全文获取类型
收费全文 | 128027篇 |
免费 | 22619篇 |
国内免费 | 13595篇 |
专业分类
化学 | 87923篇 |
晶体学 | 1388篇 |
力学 | 8169篇 |
综合类 | 822篇 |
数学 | 15597篇 |
物理学 | 50342篇 |
出版年
2024年 | 289篇 |
2023年 | 2653篇 |
2022年 | 2944篇 |
2021年 | 4373篇 |
2020年 | 5433篇 |
2019年 | 5007篇 |
2018年 | 4384篇 |
2017年 | 4075篇 |
2016年 | 6246篇 |
2015年 | 6032篇 |
2014年 | 7387篇 |
2013年 | 9547篇 |
2012年 | 11721篇 |
2011年 | 12155篇 |
2010年 | 8182篇 |
2009年 | 7855篇 |
2008年 | 8446篇 |
2007年 | 7500篇 |
2006年 | 6907篇 |
2005年 | 5722篇 |
2004年 | 4391篇 |
2003年 | 3467篇 |
2002年 | 3216篇 |
2001年 | 2710篇 |
2000年 | 2373篇 |
1999年 | 2733篇 |
1998年 | 2350篇 |
1997年 | 2252篇 |
1996年 | 2161篇 |
1995年 | 1922篇 |
1994年 | 1653篇 |
1993年 | 1411篇 |
1992年 | 1223篇 |
1991年 | 1105篇 |
1990年 | 911篇 |
1989年 | 711篇 |
1988年 | 535篇 |
1987年 | 446篇 |
1986年 | 457篇 |
1985年 | 380篇 |
1984年 | 224篇 |
1983年 | 204篇 |
1982年 | 148篇 |
1981年 | 93篇 |
1980年 | 70篇 |
1979年 | 27篇 |
1976年 | 21篇 |
1975年 | 21篇 |
1972年 | 19篇 |
1957年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Xiaohua He Hailiang Zhang Deyue Yan Xiayu Wang 《Journal of polymer science. Part A, Polymer chemistry》2003,41(18):2854-2864
A series of side‐chain liquid‐crystalline (LC) homopolymers of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with different degrees of polymerization were synthesized by atom transfer radical polymerization (ATRP), which were prepared with a wide range of number‐average molecular weights from 5.1 × 103 to 20.6 × 103 with narrow polydispersities of around 1.17. Thermal investigation showed that the homopolymers exhibit two mesophases, a smectic phase, and a nematic phase, and the phase‐transition temperatures of the homopolymers increase clearly with increasing molecular weights. A series of novel LC coil triblock copolymers with narrow polydispersities was synthesized by ATRP, and their thermotropic phase behavior was investigated with differential scanning calorimetry and polarized optical microscopy. The LC coil triblocks were designed to have an LC conformation of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with a wide range of molecular weights from 3.5 × 103 to 1.7 × 104 and the coil conformation of poly(ethylene glycol) (PEG) (number‐average molecular weight: 6000 or 12,000) segment. Their characterization was investigated with 1H NMR, Fourier transform infrared spectra, and gel permeation chromatography. Triblock copolymers exhibited a crystalline phase, a smectic phase, and a nematic phase. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased, and the crystallization of PEG depressed with increasing molecular weight of the LC block. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2854–2864, 2003 相似文献
992.
Yang Ju Yo Hirosawa Masumi Saka Hiroyuki Abé 《International Journal of Infrared and Millimeter Waves》2003,24(3):391-397
We developed a compact equipment working at 94 GHz to replace the commonly used network analyzer for nondestructive testing of materials. The compact equipment was designed to measure the variations in the amplitude and phase of the reflected signal from the material relative to a reference signal. A good accuracy of the amplitude and phase measurement of the equipment was obtained in the confirmative experiments. The distribution of a drop of water in a wood plate is clearly visible in the millimeter wave images obtained by the amplitude and phase measurement. 相似文献
993.
In this article a new technique was developed to fabricate scaffolds with a unique microstructure by solid–liquid separation in combination with particulate-leaching. Firstly, the effects of polymer concentration, quenching temperature on the porous morphology and the mechanical property of obtained scaffolds during solid–liquid separation have been investigated. Then, salt granules as porogen were introduced into the solid–liquid phase separation to produce the unique pore structure of the scaffold. The pore diameter of the scaffold could be controlled with the particulate size and the wall of pores possessed special microstructure, which enhanced the pore interconnectivity. The cell culture results confirmed that a good interconnectivity of the scaffold prepared by the improved solid–liquid separation was useful for nutrition transportation and cell proliferation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
994.
Bao Tong Cui Maoan Han Huizhong Yang 《Journal of Computational and Applied Mathematics》2005,180(2):365-375
This paper deals with the oscillation problems of delay hyperbolic systems with impulses. Some sufficient conditions for oscillations of impulsive delay hyperbolic systems with Robin boundary conditions are obtained and the criteria of oscillation of the systems are established. 相似文献
995.
Ruili?ZhangEmail author Jianming?Dai Wenhai?Song Yongqing?Ma Jie?Yang Yuping?Sun 《中国科学G辑(英文版)》2004,47(1):113-120
It is helpful to study the photo-induced effect in the perovskite manganites not only for elucidating the mechanism of colossal
magnetoresistance (CMR) effect but also for potential applications in technology. The laser-induced effect in the Co doping
layered perovskite manganites La1.2Sr1.8Mn1.8Co0.2O7, is studied in this paper and the obtained results are also compared with that gained in the Nd-doping manganites with cubic
perovskite structure. 相似文献
996.
Three mechanisms to reduce threading dislocations(TDs) in GaN films as the epitaxial films grow thicker are suggested by SEM and TEM 相似文献
997.
This paper studies a supply chain consisting of two suppliers and one retailer in a spot market, where the retailer uses the
newsvendor solution as its purchase policy, and suppliers compete for the retailer’s purchase. Since each supplier’s bidding
strategy affects the other’s profit, a game theory approach is used to identify optimal bidding strategies. We prove the existence
and uniqueness of a Nash solution. It is also shown that the competition between the supplier leads to a lower market clearing
price, and as a result, the retailer benefits from it. Finally, we demonstrate the applicability of the obtained results by
deriving optimal bidding strategies for power generator plants in the deregulated California energy market.
Supported in part by RGC (Hong Kong) Competitive Earmarked Research Grants (CUHK4167/04E and CUHK4239/03E), a Distinguished
Young Investigator Grant from the National Natural Sciences Foundation of China, and a grant from Hundred Talents Program
of the Chinese Academy of Sciences. 相似文献
998.
Chongyi Wan Shiming Liu Rongqing Tan Jin Wu Jinwen Zhou Yan Lv Yanning Yu Hua Yang 《Optics & Laser Technology》2004,36(8):2389-649
A high average power, high-repetition-rate TEA CO2 laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps. Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated. 相似文献
999.
We demonstrate a 511 W laser diode pumped composite Nd:YAG ceramic laser. The optical pumping system is consisted of five laser diode stacked arrays arranged in a pentagonal shape around the ceramic rod whose size is φ6.35×144mm. When the pumping power is 1600 W, the cw laser output up to 511 W at 1064nm can be obtained with a linear piano-piano cavity, and the optical-to-optical efficiency is 31.9%. To our knowledge, this is the highest value of laser output by using a newly invented composite Nd:YAG ceramic rod as the gain medium. 相似文献
1000.
The Wiener (Sum of All Distances) Index for three out of the four classes of hexagonal models or regular planar hex-patterns used to model graphite and similar structures have been known for a few years. In this paper we find the Wiener Index for the Crown or Beehive hexagonal model. 相似文献