全文获取类型
收费全文 | 103323篇 |
免费 | 17193篇 |
国内免费 | 11836篇 |
专业分类
化学 | 72468篇 |
晶体学 | 1135篇 |
力学 | 5876篇 |
综合类 | 666篇 |
数学 | 12617篇 |
物理学 | 39590篇 |
出版年
2024年 | 351篇 |
2023年 | 2067篇 |
2022年 | 3667篇 |
2021年 | 3820篇 |
2020年 | 4175篇 |
2019年 | 3957篇 |
2018年 | 3713篇 |
2017年 | 3334篇 |
2016年 | 5015篇 |
2015年 | 4923篇 |
2014年 | 6050篇 |
2013年 | 7780篇 |
2012年 | 9277篇 |
2011年 | 9472篇 |
2010年 | 6622篇 |
2009年 | 6354篇 |
2008年 | 6677篇 |
2007年 | 5966篇 |
2006年 | 5584篇 |
2005年 | 4658篇 |
2004年 | 3646篇 |
2003年 | 2928篇 |
2002年 | 2661篇 |
2001年 | 2229篇 |
2000年 | 1945篇 |
1999年 | 2050篇 |
1998年 | 1735篇 |
1997年 | 1559篇 |
1996年 | 1555篇 |
1995年 | 1367篇 |
1994年 | 1239篇 |
1993年 | 1004篇 |
1992年 | 901篇 |
1991年 | 776篇 |
1990年 | 652篇 |
1989年 | 503篇 |
1988年 | 378篇 |
1987年 | 338篇 |
1986年 | 335篇 |
1985年 | 263篇 |
1984年 | 189篇 |
1983年 | 153篇 |
1982年 | 125篇 |
1981年 | 78篇 |
1980年 | 59篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Chi-Kwong Li Ming-Cheng Tsai Ya-Shu Wang Ngai-Ching Wong 《Journal of Mathematical Analysis and Applications》2022,505(2):125522
Let L be an additive map between (real or complex) matrix algebras sending Hermitian idempotent matrices to Hermitian idempotent matrices. We show that there are nonnegative integers with and an unitary matrix U such that We also extend this result to the (complex) von Neumann algebra setting, and provide a supplement to the Dye-Bunce-Wright Theorem asserting that every additive map of Hermitian idempotents extends to a Jordan ?-homomorphism. 相似文献
24.
25.
26.
27.
28.
Dekun Wu Dr. Qing Xu Dr. Jing Qian Prof. Xiaopeng Li Prof. Yuhan Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3105-3111
Covalent organic frameworks (COFs) are a new class of crystalline porous polymers comprised mainly of carbon atoms, and are versatile for the integration of heteroatoms such as B, O, and N into the skeletons. The designable structure and abundant composition render COFs useful as precursors for heteroatom-doped porous carbons for energy storage and conversion. Herein, we describe a multifunctional electrochemical catalyst obtained through pyrolysis of a bimetallic COF. The catalyst possesses hierarchical pores and abundant iron and cobalt nanoparticles embedded with standing carbon layers. By integrating these features, the catalyst exhibits excellent electrochemical catalytic activity in the oxygen reduction reaction (ORR), with a 50 mV positive half-wave potential, a higher limited diffusion current density, and a much smaller Tafel slope than a Pt-C catalyst. Moreover, the catalyst displays superior electrochemical performance toward the hydrogen evolution reaction (HER), with overpotentials of −0.26 V and −0.33 V in acidic and alkaline aqueous solution, respectively, at a current density of 10 mA cm−2. The overpotential in the catalysis of the oxygen evolution reaction (OER) was 1.59 V at the same current density. 相似文献
29.
We proposed an electro-optic modulator with two-bus one-ring (TBOR) structure to improve the extinction ratio and reduce insert loss. It has a dual output compared with one-bus one-ring structure. In addition, double-layer graphene makes it possible for the modulation in the visible to mid-infrared wavelength range. It shows that this new electro-optic modulator can present two switching states well with low insertion loss, high absorption and high extinction ratio. At , when the switching states are based on the chemical potential, and , the insertion losses of both output ports are less than 2 dB, the absorption of the output port coupled via a micro-ring reaches 45 dB and the extinction ratio reaches 14 dB. When the refractive index of the dielectric material is 4.2, the applied voltage will be less than 1.2 V, thus can be used in low-voltage CMOS technology. 相似文献
30.
Yingchun Wu Haipeng Li Xuecheng Wu Gérard Gréhan Lutz Mädler Cyril Crua 《Proceedings of the Combustion Institute》2019,37(3):3211-3218
Droplet evaporation characterization, although of great significance, is still challenging. The recently developed phase rainbow refractometry (PRR) is proposed as an approach to measuring the droplet temperature, size as well as evaporation rate simultaneously, and is applied to a single flowing n-heptane droplet produced by a droplet-on-demand generator. The changes of droplet temperature and evaporation rate after a transient spark heating are reflected in the time-resolved PRR image. Results show that droplet evaporation rate increases with temperature, from ?1.28 m2/s at atmospheric 293 K to a range of (?1.5, ?8) m2/s when heated to (294, 315) K, agreeing well with the Maxwell and Stefan–Fuchs model predictions. Uncertainty analysis suggests that the main source is the indeterminate gradient inside droplet, resulting in an underestimation of droplet temperature and evaporation rate. With the demonstration on simultaneous measurements of droplet refractive index as well as droplet transient and local evaporation rate in this work, PRR is a promising tool to investigate single droplet evaporation in real engine conditions. 相似文献