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   6251篇
  免费   1055篇
  国内免费   780篇
化学   4241篇
晶体学   42篇
力学   454篇
综合类   33篇
数学   757篇
物理学   2559篇
  2024年   14篇
  2023年   134篇
  2022年   197篇
  2021年   198篇
  2020年   221篇
  2019年   248篇
  2018年   185篇
  2017年   188篇
  2016年   277篇
  2015年   307篇
  2014年   304篇
  2013年   370篇
  2012年   545篇
  2011年   595篇
  2010年   399篇
  2009年   319篇
  2008年   421篇
  2007年   376篇
  2006年   358篇
  2005年   333篇
  2004年   281篇
  2003年   197篇
  2002年   176篇
  2001年   146篇
  2000年   109篇
  1999年   149篇
  1998年   106篇
  1997年   118篇
  1996年   126篇
  1995年   116篇
  1994年   82篇
  1993年   67篇
  1992年   58篇
  1991年   65篇
  1990年   67篇
  1989年   53篇
  1988年   41篇
  1987年   27篇
  1986年   34篇
  1985年   27篇
  1984年   14篇
  1983年   9篇
  1982年   11篇
  1981年   5篇
  1980年   5篇
  1979年   2篇
  1976年   2篇
  1974年   1篇
  1957年   3篇
排序方式: 共有8086条查询结果,搜索用时 10 毫秒
951.
A hydrothermally synthesized mixed-ligand molecular solid composed of pillared bilayers has been formulated; it presents a new remarkable three-dimensional architecture sustained by the catenation of two-fold decked layers, and exhibits intense photoluminescence upon photoexcitation at 314 nm.  相似文献   
952.
Using the electrochemical method based on the "diffusion" layer concept of the convective system, the effect of lanthanide ions La3+ and Eu3+ on the activity of glutamate dehydrogenase (GLDH) has been determined. In suitable concentrations, the lanthanide ions La3+ and Eu3+ can activate the GLDH in the reductive amination of alpha-Ketoglutarate (alpha-KG). The activation mechanism would be that the lanthanide ions could interrupt the binding of NAD+ to GLDH by combining preferentially to NAD+. This mechanism was proposed by the voltammetric studies.  相似文献   
953.
The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.  相似文献   
954.
Molybdenum trioxide (MoO3) and PPyxMoO3 (x=0.5 and 1) nanobelts were obtained by the simple hydrothermal process from MoO3 sol. The morphology and structure of the samples were characterized using X-ray diffractometry (XRD), Fourier transformation infrared spectroscopy (FTIR), Raman spectra, SEM and AFM. The results show that the H atoms in polypyrrole are H-bonded with the O atoms in the Mo=O bonds of MoO3 nanobelts. Using the electrolyte, we fabricated electrochemical cells with a configuration of Li/(LiPF6+EC+DMC)/(MoO3+acetyleneblack+PTFE) and studied discharge profiles. PACS 81.07.BC; 81.05.Je; 82.47.Aa; 82.45.Fk; 82.45.Gj  相似文献   
955.
Super-hydrophobic PTFE surfaces were obtained by irradiation of 200 keV Xe+ ion with the fluence of 6.2×1013 ions/cm2. The contact angle of water on such surface is as large as 161±3°. SEM and XPS were used to investigate how the topological and chemical changes affect the wettability of the irradiated surface. Needle like structures at nanometer scale caused by irradiation are considered to be the reason of the super-hydrophobicity. The formation of oxygen containing group and defluorination effect on the treated surface are inferred to have negative contribution to the hydrophobic optimization of PTFE surface.  相似文献   
956.
We study three types of practical optimization problems faced by a firm that can control its liquid reserves by paying dividends and by issuing new equity. In the first problem, we consider the classical dividend problem without equity issuance. The second problem aims at maximizing the expected discounted dividend payments minus the expected discounted costs of issuing new equity over strategies associated with positive reserves at all times. The third problem has the same objective as the second one, but with no constraints on the reserves. Under the assumption of proportional transaction costs, we identify the value functions and the optimal strategies. We also present the relationship between three problems.  相似文献   
957.
High temperature electrical and thermal transport properties, that is, electrical conductivity, Seebeck coefficient and thermal conductivity, of CdO ceramics have been investigated. Because of the good electrical properties and low thermal conductivity, the dimensionless figure-of-merit ZT of the CdO ceramics reaches 0.34 at 1023 K. This value is comparable to the best reported ZT for the n-type oxide ceramic thermoelectric materials and remains as potential to be further improved by porosity controlling or nanostructuring.  相似文献   
958.
引入电流负反馈会使放大电路的输出电阻变大,这种变化在实验测量时几乎没有出现。我们在分析原因后,提出了一种简单、易行的解决方案,并且对电路参数进行了合理化设计,使实验效果非常理想。  相似文献   
959.
Xue B  Han J  Dai HL 《Physical review letters》2000,84(12):2606-2609
Through quantum-beat spectroscopy collision relaxation of a high vibrational level of SO2 at 44 877.52 cm(-1) is characterized. This is a first measurement of collision relaxation for a single, highly excited vibrational level. The deduced relaxation cross section of this excited level by Ar is 216 A(2), 5 times the area of the hard sphere, and by an ambient temperature SO2 molecule is 969 A(2), almost 20 times the hard sphere. These cross sections indicate that relaxation collisions of highly vibrationally excited molecules have effective distances much longer than van der Waals radii and involve mechanisms qualitatively different from lower excitations.  相似文献   
960.
Phenolics are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of plants. Plant polyphenols have drawn increasing attention due to their potent antioxidant properties and their marked effects in the prevention of various oxidative stress associated diseases such as cancer. In the last few years, the identification and development of phenolic compounds or extracts from different plants has become a major area of health- and medical-related research. This review provides an updated and comprehensive overview on phenolic extraction, purification, analysis and quantification as well as their antioxidant properties. Furthermore, the anticancer effects of phenolics in-vitro and in-vivo animal models are viewed, including recent human intervention studies. Finally, possible mechanisms of action involving antioxidant and pro-oxidant activity as well as interference with cellular functions are discussed.  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