全文获取类型
收费全文 | 4438篇 |
免费 | 102篇 |
国内免费 | 11篇 |
专业分类
化学 | 3201篇 |
晶体学 | 7篇 |
力学 | 61篇 |
数学 | 758篇 |
物理学 | 524篇 |
出版年
2020年 | 36篇 |
2019年 | 33篇 |
2016年 | 57篇 |
2015年 | 76篇 |
2014年 | 62篇 |
2013年 | 165篇 |
2012年 | 138篇 |
2011年 | 185篇 |
2010年 | 106篇 |
2009年 | 108篇 |
2008年 | 136篇 |
2007年 | 147篇 |
2006年 | 168篇 |
2005年 | 162篇 |
2004年 | 183篇 |
2003年 | 128篇 |
2002年 | 147篇 |
2001年 | 52篇 |
2000年 | 62篇 |
1999年 | 36篇 |
1998年 | 32篇 |
1997年 | 68篇 |
1996年 | 69篇 |
1995年 | 68篇 |
1994年 | 74篇 |
1993年 | 65篇 |
1992年 | 74篇 |
1991年 | 52篇 |
1990年 | 46篇 |
1989年 | 49篇 |
1988年 | 56篇 |
1987年 | 48篇 |
1986年 | 64篇 |
1985年 | 75篇 |
1984年 | 93篇 |
1983年 | 68篇 |
1982年 | 65篇 |
1981年 | 85篇 |
1980年 | 90篇 |
1979年 | 74篇 |
1978年 | 95篇 |
1977年 | 62篇 |
1976年 | 77篇 |
1975年 | 60篇 |
1974年 | 58篇 |
1973年 | 66篇 |
1972年 | 48篇 |
1971年 | 40篇 |
1970年 | 38篇 |
1968年 | 33篇 |
排序方式: 共有4551条查询结果,搜索用时 15 毫秒
1.
2.
Chase A. Salazar Joseph J. Gair Kaylin N. Flesch Ilia A. Guzei Jared C. Lewis Shannon S. Stahl 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(27):10965-10969
Mono-N-protected amino acids (MPAAs) are increasingly common ligands in Pd-catalyzed C−H functionalization reactions. Previous studies have shown how these ligands accelerate catalytic turnover by facilitating the C−H activation step. Here, it is shown that MPAA ligands exhibit a second property commonly associated with ligand-accelerated catalysis: the ability to support catalytic turnover at substoichiometric ligand-to-metal ratios. This catalytic role of the MPAA ligand is characterized in stoichiometric C−H activation and catalytic C−H functionalization reactions. Palladacycle formation with substrates bearing carboxylate and pyridine directing groups exhibit a 50–100-fold increase in rate when only 0.05 equivalents of MPAA are present relative to PdII. These and other mechanistic data indicate that facile exchange between MPAAs and anionic ligands coordinated to PdII enables a single MPAA to support C−H activation at multiple PdII centers. 相似文献
3.
Ein elektronenreiches cyclisches (Alkyl)(amino)carben auf Au(111)-, Ag(111)- und Cu(111)-Oberflächen
Anne Bakker Dr. Matthias Freitag Elena Kolodzeiski Peter Bellotti Dr. Alexander Timmer Dr. Jindong Ren Bertram Schulze Lammers Daniel Moock Prof. Dr. Herbert W. Roesky Dr. Harry Mönig Dr. Saeed Amirjalayer Prof. Dr. Harald Fuchs Prof. Dr. Frank Glorius 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13745-13749
4.
5.
6.
In a previous study (Stahl and Bredow, Chem. Phys. Lett. 2018, 695, 28–33), we have studied structural, energetic, and electronic properties of two vanadium dioxide VO2 polymorphs with modified global and range-separated hybrid functionals. Since hybrid methods are computationally demanding, we evaluate the computationally more efficient DFT + U method in the present study. We assessed the widely used Dudarev PBE + U approach with a literature value of the effective Hubbard parameter Ueff = 3.4 eV. We compared the PBE + U results for the two VO2 polymorphs with our previous results, a self-consistent hybrid functional sc-PBE0, and the meta-GGA functional SCAN. It was found that the PBE + U method yields a strongly distorted monoclinic phase and does not reproduce the metal-to-insulator transition of VO2 correctly, even with modified values of Ueff. On the other hand, sc-PBE0 and SCAN describe the relative stability and the electronic structure of both polymorphs correctly and also provide reasonable lattice parameters. The functional SCAN yields the optimal balance between computational efficiency and accuracy. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc. 相似文献
7.
Mohanad A. Hussein Dr. Uyen P. N. Tran Dr. Vien T. Huynh Dr. Junming Ho Dr. Mohan Bhadbhade Prof. Dr. Herbert Mayr Dr. Thanh V. Nguyen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(4):1471-1475
Tropylium bromide undergoes noncatalyzed, regioselective additions to a large variety of Michael acceptors. In this way, acrylic esters are converted into β-bromo-α-cycloheptatrienylpropionic esters. The reactions are interpreted as nucleophilic attack of bromide ions at the electron-deficient olefins and the approach of the tropylium ion to the incipient carbanion. Quantum chemical calculations were performed to elucidate the analogy to the amine- or phosphine-catalyzed Rauhut–Currier reactions. Subsequent synthetic transformations of the bromo-cycloheptatrienylated adducts are reported. 相似文献
8.
Simon Knig Philipp Kreis Leonie Reinders Ronald Beyer Andreas Wego Christian Herbert Mark Steinmann Erik Frank Michael R. Buchmeiser 《先进技术聚合物》2020,31(8):1827-1835
The primary use of poly(acrylonitrile) (PAN) fibers, commonly referred to as acrylic fibers, is in textile applications like clothing, furniture, carpets, and awnings. All commercially available PAN fibers are processed by solution spinning; however, alternative, more cost‐effective processes like melt spinning are still highly desired. Here, the melt spinning of PAN‐co‐poly(methyl acrylate) (PMA) plasticized with propylene carbonate (PC) at 175°C is reported. The use of methyl acrylate (MA) as comonomer and PC as an external plasticizer renders the approach a combination of internal and external plasticization. Various mixtures of PAN and PC used in this work were examined by rheology, subjected to melt spinning, followed by discontinuous and continuous washing, respectively. The best fibers were derived from a PAN‐co‐PMA copolymer containing 8.1 mol‐% of MA having a number‐average molecular weight M n of 34 000 g/mol, spun in the presence of 22.5 wt.‐% of PC. The resulting fibers were analyzed by scanning electron microscopy and wide‐angle X‐ray scattering (WAXS), and were subjected to mechanical testing. 相似文献
9.
Thies Dirksmeyer Paul Stahl Dr. Cecilia Vallet Prof. Dr. Shirley Knauer Prof. Dr. Michael Giese Prof. Dr. Carsten Schmuck Dr. Christoph Hirschhäuser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202104618
A transfection vector that can home in on tumors is reported. Whereas previous vectors that allow moderately cell selective gene transfection used larger systems, this small-molecule approach paved the way for precise structure-activity relationship optimization. For this, biotin, which mediates cell selectivity, was combined with the potent DNA-binding motif tetralysine-guanidinocarbonypyrrol via a hydrophilic linker, thus enabling SAR-based optimization. The new vector mediated biotin receptor (BR)-selective transfection of cell lines with different BR expression levels. Computer-based analyses of microscopy images revealed a preference of one order of magnitude for the BR-positive cell lines over the BR-negative controls. 相似文献
10.