全文获取类型
收费全文 | 2560篇 |
免费 | 85篇 |
国内免费 | 11篇 |
专业分类
化学 | 1621篇 |
晶体学 | 1篇 |
力学 | 78篇 |
数学 | 505篇 |
物理学 | 451篇 |
出版年
2023年 | 17篇 |
2022年 | 32篇 |
2021年 | 38篇 |
2020年 | 49篇 |
2019年 | 46篇 |
2018年 | 33篇 |
2017年 | 40篇 |
2016年 | 72篇 |
2015年 | 51篇 |
2014年 | 81篇 |
2013年 | 122篇 |
2012年 | 154篇 |
2011年 | 208篇 |
2010年 | 130篇 |
2009年 | 104篇 |
2008年 | 159篇 |
2007年 | 182篇 |
2006年 | 144篇 |
2005年 | 114篇 |
2004年 | 107篇 |
2003年 | 92篇 |
2002年 | 81篇 |
2001年 | 31篇 |
2000年 | 33篇 |
1999年 | 30篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 27篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1974年 | 10篇 |
排序方式: 共有2656条查询结果,搜索用时 31 毫秒
91.
92.
Poul Erik Hansen Bahjat A. Saeed Rita S. Rutu Teobald Kupka 《Magnetic resonance in chemistry : MRC》2020,58(8):750-762
1J(15N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp2-hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified basis sets predict significantly better the 1J(15N,H) value in ammonia and in the methylamine Schiff base of a truncated molecule of gossypol than the standard basis sets. This procure is then used on a broad set of intramolecularly hydrogen-bonded molecules, and a good correlation between calculated and experimental one-bond NH coupling constants is obtained. The 1J(15N,H) couplings are slightly overestimated. The calculated data show for hydrogen-bonded NH interatomic distances that the calculated values depend on the NH bond lengths. The shorter the bond lengths, the larger the 1J(15N,H). A useful correlation between 1J(15N,H) and NH bond length is derived that enables realistic predictions of one-bond NH coupling constants. The calculations reproduce experimentally observed trends for the studied molecules. 相似文献
93.
Giuseppe Spedalotto Dr. Robert Gericke Marta Lovisari Dr. Erik R. Farquhar Dr. Brendan Twamley Dr. Aidan R. McDonald 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(51):11983-11990
Hydroxide-bridged high-valent oxidants have been implicated as the active oxidants in methane monooxygenases and other oxidases that employ bimetallic clusters in their active site. To understand the properties of such species, bis-μ-hydroxo-NiII2 complex ( 1 ) supported by a new dicarboxamidate ligand (N,N′-bis(2,6-dimethyl-phenyl)-2,2-dimethylmalonamide) was prepared. Complex 1 contained a diamond core made up of two NiII ions and two bridging hydroxide ligands. Titration of the 1 e− oxidant (NH4)2[CeIV(NO3)6] with 1 at −45 °C showed the formation of the high-valent species 2 and 3 , containing NiIINiIII and NiIII2 diamond cores, respectively, maintaining the bis-μ-hydroxide core. Both complexes were characterised using electron paramagnetic resonance, X-ray absorption, and electronic absorption spectroscopies. Density functional theory computations supported the spectroscopic assignments. Oxidation reactivity studies showed that bis-μ-hydroxide-NiIII2 3 was capable of oxidizing substrates at −45 °C at rates greater than that of the most reactive bis-μ-oxo-NiIII complexes reported to date. 相似文献
94.
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
95.
In low- and medium-energy storage rings for synchrotron radiation (SR) production, it is necessary to use high-performance insertion devices (IDs) in order to meet the increasing demand for high X-ray flux to perform life science and material science, since the maximum beam energy and beam current cannot be changed in storage rings without major rebuilds of the accelerator systems. 相似文献
96.
97.
Identification of Compounds that Selectively Stabilize Specific G‐Quadruplex Structures by Using a Thioflavin T‐Displacement Assay as a Tool
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)
Dr. Jan Jamroskovic Dr. Madeleine Livendahl Dr. Jonas Eriksson Dr. Erik Chorell Dr. Nasim Sabouri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18932-18943
Small molecules are used in the G‐quadruplex (G4) research field in vivo and in vitro, and there are increasing demands for ligands that selectively stabilize different G4 structures. Thioflavin T (ThT) emits an enhanced fluorescence signal when binding to G4 structures. Herein, we show that ThT can be competitively displaced by the binding of small molecules to G4 structures and develop a ThT‐displacement high‐throughput screening assay to find novel and selective G4‐binding compounds. We screened approximately 28 000 compounds by using three different G4 structures and identified eight novel G4 binders. Analysis of the structural conformation and stability of the G4 structures in presence of these compounds demonstrated that the four compounds enhance the thermal stabilization of the structures without affecting their structural conformation. In addition, all four compounds also increased the G4‐structure block of DNA synthesis by Taq DNA polymerase. Also, two of these compounds showed selectivity between certain Schizosaccharomyces pombe G4 structures, thus suggesting that these compounds or their analogues can be used as selective tools for G4 DNA studies. 相似文献
98.
Dr. Erik Frank Dipl.‐Chem. Lisa M. Steudle Dr. Denis Ingildeev Dipl.‐Chem. Johanna M. Spörl Prof. Michael R. Buchmeiser 《Angewandte Chemie (International ed. in English)》2014,53(21):5262-5298
This Review gives an overview of precursor systems, their processing, and the final precursor‐dependent structure of carbon fibers (CFs) including new developments in precursor systems for low‐cost CFs. The following CF precursor systems are discussed: poly(acrylonitrile)‐based copolymers, pitch, cellulose, lignin, poly(ethylene), and new synthetic polymeric precursors for high‐end CFs. In addition, structure–property relationships and the different models for describing both the structure and morphology of CFs will be presented. 相似文献
99.
This paper presents a 3D topology optimization approach for designing shell structures with a porous or void interior. It is shown that the resulting structures are significantly more robust towards load perturbations than completely solid structures optimized under the same condi-tions. The study indicates that the potential benefit of using porous structures is higher for lower total volume fractions. Compared to earlier work dealing with 2D topology opti-mization, we found several new effects in 3D problems. Most notably, the opportunity for designing closed shells signifi-cantly improves the performance of porous structures due to the sandwich effect. Furthermore, the paper introduces improved filter boundary conditions to ensure a completely uniform coating thickness at the design domain boundary. 相似文献
100.