全文获取类型
收费全文 | 1789篇 |
免费 | 76篇 |
国内免费 | 13篇 |
专业分类
化学 | 1262篇 |
晶体学 | 14篇 |
力学 | 56篇 |
数学 | 165篇 |
物理学 | 381篇 |
出版年
2023年 | 11篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 38篇 |
2019年 | 41篇 |
2018年 | 33篇 |
2017年 | 26篇 |
2016年 | 57篇 |
2015年 | 52篇 |
2014年 | 58篇 |
2013年 | 82篇 |
2012年 | 128篇 |
2011年 | 142篇 |
2010年 | 98篇 |
2009年 | 95篇 |
2008年 | 147篇 |
2007年 | 107篇 |
2006年 | 96篇 |
2005年 | 92篇 |
2004年 | 80篇 |
2003年 | 61篇 |
2002年 | 74篇 |
2001年 | 23篇 |
2000年 | 40篇 |
1999年 | 29篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有1878条查询结果,搜索用时 343 毫秒
991.
Solvothermal reactions of manganese(II) chloride tetrahydrate with a bis-tetrazole ligand, 2,6-di(1H-tetrazol-5-yl)naphthalene (H(2)NDT), in N,N'-dimethylformamide (DMF)/MeOH mixed solvent at two slightly different temperatures, 75 and 100 °C, led to two different metal-organic frameworks (MOFs), [Mn(II)(3)O(HNDT)(2)(NDT)(DMF)(3)] (1) and [Mn(II)(5)O(2)(HNDT)(2)(NDT)(2)(DMF)(8)] (2), with different net topologies. Single-crystal X-ray diffraction studies reveal that 1 is constructed from an unprecedented trinuclear building block, [Mn(II)(3)O(CN(4))(6)], as a 6-connected trigonal prismatic secondary building unit (SBU) of topological D(3h) site symmetry, and that the ligand in the HNDT(-1)/NDT(2-) deprotonation states is a linker, where two tetrazole (CN(4)) groups of the ligand are connected via a rigid naphthyl group. The tetrazole groups in 1 adopt a 1,2-μ-bridging mode with the manganese(II) ions to form a μ(3)-oxo trinuclear SBU. The trigonalprismatic SBU in 1 is connected to six neighboring SBUs to form a three-dimensional MOF of acs net topology. 2 is constructed from an unprecedented pentanuclear building block, [Mn(II)(5)O(2)(CN(4))(8)], as an 8-connected tetragonal prismatic SBU of topological D(4h) site symmetry. The tetrazole groups in 2 adopt monodentate, 1,2-μ- and 2,3-μ-bridging bidentate and 1,2,3-μ-bridging tridentate binding modes with the manganese(II) centers to form a bis-μ(3)-oxo pentanuclear SBU of local C(2) site symmetry. The tetragonal prismatic SBU in 2 is connected to eight neighboring SBUs to form a 3-D MOF of bcu net topology. 相似文献
992.
Dong Woo Cho Ju Ho Lee Jungin Shin Won Bae Hwayong Kim Moon Sam Shin 《The Journal of chemical thermodynamics》2011,43(11):1666-1671
Ethylene glycol dimethacrylate (EGDMA) and di-ethylene glycol dimethacrylate (DEGDMA) are two of the most wildly used di-functional monomers in the polymer industry. The EGDMA and DEGDMA are applied to cross-linking polymerisation for improving the physical and chemical properties of synthesized polymers. However, residual and unreacted EGDMA and DEGDMA applied to the synthesis of dental composite and super-absorption polymer poses a health threat. This problem can be solved by using supercritical CO2, which has high diffusivity and causes polymer swelling. To design and operate the supercritical fluid extraction process using scCO2, high pressure phase behaviour data are required. The pressure–composition (P–x) isotherms for the (CO2 + EGDMA) and (CO2 + DEGDMA) binary mixture systems were measured using the static method with a variable-volume view cell at temperatures ranging from (313.2 to 363.2) K. The experimental data correlation was performed using the Peng–Robinson equation of state (PR-EOS) and the Van der Waals one fluid mixing rule. The critical constants for the PR-EOS were estimated by the Joback method and the Marrero–Gani method. The acentric factor was estimated by the Lee–Kesler method. The Marrero–Gani method showed better correlation results than the Joback method and the EGDMA is more soluble in the supercritical carbon dioxide than the DEGDMA. 相似文献
993.
Yourim Yoon Yong-Hyuk Kim Byung-Ro Moon 《Journal of Mathematical Modelling and Algorithms》2011,10(3):269-276
We analyze two essential problems arising from edge-based graph partitioning. We show that one of them is an NP-hard problem
but the other is in P, presenting a novel methodology that links linear algebra theory to the graph problems as a part of
proving the facts. This is a significant trial in that linear algebra, which has been mostly adopted as a theoretical analysis
tool, is practically applied to solving actual graph problems. As a result of the linear algebraic manipulation, we could
devise a linear-time algorithm for the problem in P. 相似文献
994.
In this paper, we investigate a self-normalized invariance principle for a ?-mixing stationary sequence {X j , j ≥ 1} of random variables such that L(x):= E(X 1 2 I{|X 1| ≤ x}) is a slowly varying function at ∞. 相似文献
995.
Jin Young Park Hong Chae Jung G. Seeta Rama Raju Jung Hyun Jeong Byung Kee Moon Jung Hwan Kim Young Kuk Lee 《Current Applied Physics》2013,13(3):441-447
The color rendering index (CRI) and structural stability of cerium doped yttrium aluminum garnet (YAG:Ce) based phosphors have been enhanced by replacing Y3+ ions by larger radius ions (Tb3+, Gd3+, Eu3+, and Sm3+) at the dodecahedral site and replacing Al3+ ions by larger ones (Ga3+, Y3+, Tb3+, Gd3+, and Sm3+) at the octahedral site. These aluminum garnet crystalline powders were prepared by solvothermal reaction method at 300 °C for 48 h. The lattice constant values of synthetic aluminum garnet crystalline powders are larger than that of YAG and the emission wavelength of Ce3+ ion of these samples is longer than that of YAG:Ce. FESEM and TEM studies revealed that the Ln3Ga2Al3O12 and Ln3Al2Al3O12 crystalline powders have 3-dimensional star-like morphology with submicron size and good crystallinity, while, Ln3(LnAl)Al3O12 garnet crystalline powders were cubic crystalline phases and shaped as cubes with the round edge having an approximate diameter of about 200–400 nm. All the prepared powders were grown along (100) direction and crystallized into single crystal. Also, the effects of treatment time and reaction temperature on the structure of aluminum garnet crystalline powders have been investigated. 相似文献
996.
K. Fujita K. Sagara T. Teranishi M. Iwasaki D. Kodama S. Liu S. Matsuda T. Mitsuzumi J. Y. Moon M. T. Rosary H. Yamaguchi 《Few-Body Systems》2013,54(7-10):1603-1606
A cross section measurement employing a direct 16O detection method for the reaction energies from E cm = 2.4 to 0.7 MeV is planned at Kyushu University Tandem Laboratory. To perform this experiment and to obtain quantitative information about the cross section to within an error of 10%, we have developed several instruments, including a blow-in type windowless gas target and a ionization chamber. A target thickness of 24 × 3.9 Torr cm was achieved using the developed gas target. The particle identification was successfully performed by using the energy deposit in the ionization chamber. Experiments were performed at E cm = 2.4 and 1.5 MeV using the developed instruments and the cross sections were obtained. 相似文献
997.
Ki-Tek Han Wook Jae Yoo Jeong Ki Seo Sang Hun Shin Dayeong Jeon Seunghan Hong Seunghyun Cho Joo Hyun Moon Bongsoo Lee 《Optical Review》2013,20(2):205-208
A fiber-optic radiation sensor (FORS), which is composed of an inorganic scintillator, a plastic optical fiber (POF), a photomultiplier tube (PMT), and a multichannel analyzer (MCA), was developed for gamma-ray energy spectroscopy. In this study, we selected a cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) as the sensitive element of the FORS and found that LYSO:Ce with dimensions of 3 × 3 × 15mm3 gives the best performance in obtaining a gammaray energy spectrum. The FORS allows us to measure the energy spectra of Co-60, Na-22, and Cs-137. 相似文献
998.
Shape optimization of staggered ribs in a rotating equilateral triangular cooling channel 总被引:1,自引:0,他引:1
A rotating equilateral triangular cooling channel with staggered square ribs inside the leading edge of a turbine blade has been optimized in this work based on surrogate modeling. The fluid flow and heat transfer in the channel have been analyzed using three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations under uniform heat flux condition. Shear stress transport turbulence model has been used as a turbulence closure. Computational results for area-averaged Nusselt number have been validated compared to the experimental data. The objectives related to the heat transfer rate and pressure drop has been linearly combined with a weighting factor to define the objective function. The angle of the rib, the rib pitch-to-hydraulic diameter ratio, and the rib width-to-hydraulic diameter ratio have been selected as the design variables. Twenty-two design points have been generated by Latin Hypercube sampling, and the values of the objective function have been calculated by the RANS analysis at these points. The surrogate model for the objective function has been constructed using the radial basis neural network method. Through the optimization, the objective function value has been improved by 21.5 % compared to that of the reference geometry. 相似文献
999.
Jae Hee Sung Seong Ku Lee Tae Moon Jeong Chang Hee Nam 《Applied physics. B, Lasers and optics》2014,116(2):287-292
We characterized the transmission properties of a color-glass-filter (RG850) saturable absorber (SA) in a wide range of pulse durations (from 25 fs to 5 ps). The transmission properties were strongly related to the energy fluence, pulse duration, and chirp parameter. On the basis of these properties, the input pulse duration, chirp parameter, and energy fluence were optimized to maintain the width of the transmitted laser spectrum as much as possible with minimal energy loss. We demonstrated that, by transmitting a positively chirped 2.8-ps laser pulse to two identical SAs at an energy fluence of 15 mJ/cm2, the temporal contrast ratio of the main pulse to the amplified spontaneous emission was enhanced by 4 orders of magnitude without any significant energy loss or strong spectral narrowing in a 10-Hz, 100-TW femtosecond laser system. 相似文献
1000.
Jung Mo Jung Doo Yeol Cha Deok Su Kim Hee Jun Yang Kyo Sang Choi Jong Myoung Choi Sung Pil Chang 《Applied Physics A: Materials Science & Processing》2014,116(3):1395-1401
The authors developed PDMS (polydimethylsiloxane)-based dry type surface electromyography (SEMG) electrodes for myoelectric prosthetic hands. The SEMG electrodes were strongly recommended to be fabricated on a flexible substrate to be compatible with the surface of skin. In this study, the authors designed a bar-shaped dry-type flexible SEMG electrodes comprised of two input electrodes and a reference electrode on a flexible PDMS substrate to measure EMG signals. The space distance between each electrode with a size of 10 mm × 2 mm was chosen to 18 mm to get optimal result according to the simulation result with taking into consideration the conduction velocity and the median frequency of EMG signals. Raw EMG signals were measured from Brachioradialis, Biceps brachii, deltoideus, and pectoralis major muscles, to drive the application of the myoelectric hand prosthesis. Measured raw EMG signals were transformed to root mean square (RMS) EMG signals using Acqknowledge4.2. The experimental peak voltage values of RMS EMG signals from Brachioradialis, Biceps brachii, deltoideus, and pectoralis major muscles were 2.96 V, 4.45 V, 1.74 V, and 2.62 V, respectively. Values from the dry type flexible SEMG electrodes showed higher peak values than a commercially available wet type Ag–AgCl electrode. The study shows that the PDMS-based flexible electrode devised for measuring myoelectric signals from the surface of skin is more useful for prosthetic hands because of its greater sensitivity and flexibility. 相似文献