全文获取类型
收费全文 | 4747篇 |
免费 | 433篇 |
国内免费 | 572篇 |
专业分类
化学 | 3269篇 |
晶体学 | 98篇 |
力学 | 245篇 |
综合类 | 27篇 |
数学 | 895篇 |
物理学 | 1218篇 |
出版年
2024年 | 3篇 |
2023年 | 62篇 |
2022年 | 129篇 |
2021年 | 166篇 |
2020年 | 186篇 |
2019年 | 164篇 |
2018年 | 146篇 |
2017年 | 150篇 |
2016年 | 189篇 |
2015年 | 178篇 |
2014年 | 206篇 |
2013年 | 393篇 |
2012年 | 339篇 |
2011年 | 394篇 |
2010年 | 298篇 |
2009年 | 294篇 |
2008年 | 343篇 |
2007年 | 304篇 |
2006年 | 317篇 |
2005年 | 297篇 |
2004年 | 212篇 |
2003年 | 170篇 |
2002年 | 157篇 |
2001年 | 122篇 |
2000年 | 74篇 |
1999年 | 73篇 |
1998年 | 51篇 |
1997年 | 38篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 17篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有5752条查询结果,搜索用时 16 毫秒
121.
Wenxuan Jiang Wei Wei Tinglian Yuan Shasha Liu Ben Niu Hui Wang Wei Wang 《Chemical science》2021,12(24):8556
The inevitable microstructural defects, including cracks, grain boundaries and cavities, make a portion of the material inaccessible to electrons and ions, becoming the incentives for electrochemically inactive zones in single entity. Herein, we introduced dark field microscopy to study the variation of scattering spectrum and optical mass centroid (OMC) of single Prussian blue nanoparticles during electrochemical reaction. The “dark zone” embedded in a single electroactive nanoparticle resulted in the incomplete reaction, and consequently led to the misalignment of OMC for different electrochemical intermediate states. We further revealed the dark zones such as lattice defects in the same entity, which were externally manifested as the fixed pathway for OMC for the migration of potassium ions. This method opens up enormous potentiality to optically access the heterogeneous intraparticle dark zones, with implications for evaluating the crystallinity and electrochemical recyclability of single electroactive nano-objects.The schematic of single cubic-shaped Prussian blue (PB) mesocrystals formed by the oriented aggregation of small nanocrystals. The dark-field images of single PB nanoparticle at PB and Prussian white (PW) states, respectively. 相似文献
122.
Ben‐Yong Lou Yan‐Bin Huang 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(4):o246-o248
4,4′‐Bipyridyl N,N′‐dioxide crystallizes with 3‐hydroxy‐2‐naphthoic acid to give a centrosymmetric three‐component adduct, C10H8N2O2·2C11H8O3, which is engineered into a two‐dimensional layer structure by two kinds of π–π interactions. Weak C—H⋯O interactions further link the two‐dimensional structure into a three‐dimensional structure. 相似文献
123.
Etude de phosphates condenses diagramme d’equilibre du systeme AgPO3−Pr(PO3)3 Données sur AgPr(PO3)4
D. Ben Hassen-Chehimi M. Trabelsi-Ayedi 《Journal of Thermal Analysis and Calorimetry》1995,44(4):961-967
The AgPO3?Pr(PO3)3 system has been studied for the first time by differential thermal analysis, X-ray diffraction and IR spectroscopy. The system shows one compound AgPr(PO3)4 which melts in a peritectic decomposition at 1069 K. An eutectic appears at 761 K. AgPr(PO3)4 belongs to the monoclinic system with space group P2t/c,Z=4. The parameters of the unit cell are:a=12.000(9),b=13.177(4),c=7.046(5) Å and β=123o,81(6),Z=4. Its IR absorption spectrum is typical of chain phosphates. 相似文献
124.
Hui Chen Yujiao Fan Nian Zhang Sylvain Trpout Bergam Ptissam Annie Brûlet Ben Zhong Tang Min-Hui Li 《Chemical science》2021,12(15):5495
Fluorescent polymer cubosomes and hexosomes with aggregation-induced emission (AIE) were prepared from amphiphilic block copolymers PEG-b-PTPEMA where the hydrophobic block PTPEMA was a polymethacrylate with tetraphenylethene (TPE) as the AIE side group. Four highly asymmetric block copolymers with hydrophilic block weight ratio fPEG ≤ 20% were synthesized. Cubosomes and hexosomes with strong fluorescence emission were obtained by nanoprecipitation of polymers with fPEG < 9% in dioxane/water and THF/water systems. Their ordered internal structures were studied by electron microscopy (cryo-EM, SEM and TEM) and the X-ray scattering technique (SAXS). To elucidate the formation mechanisms of these inverted colloids, other parameters influencing the morphologies, like the water content during self-assembly and the organic solvent composition, were also investigated. This study not only inspires people to design novel building blocks for the preparation of functional cubosomes and hexosomes, but also presents the first AIE fluorescent polymer cubosome and hexosome with potential applications in bio-related fields.Fluorescent Imm cubosome and P6mm hexosome with aggregation-induced emission (AIE) were reported, which were formed by amphiphilic block copolymers PEG-b-PTPEMA. The length of hydrophobic block PTPEMA was adjusted to control morphology formation. 相似文献
125.
Monserrat García Gerhard van Vliet Mattijs G. J. ten Cate Francisco Chvez Ben Norder Bart Kooi Werner E. van Zyl Henk Verweij Dave H. A. Blank 《先进技术聚合物》2004,15(4):164-172
Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
126.
Azioune A Slimane AB Hamou LA Pleuvy A Chehimi MM Perruchot C Armes SP 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3350-3356
Novel ester-functionalized polypyrrole-silica nanocomposite particles were prepared by oxidative copolymerization of pyrrole and N-succinimidyl ester pyrrole (50/50% initial concentrations), using FeCl3 in the presence of ultrafine silica nanoparticles (20 nm diameter). The N-succinimidyl ester pyrrole monomer was prepared in aqueous solution using 1-(2-carboxyethylpyrrole) and N-hydroxysuccinimide in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. The resulting nanocomposites (N-succinimidyl ester polypyrrole-silica) are raspberry-shaped agglomerates of silica sol particles "glued" together by the insoluble poly(pyrrole-co-N-succinimidyl pyrrole). The N-succinimidyl ester polypyrrole-silica particles were characterized in terms of their size, density, copolymer content, and polydispersity. Scanning electron microscopy and disk centrifuge sedimentometry confirmed that the nanocomposite particles had narrow size distributions. X-ray photoelectron spectroscopy analysis indicated a silica-rich surface and a high surface concentration of N-succinimidyl ester groups. These nanoparticles exhibited good long-term dispersion stability. The chemical stability of the ester functions in aqueous media after several weeks of storage was monitored by FTIR spectroscopy. The functionalized nanocomposites were tested as bioadsorbents of human serum albumin (HSA). The very high amount of immobilized HSA determined by UV-visible spectroscopy is believed to be due to covalent binding. Incubation of the HSA-grafted nanocomposite with anti-HSA resulted in immediate flocculation, an indication that they are alternative candidates for visual diagnostic assays. 相似文献
127.
The regioselectivity of the metal-catalyzed ring opening of unsymmetrical 1,2-dioxines to cis-gamma-hydroxyenones was investigated using two different Co(II) salen complexes. Regioselectivity was determined by direct examination of the enone ratios and by derivitization with a stabilized phosphorus ylide. The steric influence of the substituents on the 1,2-dioxine was the primary influence on regioselectivity. Temperature played little role; however, solvent and selection of Co(II) complex could be used to mildly influence the outcome of the rearrangement for selected substrates. The origins of the selectivity for the reaction are discussed. 相似文献
128.
Structure of microemulsions with gemini surfactant studied by solvatochromic probe and diffusion NMR
Ben Moshe M Magdassi S Cohen Y Avram L 《Journal of colloid and interface science》2004,276(1):221-226
The structure of microemulsions prepared by the anionic gemini surfactant didodecyl diphenyl ether disulfonate (C12-DADS) was investigated by a solvatochromic probe and nuclear magnetic resonance (NMR) diffusion measurements. The NMR measurements indicate the presence of bicontinuous and oil-in-water microemulsions depending on microemulsion composition. The absorbance spectra of the solvatochromic probe, Nile red, indicate the solubilization of the probe in different sites, in agreement with the NMR findings. It was also found that the microemulsions were capable of dissolving the hydrophobic probe, Nile red, up to four times better than expected if it were simply dissolved in the toluene phase. 相似文献
129.
130.
HuaRongZHAO XiaoFengLI XinJianZHAO YangPingNIU 《中国化学快报》2004,15(11):1292-1294
Aryl selenoamides react smoothly with a-haloacetic acid in various alcohol to givecorresponding bis(carboxyalkylmethyl) diselenides in good yields. 相似文献