全文获取类型
收费全文 | 298篇 |
免费 | 45篇 |
国内免费 | 27篇 |
专业分类
化学 | 70篇 |
晶体学 | 8篇 |
力学 | 48篇 |
综合类 | 4篇 |
数学 | 85篇 |
物理学 | 155篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 24篇 |
2012年 | 16篇 |
2011年 | 16篇 |
2010年 | 14篇 |
2009年 | 21篇 |
2008年 | 14篇 |
2007年 | 29篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 2篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 15 毫秒
91.
92.
在简要介绍了DGPS基准站控制网建立的特点及作业流程后,着重讨论了此类GPS控制网建立过程中几个主要技术问题的解决方法,即用坐标转移法进行偏心观测、用尺度强制约束法或投影面重新选择法处理投影变形和内业平差。工程实践表明,上述问题的有效解决对DGPS基准站坐标的准确测定发挥了良好的技术支撑作用。 相似文献
93.
We consider two quasi-electrostatic models in a multilayered piezoelectric structure. Both models only differ on the boundary conditions. For each one of them we prove a boundary observability inequality which together with the Hilbert Uniqueness Method introduced by J.L. Lions allow us to drive both systems to rest at time T with the same control function. We require suitable geometric conditions on the region and the interfaces as well as monotonicity assumptions on the coefficients of the model. 相似文献
94.
M. W. Evans 《Foundations of Physics Letters》1997,10(5):487-493
The recent claims by Rajaet al. [1,2] are corrected in this reply. It is shown that there is no Faraday induction due toB
(3)in vacuo, as observed by these authors. The observation of the inverse Faraday effect by these authors is an observation of
theB
(3)field at second order. Their data, correctly interpreted, constitute strong support for the existence and predicted properties
of theB
(3)field. 相似文献
95.
We employ in situ deposited secondary membranes of yeast (SMYs) to optimize permeate flux during microfiltration and ultrafiltration
of protein solutions. The deposited secondary membrane was periodically removed by backflushing, and a new cake layer was
deposited at the start of the next cycle. The effects of backflushing time, backflushing strength, wall shear rate, and amount
of secondary membrane deposited on the permeate flux were examined. Secondary membranes were found to increase the permeate
fluxin microfiltration by severalfold. Protein transmission was also enhanced owing to the presence of the secondary membrane,
and the amount of protein recovered was more than twice that obtained during filtration of protein-only solutions under othewise
identical conditions. In ultrafiltration, the flux enhancement owing to the secondary membrane was only 50% or less. In addition,
the flux for ultrafiltration was relatively insensitive to changes in the concentration of yeast used during deposition of
SMY and to the backflushing strength used to periodically remove the secondary membrane. 相似文献
96.
Pierre Le-Clech Yulita Marselina Yun Ye Richard M. Stuetz Vicki Chen 《Journal of membrane science》2007,290(1-2):36-45
Although many studies assessed fouling behaviour in microporous membrane processes like membrane bioreactors (MBRs), in situ or direct observation of the fouling layer has not yet been possible. The observation of the fouling layer resulting from the filtration of model solutions allowed better understanding of MBR fouling intensity and mechanisms. In this study, alginate has been used as a model for polysaccharide (one of the main foulants in MBRs). Three visualisation techniques, confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM), and direct observation (DO) have been tested to observe the alginate fouling. The work presented in this paper revealed the advantages and limitations of each technique used for this specific application. Although no coating is required for this technique, ESEM allowed distinct non-destructive observation of clean membrane. However, the lack of structure in the alginate fouling layer limited the use of this technique for fouled membranes. While CLSM requires the use of expensive fluorescent markers, DO appeared as the most promising technique for direct and in situ observation of MBR fouling. DO of alginate/bentonite and alginate/bacteria solutions revealed the creation of a well-structured dual fouling system (bentonite-concentrated layer of 50 μm embedded and covered by a concentration polarisation of alginate greater than 240 μm) on the surface of hollow fibre membrane. 相似文献
97.
TOUGHENING OF POLYCARBONATE WITH PBA-PMMA CORE-SHELL PARTICLES 总被引:1,自引:0,他引:1
The miscibility, mechanical properties, morphology and toughening mechanism of PC/PBA-PMMA blends were investigated. The dynamic mechanical results show that PC/PBA-PMMA blend has good miscibility and strong interfacial adhesion. The Izod impact strength of blend PC/PBA-PMMA with 4% (volume fraction) PBA-PMMA core-shell modifier is 16 times higher than that of pure PC. The core-shell volume fraction and thickness of the PMMA shell have effect on the toughness of PC/PBA-PMMA blends. As PMMA volume fraction increases, the toughness of PC/PBA-PMMA blend increases, and reaches a maximum value at 30% volume fraction of PMMA or so. The tensile properties of PC/PBA-PMMA blend with a minimum amount of PBA-PMMA modifier show that brittle-tough transition has no significant variance in comparison with that of pure PC. The scanning electron microscopic (SEM) observation indicates that the toughening mechanism of the blend with the pseudo-ductile matrix modified by small core-shell latex polymer particles is the synergetic effect of cavitation and shear yielding of the matrix. 相似文献
98.
杨袁庆 《广东微量元素科学》2007,14(8):67-69
为探讨软产道血肿发生的原因,预防和减少阴道分娩的并发症,对12例软产道血肿发生的情况及相关因素进行了分析。结果表明,软产道血肿的形成与有无妊娠合并症、产程长短、助产技术密切相关。提示做好围产期保健工作,提高助产技术,加强产后的观察与护理,是防止软产道血肿的关键。 相似文献
99.
利用宽带电场仪和光学纹波探头,对2006年夏季广东省从化地区发生的自然闪电的光电信号进行了同步观测,并对结果进行了统计分析。统计结果表明:闪电光信号脉冲的发生时间和峰值到达时间总是滞后于电信号,并且脉冲上升沿和宽度也比电信号宽;云闪的光信号在上述特征参数的滞后量、上升沿时间和脉宽时间差要比地闪回击放电大。从闪电光电信号时域信号特征的角度,利用BP人工神经网络,对闪电类型进行了模式识别研究。总体识别结果基本上能够满足要求,但是由于云闪放电过程比较复杂,获得的数据较少,所以对云闪识别的效果并不理想。 相似文献
100.
Generalized unscented Kalman filtering based radial basis function neural network for the prediction of ground radioactivity time series with missing data
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
On the assumption that random interruptions in the observation process are modeled by a sequence of independent Bernoulli random variables, we firstly generalize two kinds of nonlinear filtering methods with random interruption failures in the observation based on the extended Kalman filtering (EKF) and the unscented Kalman filtering (UKF), which were shortened as GEKF and GUKF in this paper, respectively. Then the nonlinear filtering model is established by using the radial basis function neural network (RBFNN) prototypes and the network weights as state equation and the output of RBFNN to present the observation equation. Finally, we take the filtering problem under missing observed data as a special case of nonlinear filtering with random intermittent failures by setting each missing data to be zero without needing to pre-estimate the missing data, and use the GEKF-based RBFNN and the GUKF-based RBFNN to predict the ground radioactivity time series with missing data. Experimental results demonstrate that the prediction results of GUKF-based RBFNN accord well with the real ground radioactivity time series while the prediction results of GEKF-based RBFNN are divergent. 相似文献