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991.
Synthesis of Heterodinuclear Hemisalen Complexes on a Hexaarylbenzene Scaffold and their Application for the Cross‐Pinacol Coupling Reaction 下载免费PDF全文
Akihiro Miyasaka Dr. Toru Amaya Prof. Toshikazu Hirao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1615-1621
Intermolecular cross‐pinacol coupling reaction between aliphatic and aromatic aldehydes by using heterodinuclear hemisalen complexes 1 cis with vanadium(V) and titanium(IV) on a hexaarylbenzene scaffold is reported. Our ligand design is based on the individual activation of two aldehydes by vanadium and titanium, which are positioned with a suitable space on the rigid scaffold. Ligands such as 1 cis were synthesized by Diels–Alder addition and decarbonylation reaction, followed by condensation of dialdehyde 3 cis with various aminophenols. The influence of the substituents on the ligands on the pinacol coupling reaction was investigated. As a result, the reductive coupling reaction between aliphatic and aromatic aldehydes by using a catalytic amount of 1 cis in the presence of Me3SiCl and Zn provided the corresponding cross‐coupled 1,2‐diol in good yields with high cross‐selectivity. 相似文献
992.
Metallic and Mott Insulating Spin‐Frustrated Antiferromagnetic States in Ionic Fullerene Complexes with a Two‐Dimensional Hexagonal C60.− Packing Motif 下载免费PDF全文
Dr. Dmitri V. Konarev Dr. Salavat S. Khasanov Dr. Akihiro Otsuka Dr. Mitsuhiko Maesato Dr. Mikio Uruichi Dr. Kyuya Yakushi Dr. Artem F. Shevchun Prof. Dr. Hideki Yamochi Prof. Dr. Gunzi Saito Prof. Rimma N. Lyubovskaya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7268-7277
(MDABCO+)(C60.?)(TPC) ( 1 ), in which MDABCO+ is N‐methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene‐based quasi‐2D metal and contains closely packed hexagonal fullerene layers with interfullerene center‐to‐center distances of 10.07 Å at 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass (m*/m0=6.7). The latter indicates a narrow‐band nature, which is consistent with the calculated bandwidth of 0.10–0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200–230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ+)(C60.?)(TPC) ( 2 ) with a hexagonal arrangement of C60.? was obtained by increasing the interfullerene distance with the bulkier N‐methylquinuclidinium cations (MQ+) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center‐to‐center distances in the layers (10.124, 10.155, and 10.177 Å at 250 K). Unit‐cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1 , 2 exhibits a nonmetallic spin‐frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is ?27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2 , and thus a Mott–Hubbard insulating state with antiferromagnetically frustrated spins results. 相似文献
993.
Strong Antiferromagnetic Coupling of Spins in the (MDABCO+)(C60.−) Salt with 3D Close Packing of the C60.− Radical Anions (MDABCO+: N‐Methyldiazabicyclooctanium Cation) 下载免费PDF全文
Dr. Dmitri V. Konarev Dr. Salavat S. Khasanov Dr. Akihiro Otsuka Prof. Hideki Yamochi Prof. Gunzi Saito Prof. Rimma N. Lyubovskaya 《化学:亚洲杂志》2014,9(6):1629-1635
A new salt, (MDABCO+)(C60.?) ( 1 ; MDABCO+=N‐methyldiazabicyclooctanium cation), was obtained as single crystals. The crystal structure of 1 determined at 250 and 100 K showed 3D close packing of fullerenes with eight fullerene neighbors for each C60.?. These neighbors are located at 10.01–10.11 Å center‐to‐center distances (250 K) and van der Waals interfullerene C???C contacts are formed with four fullerene neighbors arranged in the bc plane. Fullerene ordering observed below 160 K is accompanied by the appearance of one and a half independent C60.? and trebling of the unit cell along the b axis. Fullerenes are packed closer to each other at 100 K. As a result, fullerenes are located in the three‐dimensional packing at 9.91–10.12 Å center‐to‐center distances and 18 short interfullerene C???C contacts are formed for each C60.?. Although they are closed packed, fullerenes are not dimerized down to 1.9 K. Magnetic data indicate strong antiferromagnetic coupling of spins in the 70–300 K range with a Weiss temperature of Θ=?118 K. Magnetic susceptibility shows a round maximum at 46 K. Such behavior can be described well by the Heisenberg model for square two‐dimensional antiferromagnetic coupling of spins with an exchange interaction of J/kB=?25.3 K. This magnetic coupling is one of the strongest observed for C60.? salts. 相似文献
994.
Many experimental and modeling studies have examined several factors affecting radon emanation. Of these factors, the effect of temperature shown in earlier experiments has not been discussed with model calculations. In the present study, radon emanation fractions were calculated for various temperatures, namely different air densities, using a simple model into which the emanation processes originating from alpha recoil were incorporated. As a result, the slightly negative correlation that the radon emanation fraction decreased with increasing temperature was observed within a certain range of grain size, while temperature had no effect within the other range. Considering the current knowledge of processes through which radon emanation occurs, this result would be expected to be qualitatively reasonable. However, the result is not similar to all previous experimental results showing the positive correlation. These papers occasionally explain that the positive correlation is attributable to the adsorption of radon on solids during its transfer among grains. Since the general definition of radon emanation includes no transfer process after its release from a grain, their explanation could not be well established. The discrepancy between the calculated and measured data may suggest the needs of review and improvement of experimental and/or modeling techniques. 相似文献
995.
Akihiro Fujii Toshihiro Koura Takashi Yoshimoto Toshiyuki Kawabata Yoshinori Nakamura Keita Hamamichi Hitoshi Kakimoto Yoshimune Yamada Mitsuo Yoshioka Masayoshi Yamamoto Kazuichi Hayakawa 《Journal of Radioanalytical and Nuclear Chemistry》2014,300(2):707-717
A variety of wild mushrooms were collected in a forest on the Noto Peninsula, Japan, to determine the concentration of 137Cs and 40K. The wild mushroom species belong to the orders Agaricales and Aphyllophorales. The concentration of 137Cs varied widely (1.4–4,100 Bq/kg dry weight) in mushrooms growing in soil. On the contrary, 137Cs concentration levels were relatively low (1.9–20 Bq/kg-dry weight) in mushrooms growing on wood. The concentration of 40K varied widely (12–2,400 Bq/kg-dry weight) in contrast with several previous reports that suggest relatively constant 40K levels in mushrooms. Unusually low concentrations of 40K were observed in a few mushroom species that had very hard fruiting bodies with peculiar shapes. The mean and median of 137Cs concentration in the present study were similar to those previously reported for Japanese mushrooms. Among the Agaricales mushrooms, Entolomataceae and Tricholomataceae families growing in soil had the highest concentration of 137Cs. Among the Aphyllophorales mushrooms, Gomphaceae and Ramariaceae families growing in soil also had the highest 137Cs concentrations. The concentrations of 137Cs and stable Cs in mushroom samples were positively correlated. The concentration ratio of 137Cs/Cs differed between Agaricales and Aphyllophorales mushrooms. The average 137Cs/Cs ratio in mushrooms growing in soil was similar to that calculated for the top soil (<5 cm deep) alone because the mycelia of the mushrooms were mainly distributed near the surface of the soil. 相似文献
996.
To synthesize sulfur-containing π-conjugated polymers, reaction conditions for rhodium-catalyzed hydrothiolation of terminal alkynes with arenethiols are optimized in detail. Under the optimized conditions, rhodium-catalyzed hydrothiolation of terminal alkynes proceeds regio- and stereoselectively to afford the corresponding vinyl sulfides via an anti-Markovnikov and syn-addition process. Then, the rhodium-catalyzed hydrothiolation is applied to polymerization of 2,5-diethynylthiophene with benzene-1,4-dithiol, which successfully provides sulfur-containing π-conjugated polymers with excellent regio- and stereoselectivities. 相似文献
997.
Shunpei Nobusue Ayumi Yoshizaki Masahito MikiHirokazu Miyoshi Akihiro Shimizu Yoshito Tobe 《Tetrahedron》2014
A nucleophile-induced cyclization of octadehydrodibenzo[12]annulene derivative 1b was investigated. Treatment of 1b with BuLi gave fused 5–9-membered ring products, dibenzobicyclo[7.3.0]tetraenediynes 2a and 2b, formed via a single transannular cyclization reaction. The reason why double cyclization did not occur is ascribed to the structure of a plausible anionic intermediate in which a negative charge locates apart from the remaining triple bond carbons. The second cyclization did not take place even when once-isolated product 2b was treated with BuLi because of the higher reactivity toward a nucleophile of the fulvene moiety compared to the triple bonds. On the other hand, heating a chlorobenzene solution of 2b containing cyclohexa-1,4-diene gave products 3a–c possessing a benzonaphthopentalene framework via a Bergman cyclization pathway albeit in low yields after inter- or intramolecular hydrogen abstraction. Moreover, iodine-induced transannular cyclization of 2b afforded the corresponding diiodide 3d. 相似文献
998.
Epicoccamides A and D were synthesized through a route that utilizes fragment coupling via olefin cross-metathesis as a key step. The right-hand segment of the epicoccamides was synthesized by a tandem O-acylation–migration reaction, and the left-hand segments were stereoselectively synthesized through a modified version of Crich’s β-selective mannosylation. The previously assigned absolute configuration of the epicoccamide D was confirmed, and that of epicoccamide A was assigned as (5S,2′S) based on the NMR and CD spectra. This Letter provides the first example of the total synthesis of epicoccamide A. 相似文献
999.
Sho Matsuda Akihiro Yoshida Junki Nakagawa Mikio Watanabe Yoshiki Oda Takashi Yamanoi 《Tetrahedron letters》2014
This Letter describes a stereoselective synthetic approach to spiro[5.5]ketals from the exo-glucals, constructed from 1-(4-hydroxyalkylidene)-1,5-anhydro-d-glucitol, by spirocyclization based on intramolecular α- and β-selective glycosylation. Stereodivergent synthesis of both α- and β-glucoside of spiro[5.5]ketals was attained by combination of chiral d-glucopyranose environment and C-4′ chiral center on the side chain. 相似文献
1000.
Modulation of Electron Injection Dynamics of Ru‐Based Dye/TiO2 System in the Presence of Three Different Organic Solvents: Role of Solvent Dipole Moment and Donor Number 下载免费PDF全文
Dr. Subrata Mahanta Dr. Hiroyuki Matsuzaki Dr. Takurou N. Murakami Prof. Ryuzi Katoh Dr. Hajime Matsumoto Dr. Akihiro Furube 《Chemphyschem》2015,16(8):1657-1662
In the present work, femtosecond transient absorption spectroscopy (fs‐TAS) has been employed to investigate the electron injection efficiency (EIE) both from the singlet and triplet excited states of a well‐known ruthenium dye (N719) to the conduction band (CB) of nanostructured TiO2 in presence of three different organic solvents [γ‐butylactone (GBL), 3‐methoxypropionitrile (MPN), and dimethylformamide (DMF)] with different donor numbers (DNs) and dipole moments (DMs). The DM and DN of a solvent modulates the CB edge energy of TiO2, and this effect reflects well in the fs‐TAS results, which shows an EIE trend following the order GBL≥MPN?DMF, that is, highest in GBL and lowest in DMF solvent environments. Fs‐TAS results indicate a lower contribution of electron injection from both the singlet and triplet states in DMF, for which the dominant adsorption of DMF molecules on the TiO2 surface seems to play an important role in the mechanism. 相似文献