全文获取类型
收费全文 | 442070篇 |
免费 | 5072篇 |
国内免费 | 1231篇 |
专业分类
化学 | 237742篇 |
晶体学 | 6535篇 |
力学 | 19014篇 |
综合类 | 13篇 |
数学 | 50985篇 |
物理学 | 134084篇 |
出版年
2021年 | 3842篇 |
2020年 | 4303篇 |
2019年 | 4627篇 |
2018年 | 6009篇 |
2017年 | 5871篇 |
2016年 | 9071篇 |
2015年 | 5749篇 |
2014年 | 8743篇 |
2013年 | 20650篇 |
2012年 | 16051篇 |
2011年 | 19724篇 |
2010年 | 13735篇 |
2009年 | 13553篇 |
2008年 | 18033篇 |
2007年 | 17941篇 |
2006年 | 16610篇 |
2005年 | 14878篇 |
2004年 | 13775篇 |
2003年 | 12120篇 |
2002年 | 11930篇 |
2001年 | 13502篇 |
2000年 | 10147篇 |
1999年 | 7974篇 |
1998年 | 6605篇 |
1997年 | 6349篇 |
1996年 | 6134篇 |
1995年 | 5512篇 |
1994年 | 5429篇 |
1993年 | 5240篇 |
1992年 | 5864篇 |
1991年 | 5946篇 |
1990年 | 5682篇 |
1989年 | 5496篇 |
1988年 | 5504篇 |
1987年 | 5394篇 |
1986年 | 5099篇 |
1985年 | 6603篇 |
1984年 | 6726篇 |
1983年 | 5314篇 |
1982年 | 5426篇 |
1981年 | 5399篇 |
1980年 | 4997篇 |
1979年 | 5382篇 |
1978年 | 5519篇 |
1977年 | 5411篇 |
1976年 | 5364篇 |
1975年 | 4944篇 |
1974年 | 4908篇 |
1973年 | 4902篇 |
1972年 | 3459篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Total-reflection X-ray fluorescence spectrometry has been compared with Instrumental Neutron Activation Analysis in order to test its potential application to the study of archaeological ceramics in the archaeometric field. Two direct solid non-chemical sample preparation procedures have been checked: solid sedimentation and solid chemical homogenization. For sedimentation procedure, total-reflection X-ray fluorescence allows the analysis of the elemental composition with respect to the size fraction but not the average evaluation of the composition. For solid chemical homogenization procedure, total-reflection X-ray fluorescence provides precise (from 0.8% to 27% of coefficient of variation) and accurate results (from 91% to 110% of recovery) for 15 elements (Cr, Hf, Ni, Rb, Al, Ba, Ca, K, Mn, Ti, V, Cu, Ga, Y and Fe) with an easy sample preparation process of the solid clay and without previous chemical treatment. The influence of the particle sizes has been checked by total-reflection X-ray fluorescence sample angle scans and anomalous behaviors have been found for three additional detected elements: As, Sr and Zn, which can be attributed to interference effects of the mineral grain sizes of their associated chemical phases in the total-reflection X-ray fluorescence interference region. The solid chemical homogenization procedure produces data useful for archaeological interpretation, which is briefly illustrated by a case-study. Finally, the decantation procedure data can be also useful for size chemical speciation and, consequently, for alternative environmental total-reflection X-ray fluorescence applications. 相似文献
952.
M A Aguilar-Mendez E San Martin-Martinez J E Morales A Cruz-Orea M R Jaime-Fonseca 《Analytical sciences》2007,23(4):457-461
Water vapor diffusion coefficient (WVDC) and thermal diffusivity (alpha) were determined in gelatin-starch films through photothermal techniques. The effect of different variables in the elaboration of these films, such as starch and glycerol concentrations and pH, were evaluated through the response surface methodology. The results indicated that an increase in the glycerol concentration and pH favored the WVDC of the films. On the other hand, alpha was influenced principally by the starch content and pH of the film-forming solution. The minimum alpha value was 4.5 x 10(-4) cm2/s, which is compared with alpha values reported for commercial synthetic polymers. 相似文献
953.
954.
955.
M. A. Sakhbetdinov P. F. Kartsev 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(8):1115-1117
Schemes and calculated characteristics of effective logic elements with two inputs for classical ground-state computations are reported. These elements have a high threshold (0.48) and perform a desired logical operation in a wide range of input signals. 相似文献
956.
957.
E.R. Berger M. Diehl B. Pire 《The European Physical Journal C - Particles and Fields》2002,23(4):675-689
We investigate the exclusive photoproduction of a heavy timelike photon which decays into a lepton pair, . This can be seen as the analog of deeply virtual Compton scattering, and we argue that the two processes are complementary
for studying generalized parton distributions in the nucleon. In an unpolarized experiment the angular distribution of the
leptons readily provides access to the real part of the Compton amplitude. We estimate the possible size of this effect in
kinematics where the Compton process should be dominated by quark exchange.
Received: 9 October 2001 / Published online: 5 April 2002 相似文献
958.
Sarah E. Reybuck Robert M. Waymouth 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3323-3331
Ethylene/1‐hexene copolymerizations with disiloxane‐bridged metallocenes, rac‐ and meso‐1,1,3,3‐tetramethyldisiloxanediyl‐bis(1‐indenyl)zirconium dichloride (rac‐ 1 , meso‐ 1 ) activated by modified methylaluminoxane were performed to investigate the influence of conformational dynamics on comonomer selectivity. Although 1H NOESY (nuclear Overhauser and exchange spectroscopy) analysis indicated that the most stable conformation for the meso isomer in solution was that in which both indenes project over the metal coordination site, this isomer showed higher 1‐hexene selectivity in copolymerization (re = 140 ± 30, rh = 0.024 ± 0.004) than the rac isomer with only one indene over the coordination site (re = 240 ± 20, rh = 0.005 ± 0.001). The meso isomer showed high 1‐hexene selectivity, a high product of reactivity ratios (rerh = 3.3 ± 0.5) and produced copolymers that could be separated into fractions with different ethylene content suggesting that the active species exhibited multisite behavior and populated conformations with different comonomer selectivities during the copolymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3323–3331, 2004 相似文献
959.
960.
Hyperfine Interactions - The YFe4Al8 and ErFe4Al8 intermetallics were studied by57Fe Mössbauer spectroscopy between 2 K and room temperature. The spectra are consistent with iron occupying 8f... 相似文献