全文获取类型
收费全文 | 26028篇 |
免费 | 854篇 |
国内免费 | 144篇 |
专业分类
化学 | 18704篇 |
晶体学 | 215篇 |
力学 | 493篇 |
数学 | 3293篇 |
物理学 | 4321篇 |
出版年
2023年 | 183篇 |
2022年 | 267篇 |
2021年 | 363篇 |
2020年 | 485篇 |
2019年 | 471篇 |
2018年 | 318篇 |
2017年 | 275篇 |
2016年 | 733篇 |
2015年 | 624篇 |
2014年 | 748篇 |
2013年 | 1233篇 |
2012年 | 1619篇 |
2011年 | 1791篇 |
2010年 | 1033篇 |
2009年 | 867篇 |
2008年 | 1491篇 |
2007年 | 1413篇 |
2006年 | 1394篇 |
2005年 | 1303篇 |
2004年 | 1133篇 |
2003年 | 859篇 |
2002年 | 897篇 |
2001年 | 436篇 |
2000年 | 369篇 |
1999年 | 371篇 |
1998年 | 362篇 |
1997年 | 339篇 |
1996年 | 349篇 |
1995年 | 292篇 |
1994年 | 319篇 |
1993年 | 300篇 |
1992年 | 263篇 |
1991年 | 191篇 |
1990年 | 218篇 |
1989年 | 185篇 |
1988年 | 195篇 |
1987年 | 172篇 |
1986年 | 161篇 |
1985年 | 273篇 |
1984年 | 257篇 |
1983年 | 183篇 |
1982年 | 200篇 |
1981年 | 185篇 |
1980年 | 182篇 |
1979年 | 165篇 |
1978年 | 195篇 |
1977年 | 180篇 |
1976年 | 141篇 |
1975年 | 133篇 |
1974年 | 157篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Daniel S. Covita Dimitrios F. Anagnostopoulos Hermann Fuhrmann Hubert Gorke Detlev Gotta Alexander Gruber Albert Hirtl Tomoichi Ishiwatari Paul Indelicato Thomas S. Jensen Eric-Olivier Le Bigot Valeri E. Markushin Michael Nekipelov Vladimir N. Pomerantsev Vladimir P. Popov Joaquim M. F. dos Santos Philipp Schmid Leopold M. Simons Marian Theisen Martino Trassinelli Joao F. C. A. Veloso Johann Zmeskal 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2018,72(4):72
993.
994.
995.
Thomas Prenveille Cyrielle Garreau Mathias Matner Dirk Dijkstra Wilhelm Oppermann Diethelm Johannsmann 《Journal of polymer science. Part A, Polymer chemistry》2019,57(5):621-629
The reactivity of urethanes based on 1,6‐hexamethylene diisocyanate (HDI) and 4,4′‐methylene diphenyl diisocyanate (MDI) was investigated at temperatures between 190 °C and 235 °C. Diurethane model compounds end‐capped with either 1‐dodecanol (D‐core‐D) or 1‐hexadecanol (H‐core‐H) were mixed and annealed at high temperature. The core was either MDI or HDI. The transurethanization reaction was followed based on the formation of the compounds (H‐core‐D). The amount of H‐core‐D and of side products, which had formed after variable annealing times, were identified with 1H NMR, FTIR, SEC, and MALDI‐TOF. Transurethanization was considerably faster for MDI‐based urethanes than for HDI‐based urethanes. Only traces of side products were formed during annealing of MDI‐based urethanes, whereas a significant amount of allophanates was formed from HDI‐based urethanes under the same conditions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 621–629 相似文献
996.
Dr. Eddy W. T. Yemeli Dr. Graeme R. Blake Dr. Alexios P. Douvalis Prof. Thomas Bakas Gert O. R. Alberda van Ekenstein Dr. Petra J. van Koningsbruggen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16766-16776
The iron(III) spin-crossover compounds [Fe(Hthsa)(thsa)] ⋅ H2O ( 1 ), [Fe(Hth5Clsa)(th5Clsa)2] ⋅ H2O ( 2 ), and [Fe(Hth5Brsa)(th5Brsa)2] ⋅ H2O ( 3 ) (H2thsa=salicylaldehyde thiosemicarbazone, H2th5Clsa=5-chlorosalicylaldehyde thiosemicarbazone, and H2th5Brsa=5-bromosalicylaldehyde thiosemicarbazone) have been synthesized and their spin-transition properties investigated by magnetic susceptibility, Mössbauer spectroscopy, and differential scanning calorimetry measurements. The three compounds exhibit an abrupt spin transition with a thermal hysteresis effect. The more polarizable the substituent on the salicylaldehyde moiety, the more complete is the transition at room temperature with an increased degree of cooperativity. The molecular structures of 1 and 2 in the high-spin state are revealed. The occurrence of the light-induced excited-spin-state trapping phenomenon appears to be dependent on the substituent incorporated into the 5-position of the salicylaldehyde subunit. Whereas the compounds with an electron-withdrawing group (-Br or -Cl) exhibit light-induced trapped excited high-spin states with great longevity of metastability, the halogen-free compound does not, even though strong intermolecular interactions (such as hydrogen-bonding networks and π stacking) operate in the system. For compound 2 , the surface level of photoconversion is less than 35 %. In contrast, compound 3 displays full photoexcitation. 相似文献
997.
Dr. Carlos Sánchez-Sánchez Dr. Thomas Dienel Dr. Adrien Nicolaï Dr. Neerav Kharche Dr. Liangbo Liang Colin Daniels Prof. Vincent Meunier Dr. Junzhi Liu Prof. Xinliang Feng Prof. Klaus Müllen Dr. Juan Ramón Sánchez-Valencia Dr. Oliver Gröning Dr. Pascal Ruffieux Prof. Roman Fasel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12074-12082
A bottom up method for the synthesis of unique tetracene-based nanoribbons, which incorporate cyclobutadiene moieties as linkers between the acene segments, is reported. These structures were achieved through the formal [2+2] cycloaddition reaction of ortho-functionalized tetracene precursor monomers. The formation mechanism and the electronic and magnetic properties of these nanoribbons were comprehensively studied by means of a multitechnique approach. Ultra-high vacuum scanning tunneling microscopy showed the occurrence of metal-coordinated nanostructures at room temperature and their evolution into nanoribbons through formal [2+2] cycloaddition at 475 K. Frequency-shift non-contact atomic force microscopy images clearly proved the presence of bridging cyclobutadiene moieties upon covalent coupling of activated tetracene molecules. Insight into the electronic and vibrational properties of the so-formed ribbons was obtained by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Magnetic properties were addressed from a computational point of view, allowing us to propose promising candidates to magnetic acene-based ribbons incorporating four-membered rings. The reported findings will increase the understanding and availability of new graphene-based nanoribbons with high potential in future spintronics. 相似文献
998.
Dr. Ritesh Haldar Kamal Batra Stefan Michael Marschner Dr. Agnieszka B. Kuc Dr. Stefan Zahn Prof. Dr. Roland A. Fischer Prof. Dr. Stefan Bräse Prof. Dr. Thomas Heine Prof. Dr. Christof Wöll 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(33):7847-7851
In organic photovoltaics, porphyrins (PPs) are among the most promising compounds owing to their large absorption cross-section, wide spectral range, and stability. Nevertheless, a precise adjustment of absorption band positions to reach a full coverage of the so-called green gap has not been achieved yet. We demonstrate that a tuning of the PP Q- and Soret bands can be carried out by using a computational approach for which substitution patterns are optimized in silico. The most promising candidate structures were then synthesized. The experimental UV/Vis data for the solvated compounds were in excellent agreement with the theoretical predictions. By attaching further functionalities, which allow the use of PP chromophores as linkers for the assembly of metal-organic frameworks (MOFs), we were able to exploit packing effects resulting in pronounced redshifts, which allowed further optimization of the photophysical properties of PP assemblies. Finally, we use a layer-by-layer method to assemble the PP linkers into surface-mounted MOFs (SURMOFs), thus obtaining high optical quality, homogeneous and crystalline multilayer films. Experimental results are in full accord with the calculations, demonstrating the huge potential of computational screening methods in tailoring MOF and SURMOF photophysical properties. 相似文献
999.
Dr. Antoine Nitelet Dr. Damien Thevenet Dr. Bruno Schiavi Dr. Christophe Hardouin Dr. Jean Fournier Dr. Rodolphe Tamion Prof. Dr. Xavier Pannecoucke Prof. Dr. Philippe Jubault Prof. Dr. Thomas Poisson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3262-3266
The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (CuI/CuI*/Cu0) was suggested. 相似文献
1000.
Thomas Marmin Prof. Yves L. Dory 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6707-6711
Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C3-symmetric rings incorporating conjugated alkenes and dienes. All three C3-symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals. 相似文献