全文获取类型
收费全文 | 39258篇 |
免费 | 3719篇 |
国内免费 | 4293篇 |
专业分类
化学 | 27911篇 |
晶体学 | 520篇 |
力学 | 2065篇 |
综合类 | 338篇 |
数学 | 7761篇 |
物理学 | 8675篇 |
出版年
2024年 | 68篇 |
2023年 | 430篇 |
2022年 | 1155篇 |
2021年 | 1081篇 |
2020年 | 1338篇 |
2019年 | 1245篇 |
2018年 | 1135篇 |
2017年 | 1331篇 |
2016年 | 1511篇 |
2015年 | 1331篇 |
2014年 | 1785篇 |
2013年 | 2816篇 |
2012年 | 2055篇 |
2011年 | 2366篇 |
2010年 | 1979篇 |
2009年 | 2473篇 |
2008年 | 2338篇 |
2007年 | 2392篇 |
2006年 | 2094篇 |
2005年 | 1899篇 |
2004年 | 1928篇 |
2003年 | 1576篇 |
2002年 | 1792篇 |
2001年 | 1147篇 |
2000年 | 955篇 |
1999年 | 794篇 |
1998年 | 696篇 |
1997年 | 612篇 |
1996年 | 670篇 |
1995年 | 594篇 |
1994年 | 566篇 |
1993年 | 389篇 |
1992年 | 385篇 |
1991年 | 251篇 |
1990年 | 200篇 |
1989年 | 190篇 |
1988年 | 210篇 |
1987年 | 157篇 |
1986年 | 119篇 |
1985年 | 127篇 |
1984年 | 115篇 |
1983年 | 51篇 |
1982年 | 110篇 |
1981年 | 124篇 |
1980年 | 126篇 |
1979年 | 145篇 |
1978年 | 113篇 |
1977年 | 92篇 |
1976年 | 85篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
Liang-gen Hu 《应用数学学报(英文版)》2007,23(2):281-288
In this paper,we will establish several strong convergence theorems for the approximation ofcommon fixed points of r-strictly asymptotically pseudocontractive mappings in uniformly convex Banachspaces using the modiied implicit iteration sequence with errors,and prove the necessary and sufficient conditionsfor the convergence of the sequence.Our results generalize,extend and improve the recent work,in thistopic. 相似文献
72.
73.
1 Introduction Inrecentyears,boththetheoreticalandexperimentalinvestigationsonlasercoolingandtrappinghavebecomeoneofthemajorfieldsinatomic,molecularandoptical physics[1~ 8] .Thedevelopmentoflasercoolingandtrappingtechnologyisimportantfortheapplicationssu… 相似文献
74.
M. I. Pech-Canul F. Ortega-Celaya M. A. Pech-Canul 《Mechanics of Composite Materials》2006,42(3):283-296
The effect of SiO2 in SiCp and the following processing parameters on the microstructure and impact strength of Al/SiCp composites fabricated by pressureless infiltration was investigated: Mg content in the aluminum alloy, SiC particle size,
and holding time. Preforms of SiCp in the form of rectangular bars (10 × 1 × 1 cm) were infiltrated at 1150°C in an argon→nitrogen atmosphere for 45 and 60
min by utilizing two aluminum alloys (Al-6 Mg-11 Si and Al-9 Mg-11 Si, wt.%). The results obtained show that the presence
of SiO2 in SiC affects the microstructure and impact strength of the composites significantly. When Al4C3 is formed, the impact strength decreases. However, a high proportion of SiC to SiO2 limits the formation of the unwanted Al4C3 phase in the composites. Also, a higher content of Mg in the Al alloy lowers the residual porosity and, consequently, increases
the composite strength. The impact strength grows with decrease in SiC particle size and increases considerably when the residual
porosity is less than 1%.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 401–418, May–June, 2006. 相似文献
75.
E. Mathieu Y. Foucher P. Dellamonica J. P. Daures 《Methodology and Computing in Applied Probability》2007,9(3):389-397
In AIDS control, physicians have a growing need to use pragmatically useful and interpretable tools in their daily medical
taking care of patients. Semi-Markov process seems to be well adapted to model the evolution of HIV-1 infected patients. In
this study, we introduce and define a non homogeneous semi-Markov (NHSM) model in continuous time. Then the problem of finding
the equations that describe the biological evolution of patient is studied and the interval transition probabilities are computed.
A parametric approach is used and the maximum likelihood estimators of the process are given. A Monte Carlo algorithm is presented
for realizing non homogeneous semi-Markov trajectories. As results, interval transition probabilities are computed for distinct
times and follow-up has an impact on the evolution of patients.
相似文献
76.
77.
M. A. Posypkin I. Kh. Sigal 《Computational Mathematics and Mathematical Physics》2006,46(12):2187-2202
The efficiency of parallel implementations of the branch-and-bound method in discrete optimization problems is considered. A theoretical analysis and comparison of two parallel implementations of this method is performed. A mathematical model of the computation process is constructed and used to obtain estimates of the maximum possible speedup. Examples of problems in which none of these two parallel implementations can speed up the computations are considered. 相似文献
78.
79.
High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer (ML) up to 600 °C have been studied and reported in this paper. Ti/Ni multilayer samples having constant layer thicknesses of 50 Å each are deposited on float glass and Si(1 1 1) substrates using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions at room temperatures. The micro-structural parameters and their evolution with temperature for as-deposited as well as annealed multilayer samples up to 600 °C in a step of 100 °C for 1 h are determined by using X-ray diffraction (XRD) and grazing incidence X-ray reflectivity techniques. The X-ray diffraction pattern recorded at 300 °C annealed multilayer sample shows interesting structural transformation (from crystalline to amorphous) because of the solid-state reaction (SSR) and subsequent re-crystallization at higher temperatures of annealing, particularly at ≥400 °C due to the formation of TiNi3 and Ti2Ni alloy phases. Sample quality and surface morphology are examined by using atomic force microscopy (AFM) technique for both as-deposited as well as annealed multilayer samples. In addition to this, a temperature dependent dc resistivity measurement is also used to study the structural transformation and subsequent alloy phase formation due to annealing treatment. The corresponding magnetization behavior of multilayer samples after each stage of annealing has been investigated by using Magneto-Optical Kerr Effect (MOKE) technique and results are interpreted in terms of observed micro-structural changes. 相似文献
80.
Jiaqiang Wang Hua Fang Ying Li Junjie Li Zhiying Yan 《Journal of molecular catalysis. A, Chemical》2006,250(1-2):75-79
Cobalt-doped mesoporous titania with a crystalline framework synthesized by surfactant templating method presented highly selective (99%) and reasonable conversion rate (49%) of catalytic oxidation of para-chlorotoluene to para-chlorobenzaldehyde in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. By contrast, cobalt-doped mesoporous titania without a crystalline structure and cobalt doped the commercial titania, Degussa P25 prepared by impregnation method with the similar concentration of cobalt were found inactive. The effects of catalyst concentration, reaction time, reaction temperature, and solvents on the performance of the catalyst were also investigated. 相似文献