全文获取类型
收费全文 | 79749篇 |
免费 | 419篇 |
国内免费 | 398篇 |
专业分类
化学 | 25375篇 |
晶体学 | 793篇 |
力学 | 6764篇 |
数学 | 32333篇 |
物理学 | 15301篇 |
出版年
2021年 | 54篇 |
2020年 | 57篇 |
2019年 | 52篇 |
2018年 | 10463篇 |
2017年 | 10284篇 |
2016年 | 6134篇 |
2015年 | 889篇 |
2014年 | 368篇 |
2013年 | 469篇 |
2012年 | 3904篇 |
2011年 | 10636篇 |
2010年 | 5733篇 |
2009年 | 6121篇 |
2008年 | 6693篇 |
2007年 | 8859篇 |
2006年 | 330篇 |
2005年 | 1396篇 |
2004年 | 1591篇 |
2003年 | 2019篇 |
2002年 | 1050篇 |
2001年 | 262篇 |
2000年 | 307篇 |
1999年 | 161篇 |
1998年 | 205篇 |
1997年 | 164篇 |
1996年 | 218篇 |
1995年 | 125篇 |
1994年 | 85篇 |
1993年 | 106篇 |
1992年 | 63篇 |
1991年 | 80篇 |
1990年 | 59篇 |
1989年 | 64篇 |
1988年 | 69篇 |
1987年 | 64篇 |
1986年 | 73篇 |
1985年 | 63篇 |
1984年 | 49篇 |
1983年 | 45篇 |
1982年 | 61篇 |
1981年 | 56篇 |
1980年 | 53篇 |
1979年 | 49篇 |
1978年 | 39篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32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.
BIT Numerical Mathematics - In this article we address the problem of minimizing a strictly convex quadratic function using a novel iterative method. The new algorithm is based on the well-known... 相似文献
3.
Di Turo Francesca Parra Rafael Piquero-Cilla Joan Favero Gabriele Doménech-Carbó Antonio 《Journal of Solid State Electrochemistry》2019,23(3):771-781
Journal of Solid State Electrochemistry - Electrochemical impedance spectroscopy (EIS) and voltammetry of immobilized particles (VIMP) measurements using air-saturated mineral water and... 相似文献
4.
Yuliang Zhao 《中国科学:化学(英文版)》2018,61(12):1481-1482
正Living organisms have developed their unique strategies during the natural evolution for building hard tissues with minerals, including silica, calcium carbonate, calcium phosphate, and ferric oxide [1]. Such biomineralized materials generally have complex hierarchical structures with excellent mechanical properties. Although bioinspired approaches have led to the creation of well-defined synthetic structural materials ranging from micro to macro scales, the rational design of discrete biomimetic structures at the nanoscale remains a grand challenge. 相似文献
5.
JuHong Ge 《Nonlinear dynamics》2018,94(1):87-98
A five-neuron network model with multiple delays is proposed. This paper presents the combined effect of different delays on the dynamics of the proposed network. Pitchfork bifurcation is discussed in detail with the variation of the value of coupled weight or attenuation rate of internal neurons. By analyzing the corresponding characteristic equation, some stable criteria on delay-dependence and delay-independence are derived including multiple delays and coupled weights and the periodic oscillation arises bifurcated from the trivial equilibrium after the network loses its stability. Stable regions on delay-dependence are displayed in the two delayed parameter plane. It is shown that multiple delays can produce stability switching between resting state and periodic activity. Finally, theoretical results are justified by providing two illustrative examples. 相似文献
6.
It is shown that the countably infinite dimensional pointed vector space (the vector space equipped with a constant) over a finite field has infinitely many first order definable reducts. This implies that the countable homogeneous Boolean-algebra has infinitely many reducts. 相似文献
7.
8.
Nonlinear Dynamics - Introduction of stiffness nonlinearities to broaden the frequency bandwidth of vibratory energy harvesters has the adverse influence of complicating the response behavior of... 相似文献
9.
10.