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   2852篇
  免费   99篇
  国内免费   11篇
化学   1785篇
晶体学   114篇
力学   70篇
数学   108篇
物理学   498篇
无线电   387篇
  2023年   26篇
  2022年   52篇
  2021年   72篇
  2020年   68篇
  2019年   80篇
  2018年   60篇
  2017年   95篇
  2016年   109篇
  2015年   54篇
  2014年   86篇
  2013年   236篇
  2012年   150篇
  2011年   164篇
  2010年   114篇
  2009年   110篇
  2008年   152篇
  2007年   129篇
  2006年   134篇
  2005年   94篇
  2004年   81篇
  2003年   66篇
  2002年   63篇
  2001年   33篇
  2000年   39篇
  1999年   34篇
  1998年   23篇
  1997年   28篇
  1996年   29篇
  1995年   30篇
  1994年   34篇
  1993年   26篇
  1992年   30篇
  1991年   27篇
  1990年   20篇
  1989年   21篇
  1988年   18篇
  1987年   20篇
  1986年   24篇
  1985年   18篇
  1984年   29篇
  1983年   25篇
  1982年   33篇
  1981年   32篇
  1980年   25篇
  1979年   27篇
  1978年   22篇
  1977年   14篇
  1976年   15篇
  1975年   18篇
  1973年   18篇
排序方式: 共有2962条查询结果,搜索用时 234 毫秒
101.
在当今飞速发展的电子环境中,芯片制造商和封装技术供应商们发现传统的前段制造设备,诸如光刻步进器等,可能会实现成本高效的后段工艺流程(BEOL)器件封装。尽管高级封装市场的发展空间最初是被PCs行业的蓬勃发展带动起来的,但是现在它们已经不再是主要的增长催化因素。通信以及手持设备,如手机、PDAs(个人数字助理)、便携式游戏机以及个人通讯系统正在成为新增长阶段的推动因素。随着数字消费应用的爆炸式发展一陛能和波形系统成为必须启用高级封装(AP)技术的必要条件。在未来五年内,预计通讯芯片组、图形处理器、集成无源元件以及高速PC内存元件将成为AP技术的主要诉求。随着领先的逻辑芯片制造商们需求量的不断增大,我们共同见证了AP市场的成长过程。然而,这一细分市场的另一个转折点可能会来自高速PC内存元件对高级封装技术的诉求。  相似文献   
102.
We report a 10-GHz colliding pulse mode-locked laser fabricated with integrated active-passive waveguides. The laser fabrication adopted a deep reactive ion etching and single-step metal-organic vapor phase epitaxy regrowth process for forming the buried heterostructure waveguide. Clean output pulses resulted from laterally tilting the active-passive interface and effectively suppressing residual back-reflections at the interface. Hybrid mode-locking resulted in a synchronized transform-limited sech/sup 2/optical waveform. Pulsewidth, chirp, timing jitter, and frequency-locking range were investigated through systematic device biasing condition optimization.  相似文献   
103.
104.
105.
2-Hydroxy benzoic acid hydrazide (1) undergoes facile condensation with aromatic aldehydes to afford the corresponding 2-hydroxy benzoic acid arylidene hydrazides (2a–h) in good yields. Cyclocondensation of compounds 2a–h with thioglycolic acid yields 2-hydroxy-N(4-oxo-2-aryl-thiazolidin-3-yl)-benzamides (3a–h). These 3a–h compounds are for the reacted with benzaldehyde in the presence of sodium ethanolate affords, giving 2-hydroxy-N(5-methylene-4-oxo-2-aryl-thiazolidin-3-yl)-benzamides (4a–h). The structures of these compounds were established on the basis of analytical and spectral data. All the newly synthesized compounds were evaluated for their antibacterial and antifungal activities.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.  相似文献   
106.
Friedel-Crafts polycondensation of β-resorcylic acid (BRA) with p-xylylene dichloride (PXDC) or 4,4′-dichloromethyldiphenyl ether (DDE) in dioxane could be effected without simultaneous decarboxylation of BRA. The similar polycondensation of BRA with PXDC, DDE, or 4,4′-dichloroacetyldiphenyl ether (DADE) in nitrobenzene or in the absence of solvent at 150°C was associated with decarboxylation of BRA. Polymers having structures isomeric with those of the polycondensation product of BRA formed with subsequent in situ decarboxylation were prepared by Friedel-Crafts polycondensation of resorcinol with the above dichlorides. All the polymer samples were characterized, and those with related structures were compared. The ion-exchange properties of the polymer sample prepared from BRA and DDE in dioxane were studied.  相似文献   
107.
Polyetheramides (PEAs) are prepared by polycondensation of N,N′-diacetyl-o-tolidide with Bisphenol A, C, or F, phenolphthalein, resorcinol, catechol, hydroquinone, or 1,5- or 2,7-dihydroxynaphthalene or ethylene, butylene, propylene, diethylene, or triethylene glycol. The fusible and soluble oligomers are characterized. An attempt is made to bring out the relationship between various properties of PEAs and their structures.  相似文献   
108.

The polymeric coordination compounds have been synthesized using the dipotassium salt of N,N′‐di(carboxymethylene)terephthalaldehydediimine (K2SB1) or N,N′‐di(carboxyethylene)terephthalaldehydediimine (K2SB2) with manganese(II), cobalt(II), nickel(II), copper(II), zinc(II), and cadmium(II). The ligands have been characterized by 1H‐NMR, and 13C‐NMR spectra. The polychelates have been characterized by elemental analyses, magnetic measurements, thermogravimetric analyses, electronic spectra and infrared spectra. The coordination compounds are colored, and the central metal ions are octahedrally coordinated with two water molecules and the Schiff bases. The Schiff bases act as di‐negative tetradentate ligands, in which bonding occurs through two oxygen and two nitrogen atoms. The polymers are insoluble in all common organic solvents such as acetone, methanol, ethanol, N,N‐dimethylformamide and dimethylsulfoxide.  相似文献   
109.
A general procedure using triphenylphosphine and diethylazodicarboxylate to prepare 2-oxazolines is described.  相似文献   
110.
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