全文获取类型
收费全文 | 27053篇 |
免费 | 988篇 |
国内免费 | 157篇 |
专业分类
化学 | 18211篇 |
晶体学 | 255篇 |
力学 | 926篇 |
综合类 | 1篇 |
数学 | 2346篇 |
物理学 | 6459篇 |
出版年
2023年 | 154篇 |
2022年 | 410篇 |
2021年 | 488篇 |
2020年 | 433篇 |
2019年 | 448篇 |
2018年 | 333篇 |
2017年 | 317篇 |
2016年 | 727篇 |
2015年 | 631篇 |
2014年 | 793篇 |
2013年 | 1489篇 |
2012年 | 1948篇 |
2011年 | 2135篇 |
2010年 | 1295篇 |
2009年 | 1143篇 |
2008年 | 1741篇 |
2007年 | 1641篇 |
2006年 | 1532篇 |
2005年 | 1428篇 |
2004年 | 1262篇 |
2003年 | 982篇 |
2002年 | 967篇 |
2001年 | 672篇 |
2000年 | 575篇 |
1999年 | 338篇 |
1998年 | 252篇 |
1997年 | 293篇 |
1996年 | 334篇 |
1995年 | 257篇 |
1994年 | 274篇 |
1993年 | 276篇 |
1992年 | 264篇 |
1991年 | 204篇 |
1990年 | 154篇 |
1989年 | 139篇 |
1988年 | 140篇 |
1987年 | 118篇 |
1986年 | 95篇 |
1985年 | 168篇 |
1984年 | 112篇 |
1983年 | 97篇 |
1982年 | 122篇 |
1981年 | 88篇 |
1980年 | 79篇 |
1978年 | 80篇 |
1977年 | 85篇 |
1976年 | 94篇 |
1975年 | 101篇 |
1974年 | 79篇 |
1973年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Structure and electrical transport properties of bismuth thin films prepared by RF magnetron sputtering 总被引:1,自引:0,他引:1
Bismuth thin films were prepared on glass substrates with RF magnetron sputtering and the effects of deposition temperature on surface morphology and their electrical transport properties were investigated. Grain growth of bismuth and the coalescence of grains were observed above 393 K with field emission secondary electron microscopy. Continuous thin films could not be obtained above 448 K because of the segregation of grains. Hall effect measurements showed that substrate heating yields the decrease of carrier density and the increase of mobility in exponential ways until 403 K. Resistivity of sputter deposited bismuth films has its minimum (about 0.7 × 10−3 Ω cm) in range of 403-433 K. Annealing of bismuth films deposited at room temperature was carried out in a radiation furnace with flowing hydrogen gas. The change of resistivity was not significant due to the cancellation of the decrease of carrier density and the increase of mobility. However, the abrupt change of electrical properties of film annealed above 523 K was observed, which is caused by the oxidation of bismuth layer. 相似文献
152.
153.
Chi-So Lee 《中国化学会会志》1987,34(3):207-210
A differential pulse polarographic method for the determination of nitrate ion has been developed. With 0.5 M CaCl2 as supporting electrolyte, NO?3 is reduced to give a peak with E1/2=–1.836 Volt vs. the Ag/AgCl electrode. The differential pulse polarographic peak height is proportional to the nitrate concentration from 20 to 60 ppm. The detection limit for nitrate is 2 ppm in pure aqueous solution. In the determination of 40 ppm nitrate a relative precision (relative standard deviation) of less than 2% was achieved. Nitrite interferes seriously and should be absent if accurate results are required. The method has been applied to the determination of nitrate in Ammonium Uranyl Tricarbonate (AUT) Solution, results obtained by this method are compared to those obtained by ion chromatography. The agreement between the two sets of results suggests that the DPP method can be used with a fair degree of confidence. 相似文献
154.
Anisha Gokarna Yong Hwan Kim Yong-Hoon Cho Min Su Lee In Cheol Kang Hyun Kyu Park Min Gon Kim Bong Hyun Chung 《Optical Review》2006,13(4):288-291
We demonstrate the fluorescence mapping of protein microarrays by the technique of scanning near-field optical microscopy
(SNOM) and confocal microscopy. Micron sized spots (300 μm) of human Immunoglobulin G (hIgG) protein with and without a Cy3
dye labeling have been fabricated on glass substrates by an immobilization method which makes use of calixcrown derivatives
termed Prolinker. We have also tried to probe into the well-known “doughnut effect” observed in fluorescence images of proteins
using the SNOM technique. The topographic and fluorescence SNOM images revealed that the number of proteins at the boundary
of the spot were more than at the center in the case of the microarray spot which showed brighter luminescence at the edge
than at the center in the confocal image. 相似文献
155.
Using SF6 glass plates as intracavity Kerr lenses and double-prism pairs for dispersion compensation, we achieve tunable femtosecond passive mode locking in rhodamine 590 (R6G) and 4-dicyanomethylene-2-methyl-16-p-dimethylaminostyryl-4H-pyran (DCM) dye lasers. The R6G laser produces transform limited 240–500 fs pulses between 577 and 606 nm, and the DCM laser produces 150 fs transform-limited pulses between 650 and 671 nm. We use dilute intracavity saturable-absorber jets to make the mode locking self-starting. Characteristics of the pulses and the stability regions of the lasers agree with general theories of passive mode locking. 相似文献
156.
M.-K. Lee Y.-C. Tseng C.-H. Chu 《Applied Physics A: Materials Science & Processing》1998,67(5):541-543
2 tungsten lamp at 1.83 mA excited by a 0.85-mW 675-nm laser diode. We also demonstrate that the dark current could be greatly
reduced through rapid thermal oxidation and rapid thermal annealing.
Received: 4 August 1997/Accepted: 28 May 1998 相似文献
157.
J. Telser H. -I. Lee E. T. Smith H. Huang P. Brereton M. W. W. Adams R. C. Conover M. K. Johnson B. M. Hoffman 《Applied magnetic resonance》1998,14(2-3):305-321
The hyperthermophilic archaeonPyrococcus furiosus contains a four-Fe ferredoxin (Pf- Fd) that differs from most other 4Fe-Fd’s in that its [Fe4S4] cluster is anchored to protein by only three cysteinyl residues.Pf- Fd also is of interest because in its reduced form, [Fe4S4]+, the cluster exhibits bothS = 1/2 andS = 3/2 spin states. Addition of excess cyanide ion converts the cluster exclusively to anS = 1/2 state (g1 = 2.09, g2 = 1.95, g3 = 1.92), however dialysis restores the EPR signal of native reduced protein indicating that the cluster is not irreversibly altered by cyanide. Both the native protein and protein in the presence of excess cyanide ion (Pf- Fd 4Fe-CN) were investigated here using the techniques of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. In particular,Pf- Fd 4Fe-CN was investigated using13CN? and C15N? ligands.13C and15N ENDOR indicated that a single cyanide ion bound directly, with the cluster showing an unusually small contact interaction (aiso(13C)~ ?3 MHz, aiso(15N) ~ 0). This is in contrast to cyanide bound to monomeric low-spin Fe(III)-containing proteins such as transferrin and myoglobin, for which the13C hyperfine coupling has a large isotropic component (aiso(13C) ≈ ?30 MHz). This small contact interaction is not due to low spin density of Fe, as57Fe ENDOR of the singly and triply labeledPf- Fd 4FeCN isotopologs, [57FeFe3S4]+ and [Fe57Fe3S4]+, show hyperfine coupling characteristic for [Fe4S4]+ clusters, particularly for the Fe to which cyanide binds. Thus, the low spin density on13C is not due to low spin density on the Fe ion to which it binds. Further theoretical work is needed to explain the contrast between the strong electronic effect of cyanide ion binding with the low spin density on the ligand. 相似文献
158.
159.
160.