全文获取类型
收费全文 | 2106篇 |
免费 | 105篇 |
国内免费 | 12篇 |
专业分类
化学 | 1531篇 |
晶体学 | 16篇 |
力学 | 29篇 |
数学 | 370篇 |
物理学 | 277篇 |
出版年
2023年 | 17篇 |
2022年 | 19篇 |
2021年 | 25篇 |
2020年 | 72篇 |
2019年 | 49篇 |
2018年 | 29篇 |
2017年 | 13篇 |
2016年 | 44篇 |
2015年 | 59篇 |
2014年 | 61篇 |
2013年 | 84篇 |
2012年 | 78篇 |
2011年 | 113篇 |
2010年 | 52篇 |
2009年 | 61篇 |
2008年 | 92篇 |
2007年 | 82篇 |
2006年 | 69篇 |
2005年 | 100篇 |
2004年 | 94篇 |
2003年 | 64篇 |
2002年 | 57篇 |
2001年 | 52篇 |
2000年 | 38篇 |
1999年 | 32篇 |
1998年 | 37篇 |
1997年 | 36篇 |
1996年 | 35篇 |
1995年 | 32篇 |
1994年 | 29篇 |
1993年 | 36篇 |
1992年 | 29篇 |
1991年 | 39篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 28篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1974年 | 17篇 |
1973年 | 17篇 |
排序方式: 共有2223条查询结果,搜索用时 15 毫秒
91.
Crystal Structure of Sr(BrO3)2 · H2O, Ba(BrO3)2 · H2O, Ba(IO3)2 · H2O, Pb(ClO3)2 · H2O, and Pb(BrO3)2 · H2O The crystall structures of the isostructural halates Sr(BrO3)2 · H2O, Ba(BrO3)2 · H2O, Ba(IO3)2 · H2O, Pb(ClO3)2 · H2O, and Pb(BrO3)2 · H2O were determined using X-ray single crystal data (monoclinic space group C2/c? C, Z = 4), The mean bond lengths and bond angles of the halate ions in the Ba(ClO3)2 · 1 H2O-type compounds, which correspond to those of other halates, are Cl? O, 149.0, Br? O, 165.9, I? O, 180.2 pm, ClO3?, 106.4, BrO3?, 104.0, and IO3?, 99.6°. The structure data obtained are discussed in terms of possible orientational disorder of the water molecules, strengths of the hydrogen bonds, influence of the lead ions on the structure, and site group distortion of the halate ions. 相似文献
92.
Herbst K Zanello P Corsini M D'Amelio N Dahlenburg L Brorson M 《Inorganic chemistry》2003,42(4):974-981
By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes. 相似文献
93.
(?)-β-Caryophyllene (1) adopts three conformations in solution: αα(48%), βα(28%), and ββ(24%). The conformations were identified by an analysis of the 13C- and 1H-NMR spectra at ?87.2 and ?153.8° in connection with APT, HETCOR, and COSY spectra, and subsequent NOESY experiments. The activation parameters of the conversion αα → βα were determined from a bandshape analysis of exchange-broadened 13C-NMR spectra of 8-[methylene-13C]- 1 to give ΔH≠ = 5.9 ± 0.3 kcal/mol, ΔS? = ?8.1 ± 1.8 cal/mol. · K. and ΔG = ?8.3 ± 0.8 kcal/mol. The observed population ratio of the different conformers is best described by MM3. 相似文献
94.
Komeda S Lutz M Spek AL Yamanaka Y Sato T Chikuma M Reedijk J 《Journal of the American Chemical Society》2002,124(17):4738-4746
The reactions of the dinuclear platinum(II) complexes, [[cis-Pt(NH(3))(2)](2)(mu-OH)(mu-pz)](NO(3))(2) (1, pz = pyrazolate), [[cis-Pt(NH(3))(2)](2)(mu-OH)(mu-1,2,3-ta-N1,N2)](NO(3))(2) (2, 1,2,3-ta = 1,2,3-triazolate), and a newly prepared [[cis-Pt(NH(3))(2)](2)(mu-OH)(mu-4-phe-1,2,3-ta-N1,N2)](NO(3))(2) (3, 4-phe-1,2,3-ta = 4-phenyl-1,2,3-triazolate), whose crystal structure was determined, with 9-ethylguanine (9EtG) have been monitored in aqueous solution at 310 K by means of (1)H NMR spectroscopy. The dinuclear platinum(II) complexes 1-3 each react with 9EtG in a bifunctional way to form 1:2 complexes, [[cis-Pt(NH(3))(2)(9EtG-N7)](2)(mu-pz)](3+) (4), [[cis-Pt(NH(3))(2)(9EtG-N7)](2)(mu-1,2,3-ta-N1,N3)](3+) (5), and [[cis-Pt(NH(3))(2)(9EtG-N7)](2)(mu-4-phe-1,2,3-ta-N1,N3)](3+) (6). The reactions of 2 and 3 involve a novel isomerization, in which the Pt atom, initially bound to N2 on the 1,2,3-ta, migrates to N3 after the first substitution by N7 of 9EtG. This isomerization reaction has been unambiguously characterized by 1D and 2D NMR spectroscopy and pH titration. The reactions of 2 and 3 with 9EtG show faster kinetics, and the second-order rate constants (k) for the reactions of 1-3are 1.57 x 10(-4), 2.53 x 10(-4), and 2.56 x 10(-4) M(-1) s(-1), respectively. The pK(a) values at the N1H site of 9EtG were determined for 4-6 from the pH titration curves. Cytotoxicity assays of 1-3 were performed in L1210 murine leukemia cell lines, respectively sensitive and resistant to cisplatin. In the parent cell line, 2 and 3 exhibit higher cytotoxicity compared to cisplatin, especially, 2 is 10 times as active as cisplatin. 1 was found to be less cytotoxic than cisplatin, but still in the active range and more active than cisplatin in a cisplatin-resistant cell line. 相似文献
95.
LetM be a multiplicative set with 1M andmnM if and only ifmM,nM for (m,n)=1. It is shown by elementary means that there exists the asymptotic density of the setM(M–1) for every multiplicative setM. The density is positive if and only ifM possesses a positive density and 2M for some . This result is slightly generalized to sums over multiplicative functionsf with |f|1. 相似文献
96.
97.
98.
99.
100.
Fabian Ebner Philipp Mainik Dr. Lutz Greb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(16):5120-5124
Structural constraint represents an attractive tool to modify p-block element properties without the need for unusual oxidation or valence states. The recently reported methyl-calix[4]pyrrolato aluminate established the effect of forcing a tetrahedral aluminum anion into a square-planar coordination mode. However, the generality of this structural motif and any consequence of ligand modification remained open. Herein, a systematic ligand screening was launched, and the class of square-planar aluminum anions was extended by two derivatives that differ in the meso-substitution at the calix[4]pyrrolato ligand. Strikingly, this modification provoked opposing trends in the preference for a Lewis acidic binding mode with σ-donors versus the aluminum-ligand cooperative binding mode with carbonyls. Insights into the origin of these counterintuitive experimental observations were provided by computation and bond analysis. Importantly, this rationale might allow to exploit mode-selective binding for catalytic rate control. 相似文献