全文获取类型
收费全文 | 3643篇 |
免费 | 72篇 |
国内免费 | 30篇 |
专业分类
化学 | 2888篇 |
晶体学 | 48篇 |
力学 | 57篇 |
数学 | 177篇 |
物理学 | 575篇 |
出版年
2022年 | 24篇 |
2021年 | 29篇 |
2020年 | 31篇 |
2019年 | 36篇 |
2018年 | 23篇 |
2017年 | 31篇 |
2016年 | 42篇 |
2015年 | 66篇 |
2014年 | 78篇 |
2013年 | 262篇 |
2012年 | 164篇 |
2011年 | 223篇 |
2010年 | 124篇 |
2009年 | 102篇 |
2008年 | 189篇 |
2007年 | 193篇 |
2006年 | 214篇 |
2005年 | 200篇 |
2004年 | 178篇 |
2003年 | 191篇 |
2002年 | 192篇 |
2001年 | 43篇 |
2000年 | 51篇 |
1999年 | 54篇 |
1998年 | 40篇 |
1997年 | 37篇 |
1996年 | 51篇 |
1995年 | 50篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 29篇 |
1989年 | 35篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 46篇 |
1984年 | 46篇 |
1983年 | 27篇 |
1982年 | 55篇 |
1981年 | 39篇 |
1980年 | 54篇 |
1979年 | 58篇 |
1978年 | 41篇 |
1977年 | 29篇 |
1976年 | 24篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1973年 | 18篇 |
排序方式: 共有3745条查询结果,搜索用时 15 毫秒
991.
Deng W Onji T Yamaguchi H Ikeda N Harada A 《Chemical communications (Cambridge, England)》2006,(40):4212-4214
Photoinduced electron transfer between a porphyrin and a new guest cyclodextrin bearing viologen occurs by a supramolecular formation with conformational change of a guest molecule. 相似文献
992.
Peng Zhang Yawen Tong Yong Liu Junie Jhon M. Vequizo Hongwei Sun Can Yang Akira Yamakata Fengtao Fan Wei Lin Xinchen Wang Wonyong Choi 《Angewandte Chemie (International ed. in English)》2020,59(37):16209-16217
Polymeric carbon nitride modified with selected heteroatom dopants was prepared and used as a model photocatalyst to identify and understand the key mechanisms required for efficient photoproduction of H2O2 via selective oxygen reduction reaction (ORR). The photochemical production of H2O2 was achieved at a millimolar level per hour under visible‐light irradiation along with 100 % apparent quantum yield (in 360–450 nm region) and 96 % selectivity in an electrochemical system (0.1 V vs. RHE). Spectroscopic analysis in spatiotemporal resolution and theoretical calculations revealed that the synergistic association of alkali and sulfur dopants in the polymeric matrix promoted the interlayer charge separation and polarization of trapped electrons for preferable oxygen capture and reduction in ORR kinetics. This work highlights the key features that are responsible for controlling the photocatalytic activity and selectivity toward the two‐electron ORR, which should be the basis of further development of solar H2O2 production. 相似文献
993.
994.
Universal Reaction Mechanism of Boronic Acids with Diols in Aqueous Solution: Kinetics and the Basic Concept of a Conditional Formation Constant 下载免费PDF全文
Yuki Furikado Tomomi Nagahata Takuya Okamoto Dr. Tomoaki Sugaya Prof. Dr. Satoshi Iwatsuki Prof. Dr. Masahiko Inamo Prof. Dr. Hideo D. Takagi Prof. Dr. Akira Odani Prof. Dr. Koji Ishihara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13194-13202
To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (${K{{{\rm BL}\hfill \atop {\rm a}\hfill}}}$ ) of boronic acid diol esters (HBLs) were determined based on the well‐established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4‐difluorophenylboronic acid and chromotropic acid, 3‐nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K′, based on the main reaction: RB(OH)2+H2L ${{\mathop \leftrightarrow \limits ^{K{_{1}}}_{}}}$ RB(L)(OH)?+H3O+ instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B′) with uncomplexed diol species (L′) to form boronic acid diol complex species (esters, BL′) in aqueous solution at pH 5–11: B′+L′ ${{\mathop \leftrightarrow \limits ^{K{^\prime}}_{}}}$ BL′. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution. 相似文献
995.
Aerogels with 3D Ordered Nanofiber Skeletons of Liquid‐Crystalline Nanocellulose Derivatives as Tough and Transparent Insulators 下载免费PDF全文
Yuri Kobayashi Assoc. Prof. Tsuguyuki Saito Prof. Akira Isogai 《Angewandte Chemie (International ed. in English)》2014,53(39):10394-10397
Aerogels of high porosity and with a large internal surface area exhibit outstanding performances as thermal, acoustic, or electrical insulators. However, most aerogels are mechanically brittle and optically opaque, and the structural and physical properties of aerogels strongly depend on their densities. The unfavorable characteristics of aerogels are intrinsic to their skeletal structures consisting of randomly interconnected spherical nanoparticles. A structurally new type of aerogel with a three‐dimensionally ordered nanofiber skeleton of liquid‐crystalline nanocellulose (LC‐NCell) is now reported. This LC‐NCell material is composed of mechanically strong, surface‐carboxylated cellulose nanofibers dispersed in a nematic LC order. The LC‐NCell aerogels are transparent and combine mechanical toughness and good insulation properties. These properties of the LC‐NCell aerogels could also be readily controlled. 相似文献
996.
Synthesis of Cyclobutenes and Allenes by Cobalt‐Catalyzed Cross‐Dimerization of Simple Alkenes with 1,3‐Enynes 下载免费PDF全文
Akira Nishimura Eri Tamai Dr. Masato Ohashi Prof. Dr. Sensuke Ogoshi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6613-6617
Cobalt‐catalyzed cross‐dimerization of simple alkenes with 1,3‐enynes is reported. A [2+2] cycloaddition reaction occurred, with alkenes bearing no allylic hydrogen, by reductive elimination of a η3‐butadienyl cobaltacycle. On the other hand, aliphatic alkenes underwent 1,4‐hydroallylation by means of exo‐cyclic β‐H elimination. These reactions can provide cyclobutenes and allenes that were previously difficult to access, from simple substrates in a highly chemo‐ and regioselective manner. 相似文献
997.
We present a simple and efficient method for calculating symmetrized time correlation functions of neat quantum fluids. Using the pair-product approximation to each complex-time quantum mechanical propagator, symmetrized correlation functions are written in terms of a double integral for each degree of freedom with a purely positive integrand. At moderate temperatures and densities, where the pair-product approximation to the Boltzmann operator is sufficiently accurate, the method leads to quantitative results for the early time part of the correlation function. The method is tested extensively on liquid para-hydrogen at 25 K and used to obtain accurate quantum mechanical results for the initial 0.2 ps segment of the symmetrized velocity autocorrelation function of this system, as well as the incoherent dynamic structure factor at certain momentum transfer values. 相似文献
998.
The crystal structures of 1,3-bis(4-bromophenyl)- and 1,3-di(2-thienyl)azulenes (5 and 6) were elucidated by X-ray analysis. Two aryl groups connect to the azulenyl core with dihedral angles of 34.9-41.6° and the two aryl planes of the groups slant against the azulene ring toward different ways in their crystal structures. It was also found that the azulene rings of 5 and 6 showed a slight out-of-plane deformation in the way that the hydrogen atoms at the 4- and 8-positions are apart from the neighboring aryl ortho-hydrogen atoms to fill in the vacant space made by the slanting aryl planes. 相似文献
999.
Satoka Aoyagi Akira Yano Yasutaka Yanagida Eiji Tanihira Akio Tagawa Mitsuo Iimoto 《Chemical physics》2006
This study investigated the control of dissolved oxygen concentration using magnetic forces from gradient magnetic fields near a Nd–Fe–B permanent magnet. Maximum values of magnetic flux density and the product of the magnetic flux density and its gradient were 0.63 T and 44 T2/m, respectively. The magnet was placed under a Petri dish filled with 15 ml of 10% ammonia water. The Petri dish had a copper sheet in the center. Absorbance of tetraamminecopper(II) complex produced by the reaction in oxygen was measured using a spectrophotometer to observe oxygen concentration. Results showed that the magnetic field quantitatively enhanced tetraamminecopper(II) complex production. Moreover, remarkable enhancement of the copper complex production occurred in the magnetic field at less than 2 mm depth. The calculated magnetic force increase near the magnet surface supports this result. These results show that greater enhancement of the reaction rate occurs when the stronger magnetic force acts on oxygen molecules. 相似文献
1000.
Platinum dissolution and deposition in the polymer electrolyte membrane of a PEM fuel cell as studied by potential cycling 总被引:1,自引:0,他引:1
Yasuda K Taniguchi A Akita T Ioroi T Siroma Z 《Physical chemistry chemical physics : PCCP》2006,8(6):746-752
The behavior of platinum dissolution and deposition in the polymer electrolyte membrane of a membrane-electrode-assembly (MEA) for a proton-exchange membrane fuel cell (PEMFC) was studied using potential cycling experiment and high-resolution transmission electron microscopy (HRTEM). The electrochemically active surface area decreased depending on the cycle number and the upper potential limit. Platinum deposition was observed in the polymer electrolyte membrane near a cathode catalyst layer. Platinum deposition was accelerated by the presence of hydrogen transported through the membrane from an anode compartment. Platinum was transported across the membrane and deposited on the anode layer in the absence of hydrogen in the anode compartment. This deposition was also affected by the presence of oxygen in the cathode compartment. 相似文献