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   434638篇
  免费   5573篇
  国内免费   1232篇
化学   233520篇
晶体学   5827篇
力学   18769篇
综合类   13篇
数学   50029篇
物理学   133285篇
  2021年   3746篇
  2020年   4202篇
  2019年   4531篇
  2018年   5868篇
  2017年   5750篇
  2016年   8861篇
  2015年   5597篇
  2014年   8575篇
  2013年   20232篇
  2012年   15711篇
  2011年   19334篇
  2010年   13546篇
  2009年   13392篇
  2008年   17727篇
  2007年   17637篇
  2006年   16325篇
  2005年   14628篇
  2004年   13610篇
  2003年   11965篇
  2002年   11800篇
  2001年   13456篇
  2000年   10120篇
  1999年   7925篇
  1998年   6592篇
  1997年   6324篇
  1996年   6104篇
  1995年   5488篇
  1994年   5412篇
  1993年   5211篇
  1992年   5845篇
  1991年   5941篇
  1990年   5677篇
  1989年   5483篇
  1988年   5390篇
  1987年   5296篇
  1986年   4995篇
  1985年   6491篇
  1984年   6629篇
  1983年   5239篇
  1982年   5339篇
  1981年   5321篇
  1980年   4890篇
  1979年   5315篇
  1978年   5452篇
  1977年   5363篇
  1976年   5301篇
  1975年   4889篇
  1974年   4856篇
  1973年   4859篇
  1972年   3438篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
161.
162.
Optics and Spectroscopy - 10.1134/S0030400X17050095  相似文献   
163.
Silver-mediated α-dC–Ag+–β-dC hybrid base pairs decorated with 5-iodo- or 5-octadiynyl residues are well accommodated in duplex DNA. A strong Tm increase and favorable thermodynamic data for duplex DNA were observed after addition of silver ions. The phenomenon is particularly obvious when both nucleobases of the base pairs are functionalized. Neither the position of the base pair, nor the type of 5-substituent had a negative influence. On the contrary, functionalization of conventional silver-mediated β-dC–Ag+–β-dC homo base pairs showed a negative impact induced by the bulky substituents. To this end, cytosine modified 12-mer oligodeoxynucleotides were prepared by solid-phase synthesis employing new α-anomeric 2′-deoxycytidine phosphoramidites. A multigram scale synthesis was developed for 5-iodo-α-d -2′-deoxycytidine ( 1 ) employing the direct glycosylation of cytosine with Hoffer's α-d -halogenose followed by separation of anomeric DMT nucleosides. Regarding base-pair stability and functionalization silver-mediated α/β-dC hybrid base pairs were found to be superior to β/β-dC homo pairs. According to their extraordinary properties, they might find applications in DNA diagnostics, material science, or nanotechnology.  相似文献   
164.
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 ?1.28×10?8 m2/s at atmospheric 293 K to a range of (?1.5, ?8)×10?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   
165.
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained...  相似文献   
166.
167.
Acetyl‐l ‐carnitine (ALCAR) is a potential biomarker for the modulation of brain neurotransmitter activity, but is also present in cerebrospinal fluid (CSF). Recent studies have utilized hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC‐MS/MS) based assays to detect and quantify ALCAR within biofluids such as urine, plasma and serum, using various sample pretreatment procedures. In order to address the need to quantify ALCAR in CSF on a high‐throughput scale, a new and simple HILIC‐MS/MS assay has been successfully developed and validated. For rapid analysis, CSF sample pretreatment was performed via ‘dilute and shoot’ directly onto an advanced HILIC column prior to MS/MS detection. This newly developed HILIC‐MS/MS assay shows good recoveries of ALCAR without the need for chemical derivatization and multistep sample extraction procedures. The employment of this assay is suitable for the high‐throughput bioanalysis and quantification of ALCAR within the CSF of various animal models and human clinical studies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
168.
169.
170.
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