全文获取类型
收费全文 | 3292篇 |
免费 | 850篇 |
国内免费 | 152篇 |
专业分类
化学 | 654篇 |
晶体学 | 55篇 |
力学 | 237篇 |
综合类 | 49篇 |
数学 | 468篇 |
物理学 | 2831篇 |
出版年
2024年 | 8篇 |
2023年 | 46篇 |
2022年 | 112篇 |
2021年 | 95篇 |
2020年 | 100篇 |
2019年 | 94篇 |
2018年 | 102篇 |
2017年 | 130篇 |
2016年 | 147篇 |
2015年 | 175篇 |
2014年 | 234篇 |
2013年 | 337篇 |
2012年 | 200篇 |
2011年 | 241篇 |
2010年 | 198篇 |
2009年 | 208篇 |
2008年 | 209篇 |
2007年 | 222篇 |
2006年 | 162篇 |
2005年 | 173篇 |
2004年 | 125篇 |
2003年 | 123篇 |
2002年 | 115篇 |
2001年 | 76篇 |
2000年 | 110篇 |
1999年 | 85篇 |
1998年 | 85篇 |
1997年 | 62篇 |
1996年 | 64篇 |
1995年 | 43篇 |
1994年 | 31篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有4294条查询结果,搜索用时 6 毫秒
991.
Dr. Kecheng Cao Dr. Stephen T. Skowron Dr. Craig T. Stoppiello Dr. Johannes Biskupek Prof. Dr. Andrei N. Khlobystov Prof. Dr. Ute Kaiser 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(51):23122-23127
Porous graphene has shown promise as a new generation of selective membrane for sieving atoms, ions and molecules. However, the atomistic mechanisms of permeation through defects in the graphenic lattice are still unclear and remain unobserved in action, at the atomic level. Here, the direct observation of palladium atoms from a nanoparticle passing through a defect in a single-walled carbon nanotube one-by-one has been achieved with atomic resolution in real time, revealing key stages of the atomic permeation. Bonding between the moving atom and dangling bonds around the orifice, immediately before and after passing through the subnano-pore, plays an important role in the process. Curvature of the graphenic lattice crucially defines the direction of permeation from concave to convex side due to a difference in metal-carbon bonding at the curved surfaces as confirmed by density functional theory calculations, demonstrating the potential of porous carbon nanotubes for atom sieving. 相似文献
992.
This work aimed to synthesize a new heterogeneous catalyst (SO3H@Fe3O4 magnetic nanoparticles) and the study of its catalytic behavior in synthesizing 3,3′-(arylmethylene)-bis-(4-hydroxycoumarin), bis-(indolyl)-methane, and 1,8-dioxo-octahydroxanthene derivatives. The characterization of obtained material has been performed by means of Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, vibrating sample magnetometer, and transmission electron microscopy. The main properties of this new methodology, compared to earlier ones, are the short times of reaction, mild reaction conditions, simple recovery of the catalyst by permanent magnetic field, excellent yields, and reusability of the catalyst for a minimum of six runs. 相似文献
993.
Jo Eun Hwang Sung Hee Kim Myong Soo Choi Sung Min Cho 《Molecular Crystals and Liquid Crystals》2020,705(1):141-149
AbstractA polyorganosiloxane thin film was deposited on an optically transparent poly(ethylene 2,6-naphthalate) (PEN) film using plasma-enhanced chemical vapor deposition (PECVD) at room temperature to improve the moisture barrier property of the PEN film. In the PECVD process, hexamethyldisiloxane (HMDSO) was used as the monomer. Argon or oxygen and their mixture gases were used as the plasma carrier gas. Poly(HMDSO) thin film was successfully deposited through plasma-induced radical polymerization reaction on the surface of PEN film. It was observed that the mixture ratio of argon-oxygen carrier gas significantly affected the surface and the moisture barrier properties of the resulting poly(HMDSO) film. Chemical structures of the poly(HMDSO) were confirmed using FT-IR analysis. Surface properties of the poly(HMDSO) thin film were investigated by water contact angle measurement and atomic force microscopy (AFM). Water vapor transmission rate (WVTR) value was obtained by an electrical calcium test (Ca test) at 85?°C and 85% relative humidity condition. It was confirmed that the poly(HMDSO) thin film exhibited excellent water vapor barrier capability. WVTR value of the PEN film coated with poly(HMDSO) deposited with a mixture of argon and oxygen (Ar: O2 = 2: 8) was 5.09?g/m2-day, which is much lower than 18.4?g/m2-day of a bare PEN film. 相似文献
994.
In the user-centric, cell-free, massive multi-input, multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system, a large number of deployed access points (APs) serve user equipment (UEs) simultaneously, using the same time–frequency resources, and the system is able to ensure fairness between each user; moreover, it is robust against fading caused by multi-path propagation. Existing studies assume that cell-free, massive MIMO is channel-hardened, the same as centralized massive MIMO, and these studies address power allocation and energy efficiency optimization based on the statistics information of each channel. In cell-free, massive MIMO systems, especially APs with only one antenna, the channel statistics information is not a complete substitute for the instantaneous channel state information (CSI) obtained via channel estimation. In this paper, we propose that energy efficiency is optimized by power allocation with instantaneous CSI in the user-centric, cell-free, massive MIMO-OFDM system, and we consider the effect of CSI exchanging between APs and the central processing unit. In addition, we design different resource block allocation schemes, so that user-centric, cell-free, massive MIMO-OFDM can support enhanced mobile broadband (eMBB) for high-speed communication and massive machine communication (mMTC) for massive device communication. The numerical results verify that the proposed energy efficiency optimization scheme, based on instantaneous CSI, outperforms the one with statistical information in both scenarios. 相似文献
995.
We investigate the effects of a bar on optical transmission through Z-shaped metallic slit arrays by using the finite-difference time domain (FDTD) method. A new hybrid Fabry-Perot (FP) surface plasmon polariton (SPP) mode emerges when changing the geometric parameters of the bar, and this mode can be viewed as a coupling between FP mode and SPP mode. In addition, an obvious dip appears in a featured area when the bar deviates from the central line, and a small displacement of the bar leads to tremendous change of the dip. These behaviors can be attributed to the phase resonance. In short, the structure is very sensitive to the metal bar. Furthermore, it combines photonic device miniaturization with sensitivity, which is useful for making optical switches. 相似文献
996.
Development of a new type of electric off-road vehicle powered by microwaves transmitted through air
Akira Oida Hiroshi Nakashima Juro Miyasaka Katsuaki Ohdoi Hiroshi Matsumoto Naoki Shinohara 《Journal of Terramechanics》2007,44(5):329-338
Needless to say, we are now facing a critical state in the global environment, i.e. global warming. We have to change our way of thinking and our economic systems from those dependent on fossil resources to those dependent on renewable energy resources, such as solar energy. In our field of research, electric vehicles are considered the best choice for reducing carbon dioxide emissions. A battery is not an adequate energy source for electric vehicles, because batteries quickly get depleted because of its low energy and power density. A fuel cell is a more favorable alternative to the battery; however, it has large mass and can only replace the internal combustion engine, but the power transmission mechanisms are still necessary. The new concept of an electric off-road vehicle proposed here is entirely different from those mentioned above. The vehicle has neither a combustion engine nor a battery but only electric motors. Energy to drive the motors is transmitted through air as microwaves at 2.45 GHz. This technology was developed at the Research Institute for Sustainable Humanosphere, Kyoto University, as a method for transmitting electricity from a large-scale solar power station (SPS) orbiting in space to the Earth. We have constructed some models of electric off-road vehicles and investigated their adoptability to microwave power transmission. In this paper, some experimental results on the use of microwave power transmission for powering the vehicles are presented, and some problems such as low energy transmission efficiency are also discussed. 相似文献
997.
We have used the laser vaporization method to obtain films of the ternary compound CuIn3Se5 and have studied the composition and structure of the films obtained. We have determined the energy and nature of the optical
transitions for the indicated compound from the transmission spectra in the region of the intrinsic absorption edge. We have
calculated the valence-band crystal-field (ΔCF) and spin-orbit (ΔSO) splitting energies according to Hopfield’s quasicubic model for the ternary compound CuIn3Se5.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 82–85, January–February, 2007. 相似文献
998.
999.
1000.