全文获取类型
收费全文 | 896篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 426篇 |
晶体学 | 14篇 |
力学 | 55篇 |
数学 | 165篇 |
物理学 | 281篇 |
出版年
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 51篇 |
2012年 | 48篇 |
2011年 | 48篇 |
2010年 | 25篇 |
2009年 | 34篇 |
2008年 | 39篇 |
2007年 | 46篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 26篇 |
2003年 | 35篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 12篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1968年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有941条查询结果,搜索用时 15 毫秒
931.
The simultaneous determination of Cu(2+), Cd(2+) and Pb(2+) is demonstrated at four modified gold electrodes using N-PLS calibration. Three of the electrodes were modified with the peptides Gly-Gly-His, gamma-Glu-Cys Gly and human angiotensin I which were covalently attached to thioctic acid self-assembled monolayers and the fourth electrode was modified with thioctic acid only. Voltammetry at the modified electrodes in the presence of the three metal ions revealed one peak due to the reduction of copper and another due to the overlapping peaks of cadmium and lead which made quantification using conventional methods difficult. N-PLS was used to calibrate and predict trace concentrations (100 nM to 10 microM) of mixtures of Cu(2+), Cd(2+) and Pb(2+). 相似文献
932.
Transcritical flow over a localized obstacle generates upstream and downstream nonlinear wavetrains. In the weakly nonlinear long-wave regime, this flow has been modeled with the forced Korteweg-de Vries (fKdV) equation, where numerical simulations and asymptotic solutions have demonstrated that the upstream and downstream nonlinear wavetrains have the structure of unsteady undular bores, connected by a locally steady solution over the obstacle. Further, it has been shown that when the obstacle is replaced by a step of semi-infinite length, it is found that a positive step generates only an upstream-propagating undular bore, and a negative step generates only a downstream-propagating undular bore. This result suggests that for flow over a hole, that is a step down followed by a step up, the two wavetrains generated will interact over the hole. In this paper, this situation is explored by numerical simulations of the fKdV equation. 相似文献
933.
Gregory M. Constantine John Bartels Carson C. Chow Gilles Clermont Yoram Vodovotz 《Computational Optimization and Applications》2009,42(1):155-171
The immune system is modeled by way of a system of ordinary differential equations involving a large number of parameters,
such as growth rates and initial conditions. Key to successful implementation of the model is the estimation of such parameters
from available data. A parameter search algorithm based on linear codes is developed having as aim the identification of different
regimes of behaviour of the model, the estimation of parameters in a high dimensional space, and the model calibration to
data.
This work was funded under the NIH grant GM67240. 相似文献
934.
Chak-On Chow 《Journal of Combinatorial Theory, Series A》2009,116(4):816-830
We define a type B derangement polynomial by q-counting derangements by the number of excedances in the hyperoctahedral group Bn. Properties of the derangement polynomial, including the recurrence relation, generating function, real-rootedness, reciprocity and a unimodal decomposition arising from a symmetric function identity, are studied. The results presented generalize and unify earlier ones due to Brenti, Stanley, Stembridge and Zhang. 相似文献
935.
C.W. Chow L.G. Yang C.H. Yeh C.B. Huang J.W. Shi C.L. Pan 《Optics Communications》2012,285(21-22):4307-4311
Millimeter-wave (mm-wave) operated in W-band (75 GHz–0.11 THz) is of particular interests, since this frequency band can carry signals at much higher data rates. We demonstrate a 10 Gb/s optical carrier-distributed network with the wireless communication system. The mm-wave signal at carrier frequency of 0.1 THz is generated by a high speed near-ballistic uni-traveling carrier photodiode (NBUTC-PD) based transmitter (Tx), which is optically excited by optical short pulses. The optical pulse source is produced from a self-developed photonic mm-wave waveform generator (PMWG), which allows spectral line-by-line pulse shaping. Hence these optical pulses have high tolerance to fiber chromatic dispersion. The W-band 10 Gb/s wireless data is transmitted and received via a pair of horn antennas. The received 10 Gb/s data is envelope-detected and then used to drive an optical modulator at the remote antenna unit (RAU) to produce the upstream signal sending back to the central office (CO). 20 km single mode fiber (SMF) error free transmission is achieved. Analysis about the optimum repetition rate of the optical pulse source and the transmission performance of the upstream signal are also performed and discussed. 相似文献
936.
In this demonstration, we propose and experimentally investigate a stable wavelength-tuning laser configuration by using self-seeded
Fabry-Perot laser diode (FP-LD) and external-injected reflective semi-conductor optical amplifier (RSOA). Here, this proposed
laser can be tuned in the wavelength range of 1534.05 to 1553.00 nm with a 1.1 nm tuning-step. And the output powers and side-mode
suppression ratios (SMSRs) are measured at −5.3 to 4.6 dBm and 31.2 to 50.1 dB/0.05 nm, respectively. And, the proposed laser
also can be directly modulated at 2.5 Gb/s on-off keying (OOK) modulation format and propagates 75 km single-mode fiber (SMF)
with no optical amplifier and dispersion compensation. 相似文献
937.
In the investigation, we propose and demonstrate a Sagnac ring based fiber laser structure using a semiconductor optical amplifier (SOA) to act as a gain medium with short to long fiber cavity lengths for wavelength lasing and tuning. Here, ten fiber Bragg gratings (FBGs) with different reflected Bragg wave-lengths are used serving as the reflected element in the proposed laser configuration for wavelength lasing and remote sensing simultaneously. Furthermore, the different cavity fiber lengths of a few ten m to 25 km, which are used in the proposed laser scheme, has been analyzed and discussed. 相似文献
938.
939.
H. J. Zhang L. Zhu X. L. Meng Z. H. Yang C. Q. Wang W. T. Yu Y. T. Chow M. K. Lu 《Crystal Research and Technology》1999,34(8):1011-1016
Nd:YVO4 crystal has been grown by Czochralski method. The data of thermal expansion and specific heat have been measured. The thermal expansion coefficients along a- and c-axis are a1 = 2.2 x 10-6 /K, and a3 = 8.4 x 10-6 /K respectively. The specific heat is 24.6 cal/mol x K at 330 K. The large anisotropy along c- and a-axis of thermal expansion coefficients is explained by the structure of YVO4 crystal. 921 mW output laser at 1.06 mikrom has been obtained with a 3 mm x 3 mm x 1mm crystal sample when pumped by 1840 mW cw laser diode, and the slope efficiency is 55.5%. 相似文献
940.
Examples of NMR imaging used to study the evolution of microstructure and flow velocities in sheared, highly filled suspensions are described. Fast NMR imaging methods were used to freeze the motion in a falling-ball experiment, allowing us to monitor the local concentrations of suspended particles and ball position during the course of the experiment The migration of particles induced by shear and concentration gradients was followed in a Couette cell. Flow imaging methods were developed and applied to a Newtonian fluid and a non-Newtonian suspension flowing in an axisymmetric pipe contraction. 相似文献