全文获取类型
收费全文 | 12192篇 |
免费 | 1378篇 |
国内免费 | 764篇 |
专业分类
化学 | 8327篇 |
晶体学 | 171篇 |
力学 | 551篇 |
综合类 | 72篇 |
数学 | 1615篇 |
物理学 | 3598篇 |
出版年
2024年 | 22篇 |
2023年 | 211篇 |
2022年 | 265篇 |
2021年 | 389篇 |
2020年 | 465篇 |
2019年 | 464篇 |
2018年 | 420篇 |
2017年 | 355篇 |
2016年 | 553篇 |
2015年 | 506篇 |
2014年 | 639篇 |
2013年 | 859篇 |
2012年 | 893篇 |
2011年 | 995篇 |
2010年 | 649篇 |
2009年 | 566篇 |
2008年 | 737篇 |
2007年 | 652篇 |
2006年 | 600篇 |
2005年 | 529篇 |
2004年 | 388篇 |
2003年 | 355篇 |
2002年 | 279篇 |
2001年 | 194篇 |
2000年 | 207篇 |
1999年 | 188篇 |
1998年 | 167篇 |
1997年 | 164篇 |
1996年 | 177篇 |
1995年 | 132篇 |
1994年 | 133篇 |
1993年 | 121篇 |
1992年 | 95篇 |
1991年 | 100篇 |
1990年 | 89篇 |
1989年 | 61篇 |
1988年 | 58篇 |
1987年 | 52篇 |
1986年 | 57篇 |
1985年 | 48篇 |
1984年 | 52篇 |
1983年 | 35篇 |
1982年 | 39篇 |
1981年 | 42篇 |
1980年 | 33篇 |
1979年 | 32篇 |
1978年 | 28篇 |
1977年 | 29篇 |
1975年 | 25篇 |
1974年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
13.
杂多酸催化合成乙酸乙酯 总被引:14,自引:0,他引:14
回流吸附法制备的负载型12-钨磷酸(HPW/C)是合成乙酸乙酯的高效催化剂。最佳反应条件下乙醇转化率达96%,酯化选择性100%。催化剂的高活性是由于HPW在活性炭上高度分散,使活性位增多,有效酸量增大。HPW/C还具有热稳定性高和不易流失等优点。 相似文献
14.
15.
16.
Wei Shi Yujie J. Ding Changshui Fang Qiwei Pan Qingtian Gu 《Optics and Lasers in Engineering》2002,38(6):361-371
Mode-matching and effective index methods are used to analyze single-mode operation of optical rib polymer waveguides. Their single-mode waveguiding conditions are determined. Single-mode rib waveguides fabricated from guest–host polyetherketone are presented. The estimated propagation loss of straight rib-waveguides is 0.7 dB/cm at 1.55 μm. Furthermore, by using the mode field-transfer matrix method, 2×2 and 4×4 polymer Mach–Zehnder interference switch operating at 1.55 μm wavelength has been designed based on optical multi-mode interference. 相似文献
17.
Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H2O)2 (C4H5O5)2] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound CuII. The electronic structure of the compound is consistent with its crystal structure. 相似文献
18.
A new electroactive polynuclear inorganic compound of rare earth metal, gadolinium hexacyanoferrate (GdHCF), was prepared and characterized using the techniques of FTIR spectroscopy, thermogravimetric analysis (TG), UV-Vis spectrometry, X-ray photoelectron spectroscopy (XPS), ICP atomic emission spectroscopy, and EDX. The results of ICP atomic emission spectroscopy, EDX, and TGA indicated that the prepared GdHCF sample had a stoichiometry of NaGdFe(CN)6·12H2O (when GdHCF was prepared in NaCl solution). The FTIR spectrum of GdHCF showed that there were two types of water molecules in the structure of GdHCF: one was the interstitial water (5 H2O), which resulted from the association of water due to H-bonding, and the other was water coordinated with Gd (7 H2O). The results obtained using XPS showed that the oxidation state of Fe and Gd in the GdHCF sample was +2 and +3, respectively. GdHCF was immobilized on the surface of spectroscopically pure graphite (SG) electrode forming the GdHCF/SG electrode, and the solid-state electrochemistry of the resultant electrode was studied using cyclic voltammetry. The cyclic voltammetric results indicated that the GdHCF/SG electrode exhibited a pair of well-defined and stable redox peaks with the formal potential of E0′=(197±3) mV. The effects of the concentration of the supporting electrolyte on the electrochemical characteristics of GdHCF were studied, and the results showed that the value of E0′ increased linearly with the activity of the cationic ion of the supporting electrolyte (lgaNa+), with a slope of 54.1 mV, which may become a novel method for determining the activity of Na+ in solution. Further experimental results indicated that GdHCF had electrocatalytic activities toward the oxidation of dopamine (DA) and ascorbic acid (AA), and the electrocatalytic current increased linearly with the concentration of DA (or AA) in the range of 1.0–10.0 mmol·L?1 (for DA) or 0.5–20.0 mmol·L?1 (for AA). 相似文献
19.
Pan Yifei Department of Mathematical Sciences Indiana University-Purdue University Fort Wayne Fort Wayne IN - U.S.A. School of Mathematics Informatics Jiangxi Normal University Nanchang China 《中国科学A辑(英文版)》2005,48(Z1)
It is proved that every proper holomorphic self-map of a smooth bounded Reinhardt domain of D'Angelo finite type in Cn (n > 1) is an automorphism. 相似文献
20.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献