全文获取类型
收费全文 | 9073篇 |
免费 | 310篇 |
国内免费 | 75篇 |
专业分类
化学 | 6659篇 |
晶体学 | 41篇 |
力学 | 205篇 |
数学 | 1353篇 |
物理学 | 1200篇 |
出版年
2023年 | 33篇 |
2022年 | 51篇 |
2021年 | 110篇 |
2020年 | 145篇 |
2019年 | 141篇 |
2018年 | 101篇 |
2017年 | 73篇 |
2016年 | 220篇 |
2015年 | 189篇 |
2014年 | 222篇 |
2013年 | 514篇 |
2012年 | 538篇 |
2011年 | 681篇 |
2010年 | 307篇 |
2009年 | 237篇 |
2008年 | 518篇 |
2007年 | 598篇 |
2006年 | 626篇 |
2005年 | 502篇 |
2004年 | 458篇 |
2003年 | 393篇 |
2002年 | 361篇 |
2001年 | 135篇 |
2000年 | 91篇 |
1999年 | 85篇 |
1998年 | 80篇 |
1997年 | 107篇 |
1996年 | 113篇 |
1995年 | 84篇 |
1994年 | 76篇 |
1993年 | 90篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 89篇 |
1989年 | 46篇 |
1988年 | 62篇 |
1987年 | 61篇 |
1986年 | 75篇 |
1985年 | 108篇 |
1984年 | 106篇 |
1983年 | 68篇 |
1982年 | 95篇 |
1981年 | 93篇 |
1980年 | 94篇 |
1979年 | 68篇 |
1978年 | 84篇 |
1977年 | 62篇 |
1976年 | 58篇 |
1975年 | 53篇 |
1973年 | 60篇 |
排序方式: 共有9458条查询结果,搜索用时 78 毫秒
991.
Miller SA West BA Curtis AC Papanikolas JM Moran AM 《The Journal of chemical physics》2011,135(8):081101
Femtosecond transient grating experiments are used to investigate electronic structures and transport mechanisms in dye-sensitized nanocrystalline TiO(2) films. This study examines two molecular sensitizers spanning the weak (a phosphonated Ruthenium complex) and strong (catechol) molecule-TiO(2) coupling regimes. It is shown that strong molecule-TiO(2) interactions give rise to photoinduced vibrational coherences at the interface between species. We suggest that the amplitudes of these coherences reflect the molecule-TiO(2) coupling strength and signify the delocalization of excited state wavefunctions. 相似文献
992.
We compare, using single-particle optical imaging, trajectories of rotation and translation for micron-sized spheres in index-matched colloidal suspensions near their glass transition. Rotational trajectories, while they show intermittent caged behavior associated with supercooled and glassy behavior, explore a sufficiently wider phase space such that in the averaged mean-square angular displacement there appears no plateau regime, but instead sub-Fickian angular diffusion that follows an apparent power law in time. We infer translation and rotation time constants, the former being the time to diffuse a particle diameter and the latter being the time to rotate a full revolution. Correlation between time constants increases with increasing volume fraction, but unlike the case for molecular glasses, the rotation time constant slows more weakly than the translation time. 相似文献
993.
Photoelectron angular distributions (PADs) are obtained for a pair of 4s(1)4p(6)6p(1) (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s(1)4p(6) continuum with femtosecond time resolution. The ejected electrons are detected with velocity map imaging to retrieve the time-resolved photoelectron spectrum and PADs. The PAD for the triplet state is inherently separable by virtue of its longer autoionization lifetime. Measuring the total signal over time allows for the PADs to be extracted for both the singlet state and the triplet state. Anisotropy parameters for the triplet state are measured to be β(2)=0.55 ± 0.17 and β(4)=-0.01 ± 0.10, while the singlet state yields β(2)=2.19 ± 0.18 and β(4)=1.84 ± 0.14. For the singlet state, the ratio of radial transition dipole matrix elements, X, of outgoing S to D partial waves and total phase shift difference between these waves, Δ, are determined to be X=0.56 ± 0.08 and Δ=2.19 ± 0.11 rad. The continuum quantum defect difference between the S and D electron partial waves is determined to be -0.15 ± 0.03 for the singlet state. Based on previous analyses, the triplet state is expected to have anisotropy parameters independent of electron kinetic energy and equal to β(2)=5∕7 and β(4)=-12∕7. Deviations from the predicted values are thought to be a result of state mixing by spin-orbit and configuration interactions in the intermediate and final states; theoretical calculations are required to quantify these effects. 相似文献
994.
995.
Relative partial ionization cross sections (PICS) for the formation of fragment ions following electron ionization of SiCl(4), in the electron energy range 30-200 eV, have been determined using time-of-flight mass spectrometry coupled with an ion coincidence technique. By this method, the contributions to the yield of each fragment ion from dissociative single, double, and triple ionization, are distinguished. These yields are quantified in the form of relative precursor-specific PICS, which are reported here for the first time for SiCl(4). For the formation of singly charged ionic fragments, the low-energy maxima appearing in the PICS curves are due to contributions from single ionization involving predominantly indirect ionization processes, while contributions to the yields of these ions at higher electron energies are often dominated by dissociative double ionization. Our data, in the reduced form of relative PICS, are shown to be in good agreement with a previous determination of the PICS of SiCl(4). Only for the formation of doubly charged fragment ions are the current relative PICS values lower than those measured in a previous study, although both datasets agree within combined error limits. The relative PICS data presented here include the first quantitative measurements of the formation of Cl(2) (+) fragment ions and of the formation of ion pairs via dissociative double ionization. The peaks appearing in the 2D ion coincidence data are analyzed to provide further information concerning the mechanism and energetics of the charge-separating dissociations of SiCl(4) (2+). The lowest energy dicationic precursor state, leading to SiCl(3) (+) + Cl(+) formation, lies 27.4 ± 0.3 eV above the ground state of SiCl(4) and is in close agreement with a calculated value of the adiabatic double ionization energy (27.3 eV). 相似文献
996.
Treatment of the complex [U(Tren(TMS))(Cl)(THF)] [1, Tren(TMS) = N(CH(2)CH(2)NSiMe(3))(3)] with Me(3)SiI at room temperature afforded known crystalline [U(Tren(TMS))(I)(THF)] (2), which is reported as a new polymorph. Sublimation of 2 at 160 °C and 10(-6) mmHg afforded the solvent-free dimer complex [{U(Tren(TMS))(μ-I)}(2)] (3), which crystallizes in two polymorphic forms. During routine preparations of 1, an additional complex identified as [U(Cl)(5)(THF)][Li(THF)(4)] (4) was isolated in very low yield due to the presence of a slight excess of [U(Cl)(4)(THF)(3)] in one batch. Reaction of 1 with one equivalent of lithium dicyclohexylamide or bis(trimethylsilyl)amide gave the corresponding amide complexes [U(Tren(TMS))(NR(2))] (5, R = cyclohexyl; 6, R = trimethylsilyl), which both afforded the cationic, separated ion pair complex [U(Tren(TMS))(THF)(2)][BPh(4)] (7) following treatment of the respective amides with Et(3)NH·BPh(4). The analogous reaction of 5 with Et(3)NH·BAr(f)(4) [Ar(f) = C(6)H(3)-3,5-(CF(3))(2)] afforded, following addition of 1 to give a crystallizable compound, the cationic, separated ion pair complex [{U(Tren(TMS))(THF)}(2)(μ-Cl)][BAr(f)(4)] (8). Reaction of 7 with K[Mn(CO)(5)] or 5 or 6 with [HMn(CO)(5)] in THF afforded [U(Tren(TMS))(THF)(μ-OC)Mn(CO)(4)] (9); when these reactions were repeated in the presence of 1,2-dimethoxyethane (DME), the separated ion pair [U(Tren(TMS))(DME)][Mn(CO)(5)] (10) was isolated instead. Reaction of 5 with [HMn(CO)(5)] in toluene afforded [{U(Tren(TMS))(μ-OC)(2)Mn(CO)(3)}(2)] (11). Similarly, reaction of the cyclometalated complex [U{N(CH(2)CH(2)NSiMe(2)Bu(t))(2)(CH(2)CH(2)NSiMeBu(t)CH(2))}] with [HMn(CO)(5)] gave [{U(Tren(DMSB))(μ-OC)(2)Mn(CO)(3)}(2)] [12, Tren(DMSB) = N(CH(2)CH(2)NSiMe(2)Bu(t))(3)]. Attempts to prepare the manganocene derivative [U(Tren(TMS))MnCp(2)] from 7 and K[MnCp(2)] were unsuccessful and resulted in formation of [{U(Tren(TMS))}(2)(μ-O)] (13) and [MnCp(2)]. Complexes 3-13 have been characterized by X-ray crystallography, (1)H NMR spectroscopy, FTIR spectroscopy, Evans method magnetic moment, and CHN microanalyses. 相似文献
997.
A method for the room temperature copper-mediated trifluoromethylation of aryl and heteroaryl boronic acids has been developed. This protocol is amenable to normal benchtop setup and reactions typically require only 1-4 h. Proceeding under mild conditions, the method tolerates a range of functional groups, allowing access to a variety of trifluoromethylarenes. 相似文献
998.
Win-Mason AL Jongkees SA Withers SG Tyler PC Timmer MS Stocker BL 《The Journal of organic chemistry》2011,76(23):9611-9621
New methodology for the preparation of a variety of aminoiminohextitols is described. Key in the synthesis is the application of a diastereoselective Strecker reaction and the extension of our carbamate annulation methodology to protected and functionalized alkenylamines. Insight into the effects that the substitution patterns of the alkenylamines have on the diastereoselectivity of the iodocyclization and carbamate annulation is discussed. An evaluation of the glycosidase inhibitory activity of the aminoiminohexitols and derivatives is also presented, with the previously undisclosed D-talo isomer showing good selective inhibition of β-D-glucosidase. 相似文献
999.
Kornilov O Bünermann O Haxton DJ Leone SR Neumark DM Gessner O 《The journal of physical chemistry. A》2011,115(27):7891-7900
Ultrafast relaxation of electronically excited pure He droplets is investigated by femtosecond time-resolved photoelectron imaging. Droplets are excited by extreme ultraviolet (EUV) pulses with photon energies below 24 eV. Excited states and relaxation products are probed by ionization with an infrared (IR) pulse with 1.6 eV photon energy. An initially excited droplet state decays on a time scale of 220 fs, leading predominantly to the emission of unaligned 1s3d Rydberg atoms. In a second relaxation channel, electronically aligned 1s4p Rydberg atoms are emitted from the droplet within less than 120 fs. The experimental results are described within a model that approximates electronically excited droplet states by localized, atomic Rydberg states perturbed by the local droplet environment in which the atom is embedded. The model suggests that, below 24 eV, EUV excitation preferentially leads to states that are localized in the surface region of the droplet. Electronically aligned 1s4p Rydberg atoms are expected to originate from excitations in the outermost surface regions, while nonaligned 1s3d Rydberg atoms emerge from a deeper surface region with higher local densities. The model is used to simulate the He droplet EUV absorption spectrum in good agreement with previously reported fluorescence excitation measurements. 相似文献
1000.
Shen M Zhang L Lee KM Vermeulen R Hosgood HD Li G Yin S Rothman N Chanock S Smith MT Lan Q 《Experimental & molecular medicine》2011,43(6):374-378
Benzene, a recognized hematotoxicant and carcinogen, can damage the human immune system. We studied the association between single nucleotide polymorphisms (SNPs) in genes involved in innate immunity and benzene hematotoxicity in a cross-sectional study of workers exposed to benzene (250 workers and 140 controls). A total of 1,236 tag SNPs in 149 gene regions of six pathways were included in the analysis. Six gene regions were significant for their association with white blood cell (WBC) counts (MBP, VCAM1, ALOX5, MPO, RAC2, and CRP) based on gene-region (P<0.05) and SNP analyses (FDR<0.05). VCAM1 rs3176867, ALOX5 rs7099684, and MPO rs2071409 were the three most significant SNPs. They showed similar effects on WBC subtypes, especially granulocytes, lymphocytes, and monocytes. A 3-SNP block in ALOXE3 (rs7215658, rs9892383, and rs3027208) showed a global association (omnibus P = 0.0008) with WBCs even though the three SNPs were not significant individually. Our study suggests that polymorphisms in innate immunity genes may play a role in benzene-induced hematotoxicity; however, independent replication is necessary. 相似文献