全文获取类型
收费全文 | 85573篇 |
免费 | 1632篇 |
国内免费 | 1635篇 |
专业分类
化学 | 29884篇 |
晶体学 | 878篇 |
力学 | 7344篇 |
综合类 | 94篇 |
数学 | 32961篇 |
物理学 | 17679篇 |
出版年
2023年 | 161篇 |
2022年 | 183篇 |
2021年 | 251篇 |
2020年 | 313篇 |
2019年 | 300篇 |
2018年 | 10589篇 |
2017年 | 10429篇 |
2016年 | 6421篇 |
2015年 | 1167篇 |
2014年 | 703篇 |
2013年 | 873篇 |
2012年 | 4449篇 |
2011年 | 11091篇 |
2010年 | 6149篇 |
2009年 | 6479篇 |
2008年 | 7068篇 |
2007年 | 9153篇 |
2006年 | 633篇 |
2005年 | 1698篇 |
2004年 | 1863篇 |
2003年 | 2282篇 |
2002年 | 1383篇 |
2001年 | 590篇 |
2000年 | 528篇 |
1999年 | 398篇 |
1998年 | 374篇 |
1997年 | 313篇 |
1996年 | 376篇 |
1995年 | 253篇 |
1994年 | 203篇 |
1993年 | 187篇 |
1992年 | 122篇 |
1991年 | 132篇 |
1990年 | 92篇 |
1989年 | 84篇 |
1988年 | 92篇 |
1987年 | 75篇 |
1986年 | 85篇 |
1985年 | 66篇 |
1984年 | 51篇 |
1983年 | 50篇 |
1982年 | 50篇 |
1981年 | 47篇 |
1980年 | 50篇 |
1979年 | 45篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
Coordination reactions of copper(II) ions and their effect on non-covalent interactions in uridine (Urd) or uridine 5′-monophosphate (UMP) systems with nucleosides (Ado, Cyd, Thd) and nucleotides (AMP and CMP) in aqueous solutions have been studied. At high pH the effective coordination centers are deprotonated N(3) atoms from Urd and Thd, whereas at low pH, the N(3) atoms of pyrimidine nucleosides are blocked for coordination and the metallation sites are endocyclic
nitrogen atoms from Ado, Cyd, AMP and CMP. Moreover, at low pH, the main reaction center in nucleotide solutions is the phosphate group. The NMR study has proven the
occurrence of non-covalent ion-dipole interactions and stacking interactions in the systems considered. Introduction of a
copper ion in the majority of systems causes the disappearance of weak interactions between ligands. The structures of the
complexes in solution have been inferred from the equilibrium study: an analysis of the pH range of their occurrence with
respect to the pH range of deprotonation of particular groups in the compounds studied, using Vis, EPR and 13C as well as 31P NMR spectral analysis. 相似文献
982.
We present a method for computing classical Newtonian trajectories that minimize the path length or transit time from reactant
to product. Our approach is based on a generalization of the fast-marching method, which allows us to construct the solution
of the Hamilton-Jacobi equation for the action that optimizes the desired quantity. The resulting “reactive paths” can be
interpreted as reaction coordinates but, unlike more conventional choices, they contain dynamical information about the chemical
system of interest. 相似文献
983.
Jeong Hwan Kim Ji Hoon Ko Byeong-Soo Bae 《Journal of Sol-Gel Science and Technology》2007,41(3):249-255
Multi-scale hybrid nanocomposites containing both ∼15 nm silica colloids and ∼2 nm oligosiloxanes in a methacryl polymer matrix
were newly designed and fabricated. Colloidal silica sols were dispersed in methacryl oligosiloxanes nano-hybrid resins synthesized
by sol-gel reaction of methacryloxypropylmethoxysilane and diphenylsilanediol. On the basis of TEM and SANS analyses, it was
confirmed that the silica colloids were compatibly dispersed and different sizes of colloidal silica and oligosiloxanes co-exist
in the solutions. Multi-scale hybrid nanocomposites fabricated by UV and thermal curing with incorporation of silica colloids
in the nano-hybrid materials show enhanced mechanical and thermal characteristics. 相似文献
984.
The geometry of the 4′-cyano-(4′-CNPTB) and the 4′-methoxy-(4′-MePTB) phenylthiolbenzoates were obtained by ab initio calculations
employing 6–31G basis set at Hartee-Fock level of theory. The results predict an extended form of the molecules and torsional
angle between the phenyl rings at 90.85(6)0 and 90.87(3)0, respectively. On the basis of vibrational analysis the frequency assignment was carried out. The calculated frequencies
were compared with the experimental IR spectral data in carbon tetrachloride, carbon disulfide solutions and in solid state. 相似文献
985.
Peng Xu Wei Zhong Haitao Wang Rong Tong Qiangguo Du 《Colloid and polymer science》2004,282(12):1409-1414
Copolymerization of methyl methacrylate, methyl acrylate, butyl methacrylate, and butyl acrylate in turn was performed in the modified microemulsion polymerization process, i.e., continuous addition of monomer to a preemulsified system. It was found that the particle size of the copolymer microlatex did not change distinctly with the monomer composition. The estimation of emulsifier coverage on the microlatex particles indicated that the process switched from a traditional microemulsion to a normal seeded emulsion polymerization very soon after monomer dropping began. Therefore, a longer dropping time is needed to produce a microlatex with narrow dispersed particle size. Besides, in the modified microemulsion polymerization less emulsifier is needed to produce a stable microlatex. This behavior is related to the mechanism of normal seeded emulsion polymerization during monomer dropping. 相似文献
986.
987.
Yong Deng Da Cheng Yang Yi Shen Yu Guo Zhong 《中国化学快报》2007,18(1):7-9
Based on the structure-activity relationships and antiangiogenic mechanism of RGD-containing peptides,a series of 5-amino- 1,3-dihydro-1,3-dioxo-2H-isoindole derivatives were synthesized.The structures were characterized by ~1H NMR,MS and elementary analysis.There ability to inhibit angiogenesis were evaluated by chick embryo chorioallantoic membrane assay at 10~(-5) mol/L.Compounds 7a and 7b displayed obvious antiangiogenic activity. 相似文献
988.
František Kvasnička Rudolf Ševčík Michal Voldřich Jana Krátká 《Central European Journal of Chemistry》2004,2(3):417-424
A simple and rapid capillary zone electrophoresis (CZE) method for the determination of aristolochic acid (AA) in dietary
supplements and selected herbs is described. A clear separation of AA from other sample constituents was achieved within 5
minutes without any sample clean up. A mixture of 20 mM-morpholinethanesulphonic acid+10 mM-BisTrisPropane+0.2% hydroxyethylcelullose
in 10% methanol serves as a background electrolyte. The linearity, accuracy, intra-assay and detection limit of the developed
method are 200–6000 ng/mL, 95–103%, 3.5%, and 50 ng/ml, respectively. Ease of use, sufficient sensitivity and low running
cost are the most important attributes of the CZE method. The proposed CZE method was compared with HPLC. 相似文献
989.
Robert Pietrzak Mieczysław Kozłowski Helena Wachowska Jan Yperman 《Central European Journal of Chemistry》2004,2(2):278-289
Soluble products obtained from the oxidation of four types of coal, each characterised by different degree of coalification
and different degree of sulphur content, are studied. The coals are oxidised with peracetic acid (PAA) and nitric acid. Analyses
are performed by Atmospheric Pressure-Temperature Programmed Reduction (AP-TPR) and Fourier Transform Infrared Spectroscopy
(FTIR). The soluble products contain much more sulphur than the insoluble products of oxidation. The products obtained from
the reaction with HNO3 contain higher amounts of inorganic sulphur compounds, while those obtained from the reaction with PAA are characterised
by an increased content of organic sulphur species. 相似文献
990.
RongZhongYUAN ZuoLongYU MeiZhenQU 《中国化学快报》2003,14(7):755-758
A novel gel-like process has been developed for synthesizing LiaNi0.8Co0.2O2 powders,using citric acid as a chelating agent. This process improves the homogeneity of constituent cation and enhances their reactivity in the obtained precursor. The results of electrochemical test demonstrated that these materials exhibited excellent electrochemical properties. Its initial capacity reached 181.6 mAh/g and reversible efficiency at the first cycle is about 88.6%. 相似文献