全文获取类型
收费全文 | 6018篇 |
免费 | 1038篇 |
国内免费 | 853篇 |
专业分类
化学 | 4774篇 |
晶体学 | 103篇 |
力学 | 306篇 |
综合类 | 34篇 |
数学 | 702篇 |
物理学 | 1990篇 |
出版年
2024年 | 21篇 |
2023年 | 110篇 |
2022年 | 216篇 |
2021年 | 217篇 |
2020年 | 276篇 |
2019年 | 286篇 |
2018年 | 229篇 |
2017年 | 205篇 |
2016年 | 329篇 |
2015年 | 332篇 |
2014年 | 376篇 |
2013年 | 492篇 |
2012年 | 523篇 |
2011年 | 565篇 |
2010年 | 397篇 |
2009年 | 365篇 |
2008年 | 378篇 |
2007年 | 313篇 |
2006年 | 326篇 |
2005年 | 244篇 |
2004年 | 243篇 |
2003年 | 189篇 |
2002年 | 230篇 |
2001年 | 171篇 |
2000年 | 119篇 |
1999年 | 106篇 |
1998年 | 66篇 |
1997年 | 67篇 |
1996年 | 52篇 |
1995年 | 38篇 |
1994年 | 52篇 |
1993年 | 32篇 |
1992年 | 27篇 |
1991年 | 37篇 |
1990年 | 31篇 |
1989年 | 28篇 |
1988年 | 32篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 6篇 |
排序方式: 共有7909条查询结果,搜索用时 31 毫秒
181.
182.
183.
Fu A Huang X Li J Yuen T Lin CL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(10):2239-2247
Controlled synthesis of transition metal complexes with mixed ligands has led to two new compounds with the same empirical formula [Fe(N3)2(4,4'-bpy)] (4,4'-bpy=4,4'- bipyridine). The compound 2D-[Fe(N3)2(4,4'-bpy)] (I) contains end-on (EO) bridging azido ligands. It crystallizes in the orthorhombic crystal system, space group Cmmm (No. 65): a=11.444(2) A, b=15.181(3) A, c=3.458(1) A, V=600.8(2) A(3), and Z=2. The compound 3D-[Fe(N3)2(4,4'-bpy)] (II) contains end-to-end (EE) azido bridges. It belongs to the tetragonal crystal system, space group P4(1)2(1)2 (No. 92): a=8.132(1) A, b=8.132(1) A, c=16.708(3) A, V=1104.9(5) A(3), and Z=4. Crystals of I and II have been grown by the diffusion method. Phase-pure samples of both compounds have been obtained by means of an optimal solution synthesis. Spontaneous long-range magnetic ordering was found in both I and II, with I being a metamagnet, and II being a ferromagnet. For I, in the low-field region, multiple transitions at TN1=20 K and TN2=5 K were observed, and these indicated the existence of Fe moment reorientation. Heat capacity measurements on II confirmed ferromagnetic transition at TC=20 K. 相似文献
184.
185.
Long JW Logan MS Rhodes CP Carpenter EE Stroud RM Rolison DR 《Journal of the American Chemical Society》2004,126(51):16879-16889
We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties. 相似文献
186.
Hydrogen storage in the dehydrated prussian blue analogues M3[Co(CN)6]2 (M = Mn, Fe, Co, Ni, Cu, Zn)
The porosity and hydrogen storage properties for the dehydrated Prussian blue analogues M3[Co(CN)6]2 (M = Mn, Fe, Co, Ni, Cu, Zn) are reported. Argon sorption isotherms measured at 87 K afford BET surface areas ranging from 560 m2/g for Ni3[Co(CN)6]2 to 870 m2/g for Mn3[Co(CN)6]2; the latter value is comparable to the highest surface area reported for any known zeolite. All six compounds show significant hydrogen sorption at 77 K and 890 Torr, varying from 1.4 wt % and 0.018 kg H2/L for Zn3[Co(CN)6]2 to 1.8 wt % and 0.025 kg H2/L for Cu3[Co(CN)6]2. Fits to the sorption data employing the Langmuir-Freundlich equation give maximum uptake quantities, resulting in a predicted storage capacity of 2.1 wt % and 0.029 kg H2/L for Cu3[Co(CN)6]2 at saturation. Enthalpies of adsorption for the frameworks were calculated from hydrogen isotherms measured at 77 and 87 K and found to increase with M varying in the order Mn < Zn < Fe < Co < Cu < Ni. In all cases, the binding enthalpies, which lie in the range of 5.3-7.4 kJ/mol, are higher than the 4.7-5.2 kJ/mol measured for Zn4O(1,4-benzenedicarboxylate)3. 相似文献
187.
Danny K. Long Wolfgang Bangerth Derek R. Handwerk Christopher B. Whitehead Patrick D. Shipman Richard G. Finke 《Journal of computational chemistry》2022,43(1):43-56
In order to quantitatively predict nano- as well as other particle-size distributions, one needs to have both a mathematical model and estimates of the parameters that appear in these models. Here, we show how one can use Bayesian inversion to obtain statistical estimates for the parameters that appear in recently derived mechanism-enabled population balance models (ME-PBM) of nanoparticle growth. The Bayesian approach addresses the question of “how well do we know our parameters, along with their uncertainties?.” The results reveal that Bayesian inversion statistical analysis on an example, prototype nanoparticle formation system allows one to estimate not just the most likely rate constants and other parameter values, but also their SDs, confidence intervals, and other statistical information. Moreover, knowing the reliability of the mechanistic model's parameters in turn helps inform one about the reliability of the proposed mechanism, as well as the reliability of its predictions. The paper can also be seen as a tutorial with the additional goal of achieving a “Gold Standard” Bayesian inversion ME-PBM benchmark that others can use as a control to check their own use of this methodology for other systems of interest throughout nature. Overall, the results provide strong support for the hypothesis that there is substantial value in using a Bayesian inversion methodology for parameter estimation in particle formation systems. 相似文献
188.
Jeremy R. Lizotte Brian M. Erwin Ralph H. Colby Timothy E. Long 《Journal of polymer science. Part A, Polymer chemistry》2002,40(4):583-590
The feasibility of utilizing stable free‐radical polymerization (SFRP) in the synthesis of well‐defined poly(2‐vinylnaphthalene) homopolymers has been investigated. Efforts to control molecular weight by manipulating initiator concentration while maintaining a 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO):benzoyl peroxide (BPO) molar ratio of 1.2:1 proved unsuccessful. In addition, systematic variations of the TEMPO: BPO molar ratio did not result in narrow molecular weight distributions. In situ Fourier transform infrared spectroscopy (FTIR) indicated that the rate of monomer disappearance under SFRP and thermal conditions were identical. This observation indicated a lack of control in the presence of the stable free radical, TEMPO. The similarities in chemical structure between styrene and 2‐vinylnaphthalene suggested thermally initiated polymerization occurred via the Mayo mechanism. A kinetic analysis of the thermal polymerization of styrene and 2‐vinylnaphthalene suggested that the additional fused ring in 2‐vinylnaphthalene increased the propensity for thermal polymerization. The observed rate constant for thermal polymerization of 2‐vinylnaphthalene was determined using in situ FTIR spectroscopy and was one order of magnitude greater than styrene, assuming pseudo‐first‐order kinetics. Also, an Arrhenius analysis indicated that the activation energy for the thermal polymerization of 2‐vinylnaphthalene was 30 kJ/mol less than styrene. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 583–590, 2002; DOI 10.1002/pola.10131 相似文献
189.
190.
Back Cover: Porous Mn2O3: A Low‐Cost Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media with Comparable Activity to Pt/C (Chem. Eur. J. 29/2016)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wenhai Wang Jing Geng Long Kuai Min Li Prof. Dr. Baoyou Geng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10256-10256