全文获取类型
收费全文 | 121113篇 |
免费 | 27197篇 |
国内免费 | 8037篇 |
专业分类
化学 | 105266篇 |
晶体学 | 775篇 |
力学 | 7016篇 |
综合类 | 386篇 |
数学 | 11687篇 |
物理学 | 31217篇 |
出版年
2024年 | 587篇 |
2023年 | 5095篇 |
2022年 | 4195篇 |
2021年 | 5322篇 |
2020年 | 7374篇 |
2019年 | 5252篇 |
2018年 | 4748篇 |
2017年 | 3054篇 |
2016年 | 8859篇 |
2015年 | 8768篇 |
2014年 | 9006篇 |
2013年 | 10526篇 |
2012年 | 10143篇 |
2011年 | 8089篇 |
2010年 | 7998篇 |
2009年 | 7752篇 |
2008年 | 5946篇 |
2007年 | 5144篇 |
2006年 | 4148篇 |
2005年 | 3411篇 |
2004年 | 2642篇 |
2003年 | 2068篇 |
2002年 | 1909篇 |
2001年 | 1583篇 |
2000年 | 1442篇 |
1999年 | 1616篇 |
1998年 | 1368篇 |
1997年 | 1409篇 |
1996年 | 1399篇 |
1995年 | 1204篇 |
1994年 | 1029篇 |
1993年 | 997篇 |
1992年 | 783篇 |
1991年 | 658篇 |
1990年 | 570篇 |
1989年 | 475篇 |
1988年 | 468篇 |
1987年 | 384篇 |
1986年 | 336篇 |
1985年 | 318篇 |
1977年 | 362篇 |
1976年 | 402篇 |
1975年 | 488篇 |
1974年 | 490篇 |
1973年 | 317篇 |
1972年 | 384篇 |
1971年 | 361篇 |
1970年 | 547篇 |
1969年 | 416篇 |
1968年 | 461篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Gu De-shan Jing Shi-wei Sang Hai-feng Qiao Shuang Liu Yu-ren Liu Lin-mao 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):493-496
This paper introduces the analysis method and principle of pulse fast-thermal neutron analysis (PFTNA). A system for the measurement
of low caloric power of coal by PFTNA is also presented. The 14 MeV pulse neutron generator and BGO detector and 4096 MCA
were applied in this system. A multiple linear regression method applied to the data solved the interferential problem of
multiple elements. The error of low caloric power between chemical analysis and experiment was less than 0.4 MJ/kg.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
102.
103.
Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings. 相似文献
104.
105.
Summary Our purpose is to extend results due to P. Chandra and L. Leindler concerning the order of approximation by means of Fourier series for functions belonging to generalized Lipschitz-classes. 相似文献
107.
为了使光盘获得优良的记录/读出性能并能够长期稳定地使用,必须优化设计相变光盘的多层膜结构。采用自行设计的模拟分析相变光盘读出过程设计软件,从光学角度出发模拟计算了蓝光(405nm)相变光盘的膜层结构,研究了多层膜系的反射率和反射率对比度等光学参量与各层膜厚度和槽深的关系。研究得出的最佳多层膜结构为:下介电层/记录层/上介电层/反射层的厚度对于台记录为100nm/10nm/25nm,/60nm,而对于槽记录则为140nm/15nm/30nm,/60nm,槽深为50nm。模拟计算结果对于将来高密度蓝光相变光盘的制备具有一定的指导意义。 相似文献
108.
YunFei Liu ShengCai Shi ShengLin Yu 《International Journal of Infrared and Millimeter Waves》2003,24(12):2069-2077
When electromagnetic waves propagate through a wire grid, there will be some evanescent space harmonics generated around the wire grid. In this paper, we mainly investigate their effects on the transmission characteristics of a Gaussian beam by cylindrical wire grids. The results are compared with those without taking account of evanescent space-harmonics. 相似文献
109.
Piaoping Yang Jianfeng Yu Zhenlü Wang Qingsheng Liu Tonghao Wu 《Reaction Kinetics and Catalysis Letters》2004,83(2):275-282
Mg-Al, Zn-Al and Ni-Al hydrotalcite-like compounds with high crystallinity were synthesized by using the decomposing property
of urea at high temperature. The crystallinity and the regularly of the samples were much preferable to those synthesized
by other methods.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
110.
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