全文获取类型
收费全文 | 5968篇 |
免费 | 954篇 |
国内免费 | 713篇 |
专业分类
化学 | 3187篇 |
晶体学 | 149篇 |
力学 | 1445篇 |
综合类 | 64篇 |
数学 | 621篇 |
物理学 | 2169篇 |
出版年
2024年 | 6篇 |
2023年 | 54篇 |
2022年 | 160篇 |
2021年 | 172篇 |
2020年 | 214篇 |
2019年 | 193篇 |
2018年 | 183篇 |
2017年 | 206篇 |
2016年 | 275篇 |
2015年 | 239篇 |
2014年 | 321篇 |
2013年 | 508篇 |
2012年 | 378篇 |
2011年 | 404篇 |
2010年 | 326篇 |
2009年 | 394篇 |
2008年 | 364篇 |
2007年 | 406篇 |
2006年 | 323篇 |
2005年 | 287篇 |
2004年 | 279篇 |
2003年 | 242篇 |
2002年 | 201篇 |
2001年 | 189篇 |
2000年 | 155篇 |
1999年 | 134篇 |
1998年 | 121篇 |
1997年 | 117篇 |
1996年 | 134篇 |
1995年 | 88篇 |
1994年 | 70篇 |
1993年 | 74篇 |
1992年 | 71篇 |
1991年 | 57篇 |
1990年 | 45篇 |
1989年 | 36篇 |
1988年 | 34篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有7635条查询结果,搜索用时 93 毫秒
81.
The determination of nanometer thick layers of poly(methyl methacrylate) coated on to the surface of poly(ethylene terephthalate) film has been investigated by high resolution pyrolysis gas chromatography without sample pretreatment or modification of the instrumentation used. A good linear relationship was observed between the quantity of the characteristic pyrolysate and the thickness of the poly(methyl methacrylate) layer; the detection limit was sufficient to enable the quantitation of poly(methyl methacrylate)-to-poly(ethylene terephthalate) film thickness ratios of 1:20000 in composite materials. 相似文献
82.
Layer-by-layer fluorescent conjugated polyelectrolyte films have been studied. The photoluminescence of conjugate polyelectrolytes was observed to be highly tunable during this film assembly process. Efficient photoinduced electron transfer from thus prepared highly luminescent film to a natural electron-transfer protein cytochrome c has also been observed. 相似文献
83.
[Co(H2o)4(NCS)2](18—C—6)的薄层光谱电化学研究 总被引:2,自引:0,他引:2
利用光谱电化学方法来研究冠醚类化合物的文章尚未见报导.本文在测定用凝胶法合成的[Co(H_2O)(NCS)_2](18-C-6)的核磁共振谱和红外光谱的基础上,使用循环伏安法和薄层光谱电化学技术,在金微栅电极上测定了此配合物在乙腈溶剂中的第一步克式量电势(E~0′)和电子转移数(n),并推测了电还原反应机理. 相似文献
84.
A layer of elemental silicon has been deposited on the surface of stainless steel tubing by means of chemical vapor deposition (CVD). Two kinds of capillary column were prepared from the deactivated tubing: cross-linked, silanol-terminated polydime-thylsiloxane wall coated open tubular (WCOT) columns and molecular sieve 13X porous layer open tubular (PLOT) columns. Unlike fused silica capillary columns, stainless steel WCOT and PLOT columns can be operated at temperatures in excess of 400°C. High temperature simulated distillation has been performed successfully with a macro bore WCOT column and rapid PNA (paraffin, naphthene, and aromatic) analysis with a multidimensional gas solid chromatographic (GSC) system using PLOT columns. 相似文献
85.
The effect of calcining conditions on the rehydration of dead burnt magnesium oxide using magnesium acetate as a hydrating agent 总被引:1,自引:0,他引:1
C. A. Strydom E. M. van der Merwe M. E. Aphane 《Journal of Thermal Analysis and Calorimetry》2005,80(3):659-662
Summary Magnesium oxide was produced through calcination of magnesite ore. A rehydration percentage of MgO to Mg(OH)2 of higher than 60% is obtained using calcination temperatures of 1000°C and below. At these temperatures medium reactive MgO was formed. The extend to which dead burnt MgO (obtained after calcination at 1200°C and higher) may be rehydrated is dependent on the calcination time, but even after 1 h and using magnesium acetate as a hydrating agent only 40% of the initial product has rehydrated to Mg(OH)2. After 4 and more hours of calcinations at 1200°C, a maximum of approximately 14% of the initial MgO is rehydrated back to Mg(OH)2. Thermogravimetric analysis was performed on the various compounds to determine the amounts of Mg(OH)2 that formed. 相似文献
86.
P. Torline G. du Plessis N. Schnautz J. C. Thompson 《Journal of separation science》1979,2(10):613-616
A detailed method for the routine preparation of glass capillary columns is presented. The method consists of coating a glass tube with quartz powder prior to pulling the tube into a capillary. The inner surface of the capillary consists of an even distribution of quartz particles fused to the walls. This surface has been found readily deactivated by standard procedures and ideal for the preparation of thick-film glass capillary columns. The method has been thoroughly tested in two independent laboratories to ensure that the procedures described are reproducible. 相似文献
87.
Lamination Design Optimization for Continuous Fiber Reinforced Composites of Variable Thicknesses北大核心CSCD
下载免费PDF全文
![点击此处可从《应用数学和力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
由于具备高的比强度、比刚度,利用连续纤维增强复合材料代替传统金属材料以实现结构轻量化正受到设计者们的广泛关注。然而,结构的复杂性给复合材料的铺层设计与优化带来了很大的挑战。针对航空用复合材料铺层设计约束多的问题,通过逐步构建设计变量准确表达结构的铺层信息。基于经典遗传算法框架,结合各设计变量特点,定义了铺层优化算法中的遗传算子,通过引入“修复”策略保证了每一代解都能满足设计约束,分布在可行域区间内。最后利用精英保留策略提高了算法的局部寻优能力,可以降低复杂复合材料结构铺层设计的计算成本。通过解决经典benchmark问题并与已有优化结果的比较,验证了前述铺层优化算法的全局、局部寻优能力,为工程实际中的复合材料铺层设计优化提供了理论支撑。 相似文献
88.
Direct analysis of thin-layer chromatographic spots of narcotics by means of diffuse reflectance Fourier transform infrared spectroscopy 总被引:1,自引:0,他引:1
The technique of diffuse reflectance Fourier transform infrared spectrometry (DRIFT) as an in situ detection method was used for the qualitative and quantitative analysis of drugs (heroin, cocaine and codeine) separated by thin layer chromatography.It was found that at a given interferometer throughput and detector sensitivity the quality of the spectrum depends strongly in the type of the chromatographic thin layer used. A detection limit of approx. 2 g was attained on a microcrystalline cellulose thin layer with a dynamically aligned Bio-Rad Digilab FTS 60A/896 type interferometer and room temperature DTGS detector. A reliable qualitative analysis can be made with as little as 10 to 15 g drug per spot. 相似文献
89.
N. Kallay M. Čolić D. W. Fuerstenau H. M. Jang E. Matijević 《Colloid and polymer science》1994,272(5):554-561
Potentiometric, electrokinetic, and coagulation experiments with a rutile dispersion in the pH region above the point of zero charge exhibit an inverse lyotropic sequence for counterions: Li+>K+>Cs+. The potentiometric and electrokinetic data were interpreted by a surface complexation model assuming the Stern-Gouy-Chapman structure of the interfacial layer, which yielded the values of inner layer capacitances,C, and the intrinsic equilibrium constants,K
ass
0
, characterizing the specificity of each counterion. These parameters were used to explain the order of lyotropic sequences in the adsorption, coagulation, and electrokinetic phenomena. 相似文献
90.
Jeffrey Axten Jennifer Troy Peter Jiang Mendel Trachtman Charles W. Bock 《Structural chemistry》1994,5(2):99-108
Ab initio molecular orbital calculations are used to study the modified Schlenk equilibrium: 2RMgCl (RMgCl)2 MgR2 + MgCl2 Mg(Cl2)MgR2 with R=H and CH3. In the absence of any solvents, calculations indicate that the formation of the various possible bridged dimers (RMgCl)2 is substantially exothermic. However, using dimethylether as a model solvent, we show that the formation of the dimer (Me2O)(CH3)Mg(Cl2)Mg(CH3)(OMe2) is exothermic only when entropic effects are included. 相似文献