全文获取类型
收费全文 | 132046篇 |
免费 | 850篇 |
国内免费 | 147篇 |
专业分类
化学 | 52763篇 |
晶体学 | 1839篇 |
力学 | 8196篇 |
数学 | 27932篇 |
物理学 | 42313篇 |
出版年
2023年 | 131篇 |
2022年 | 261篇 |
2021年 | 567篇 |
2020年 | 428篇 |
2019年 | 435篇 |
2018年 | 10093篇 |
2017年 | 11049篇 |
2016年 | 5140篇 |
2015年 | 1549篇 |
2014年 | 949篇 |
2013年 | 1529篇 |
2012年 | 6480篇 |
2011年 | 15704篇 |
2010年 | 9092篇 |
2009年 | 9058篇 |
2008年 | 13358篇 |
2007年 | 17076篇 |
2006年 | 1650篇 |
2005年 | 8794篇 |
2004年 | 4903篇 |
2003年 | 4685篇 |
2002年 | 2425篇 |
2001年 | 707篇 |
2000年 | 820篇 |
1999年 | 376篇 |
1998年 | 261篇 |
1997年 | 225篇 |
1996年 | 462篇 |
1995年 | 295篇 |
1994年 | 294篇 |
1993年 | 288篇 |
1992年 | 226篇 |
1991年 | 204篇 |
1990年 | 204篇 |
1989年 | 185篇 |
1988年 | 166篇 |
1987年 | 165篇 |
1986年 | 135篇 |
1985年 | 171篇 |
1984年 | 164篇 |
1983年 | 143篇 |
1982年 | 160篇 |
1981年 | 160篇 |
1980年 | 129篇 |
1979年 | 162篇 |
1978年 | 169篇 |
1976年 | 112篇 |
1975年 | 93篇 |
1973年 | 131篇 |
1968年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Mohammad A. Khalilzadeh Soo Young Kim Ho Won Jang Rafael Luque Rajender S. Varma Richard A. Venditti Mohammadreza Shokouhimehr 《Materials Today Chemistry》2022
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well. 相似文献
2.
Pengjin Qin Li-An Wang Prof. Joseph M. O'Connor Prof. Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof. Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18114-18121
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献
3.
4.
5.
6.
7.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation. 相似文献
8.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant. 相似文献
9.
10.
V. A. Bespalov V. M. Glazov E. A. Il’ichev Yu. A. Klimov S. V. Kuklev A. E. Kuleshov R. M. Nabiev G. N. Petrukhin B. G. Potapov G. S. Rychkov D. S. Sokolov V. V. Fandeev E. A. Fetisov S. S. Yakushov 《Technical Physics》2015,60(4):553-560
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied. 相似文献