全文获取类型
收费全文 | 358457篇 |
免费 | 2951篇 |
国内免费 | 1085篇 |
专业分类
化学 | 191595篇 |
晶体学 | 5718篇 |
力学 | 14699篇 |
综合类 | 9篇 |
数学 | 41343篇 |
物理学 | 109129篇 |
出版年
2020年 | 3118篇 |
2019年 | 3532篇 |
2018年 | 4794篇 |
2017年 | 4782篇 |
2016年 | 6828篇 |
2015年 | 3967篇 |
2014年 | 6434篇 |
2013年 | 15851篇 |
2012年 | 11764篇 |
2011年 | 14165篇 |
2010年 | 10276篇 |
2009年 | 10067篇 |
2008年 | 13523篇 |
2007年 | 13497篇 |
2006年 | 12617篇 |
2005年 | 11391篇 |
2004年 | 10325篇 |
2003年 | 9391篇 |
2002年 | 9107篇 |
2001年 | 10137篇 |
2000年 | 7827篇 |
1999年 | 5959篇 |
1998年 | 5078篇 |
1997年 | 5028篇 |
1996年 | 4711篇 |
1995年 | 4151篇 |
1994年 | 4205篇 |
1993年 | 4123篇 |
1992年 | 4499篇 |
1991年 | 4530篇 |
1990年 | 4410篇 |
1989年 | 4332篇 |
1988年 | 4249篇 |
1987年 | 4249篇 |
1986年 | 4020篇 |
1985年 | 5266篇 |
1984年 | 5483篇 |
1983年 | 4616篇 |
1982年 | 4961篇 |
1981年 | 4692篇 |
1980年 | 4486篇 |
1979年 | 4804篇 |
1978年 | 4975篇 |
1977年 | 4896篇 |
1976年 | 4957篇 |
1975年 | 4724篇 |
1974年 | 4653篇 |
1973年 | 4977篇 |
1972年 | 3291篇 |
1971年 | 2812篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
91.
The adsorption of hydrogen on a clean Cu10%/Ni90% (110) alloy single crystal was studied using flash desorption spectroscopy (FDS), Auger electron spectroscopy (AES), and work function measurements. Surface compositions were varied from 100% Ni to 35% Ni. The hydrogen chemisorption on a-surface of 100% nickel revealed strong attractive interactions between the hydrogen atoms in accordance with previous work on Ni(100). Three desorption states (β1, β2 and α) appeared in the desorption spectra. The highest temperature (α) state was occupied only after the initial population of the β2-state. As the amount of copper was increased in the nickel substrate, desorption from the higher energy binding α-state was reduced, indicating a decrease in the attractive interactions among hydrogen atoms. The hydrogen coverage at saturation was not affected by the addition of copper to the nickel substrate until the copper concentration was greater than 25% at which a sharp reduction in saturation coverage occurred. This phenomenon was apparently due to the adsorption of hydrogen on Ni atoms followed by occupation of NiNi and CuNi bridged adsorption sites, while occupation of CuCu sites was restricted due to an energy barrier to migration. 相似文献
92.
E. V. Morozov 《Journal of Mathematical Sciences》1991,57(4):3302-3305
Translated fromProblemy Ustoichivosti Stokhasticheskikh Modelei. Trudy Seminara, 1988, pp. 115–120. 相似文献
93.
94.
95.
C. Ghezzi E. Gombia R. Mosca M. Pillan 《Applied Physics A: Materials Science & Processing》1989,48(5):457-463
Capacitance DLTS measurements have been performed in VPE GaAs MESFETs prepared on Bridgman Cr-doped and LEC undoped semi-insulating substrates. A band of electron traps not intrinsically related to the VPE growth process and accumulating near the metal (gate) — semiconductor interface was detected in all the samples. Deeper regions into the channel were free from any detectable trap. Near pinch-off conditions, a positive capacitance signal was found to dominate the DLTS spectra only in the case of samples prepared on Cr-doped substrates. The hypothesis of this positive transient being related to changes in the occupation of surface states in the ungated surface access regions has been checked by comparing experimental and calculated dependencies of the signal amplitude on reverse gate voltage. Unexplained discrepancies, together with the absence of positive signal in MESFETs prepared on LEC undoped substrates, suggest the possibility of hole emission from hole traps within the bulk of the device. 相似文献
96.
The singular-perturbation expansion of the plasma cold-fluid equations for crossed fields in a planar geometry is presented. The general expansion is carried out to third order. Various instabilities that occur in the first, second, and third orders are discussed. 相似文献
97.
B. R. Harvey M. B. Lovett S. J. Boggis 《Journal of Radioanalytical and Nuclear Chemistry》1987,115(2):357-368
Selected experiences in the control of contamination and the threat it poses to the quality of analytical date are discussed in the context of the whole analytical process from collection of marine environmental samples, through handling and radiochemical separation, to the final interpretation of results. Examples include a demonstration of the contamination introduced during sediment core sectioning, contamination of sea water by a ship's pumping system, and the effect of filtration on the apparent partitioning of radionuclides between solid and liquid phases of sea water. 相似文献
98.
Periodic sound-pressure time functions with frequency components below 50 Hz were used to measure within their period (a) the temporal course of masking, called a masking-period pattern (MPP), and (b) the temporal course of suppression of delayed evoked otoacoustic emissions, called a suppression-period pattern (SPP). Three different time functions were used: an alternating Gaussian impulse, its first integral, and its second integral. In each case, the course of the SPP is a mirror image of that of the MPP: Small masking corresponds to small suppression, while strong masking coincides with almost total suppression. Since otoacoustic emissions are assumed to have their origin in the inner ear, it can be argued that simultaneous masking, an effect including central processing, is very strongly based on peripheral processes located in the cochlea. Both MPP and SPP are closely related to the second derivative of the sound-pressure time function. 相似文献
99.
100.
The acoustic field inside a shell excited by a spatially inhomogeneous harmonic pressure field is studied. The shell is assumed
to have a finite length, a set of orthogonal stiffening ribs, two ends bounding the acoustic volume, and a sound-insulating
structure, which includes layers of sound-insulating material, resonant elements, and an interior panel. The shell is considered
to be orthotropic with boundary conditions corresponding to a free support. For the acoustic field in the closed volume, analytical
expressions are derived with allowance for the elastoacoustic interaction of the shell with the sound-insulating layers and
with the medium both inside the shell (with arbitrary impedance values at the ends) and outside it. These expressions are
used to investigate the effect of different types of resonant systems on the sound field inside the shell. 相似文献