全文获取类型
收费全文 | 2777篇 |
免费 | 184篇 |
国内免费 | 399篇 |
专业分类
化学 | 2779篇 |
晶体学 | 35篇 |
力学 | 7篇 |
综合类 | 21篇 |
数学 | 1篇 |
物理学 | 517篇 |
出版年
2024年 | 6篇 |
2023年 | 39篇 |
2022年 | 45篇 |
2021年 | 62篇 |
2020年 | 126篇 |
2019年 | 74篇 |
2018年 | 70篇 |
2017年 | 72篇 |
2016年 | 136篇 |
2015年 | 114篇 |
2014年 | 112篇 |
2013年 | 177篇 |
2012年 | 150篇 |
2011年 | 182篇 |
2010年 | 159篇 |
2009年 | 176篇 |
2008年 | 186篇 |
2007年 | 171篇 |
2006年 | 162篇 |
2005年 | 147篇 |
2004年 | 134篇 |
2003年 | 94篇 |
2002年 | 88篇 |
2001年 | 85篇 |
2000年 | 51篇 |
1999年 | 86篇 |
1998年 | 60篇 |
1997年 | 68篇 |
1996年 | 59篇 |
1995年 | 38篇 |
1994年 | 35篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 29篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有3360条查询结果,搜索用时 484 毫秒
1.
《Mendeleev Communications》2022,32(6):777-779
The reactions of aryllithium reagents o-LiC6H4CH2NR2 with (MeO)2CO afford two new tris(aryl)carbinols bearing pendant-NR2 donor groups in the side chain [o-R NCH C H ] COH [R = Me, R + R = (CH) ]. These alcohols feature helical chirality due to differently inclined aromatic fragments and are presented in a crystalline cell as two M and P enantiomers. Carbinol (R = Me) readily reacts with (Me3SiCH2)3Sc(THF)2 to give a scandium bis(alkyl) complex [(o-C6H4CH2NMe2)3CO]Sc(CH2SiMe3)2 featuring rigid binding of the alkoxy anion through a κ1-O, κ2-N chelating coordination mode 相似文献
2.
Edward G. Sheetz Zhao Zhang Alyssa Marogil Minwei Che Dr. Maren Pink Dr. Veronica Carta Prof. Dr. Krishnan Raghavachari Prof. Dr. Amar H. Flood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201584
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3−). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3−, by cyanostar macrocycles that are size-complementary to the inorganic BF4− progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3− anions. 相似文献
3.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes 下载免费PDF全文
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
4.
S. Meenakshi B.K. Godwal I. Orgzall S. Tkachev 《Journal of Physics and Chemistry of Solids》2006,67(8):1660-1667
We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes. 相似文献
5.
Electrical impedance measurements of Na3H(SO4)2 were performed as a function of both temperature and frequency. The electrical conductivity and dielectric relaxation have been evaluated. The temperature dependence of electrical conductivity reveals that the sample crystals transformed to the fast ionic state in the high temperature phase. The dynamical disordering of hydrogen and sodium atoms and the orientation of SO4 tetrahedra results in fast ionic conductivity. In addition to the proton conduction, the possibility of a Na+ contribution to the conductivity in the high temperature phase is proposed. The frequency dependence of AC conductivity is proportional to ωs. The value of the exponent, s, lies between 0.85 and 0.46 in the room temperature phase, whereas it remains almost constant, 0.6, in the high-temperature phase. The dielectric dispersion is examined using the modulus formalism. An Arrhenius-type behavior is observed when the crystal undergoes the structural phase transition. 相似文献
6.
烷基硫酸盐表面张力的量子化学研究 总被引:1,自引:0,他引:1
用AMl量子化学计算法优化了十三烷基硫酸根阴离子和——CH3在不同取代位的十二烷基硫酸根阴离子的几何构型,得到最优构型时最高占据分子轨道能级EHOMO、最低空轨道能级ELUMO、电子能量Eele和偶极矩μ等数据.将这些电子结构数据分别与表面张力相拟合,得到很好的相关性。文中讨论了——CH3在不同位置取代对表面张力的影响。 相似文献
7.
Ernesto Quesada 《Tetrahedron letters》2004,45(25):4877-4881
The first syntheses of newly isolated members of the Preussomerin family, Preussomerins K and L, are reported. Key steps include the functionalisation of a 2-arylacetal anion, one-pot Friedel-Crafts cyclisation-deprotection and reductive opening of epoxides. 相似文献
8.
Enrique J. Baran 《Monatshefte für Chemie / Chemical Monthly》1991,122(6-7):479-481
Summary Mean amplitudes of vibration for OTeF
5
–
have been calculated from known spectroscopic and structural data in a wide temperature range. The results are briefly discussed in comparison with those of related species. 相似文献
9.
Thermal, spectroscopic and electrical properties of lead pyrophosphate glass prepared by melt quenching have been examined.
A model based on the structural disproportionation of the P2O
7
4−
ions has been proposed and is shown to consistently explain all the observations. The equilibrium of various anionic species
has been discussed on the basis of their electronegativities which are in turn related to their basicities.
Communication No. 129 from the Materials Research Centre 相似文献
10.
Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy was employed to observe the visible absorption spectra of the B^2Σ^+_u-X^2Σ^+_g electronic transition of C^-_2. Four hot bands (0,1), (1,2), (2,3) and (3,4) have been observed and the band (3,4) is measured directly for the first time, so far as we know, by absorption. A rotational analysis was carried out to obtain molecular constants. With the Franck-Condon principle and the vibrational Boltzmann distribution, we have estimated the vibrational temperature of C^-_2 to be about 3000K. 相似文献