全文获取类型
收费全文 | 26582篇 |
免费 | 3931篇 |
国内免费 | 3745篇 |
专业分类
化学 | 20332篇 |
晶体学 | 422篇 |
力学 | 1278篇 |
综合类 | 289篇 |
数学 | 3138篇 |
物理学 | 8799篇 |
出版年
2024年 | 83篇 |
2023年 | 472篇 |
2022年 | 917篇 |
2021年 | 917篇 |
2020年 | 1023篇 |
2019年 | 1063篇 |
2018年 | 827篇 |
2017年 | 791篇 |
2016年 | 1206篇 |
2015年 | 1252篇 |
2014年 | 1589篇 |
2013年 | 1999篇 |
2012年 | 2331篇 |
2011年 | 2370篇 |
2010年 | 1772篇 |
2009年 | 1607篇 |
2008年 | 1867篇 |
2007年 | 1654篇 |
2006年 | 1549篇 |
2005年 | 1334篇 |
2004年 | 1029篇 |
2003年 | 882篇 |
2002年 | 975篇 |
2001年 | 765篇 |
2000年 | 552篇 |
1999年 | 482篇 |
1998年 | 415篇 |
1997年 | 332篇 |
1996年 | 351篇 |
1995年 | 285篇 |
1994年 | 258篇 |
1993年 | 230篇 |
1992年 | 183篇 |
1991年 | 190篇 |
1990年 | 120篇 |
1989年 | 131篇 |
1988年 | 79篇 |
1987年 | 68篇 |
1986年 | 50篇 |
1985年 | 66篇 |
1984年 | 56篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
利用微扰展开技术推导出变参数波振器的小信号增益两个近似求积表达式并将其计算结果与数值模拟结果进行了比较,二者吻合很好。利用近似解析式对小信号增益进行了初步探讨,得到了电子入射能量可低于初始谐振能,能散度允许范围受波振器设计影响以及降低锥度改变率可提高小信号增益等新结论。 相似文献
72.
Ying Guang Shi 《Constructive Approximation》1994,10(4):439-450
In this paper we give a theorem of Grünwald-type for (0, 1,...,m-1) Hermite-Fejér interpolation (m=2, 4,...), which extends the famous result for a strongly normal system of nodes in the casem=2 given by Grünwald in [1]. 相似文献
73.
Hydroxyapatite coating on porous silicon substrate obtained by precipitation process 总被引:2,自引:0,他引:2
Chen Shaoqiang Zhu Ziqiang Zhu Jianzhong Zhang Jian Shi Yanling Yu Ke Wang Weiming Wang Xiaohua Feng Xiao Luo Laiqiang Shao Li 《Applied Surface Science》2004,230(1-4):418-424
Hydroxyapatite Ca10(PO4)6(OH)2 (HAP) is known as a bioactive and biocompatible material, HAP coatings were used to improve the biocompatible of substrate by many researcher, In this work, HAP thin films on porous silicon (PS) substrates have been prepared by aqueous precipitation method with rapid thermal annealing (RTA) processes. The HAP films had been prepared under the annealing temperature ranging from 300 to 1000 °C. By the measurement of X-ray diffraction (XRD), it was found that for the crystallinity optimization, the heat-treatment at 850–950 °C for 1 h would be favorable. Atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements reveal a dense and smooth surface of the HAP film, and tightly adherence of the coating on porous silicon substrate after sintered. Thus, by this method, porous silicon could be increased its bioactivity and so that could be used in the biomedical area. 相似文献
74.
本文提出一种简单实用的MTBF(Mean time between failures-平均无故障工作时间)分配方法.这种方法适合于工程系统设计的对分系统的结构(可靠性模型)有了初步的了解,并能估算出各分系统故障率的情况.同时对于需要进行可靠性分配,又苦于对可靠性理论知识缺乏深入了解的人员也非常适用. 相似文献
75.
离子表面活性剂胶团对阿斯匹林碱水解反应的影响 总被引:3,自引:0,他引:3
离子表面活性剂胶团对阿斯匹林碱水解反应的影响史振民*刘生昆张祝莲巩育军(延安大学化学系延安716000)关键词表面活性剂,阿斯匹林,碱水解反应,胶团,抑制作用1996-05-04收稿,1996-08-12修回阿斯匹林(ASP),学名为乙酰水杨酸,有较... 相似文献
76.
商标数据库存储模式及其检索算法研究 总被引:6,自引:0,他引:6
依据商标专家的先验知识和基于内容的图像检索技术,提出了一种新的商标库存储结构,并依据该存储结构设计了以三级检索算法为核心的实用商标登记注册管理系统,对于检索算法,一级检索采用人工确认,二级检索采用傅立叶描述子作为边缘特征向量,三级检索采用hu不变矩组作为矩特征向量,从而达到提高商标申请注册中的检索速度和查准率。 相似文献
77.
Katsumasa Iwai Yi-Wei Shi Mitsunobu Miyagi Yuji Matsuura 《Optics & Laser Technology》2007,39(8):1528-1531
An improved coating method was proposed in order to form a uniform polymer layer in the fabrication of cyclic olefin polymer-coated silver (COP/Ag) hollow fiber. A COP solution was flowed in a closed loop, in which the silver-coated tube was used as a part of the loop. Owing to the constant flowing speed of the COP solution and the airtight flowing environment, a COP layer was uniformly formed. The hollow fibers attain high performance and deliver multi-wavelength laser light from the infrared to the visible simultaneously. The method was successfully applied to the fabrication of practical hollow fibers with 2 m length for the near and mid-infrared lasers. 相似文献
78.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献
79.
Ye Lin Feng Zeng‐Guo Zhao Yu‐Mei Wu Feng Chen Shi Wang Guo‐Qing 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3650-3665
A novel cyclic ether monomer 3‐{2‐[2‐(2‐hydroxyethoxy)ethoxy]ethoxy‐methyl}‐3′‐methyloxetane (HEMO) was prepared from the reaction of 3‐hydroxymethyl‐3′‐methyloxetane tosylate with triethylene glycol. The corresponding hyperbranched polyether (PHEMO) was synthesized using BF3·Et2O as initiator through cationic ring‐opening polymerization. The evidence from 1H and 13C NMR analyses revealed that the hyperbranched structure is constructed by the competition between two chain propagation mechanisms, i.e. active chain end and activated monomer mechanism. The terminal structure of PHEMO with a cyclic fragment was definitely detected by MALDI‐TOF measurement. A DSC test implied that the resulting polyether has excellent segment motion performance potentially beneficial for the ion transport of polymer electrolytes. Moreover, a TGA assay showed that this hyperbranched polymer possesses high thermostability as compared to its liquid counterpart. The ion conductivity was measured to reach 5.6 × 10?5 S/cm at room temperature and 6.3 × 10?4 S/cm at 80 °C after doped with LiTFSI at a ratio of Li:O = 0.05, presenting the promise to meet the practical requirement of lithium ion batteries for polymer electrolytes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3650–3665, 2006 相似文献
80.
J.-S. Kang G. Kim S.S. Lee S. Choi S. Cho S.W. Han H.J. Shin B.I. Min 《Journal of magnetism and magnetic materials》2006
The spatial concentration distribution and local electronic structure of ferromagnetic Ge1−xTx (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge1−xTx. 相似文献