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   374086篇
  免费   5763篇
  国内免费   3052篇
化学   183722篇
晶体学   4573篇
力学   19721篇
综合类   196篇
数学   54731篇
物理学   119958篇
  2020年   2894篇
  2019年   3097篇
  2018年   11762篇
  2017年   12545篇
  2016年   9186篇
  2015年   4400篇
  2014年   5503篇
  2013年   12316篇
  2012年   13822篇
  2011年   23056篇
  2010年   14809篇
  2009年   14680篇
  2008年   20253篇
  2007年   23475篇
  2006年   10223篇
  2005年   14851篇
  2004年   11193篇
  2003年   10503篇
  2002年   8540篇
  2001年   7915篇
  2000年   6401篇
  1999年   4781篇
  1998年   3996篇
  1997年   4011篇
  1996年   3929篇
  1995年   3692篇
  1994年   3842篇
  1993年   3423篇
  1992年   3873篇
  1991年   3864篇
  1990年   3734篇
  1989年   3584篇
  1988年   3660篇
  1987年   3569篇
  1986年   3358篇
  1985年   4450篇
  1984年   4727篇
  1983年   3936篇
  1982年   4053篇
  1981年   3961篇
  1980年   3937篇
  1979年   3922篇
  1978年   4247篇
  1977年   4099篇
  1976年   4188篇
  1975年   3847篇
  1974年   3912篇
  1973年   4086篇
  1972年   2858篇
  1971年   2370篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Journal of Fluorescence - This report describes a combined immunofluorescence and fluorescence viability stain applied as one staining solution for rapid detection of live Legionella...  相似文献   
2.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...  相似文献   
3.
Kinetics and Catalysis - A new ruthenium(II) cage complex with polar terminal groups in the apical substituents has been synthesized; the molecular design of the complex contributes to the...  相似文献   
4.
Zhang  Bing  Yang  Jie-qin  Liu  Ying  Hu  Bin  Yang  Yang  Zhao  Li  Lu  Qiang 《Cellulose (London, England)》2022,29(12):6565-6578
Cellulose - Heating is essential in various biomass pre-treatments and thermal conversion processes. It is of practical significance to study the characteristics of cellulose-lignin and...  相似文献   
5.
Automotive proton exchange membrane fuel cell stacks need to meet manufacturer specified rated beginning-of-life (BOL) performance before being assembled into vehicles and shipped off to customers. The process of “breaking-in” of a freshly assembled stack is often referred to as “conditioning.” It has become an intensely researched area especially in automotive companies, where imminent commercialization of fuel cell electric vehicles (FCEVs) demands a short, energy- and cost-efficient, and practical conditioning protocol. Significant advances in reducing the conditioning time from 1 to 2 days to as low as 4h or less, in some cases without the use of additional inert gases such as nitrogen, and with minimal use of hydrogen, and specialized test stations will be discussed.  相似文献   
6.
7.
Chemistry of Natural Compounds - O- and N-propylamino-derivatives of betulin and betulonic acid oxime and methyl ester were synthesized. Their antitumor activity against a panel of 60 human cancer...  相似文献   
8.
Fan  K.  Lu  R. S.  Liang  K. K.  Hou  Z. C. 《High Energy Chemistry》2022,56(4):264-269
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was...  相似文献   
9.
Journal of Structural Chemistry - The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L1) and iminonitroxide (L2) diradicals (HL1 is...  相似文献   
10.
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties.  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