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   1564490篇
  免费   32543篇
  国内免费   8353篇
化学   686731篇
晶体学   20384篇
力学   75383篇
综合类   116篇
数学   245415篇
物理学   378934篇
无线电   198423篇
  2021年   14899篇
  2020年   17495篇
  2019年   17680篇
  2018年   13995篇
  2016年   30215篇
  2015年   22157篇
  2014年   33128篇
  2013年   79317篇
  2012年   42689篇
  2011年   40076篇
  2010年   41402篇
  2009年   45911篇
  2008年   42348篇
  2007年   39641篇
  2006年   46158篇
  2005年   38040篇
  2004年   39260篇
  2003年   36819篇
  2002年   37556篇
  2001年   37540篇
  2000年   32844篇
  1999年   29613篇
  1998年   27762篇
  1997年   27572篇
  1996年   27067篇
  1995年   24795篇
  1994年   24290篇
  1993年   23671篇
  1992年   23742篇
  1991年   23897篇
  1990年   22716篇
  1989年   22287篇
  1988年   21469篇
  1987年   20192篇
  1986年   18992篇
  1985年   25516篇
  1984年   26562篇
  1983年   22429篇
  1982年   23796篇
  1981年   22975篇
  1980年   22236篇
  1979年   22275篇
  1978年   23405篇
  1977年   23046篇
  1976年   22685篇
  1975年   21399篇
  1974年   21001篇
  1973年   21539篇
  1972年   15702篇
  1967年   13457篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
761.
762.
763.
764.
765.
766.
The discharge of diverse pollutants has led to a complex water environment and posed a huge health threat to humans and animals. Self-propelled micromotors have recently attracted considerable attention for efficient water remediation due to their strong localized mass transfer effect. However, a single functionalized component is difficult to tackle with multiple contaminants and requires to combine different decontamination effects together. Here, we introduced a multifunctional micromotor to implement the adsorption and degradation roles simultaneously by integrating the poly(aspartic acid) (PASP) adsorbent with a MnO2-based catalyst. The as-prepared micromotors are well propelled in contaminated waters by MnO2 catalyzing hydrogen peroxide. In addition, the catalytic ramsdellite MnO2(R-MnO2) inner layer is decorated with Fe2O3 nanoparticles to improve their catalytic performance, contributing to an excellent degradation ability with 90% tetracycline (TC) removal in 50 minutes by enhanced Fenton-like reactions. Combining the attractive adsorption capability of poly (aspartic acid) (PASP), the composite micromotors offer an efficient removal of heavy metal ions in short time. Moreover, the designed micromotors are able to simultaneously remove antibiotic and heavy metals in mixed contaminants circumstance just in single treatment. This multifunctional micromotor with distinctive decontamination ability exhibits a promising prospective in treating multiple pollutants in the future.  相似文献   
767.
Journal of Analytical Chemistry - A new liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method has been developed and validated for alfuzosin quantification in...  相似文献   
768.
A photo-switchable hetero-complementary quadruple H-bonding array, which consists of an azobenzene-derived ureidopyrimidinone (UPy) module ( Azo-UPy ) and a nonphotoactive diamidonaphthyridine (DAN) derivative ( Napy-1 ), is constructed based on a reversible photo-locking approach. Upon UV (390 nm)/Vis (460 nm) light irradiations, photo-switchable quadruple H-bonded dimerization between Azo-UPy and Napy-1 can be achieved with exhibiting 4.8×104-fold differences in binding strength (ON/OFF ratios). Furthermore, smart polymeric gels with unique photo-controlled macroscopic self-assembly behavior can be fabricated by introducing such quadruple H-bonding array as photo-regulable noncovalent interfacial connections.  相似文献   
769.
The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism.  相似文献   
770.
π-Extended molecules are key components for the development of materials science. In fact, polyaromatic structures are fundamental for the scientific and technological progress of fields such as organic electronics and bio-applications. Beneficial properties of π-extended structures are absorption in the visible region, often luminescence, high electron mobilities and stability. Common approaches to adjust the properties of polyaromatic structures to functional setups involve changes in shape and size at the molecular level. Recently, incorporating hetero-elements emerged as successful approach. In this regard, organophosphorus conjugated molecules are new materials holding great promise for potential applications. In this review, we comprehensively discuss the design/development of polyaromatic phosphorus materials and their applicability. We establish structure/property/applicability relationships to provide key guidelines for the engineering of newer, future applications. This article thus provides a source of information for the further development of this rapidly evolving field of research.  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