全文获取类型
收费全文 | 30172篇 |
免费 | 4058篇 |
国内免费 | 2712篇 |
专业分类
化学 | 20502篇 |
晶体学 | 284篇 |
力学 | 1945篇 |
综合类 | 273篇 |
数学 | 3282篇 |
物理学 | 10656篇 |
出版年
2024年 | 105篇 |
2023年 | 589篇 |
2022年 | 907篇 |
2021年 | 1011篇 |
2020年 | 1112篇 |
2019年 | 1082篇 |
2018年 | 911篇 |
2017年 | 813篇 |
2016年 | 1279篇 |
2015年 | 1268篇 |
2014年 | 1536篇 |
2013年 | 2049篇 |
2012年 | 2630篇 |
2011年 | 2658篇 |
2010年 | 1646篇 |
2009年 | 1632篇 |
2008年 | 1736篇 |
2007年 | 1660篇 |
2006年 | 1489篇 |
2005年 | 1229篇 |
2004年 | 941篇 |
2003年 | 789篇 |
2002年 | 752篇 |
2001年 | 561篇 |
2000年 | 559篇 |
1999年 | 655篇 |
1998年 | 579篇 |
1997年 | 574篇 |
1996年 | 659篇 |
1995年 | 506篇 |
1994年 | 468篇 |
1993年 | 390篇 |
1992年 | 378篇 |
1991年 | 324篇 |
1990年 | 257篇 |
1989年 | 204篇 |
1988年 | 158篇 |
1987年 | 138篇 |
1986年 | 129篇 |
1985年 | 122篇 |
1984年 | 88篇 |
1983年 | 61篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Area postrema (AP) is a circumventricular organ plays an important role in sodium homeostasis and cardiovascular regulation. Since sleep deficiency will cause cardiovascular dysfunction, the present study aims to determine whether sodium level would significantly alter in AP following total sleep deprivation (TSD). Sodium level was investigated in vivo by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Clinical manifestation of cardiovascular function was demonstrated by mean arterial pressure (MAP) values. Results indicated that in normal rats, TOF-SIMS spectrum revealed a major peak of sodium ion counting as 5.61 × 105 at m/z 23. The sodium ions were homogeneous distributed in AP without specific localization. However, following TSD, the sodium intensity was relatively increased (6.73 × 105) and the signal for sodium image was strongly expressed throughout AP with definite spatial distribution. MAP of TSD rats is 138 ± 5 mmHg, which is significantly higher than that of normal ones (121 ± 3 mmHg). Regarding AP is an important area for sodium sensation and development of hypernatremic related sympatho-excitation; up-regulation of sodium expression following TSD suggests that high sodium level might over-activate AP, through complex neuronal networks involving in sympathetic regulation, which could lead to the formation of TSD relevant cardiovascular diseases. 相似文献
992.
Recently, the (2+1)-dimensional modified Kadomtsev-Petviashvili (mKP) equation was decomposed into two known (1+1)-dimensional soliton equations by Dai and Geng [H.H. Dai, X.G. Geng, J. Math. Phys. 41 (2000) 7501]. In the present paper, a systematic and simple method is proposed for constructing three kinds of explicit N-fold Darboux transformations and their Vandermonde-like determinants’ representations of the two known (1+1)-dimensional soliton equations based on their Lax pairs. As an application of the Darboux transformations, three explicit multi-soliton solutions of the two (1+1)-dimensional soliton equations are obtained; in particular six new explicit soliton solutions of the (2+1)-dimensional mKP equation are presented by using the decomposition. The explicit formulas of all the soliton solutions are also expressed by Vandermonde-like determinants which are remarkably compact and transparent. 相似文献
993.
Y.P. Huang K.W. Su A. Li Y.F. Chen K.F. Huang 《Applied physics. B, Lasers and optics》2008,91(3-4):429-432
We demonstrate a high-peak-power quasi-continuous-wave diode-pumped passive Q-switched Nd:YAG laser at 946 nm. We make a thorough comparison of the output performance between the saturable absorbers of InGaAs quantum wells (QWs) and a Cr4+:YAG crystal. Experimental results reveal that the saturable absorber of InGaAs QWs is superior to the Cr4+:YAG crystal because of the low nonsaturable losses and leads to a pulse energy of 330 μJ with a peak power greater than 11 kW. 相似文献
994.
降频助听算法是改善听障患者声音辨识能力的最安全有效的方法. 本文以主观测试实验为手段, 通过分析当前算法的声音识别能力的不足, 提出一种自适应慢放降频算法. 算法结合慢放算法和频移算法的优点, 并能根据信号的频谱结构, 自适应调整慢放因子, 降低时域不同步性. 并且, 通过分析含噪信号和噪声信号的频谱关系, 提出一种噪声下的慢放因子评估方法. 实验结果显示, 同其他降频算法相比, 该算法可以提高15%到20%的识别率. 在对听障患者的测试中, 同传统的助听设备相比, 平均识别率也获得显著改善. 相似文献
995.
Using a water-confined carbon nanotube to probe the electricity of sequential charged segments of macromolecules 下载免费PDF全文
The detection of macromolecular conformation is particularly important in many physical and biological applications. Here we theoretically explore a method for achieving this detection by probing the electricity of sequential charged segments of macromolecules. Our analysis is based on molecular dynamics simulations, and we investigate a single file of water molecules confined in a half-capped single-walled carbon nanotube (SWCNT) with an external electric charge of +e or -e (e is the elementary charge). The charge is located in the vicinity of the cap of the SWCNT and along the centerline of the SWCNT. We reveal the picosecond timescale for the re-orientation (namely, from one unidirectional direction to the other) of the water molecules in response to a switch in the charge signal, -e → +e or +e →-e. Our results are well understood by taking into account the electrical interactions between the water molecules and between the water molecules and the external charge. Because such signals of re-orientation can be magnified and transported according to Tu et al. [2009 Proc. Natl. Acad. Sci. USA 106 18120], it becomes possible to record fingerprints of electric signals arising from sequential charged segments of a macromolecule, which are expected to be useful for recognizing the conformations of some particular macromolecules. 相似文献
996.
Jianguo Lv Kai Huang Xuemei Chen Jianbo Zhu Lijun Wang Xueping Song Zhaoqi Sun 《Superlattices and Microstructures》2011
The chemical composition, crystalline structure, surface morphology and photoluminescence spectra of Na-doped ZnO thin films with different heat treatment process were investigated by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and a fluorescence spectrometer. The results show that preferred orientation, residual stress, average crystal size and surface morphology of the thin films are strongly determined by the preheating temperature. The effects of preheating temperature on microstructure and surface morphology have been discussed in detail. The photoluminescence spectra show that there are strong violet & UV emission, blue emission and green emission bands. The violet & UV emission is ascribed to the electron transition from the localized level below the conduction band to the valence band. The blue emission is attributed to the electron transition from the shallow donor level of oxygen vacancies to the valence band, and the electron transition from the shallow donor level of interstitial zinc to the valence band. The green emission is assigned to the electron transition from the level of ionized oxygen vacancies to the valence band. 相似文献
997.
Chunye Gong Jie Liu Lihua Chi Haowei Huang Jingyue Fang Zhenghu Gong 《Journal of computational physics》2011,230(15):6010-6022
Graphics Processing Unit (GPU), originally developed for real-time, high-definition 3D graphics in computer games, now provides great faculty in solving scientific applications. The basis of particle transport simulation is the time-dependent, multi-group, inhomogeneous Boltzmann transport equation. The numerical solution to the Boltzmann equation involves the discrete ordinates (Sn) method and the procedure of source iteration. In this paper, we present a GPU accelerated simulation of one energy group time-independent deterministic discrete ordinates particle transport in 3D Cartesian geometry (Sweep3D). The performance of the GPU simulations are reported with the simulations of vacuum boundary condition. The discussion of the relative advantages and disadvantages of the GPU implementation, the simulation on multi GPUs, the programming effort and code portability are also reported. The results show that the overall performance speedup of one NVIDIA Tesla M2050 GPU ranges from 2.56 compared with one Intel Xeon X5670 chip to 8.14 compared with one Intel Core Q6600 chip for no flux fixup. The simulation with flux fixup on one M2050 is 1.23 times faster than on one X5670. 相似文献
998.
Dongmin Gang Yu-tin Huang Eunkyung Koh Sangmin Lee Arthur E. Lipstein 《Journal of High Energy Physics》2011,2011(3):116
We propose a recursion relation for tree-level scattering amplitudes in three-dimensional Chern-Simons-matter theories. The recursion relation involves a complex deformation of momenta which generalizes the BCFW-deformation used in higher dimensions. Using background field methods, we show that all tree-level superamplitudes of the ABJM theory vanish for large deformations, establishing the validity of the recursion formula. Furthermore, we use the recursion relation to compute six-point and eight-point component amplitudes and match them with independent computations based on Feynman diagrams or the Grassmannian integral formula. As an application of the recursion relation, we prove that all tree-level amplitudes of the ABJM theory have dual superconformal symmetry. Using generalized unitarity methods, we extend this symmetry to the cut-constructible parts of the loop amplitudes. 相似文献
999.
In this article, we present the design of the beam transport line and injection system of the compact storage ring for the Tsinghua Thomson scattering X-ray (TTX) source. The layout of the beam transport line fits in with the limited available space. The injection system is simplified, consisting of only one single kicker; the stray field on the reference orbit is also reduced without the septum magnet. We choose a travelling wave kicker and present both 2D and 3D simulations for the structure design. 相似文献
1000.
实验获得了Ar+激光514.5nm线诱导23Na39K分子产生的D1∏→X1∑+跃迁荧光谱.通过测量激光感生荧光光谱强度随泵浦功率、热管炉温度及缓冲气压变化规律,详细研究了其跃迁机制.用最小二乘法拟合获得23Na39K分于X1∑+态振动常数.理论计算了各跃迁谱支波长值及Franck-Condon因子和光谱强度值,与实验观测值符合得相当好,充分表明本文对激光感生荧光光谱的归属以及对各支谱线振、转量子数的赋值是合理的. 相似文献