全文获取类型
收费全文 | 4781篇 |
免费 | 164篇 |
国内免费 | 25篇 |
专业分类
化学 | 3274篇 |
晶体学 | 41篇 |
力学 | 179篇 |
数学 | 448篇 |
物理学 | 1028篇 |
出版年
2024年 | 23篇 |
2023年 | 41篇 |
2022年 | 288篇 |
2021年 | 220篇 |
2020年 | 161篇 |
2019年 | 148篇 |
2018年 | 175篇 |
2017年 | 125篇 |
2016年 | 177篇 |
2015年 | 171篇 |
2014年 | 179篇 |
2013年 | 337篇 |
2012年 | 293篇 |
2011年 | 325篇 |
2010年 | 188篇 |
2009年 | 174篇 |
2008年 | 185篇 |
2007年 | 203篇 |
2006年 | 153篇 |
2005年 | 163篇 |
2004年 | 104篇 |
2003年 | 103篇 |
2002年 | 95篇 |
2001年 | 76篇 |
2000年 | 65篇 |
1999年 | 62篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 49篇 |
1995年 | 43篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 44篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 40篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 27篇 |
1977年 | 27篇 |
1976年 | 18篇 |
1968年 | 10篇 |
排序方式: 共有4970条查询结果,搜索用时 31 毫秒
1.
Maravanji S. Balakrishna Tristram Chivers Masood Parvez 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):o617-o619
In both title structures, C40H32N4Si and C40H32N4Si·3C4H8O, the angles around the Si atom deviate significantly from the tetrahedral value [104.34 (7)–116.63 (7)° in the nonsolvate and 99.91 (15)–116.85 (15)° in the solvate]. The amino H atoms in the solvated structure are involved in hydrogen bonding with two of the tetrahydrofuran solvent molecules. 相似文献
2.
M. Niyaz Khan 《国际化学动力学杂志》1991,23(7):561-566
The effects of the concentrations of LiCl, NaCl, KCl, CsCl, Na2CO3, BaCl2, and Me4NCl on the rates of reactions of hydroxide ion with ionized N-hydroxyphthalimide (NHP) at 30°C and in a H2O–MeCN solvent containing 98%, v/v, H2O reveal a nonlinear increase in observed rate constants with increase in salt concentrations. The observed rate constants are highly sensitive to the valence state of cations and almost insensitive to the valence state of anions of the salts. These observations are explained in terms of ion-pair formation between cations and NHP?. 相似文献
3.
4.
5.
6.
Methotrexate (MTX) has been convalently attached to an IgG-type monoclonal antibody (791T/36) directed to tumour-associated antigen gp72. Conjugates were synthesized by the active ester method using MTX N-succinimidyl ester at various pH values (7.5-10.5). Following purification by gel filtration, high performance liquid chromatography was used to assess the free drug or its derivatives in samples of MTX-791T/36 conjugates previously treated (or not) with hydroxylamine. Quantitative analysis, performed on a reversed phase column (pore size 300 A) with isocratic acetonitrile-sodium acetate buffer (pH 4.8) as mobile phase, indicated no detectable amount of free methotrexate in hydroxylamine-treated conjugates even six months after their preparation. Similar observations were made with conjugates, whose synthesis were performed at pH greater than or equal to 10. In contrast, the presence of increasing amounts of drug/metabolite could be demonstrated in samples produced at lower pH values. Based on these findings, the pH-dependent kinetics of MTX release has been determined and used to design conditions under which stable MTX-791T/36 conjugates could be prepared without hydroxylamine reaction. 相似文献
7.
Ali Reza Ashrafi Masood Hamadanian 《Journal of Applied Mathematics and Computing》2004,14(1-2):289-303
The non-rigid molecule group theory (NRG) in which the dynamical symmetry operations are defined as physical operations is a new field of chemistry. Smeyers in a series of papers applied this notion to determine the character table of restricted NRG of some molecules. In this work, a simple method is described, by means of which it is possible to calculate character tables for the symmetry group of molecules consisting of a number of NH3 groups attached to a rigid framework. We study the full non-rigid group (f-NRG) of tetraammineplatinum (II) with two separate symmetry groups C2v and C4v. We prove that they are groups of order 216 and 5184 with 27 and 45 conjugacy classes, respectively. Also, we will compute the character tables of these groups. 相似文献
8.
Recoil proton tracks in nuclear emulsion are counted by scanning them using strip, square or circular field of view of optical microscope. In this paper, the overestimate due to the edge effects in counting recoil proton tracks at different neutron energies produced from the T(d,n)4He reaction has been determined by measuring the true track density in NTA film. The overestimate has also been calculated using the measured value of the mean projected track length (L) in the film. The percentage of measured overestimates has been compared with those obtained by calculation and the results agree reasonably well. Fading effect in NTA film has been studied and found to be 22% more in the summer than in the winter season. A great reduction in fading rate could be achieved if the films are desiccated and sealed in highly pure dry nitrogen maintained at an over-pressure of 1000 Pa to reduce water vapour ingress. After the edge effect correction, the sensitivity of NTA film has been calculated from (1.72±0.08)×10−3 tracksn−1 to (1.97±0.16)×10−3 tracksn−1 in the neutron energy ranges from 15.91 to 18.88 MeV. The response was found to be from 0.24±0.02 trackscm−2 permSv to 0.26±0.01 trackscm−2 permSv in the same energy range. 相似文献
9.
10.
Poly(ortho‐phenylene ethynylene)s (PoPEs) have been synthesized via an in situ activation/coupling AB′ polycondensation protocol. The resulting polymers have been characterized by several analytical methods and are shown to have no structural defects. Although the Sonogashira–Hagihara polycondensation reaction is less efficient than for the preparation of the corresponding meta‐ and para‐linked polymers, presumably because of steric hindrance caused by the ortho substituents, the process can be accelerated by the use of microwave irradiation. Optical spectroscopy indicates solvent‐dependent conformational changes between extended transoid and helical cisoid conformations, providing the first experimental evidence for solvophobically driven folding of the PoPE backbone. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1619–1627, 2006 相似文献