全文获取类型
收费全文 | 31380篇 |
免费 | 6115篇 |
国内免费 | 9554篇 |
专业分类
化学 | 24702篇 |
晶体学 | 1182篇 |
力学 | 2060篇 |
综合类 | 1073篇 |
数学 | 4576篇 |
物理学 | 13456篇 |
出版年
2024年 | 85篇 |
2023年 | 342篇 |
2022年 | 940篇 |
2021年 | 1007篇 |
2020年 | 1111篇 |
2019年 | 1070篇 |
2018年 | 1005篇 |
2017年 | 1231篇 |
2016年 | 1232篇 |
2015年 | 1611篇 |
2014年 | 1889篇 |
2013年 | 2430篇 |
2012年 | 2562篇 |
2011年 | 2774篇 |
2010年 | 2502篇 |
2009年 | 2586篇 |
2008年 | 3008篇 |
2007年 | 2571篇 |
2006年 | 2486篇 |
2005年 | 2170篇 |
2004年 | 1828篇 |
2003年 | 1441篇 |
2002年 | 1456篇 |
2001年 | 1402篇 |
2000年 | 1369篇 |
1999年 | 916篇 |
1998年 | 518篇 |
1997年 | 395篇 |
1996年 | 404篇 |
1995年 | 369篇 |
1994年 | 300篇 |
1993年 | 296篇 |
1992年 | 246篇 |
1991年 | 212篇 |
1990年 | 195篇 |
1989年 | 183篇 |
1988年 | 167篇 |
1987年 | 130篇 |
1986年 | 106篇 |
1985年 | 70篇 |
1984年 | 84篇 |
1983年 | 82篇 |
1982年 | 74篇 |
1981年 | 55篇 |
1980年 | 41篇 |
1979年 | 32篇 |
1978年 | 17篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gao‐Feng Chen Yu‐Zhi Su Pan‐Yong Kuang Zhao‐Qing Liu Dao‐Yi Chen Xu Wu Nan Li Prof. Shi‐Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4614-4621
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively). 相似文献
12.
Acta Mathematica Sinica, English Series - We are interested in the existence and asymptotic behavior for the least energy solutions of the following fractional eigenvalue problem $$\left({\rm{P}}... 相似文献
13.
14.
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
15.
Sung Hwan Koo Dong Jun Li Taeyeong Yun Dong Sung Choi Kyung Eun Lee Gil Yong Lee Youngtak Oh Joonwon Lim Suchithra Padmajan Sasikala Ho Jin Lee In Ho Kim Hong Ju Jung Rishabh Jain Sang Ouk Kim 《Particle & Particle Systems Characterization》2019,36(7)
Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS2, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec?1 and a charge transfer resistance (Rct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer. 相似文献
16.
Ling-Yang Hsu Qiumin Liang Zhiheng Wang Hsin-Hung Kuo Wun-Shan Tai Shi-Jian Su Xiuwen Zhou Yi Yuan Yun Chi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(67):15375-15386
Iridium complexes bearing chelating cyclometalates are popular choices as dopant emitters in the fabrication of organic light-emitting diodes (OLEDs). In this contribution, we report a series of blue-emitting, bis-tridentate IrIII complexes bearing chelates with two fused five-six-membered metallacycles, which are in sharp contrast to the traditional designs of tridentate chelates that form the alternative, fused five-five metallacycles. Five IrIII complexes, Px-21 – 23 , Cz-4 , and Cz-5 , have been synthesized that contain a coordinated dicarbene pincer chelate incorporating a methylene spacer and a dianionic chromophoric chelate possessing either a phenoxy or carbazolyl appendage to tune the coordination arrangement. All these tridentate chelates afford peripheral ligand–metal–ligand bite angles of 166–170°, which are larger than the typical bite angle of 153–155° observed for their five-five-coordinated tridentate counterparts, thereby leading to reduced geometrical distortion in the octahedral frameworks. Photophysical measurements and TD-DFT studies verified the inherent transition characteristics that give rise to high emission efficiency, and photodegradation experiments confirmed the improved stability in comparison with the benchmark fac-[Ir(ppy)3] in degassed toluene at room temperature. Phosphorescent OLED devices were also fabricated, among which the carbazolyl-functionalized emitter Cz-5 exhibited the best performance among all the studied bis-tridentate phosphors, showing a maximum external quantum efficiency (EQEmax) of 18.7 % and CIEx,y coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m−2 due to efficiency roll-off. 相似文献
17.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework. 相似文献
18.
Summary Consider the solution of one-dimensional linear initial-boundary value problems by a finite element method of lines using a piecewiseP
th
-degree polynomial basis. A posteriori estimates of the discretization error are obtained as the solutions of either local parabolic or local elliptic finite element problems using piecewise polynomial corrections of degreep+1 that vanish at element ends. Error estimates computed in this manner are shown to converge in energy under mesh refinement to the exact finite element discretization error. Computational results indicate that the error estimates are robust over a wide range of mesh spacings and polynomial degrees and are, furthermore, applicable in situations that are not supported by the analysis.This research was partially supported by the U.S. Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant Number AFOSR 90-0194; by the U.S. Army Research Office under Contract Number DAAL03-91-G-0215; and by the National Science Foundation under Institutional Infrastructure Grant Number CDA-8805910 相似文献
19.
20.