全文获取类型
收费全文 | 14536篇 |
免费 | 455篇 |
国内免费 | 322篇 |
专业分类
化学 | 9088篇 |
晶体学 | 100篇 |
力学 | 405篇 |
综合类 | 30篇 |
数学 | 1886篇 |
物理学 | 3804篇 |
出版年
2022年 | 157篇 |
2021年 | 184篇 |
2020年 | 175篇 |
2019年 | 176篇 |
2018年 | 170篇 |
2017年 | 139篇 |
2016年 | 328篇 |
2015年 | 298篇 |
2014年 | 364篇 |
2013年 | 776篇 |
2012年 | 622篇 |
2011年 | 718篇 |
2010年 | 515篇 |
2009年 | 493篇 |
2008年 | 659篇 |
2007年 | 698篇 |
2006年 | 561篇 |
2005年 | 577篇 |
2004年 | 575篇 |
2003年 | 577篇 |
2002年 | 611篇 |
2001年 | 440篇 |
2000年 | 398篇 |
1999年 | 307篇 |
1998年 | 223篇 |
1997年 | 203篇 |
1996年 | 221篇 |
1995年 | 236篇 |
1994年 | 227篇 |
1993年 | 177篇 |
1992年 | 168篇 |
1991年 | 175篇 |
1990年 | 191篇 |
1989年 | 154篇 |
1988年 | 138篇 |
1987年 | 135篇 |
1986年 | 123篇 |
1985年 | 216篇 |
1984年 | 233篇 |
1983年 | 159篇 |
1982年 | 178篇 |
1981年 | 147篇 |
1980年 | 151篇 |
1979年 | 139篇 |
1978年 | 115篇 |
1977年 | 162篇 |
1976年 | 142篇 |
1975年 | 118篇 |
1974年 | 110篇 |
1973年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
S. Barlag H. Becker T. Böhringer M. Bosman V. Castillo V. Chabaud D. Buchholz C. Damerell C. Daum H. Dietl H. Fawcett S. Gill A. Gillman R. Gilmore T. Gooch L. Görlich P. Gras Z. Hajduk E. Higon B. D. Hyams D. P. Kelsey J. Kemmer R. Klanner U. Kötz S. Kwan B. Lücking G. Lütiens G. Lutz J. Malos W. Männer E. Neugebauer H. Palka M. Pepé J. Richardson G. De Rijk K. Rybicki H. J. Seebrunner U. Stierlin H. G. Tiecke M. Turala G. Waltermann S. Watts P. Weilhammer F. Wickens L. W. Wiggers A. Wylie T. Zeludziewicz ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1987,37(1):17-23
We have measured the lifetimes of hadronically produced charged and neutralD mesons using silicon microstrip detectors and an active silicon target in the NA32 spectrometer at the CERN SPS. We obtainτ D± = (10.9± 1.5 1.9 )·10?13s andτ D (?)10 = (4.2±0.5)·10?13s based on 59 and 90 fully reconstructed decays respectively, giving a ratioτ D±/τ D (?)10 of 2.6 ±0.5. 相似文献
192.
We consider a one-dimensional version of the model introduced in Ref. l. At each site of Z there is a particle with spin ± 1. Particles move according to the Stirring Process and spins change according to the Glauber dynamics. In the hydrodynamical limit, with the stirring process suitably speeded up, the local magnetic densitym t(r) is proven in Ref. 1 to satisfy the reaction-diffusion equation (*) $$\partial _t m_t (r) = \tfrac{1}{2}\partial _r^2 m_t (r) - V'(m_t )$$ \(V(m) = - \tfrac{1}{2}\alpha m^2 + \tfrac{1}{4}\beta m^4 \) ,α andβ being determined by the parameters of the Glauber dynamics. In the present paper we consider an initial state with zero magnetization,m 0(r)=0. We then prove that at long times, before taking the hydrodynamical limit, the evolution departs from that predicted by (*) and that the microscopic state becomes a nontrivial mixture of states with different magnetizations. 相似文献
193.
Tessore F Roberto D Ugo R Pizzotti M Quici S Cavazzini M Bruni S De Angelis F 《Inorganic chemistry》2005,44(24):8967-8978
Coordination of 4'-(C6H4-p-X)-2,2':6',2'-terpyridines [X = NO2, NBu2, (E)-CH=CH-C6H4-p-NBu2, (E,E)-(CH=CH)2-C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of the second-order nonlinear optical (NLO) response of the terpyridine, measured by means of both electric field induced second harmonic generation and solvatochromic methods. By varying the nature of the metal center, the enhanced second-order NLO response shifts from positive to negative. Such a shift is controlled by electronic charge-transfer transitions, such as metal-to-ligand or ligand-to-metal transitions, in addition to the intraligand charge transfer. The enhancement generated by coordination is also controlled by the chelation effect and by fine-tuning of the ancillary ligands. 相似文献
194.
Rüdiger O Abad JM Hatchikian EC Fernandez VM De Lacey AL 《Journal of the American Chemical Society》2005,127(46):16008-16009
The orientation of hydrogenase bound covalently to a pyrolytic graphite edge electrode modified with a 4-aminophenyl monolayer can be modulated via electrostatic interactions during the immobilization step. At low ionic strength and when the amino groups of the electrode surface are mostly protonated, the hydrogenase is immobilized with the negatively charged region that surrounds its 4Fe4S cluster nearer to the protein surface facing the electrode. This allows direct electron transfer between the immobilized hydrogenase and the electrode, which is observed by the strong catalytic currents measured in the presence of the H2 substrate. Therefore, a very stable enzymatic electrode is produced that catalyzes nonmediated H2 oxidation. 相似文献
195.
Maly J Di Meo C De Francesco M Masci A Masojidek J Sugiura M Volpe A Pilloton R 《Bioelectrochemistry (Amsterdam, Netherlands)》2004,63(1-2):271-275
Electrochemical synthesis of nickel-nitrilotriacetic acid (Ni-NTA) chelators, for subsequent immobilization of (His)(6)-tagged proteins (Photosystem II (PSII) as model molecule), on Au or Au-graphite electrodes is compared to chemical synthesis. Results show: (i) higher Ni-NTA surface density, (ii) shorter treatment time (1-12 min vs. 16 h normally needed for self-assembled monolayer (SAM)), (iii) possibility of addressing the chelator to only one Au electrode, in a sensor micro-array. 相似文献
196.
The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10−4–1.0×10−2 M H2PO4−. Anion corrections for interferences by Cl−, NO3− and SO42− were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions. 相似文献
197.
A number of ruthenium triphenylphosphine complexes catalyse the reduction of ketones to their corresponding alcohols in the presence of water. The most convenient catalyst precursors are carbonyl containing complexes which do not promote decarbonylation of the substrate. The hydrogenation of acetone with hydridochlorocarbonyltris(triphenylphosphine)ruthenium is first order with respect to the substrate concentration, the catalyst concentration, the hydrogen pressure and the water concentration. Turnover numbers up to 15,000 have been achieved with this catalyst. Other ketones are also reduced by RuHCl(CO)(PPh3)3 and the rate of the reaction is dependent on the nature of the substrate. 相似文献
198.
Density functional calculations were performed on the sulfoxidation reaction by a model compound I (Cpd I) of cytochrome P450. By contrast to previous alkane hydroxylation studies, which exhibit a dominant low-spin (LS) pathway, the sulfoxidation follows a dominant high-spin (HS) reaction. Thus, competing hydroxylation and sulfoxidation processes as observed for instance by Jones et al. (Volz, T. J.; Rock, D. A.; Jones, J. P. J. Am. Chem. Soc. 2002, 124, 9724) are the result of a two-state reactivity scenario, whereby the hydroxylation originates from the LS pathway and the sulfoxidation from the HS pathway. In this manner, two spin states of a single oxidant (Cpd I) can be disguised as two different oxidants. The calculations rule out the possibility that a second oxidant (the ferric peroxide, Cpd 0 species) interferes in the observed results of Jones et al. 相似文献
199.
Katleen Boussu Jérémie De Baerdemaeker Charles Dauwe Marc Weber Kelvin G Lynn Diederik Depla Steliana Aldea Ivo F J Vankelecom Carlo Vandecasteele Bart Van der Bruggen 《Chemphyschem》2007,8(3):370-379
This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly. 相似文献
200.
Carlos Cativiela Maria D. Diaz De Villegas Jos A. Mayoral Alberto Avenoza Miguel A. Roy 《Journal of heterocyclic chemistry》1988,25(3):851-855
3(5)-Carbomethoxy-4-hetarylpyrazoles 3 can be obtained by the aromatization of the corresponding cis-3-benzamido-3-carbomethoxy-4-hetaryl-Δ1-pyrazolines 2 obtained by 1,3-dipolar cycloaddition of diazo-methane with methyl Z-2-benzamido-3-hetarylpropenoates 1. An explanation, based on FMO theory, for the different reactivity of the dipolarophiles with diazomethane is given. 相似文献