全文获取类型
收费全文 | 5225篇 |
免费 | 956篇 |
国内免费 | 355篇 |
专业分类
化学 | 445篇 |
晶体学 | 8篇 |
力学 | 535篇 |
综合类 | 110篇 |
数学 | 3056篇 |
物理学 | 913篇 |
无线电 | 1469篇 |
出版年
2024年 | 23篇 |
2023年 | 89篇 |
2022年 | 107篇 |
2021年 | 149篇 |
2020年 | 199篇 |
2019年 | 188篇 |
2018年 | 220篇 |
2017年 | 255篇 |
2016年 | 257篇 |
2015年 | 210篇 |
2014年 | 292篇 |
2013年 | 554篇 |
2012年 | 318篇 |
2011年 | 295篇 |
2010年 | 235篇 |
2009年 | 259篇 |
2008年 | 268篇 |
2007年 | 308篇 |
2006年 | 271篇 |
2005年 | 259篇 |
2004年 | 205篇 |
2003年 | 202篇 |
2002年 | 208篇 |
2001年 | 164篇 |
2000年 | 154篇 |
1999年 | 127篇 |
1998年 | 122篇 |
1997年 | 117篇 |
1996年 | 85篇 |
1995年 | 67篇 |
1994年 | 54篇 |
1993年 | 51篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1957年 | 2篇 |
排序方式: 共有6536条查询结果,搜索用时 18 毫秒
81.
通过逆矩法的估计方法,得到了定数截尾下双参数指数分布E(μ,A)中位置参数μ的逆估计量。模拟结果表明逆矩法估计量是可行的。同时,也得到构造位置参数区间估计的方法。 相似文献
82.
正交匹配追踪(Orthogonal Matching Pursuit, OMP)算法是一种重要的压缩感知重构算法. OMP算法在每次迭代中选择与当前残差最相关的原子. 针对每次迭代需要重新计算残差的问题, 本文考虑偶数次迭代下残差未知的情况. 首先, 研究了奇数次迭代的残差与下一次迭代的残差之间的关系, 得到了一种偶数次迭代时选择原子的标准. 然后, 引入一种回溯机制来处理前面所得的迭代结果, 这种机制通过剔除其中多余的原子来实现精确重建. 据此, 提出了可减少计算残差的改进型正交匹配追踪算法. 相似文献
83.
84.
85.
86.
Existence and Approximate Controllability of Solutions for an Impulsive Evolution Equation with Nonlocal Conditions in Banach Space 下载免费PDF全文
Lixin Sheng Weimin Hu You-Hui Su Yongzhen Yun 《Journal of Nonlinear Modeling and Analysis》2024,6(1):194-209
In this article, we study the existence of mild solutions and approximate controllability for non-autonomous impulsive evolution equations with nonlocal conditions in Banach space. The existence of mild solutions and some conditions for approximate controllability of these non-autonomous impulsive evolution equations are given by using the Krasnoselskii''s fixed point theorem, the theory of evolution family and the resolvent operator. In particular,the impulsive functions are supposed to be continuous and the nonlocal item is divided into Lipschitz continuous and completely bounded. An example is given as an application of the results. 相似文献
87.
Tumor hypoxia was discovered a century ago, and the interference of hypoxia with all radiotherapies is well known. Here, we demonstrate the potentially extreme effects of hypoxia heterogeneity on radiotherapy and combination radiochemotherapy. We observe that there is a decrease in hypoxia from tumor periphery to tumor center, due to oxygen diffusion, resulting in a gradient of radiative cell-kill probability, mathematically expressed as a probability gradient of occupied space removal. The radiotherapy-induced break-up of the tumor/TME network is modeled by the physics model of inverse percolation in a shell-like medium, using Monte Carlo simulations. The different shells now have different probabilities of space removal, spanning from higher probability in the periphery to lower probability in the center of the tumor. Mathematical results regarding the variability of the critical percolation concentration show an increase in the critical threshold with the applied increase in the probability of space removal. Such an observation will have an important medical implication: a much larger than expected radiation dose is needed for a tumor breakup enabling successful follow-up chemotherapy. Information on the TME’s hypoxia heterogeneity, as shown here with the numerical percolation model, may enable personalized precision radiation oncology therapy. 相似文献
88.
Lei Jia Jianzhu Wang Tianyuan Wang Xiaobao Li Haomin Yu Qingyong Li 《Entropy (Basel, Switzerland)》2022,24(4)
Vehicles carrying hazardous material (hazmat) are severe threats to the safety of highway transportation, and a model that can automatically recognize hazmat markers installed or attached on vehicles is essential for intelligent management systems. However, there is still no public dataset for benchmarking the task of hazmat marker detection. To this end, this paper releases a large-scale vehicle hazmat marker dataset named VisInt-VHM, which includes 10,000 images with a total of 20,023 hazmat markers captured under different environmental conditions from a real-world highway. Meanwhile, we provide an compact hazmat marker detection network named HMD-Net, which utilizes a revised lightweight backbone and is further compressed by channel pruning. As a consequence, the trained-model can be efficiently deployed on a resource-restricted edge device. Experimental results demonstrate that compared with some established methods such as YOLOv3, YOLOv4, their lightweight versions and popular lightweight models, HMD-Net can achieve a better trade-off between the detection accuracy and the inference speed. 相似文献
89.
90.