全文获取类型
收费全文 | 80648篇 |
免费 | 12846篇 |
国内免费 | 15188篇 |
专业分类
化学 | 37798篇 |
晶体学 | 1470篇 |
力学 | 3151篇 |
综合类 | 1716篇 |
数学 | 7319篇 |
物理学 | 21400篇 |
无线电 | 35828篇 |
出版年
2024年 | 323篇 |
2023年 | 1138篇 |
2022年 | 2415篇 |
2021年 | 2589篇 |
2020年 | 2381篇 |
2019年 | 2284篇 |
2018年 | 2181篇 |
2017年 | 2743篇 |
2016年 | 2767篇 |
2015年 | 3610篇 |
2014年 | 4339篇 |
2013年 | 5697篇 |
2012年 | 6113篇 |
2011年 | 6617篇 |
2010年 | 5921篇 |
2009年 | 6305篇 |
2008年 | 6735篇 |
2007年 | 6485篇 |
2006年 | 6110篇 |
2005年 | 5256篇 |
2004年 | 4311篇 |
2003年 | 3305篇 |
2002年 | 3231篇 |
2001年 | 3219篇 |
2000年 | 3006篇 |
1999年 | 1716篇 |
1998年 | 937篇 |
1997年 | 834篇 |
1996年 | 759篇 |
1995年 | 631篇 |
1994年 | 613篇 |
1993年 | 650篇 |
1992年 | 515篇 |
1991年 | 391篇 |
1990年 | 375篇 |
1989年 | 359篇 |
1988年 | 278篇 |
1987年 | 233篇 |
1986年 | 203篇 |
1985年 | 146篇 |
1984年 | 154篇 |
1983年 | 142篇 |
1982年 | 97篇 |
1981年 | 115篇 |
1980年 | 88篇 |
1979年 | 68篇 |
1978年 | 56篇 |
1977年 | 31篇 |
1976年 | 23篇 |
1965年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
61.
Soon-Tae Hong 《General Relativity and Gravitation》2004,36(8):1919-1929
We study global flat embeddings inside and outside of event horizons of black holes such as Schwarzschild and Reissner-Nordström black holes, and of de Sitter space. On these overall patches of the curved manifolds we investigate four accelerations and Hawking temperatures by introducing relevant Killing vectors. 相似文献
62.
Jin Sun Yihu Song Qiang Zheng Hong Tan Jie Yu Hong Li 《Journal of Polymer Science.Polymer Physics》2007,45(18):2594-2602
The reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO2) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO2 causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO2 hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007 相似文献
63.
64.
Kan‐Yi Pu Yi Chen Xiao‐Ying Qi Chun‐Yang Qin Qing‐Quan Chen Hong‐Yu Wang Yun Deng Qu‐Li Fan Yan‐Qin Huang Shu‐Juan Liu Wei Wei Bo Peng Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3776-3787
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007 相似文献
65.
66.
设G是B核,记用dn,dn和δn分别表示Kolmogorov,Gel''fand和线性n宽度。本文求出了和的精确值,找到了各自的极子空间(或最优算子)。由此证明了Pinkus猜想(即是的极子空间,)在p=q时的正确性。 相似文献
67.
A simple and sensitive method was conducted for the determination of trace amounts of proteins with benzeneazo-8-acetylamino-1-naphthol-3,6-disulfonic acid sodium salt (azophloxine, AP) using a Rayleigh light-scattering (RLS) technique. At pH 2.60 and in the presence of an emulsifier OP microemulsion, the RLS of AP can be greatly enhanced by proteins, owing to the interaction between AP and protein. The enhanced intensity is proportional to the concentration of proteins. Four proteins, including bovine serum albumin (BSA), human serum albumin (HSA), lysozyme (Lys) and gamma globulin (gamma-G) have been tested. For example, the linear range of BSA was 0 - 0.06 microg mL(-1) with detection limits of 2.38 ng mL(-1). The method was applied to the analysis of protein in human urine and penicillin samples with satisfactory results. The relative standard deviation was in all instances less than 4.0%, and the recovery was in the range of 97.5 - 104%. 相似文献
68.
Hong Bi Qianwang Chen Yonglong Zhuang Shenqiang Zhao 《Journal of magnetism and magnetic materials》2006
Molecular magnet {NBu4[Fe Cr(ox)3]}x (NBu4+=tetra(n-buty1) ammonium ion; ox2−=oxalate ion) was synthesized under an applied low magnetic field of 0.3 T in comparison to that synthesized without a field. Their crystallinities, morphologies and magnetic properties were characterized by using the X-ray diffractionmeter, the transmission electron microscope, and a superconducting quantum interference device. It is found that the average size of particles synthesized under the applied field appears larger than that synthesized without a field. Moreover, its crystallinity, morphology and magnetic susceptibility have also been improved. However, its chemical structure and ferromagnetic phase transition temperature Tc do not change. Possible reasons to explain this effect are also discussed. 相似文献
69.
70.
郑洪 《浙江大学学报(理学版)》1996,23(4):342-347
本文介绍了一种钢卷尺刻度在线测量系统 ,它采用了高速摄像及计算机数据处理技术 ,文章阐述了系统的非接触动态测量原理 ,描述了光电信号的处理方法 . 相似文献