全文获取类型
收费全文 | 487篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
化学 | 254篇 |
晶体学 | 1篇 |
数学 | 51篇 |
物理学 | 191篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 3篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 25篇 |
2009年 | 18篇 |
2008年 | 19篇 |
2007年 | 25篇 |
2006年 | 17篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 23篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 18篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 13篇 |
1973年 | 13篇 |
1972年 | 10篇 |
1971年 | 7篇 |
1968年 | 5篇 |
1967年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有497条查询结果,搜索用时 140 毫秒
1.
Beyond Stereoselectivity,Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters 下载免费PDF全文
Dr. Sophie M. Guillaume Dr. Evgueni Kirillov Dr. Yann Sarazin Prof. Dr. Jean‐François Carpentier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):7988-8003
Metal‐based catalysts and initiators have played a pivotal role in the ring‐opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis—stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal‐based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts—primarily metal‐based catalysts, but also organocatalysts—that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted. 相似文献
2.
It has been shown that the kinetics of intramolecular processes and time-resolved spectra with allowance for the quantum beats of the resonant states of isomers or isolated subsystems of levels of one isomeric form can be described with the use of a molecular model interpreting the effect of beats as a nonradiative transition. We have obtained an expression for the nonradiative transition probability, which is directly proportional to the beat frequency and depends oscillatorily on time, thus modeling the effect of beats. The parameter of the molecular system model is the beat frequency directly related to the parameter characterizing the intramolecular interisomeric interactions (the corresponding nondiagonal element of the energy matrix) rather than the value of the nonradiative transition probability. The character of the change in the level populations and, accordingly, in the band intensities in the spectra in the proposed model is in good agreement with the experiment, including the fine structure of the time dependences — oscillations of the line intensities. In analyzing the temporal experiment with a high resolution, it is necessary to take into account the instrument function leading to quantitative and qualitative changes in the time dependences. The traditional model of nonradiative transitions with a constant probability value has a very limited range of applicability — very high beat frequencies compared to the probability of optical transitions. 相似文献
3.
Based on an analysis of the processes of intramolecular signal transfer (the ordered motion of a quasiparticle, vibron) and structural isomerization, it was pointed out that, in principle, reagents of a new type can be developed with analytical effects fundamentally different from usual ones. The type of analytical response can vary depending on the molecular structure and intramolecular processes induced. General principles of the molecular design of systems of this kind are discussed. 相似文献
4.
Spoto G Gribov E Bordiga S Lamberti C Ricchiardi G Scarano D Zecchina A 《Chemical communications (Cambridge, England)》2004,(23):2768-2769
Cu(I) ions in Cu-ZSM-5 form Cu+(H2) complexes, stable at room temperature and sub-atmospheric H2 pressure, which do not have any homogeneous analogue except for matrix-isolated [Cu(eta2-H2)Cl]. Comparison with the unstable Na+(H2) adducts formed in the parent Na-ZSM-5 zeolite allow the conclusion that the Cu(I)/H2 bond is governed by sigma-pi overlap forces. 相似文献
5.
L. A. Gribov 《Journal of Structural Chemistry》2005,46(5):921-923
A simple matrix method for calculating the vibrational and electron energy levels and spectra in molecular crystals is proposed. 相似文献
6.
Duncan K. Brownsey Ben C. Rowley Evgueni Gorobets Benjamin S. Gelfand Darren J. Derksen 《Chemical science》2021,12(12):4519
Current methods for the preparation of heterobifunctional pomalidomide-conjugates rely on methods that are often low yielding and produce intractable byproducts. Herein we describe our strategy for the reliable and succinct preparation of pomalidomide-linkers which is essential to the formation of these conjugates. We present the preparation of 18 pomalidomide-linkers in high yield compared to current literature methods. Our findings show that secondary amines consistently afford greater yields than their primary counterparts, a trend that we were able to exploit in the synthesis of several new pomalidomide homo-dimers in enhanced yields compared to similar literature syntheses. This trend was further utilised to develop the first one-pot synthesis of JQ1-pomalidomide conjugates in yields up to 62%, providing a method that is suited to rapid preparation of conjugate libraries as is frequently required for the development of new protein degraders.Current methods for the preparation of heterobifunctional pomalidomide-conjugates rely on methods that are often low yielding and produce intractable byproducts. Herein we describe our strategy for the succinct preparation of pomalidomide-linkers. 相似文献
7.
Dependence of the Daman intensities of combinations and overtones on the frequency of incident light
is shown that the combined method for calculating the Raman tensor elements suggested earlier [1, 2] may be extended to calculations
of the intensities of second-order Raman bands (overtones and combinations). The behavior of the intensities of the first-
and second-order Raman bands is studied in a wide range of frequencies of incident light, including the resonance region.
The resulting equations for the Raman scattering tensor elements are convenient from computational viewpoint; this is especially
important for the intermediate frequencies, which are most difficult for calculations.
Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 3, pp. 465–469, May–June, 1997. 相似文献
8.
B. F. Myasoedov L. A. Gribov A. I. Pavlyuchko I. V. Rybalchenko G. I. Sigeikin A. F. Kireev V. N. Suvorkin 《Journal of Structural Chemistry》2006,47(3):434-441
For highly toxic organophosphorus compounds on the limiting lists of the International Chemical Weapons Ban Treaty, fragment methods may be used for calculating their IR vibrational spectra; this is shown for O-alkyl alkylfluorophosphonates used as examples. The geometrical parameters and the parameters of the potential and electrooptic functions are found for the major fragments of these compounds. Due to this, fast predictive computation of IR spectra of O-alkyl alkylfluorophosphonates is possible, the accuracy of calculation being sufficient for spectral identification of these compounds; a database of the calculated IR spectra may be created. 相似文献
9.
L. A. Gribov 《High Energy Chemistry》2018,52(1):1-5
A way how a general rovibronic Hamiltonian for a polyatomic molecule can be obtained using generalized coordinates and introducing a “well” for the potential function of nuclear oscillations has been shown. Eigenfunctions for individual types of motion have a very simple form, which makes it possible to analyze both low-and high-energy states of molecules without changing the solution algorithm and to form an energy matrix without changing the basis set. 相似文献
10.