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   37639篇
  免费   1042篇
  国内免费   124篇
化学   22695篇
晶体学   245篇
力学   1112篇
综合类   10篇
数学   5199篇
物理学   9544篇
  2023年   203篇
  2022年   489篇
  2021年   657篇
  2020年   605篇
  2019年   552篇
  2018年   654篇
  2017年   591篇
  2016年   1152篇
  2015年   924篇
  2014年   1024篇
  2013年   1837篇
  2012年   2121篇
  2011年   2351篇
  2010年   1359篇
  2009年   1275篇
  2008年   2048篇
  2007年   2007篇
  2006年   1735篇
  2005年   2116篇
  2004年   2002篇
  2003年   1528篇
  2002年   1104篇
  2001年   877篇
  2000年   800篇
  1999年   512篇
  1998年   429篇
  1997年   397篇
  1996年   499篇
  1995年   412篇
  1994年   405篇
  1993年   447篇
  1992年   426篇
  1991年   337篇
  1990年   272篇
  1989年   253篇
  1988年   227篇
  1987年   216篇
  1986年   212篇
  1985年   303篇
  1984年   290篇
  1983年   227篇
  1982年   236篇
  1981年   226篇
  1980年   217篇
  1979年   175篇
  1978年   213篇
  1977年   162篇
  1976年   162篇
  1975年   140篇
  1974年   157篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Development of biocompatible porous supports is a promising strategy in the field of tissue engineering for the repair and regeneration of bone tissues with severe damage. Graphene oxide aerogels (GOAs) are excellent candidates for the manufacture of these systems due to their porosity, ability to imitate bone structure, and mechanical resistance, and according to their surface chemical reactivity, they can facilitate osseointegration, osteogenesis, osteoinduction and osteoconduction. In this review, synthesis of GOAs from the most primary source is described, and recent studies on the use of these functionalized carbonaceous foams as scaffolding for bone tissue regeneration are presented.  相似文献   
14.
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures...  相似文献   
15.
16.
17.
Raman chemical imaging provides chemical and spatial information about pharmaceutical drug product. By using resolution methods on acquired spectra, the objective is to calculate pure spectra and distribution maps of image compounds. With multivariate curve resolution-alternating least squares, constraints are used to improve the performance of the resolution and to decrease the ambiguity linked to the final solution. Non negativity and spatial local rank constraints have been identified as the most powerful constraints to be used.  相似文献   
18.
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes.  相似文献   
19.
A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m2 g?1. The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities.  相似文献   
20.
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