全文获取类型
收费全文 | 23318篇 |
免费 | 3031篇 |
国内免费 | 2775篇 |
专业分类
化学 | 16876篇 |
晶体学 | 199篇 |
力学 | 1909篇 |
综合类 | 164篇 |
数学 | 1455篇 |
物理学 | 8521篇 |
出版年
2024年 | 34篇 |
2023年 | 210篇 |
2022年 | 461篇 |
2021年 | 676篇 |
2020年 | 798篇 |
2019年 | 666篇 |
2018年 | 582篇 |
2017年 | 681篇 |
2016年 | 830篇 |
2015年 | 884篇 |
2014年 | 1173篇 |
2013年 | 1963篇 |
2012年 | 1355篇 |
2011年 | 1700篇 |
2010年 | 1337篇 |
2009年 | 1460篇 |
2008年 | 1555篇 |
2007年 | 1566篇 |
2006年 | 1478篇 |
2005年 | 1283篇 |
2004年 | 1156篇 |
2003年 | 997篇 |
2002年 | 985篇 |
2001年 | 666篇 |
2000年 | 629篇 |
1999年 | 517篇 |
1998年 | 523篇 |
1997年 | 451篇 |
1996年 | 371篇 |
1995年 | 338篇 |
1994年 | 293篇 |
1993年 | 241篇 |
1992年 | 239篇 |
1991年 | 160篇 |
1990年 | 152篇 |
1989年 | 102篇 |
1988年 | 109篇 |
1987年 | 67篇 |
1986年 | 64篇 |
1985年 | 61篇 |
1984年 | 54篇 |
1983年 | 20篇 |
1982年 | 55篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 21篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
Thomas J. Gedemer 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(1):95-104
It is difficult to estimate the degree of thermal degradation which has taken place in complex parts composed of cellulosics and polymeric insulation unless complete failure has occurred. There is a definite need for a parameter which can quickly and easily measure the relative degree of thermal attack on organic insulation subjected to various known environmental and processing conditions. This paper reports preliminary work using derivative thermogravimetry to perform this function. Derivative thermogravimetric analysis (TGA) was used to produce a value, TGA Index, related to the peak height of the major TGA derivative signal. This TGA Index was found to correlate with the copper number of insulating paper measured after thermal degradation. The application of TGA Index to evaluation of polymer degradation after thermal shock, water absorption, and accelerated UV attack is also discussed. Finally, preliminary studies on the use of derivative TGA to evaluate coatings exposed to various outdoor environments around the country are reported. 相似文献
962.
Polymer-bound alkylthiopurine and -pyrimidine bases were prepared and used as the polymeric reagents for the reactions of nitrile, olefin, and enone formation. The corresponding low molecular weight compounds were also prepared for comparison. Differences in the reactivity of these reagents were related to the change in tautomerism of the purine and pyrimidine moieties. 相似文献
963.
Sodiun borohydride reacts with oxazolidinium methiodides derived from ephedrine and pseudoephedrine, in ethereal solvents, cleaving regioselectively the C-N bond of the ring and leading, in good yields, to chiral amine-borane adducts of know absolute configuration. The 1HNMR data allow to predict the most stable conformation. 相似文献
964.
Dr. James P. Dombrowski Dr. Micah S. Ziegler Dr. Neelay M. Phadke Erum Mansoor Dr. Daniel S. Levine Dr. Ryan J. Witzke Prof. Dr. Martin Head-Gordon Prof. Dr. Alexis T. Bell Prof. Dr. T. Don Tilley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):307-315
Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)3]4− and HOM[OSi(OtBu)3]3− (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)3]3Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)3]4− with outer-sphere [([12]crown-4)2Li]+ cations, and hydroxides {HOM[OSi(OtBu)3]3} with pendant [([12]crown-4)Li]+ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)3]3} complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts. 相似文献
965.
Attapulgite grafted with polystyrene via a simultaneous reverse and normal initiation atom transfer radical polymerization
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haicun Yang Hongting Pu Fanghong Gong 《Journal of polymer science. Part A, Polymer chemistry》2016,54(11):1508-1516
The surface grafting of attapulgite (ATP) with polystyrene (PS) was established via a simultaneous reverse and normal initiation atom transfer radical polymerization (SR&NIATRP). 4‐(chloromethyl)phenyltrimethoxysilane (CMPTMS) chemical bounded on the surface of ATP (ATP‐Cl, Cl‐I) was prepared via one‐step self‐assembly. SR&NI ATRP of styrene was conducted using CuCl2 complex tris(2‐(dimethylamino)ethyl)amine (Me6‐TREN) as the catalytic system, initiated by 2,2‐azobis(isobutyronitrile) (AIBN) and ATP‐Cl. FT‐IR, XRD, XPS, TGA and TEM data were consistent with the grafting of benzyl chloride groups and PS chains on ATP surface. The controllability of polymerization was investigated by the kinetics behavior under different molar ratio of AIBN and CuCl2. The obtained polymer possessed a uniform distribution of molecular weights with a lower polydispersity index of 1.2~1.4. The relationship between polymerization on the surface of ATP and in solution was discussed in detail based on TGA data of hybrid particles and GPC trace of free polymer in solution. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1508–1516 相似文献
966.
In this paper, we have investigated the motion of a heated viscoelastic fluid layer in a rectangular tank that is subjected to a horizontal periodic oscillation. The mathematical model of the current problem is communicated with the linearized Navier–Stokes equation of the viscoelastic fluid and heat equation together with the boundary conditions that are solved by means of Laplace transform. Time domain solutions are consequently computed by using Durbin's numerical inverse Laplace transform scheme. Various numerical results are provided and thereby illustrated graphically to show the effects of the physical parameters on the free-surface elevation time histories and heat distribution. The numerical applications revealed that increasing the Reynolds number as well as the relaxation time parameter leads to a wider range of variation of the free-surface elevation, especially for the short time history. 相似文献
967.
Alexander P. Filippov Elena V. Belyaeva Tamara K. Meleshko Alexander V. Yakimansky 《Journal of Polymer Science.Polymer Physics》2014,52(23):1539-1546
A polyimide‐graft‐polystyrene (PI‐g‐PS) copolymer with a polyimide backbone and polystyrene side chains was synthesized by the “grafting from” method using styrene polymerization on a polyimide multicenter macroinitiator via ATRP mechanism. The side chain grafting density z = 0.86 of PI‐g‐PS is rather high for graft‐copolymers synthesized by the ATRP method. Molecular characteristics and solution behavior of PI‐g‐PS were studied in selective solvents using light scattering and viscometry methods. In all solvents, the backbone tends to avoid contact with a poor solvent. To describe the conformation and hydrodynamic properties of PI‐g‐PS macromolecules in thermodynamically good solvents for side chains and PI‐g‐PS, the wormlike spherocylinder model is used. Macromolecules of the studied graft‐copolymer are characterized by high equilibrium rigidities (Kuhn segment length >20 nm). In Θ‐conditions, PI‐g‐PS macromolecules may be modeled by a rigid prolate ellipsoid of revolution with a low asymmetry form and a collapsed backbone as the ellipsoid core. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1539–1546 相似文献
968.
Dr. Yungen Liu Dr. Chun-Wai Tse Dr. Kar-Yee Lam Dr. Xiao-Yong Chang Dr. Xiangguo Guan Meng-Yao Chao Dr. Jie-Sheng Huang Prof. Dr. Chi-Ming Che 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10828-10833
Ruthenium(II) complexes bearing a tridentate bis(N-heterocyclic carbene) ligand reacted with iminoiodanes (PhI=NR) resulting in the formation of isolable ruthenium(III)–amido intermediates, which underwent cleavage of a C−N bond of the tridentate ligand and formation of an N-substituted imine group. The RuIII–amido intermediates have been characterized by 1H NMR, UV/Vis, ESI-MS, and X-ray crystallography. DFT calculations were performed to provide insight into the reaction mechanism. 相似文献
969.
《Journal of Polymer Science.Polymer Physics》2018,56(13):965-969
Interchain interactions can play a positive role in reaching amplified spontaneous emission in an interesting core–polymer system where the donor (side chains) and the acceptor (core) are chemically linked together. Different degree of interchain interactions modifies the photophysical characteristics of the polymer. By means of transient absorption spectroscopy we show that the stimulated emission from the core decreases passing from solid state to concentrated solution and it is almost absent in the diluted solution. The conformational rearrangements of the core–polymer chain in solution limits the efficiency of the intrachain Förster energy transfer mechanism. The free chain rotations decrease the exciton hopping along the conjugated chains, the ratio between donor and acceptor moieties in the polymer, and change the relative orientation of the transition dipoles of the donor and acceptor causing a strong decrease of energy transfer efficiency and subsequently of the gain. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 965–969 相似文献
970.
Yongqiang Chen Ruchao Huang Zhuping Huang Lizhi Sun 《Acta Mechanica Solida Sinica》2012,25(3):262-276
This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion tensor, and specific heats of the multi-phase composites are derived by means of the volume average of free-energies of these phases. Particular emphasis is placed on the derivation of new analytical expressions of effective specific heats at constant-strain and constant-stress situations, in which a modified Eshelby’s micromechanics theory is developed and the interaction between inclusions is considered. As an illustrative example, the analytical expression of the effective specific heat for a three-phase thermoelastic composite is presented. 相似文献