全文获取类型
收费全文 | 14634篇 |
免费 | 2367篇 |
国内免费 | 1901篇 |
专业分类
化学 | 10867篇 |
晶体学 | 183篇 |
力学 | 844篇 |
综合类 | 142篇 |
数学 | 1885篇 |
物理学 | 4981篇 |
出版年
2024年 | 36篇 |
2023年 | 330篇 |
2022年 | 374篇 |
2021年 | 480篇 |
2020年 | 623篇 |
2019年 | 612篇 |
2018年 | 477篇 |
2017年 | 375篇 |
2016年 | 663篇 |
2015年 | 661篇 |
2014年 | 836篇 |
2013年 | 1079篇 |
2012年 | 1285篇 |
2011年 | 1307篇 |
2010年 | 938篇 |
2009年 | 803篇 |
2008年 | 921篇 |
2007年 | 883篇 |
2006年 | 808篇 |
2005年 | 731篇 |
2004年 | 535篇 |
2003年 | 475篇 |
2002年 | 503篇 |
2001年 | 444篇 |
2000年 | 306篇 |
1999年 | 305篇 |
1998年 | 271篇 |
1997年 | 241篇 |
1996年 | 256篇 |
1995年 | 211篇 |
1994年 | 201篇 |
1993年 | 168篇 |
1992年 | 140篇 |
1991年 | 127篇 |
1990年 | 90篇 |
1989年 | 94篇 |
1988年 | 64篇 |
1987年 | 43篇 |
1986年 | 33篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
The recently described pressure reaction in the presence of trithylamine with subsequent thermal (200°C) cyclization provided 13N‐pyridylcantharidinimides 4a‐4m from aminopyridines and cantharidin in yields of 15–83%. 2‐Amino‐3,5‐dichloropyridine failed to yield 4n . 相似文献
992.
Effect of the stoichiometry on the electronic structure of the Ni(111)/α-Al2O3(0001) interface: a first-principles investigation 下载免费PDF全文
In this paper first-principles calculations of Ni(111)/α-Al2O3(0001) interfaces have been performed, and are compared with the preceding results of the Cu (111)/α-Al2O3(0001) interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu(111)/α Al2O3(0001) interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni(111)/α-A1203(0001) interfaces is similar to that in the corresponding Cu(111)/α- Al2O3(0001) interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively. 相似文献
993.
Resonances of a hydrogen atom in strong parallel electric and magnetic fields using B-spline basis sets 下载免费PDF全文
The B-spline basis set plus complex scaling method is applied to the numerical calculation of the exact resonance parameters Er and Г/2 of a hydrogen atom in parallel electric and magnetic fields. The method can calculate the ground and higher excited resonances accurately and efficiently. The resonance parameters with accuracies of 10^-9 - 10^-12 for hydrogen atom in parallel fields with different field strengths and symmetries are presented and compared with previous ones. Extension to the calculation of Rydberg atom in crossed electric and magnetic fields and of atomic double excited states in external electric fields is discussed. 相似文献
994.
Bin Liu Rong Zhang Zili Xie XiangQian Xiu Liang Li Jieying Kong Huiqiang Yu Pin Han Shulin Gu Yi Shi Zheng YouDou Tang ChenGuang Chen YongHai Wang ZhanGuo 《中国科学G辑(英文版)》2008,51(3):237-242
InN films grown on sapphire at different substrate temperatures from 550°C to 700°C by metalorganic chemical vapor deposition
were investigated. The low-temperature GaN nucleation layer with high-temperature annealing (1100°C) was used as a buffer
for main InN layer growth. X-ray diffraction and Raman scattering measurements reveal that the quality of InN films can be
improved by increasing the growth temperature to 600°C. Further high substrate temperatures may promote the thermal decomposition
of InN films and result in poor crystallinity and surface morphology. The photoluminescence and Hall measurements were employed
to characterize the optical and electrical properties of InN films, which also indicates strong growth temperature dependence.
The InN films grown at temperature of 600°C show not only a high mobility with low carrier concentration, but also a strong
infrared emission band located around 0.7 eV. For a 600 nm thick InN film grown at 600°C, the Hall mobility achieves up to
938 cm2/Vs with electron concentration of 3.9 × 1018 cm−3.
Supported by the National Basic Research Program of China (Grant No. 2006CB6049), the National Natural Science Foundation
of China (Grant Nos. 6039072, 60476030 and 60421003), the Great Fund of the Ministry of Education of China (Grant No. 10416),
the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004), and the Natural
Science Foundation of Jiangsu Province of China (Grant Nos. BK2005210 and BK2006126) 相似文献
995.
Low-temperature heat capacities and standard molar enthalpy of formation of N-methylnorephedrine C11H17NO(s) 下载免费PDF全文
This paper reports that low-temperature heat capacities of N-methylnorephedrine C11H17NO(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T=78K to T=400K. A solid to liquid phase transition of the compound was found in the heat capacity curve in the temperature range of T=342-364 K. The peak temperature, molar enthalpy and entropy of fusion of the substance were determined. The experimental values of the molar heat capacities in the temperature regions of T=78-342 K and T=364-400 K were fitted to two poly- nomial equations of heat capacities with the reduced temperatures by least squares method. The smoothed molar heat capacities and thermodynamic functions of N-methylnorephedrine C11H17NO(s) relative to the standard refer- ence temperature 298.15 K were calculated based on the fitted polynomials and tabulated with an interval of 5 K. The constant-volume energy of combustion of the compound at T=298.15 K was measured by means of an isoperibol precision oxygen-bomb combustion calorimeter. The standard molar enthalpy of combustion of the sample was calculated. The standard molar enthalpy of formation of the compound was determined from the combustion enthalpy and other auxiliary thermodynamic data through a Hess thermochemical cycle. 相似文献
996.
The coupled numerical simulation on fluid flow, heat transfer, and mass transfer in the process of laser cladding is undertaken on the basis of the continuum model.In the simulation of mass transfer in the laser molten pool, the concentration distribution in the regions on different sides of the interface between cladding layer and substrate is calculated separately and coupled at the co-boundary.The non-equilibrium solute partition coefficient is obtained from equilibrium solute partition coefficient according to the Sobolev model.By using the developed software which is based on the commercial software PHOENICS 1.4, the distribution of Fe in laser molten pool in an experiment of cladding Stellite 6 on 12CrMoV is calculated.The obtained results well coincide with the experimental ones. 相似文献
997.
The three-dimensional (3D) problem of the ground vibration isolation by an in-filled trench as a passive barrier is studied
theoretically. Integral equations governing Rayleigh wave scattering are derived based on the Green’s solution of Lamb problem.
The integral equations are solved accurately and efficiently with an iteration technique. They are used to evaluate the complicated
Rayleigh wave field generated by irregular scatterers embedded in an elastic half-space solid. The passive isolation effectiveness
of ground vibration by the in-filled trench for screening Rayleigh wave is further studied in detail. Effects of relevant
parameters on the effectiveness of vibration isolation are investigated and presented. The results show that a trench filled
with stiff backfill material gets a better isolation effect than a soft one, and increasing the depth or width of the in-filled
trench also improves its screening effectiveness. The effectiveness and the area of the screened zone are surging with the
increase in the length of the in-filled trench.
Supported by the National Natural Science Foundation of China (Grant Nos. 50678128 and 50538010) and the Research Fund for
PhD Student of Chinese College (Grant No. 20050247030) 相似文献
998.
L-Fuzzy拓扑空间中一种新型的强F仿紧性 总被引:8,自引:1,他引:8
本文引入一种新型的强F仿紧性─—Ⅲ型强F仿紧性,它是基于α-局部有限族概念提出的,这种α-局部有限族概念可用于刻划强F可数紧性。 相似文献
999.
In this paper, the idea of random selection in the theorem on gambling system is extended to Markov chains, by using the notion likelihood ratio and an analytic technique. A strong limit theorem on the relative frequency of ordered couple under random selection is established.AMS Subject Classification (2001)
primary 60F15 Secondary 60J10 相似文献
1000.
Suppose that independent U(0, 1) weights are assigned to the ${d\choose 2}n^{2}$ edges of the complete d‐partite graph with n vertices in each of the d maximal independent sets. Then the expected weight of the minimum‐weight perfect d‐dimensional matching is at least $\frac{3}{16}n^{1-(2/d)}$. We describe a randomized algorithm that finds a perfect d‐dimensional matching whose expected weight is at most 5d3n1?(2/d)+d15 for all d≥3 and n≥1. © 2002 John Wiley & Sons, Inc. Random Struct. Alg., 20, 50–58, 2002 相似文献