全文获取类型
收费全文 | 201964篇 |
免费 | 5339篇 |
国内免费 | 3165篇 |
专业分类
化学 | 102757篇 |
晶体学 | 2679篇 |
力学 | 8418篇 |
综合类 | 137篇 |
数学 | 19301篇 |
物理学 | 59312篇 |
综合类 | 17864篇 |
出版年
2022年 | 1336篇 |
2021年 | 1736篇 |
2020年 | 1819篇 |
2019年 | 1859篇 |
2018年 | 1752篇 |
2017年 | 1796篇 |
2016年 | 3181篇 |
2015年 | 2879篇 |
2014年 | 3798篇 |
2013年 | 9306篇 |
2012年 | 8314篇 |
2011年 | 10121篇 |
2010年 | 6442篇 |
2009年 | 6531篇 |
2008年 | 9012篇 |
2007年 | 8999篇 |
2006年 | 8459篇 |
2005年 | 7835篇 |
2004年 | 6955篇 |
2003年 | 5901篇 |
2002年 | 5841篇 |
2001年 | 7040篇 |
2000年 | 5465篇 |
1999年 | 4217篇 |
1998年 | 3093篇 |
1997年 | 3051篇 |
1996年 | 2994篇 |
1995年 | 2660篇 |
1994年 | 2511篇 |
1993年 | 2327篇 |
1992年 | 2762篇 |
1991年 | 2703篇 |
1990年 | 2390篇 |
1989年 | 2336篇 |
1988年 | 2308篇 |
1987年 | 2250篇 |
1986年 | 2113篇 |
1985年 | 2999篇 |
1984年 | 2914篇 |
1983年 | 2322篇 |
1982年 | 2460篇 |
1981年 | 2342篇 |
1980年 | 2308篇 |
1979年 | 2343篇 |
1978年 | 2379篇 |
1977年 | 2318篇 |
1976年 | 2244篇 |
1975年 | 2250篇 |
1974年 | 2216篇 |
1973年 | 2206篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Yang T. L. Kao C. L. Kuo C. E. Yeh H. C. Li W. J. Li H. T. Chen C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the... 相似文献
2.
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was... 相似文献
3.
In the pursuit to enlarge the library of polyimide materials for energy applications, new polyimide/MWCNTs composite films have been developed by MWCNTs-assisted polycondensation reaction of a hydroxyl and triphenylmethane-containing diamine with benzophenone tetracarboxylic dianhydride targeting to highlight their electrical storage capability as flexible electrodes in micro-supercapacitors (mSCs). The Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, UV–vis, fluorescence, and Raman spectroscopies were used to demonstrate the evolution of interfacial interactions between MWCNTs and the precursors (diamine monomer and intermediate polyamidic acid) and polyimide matrix that proved to be the origin of MWCNTs homogeneous dispersion. Thus, composite films incorporating 1, 3, 5, and 10 w.t.% MWCNTs were obtained and thoroughly investigated with regard to their morphology, mechanical behavior, thermal stability, and electrical conductivity. The electrochemical performance of these composites was first analyzed in a classical three-electrode cell by cyclic voltammetry and galvanostatic charge-discharge in both aqueous and organic electrolyte systems. By far, the best electrical storage capacity was obtained with the composite polyimide film containing 10% MWCNTs that was further used as both active material and current collector in a flexible symmetric mSC realized by a straightforward and low-cost procedure. In the attempt to better exploit the advantages of this composite film, it was layered with a graphite-containing paint and tested as an electrode in a flexible mSC, which provided satisfactory results. To our knowledge, this is the first report on the electrical charge storage capability of a polyimide/MWCNTs free-standing film as a flexible electrode in mSCs, which do not require time- and resource-consuming processing steps. 相似文献
4.
5.
已完钻超深裸眼水平井侧钻技术是经济、高效开发油藏剩余油的主要手段之一,传统的磨铣钢套管开窗侧钻技术存在下入摩阻大、磨铣耗时长导致开窗失败等问题。为此,提出了基于多材质复合管柱的超深水平井裸眼井壁支撑工艺,结合中国西北油田已完钻超深裸眼水平井井况,首先,提出了基于“铝合金+碳钢”的多材质复合管柱组合及设计方法;其次,开展了基于管柱实物屈曲实验数据的管柱临界屈曲载荷计算模型适用性评价,并优选出了适合于“铝合金+碳钢”多材质复合管柱的屈曲临界载荷计算模型;最后,研究了综合考虑管柱扭矩、摩阻、刚性、井眼条件、管柱强度及材质的多材质复合管柱下入性分析方法,并利用下入性分析软件对西北油田顺北X1井、X2井、X3井、X4井复合管柱进行了下入可行性评价。该方法在X1井和X2井得到成功应用,进一步论证了该工艺现场应用的可行性。研究成果可为超深水平井裸眼井壁支撑的复合管柱设计和下入可行性评价提供理论参考。 相似文献
6.
Zhang Ya-Li Han Rong-Sheng Chen Liang 《International Journal of Theoretical Physics》2021,60(4):1384-1398
International Journal of Theoretical Physics - In this work, we give an analytical derivation of the reduced density matrix between two qubits in a cavity field, which is described by the quantum... 相似文献
7.
M. Amar D. Andreucci R. Gianni C. Timofte 《Journal of Mathematical Analysis and Applications》2021,493(2):124533
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation. 相似文献
8.
9.
10.
Nonlinear Dynamics - In this article, the authors simulate and study dark and bright soliton solutions of 1D and 2D regularized long wave (RLW) models. The RLW model occurred in various fields such... 相似文献