全文获取类型
收费全文 | 1728篇 |
免费 | 51篇 |
国内免费 | 6篇 |
专业分类
化学 | 1271篇 |
晶体学 | 24篇 |
力学 | 14篇 |
数学 | 107篇 |
物理学 | 369篇 |
出版年
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 8篇 |
2016年 | 35篇 |
2015年 | 38篇 |
2014年 | 34篇 |
2013年 | 56篇 |
2012年 | 71篇 |
2011年 | 87篇 |
2010年 | 56篇 |
2009年 | 47篇 |
2008年 | 88篇 |
2007年 | 106篇 |
2006年 | 82篇 |
2005年 | 89篇 |
2004年 | 98篇 |
2003年 | 83篇 |
2002年 | 80篇 |
2001年 | 48篇 |
2000年 | 42篇 |
1999年 | 17篇 |
1998年 | 26篇 |
1997年 | 12篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 25篇 |
1985年 | 22篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 23篇 |
1976年 | 9篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 15篇 |
排序方式: 共有1785条查询结果,搜索用时 31 毫秒
191.
Okuno Y. Ohtsu Y. Fujita H. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(3):253-259
Effects of a magnetic held collimation on ion behavior in the downstream region of an electron cyclotron resonance (ECR) plasma device are clarified experimentally using a directional ion energy analyzer. The drift energy and its spread of the ion beam observed in the downstream region decrease and the beam temperature increases with the collimating magnetic flux density. Then, the ion temperature measured perpendicular to the axis of the plasma stream slightly decreases. The ion beam is found to be almost parallel to the magnetic field lines, that is, the beam tends to be collimated 相似文献
192.
K. Yoshida F. Nakamura Y. Tanaka Y. Maeno T. Fujita 《Physica C: Superconductivity and its Applications》1994,230(3-4):371-377
A structural transition to a low-temperature tetragonal (TLT) phase occurs below Td2≈60 K in La2−xBaxCuO4 only around x=0.125, accompanied by sharp suppression of superconductivity. In this study we investigated the effects of partial substitution of smaller divalent cations for Ba2+ ions (Ba2+ > Sr2+ > Ca2+) on these anomalous low-temperature properties. The suppression of superconductivity is strongly affected by the appearance of the TLT phase for this carrier concentration. We also show that the variations of Td2 and Tc are quantitatively scaled by the averaged size of cations at the La site. This dependence can be interpreted as chemical effects acting effectively as applied pressure. We discuss how our observation is related to recent reports which claim that the TLT structure itself does not necessarily destroy the superconductivity. 相似文献
193.
194.
Using diamond anvil cell, the57Fe Mössbauer spectra of pure iron foil and α-Fe2O3 powder under high pressure have been measured at room temperature.57Fe Mössbauer spectra of α-Fe were measured from 15 GPa to 45 GPa. Isomer shift value decreased and the quadrupole splitting slightly increased as the pressure increased.57Fe Mössbauer spectra of Fe2O3 under high pressure up to 72 GPa were observed. Above 52 GPa, the new lines appeared at the center portion of the spectrum corresponding to the new high pressure phase. The spectrum of new high pressure phase consisted of 6-line splitting and doublet, suggesting the existence of the two different kinds of iron states in it. 相似文献
195.
Carbazole Dendrimers as Solution‐Processable Thermally Activated Delayed‐Fluorescence Materials 下载免费PDF全文
Assist. Prof. Ken Albrecht Assist. Prof. Kenichi Matsuoka Assoc. Prof. Katsuhiko Fujita Prof. Kimihisa Yamamoto 《Angewandte Chemie (International ed. in English)》2015,54(19):5677-5682
Recently, thermally activated delayed fluorescence (TADF) materials have received increasing attention as effective emitters for organic light‐emitting diodes (OLEDs). However, most of them are usually employed as dopants in a host material. In this report, carbazole dendrimers with a triphenyl‐s‐triazine core are reported, which are the first solution‐processable, non‐doped, high‐molecular‐weight TADF materials. The dendrimers were obtained by a new and facile synthetic route using the tert‐butyldimethylsilyl moiety as a protecting group. All dendrimers showed TADF in toluene. Measurements of the temperature‐dependent luminescence lifetime revealed that spin‐coated neat films also showed TADF with moderate quantum yields. OLED devices incorporating these dendrimers as spin‐coated emitting layers gave external quantum efficiencies of up to a 3.4 %, which suggests that this device is harvesting triplet excitons. This result indicates that carbazole dendrimers with attached acceptors are potential TADF materials owing to their polarized electronic structure (with HOMO–LUMO separation). 相似文献
196.
Hydrogen Production from a Methanol–Water Solution Catalyzed by an Anionic Iridium Complex Bearing a Functional Bipyridonate Ligand under Weakly Basic Conditions 下载免费PDF全文
Prof. Dr. Ken‐ichi Fujita Dr. Ryoko Kawahara Takuya Aikawa Prof. Dr. Ryohei Yamaguchi 《Angewandte Chemie (International ed. in English)》2015,54(31):9057-9060
An efficient catalytic system for the production of hydrogen from a methanol–water solution has been developed using a new anionic iridium complex bearing a functional bipyridonate ligand as a catalyst. This system can be operated under mild conditions [weakly basic solution (0.046 mol L?1 NaOH) below 100 °C] without the use of an additional organic solvent. Long‐term continuous hydrogen production from a methanol–water solution catalyzed by the anionic iridium complex was also achieved. 相似文献
197.
Dr. Yasuhide Akizuki Dr. Ikuya Yamada Dr. Koji Fujita Kazuya Taga Dr. Takateru Kawakami Dr. Masaichiro Mizumaki Prof. Katsuhisa Tanaka 《Angewandte Chemie (International ed. in English)》2015,54(37):10870-10874
Of particular interest is a peculiar motion of guest atoms or ions confined to nanospace in cage compounds, called rattling. While rattling provides unexplored physical properties through the guest–host interactions, it has only been observed in a very limited class of materials. Herein, we introduce an A‐site‐ordered quadruple perovskite, CuCu3V4O12, as a new family of cage compounds. This novel AA′3B4O12‐type perovskite has been obtained by a high‐pressure synthesis technique and structurally characterized to have cubic Im$\bar 3$ symmetry with an ionic model of Cu2+Cu2+3V4+4O12. The thermal displacement parameter of the A‐site Cu2+ ion is as large as Uiso≈0.045 Å2 at 300 K, indicating its large‐amplitude thermal oscillations in the oversized icosahedral cages. Remarkably, the presence of localized phonon modes associated with rattling of the A‐site Cu2+ ion manifests itself in the low‐temperature specific heat data. This work sheds new light on the structure–property relations in perovskites. 相似文献
198.
High Catalytic Activity of Nitrogen and Sulfur Co‐Doped Nanoporous Graphene in the Hydrogen Evolution Reaction 下载免费PDF全文
Dr. Yoshikazu Ito Weitao Cong Dr. Takeshi Fujita Prof. Zheng Tang Prof. Mingwei Chen 《Angewandte Chemie (International ed. in English)》2015,54(7):2131-2136
Chemical doping has been demonstrated to be an effective way to realize new functions of graphene as metal‐free catalyst in energy‐related electrochemical reactions. Although efficient catalysis for the oxygen reduction reaction (ORR) has been achieved with doped graphene, its performance in the hydrogen evolution reaction (HER) is rather poor. In this study we report that nitrogen and sulfur co‐doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt‐free HER catalyst, 2D MoS2. The interplay between the chemical dopants and geometric lattice defects of the nanoporous graphene plays the fundamental role in the superior HER catalysis. 相似文献
199.
Komal Garg Yasuo Matsubara Mehmed Z. Ertem Anna Lewandowska‐Andralojc Shunsuke Sato David J. Szalda James T. Muckerman Etsuko Fujita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(47):14334-14338
We prepared two geometric isomers of [Ir(tpy)(ppy)H]+, previously proposed as a key intermediate in the photochemical reduction of CO2 to CO, and characterized their notably different ground‐ and excited‐state interactions with CO2 and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]+, reacts with CO2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH3CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]0 species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO2 and produces CO with the same catalytic efficiency. 相似文献
200.
Nonintrusive measurements in a sediment-laden flow using two laser-based techniques, Discriminator Laser-Doppler Velocimetry
(DLDV) and Particle Tracking Velocimetry (PTV), are compared. DLDV was previously developed at the Iowa Institute of Hydraulic
Research, while PTV was specially configured for this application. Mean and fluctuating velocity components for both flow
fractions were simultaneously measured in a laboratory-scale, submerged water jet loaded with alluvial sand. This information
cannot be obtained using existing measurement techniques. The jet Reynolds number was 6120, and the sediment sieve diameter
ranged from 0.5 to 0.6 mm. Small mass loadings of sand with inertial time constant τ
p
of 0.6 ms were examined.
The configuration, operation, and results obtained using the DLDV and PTV are presented. For each technique, means to precisely
distinguish between the light scattered by suspended sand and that originating from seed-particles following the water were
implemented. The agreement in measurement for the two methods validates one another since they are based on completely different
principles of operation. The capabilities of DLDV and PTV to reliably measure sand and water velocities in sediment-laden
flows are further indicated by the agreement of the present findings with those obtained previously in similar studies. The
comparison suggests that PTV, due to its whole field nature, could become a powerful tool for flow and particle-related diagnostics,
yielding fundamental information in an area with a long history of conflicting experimental evidence.
Received: 27 August 1996 / Accepted: 25 June 1997 相似文献