全文获取类型
收费全文 | 104334篇 |
免费 | 13366篇 |
国内免费 | 8732篇 |
专业分类
化学 | 51378篇 |
晶体学 | 669篇 |
力学 | 4745篇 |
综合类 | 317篇 |
数学 | 8284篇 |
物理学 | 28949篇 |
综合类 | 32090篇 |
出版年
2024年 | 516篇 |
2023年 | 2057篇 |
2022年 | 3280篇 |
2021年 | 3677篇 |
2020年 | 3492篇 |
2019年 | 3081篇 |
2018年 | 2832篇 |
2017年 | 2684篇 |
2016年 | 3949篇 |
2015年 | 4135篇 |
2014年 | 5168篇 |
2013年 | 6266篇 |
2012年 | 7786篇 |
2011年 | 7757篇 |
2010年 | 5460篇 |
2009年 | 5358篇 |
2008年 | 5763篇 |
2007年 | 5377篇 |
2006年 | 4848篇 |
2005年 | 4330篇 |
2004年 | 3286篇 |
2003年 | 2637篇 |
2002年 | 2433篇 |
2001年 | 2278篇 |
2000年 | 2248篇 |
1999年 | 3308篇 |
1998年 | 2841篇 |
1997年 | 2906篇 |
1996年 | 2781篇 |
1995年 | 2329篇 |
1994年 | 2030篇 |
1993年 | 1742篇 |
1992年 | 1501篇 |
1991年 | 1326篇 |
1990年 | 1169篇 |
1989年 | 972篇 |
1988年 | 823篇 |
1987年 | 573篇 |
1986年 | 410篇 |
1985年 | 263篇 |
1984年 | 154篇 |
1983年 | 106篇 |
1982年 | 82篇 |
1981年 | 70篇 |
1980年 | 66篇 |
1979年 | 35篇 |
1978年 | 31篇 |
1977年 | 42篇 |
1976年 | 30篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献
22.
“人口城镇化”是社会发展的必然趋势。本文从河南沁阳等九个“小城镇”的实际调查材料出发,较详细地讨论了农村劳动力向小城镇转移的流量,形成、就业层次和社会影响,说明中国的“人口城镇化”方向关键在于积极发展小城镇。 相似文献
23.
Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
24.
Z. J. Yu L. J. Liu R. X. Zhuo 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):13-21
The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (Mw) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (Mw/Mn)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with Mw = 12,100 and Mw/Mn = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in Mw of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003 相似文献
25.
H. -Q. Liu 《manuscripta mathematica》1995,87(1):159-166
This article was processed by the author using the IATEX style filecljourl from Springer-Verlag. 相似文献
26.
A hybrid finite-element method, combining ideas from a modified method of characteristics and the streamline diffusion method, delivers accurate solutions to the advection–diffusion equation. An error analysis for the case of tensorial diffusion shows that the lowest-order version of the scheme, which allows one to use a symmetric linear solvers at each time step, possesses first-order accuracy in time and space. Numerical experiments demonstrate the scheme's ability to model advection-dominated transport of solute plumes without distorting sharp fronts. © 1995 John Wiley & Sons, Inc. 相似文献
27.
In this work, the melting behaviors of nonisothermally and isothermally melt‐crystallized poly(L ‐lactic acid) (PLLA) from the melt were investigated with differential scanning calorimetry (DSC) and temperature‐modulated differential scanning calorimetry (TMDSC). The isothermal melt crystallizations of PLLA at a temperature in the range of 100–110 °C for 120 min or at 110 °C for a time in the range of 10–180 min appeared to exhibit double melting peaks in the DSC heating curves of 10 °C/min. TMDSC analysis revealed that the melting–recrystallization mechanism dominated the formation of the double melting peaks in PLLA samples following melt crystallizations at 110 °C for a shorter time (≤30 min) or at a lower temperature (100, 103, or 105 °C) for 120 min, whereas the double lamellar thickness model dominated the formation of the double melting peaks in those PLLA samples crystallized at a higher temperature (108 or 110 °C) for 120 min or at 110 °C for a longer time (≥45 min). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 466–474, 2007 相似文献
28.
In the present paper, some types of general solutions of a first-order nonlinear ordinary differential equation with six degree are given and a new generalized algebra method is presented to find more exact solutions of nonlinear differential equations. As an application of the method and the solutions of this equation, we choose the (2 + 1) dimensional Boiti Leon Pempinelli equation to illustrate the validity and advantages of the method. As a consequence, more new types and general solutions are found which include rational solutions and irrational solutions and so on. The new method can also be applied to other nonlinear differential equations in mathematical physics. 相似文献
29.
30.
介绍了钢筋混凝土结构,钢结构和钢骨钢筋混凝土结构建筑在坂神地震中的破坏情况,了建筑结构的震害与建筑年代及建筑规范的变迁有关,高层建筑中的薄弱层和东同结构型式的转换层是震害的集中部位。 相似文献