全文获取类型
收费全文 | 437篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
化学 | 308篇 |
晶体学 | 6篇 |
力学 | 13篇 |
数学 | 32篇 |
物理学 | 114篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 28篇 |
2012年 | 30篇 |
2011年 | 42篇 |
2010年 | 20篇 |
2009年 | 17篇 |
2008年 | 26篇 |
2007年 | 25篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 17篇 |
2003年 | 18篇 |
2002年 | 21篇 |
2001年 | 11篇 |
2000年 | 18篇 |
1999年 | 9篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1986年 | 3篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1970年 | 4篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有473条查询结果,搜索用时 0 毫秒
41.
With the increasing demand for finer lines/spaces on PCB boards, a new technology—laser structuring—has emerged in recent years. In this research, the frequency-tripled Nd:YAG laser is selected as the laser source in laser structuring; this laser is often used in miniaturization machining. This paper describes in detail the processing parameters’ influences, such as laser power, numbers of repetition, repetition rate and bite size, on laser structuring results. From the research results, it can be concluded that the line width and depth are increased with increases in the laser power and numbers of repetition. Repetition rate, bite size and velocity are related to one another. When the bite size is fixed, the velocity increases with the repetition rate and the depth of the line is decreased at the same time. When the repetition rate is fixed, velocity increases with the bite size. 相似文献
42.
Paul W. Wang Jin‐Cherng Hsu Yung‐Hsin Lin Huang‐Lu Chen 《Surface and interface analysis : SIA》2011,43(7):1089-1094
Aluminum oxynitride films were deposited by ion beam sputtering technique at room temperature. The optical properties and morphologies of the aluminum oxynitride films were studied and reported previously. It was found that the optical properties are closely related to the O contents in the films. In this study, the structures of the films were investigated by X‐ray diffractometer and XPS. Three oxidation states of N1s in oxynitride films, N+, N2+ and N3+, were clearly deduced from N1s spectra in the amorphous films fabricated under various oxygen partial pressures (PO2). To our knowledge, three oxidation states of N1s have not been simultaneously observed and reported in the aluminum oxynitride films previously. Corresponding bonding variations in Al2p and O1s spectra indicated more oxygen in oxynitride in the film as PO2 increases. Three aluminum oxynitride networks, AlO2N, AlO2.5N and AlO3N were deduced. Optical properties of aluminum oxynitride films resemble those of AlN and Al2O3 films when PO2 is low and high during the deposition. The refractive indices and extinction coefficients of the aluminum oxynitride films can be adjusted by using proper PO2 during the film depositions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
43.
This study analyzed variations of tribological behaviors that depend on the injection molding techniques during the blending of short glass fiber (SGF) and polytetrafluoroethylene (PTFE) reinforced polycarbonate (PC) composites. The proposed planning of blending experiments is to use a D‐optimal mixture design (DMD). The tribological behaviors of friction coefficient and wear mass loss were selected for discussion. Nine experimental runs, based on a DMD method, utilized to train the back‐propagation neural network (BPNN) and then the simulated annealing algorithm (SAA) approach is applied to search for an optimal mixture ratio setting. In addition, the result of BPNN integrating SAA was also compared with response surface methodology (RSM) approach. The results of confirmation experiment show that DMD, RSM, and BPNN integrating SAA method are effective tools for the optimization of reinforced process. Furthermore, the scanning electron microscope (SEM) images show that the abundant debris are peeled off from the matrix materials and predominant delamination mechanisms and plastic deformation are shown on the worn surface after tribological behavior tests. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
44.
Wei-Chiang Hong Yucheng DongFeifeng Zheng Shih Yung Wei 《Applied mathematics and computation》2011,217(15):6733-6747
Accurate urban traffic flow forecasting is critical to intelligent transportation system developments and implementations, thus, it has been one of the most important issues in the research on road traffic congestion. Due to complex nonlinear data pattern of the urban traffic flow, there are many kinds of traffic flow forecasting techniques in literature, thus, it is difficult to make a general conclusion which forecasting technique is superior to others. Recently, the support vector regression model (SVR) has been widely used to solve nonlinear regression and time series problems. This investigation presents a SVR traffic flow forecasting model which employs the hybrid genetic algorithm-simulated annealing algorithm (GA-SA) to determine its suitable parameter combination. Additionally, a numerical example of traffic flow data from northern Taiwan is used to elucidate the forecasting performance of the proposed SVRGA-SA model. The forecasting results indicate that the proposed model yields more accurate forecasting results than the seasonal autoregressive integrated moving average (SARIMA), back-propagation neural network (BPNN), Holt-Winters (HW) and seasonal Holt-Winters (SHW) models. Therefore, the SVRGA-SA model is a promising alternative for forecasting traffic flow. 相似文献
45.
46.
Devan RS Gao SY Lin YR Cheng SR Hsu CE Chen CH Shiu HW Liou Y Ma YR 《Microscopy and microanalysis》2011,17(6):944-949
Atomic force microscopy probe-induced large-area ultrathin SiO(x) (x ≡ O/Si content ratio and x > 2) protrusions only a few nanometers high on a SiO(2) layer were characterized by scanning photoemission microscopy (SPEM) and X-ray photoemission spectroscopy (XPS). SPEM images of the large-area ultrathin SiO(x) protrusions directly showed the surface chemical distribution and chemical state specifications. The peak intensity ratios of the XPS spectra of the large-area ultrathin SiO(x) protrusions provided the elemental quantification of the Si 2p core levels and Si oxidation states (such as the Si(4+), Si(3+), Si(2+), and Si(1+) species). The O/Si content ratio (x) was evidently determined by the height of the large-area ultrathin SiO(x) protrusions. 相似文献
47.
48.
Chunhao Zhai Yung P. Koh Bryan D. Vogt Sindee L. Simon 《Journal of polymer science. Part A, Polymer chemistry》2024,62(9):1922-1933
The effect of nanoconfinement on the kinetics of benzyl methacrylate radical polymerization is investigated using differential scanning calorimetry. Controlled pore glass (CPG), ordered mesoporous carbons, and mesoporous silica are used as confinement media with pore sizes from 2 to 8 nm. The initial polymerization rate in CPG and mesoporous silica increases relative to the bulk and increases linearly with reciprocal pore size; whereas, the rate in the carbon mesopores decreases linearly with reciprocal pore size; the changes are consistent with the rate being related to the ratio of the pore surface area to pore volume. Induction times are longer for nanoconfined polymerizations, and in the case of CPG and carbon mesopores, autoacceleration occurs earlier, presumably due to the limited diffusivity and lower termination rates for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The equilibrium conversion under nanoconfinement decreases with decreasing temperature and with confinement size, exhibiting what appears to be a floor temperature at low temperatures. 相似文献
49.
Bagchi S Kim YS Charnley AK Smith AB Hochstrasser RM 《The journal of physical chemistry. B》2007,111(11):3010-3018
The linear infrared and two-dimensional infrared (2D IR) spectra in the amide-I region of N-acetyl tryptophan methyl amide (NATMA) in solvents of varying polarity are reported. The two amide-I transitions have been assigned unambiguously by using 13C isotopic substitution of the carbonyl group. The amide unit at the amino end shows a lower transition frequency in CH2Cl2 and methanol, while the acetyl end has a lower transition frequency in D2O. Multiple conformers exist in CH2Cl2 and methanol, but only one conformer is evident in D2O. The 2D IR cross peaks from the intermode coupling yield off-diagonal anharmonicities 2.5 +/- 0.5, 3.25 +/- 0.5, and 3.0 +/- 0.5 cm(-1) in CH2Cl2, methanol, and D2O, respectively, which by simple matrix diagonalization yield the coupling constants 8.0 +/- 0.5, 8.0 +/- 1.0, and 5.5 +/- 1.0 cm(-1). The major conformer in CH2Cl2 corresponds to a C7 structure, in agreement with that found in the gas phase [Dian, B. C.; Longarte, A.; Mercier, S.; Evans, D. A.; Wales, D. J.; Zwier, T. S. J. Chem. Phys. 2002, 117, 10688-10702] with intramolecular hydrogen bonding between the acetyl end C=O and the amino end N-H. The backbone dihedral angles (phi, psi) are determined to be in the ranges of (-55 +/- 5 degrees , 30 +/- 5 degrees ), (120 +/- 10 degrees , -20 +/- 10 degrees ), and (+/-160 +/- 10 degrees , +/-75 +/- 10 degrees ) in CH2Cl2, methanol, and D2O, respectively. 相似文献
50.
Tzu‐Wei Tsai Eng‐Chi Wang Sie‐Rong Li Yung‐Hua Chen Yu‐Li Lin You‐Feng Wang Keng‐Shiang Huang 《中国化学会会志》2004,51(6):1307-1318
Based on Claisen rearrangement, the double bond isomerization of O‐allyl function together with the formation of O‐vinyl function in one pot, and ring‐closing metathesis (RCM), various phenols were transformed into various benzofurans in good yields. 相似文献