全文获取类型
收费全文 | 248714篇 |
免费 | 18818篇 |
国内免费 | 12318篇 |
专业分类
化学 | 147236篇 |
晶体学 | 3421篇 |
力学 | 12434篇 |
综合类 | 673篇 |
数学 | 28496篇 |
物理学 | 87590篇 |
出版年
2023年 | 2287篇 |
2022年 | 4149篇 |
2021年 | 4319篇 |
2020年 | 4821篇 |
2019年 | 4602篇 |
2018年 | 5424篇 |
2017年 | 5097篇 |
2016年 | 6849篇 |
2015年 | 6293篇 |
2014年 | 7714篇 |
2013年 | 13172篇 |
2012年 | 13790篇 |
2011年 | 14711篇 |
2010年 | 9961篇 |
2009年 | 9615篇 |
2008年 | 11091篇 |
2007年 | 10424篇 |
2006年 | 10101篇 |
2005年 | 11844篇 |
2004年 | 10236篇 |
2003年 | 7864篇 |
2002年 | 6062篇 |
2001年 | 6323篇 |
2000年 | 4967篇 |
1999年 | 4579篇 |
1998年 | 3818篇 |
1997年 | 3623篇 |
1996年 | 3542篇 |
1995年 | 3293篇 |
1994年 | 2925篇 |
1993年 | 2656篇 |
1992年 | 2778篇 |
1991年 | 2620篇 |
1990年 | 2425篇 |
1989年 | 2259篇 |
1988年 | 2138篇 |
1987年 | 2069篇 |
1986年 | 1975篇 |
1985年 | 2460篇 |
1984年 | 2487篇 |
1983年 | 2066篇 |
1982年 | 2349篇 |
1981年 | 2124篇 |
1980年 | 2142篇 |
1979年 | 2095篇 |
1978年 | 2223篇 |
1977年 | 2120篇 |
1976年 | 2157篇 |
1975年 | 2094篇 |
1973年 | 2129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
The Al2O3−CdSe interface of a thin-film transistor is investigated in the frequency range 30 Hz-30 kHz under weak depletion and accumulation.
The surface states are, most likely, located in the insulator Al2O3 with a concentration varying from 4·1018 to 1019 cm−3 eV−1. The surface states have a negligible influence on the thin-film transistor operation. 相似文献
182.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
183.
184.
A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans. 总被引:12,自引:0,他引:12
L T Cohen F W Rickards G M Clark 《The Journal of the Acoustical Society of America》1991,90(5):2467-2479
Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation. 相似文献
185.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems. 相似文献
186.
187.
采用顶部籽晶提拉法(TSSG)生长出Yb:KY(WO4)2(Yb:KYW)激光晶体.对预烧后的原料及晶体进行了XRD分析,结果表明,分别在920℃和600℃预烧8h后的熔质和助熔剂基本上形成一相,抑止了实验中的挥发问题;所生长的晶体为β-Yb:KYW,计算其晶格常数为a=1.063nm,b=1.034nm,c=0.755nm,β=130.75°.测得不同厚度样品的吸收光谱,结果表明样品在933nm和981nm有较强的吸收峰,计算出主峰981nm的吸收截面σ关键词:
Yb:KYW
TSSG法
晶体结构
光谱参数 相似文献
188.
针对VO2薄膜在微测辐射热计上的应用,采用射频反应溅射法,在室温下制备氧化钒薄膜;研究了氧分压对薄膜沉积速率、电学性质及成分的影响.通过调节氧分压,先获得成分接近VO2的非晶化薄膜,再在400℃空气中氧化退火,便可制得高电阻温度系数,低电阻率的VO2薄膜,电阻温度系数约为-4%/℃,薄膜方块电阻为R□为100—300kΩ;薄膜在室温下沉积,400℃下退火的制备方法与微机电加工(micro electromechanic
关键词:
二氧化钒
电阻温度系数
氧分压
射频反应溅射法 相似文献
189.
A numerical procedure, with an exact strain-displacement relationship of twisted and curved cylindrical panels having variable thickness derived by considering the Green strain tensor on general shell theory, is presented using the principle of virtual work and the Rayleigh-Ritz method with algebraic polynomials as in-plane and transverse displacement functions. The accuracy and applicability of the procedure are verified by comparing the present results with previous experimental and theoretical results for several panels. The effects of variation ratio of thickness in chordwise and lengthwise directions, twist, and curvature both in two directions aforementioned on vibrations of cylindrical panels are studied in detail, and typical vibration mode shapes are plotted to demonstrate the effects. 相似文献
190.
Li Boyu 《数学学报(英文版)》1991,7(3):247-251
H. Crapo raised in 1982 the following problem: IfP is a complete lattice, is Retr (P) a complete lattice? here Retr (P) denotes the set of all retraction operators onP with the pointwise order, that is,f≤g in Retr (P) ifff(x)≤g(x) for everyx inP. An affirmative answer will be given in the present paper. 相似文献