全文获取类型
收费全文 | 30263篇 |
免费 | 5125篇 |
国内免费 | 4938篇 |
专业分类
化学 | 23513篇 |
晶体学 | 530篇 |
力学 | 1556篇 |
综合类 | 382篇 |
数学 | 3474篇 |
物理学 | 10871篇 |
出版年
2024年 | 33篇 |
2023年 | 514篇 |
2022年 | 707篇 |
2021年 | 975篇 |
2020年 | 1243篇 |
2019年 | 1318篇 |
2018年 | 1071篇 |
2017年 | 1119篇 |
2016年 | 1461篇 |
2015年 | 1503篇 |
2014年 | 1907篇 |
2013年 | 2368篇 |
2012年 | 2806篇 |
2011年 | 2924篇 |
2010年 | 2255篇 |
2009年 | 2153篇 |
2008年 | 2284篇 |
2007年 | 2139篇 |
2006年 | 1989篇 |
2005年 | 1621篇 |
2004年 | 1220篇 |
2003年 | 939篇 |
2002年 | 920篇 |
2001年 | 788篇 |
2000年 | 657篇 |
1999年 | 606篇 |
1998年 | 431篇 |
1997年 | 372篇 |
1996年 | 318篇 |
1995年 | 300篇 |
1994年 | 275篇 |
1993年 | 200篇 |
1992年 | 164篇 |
1991年 | 147篇 |
1990年 | 139篇 |
1989年 | 94篇 |
1988年 | 77篇 |
1987年 | 59篇 |
1986年 | 63篇 |
1985年 | 50篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1971年 | 4篇 |
1957年 | 4篇 |
1936年 | 4篇 |
1909年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
A new asymmetric Salamo‐based ligand H2L was synthesized using 3‐tert‐butyl‐salicylaldehyde and 6‐methoxy‐2‐[O‐(1‐ethyloxyamide)]‐oxime‐1‐phenol. By adjusting the ratio of the ligand H2L and Cu (II), Co (II), and Ni (II) ions, mononuclear, dinuclear, and trinuclear transition metal (II) complexes, [Cu(L)], [{Co(L)}2], and [{Ni(L)(CH3COO)(CH3CH2OH)}2Ni] with the ligand H2L possessing completely different coordination modes were obtained, respectively. The optical spectra of ligand H2L and its Cu (II), Co (II) and Ni (II) complexes were investigated. The Cu (II) complex is a mononuclear structure, and the Cu (II) atom is tetracoordinated to form a planar quadrilateral structure. The Co (II) complex is dinuclear, and the two Co (II) atoms are pentacoordinated and have coordination geometries of distorted triangular bipyramid. The Ni (II) complex is a trinuclear structure, and the terminal and central Ni (II) atoms are all hexacoordinated, forming distorted octahedral geometries. Furthermore, optical properties including UV–Vis, IR, and fluorescence of the Cu (II), Co (II), and Ni (II) complexes were investigated. Finally, the antibacterial activities of the Cu (II), Co (II), and Ni (II) complexes were explored. According to the experimental results, the inhibitory effect was found to be enhanced with increasing concentrations of the Cu (II), Co (II), and Ni (II) complexes. 相似文献
33.
现有的基于磁共振测量的嗅觉刺激器,通过调节嗅剂液体浓度的方法可以实现不同浓度的嗅觉刺激,但随着实验进行,受到嗅剂挥发以及实验环境(温度、湿度、气流量)变化的影响,很难确保输送至鼻腔的嗅剂气体浓度的稳定性,进而影响实验结果的准确性.本研究对本实验室前期开发的嗅觉刺激装置进行改进,实现了气体浓度精确定量.改进后的嗅觉刺激器主要分为三个部分:控制系统、反馈系统和气路系统.控制系统主要实现气路系统的送气控制和嗅剂气体浓度调节;反馈系统则负责对气体浓度进行测量;气路系统则在原有基础上添加活性炭装置,降低无关因素干扰.装置改进之后,不同气路切换时间为75.2 ms,比原装置减少了1 s,有效提高刺激精度.实验结果显示,气体浓度调节前,300 s内乙醇、吡啶、乙酸戊酯嗅剂气体浓度分别下降6.7%、71.4%、79.2%,嗅剂气体浓度短时间内发生较大改变.加入气体浓度调节功能后,当气体浓度下降至目标浓度的90%时,可通过调节气泵电压改变嗅剂气流与空气气流比例,从而调节嗅剂气体浓度至目标值,其中吡啶、乙酸戊酯用时13 s. 相似文献
34.
35.
JETP Letters - Optimal control of quantum system is significant for information science and technology. Here, an efficient scheme is proposed for implementing fast population transfer in a spin... 相似文献
36.
We report a spatially modulated polarimetry scheme by using a zero-order vortex half-wave retarder(ZVHR)and a spatial Fourier analysis method.A ZVHR is employed to analyze the input polarized light and convert it into a vectorial optical field,and an analyzer is set after the ZVHR to form an hourglass intensity pattern due to the spatial polarization modulation.Then,the input light’s Stokes parameters can be calculated by spatial Fourier analysis of the hourglass pattern with a single shot.The working principle of the polarimeter has been analyzed by the Stokes-Mueller formalism,and some quantitative measuring experiments of different polarization states have been demonstrated.The experimental results indicate that the proposed polarimeter is accurate,robust,and simple to use. 相似文献
37.
Nonlinear Dynamics - This article considers a reaction–diffusion predator–prey model with schooling behavior both in predator and prey species and subject to the homogeneous Neumann... 相似文献
38.
Covalent organic frameworks(COFs), as a class of crystalline porous materials with periodic lattices and porous structures, have received extensive attention in the fields of gas storage and separation, energy storage, catalysis and optoelectronics and so on. However, COFs are still in their infancy in the field of nuclear waste treatment, especially for sequestration of long-live problematic radionuclides, such as 99Tc. Battle of decontamination of pertechnetate(TcO4–), a main existence of 99Tc under aerobic environments, is far from finished. In this review, recent progresses of COFs and some relative materials in the sequestration of pertechnetate, and perspective on surmounting the unmet issues are elucidated. 相似文献
40.
Liu Shuling Chen Yan Ren Jing Wang Yueyan Wei Wei 《Journal of Solid State Electrochemistry》2019,23(12):3409-3418
Journal of Solid State Electrochemistry - Polypyrrole/nickel phosphide (PPy/Ni2P) composites were synthesized through a facile two-step method. The results show that when there is 30% Ni2P in... 相似文献