全文获取类型
收费全文 | 3811篇 |
免费 | 160篇 |
国内免费 | 14篇 |
专业分类
化学 | 3103篇 |
晶体学 | 37篇 |
力学 | 73篇 |
数学 | 268篇 |
物理学 | 504篇 |
出版年
2023年 | 24篇 |
2022年 | 9篇 |
2021年 | 49篇 |
2020年 | 77篇 |
2019年 | 77篇 |
2018年 | 48篇 |
2017年 | 54篇 |
2016年 | 112篇 |
2015年 | 81篇 |
2014年 | 100篇 |
2013年 | 179篇 |
2012年 | 294篇 |
2011年 | 342篇 |
2010年 | 141篇 |
2009年 | 121篇 |
2008年 | 268篇 |
2007年 | 289篇 |
2006年 | 284篇 |
2005年 | 250篇 |
2004年 | 234篇 |
2003年 | 181篇 |
2002年 | 154篇 |
2001年 | 26篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 27篇 |
1997年 | 39篇 |
1996年 | 41篇 |
1995年 | 23篇 |
1994年 | 38篇 |
1993年 | 30篇 |
1992年 | 24篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 10篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 11篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有3985条查询结果,搜索用时 15 毫秒
1.
2.
Mathematische Zeitschrift - Let G be a connected algebraic group. An unrefinable chain of G is a chain of subgroups $$G = G_0> G_1> \cdots > G_t = 1$$ , where each $$G_i$$ is a... 相似文献
3.
Timothy F. L. McKenna 《大分子反应工程》2019,13(2)
This review gives an overview of the evolution of the technology of condensed mode cooling, primarily for the case of ethylene polymerization on supported catalysts in fluidized bed reactors. It is well known that this mode of heat removal is quite effective in allowing polyolefin manufacturers to increase significantly production rates. What is perhaps less well understood are all of the issues that, in addition to the effect of the latent heat of vaporization of injected liquid components, also have an impact on the rate of production and behavior of the reactor. However, the liquid components injected into the reactor can vaporize rapidly under full‐scale conditions, leaving behind several heavy components (with respect to ethylene) that have numerous effects on how the particles behave, on the reaction rate, and on fluidization, fouling, and other parameters related to reactor and process performance. 相似文献
4.
Journal of Chemical Crystallography - A new Group 2 bimetallic nitride fluoride phase of approximate composition SrCaNF has been prepared and characterized via high resolution single crystal X-ray... 相似文献
5.
Ashley M. Nelson Sean T. Hemp Jessica Chau Timothy E. Long 《Journal of polymer science. Part A, Polymer chemistry》2015,53(24):2829-2837
The incorporation of acrylic functionality into caffeine enables the preparation of a vast array of novel thermoplastics and thermosets. A two‐step derivatization provided a novel caffeine‐containing methacrylate monomer capable of free radical polymerization. Copolymers of 2‐ethylhexyl methacrylate and caffeine methacrylate (CMA) allowed for a systematic study of the effect of covalently bound caffeine on polymer properties. 1H NMR and UV‐vis spectroscopy confirmed caffeine incorporation at 5 and 13 mol %, and SEC revealed the formation of high molecular weight (co)polymers (>40,000 g/mol). CMA incorporation resulted in a multistep degradation profile with initial mass loss closely correlating to caffeine content. Differential scanning calorimetry, rheological, and thermomechanical analysis demonstrated that relatively low levels of CMA increased the glass transition temperature, resulting in higher moduli and elucidating the benefits of incorporating caffeine into polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2829–2837 相似文献
6.
Transport in Porous Media - The RANS modelling of turbulence across fluid-porous interface regions within ribbed channels has been investigated by applying double (both volume and Reynolds)... 相似文献
7.
Hao Wang Hari Krishna Bisoyi Bing‐Xiang Li Michael E. McConney Timothy J. Bunning Quan Li 《Angewandte Chemie (International ed. in English)》2020,59(7):2684-2687
Visible‐light‐driven molecular switches endowing reversible modulation of the functionalities of self‐organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room‐temperature achiral liquid crystal host 5CB, which also acts as a halogen‐bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible‐light‐driven reversible unwinding, that is, a cholesteric–nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible‐light‐driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented. 相似文献
8.
9.
Timothy R. Totsch Victoria L. Stanford Oleksander Klep Mary K. Burdette Benjamin Grant Stephen H. Foulger Gary M. Gray 《Journal of polymer science. Part A, Polymer chemistry》2020,58(13):1825-1842
Linear polyphosphonates with the generic formula –[P(Ph)(X)OR′O]n– (X = S or Se) have been synthesized by polycondensations of P(Ph)(NEt2)2 and a diol (HOR′OH = 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, tetraethylene glycol, or 1,12-dodecanediol) followed by reaction with a chalcogen. Random copolymers have been synthesized by polycondensations of P(Ph)(NEt2)2 and mixture of two of the diols in a 2:1:1 mol ratio followed by reaction with a chalcogen. Block copolymers with the generic formula –[P(Ph)(X)OR′O](x + 2) –[P(Ph)(X)OR′O](x + 3)– (X = S or Se) have been synthesized by the polycondensations of Et2N[P(Ph)(X)OR′O](x + 2)P(Ph)NEt2 oligomers with HOR′O[P(Ph)(X)OR′O](x + 3)H oligomers followed by reaction with a chalcogen. The Et2N[P(Ph)(X)OR′O](x + 2)P(Ph)NEt2 oligomers are prepared by the reaction of an excess of P(Ph)(NEt2)2 with a diol while the HOR′O[P(Ph)(X)OR′O](x + 3)H oligomers are prepared by the reaction of P(Ph)(NEt2)2 with an excess of the diol. In each case the excess, x is the same and determines the average block sizes. All of the polymers were characterized using 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, TGA, DSC, and SEC. 31P{1H} NMR spectroscopy demonstrates that the random and block copolymers have the expected arrangements of monomers and, in the case of block copolymers, verifies the block sizes. All polymers are thermally stable up to ~300°C, and the arrangements of monomers in the copolymers (block vs. random) affect their degradation temperatures and Tg profiles. The polymers have weight average MWs of up to 3.8 × 104 Da. 相似文献
10.
Dr. David Scheerer Prof. Dr. Heng Chi Dr. Dan McElheny Prof. Dr. Timothy A. Keiderling Prof. Dr. Karin Hauser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3524-3534
Site-specific isotopic labeling of molecules is a widely used approach in IR spectroscopy to resolve local contributions to vibrational modes. The induced frequency shift of the corresponding IR band depends on the substituted masses, as well as on hydrogen bonding and vibrational coupling. The impact of these different factors was analyzed with a designed three-stranded β-sheet peptide and by use of selected 13C isotope substitutions at multiple positions in the peptide backbone. Single-strand labels give rise to isotopically shifted bands at different frequencies, depending on the specific sites; this demonstrates sensitivity to the local environment. Cross-strand double- and triple-labeled peptides exhibited two resolved bands that could be uniquely assigned to specific residues, the equilibrium IR spectra of which indicated only weak local-mode coupling. Temperature-jump IR laser spectroscopy was applied to monitor structural dynamics and revealed an impressive enhancement of the isotope sensitivity to both local positions and coupling between them, relative to that of equilibrium FTIR spectroscopy. Site-specific relaxation rates were altered upon the introduction of additional cross-strand isotopes. Likewise, the rates for the global β-sheet dynamics were affected in a manner dependent on the distinct relaxation behavior of the labeled oscillator. This study reveals that isotope labels provide not only local structural probes, but rather sense the dynamic complexity of the molecular environment. 相似文献