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   689695篇
  免费   7372篇
  国内免费   1824篇
化学   351339篇
晶体学   7532篇
力学   33036篇
综合类   20篇
数学   94679篇
物理学   212285篇
  2020年   5795篇
  2019年   6256篇
  2018年   13402篇
  2017年   13787篇
  2016年   14510篇
  2015年   8034篇
  2014年   11810篇
  2013年   29169篇
  2012年   24570篇
  2011年   34502篇
  2010年   23529篇
  2009年   23367篇
  2008年   31529篇
  2007年   33301篇
  2006年   23194篇
  2005年   25003篇
  2004年   21171篇
  2003年   18921篇
  2002年   16311篇
  2001年   18289篇
  2000年   13670篇
  1999年   10296篇
  1998年   8669篇
  1997年   8537篇
  1996年   8247篇
  1995年   7855篇
  1994年   7847篇
  1993年   7469篇
  1992年   8403篇
  1991年   8428篇
  1990年   8113篇
  1989年   7872篇
  1988年   7941篇
  1987年   7816篇
  1986年   7306篇
  1985年   9671篇
  1984年   9963篇
  1983年   8229篇
  1982年   8477篇
  1981年   8196篇
  1980年   7759篇
  1979年   8487篇
  1978年   8732篇
  1977年   8433篇
  1976年   8471篇
  1975年   8015篇
  1974年   8020篇
  1973年   8112篇
  1972年   5622篇
  1971年   4679篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Cascade reactions have been widely recognized to cut costs, decrease solvent usage, and reduce cycle times in chemical processes. Recently, biocatalytic cascades have altered how we design synthetic routes to complex molecules to achieve sustainable commercial processes for pharmaceutical, agricultural, and fine chemical industries. With advancements in protein engineering and an increase in the number of enzyme classes available to chemists, industrial and academic groups alike have endeavored to expand the scope of biocatalysis from single reactions to multi-enzyme cascades to rapidly build complex molecular structures. Recent reports have drawn inspiration from biosynthetic pathways and have applied engineered enzymes to in vitro enzymatic cascades. Furthermore, combining transition-metal catalysis and enzymes in one-pot chemoenzymatic cascades likewise serves to broaden the scope of biocatalysis, enabling traditional chemical reactions to be performed under mild aqueous conditions. In this article, we review recent biocatalytic and chemoenzymatic cascades from 2019 to 2021.  相似文献   
2.
Different strategies for the preparation of efficient and robust immobilized biocatalysts are here reviewed. Different physico-chemical approaches are discussed.i.- The stabilization of enzyme by any kind of immobilization on pre-existing porous supports.ii.- The stabilization of enzymes by multipoint covalent attachment on support surfaces.iii.- Additional stabilization of immobilized-stabilized enzyme by physical or chemical modification with polymers.These three strategies can be easily developed when enzymes are immobilized in pre-existing porous supports. In addition to that, these immobilized-stabilized derivatives are optimal to develop enzyme reaction engineering and reactor engineering. Stabilizations ranging between 1000 and 100,000 folds regarding diluted soluble enzymes are here reported.  相似文献   
3.
Hydrothermal synthesis using graphene oxide (GO) as a precursor has been used to produce luminescent graphene quantum dots (GQDs). However, such a method usually requires many reagents and multistep pretreatments, while can give rise to GQDs with low quantum yield (QY). Here, we investigated the concentration, the temperature of synthesis, and the pH of the GO solution used in the hydrothermal method through factorial design experiments aiming to optimize the QY of GQDs to reach a better control of their luminescent properties. The best synthesis condition (2 mg/mL, 175 °C, and pH = 8.0) yielded GQDs with a relatively high QY (8.9%) without the need of using laborious steps or dopants. GQDs synthesized under different conditions were characterized to understand the role of each synthesis parameter in the materials' structure and luminescence properties. It was found that the control of the synthesis parameters enables the tailoring of the amount of specific oxygen functionalities onto the surface of the GQDs. By changing the synthesis' conditions, it was possible to prioritize the production of GQDs with more hydroxyl or carboxyl groups, which influence their luminescent properties. The as-developed GQDs with tailored composition were used as luminescent probes to detect Fe3+. The lowest limit of detection (0.136 μM) was achieved using GQDs with higher amounts of carboxylic groups, while wider linear range was obtained by GQDs with superior QY. Thus, our findings contribute to rationally produce GQDs with tailored properties for varied applications by simply adjusting the synthesis conditions and suggest a pathway to understand the mechanism of detection of GQDs-based optical sensors.  相似文献   
4.
Fluid Dynamics - Steady-state subsonic flows of nonequilibrium air plasma past a cylindrical body with plane face and heat transfer are investigated under the conditions characteristic of testing...  相似文献   
5.
Massoumi  Sina  Challamel  Noël  Lerbet  Jean  Wautier  Antoine  Nicot  François  Darve  Félix 《Meccanica》2022,57(8):2043-2066
Meccanica - This study is an attempt towards a better understanding of the length scale effects on the bending response of the granular beams. To this aim, a unidimensional discrete granular chain...  相似文献   
6.
Awad  A. M.  Askar  S. S.  Elsadany  A. A. 《Nonlinear dynamics》2022,107(4):3983-3999
Nonlinear Dynamics - In this paper, an economic competition between two firms that want to maximize the weighted-average social welfare and own profits is proposed. This kind of competition is...  相似文献   
7.
Crystallography Reports - The review presents the important unique results of the cycle of research led by M.V. Kovalchuk on the fundamental patterns of protein interactions and the protein...  相似文献   
8.
Physics of the Solid State - Magnetoelectric effects in multiferroics with a perovskite structure, such as bismuth ferrite, rare-earth orthochromites, and Ruddlesden–Popper structures...  相似文献   
9.
Russian Physics Journal - Using the methods of modern physical materials science, the structural phase state, the defect substructure and the fracture surface of low-carbon alloy steel welds formed...  相似文献   
10.
Russian Journal of General Chemistry - On the basis of 4-(thien-2-yl)-3-aminopyridine-2(1H)-one, the corresponding chloroacetamide and condensed 1H-pyrido[2,3-b][1,4]oxazine-2(3H)-one were...  相似文献   
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