全文获取类型
收费全文 | 9114篇 |
免费 | 807篇 |
国内免费 | 542篇 |
专业分类
化学 | 6038篇 |
晶体学 | 125篇 |
力学 | 375篇 |
综合类 | 49篇 |
数学 | 1236篇 |
物理学 | 2640篇 |
出版年
2023年 | 133篇 |
2022年 | 301篇 |
2021年 | 304篇 |
2020年 | 345篇 |
2019年 | 318篇 |
2018年 | 286篇 |
2017年 | 251篇 |
2016年 | 372篇 |
2015年 | 388篇 |
2014年 | 406篇 |
2013年 | 666篇 |
2012年 | 615篇 |
2011年 | 637篇 |
2010年 | 459篇 |
2009年 | 409篇 |
2008年 | 471篇 |
2007年 | 412篇 |
2006年 | 392篇 |
2005年 | 327篇 |
2004年 | 247篇 |
2003年 | 254篇 |
2002年 | 228篇 |
2001年 | 206篇 |
2000年 | 160篇 |
1999年 | 125篇 |
1998年 | 81篇 |
1997年 | 75篇 |
1996年 | 87篇 |
1995年 | 59篇 |
1994年 | 100篇 |
1993年 | 80篇 |
1992年 | 85篇 |
1991年 | 72篇 |
1990年 | 65篇 |
1989年 | 51篇 |
1988年 | 49篇 |
1987年 | 42篇 |
1986年 | 45篇 |
1985年 | 66篇 |
1984年 | 65篇 |
1983年 | 40篇 |
1982年 | 62篇 |
1981年 | 53篇 |
1980年 | 57篇 |
1979年 | 51篇 |
1978年 | 58篇 |
1977年 | 51篇 |
1976年 | 47篇 |
1975年 | 37篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Multi‐Species Multi‐Channel (MSMC): An Ab Initio‐based Parallel Thermodynamic and Kinetic Code for Complex Chemical Systems 下载免费PDF全文
Multi‐Species Multi‐Channel (MSMC) is an ab initio parallel program to calculate thermodynamic quantities (e.g., , , , and , time‐dependent species profiles, and rate coefficients as functions of temperature and pressure for complex chemical reaction systems, which consist of multiple stable species and multiple reaction channels interconnecting them. Thermodynamic properties of the species involved are calculated using statistical mechanics with molecular information from electronic structure calculations. Temperature‐ and pressure‐dependent behaviors are rigorously characterized within the eigenpair master equation/Rice–Ramsperger–Kassel–Marcus (ME/RRKM) framework. Corrections, e.g., for hindered internal rotation and tunneling treatment, are included. With the implementation of an ultra‐high precision package and rigorous matrix setup, MSMC is able to correctly mimic real behaviors of different types of chemical systems. Different eigenpair‐based approaches to extract phenomenological/macroscopic rate coefficients are implemented for different applications. Moreover, a friendly and platform‐independent graphical‐user‐interface (GUI) is provided to facilitate the use of MSMC and the pre‐/postcalculation data visualization/analysis on the fly. The program can be freely downloaded at https://sites.google.com/site/msmccode/ . 相似文献
993.
手性有机硼化合物在有机合成、医药、材料等诸多领域中有广泛的应用,发展该类化合物的高效合成方法一直广受关注.此前,我们发展了过渡金属催化卡宾对硼氢键(B—H)的插入反应,并实现了α-重氮酯对B—H键的不对称插入反应.本文以手性螺环双噁唑啉配体和铜的络合物作为催化剂,首次实现了α-重氮酮对膦-硼烷加合物的B—H键不对称插入反应,获得了较高的收率和高达83%ee的对映选择性.该研究成果是为数不多的以α-重氮酮作为卡宾前体的不对称杂原子氢键插入反应,为手性α-硼取代酮化合物这类新的有机硼化合物的合成提供了有效方法. 相似文献
994.
Prof. Ewald Janssens Hai Thuy Le Prof. Peter Lievens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15256-15262
The adsorption of propene on neutral gold clusters is investigated in a collision cell under a few collision conditions. The adsorption reaction is studied by pressure‐dependent kinetic measurements and delayed unimolecular dissociation of the excited Aun?propene complexes. The cluster size (n=9–25) and temperature (T=90–300 K) dependence of the propene adsorption is analyzed. Strong size dependences of the absorption reaction are observed; a larger propene adsorption probability was found for gold clusters composed of an even number of atoms. Propene binding energies are estimated by comparison of the temperature‐dependent unimolecular dissociation rates with rates obtained by using statistical RRKM modeling. The Aun–propene binding energies decrease non‐monotonously with cluster size and are in the range of 1.2–0.85 eV for n=9–25. Finally, the bonding of C3H6 on Aun is qualitatively described and similarities with the absorption of CO molecules on gold clusters are discussed. 相似文献
995.
Xiaobei Wang Dongliang Xia Ling Tan Huan Chen Hongxiu Huang Dr. Hao Song Prof. Dr. Yong Qin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14602-14607
Total syntheses of (?)‐isoschizogamine and (?)‐2‐hydroxyisoschizogamine are described. The synthesis employs two asymmetric Michael additions to establish chiral centers at C7 and the quaternary carbon C20. Regioselective reduction of the methylthioiminium cation rather than the enamine generates an isoschizogamine‐type pentacyclic skeleton. Acidic hydrolysis of the isoschizogamine‐type intermediate in the absence of oxygen provides natural (?)‐isoschizogamine. Conducting the reaction in the presence of oxygen leads to a multistep oxidative hydrolysis cascade that affords unnatural (?)‐2‐hydroxyisoschizogamine. 相似文献
996.
Clean Synthesis of an Economical 3D Nanochain Network of PdCu Alloy with Enhanced Electrocatalytic Performance towards Ethanol Oxidation 下载免费PDF全文
Jiawei Liu Zhao Huang Kai Cai Huan Zhang Dr. Zhicheng Lu Tingting Li Yunpeng Zuo Prof. Heyou Han 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17779-17785
A one‐pot method for the fast synthesis of a 3D nanochain network (NNC) of PdCu alloy without any surfactants is described. The composition of the as‐prepared PdCu alloy catalysts can be precisely controlled by changing the precursor ratio of Pd to Cu. First, the Cu content changes the electronic structure of Pd in the 3D NNC of PdCu alloy. Second, the 3D network structure offers large open pores, high surface areas, and self‐supported properties. Third, the surfactant‐free strategy results in a relatively clean surface. These factors all contribute to better electrocatalytic activity and durability towards ethanol oxidation. Moreover, the use of copper in the alloy lowers the price of the catalyst by replacing the noble metal palladium with non‐noble metal copper. The composition‐optimized Pd80Cu20 alloy in the 3D NNC catalyst shows an increased electrochemically active surface area (80.95 m2 g?1) and a 3.62‐fold enhancement of mass activity (6.16 A mg?1) over a commercial Pd/C catalyst. 相似文献
997.
Cyclotetrabenzoin: Facile Synthesis of a Shape‐Persistent Molecular Square and Its Assembly into Hydrogen‐Bonded Nanotubes 下载免费PDF全文
Qing Ji Ha T. M. Le Dr. Xiqu Wang Dr. Yu‐Sheng Chen Dr. Tatyana Makarenko Prof. Allan J. Jacobson Prof. Ognjen Š. Miljanić 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17205-17209
Cyanide‐catalyzed benzoin condensation of terephthaldehyde produces a cyclic tetramer, which we propose to name cyclotetrabenzoin. Cyclotetrabenzoin is a square‐shaped macrocycle ornamented with four α‐hydroxyketone functionalities pointing away from the central cavity, the dimensions of which are 6.9×6.9 Å. In the solid state, these functional groups extensively hydrogen bond, resulting in a microporous three‐dimensional organic framework with one‐dimensional nanotube channels. This material exhibits permanent—albeit low‐porosity, with a Langmuir surface area of 52 m2 g?1. Cyclotetrabenzoin’s easy and inexpensive synthesis and purification may inspire the creation of other shape‐persistent macrocycles and porous molecular crystals by benzoin condensation. 相似文献
998.
A novel method is developed for the direct determination of naphazoline hydrochloride(NAP) and pyridoxine hydrochloride(VB6) in commercial eye drops. By using excitation–emission matrix(EEM)fluorescence coupled with second-order calibration method based on the alternating trilinear decomposition(ATLD) algorithm, the proposed approach can achieve quantitative analysis successfully even in the presence of unknown and uncalibrated interferences. The method shows good linearity for NAP and VB6 with correlation coefficients greater than 0.99. The results were in good agreement with the labeled contents. To further confirm the feasibility and reliability of the proposed method, the same batch samples were analyzed by multiple reaction monitoring(MRM) based on LC–MS/MS method.T-test demonstrated that there are no significant differences between the prediction results of the two methods. The satisfactory results obtained in this work indicate that the use of the second-order calibration method coupled with the EEM is a promising tool for industrial quality control and pharmaceutical analysis due to its advantages of high sensitivity, low-cost and simple implementation. 相似文献
999.
1000.
建立了用铝基体火花源原子发射光谱仪现有通道硬件测定镁合金(MB1)中锰元素含量的方法.方法线性相关系数为0.967 6,RSD为1.66%.对8个未知样品进行了测试,结果与化学分析方法所得结果一致. 相似文献