全文获取类型
收费全文 | 17948篇 |
免费 | 716篇 |
国内免费 | 9篇 |
专业分类
化学 | 10336篇 |
晶体学 | 71篇 |
力学 | 323篇 |
数学 | 2287篇 |
物理学 | 5656篇 |
出版年
2023年 | 144篇 |
2021年 | 182篇 |
2020年 | 235篇 |
2019年 | 158篇 |
2018年 | 219篇 |
2017年 | 201篇 |
2016年 | 471篇 |
2015年 | 453篇 |
2014年 | 466篇 |
2013年 | 828篇 |
2012年 | 814篇 |
2011年 | 987篇 |
2010年 | 456篇 |
2009年 | 419篇 |
2008年 | 878篇 |
2007年 | 849篇 |
2006年 | 810篇 |
2005年 | 678篇 |
2004年 | 529篇 |
2003年 | 512篇 |
2002年 | 466篇 |
2001年 | 399篇 |
2000年 | 339篇 |
1999年 | 283篇 |
1998年 | 227篇 |
1997年 | 238篇 |
1996年 | 232篇 |
1995年 | 237篇 |
1994年 | 206篇 |
1993年 | 246篇 |
1992年 | 230篇 |
1991年 | 203篇 |
1990年 | 178篇 |
1989年 | 159篇 |
1988年 | 144篇 |
1987年 | 155篇 |
1986年 | 174篇 |
1985年 | 192篇 |
1984年 | 224篇 |
1983年 | 194篇 |
1982年 | 194篇 |
1981年 | 208篇 |
1980年 | 183篇 |
1979年 | 177篇 |
1978年 | 192篇 |
1977年 | 184篇 |
1976年 | 161篇 |
1975年 | 157篇 |
1974年 | 138篇 |
1973年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Central European Journal of Operations Research - This paper deals with the dynamic efficiency analysis based on Data Envelopment Analysis (DEA) models. Our aim is to formulate new dynamic DEA... 相似文献
2.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
3.
4.
G. Grätzer 《Algebra Universalis》2015,74(3-4):351-359
5.
A protocol to correct for intra‐ and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
6.
Yingchun Wu Haipeng Li Xuecheng Wu Gérard Gréhan Lutz Mädler Cyril Crua 《Proceedings of the Combustion Institute》2019,37(3):3211-3218
Droplet evaporation characterization, although of great significance, is still challenging. The recently developed phase rainbow refractometry (PRR) is proposed as an approach to measuring the droplet temperature, size as well as evaporation rate simultaneously, and is applied to a single flowing n-heptane droplet produced by a droplet-on-demand generator. The changes of droplet temperature and evaporation rate after a transient spark heating are reflected in the time-resolved PRR image. Results show that droplet evaporation rate increases with temperature, from ?1.28 m2/s at atmospheric 293 K to a range of (?1.5, ?8) m2/s when heated to (294, 315) K, agreeing well with the Maxwell and Stefan–Fuchs model predictions. Uncertainty analysis suggests that the main source is the indeterminate gradient inside droplet, resulting in an underestimation of droplet temperature and evaporation rate. With the demonstration on simultaneous measurements of droplet refractive index as well as droplet transient and local evaporation rate in this work, PRR is a promising tool to investigate single droplet evaporation in real engine conditions. 相似文献
7.
8.
9.
10.
Dr. Man-Bo Li Daniels Posevins Dr. Karl P. J. Gustafson Dr. Cheuk-Wai Tai Dr. Andrey Shchukarev Dr. Youai Qiu Dr. Jan-E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):210-215
A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution. 相似文献