全文获取类型
收费全文 | 24709篇 |
免费 | 3935篇 |
国内免费 | 3034篇 |
专业分类
化学 | 13641篇 |
晶体学 | 177篇 |
力学 | 1129篇 |
综合类 | 118篇 |
数学 | 2719篇 |
物理学 | 7441篇 |
无线电 | 6453篇 |
出版年
2024年 | 122篇 |
2023年 | 652篇 |
2022年 | 723篇 |
2021年 | 930篇 |
2020年 | 1024篇 |
2019年 | 939篇 |
2018年 | 810篇 |
2017年 | 801篇 |
2016年 | 1125篇 |
2015年 | 1184篇 |
2014年 | 1339篇 |
2013年 | 1757篇 |
2012年 | 2028篇 |
2011年 | 2063篇 |
2010年 | 1556篇 |
2009年 | 1395篇 |
2008年 | 1576篇 |
2007年 | 1402篇 |
2006年 | 1286篇 |
2005年 | 1169篇 |
2004年 | 893篇 |
2003年 | 845篇 |
2002年 | 917篇 |
2001年 | 764篇 |
2000年 | 596篇 |
1999年 | 579篇 |
1998年 | 472篇 |
1997年 | 401篇 |
1996年 | 434篇 |
1995年 | 355篇 |
1994年 | 292篇 |
1993年 | 212篇 |
1992年 | 211篇 |
1991年 | 203篇 |
1990年 | 143篇 |
1989年 | 104篇 |
1988年 | 68篇 |
1987年 | 67篇 |
1986年 | 76篇 |
1985年 | 51篇 |
1984年 | 38篇 |
1983年 | 28篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
本文介绍事后分层技术,说明了它不仅可用于简单随机抽样,而且可以用于放回PPS抽样。给出了事后分层估计量的形式,证明了它的无编性,并给出了它在交通运输抽样调查中的应用。 相似文献
93.
郭飞 《应用数学与计算数学学报》1997,11(1):19-26
Wilson,Han和Powell提出的序列二次规划方法(简称SQP方法)是求解非线性规划问题的一个著名方法,这种方法每次迭代的搜索方向是通过求解一个二次规划子问题得到的,本文受[1]启发,得到二次规划子问题的一个近似解,进而给出了一类求解线性约束非线性规划问题的可行方向法,在约束集合满足正则性的条件下,证明了该算法对五种常用线性搜索方法具有全局收敛性。 相似文献
94.
95.
Cheng Chen Zheng Guo Li Yeng Chai Soh 《Networking, IEEE/ACM Transactions on》2007,15(3):697-708
In this paper, we shall generalize the concepts of fairness, TCP-friendliness and TCP-compatibility such that more source adaptation schemes can be designed to support diverse applications over the Internet. A simple but efficient framework, in the form of a monotonic response function (MRF), is proposed for the analysis and the design of memoryless window-based source adaptation protocols by using these concepts. We first derive a necessary and sufficient condition for step-wise convergence to the weighted fairness. It is then used to construct increase-decrease policies. The requirements of our increase-decrease policy are less conservative than those of the CYRF (Choose Your Response Function) that was proposed in . Our MRF is suitable for transmission control protocol (TCP) and user datagram protocol (UDP), and can be used to design TCP-friendly and multimedia-friendly source adaptation schemes. Meanwhile, our MRF can be applied to provide bandwidth differentiation service without any change to the router of the existing Internet. 相似文献
96.
97.
ZrO2 nanoparticles was uniformly co-deposited into a nickel matrix by electroplating of nickel from a Watts bath containing particles in suspension which were monodispersed with dispersant under DC electrodeposition condition. It was found that morphology, orientation and hardness of the nanocomposite coatings with monodispersed ZrO2 nanoparticles had lots of difference from the nanocomposite coatings with agglomerated ZrO2 nanoparticles and pure nickel coatings. Especially, the result of hardness showed that only a very low volume percent (less than 1 wt.%) of monodispered ZrO2 nanoparticles in Ni-ZrO2 nanocomposite coatings would result in higher hardness of the coatings. The hardness of Ni-ZrO2 nanocomposite coatings with monodispersed and agglomerated ZrO2 nanoparticles were 529 and 393 HV, respectively. The hardness value of the former composite coatings was over 1.3 times higher than that of the later. All these composite coatings were two-three times higher than that of pure nickel plating (207 HV) prepared under the same condition. The strengthening mechanisms of the Ni-ZrO2 nanocomposite coatings based on a combination of grain refinement strengthening from nickel matrix grain refining and dispersion strengthening from dispersion state of ZrO2 nanoparticles in the coatings. 相似文献
98.
The behavior of a two-level entangled atom in an optical field with circular polarization is studied in this paper. The interaction of an optical field and one of the entangled atoms is analyzed in detail. A general solution of the SchrAo¨Gdinger equation about the motion of the entangled atom is obtained. The properties of the action are dependent on the initial state of the atom. By detecting the entangled atom out of the field, we can obtain the state of the other atom moving in the field. It is shown that the state of the atom out of the field will influence the energies of the split-levels of the atom in the field. 相似文献
99.
100.