全文获取类型
收费全文 | 204122篇 |
免费 | 19399篇 |
国内免费 | 465篇 |
专业分类
化学 | 144411篇 |
晶体学 | 2571篇 |
力学 | 7522篇 |
综合类 | 3篇 |
数学 | 18576篇 |
物理学 | 50903篇 |
出版年
2023年 | 4458篇 |
2022年 | 2230篇 |
2021年 | 3530篇 |
2020年 | 5948篇 |
2019年 | 3641篇 |
2018年 | 4339篇 |
2017年 | 2648篇 |
2016年 | 8553篇 |
2015年 | 7370篇 |
2014年 | 7621篇 |
2013年 | 12259篇 |
2012年 | 9022篇 |
2011年 | 8161篇 |
2010年 | 8094篇 |
2009年 | 8003篇 |
2008年 | 7816篇 |
2007年 | 7315篇 |
2006年 | 6531篇 |
2005年 | 5964篇 |
2004年 | 5385篇 |
2003年 | 4849篇 |
2002年 | 4669篇 |
2001年 | 6036篇 |
2000年 | 4418篇 |
1999年 | 3427篇 |
1998年 | 2377篇 |
1997年 | 2486篇 |
1996年 | 2438篇 |
1995年 | 2237篇 |
1994年 | 2229篇 |
1993年 | 2121篇 |
1992年 | 2485篇 |
1991年 | 2547篇 |
1990年 | 2357篇 |
1989年 | 2319篇 |
1988年 | 2326篇 |
1987年 | 2306篇 |
1986年 | 2109篇 |
1985年 | 2646篇 |
1984年 | 2673篇 |
1983年 | 2115篇 |
1982年 | 2131篇 |
1981年 | 1992篇 |
1979年 | 2238篇 |
1978年 | 2310篇 |
1977年 | 2336篇 |
1976年 | 2264篇 |
1975年 | 2150篇 |
1974年 | 2118篇 |
1973年 | 2085篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
21.
Verdecho María-José Alarcón-Valero Faustino Pérez-Perales David Alfaro-Saiz Juan-José Rodríguez-Rodríguez Raúl 《Central European Journal of Operations Research》2021,29(4):1231-1251
Central European Journal of Operations Research - Sustainability practice within supply chains remains in an early development phase. Enterprises still need tools that support the integration of... 相似文献
22.
Numerical Algorithms - This paper considers different versions of block-column iterative (BCI) methods for solving nonnegative constrained linear least squares problems. We present the convergence... 相似文献
23.
Set-Valued and Variational Analysis - In a Hilbert framework ℌ, we study the convergence properties of a Newton-like inertial dynamical system governed by a general maximally monotone... 相似文献
24.
Theoretical and Mathematical Physics - We consider three one-dimensional superconducting structures: 1) the one with $$p$$ -wave superconductivity; 2) the main experimental model of a nanowire with... 相似文献
25.
26.
Reza Kordnezhadian Bing-Yu Li Armir Zogu Dr. Joachim Demaerel Prof. Dr. Wim M. De Borggraeve Dr. Ermal Ismalaj 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201491
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015. 相似文献
27.
Dr. Manussada Ratanasak Takumi Murata Taishin Adachi Prof. Jun-ya Hasegawa Prof. Tadashi Ema 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(58):e202202210
BPh3 catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent-free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]−. The detailed mechanism of the BPh3-catalyzed N-methylation of N-methylaniline ( 1 ) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N-methylaniline and CO2) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N+CO2−⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3]−, which is used to produce key CO2-derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1 . DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3]− species. 相似文献
28.
Meihua Shen Dr. Xinpeng Zhao Dr. Lu Han Nanxi Jin Prof. Song Liu Prof. Tao Jia Prof. Zhijun Chen Prof. Xiuhua Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(20):e202104137
Solar-driven interfacial vaporization by localizing solar-thermal energy conversion to the air−water interface has attracted tremendous attention. In the process of converting solar energy into heat energy, photothermal materials play an essential role. Herein, a flexible solar-thermal material di-cyan substituted 5,12-dibutylquinacridone (DCN−4CQA)@Paper was developed by coating photothermal quinacridone derivatives on the cellulose paper. The DCN−4CQA@Paper combines desired chemical and physical properties, broadband light-absorbing, and shape-conforming abilities that render efficient photothermic vaporization. Notably, synergetic coupling of solar-steam and solar-electricity technologies by integrating DCN−4CQA@Paper and the thermoelectric devices is realized without trade-offs, highlighting the practical consideration toward more impactful solar heat exploitation. Such solar distillation and low-grade heat-to-electricity generation functions can provide potential opportunities for fresh water and electricity supply in off-grid or remote areas. 相似文献
29.
Dr. Ruijuan Yao Prof. Di Liu Dr. Huihui Wan Dr. Yongqiang Mei Jiahui Wang Dr. Rui Cai Dr. Huimin Zhang Dr. Yuzhen Zhao Dr. Zemin He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202269
By linking the carbazole unit to the nitrogen atom of acridone through phenyl or pyridyl, two compounds, named 10-(4-(9H-carbazol-9-yl)phenyl)acridin-9(10H)-one (AC-Ph-Cz) and 10-(5-(9H-carbazol-9-yl)pyridin-2-yl)acridin-9(10H)-one (AC-Py-Cz) were designed and synthesized. These two materials, characterized with highly twisted and rigid structure, good thermal stability, and balanced carrier-transporting properties, were employed as host materials for green phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes (OLEDs). The carbazole group, despite its small contribution to the highest occupied molecular orbitals (HOMOs) of these two materials, plays an essential role as an intramolecular host in energy delivering and improving the hole transporting ability of these two hosts. The incorporation of the electron-deficient pyridyl group as a linking group slightly improves the electron transporting capability of AC-Py-Cz. The green phosphorescent OLED (PhOLED) based on AC-Py-Cz exhibited excellent device performance with a turn-on voltage of 2.5 V, a maximum power efficiency and an external quantum efficiency (ηext) of 89.8 lm W−1 and 25.2 %, respectively, benefitting from the better charge-balancing ability of AC-Py-Cz host due to the presence of the pyridyl bridge. More importantly, all the devices based on these two hosts showed low efficiency roll-off at high brightness due to the suppressed non-radiative transition in the emitting layer. In particular, the AC-Py-Cz-hosted green PhOLED exhibited an efficiency roll-off of 1.6 % from the maximum next at a high brightness of 1000 cd m−2 and a roll-off of 15.9 % at an extremely high brightness of 10000 cd m−2. This study manifests that acridone-based host materials have great potential in fabricating OLEDs with low efficiency roll-off. 相似文献
30.