首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   62079篇
  免费   1062篇
  国内免费   321篇
化学   29927篇
晶体学   1060篇
力学   3249篇
综合类   8篇
数学   4908篇
物理学   24310篇
  2022年   603篇
  2021年   559篇
  2020年   511篇
  2019年   495篇
  2018年   621篇
  2017年   541篇
  2016年   1030篇
  2015年   740篇
  2014年   1140篇
  2013年   2711篇
  2012年   2606篇
  2011年   3299篇
  2010年   2291篇
  2009年   2329篇
  2008年   2959篇
  2007年   2785篇
  2006年   2615篇
  2005年   2331篇
  2004年   2153篇
  2003年   1868篇
  2002年   1778篇
  2001年   3054篇
  2000年   2221篇
  1999年   1587篇
  1998年   1097篇
  1997年   1070篇
  1996年   907篇
  1995年   805篇
  1994年   721篇
  1993年   643篇
  1992年   988篇
  1991年   963篇
  1990年   854篇
  1989年   755篇
  1988年   737篇
  1987年   803篇
  1986年   662篇
  1985年   898篇
  1984年   834篇
  1983年   572篇
  1982年   567篇
  1981年   544篇
  1980年   504篇
  1979年   626篇
  1978年   656篇
  1977年   670篇
  1976年   580篇
  1975年   488篇
  1974年   529篇
  1973年   454篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity).  相似文献   
2.
Unsteady transitions of separation patterns in single expansion ramp nozzle   总被引:2,自引:0,他引:2  
Y. Yu  J. Xu  K. Yu  J. Mo 《Shock Waves》2015,25(6):623-633
  相似文献   
3.
4.
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages.  相似文献   
5.
Triazines are widely used in agriculture around the world as selective pre‐ and post‐emergence herbicides for the control of broad leaf and grassy weeds. With high toxicity and persistence, triazines can contaminate the environment and crops, so the development of rapid and sensitive methods for the determination of different triazines is necessary. Capillary electrophoresis comprises a group of techniques used to separate chemical mixtures. Analytical separation is based on different electrophoretic mobilities. This review focuses on the analysis of triazine herbicides with different modes of capillary electrophoresis, including capillary zone electrophoresis, micellar electrokinetic capillary electrophoresis, capillary electrochromatography and nonaqueous capillary electrophoresis. Determinations of triazines in various matrices such as surface water, groundwater, vegetables, soil and grains are emphasized. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
6.
7.
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors.  相似文献   
8.
Plant derived flavonoids have not been well explored in tissue engineering applications due to difficulties in efficient formulations with biomaterials for controlled presentation. Here, the authors report that surface coating of epigallocatechin gallate (EGCG) on polymeric substrates including poly (L‐lactic acid) (PLLA) nanofibers can be performed via oxidative polymerization of EGCG in the presence of cations, enabling regulation of biological functions of multiple cell types implicated in bone regeneration. EGCG coating on the PLLA nanofiber promotes osteogenic differentiation of adipose‐derived stem cells (ADSCs) and is potent to suppress adipogenesis of ADSCs while significantly reduces osteoclastic maturation of murine macrophages. Moreover, EGCG coating serves as a protective layer for ADSCs against oxidative stress caused by hydrogen peroxide. Finally, the in vivo implantation of EGCG‐coated nanofibers into a mouse calvarial defect model significantly promotes the bone regeneration (61.52 ± 28.10%) as compared to defect (17.48 ± 11.07%). Collectively, the results suggest that EGCG coating is a simple bioinspired surface modification of polymeric biomaterials and importantly can thus serve as a promising interface for tuning activities of multiple cell types associated with bone fracture healing.  相似文献   
9.
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号