全文获取类型
收费全文 | 9292篇 |
免费 | 706篇 |
国内免费 | 2027篇 |
专业分类
化学 | 10031篇 |
晶体学 | 97篇 |
力学 | 170篇 |
综合类 | 68篇 |
数学 | 580篇 |
物理学 | 1079篇 |
出版年
2024年 | 2篇 |
2023年 | 128篇 |
2022年 | 167篇 |
2021年 | 260篇 |
2020年 | 372篇 |
2019年 | 290篇 |
2018年 | 316篇 |
2017年 | 333篇 |
2016年 | 366篇 |
2015年 | 300篇 |
2014年 | 438篇 |
2013年 | 938篇 |
2012年 | 486篇 |
2011年 | 486篇 |
2010年 | 457篇 |
2009年 | 555篇 |
2008年 | 519篇 |
2007年 | 620篇 |
2006年 | 623篇 |
2005年 | 603篇 |
2004年 | 600篇 |
2003年 | 578篇 |
2002年 | 355篇 |
2001年 | 318篇 |
2000年 | 260篇 |
1999年 | 247篇 |
1998年 | 198篇 |
1997年 | 194篇 |
1996年 | 136篇 |
1995年 | 196篇 |
1994年 | 128篇 |
1993年 | 125篇 |
1992年 | 102篇 |
1991年 | 72篇 |
1990年 | 54篇 |
1989年 | 42篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Eriko Sato Noboru Tamari Hideo Horibe 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2474-2480
Graft copolymers show microphase separated structure as seen in block copolymers and have lower intrinsic viscosity than block copolymers because of a branching structure. Therefore, considering molding processability, especially for polymers containing rigid segments, graft copolymers are useful architectures. In this work, graft copolymers containing rigid poly(diisopropyl fumarate) (PDiPF) branches were synthesized by full free‐radical polymerization process. First, synthesis of PDiPF macromonomers by addition‐fragmentation chain transfer (AFCT) was investigated. 2,2‐Dimethyl‐4‐methylene‐pentanedioic acid dimethyl ester was found to be an efficient AFCT agent for diisopropyl fumarate (DiPF) polymerization because of the suppression of undesired primary radical termination, which significantly took place when common AFCT agent, methyl 2‐(bromomethyl)acrylate, was used. Copolymerization of PDiPF macromonomer with ethyl acrylate accomplished the generation of the graft copolymer having flexible poly(ethyl acrylate) backbone and rigid PDiPF branches. The graft copolymer showed a microphase separated structure, high transparency, and characteristic thermal properties to PDiPF and poly(ethyl acrylate). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2474–2480 相似文献
3.
Shunsuke Shimo Dr. Kohei Takahashi Prof. Nobuharu Iwasawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3790-3794
A new chiral probe molecule for mono-alcohols is developed by using 1,2-dihydro-1-hydroxy-2,3,1-benzodiazaborine (DAB) bearing an acridine moiety 1 . In the presence of mono-alcohols, DAB 1 forms borate 2 by boronic ester formation, followed by coordination of the acridine moiety to the boron atom. Borate 2 has a chiral center on the boron atom and works as a stereodynamic circular dichroism (CD) probe molecule for chiral mono-alcohols based on the π–π interaction between the acridine moiety and the carbon–carbon unsaturated moiety on mono-alcohols. 相似文献
4.
In this work, for the first time, Solanum melongena plant extract was used for the green synthesis of Pd/MnO2 nanocomposite via reduction osf Pd(II) ions to Pd(0) and their immobilization on the surface of manganese dioxide (MnO2) nanoparticles (NPs) as an effective support. The synthesized nanocomposite were characterized by various analytical techniques such as Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity of Pd/MnO2 nanocomposite was used as a heterogeneous catalyst for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides containing various electron‐donating or electron‐withdrawing groups in the presence of K 4 [Fe (CN) 6 ] as non‐toxic cyanide source and sodium azide. The products were obtained in good yields via a simple methodology and easy work‐up. The nanocatalyst can be recycled and reused several times with no remarkable loss of activity. 相似文献
5.
Ariel Carreño-Montero Luis A. Maldonado María Isabel Chávez Simón Hernández-Ortega Guillermo Delgado 《Tetrahedron letters》2019,60(48):151282
The synthesis of ethyl (2′-hydroxy-4′,5′-methylendioxophenyl)acetate, a fragment of the antihyperglycemic natural coumarin subcoriacin, is reported. We found an expeditious route to the title compound in five steps. Final metal catalyzed acid ethanolysis of the vinylic 1,1-methylthio methylsulfoxide derivative afforded the required aryl acetic ester, but in the absence of metal catalyst, an unexpected Pummerer rearrangement produced the 2,3-dimethylthiofuran derivative as the major product. This last result provides an alternative entry to 2,3-dimethlythiobenzofurans. 相似文献
6.
Aiming to obtain the more effective pathogen inhibitive ingredients and explore the influence of introducing different heterocyclic units to carvacrol and thymol esters, twenty ester derivatives with different heterocyclic units were synthesized. And the in vitro antifungal activity of title compounds against five plant pathogenic fungi was evaluated by mycelium growth rate method. The results showed that some carvacrol and thymol esters showed good to excellent antifungal activity, and compound 9d (4-bromo-5-isopropyl-2-methylphenyl picolinate) exhibited a broad antifungal spectrum. Preliminary study indicated that the introduction of furan, thiophene and pyridine unit could enhance the antifungal activity of carvacrol and thymol esters against Botrytis cinerea and a bromine atom on the para position of benzene moiety could enhance their antifungal activity. 相似文献
7.
Propranolol, a β‐adrenergic receptor antagonist, is a chiral compound that is marketed as a racemate, but only the (S)‐(?)‐enantiomer is responsible for the β‐adrenoceptor blocking activity. Different chromatographic methods have been applied for separation and determination of enantiomers of (RS)‐propranolol. In this article a review is presented on different liquid chromatographic methods used for enantioseparation of (RS)‐propranolol, using both HPLC and TLC. In addition, some aspects of enantioseparation under achiral phases of liquid chromatography have been briefly mentioned. 相似文献
8.
Andrey V. Lunchev Dr. Samuel A. Morris Dr. Rakesh Ganguly Prof. Andrew C. Grimsdale 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1819-1823
A route to the synthesis of novel 5,7-diazapentacenes and some preliminary studies on their properties is reported. A single crystal X-ray diffraction study of the dihexyl derivative showed it had formed a dimer during the analysis. The materials possess lower lying frontier orbitals than pentacene and may have potential applications in organic electronic devices. This synthetic method may be applicable to the synthesis of other azaacenes. 相似文献
9.
Gabriel Hancu Daniela Lupu Andreea Milan Monica Budu Enik Barabs‐Hajdu 《Biomedical chromatography : BMC》2021,35(1)
Venlafaxine (VFX) is a serotonin and norepinephrine reuptake inhibitor chiral drug used in therapy as an antidepressant in the form of a racemate consisting of R‐ and S‐VFX. The two enantiomers of VFX exhibit different pharmacological activities: R‐VFX inhibits both norepinephrine and serotonin synaptic reuptake, whereas S‐VFX inhibits only the serotonin one. R‐ and S‐VFX are metabolized in the liver to the respective R‐ and S‐O‐desmethylvenlafaxine (ODVFX), R‐ and S‐N‐desmethylvenlafaxine (NDVFX), and R‐ and S‐N,O‐didesmethylvenlafaxine (NODVFX). The pharmacological profile of ODVFX is close to that of VFX, whereas the other two chiral metabolites (NDVFX and NODVFX) have lower affinity for the receptor sites. The pharmacokinetics of the VFX enantiomers appear stereoselective, including the metabolism process. In the past 20 years, several studies describing the enantioselective analysis of R‐ and S‐VFX in pharmaceutical formulations and its chiral metabolites in biological matrices were published. These methods encompass liquid chromatography coupled with UV detection, mass spectrometry, or tandem mass spectrometry, and capillary electrophoresis. This paper reviews the published methods used for the determination of the individual enantiomers of VFX and its chiral metabolites in different matrices. 相似文献
10.
The chiral phase transition and equation of state are studied within a novel self-consistent mean-field approximation of the two-flavor Nambu-Jona-Lasinio model. In this newly developed model, modifications to the chemical μ and chiral chemical \begin{document}$\mu_5$\end{document} ![]()
![]()
potentials are naturally included by introducing vector and axial-vector channels from Fierz-transformed Lagrangian to the standard Lagrangian. In the proper-time scheme, the chiral phase transition is a crossover in the \begin{document}$T-\mu$\end{document} ![]()
![]()
plane. However, when \begin{document}$\mu_5$\end{document} ![]()
![]()
is incorporated, our study demonstrates that a first order phase transition may emerge. Furthermore, the chiral imbalance will soften the equation of state of quark matter. The mass-radius relationship and tidal deformability of quark stars are calculated. The maximum mass and radius decrease as \begin{document}$\mu_5$\end{document} ![]()
![]()
increases. Our study also indicates that the vector and axial-vector channels exhibit an opposite influence on the equation of state. 相似文献