全文获取类型
收费全文 | 3552篇 |
免费 | 171篇 |
国内免费 | 12篇 |
专业分类
化学 | 2415篇 |
晶体学 | 7篇 |
力学 | 117篇 |
数学 | 627篇 |
物理学 | 569篇 |
出版年
2024年 | 5篇 |
2023年 | 46篇 |
2022年 | 74篇 |
2021年 | 89篇 |
2020年 | 77篇 |
2019年 | 103篇 |
2018年 | 77篇 |
2017年 | 52篇 |
2016年 | 152篇 |
2015年 | 128篇 |
2014年 | 130篇 |
2013年 | 205篇 |
2012年 | 310篇 |
2011年 | 335篇 |
2010年 | 191篇 |
2009年 | 165篇 |
2008年 | 256篇 |
2007年 | 237篇 |
2006年 | 221篇 |
2005年 | 186篇 |
2004年 | 158篇 |
2003年 | 118篇 |
2002年 | 104篇 |
2001年 | 46篇 |
2000年 | 45篇 |
1999年 | 33篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1929年 | 4篇 |
排序方式: 共有3735条查询结果,搜索用时 15 毫秒
101.
Dr. Marc Presset Dr. Jérôme Paul Ghania Nait Cherif Nisanthan Ratnam Nicolas Laloi Prof. Eric Léonel Dr. Corinne Gosmini Prof. Erwan Le Gall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(17):4491-4495
The reductive Barbier coupling of aromatic halides and electrophiles has been achieved using a CoBr2/1,10-phenanthroline catalytic system and over stoichiometric amounts of zinc. The reaction displayed a broad scope of substrates, including (hetero)aryl chlorides as pro-nucleophiles and aldehydes or imines as electrophiles, leading to diarylmethanols and diarylmethylamines in moderate to excellent yields, respectively. 相似文献
102.
103.
Dr. Yanhui Wang Dr. Sanghoon Kim Dr. Nicolas Louvain Dr. Johan G. Alauzun Dr. P. Hubert Mutin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4767-4774
An original, halide-free non-hydrolytic sol–gel route to mesoporous anatase TiO2 with hierarchical porosity and high specific surface area is reported. This route is based on the reaction at 200 °C of titanium(IV) isopropoxide with acetic anhydride, in the absence of a catalyst or solvent. NMR spectroscopic studies indicate that this method provides an efficient, truly non-hydrolytic and aprotic route to TiO2. Formation of the oxide involves successive acetoxylation and condensation reactions, both with ester elimination. The resulting TiO2 materials were nanocrystalline, even before calcination. Small (about 10 nm) anatase nanocrystals spontaneously aggregated to form mesoporous micron-sized particles with high specific surface area (240 m2 g−1 before calcination). Evaluation of the lithium storage performances shows a high reversible specific capacity, particularly for the non-calcined sample with the highest specific surface area favouring pseudo-capacitive storage: 253 mAh g−1 at 0.1 C and 218 mAh g−1 at 1 C (C=336 mA g−1). This sample also shows good cyclability (92 % retention after 200 cycles at 336 mA g−1) with a high coulombic efficiency (99.8 %). Synthesis in the presence of a solvent (toluene or squalane) offers the possibility to tune the morphology and texture of the TiO2 nanomaterials. 相似文献
104.
Ting Quan Dr. Nicolas Goubard-Bretesché Dr. Eneli Härk Dr. Zdravko Kochovski Dr. Shilin Mei Prof. Dr. Nicola Pinna Prof. Dr. Matthias Ballauff Prof. Dr. Yan Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4757-4766
MoS2, a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon–MoS2–carbon was successfully synthesized through an l -cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m2 g−1, a total pore volume of 0.677 cm3 g−1, and fairly small mesopores (≈5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g−1 (0.12 F cm−2) at a constant current density of 0.1 A g−1; thus suggesting that hollow carbon–MoS2–carbon nanoplates are promising candidate materials for supercapacitors. 相似文献
105.
106.
We study the mechanical response, and tearing features of crêpe paper, a two-dimensional, very anisotropic material, with one direction much less stiff than the other one. Depending on how the soft direction has been pre-stretched or not, the apparent Young modulus of the material can be varied over a broad range, while its fracture energy remains unaltered. The classical tearing concertina problem shows that a macroscopic measurement (the shape of the teared region) provides a direct access to the fracture properties of the material (effective Young's modulus, and fracture energy). The overall discussion is conducted in the frame of Griffith's theory of fracture. 相似文献
107.
Charlotte Menager Nathanaël Guigo Luc Vincent Nicolas Sbirrazzuoli 《Journal of polymer science. Part A, Polymer chemistry》2020,58(12):1717-1727
The curing of epoxidized linseed oil (ELO) with three different bio-based dicarboxylic acids (sebacic acid, suberic acid, and succinic acid) has been investigated. No accelerators or catalysts were used and the resulting thermosets are 100% bio-based. Structural investigations of the three crosslinked ELO resins were made using FTIR spectroscopy and TMA, that is, tensile tests, TGA, and DMA. As evidenced by FTIR measurements ELO and dicarboxylic acids reacts but no major differences can be distinguished between the dicarboxylic acids. Non-isothermal curing has been conducted by rheological and DSC measurements. Advanced isoconversional analysis applied to DSC data in association with the complex viscosity variations gives new insights into the polymerization mechanism. The length of dicarboxylic acid carbon chain modifies the reaction rate. Then, a correlation between reaction rate, activation energy, pre-exponential factors, polymerization mechanism, and change in rate-limiting step was shown. DMA and tensile tests highlight the relationship between the carbon chain length, reactivity, and thermomechanical properties. The use of succinic acid allows reaching a higher Tg and thermal stability. 相似文献
108.
109.
Séan J. Cassady Rishav Choudhary Vivek Boddapati Nicolas H. Pinkowski David F. Davidson Ronald K. Hanson 《国际化学动力学杂志》2020,52(11):725-738
The pyrolysis of propane plays an important role in determining the combustion properties of natural gas mixtures and offers insight into the cracking patterns of larger fuels. This work investigates propane pyrolysis behind reflected shock waves with a multiwavelength laser-absorption speciation technique. Nine laser wavelengths, sensitive to key pyrolysis species, were used to measure absorbance time histories during the decomposition of 2% propane in argon between 1022 and 1467 K, 3.7-4.3 atm. Absorbance models were developed at each diagnostic wavelength to interrogate common initial conditions, and time histories of all major species are reported at 1250, 1290, 1330, 1370, and 1410 K. Nearly complete carbon recovery observed at lower temperatures enabled the inference of hydrogen formation from atomic conservation, while decaying carbon recovery at high temperatures suggests the formation of allene and 1-butene. The results show systematically faster pyrolysis than predicted by kinetic modeling and motivate further study into the kinetics of propane pyrolysis. 相似文献
110.
Bertin Karine Klutchnikoff Nicolas Panloup Fabien Varvenne Maylis 《Statistical Inference for Stochastic Processes》2020,23(2):271-300
Statistical Inference for Stochastic Processes - We build and study a data-driven procedure for the estimation of the stationary density f of an additive fractional SDE. To this end, we also prove... 相似文献