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991.
A novel structure of AIGaN/GaN Schottky barrier diode (SBD) featuring electric field optimization techniques of anode-connected-field-plate (AFP) and magnesium-doped p-type buried layer under the two-dimensional electron gas (2DEG) channel is proposed. In comparison with conventional A1GaN/GaN SBDs, the magnesium-doped p-type buried layer in the proposed structure can provide holes that can help to deplete the surface 2DEG. As a result, surface field strength around the electrode edges is significantly suppressed and the electric field along the channel is distributed more evenly. Through 2D numerical analysis, the AFP parameters (field plate length, LAFP, and field plate height, TAFP) and p-type buried layer parameters (p-type layer concentration, Np, and p-type layer thickness, Tp) are optimized to achieve a three-equal-peak surface channel field distribution under exact charge balance conditions. A novel structure with a total drift region length of 10.5 μm and a magnesium-doped p-type concentration of 1 × 10^17 cm 3 achieves a high breakdown voltage (VB) of 1.8 kV, showing 5 times improvement compared with the conventional SBD with the same device dimension. 相似文献
992.
Wei Lin Wei Jiang Na Gao Duanjun Cai Shuping Li Junyong Kang 《Laser \u0026amp; Photonics Reviews》2013,7(4):572-579
Symmetric anisotropy in wurtzite semiconductors, e.g., AlGaN, has led to the significant optical anisotropy that is rather difficult to resolve. Here, a novel scheme for achieving optical isotropization in Al‐rich AlGaN through the introduction of additional asymmetric elements is demonstrated to compensate the native asymmetry. Asymmetric modulation of alloy composition and periodicity of (GaN)m/(AlN)n superlatices was proposed with first‐principles simulations. Results showed that the compensation for the c‐axial symmetry with the asymmetric ultrathin (GaN)m/(AlN)n superlatices (m ≤ 2) could well achieve the equivalence of the ordinary and extraordinary imaginary dielectric functions ε2 at the band edge. Measurement with spectroscopic ellipsometry for this (GaN)m/(AlN)n superlatice insertion in AlGaN host confirmed the theoretical predictions of the optical isotropization. This method can be transferred to other semiconductors in anisotropic structure and with troubles of optical anisotropy. 相似文献
993.
LiHua Gan 《中国科学B辑(英文版)》2009,52(5):584-589
Based on the calculated findings that the sizes of encaged clusters determine the structures and the stability of C80-based trimetallic nitride fullerenes (TNFs), more extensive density functional theory calculations were performed on M3N@C68, M3N@C78 and M3N@C80 (M=Sc, Y and La). The calculated results demonstrated that the structures and stability undergo a transition with the increasing
of the sizes of the cages and clusters. Sc3N is planar inside the three considered cages, Y3N is slightly pyramidal inside C68-6140 and C78-5 and planar inside Ih C80-7, however, La3N is pyramidal inside all the three cages. Those cages with pyramidal clusters inside deformed considerably, compared with
their parent cages. In these cases, the bonding of metallic atoms toward the cages does not play an important role, and the
encaged cluster tends to be located inside the cages with the largest M-M and M-C distances so that the strain energy can
be released mostly. These calculations revealed the size effect of fullerene cages and encaged clusters, and can explain the
position priority of M3N inside fullerene cages and the differences in yield of M3N@C2n
.
Supported by the Southwest University, China (Grant No. SWNUB2005002) 相似文献
994.
To evaluate the electronic and optical properties of Cr‐doped anatase TiO2, three possible Cr‐doped TiO2 models, including Cr at a Ti site (model I), Cr at a Ti site with an oxygen vacancy compensation (model II), and an interstitial Cr site (model III), are studied by means of first principles density functional theory calculations. In model I, the splitting behavior of the Cr 3d states and the insulating properties are successfully depicted by the GGA+U method, from which it is proposed that Cr at a Ti site should exist as Cr4+ instead of the generally believed Cr3+. As a result, the electron transitions between these impurity states, the conduction band (CB), and the valence band (VB), as well as the d–d transitions between occupied and unoccupied Cr 3d states, provide a reasonable explanation for the experimentally observed major and minor absorption bands. In models II and III, the impurity states and associated optical transition processes—as well as the corresponding electron configurations—are examined. 相似文献
995.
Pedro Atienzar Dr. Maite Navarro Dr. Avelino Corma Prof. Dr. Hermenegildo Garcia Prof. Dr. 《Chemphyschem》2009,10(1):252-256
Ti/MCM‐41 is a well‐known heterogeneous catalyst for alkene epoxidation with organic peroxides. This titanosilicate contains isolated titanium atoms forming part of a framework of mesoporous silica whose structure is formed by parallel hexagonal channels 3.2 nm in diameter. The surface area and porosity of Ti/MCM‐41 are about 880 m2 g?1 and 0.70 cm3 g?1, respectively. These values are among the highest for any material. Herein, we show that Ti/MCM‐41 exhibits photovoltaic activity. Dye‐sensitized solar cells using mesoporous Ti/MCM‐41 (2.8–5.7 % Ti content) as active layer, black dye N3 as photosensitizer and I3?/I? in methoxyacetonitrile as electrolyte exhibit a VOC, JSC and FF of 0.44 V, 0.045 mA cm?2 and 0.33, respectively. These values compare well against 0.75 V, 4.1 mA cm?2 and 0.64, respectively, measured for analogous solar cells using conventional P‐25 TiO2. However, the specific current density (JSC/Ti atom) for the Ti/MCM‐41 is very similar to that of P25 TiO2. 相似文献
996.
以三聚氰胺、甲醛、尿素等原料合成具有可塑性的三聚氰胺树脂,通过发泡法构建前驱体支架,并通过磁控溅射法在支架表面沉积金,550℃下热聚合后,成功制备得到负载Au的石墨相氮化碳(Au@g-C3N4)支架,其比表面积可达1 480 m2·g-1。负载6%Au后,Au@g-C3N4支架的紫外吸收光谱在550nm处出现了新的吸收峰,吸收带边红移至507nm,禁带宽度缩小至2.45eV,Au@g-C3N4支架荧光强度和阻抗显著降低,光电流从0.28μA·cm-2提升至0.62μA·cm-2。负载Au既拓宽了Au@g-C3N4支架可见光吸收性能,又抑制了电子-空穴对的复合,光催化性能稳定,光催化降解罗丹明B的降解率提高近1倍。此外,Au@g-C3N4支架强度适中,具有一定韧性,在光催化领域应用中便于回收和再利用。 相似文献
997.
María García‐Castro Dr. Avelino Martín Dr. Miguel Mena Dr. Carlos Yélamos Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(29):7180-7191
Several heterometallic nitrido complexes were prepared by reaction of the imido–nitrido titanium complex [{Ti(η5‐C5Me5)(μ‐NH)}3(μ3‐N)] ( 1 ) with amido derivatives of Group 13–15 elements. Treatment of 1 with bis(trimethylsilyl)amido [M{N(SiMe3)2}3] derivatives of aluminum, gallium, or indium in toluene at 150–190 °C affords the single‐cube amidoaluminum complex [{(Me3Si)2N}Al{(μ3‐N)2(μ3‐NH)Ti3(η5‐C5Me5)3(μ3‐N)}] ( 2 ) or the corner‐shared double‐cube compounds [M(μ3‐N)3(μ3‐NH)3{Ti3(η5‐C5Me5)3(μ3‐N)}2] [M=Ga ( 3 ), In ( 4 )]. Complexes 3 and 4 were also obtained by treatment of 1 with the trialkyl derivatives [M(CH2SiMe3)3] (M=Ga, In) at high temperatures. The analogous reaction of 1 with [{Ga(NMe2)3}2] at 110 °C leads to [{Ga(μ3‐N)2(μ3‐NH)Ti3(η5‐C5Me5)3(μ3‐N)}2] ( 5 ), in which two [GaTi3N4] cube‐type moieties are linked through a gallium–gallium bond. Complex 1 reacts with one equivalent of germanium, tin, or lead bis(trimethylsilyl)amido derivatives [M{N(SiMe3)2}2] in toluene at room temperature to give cube‐type complexes [M{(μ3‐N)2(μ3‐NH)Ti3(η5‐C5Me5)3(μ3‐N)}] [M=Ge ( 6 ), Sn ( 7 ), Pb ( 8 )]. Monitoring the reaction of 1 with [Sn{N(SiMe3)2}2] and [Sn(C5H5)2] by NMR spectroscopy allows the identification of intermediates [RSn{(μ3‐N)(μ3‐NH)2Ti3(η5‐C5Me5)3(μ3‐N)}] [R=N(SiMe3)2 ( 9 ), C5H5 ( 10 )] in the formation of 7 . Addition of one equivalent of the metalloligand 1 to a solution of lead derivative 8 or the treatment of 1 with a half equivalent of [Pb{N(SiMe3)2}2] afford the corner‐shared double‐cube compound [Pb(μ3‐N)2(μ3‐NH)4{Ti3(η5‐C5Me5)3(μ3‐N)}2] ( 11 ). Analogous antimony and bismuth derivatives [M(μ3‐N)3(μ3‐NH)3{Ti3(η5‐C5Me5)3(μ3‐N)}2] [M=Sb ( 12 ), Bi ( 13 )] were obtained through the reaction of 1 with the tris(dimethylamido) reagents [M(NMe2)3]. Treatment of 1 with [AlCl2{N(SiMe3)2}(OEt2)] affords the precipitation of the singular aluminum–titanium square‐pyramidal aggregate [{{(Me3Si)2N}Cl3Al2}(μ3‐N)(μ3‐NH)2{Ti3(η5‐C5Me5)3(μ‐Cl)(μ3‐N)}] ( 14 ). The X‐ray crystal structures of 5 , 11 , 13 , 14 , and [AlCl{N(SiMe3)2}2] were determined. 相似文献
998.
Jorge J. Carbó Dr. Noelia Martínez‐Espada Miguel Mena Dr. Marta E. G. Mosquera Dr. Josep‐M. Poblet Prof. Carlos Yélamos Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11619-11631
The Lewis base behavior of μ3‐nitrido ligands of the polynuclear titanium complexes [{Ti(η5‐C5Me5)(μ‐NH)}3(μ3‐N)] ( 1 ) and [{Ti(η5‐C5Me5)}4(μ3‐N)4] ( 2 ) to MX Lewis acids has been observed for the first time. Complex 1 entraps one equivalent of copper(I ) halide or copper(I ) trifluoromethanesulfonate through the basal NH imido groups to give cube‐type adducts [XCu{(μ3‐NH)3Ti3(η5‐C5Me5)3(μ3‐N)}] (X=Cl ( 3 ), Br ( 4 ), I ( 5 ), OSO2CF3 ( 6 )). However, the treatment of 1 with an excess (≥2 equiv) of copper reagents afforded complexes [XCu{(μ3‐NH)3Ti3(η5‐C5Me5)3(μ4‐N)(CuX)}] (X=Cl ( 7 ), Br ( 8 ), I ( 9 ), OSO2CF3 ( 10 )) by incorporation of an additional CuX fragment at the μ3‐N nitrido apical group. Similarly, the tetranuclear cube‐type nitrido derivative 2 is capable of incorporating one, two, or up to three CuX units at the μ3‐N ligands to give complexes [{Ti(η5‐C5Me5)}4(μ3‐N)4?n{(μ4‐N)CuX}n] (X=Br ( 11 ), n=1; X=Cl ( 12 ), n=2; X=OSO2CF3 ( 13 ), n=3). Compound 2 also reacts with silver(I ) trifluoromethanesulfonate (≥1 equiv) to give the adduct [{Ti(η5‐C5Me5)}4(μ3‐N)3{(μ4‐N)AgOSO2CF3}] ( 14 ). X‐ray crystal structure determinations have been performed for complexes 8 – 13 . Density functional theory calculations have been carried out to understand the nature and strength of the interactions of [{Ti(η5‐C5H5)(μ‐NH)}3(μ3‐N)] ( 1′ ) and [{Ti(η5‐C5H5)}4(μ3‐N)4] ( 2′ ) model complexes with copper and silver MX fragments. Although coordination through the three basal NH imido groups is thermodynamically preferred in the case of 1′ , in both complexes the μ3‐nitrido groups act as two‐electron donor Lewis bases to the appropriate Lewis acids. 相似文献
999.
Julio R. Pinzón Claudia M. Cardona Dr. Maria Ángeles Herranz Dr. Marta E. Plonska‐Brzezinska Dr. Amit Palkar Andreas J. Athans Dr. Nazario Martín Prof. Dr. Antonio Rodríguez‐Fortea Dr. Josep M. Poblet Prof. Dr. Giovanni Bottari Dr. Tomás Torres Prof. Dr. S. Shankara Gayathri Dr. Dirk M. Guldi Prof. Dr. Luis Echegoyen Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(4):864-877
The first pyrrolidine and cyclopropane derivatives of the trimetallic nitride templated (TNT) endohedral metallofullerenes Ih‐Sc3N@C80 and Ih‐Y3N@C80 connected to an electron‐donor unit (i.e., tetrathiafulvalene, phthalocyanine or ferrocene) were successfully prepared by 1,3‐dipolar cycloaddition reactions of azomethine ylides and Bingel–Hirsch‐type reactions. Electrochemical studies confirmed the formation of the [6,6] regioisomers for the Y3N@C80‐based dyads and the [5,6] regioisomers in the case of Sc3N@C80‐based dyads. Similar to other TNT endohedral metallofullerene systems previously synthesized, irreversible reductive behavior was observed for the [6,6]‐Y3N@C80‐based dyads, whereas the [5,6]‐Sc3N@C80‐based dyads exhibited reversible reductive electrochemistry. Density functional calculations were also carried out on these dyads confirming the importance of these structures as electron transfer model systems. Furthermore, photophysical investigations on a ferrocenyl–Sc3N@C80‐fulleropyrrolidine dyad demonstrated the existence of a photoinduced electron‐transfer process that yields a radical ion pair with a lifetime three times longer than that obtained for the analogous C60 dyad. 相似文献
1000.
[M(N)X2]-(M=Ru, Os; X=S2C6H4, mnt)的电子结构和光谱性质的理论研究 总被引:2,自引:0,他引:2
利用密度泛函理论(DFT)中的B3LYP方法优化了氮化钌和氮化锇配合物[M(N)X2]-[M=Ru, Os; X=S2C6H4, mnt(maleonitriledithiolate)]的基态几何结构, 得到的几何参数与实验结果吻合得很好. 采用TD-DFT方法, 得到了配合物在CH3CN溶液中的激发态电子结构和电子吸收光谱. 利用SCRF方法中的CPCM模型来模拟溶剂化效应. 研究结果表明, 配合物1~4在CH3CN溶液中的吸收跃迁性质相似, 低能吸收均被指认为LMCT和LLCT的混合跃迁, 高能吸收均被指认为ILCT/LLCT跃迁. 相似文献