全文获取类型
收费全文 | 2398篇 |
免费 | 77篇 |
国内免费 | 66篇 |
专业分类
化学 | 1527篇 |
晶体学 | 19篇 |
力学 | 109篇 |
综合类 | 1篇 |
数学 | 308篇 |
物理学 | 577篇 |
出版年
2023年 | 23篇 |
2022年 | 32篇 |
2021年 | 44篇 |
2020年 | 28篇 |
2019年 | 38篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 44篇 |
2015年 | 38篇 |
2014年 | 84篇 |
2013年 | 116篇 |
2012年 | 174篇 |
2011年 | 183篇 |
2010年 | 114篇 |
2009年 | 117篇 |
2008年 | 120篇 |
2007年 | 132篇 |
2006年 | 139篇 |
2005年 | 117篇 |
2004年 | 99篇 |
2003年 | 65篇 |
2002年 | 71篇 |
2001年 | 56篇 |
2000年 | 42篇 |
1999年 | 34篇 |
1998年 | 33篇 |
1997年 | 27篇 |
1996年 | 20篇 |
1995年 | 29篇 |
1994年 | 30篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1985年 | 31篇 |
1984年 | 36篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 11篇 |
排序方式: 共有2541条查询结果,搜索用时 31 毫秒
991.
A series of metal coordination polymers, [Co2(NB)4(bpp)2(H2O)]·H2O ( 1 ), [Co2(e,e‐trans‐chdc)(e,a‐cis‐chdc)(bpp)2] ( 2 ), [Ni(e,e‐trans‐chdc)(bpp)(H2O)2] ( 3 ), [Ni2(PDA)2(bpp)2(H2O)3]·H2O ( 4 ), and [Ni‐(mBDC)(bpp)] ( 5 ) (NB = 3‐nitrobenzoate anion; bpp = 4,4′‐trimethylene dipyridine; chdc = cyclohexane‐1,4‐dicarboxylate anion; PDA = 1,4‐phenylenediacetate anion; mBDC = 1,3‐benzene dicarboxylate anion), were synthesized from metal ions and organic mixed‐ligands by hydrothermal reactions. The single crystal structure analysis revealed that 1, 3, and 4 were 2D sheets with bilayer (1 and 4) and 2‐fold interpenetrated layers (3), 2 is a 3D binodal (4,5)‐connected framework, and 5 is a 1D chains. The non‐covalent interactions of H‐bonds and π–π stacking caused this conformation of highly cross‐linked networks. Compounds 1‐5 were further characterized by thermal gravimetric analysis, powder X‐ray diffraction, UV‐vis, infrared, and PL spectroscopy. 相似文献
992.
GeO2 thin films were prepared by sol‐gel method on ITO/Glass substrate. The electrical and optical properties and the microstructures of these films were investigated with special emphasis on the effects of an annealing treatment in ambient air. The films were annealed at various temperatures from 500 °C to 700 °C. Structural analysis through X‐ray diffraction (XRD) and atomic force microscope (AFM) showed that surface structure and morphological characteristics were sensitive to the treatment conditions. The optical transmittance spectra of the GeO2/ITO/Glass were measured using a UV‐visible spectrophotometer. All films exhibited GeO2 (101) orientation perpendicular to the substrate surface where the grain size increased with increasing annealing temperature. The optical transmittance spectroscopy further revealed high transparency (over 70 %) in the wave range 400 – 800 nm of the visible region. At an annealing temperature level of 700 °C, the GeO2 films were found to possess a leakage current density of 1.31×10‐6A/cm2 at an electrical field of 20 kV/cm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
993.
Chang S. Hsu 《光谱学快报》2013,46(9):439-447
The vibrational analysis of allyl mercaptan has vener been published. There are two internal rotors, the SH group and the CH2SH group, in the allyl mercaptan molecule. As in the case of propylene (1), the molecule has only one plane of symmetry (Cs point group) in its most symmetrical configuration (when the thiol group lies in the plane of the vinyl group). However, microwave studies have shown that it exhibits C1 symmetry (2). The infrared and Raman spectra of allyl mercaptan have been investigated in this study. The assignment of its fundamental modes has been made based on C1 symmetry of the molecule. 相似文献
994.
995.
Jaw-Luen Tang Jiunn-Yuan Lin Wei-Dong Li Chia-Chen Hsu Tai-Huei Wei Tzer-Hsiang Huang 《Molecular physics》2013,111(18):1919-1931
The pump–probe Raman-induced optical Kerr effect (RIKE) of simple molecular liquids, studied with femtosecond laser pulses, exhibit long lasting beats ascribable to vibrational quantum interference (QI). While energy conservation entails vibrational resonances in RIKE, momentum conservation boils down to wave vector-matching in the pump and probe processes, which calls for the participation of a vibrational excitation wave. The refractive index dispersion around vibrational resonances is intimately related to the focusing angle of the pump (also probe) beam. The larger the focusing angle, the greater the excitation wave number, i.e. the more energetic the vibration in resonance; if the focusing angle is too small, energetic vibrations cannot be observed in vibrational QI, even if energy conservation is fulfilled. If the pump and probe beams are perfectly collimated, then all beams must be collinear in order to conserve momentum. 相似文献
996.
J. R. Chen J. C. Chang L. H. Chang F. Z. Hsiao K. T. Hsu G. Y. Hsiung 《Synchrotron Radiation News》2013,26(5):41-45
Macromolecular crystallographic (MX) structure determination at synchrotron radiation sources has the potential to advance significantly through use of X-ray beams of one micron or smaller cross-sections. Recently, the MX Frontiers at the One Micron Scale Workshop explored structural biology scientific opportunities made possible through the use of micro-beams, and anticipated technical challenges for developers of MX beamlines at the National Synchrotron Light Source II (NSLS-II). More than 100 attendees participated in the workshop, which included one-and-a-half days of lectures, discussions, and a semi-formal poster session on July 23–24, 2009, at Brookhaven National Laboratory (BNL). 相似文献
997.
Chor Yong Tay Wanru Fang Magdiel Inggrid Setyawati Chee Peng Sum Jianping Xie Kee Woei Ng Xiaodong Chen Catherine Hsu Ling Hong David Tai Leong 《Particle & Particle Systems Characterization》2013,30(9):784-793
Silica nanoparticles (SiO2 NPs) are one of the most widely used engineered nanoparticles and can been found in a wide range of consumer products. Despite their massive global production scale, little is known about their potential effects in the context of unintended exposure or ingestion. Using TR146 cells as an in vitro model of the human oral buccal mucosa, the uptake, spatial intracellular distribution, reactive oxygen species (ROS) production, inflammatory response, and cytotoxic effects of commercial SiO2 NPs are examined. SiO2 NPs are shown to dock and cross the cellular membrane barrier in a dose–time‐dependent manner. Confocal sectioning reveals translocation of SiO2 NPs into the cell nucleus after 12 h of exposure. A concentration threshold of more than 500 × 10?6 m is observed, above which SiO2 NPs are shown to exert significant oxidative stress with concomitant upregulation of inflammatory genes IL6 and TNFA. Further analysis of the p53 pathway and a series of apoptotic and cell cycle biomarkers reveals intracellular accumulation of SiO2 NPs exert marginal nanotoxicity. Collectively, this study provides important information regarding the uptake, intracellular distribution, and potential adverse cellular effects of SiO2 NPs commonly found in consumer products in the human oral epithelium. 相似文献
998.
High performance IGZO/TiO2 thin film transistors using Y2O3 buffer layers on polycarbonate substrate
H. H. Hsu C. Y. Chang C. H. Cheng 《Applied Physics A: Materials Science & Processing》2013,112(4):817-820
In this work, we fabricate IGZO TFT devices on flexible substrate at room temperature. The IGZO/TiO2 TFT has small subthreshold swing of 0.16 V/dec, but suffers large gate leakage and negative threshold voltage. However, the TiO2 TFT with Y2O3 buffer layers shows improved characteristics including a low threshold voltage of 0.55 V, a small sub-threshold swing of 0.175 V/decade and high field-effect mobility of 43 cm2/Vs. Such good performance can be attributed to the enhanced capacitance density and lowered gate leakage owing to the integration of large band gap Y2O3 and low-temperature higher-κ TiO2. 相似文献
999.
It is in general challenging to characterize planar mechanical properties of extremely soft tissues such as cell-seeded collagen gels. One of the difficulties is related to premature failure of specimens. This issue may be resolved by employing fillets on stress-concentrated spots of the specimen. The existence of fillets, however, complicates the estimation of stress at the center of the specimen where stiffness data are collected. In this study, cruciform rubber specimens with two types of fillets (general vs. cut-in fillets) at the intersections of perpendicular arms were prepared and subjected to planar biaxial mechanical testing, aiming at investigating how the fillets affect the estimation of mechanical properties of cruciform specimens. Digital image correlation was used to analyze full-field deformation in the central region of the specimens. Finite element analysis with a Neo-Hookean model was performed to simulate the full-field deformation under the same experimental boundary conditions. The strain distribution for each specimen geometry obtained by finite element analysis was found to be in good agreement with that analyzed by digital image correlation, validating the finite element models. Finite element simulation showed that the greatest value of the maximum principal strain decreased with increasing the fillet radius regardless of the fillet type. Increasing the fillet radius, in general, also reduced the strain field uniformity in the central region. Compared with general fillets, however, the use of cut-in fillets provided greater strain field uniformity given the same fillet radius. Finite element analysis was also used to estimate effective transverse length required to convert tensile force at the boundary to local stress at the center. It was found that the effective transverse length for each specimen geometry remained relatively constant if the specimen was not excessively deformed (i.e., global equibiaxial stretch ≤ 1.2). We suggest using cut-in fillets at the intersections of perpendicular arms when preparing cruciform specimens for testing extremely soft tissues. 相似文献
1000.
In this paper the problem of wave propagation over an adjoining-type of composite submerged poroelastic breakwater with different materials is investigated theoretically. A new analytical solution for describing the dynamic response of wave interaction with poroelastic structures is presented. A set of simultaneous equations is developed and numerically solved in order to produce a general solution for each region subject to matching boundary conditions. The present paper focuses on the changes of influence parameters such as different component widths of the composite breakwater, permeability coefficients, composite materials and configurations of breakwater on wave variations. 相似文献