全文获取类型
收费全文 | 67297篇 |
免费 | 10031篇 |
国内免费 | 6548篇 |
专业分类
化学 | 45188篇 |
晶体学 | 638篇 |
力学 | 4541篇 |
综合类 | 516篇 |
数学 | 8410篇 |
物理学 | 24583篇 |
出版年
2024年 | 59篇 |
2023年 | 1356篇 |
2022年 | 1351篇 |
2021年 | 1979篇 |
2020年 | 2491篇 |
2019年 | 2383篇 |
2018年 | 2127篇 |
2017年 | 1880篇 |
2016年 | 2882篇 |
2015年 | 2947篇 |
2014年 | 3507篇 |
2013年 | 4701篇 |
2012年 | 5796篇 |
2011年 | 6015篇 |
2010年 | 4079篇 |
2009年 | 4019篇 |
2008年 | 4187篇 |
2007年 | 3787篇 |
2006年 | 3568篇 |
2005年 | 3092篇 |
2004年 | 2473篇 |
2003年 | 1868篇 |
2002年 | 1574篇 |
2001年 | 1457篇 |
2000年 | 1329篇 |
1999年 | 1481篇 |
1998年 | 1278篇 |
1997年 | 1117篇 |
1996年 | 1170篇 |
1995年 | 1060篇 |
1994年 | 1000篇 |
1993年 | 859篇 |
1992年 | 757篇 |
1991年 | 661篇 |
1990年 | 549篇 |
1989年 | 481篇 |
1988年 | 363篇 |
1987年 | 346篇 |
1986年 | 295篇 |
1985年 | 300篇 |
1984年 | 201篇 |
1983年 | 174篇 |
1982年 | 145篇 |
1981年 | 112篇 |
1980年 | 82篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1976年 | 50篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 35 毫秒
41.
Tian Jie Yang Weifeng Chen Min Zheng Minfang Chen Ding Qiu Yusheng 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(2):1039-1049
Journal of Radioanalytical and Nuclear Chemistry - This study presents a time-efficient method of analysing 210Pb, 210Bi, and 210Po in natural waters. The optimum pH (1.00), temperature... 相似文献
42.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
43.
44.
In this paper, we study the well-posedness and the asymptotic stability of a one-dimensional thermoelastic microbeam system, where the heat conduction is given by Gurtin-Pipkin thermal law. We first establish the well-posedness of the system by using the semigroup arguments and Lumer-Phillips theorem. We then obtain an explicit and general formula for the energy decay rates through perturbed energy method and some properties of the convex functions. 相似文献
45.
正following Cayley-Hamilton theorem:(1)where I1, I2, and I3denote the first, second, and third principal invariants of and N-dimensional space,(2) 相似文献
46.
Recent success in strain engineering has triggered tremendous interest in its study and potential applications in nanodevice design. In this paper, we establish a coupled piezoelectric/semiconducting model for a wurtzite structure ZnO nanofiber under the local mechanical loading. The energy band structure tuned by the local mechanical loading and local length is calculated via an eight-band k·p method, which includes the coupling of valance and conduction bands. Poisson's effect on the distribution of electric potential inversely depends on the local mechanical loading. Numerical results reveal that both the applied local mechanical loading and the local length exhibit obvious tuning effects on the electric potential and energy band. The band gap at band edges varies linearly with the applied loading. Changing the local length shifts the energy band which is far away from the band edges. This study will be useful in the electronic and optical enhancement of semiconductor devices. 相似文献
47.
Numerical Algorithms - The purpose of this paper is to propose an algorithm for solving the split common fixed point problem for strict quasi-?-pseudocontractive mappings in Banach spaces. It... 相似文献
48.
49.
50.
Acta Mechanica Sinica - 相似文献