全文获取类型
收费全文 | 6452篇 |
免费 | 1084篇 |
国内免费 | 729篇 |
专业分类
化学 | 4503篇 |
晶体学 | 73篇 |
力学 | 387篇 |
综合类 | 38篇 |
数学 | 775篇 |
物理学 | 2489篇 |
出版年
2024年 | 10篇 |
2023年 | 130篇 |
2022年 | 136篇 |
2021年 | 197篇 |
2020年 | 238篇 |
2019年 | 264篇 |
2018年 | 213篇 |
2017年 | 198篇 |
2016年 | 298篇 |
2015年 | 316篇 |
2014年 | 351篇 |
2013年 | 424篇 |
2012年 | 567篇 |
2011年 | 630篇 |
2010年 | 391篇 |
2009年 | 337篇 |
2008年 | 397篇 |
2007年 | 370篇 |
2006年 | 372篇 |
2005年 | 290篇 |
2004年 | 227篇 |
2003年 | 210篇 |
2002年 | 150篇 |
2001年 | 150篇 |
2000年 | 148篇 |
1999年 | 176篇 |
1998年 | 143篇 |
1997年 | 127篇 |
1996年 | 118篇 |
1995年 | 118篇 |
1994年 | 110篇 |
1993年 | 73篇 |
1992年 | 75篇 |
1991年 | 85篇 |
1990年 | 53篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 29篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 19篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有8265条查询结果,搜索用时 15 毫秒
991.
992.
993.
Candong Liu Yinghui Zheng Zhinan Zeng Peng Liu Ruxin Li Zhizhan Xu 《Laser Physics》2009,19(8):1600-1606
We propose a scheme to generate broadband high harmonic supercontinuum and single attosecond pulse emission in time domain by employing a chirped polarization-gating laser field. It is shown that this scheme can significantly extend the high harmonic cutoff to higher energy region, and the produced isolated attosecond pulse is shorter than 100 attoseconds after proper dispersion compensation, when a 7 fs driving laser pulse is used. 相似文献
994.
Haifeng Zeng Sean Bowen Christian Hilty 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,199(2):159-165
A scheme capable of acquiring heteronuclear 2D NMR spectra of hyperpolarized sample is described. Hyperpolarization, the preparation of nuclear spins in a polarized state far from thermal equilibrium, can increase the NMR signal by several orders of magnitude. It presents opportunities to apply NMR spectroscopy to dilute samples that would otherwise yield insufficient signal. However, conventional 2D NMR spectroscopy, which is commonly applied for the determination of molecular structure, relies on the recovery of the initial polarization after each transient. For this reason, it cannot be applied directly to a sample that has been hyperpolarized once. With appropriately modified pulse schemes, two-dimensional NMR spectra an however be acquired sequentially by utilizing a small portion of the hyperpolarized signal in every scan, while keeping the remaining polarization for future scans. We present heteronuclear multi-quantum spectra of single hyperpolarized samples using this technique, and discuss different options for distributing the polarization among different scans. This robust method takes full advantage of Fourier NMR to resolve overlapping chemical shifts, and may prove particularly useful for the structural elucidation of compounds in mass-limited samples. 相似文献
995.
The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods. 相似文献
996.
Dynamic wind loads, thermal expansion and other mechanical reasons cause optical platform mounts to sway. The sway distorts the alignment between transmitters and receivers, causing random pointing jitter, the outcome of which is the phase fluctuation of optical waves from the transmitter. Furthermore, atmospheric turbulence causes fluctuations in the phase of those optical waves. By using the extended Huygens-Fresnel principle, both phase fluctuations are considered and an analytic formulation for the angle-of-arrival variance of optical waves propagating through turbulent atmosphere in the presence of motion-induced pointing jitter is derived. The result shows that the angle-of-arrival variance of optical waves under the combined impact of motion-induced pointing jitter and atmospheric turbulence is the sum of the angle-of-arrival variances induced by them independently. 相似文献
997.
Chih T’sung Shih Zhi Wei Zeng Yin Cheng Chang Yao-Jen Lee Shiuh Chao 《Optical Review》2009,16(4):413-415
We provided a single-mode bent MOS-cross-section rib waveguide design with 0.9 dB/cm bending loss at 25 μm bending radius.
The peak position for the TE-like mode was tuned to the gate oxide around which the maximum amount of free carriers are accumulated
to optimize the free carrier dispersion effect. 相似文献
998.
In this paper, we proposed a novel quantum secure direct communication scheme with one-time pad in stabilizer formalism. Based
on the reuse of qubit sequence, an efficient secure communication of secret messages without first producing a shared secret
key can be achieved. One hence may find that the amount of private key needed for quantum communication is smaller than that
in the general case. Therefore, the present protocol which is feasible with the present-day techniques may be applied to quantum
communication with short-length encoding. 相似文献
999.
Garnet M. Cluff Michael A. Short Harvey Lui David I. McLean Haishan Zeng Mladen Korbelik Michael X. Chen 《Journal of Raman spectroscopy : JRS》2009,40(8):1087-1090
We have measured the micro‐Raman spectra of mouse tissues invaded by Lewis lung carcinoma (LLC). We have also carried out categorical principal component analysis (CATPCA) on the acquired spectra. The results indicate that the tumor tissues can be well discriminated from normal tissues by the first two principal components extracted from the spectra. Furthermore, we have found that the concentrations of nucleic acids and lipids/fatty acids in the tumor are considerably higher than those in the normal tissue, whereas the collagen concentration is lower. These differences can be detected and characterized by Raman images using the 788 cm−1 DNA/RNA band and the 1301 cm−1 lipid/fatty acid band. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
1000.
研究了金属有机物化学气相沉积法制备的不同厚度InN薄膜的位错特性与光电性质.基于马赛克微晶模型,通过X射线衍射非对称面摇摆曲线测量,拟合出样品刃型位错密度分别为4.2×1010cm-2和6.3×1010cm-2,并发现样品的微晶扭转角与位错密度随薄膜厚度增加而减小.通过室温霍尔效应测量得到样品载流子浓度分别为9×1018cm-3和1.2×1018cm关键词:
氮化铟
位错
载流子起源
局域态 相似文献