全文获取类型
收费全文 | 4139篇 |
免费 | 105篇 |
国内免费 | 24篇 |
专业分类
化学 | 2652篇 |
晶体学 | 52篇 |
力学 | 102篇 |
数学 | 585篇 |
物理学 | 877篇 |
出版年
2021年 | 36篇 |
2020年 | 38篇 |
2019年 | 32篇 |
2018年 | 40篇 |
2017年 | 29篇 |
2016年 | 74篇 |
2015年 | 65篇 |
2014年 | 79篇 |
2013年 | 155篇 |
2012年 | 172篇 |
2011年 | 213篇 |
2010年 | 119篇 |
2009年 | 91篇 |
2008年 | 191篇 |
2007年 | 184篇 |
2006年 | 187篇 |
2005年 | 179篇 |
2004年 | 131篇 |
2003年 | 135篇 |
2002年 | 138篇 |
2001年 | 91篇 |
2000年 | 79篇 |
1999年 | 73篇 |
1998年 | 63篇 |
1997年 | 52篇 |
1996年 | 71篇 |
1995年 | 53篇 |
1994年 | 55篇 |
1993年 | 57篇 |
1992年 | 49篇 |
1991年 | 61篇 |
1990年 | 34篇 |
1989年 | 44篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 54篇 |
1985年 | 56篇 |
1984年 | 62篇 |
1983年 | 47篇 |
1982年 | 53篇 |
1981年 | 55篇 |
1980年 | 54篇 |
1979年 | 46篇 |
1978年 | 54篇 |
1977年 | 50篇 |
1976年 | 48篇 |
1975年 | 48篇 |
1974年 | 47篇 |
1973年 | 53篇 |
1971年 | 27篇 |
排序方式: 共有4268条查询结果,搜索用时 78 毫秒
61.
Razak J. Al-Essa Richard J. Puddephatt Charles F.H. Tipper Peter J. Thompson 《Journal of organometallic chemistry》1978,157(2):C40-C42
The platinacyclobutane complexes PtCl2L2(C3H5Me)], L pyridine, CD3CN, or tetrahydrofuran, exist as mixtures of isomers containing PH2 or P groups in rapid equilibrium. Decomposition occurs in some cases to give [PtCl2L(CH3CH2CHCH2)]. Stereospecific skeletal isomerisation also occurs in metallocyclobutanes containing the groups PH2 PHR, when R aryl further decomposition gives ν-allylplatinum complexes. 相似文献
62.
Several research groups have reported the presence of nanometer-sized particles (nanoslabs) in clear solutions, which precipitate the crystalline MFI (ZSM-5) structure. Debate about the growth mechanism for Al-free ZSM-5 (silicalite-1) has revolved around growth by small silicate units (monomers, dimers, etc.) from solution vs growth by nanoslab addition. A model developed for precipitation of uniform sized colloids by addition of sub-colloidal precursor units has been adapted for this zeolite synthesis system. Parameter values were adjusted for the simulation results to match experimental observations from work reported previously, at least to the extent possible. The model involved the simultaneous solution of up to 6000 ordinary differential equations, and required computation times of up to 24 h. The results shed light on the crystal growth mechanism, but pose questions for further investigations of the nucleation mechanism. 相似文献
63.
Damien Thompson 《Chemphyschem》2007,8(11):1684-1693
Molecular recognition between guest ink molecules and beta-cyclodextrin (beta-CD) cavities at self-assembled monolayers provides a molecular printboard for nanopatterning applications. We recently used molecular dynamics (MD) simulations to describe the specificity of ink-printboard binding and here extend the simulations to include charged cyclodextrin hosts, necessary to broaden the chemistry of molecular printboards and bind charged inks such as the ferrocenium cation. Shifting to high pH, or alternatively grafting a charged sidearm onto beta-CD, created three distinct types of anionic beta-CD cavity and we used electronic structure calculations and MD simulations to measure host-guest charge transfer and binding strengths. We find that steric recognition of uncharged organic molecules is retained at the charged printboards, and that improved guest-host electrostatic contacts can strengthen binding of larger inks while penalising small inks, enhancing the level of discrimination. A prudent choice of complementary host-guest shape and charge states thus provides a means of tuning both ink binding strength and specificity at molecular printboards. 相似文献
64.
The photoelectron spectra of the six propellanes 1 to 6 have been recorded. Those bands which correspond to ejection of an electron from a π-orbital have been assigned, using the concept of through bond and through space interaction. Homoconjugative interaction between the π-systems of the two butadiene moieties of 6 is of the same order as that of the π-orbitals in norbornadiene. 相似文献
65.
Wolfgang Marterer Horst Prinzbach Grety Rihs Jakob Wirz Jaques Lecoultre Edgar Heilbronner 《Helvetica chimica acta》1988,71(8):1937-1965
The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I1 = 8.00, I2 = 9.05 eV; 2 ; I1 = 8.00, I2 = 9.25eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond. 相似文献
66.
The total syntheses of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine are described. Evidence that the alkaloid propyleine is actually a rapidly interconverting mixture of propyleine and a previously unknown isomer isopropyleine is presented. 相似文献
67.
Zhang Z Blom DA Gai Z Thompson JR Shen J Dai S 《Journal of the American Chemical Society》2003,125(25):7528-7529
One-dimensional (1D) magnetic nanomaterials have attracted much attention recently because of their applications in magnetic recording and spintronics. Nevertheless, it remains a challenge to prepare free-standing magnetic nanowires in high yield. This Communication reports the successful high-yield synthesis of an interesting 1D ferromagnetic CoPt alloy by direct decomposition of platinum acetylacetonate and cobalt carbonyl compound in ethylenediamine solvent through a solvothermal reaction. The CoPt alloy nanowires obtained have a tunable diameter of 10-50 nm and a length along the longitudinal axis of up to several microns, depending on crystallization temperature and reaction time. A unique formation mechanism involving coarsening and ripening under solvothermal conditions was discovered. This research opens new opportunities in synthesizing nanomaterials through low-temperature solvothermal processes. 相似文献
68.
Thompson M Wilkins SJ Compton RG Viles HA 《Journal of colloid and interface science》2003,259(2):338-345
The dissolution kinetics of surface-pretreated and weathered calcite was investigated in dilute acid using a channel flow cell with microdisk detection. Two pretreatments were studied, polymaleic acid and phosphoric acid. Treatment with polymaleic acid was shown to significantly passivate calcite but to a lesser extent than the phosphoric acid and the former coating was found to be less effective for protection of calcite from acid attack. However, treatment of calcite with phosphoric acid resulted in the passivation of calcite from acid attack which strongly inhibited dissolution, an effect that was enhanced even further after exposure to the environment. 相似文献
69.
Thompson RS Guler LP Nelson ED Yu YQ Kenttämaa HI 《The Journal of organic chemistry》2002,67(15):5076-5084
The 1,3-dioxolane-2-phosphenium ion, 1,3-benzodioxole-2-phosphenium ion, and o-biphenylenephosphenium ion are reported to react in a stereoselective manner with cis- and trans-1,2-diaminocyclohexanes in the gas phase in a Fourier transform ion cyclotron resonance mass spectrometer. Elimination of NH3 from an addition product was observed only for the trans isomer. Several reaction mechanisms were experimentally and computationally examined (B3LYP/6-31G(d)//HF/6-31G(d) + ZPVE level of theory). The most plausible mechanism is initiated by addition of one of the amino groups to the electrophilic phosphorus atom followed by proton transfer between the amino groups. A change to a diaxial conformation for the trans isomer facilitates anchimeric assistance by the now nucleophilic phosphorus atom as the C-N bond breaks to release NH3. Intramolecular proton transfer competes with the conformational change and ultimately leads to ethylene glycol elimination. The transition states for the critical steps of these two reactions are calculated to be nearly equal in magnitude, which rationalizes the observation of both reactions for the trans-diamine. In contrast, the adduct of the cis isomer can eliminate NH3 via a concerted 1,2-hydride shift without a need for a conformational change. However, the barrier associated with this reaction was found to be substantially greater than for proton transfer between the N- and O-atoms. The latter reaction dominates and ultimately leads to ethylene glycol elimination. 相似文献
70.
A theory of electrostriction which follows from studies of dipolar ordering at an electrified wall is discussed in the quadratic hypernetted chain approximation. Bridge diagrams for the wall-particle correlation functions contribute significantly to electrostriction even to lowest order in the electric field The form of the constitutive relation between the polarization density and the field in strong fields is discussed. 相似文献