identify GTX1–4 in human urine with tandem mass spectrometry. The reportable range varied for each analyte, with all falling within 0.899 and 250 ng/mL in urine with precision <15% and >85% accuracy as determined for all quality control samples. This new online method quantitates GTX1–4 following exposures to PSTs, supporting the work of public health authorities. 相似文献
62.
Boosting is one of the most important strategies in ensemble learning because of its ability to improve the stability and performance of weak learners. It is nonparametric, multivariate, fast and interpretable but is not robust against outliers. To enhance its prediction accuracy as well as immunize it against outliers, a modified version of a boosting algorithm (AdaBoost R2) was developed and called AdaBoost R3. In the sampling step, extremum samples were added to the boosting set. In the robustness step, a modified Huber loss function was applied to overcome the outlier problem. In the output step, a deterministic threshold was used to guarantee that bad predictions do not participate in the final output. The performance of the modified algorithm was investigated with two anticancer data sets of tyrosine kinase inhibitors, and the mechanism of inhibition was studied using the relative weighted variable importance procedure. Investigating the effect of base learner's strength reveals that boosting is only successful using the classification and regression tree method (a weak to moderate learner) and does not have a significant effect using the radial basis functions partial least square method (a strong base learners). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
63.
X. Z. Wang F. V. Buontempo A. Young D. Osborn 《SAR and QSAR in environmental research》2013,24(5):451-471
Recent literature has demonstrated the applicability of genetic programming to induction of decision trees for modelling toxicity endpoints. Compared with other decision tree induction techniques that are based upon recursive partitioning employing greedy searches to choose the best splitting attribute and value at each node that will necessarily miss regions of the search space, the genetic programming based approach can overcome the problem. However, the method still requires the discretization of the often continuous-valued toxicity endpoints prior to the tree induction. A novel extension of this method, YAdapt, is introduced in this work which models the original continuous endpoint by adaptively finding suitable ranges to describe the endpoints during the tree induction process, removing the need for discretization prior to tree induction and allowing the ordinal nature of the endpoint to be taken into account in the models built. 相似文献
64.
E.V. Sobolev O.V. Sobolev D.A. Tikhonov 《SAR and QSAR in environmental research》2013,24(3-4):303-315
An online resource has been developed for the theoretical study of hydration of biopolymers by the RISM (Reference Interaction Site Model) method, deriving from the integral equation theory of liquids. The online resource is based upon original software developed by the authors and includes all steps in studying a biopolymer with a given spatial structure and force field. It prepares the input data and carries out the RISM calculation yielding the atom-atom correlation functions of the biopolymer with water as solvent. From these functions the algorithm finds atomic partial contributions to the hydration free energy using various free energy expressions from integral equation theory. The calculated results are automatically recorded in a database, and become available on the website as tables of partial thermodynamic quantities. In addition, the website displays an interactive 3D model of a given molecule, the atoms of which can be painted in different colors in accordance with their partial contributions to the thermodynamic quantity chosen by the user. The user can interactively choose atoms on this molecule and their correlation functions will be displayed. The aim of our work was to develop and present a publicly-accessible resource on the basis of original software which could be used for scientific and educational purposes. 相似文献
65.
66.
针对现有的蜂窝网络的在线动态分配模型具有的信道需求量大、呼叫动态变化时阻塞率高和收敛速度慢的缺点,设计了一种基于MetropoisQ学习的蜂窝网络的在线信道分配方法。首先,在考虑同信道限制、邻居信道限制和同小区限制的基础上,设计了在线信道分配的数学模型,然后在Q-Learning算法基础上的设计了一种基于资格迹的Q(λ)算法实现信道的在线分配,为了进一步提高收敛速度,采用Metropois规则对算法中动作的选择方式进行改进,实现探索和利用的平衡。为了验证文中方法,采用Matlab工具上进行实验,仿真实验结果表明文中方法能实现蜂窝通信网络的在线信道分配,且与其它方法比较,具有较少的信道需求量、较低的阻塞率和收敛速度,较其它方法具有较大优越性。 相似文献
67.
68.
69.
70.