全文获取类型
收费全文 | 73332篇 |
免费 | 1304篇 |
国内免费 | 344篇 |
专业分类
化学 | 37184篇 |
晶体学 | 1251篇 |
力学 | 3661篇 |
综合类 | 9篇 |
数学 | 5762篇 |
物理学 | 27113篇 |
出版年
2022年 | 968篇 |
2021年 | 900篇 |
2020年 | 909篇 |
2019年 | 940篇 |
2018年 | 1055篇 |
2017年 | 953篇 |
2016年 | 1544篇 |
2015年 | 1103篇 |
2014年 | 1724篇 |
2013年 | 3727篇 |
2012年 | 3424篇 |
2011年 | 4141篇 |
2010年 | 2868篇 |
2009年 | 2751篇 |
2008年 | 3445篇 |
2007年 | 3294篇 |
2006年 | 2997篇 |
2005年 | 2656篇 |
2004年 | 2354篇 |
2003年 | 2058篇 |
2002年 | 1892篇 |
2001年 | 3156篇 |
2000年 | 2275篇 |
1999年 | 1652篇 |
1998年 | 1151篇 |
1997年 | 1154篇 |
1996年 | 975篇 |
1995年 | 854篇 |
1994年 | 768篇 |
1993年 | 712篇 |
1992年 | 1046篇 |
1991年 | 1018篇 |
1990年 | 917篇 |
1989年 | 816篇 |
1988年 | 780篇 |
1987年 | 838篇 |
1986年 | 696篇 |
1985年 | 944篇 |
1984年 | 887篇 |
1983年 | 620篇 |
1982年 | 609篇 |
1981年 | 570篇 |
1980年 | 541篇 |
1979年 | 682篇 |
1978年 | 698篇 |
1977年 | 712篇 |
1976年 | 616篇 |
1975年 | 515篇 |
1974年 | 538篇 |
1973年 | 474篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
K. Suzuki S. Miyashita K. Takashina Y. Hirayama 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):232
We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer-νnet discontinuous. Under tilted magnetic fields, these Rxx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings. 相似文献
202.
G. M. Ter-Akopian A. V. Daniel A. S. Fomichev G. S. Popeko A. M. Rodin Yu. Ts. Oganessian J. H. Hamilton A. V. Ramayya J. Kormicki J. K. Hwang D. Fong P. Gore J. D. Cole M. Jandel J. Kliman L. Krupa J. O. Rasmussen I. Y. Lee A. O. Macchiavelli P. Fallon M. A. Stoyer R. Donangelo S. -C. Wu W. Greiner 《Physics of Atomic Nuclei》2004,67(10):1860-1865
Ternary fission of 252Cf was studied at Gammasphere using eight ΔE×E particle telescopes. Helium, beryllium, boron, and carbon light charged particles (LCPs) emitted with kinetic energy more than 9, 21, 26, and 32 MeV, respectively, were identified. The 3368-keV γ transition from the first 2+ excited state in 10Be was found and the population probability ratio N(2+)/N(0+) = 0.160 ± 0.025 was estimated. No evidence was found for 3368-keV γ rays emitted from a triple molecular state. For the first time, charge distributions are obtained for ternary fission fragments emitted with helium, beryllium, and carbon LCPs. 相似文献
203.
204.
We propose a minimum mean absolute error linear interpolator (MMAELI), based on theL
1 approach. A linear functional of the observed time series due to non-normal innovations is derived. The solution equation
for the coefficients of this linear functional is established in terms of the innovation series. It is found that information
implied in the innovation series is useful for the interpolation of missing values. The MMAELIs of the AR(1) model with innovations
following mixed normal andt distributions are studied in detail. The MMAELI also approximates the minimum mean squared error linear interpolator (MMSELI)
well in mean squared error but outperforms the MMSELI in mean absolute error. An application to a real series is presented.
Extensions to the general ARMA model and other time series models are discussed.
This research was supported by a CityU Research Grant and Natural Science Foundation of China. 相似文献
205.
Y. Gu Igor L. Kuskovsky R.D. Robinson G.F. Neumark S.P. Guo M.C. Tamargo 《Solid State Communications》2005,134(10):677-681
The composition and size of optically active CdxZn1−xSe/ZnSe quantum dots are estimated with a previously developed method. The results are then compared with those obtained for CdxZn1−xSe/Zn0.97Be0.03Se QDs. We show that introducing Be into the barrier material enhances both Cd composition and quantum size effect of optically active quantum dots. 相似文献
206.
207.
Artificial intelligence techniques involving neural networks became vital modeling tools where model dynamics are difficult to track with conventional techniques. The paper make use of the feed forward neural networks (FFNN) to model the charged multiplicity distribution of K–P interactions at high energies. The FFNN was trained using experimental data for the multiplicity distributions at different lab momenta. Results of the FFNN model were compared to that generated using the parton two fireball model and the experimental data. The proposed FFNN model results showed good fitting to the experimental data. The neural network model performance was also tested at non-trained space and was found to be in good agreement with the experimental data. 相似文献
208.
An age-dependent branching process where disasters occur as a renewal process leading to annihilation or survival ofall the cells, is considered. For such a process, the total mean sojourn time of all the cells in the system is analysed using the regeneration point technique. The mean number of cells which die in timet and its asymptotic behaviour are discussed. When the disasters arrival as a Poisson process and the lifetime of the cells follows exponential distribution, elegant inter-relationships are found among the means of (i) the total number of cells which die in timet (ii) the total sojourn time of all cells in the system upto timet and (iii) the number of living cells at timet. Some of the existing results are deduced as special cases for related processes. 相似文献
209.
The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index,A
P ≥ 20 and the range of horizontal component of the Earth’s magnetic fieldH such that 250γ <H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data
(SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum
solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot
numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of
disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing
a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance ofH
α
, X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e.,
SF during the period 1978-93.H
α
, X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. NoH
α
, X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S,
the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number
of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares,
type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated
with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and
maximum activity lies between 58 and 118 h causing GMSs at the Earth. 相似文献
210.
Cellular neural network to detect spurious vectors in PIV data 总被引:2,自引:0,他引:2