全文获取类型
收费全文 | 889篇 |
免费 | 41篇 |
国内免费 | 3篇 |
专业分类
化学 | 617篇 |
晶体学 | 9篇 |
力学 | 17篇 |
数学 | 170篇 |
物理学 | 120篇 |
出版年
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 29篇 |
2019年 | 30篇 |
2018年 | 20篇 |
2017年 | 7篇 |
2016年 | 31篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 46篇 |
2012年 | 53篇 |
2011年 | 58篇 |
2010年 | 33篇 |
2009年 | 33篇 |
2008年 | 42篇 |
2007年 | 28篇 |
2006年 | 27篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 34篇 |
2002年 | 19篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 12篇 |
1992年 | 14篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1969年 | 7篇 |
1944年 | 6篇 |
1943年 | 7篇 |
1910年 | 5篇 |
排序方式: 共有933条查询结果,搜索用时 15 毫秒
1.
2.
3.
Lorenzo CaggianoDamiano Castoldi Raphael BeumerPau Bayón Joachim TelserCesare Gennari 《Tetrahedron letters》2003,44(43):7913-7919
During the course of our synthetic studies towards simplified eleuthesides, we have found that p-methoxyphenyl (PMP) protected allylic alcohols are compatible with the RCM reaction and can give better yields than the corresponding free allylic alcohols. 相似文献
4.
5.
Depecker G Patino N Di Giorgio C Terreux R Cabrol-Bass D Bailly C Aubertin AM Condom R 《Organic & biomolecular chemistry》2004,2(1):74-79
A cyclic molecule including a hexameric PNA sequence has been designed and synthesized in order to target the TAR RNA loop of HIV-1 through the formation of a "kissing complex". For comparison, its linear analogue has also been investigated. The synthesis of the cyclic and linear PNA has been accomplished following a liquid-phase strategy using mixed PNA and fully N-protected (aminoethylglycinamide) fragments. The interactions of this cyclic PNA and its linear analogue with TAR RNA have been studied and the results indicate clearly that no interaction occurs between the cyclic antisense PNA and TAR RNA, whereas a tenuous interaction has been detected with its linear PNA analogue. 相似文献
6.
A new complex of bis-axially coordinated iron(II) phthalocyanine by 4-cyanopyridine (4-CNpy) has been obtained in crystalline form as an adduct with two 4-CNpy molecules. The [FePc(4-CNpy)2] · 2(4-CNpy) crystallises in the monoclinic system, space group P21/c with two molecules in the unit cell. The iron(II) coordinates four isoindole nitrogen atoms of the almost planar phthalocyaninato(2−) macroring and axially two nitrogen atoms of 4-CNpy molecules. The coordination polyhedron around the Fe(II) atom approximates to a tetragonal by-pyramid. Four equatorial Fe–N bonds are shorter (1.936(2) Å) than two axial Fe–N bonds (2.027(2) Å). The centrosymmetric FePc(4-CNpy)2 molecules form alternating sheets parallel to the bc crystallographic plane and solvated 4-CNpy molecules that are anti-parallel oriented by their polar cyano groups are located between the sheets of FePc(4-CNpy)2 molecules. Ligation of the intermediate-spin iron(II) phthalocyanine by 4-CNpy molecules leads to the low spin Fe(II) complex. The importance of the d(π) → π∗(Pc) back donation is manifested in the difference between the values of C–N isoindole and C–N azamethine bond lengths of the Pc macrocycle. The thermal analysis of the crystals of [FePc(4-CN)2] · 2(4-CNpy) shows two steps responsible for a loss of solvated (∼170 °C) and coordinated (∼235 °C) 4-CNpy molecules. 相似文献
7.
8.
Sequential injection analysis (SIA) technique has been applied to anodic stripping voltammetry (ASV). The sample and reagent volumes can easily be controlled by SIA. The technique also allows plating of the mercury film on-line and therefore substantially reduces generation of mercury containing waste. Repeated sample passage through the detector was used during the deposition step to enhance the sensitivity. The way solution handling is done in SIA allows an easy and effective medium exchange procedure increasing the selectivity of the method. This has been demonstrated by changing the stripping medium and having different complexing agents in the stripping solution. The observed potential shifts of the stripping peaks could theoretically be explained in the cases where the complexation constants are known. Calibration and the standard addition methods are discussed and demonstrated by determining copper in tap water as a method of testing the procedure. 相似文献
9.
Photoelectron energy and angular distributions are measured for the 2+1 multiphoton ionization process H2 X1Σg+ (ν = 0,J) + 2hv → E,F1Σg+(νE,JE = J) + hν → H2+X2Σg+ (ν+) + e?, for νE = 0, 1, or 2 and for JE = 0 or 1 of the inner well of the double-minimum E,F state. Although a strong preference is found for ν+ = νE, the detailed H2+ vibrational distribution does not exhibit Franck-Condon behavior, and the photoelectron angular distributions vary markedly with both the JE value of the intermediate state and the ν+ value of the ion. 相似文献
10.
Based on theoretical thermodynamic principles, the possibility of environmental degradation of polyacrylamide to its starting monomer was investigated. Theoretical electronic structure studies on the geometry and fragmentation energy of acrylamide and N,N‐dimethyl acrylamide tetramer models were carried out using a first principles gradient corrected density functional approach. Thermal degradation to form a radical would require the cleavage of carbon–carbon bonds in the polymer chain; the energy needed for this cleavage was found to depend on the structure of the repeat unit which ranged from low of 72.5 kcal for a rare head‐to‐head construct to 86.2 kcal for a normal head‐to‐tail polymer construct (therefore, for the cleavage of a normal head‐to‐tail repeat unit, temperatures of approximately 450°C would be required). The thermodynamics of the unzipping, disproportionation, and back‐biting reactions in the resulting radical fragments were also investigated; the back‐biting process was found to require the least energy and provided the most stable radical fragment with a low probability for disproportionation or releasing of monomer to occur. The effect of solvation on the hydrogen‐bonding network in the acrylamide tetramer was studied by adding explicit molecules of water to the tetramer models. The addition of water had a significant effect on the stability of the model polymer slightly stabilizing the head‐to‐head polymer, and slightly destabilizing the head to tail polymer. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献