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   4270篇
  免费   833篇
  国内免费   395篇
化学   2963篇
晶体学   39篇
力学   278篇
综合类   55篇
数学   498篇
物理学   1665篇
  2024年   10篇
  2023年   92篇
  2022年   172篇
  2021年   187篇
  2020年   215篇
  2019年   192篇
  2018年   170篇
  2017年   136篇
  2016年   229篇
  2015年   217篇
  2014年   272篇
  2013年   357篇
  2012年   388篇
  2011年   361篇
  2010年   281篇
  2009年   209篇
  2008年   254篇
  2007年   243篇
  2006年   203篇
  2005年   170篇
  2004年   112篇
  2003年   114篇
  2002年   103篇
  2001年   95篇
  2000年   85篇
  1999年   120篇
  1998年   73篇
  1997年   88篇
  1996年   68篇
  1995年   65篇
  1994年   49篇
  1993年   45篇
  1992年   27篇
  1991年   28篇
  1990年   19篇
  1989年   10篇
  1988年   5篇
  1987年   5篇
  1986年   13篇
  1985年   5篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   4篇
  1957年   3篇
排序方式: 共有5498条查询结果,搜索用时 31 毫秒
991.
A series of novel quinoline-3-carboxamide derivatives 10-17 and 23-27 were designed and synthesized as cholesteryl ester transfer protein (CETP) inhibitors. All of them exhibited activity against CETP. Particularly, compounds 24 and 26 displayed the best activity against CETP with the same inhibitory rate of 80.1%.  相似文献   
992.
The objective of this study was to test the hypothesis that p-cymene can attenuate acute lung injury induced by lipopolysaccharide (LPS) in vivo. In the mouse model of LPS-induced acute lung injury, intraperitoneal preconditioning with p-cymene resulted in a significant reduction of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6), lung water gain, inflammatory cell infiltration, lung tissue myeloperoxidase activity. In addition, p-cymene blocked the phosphorylation of IκBα protein and mitogen-activated protein kinases (MAPK) signaling pathway activation. Histopathologic examination of lung tissue indicated that p-cymene treatment markedly decreased focal thickening, congestion, pulmonary edema, and inflammatory cells infiltration. The results showed that p-cymene had a protective effect on LPS-induced ALI in mice.  相似文献   
993.
Resveratrol (Res) is a plant-based polyphenol compound and is known to inhibit the growth of a variety of cancer cells and protect lipoproteins against oxidative damage. However the poor solubility and labile property may constitute a serious problem for its bioavailability. The problem could be overcome by the formation of inclusion complexes with cyclodextrins (CDs). The aim of this work is to include Res by β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-CD) to form the Res/β-CD and Res/HP-CD inclusion complexes and evaluate their cytotoxicity on cancer cells and inhibition of lipid peroxidation activity. The complexes are characterized by powder X-ray diffraction, fourier transform infrared spectroscopy and scanning electron microscopy. The cytotoxicity of the two complexes has been evaluated by methylthiazoletetrazolium reduction assay on two cancer cell lines (cervical carcinoma cells HeLa and hepatocellular liver cancer cells Hep3B) and one normal cell line (umbililical vein endothelial cell HUVEC). The results showed that the two complexes exhibit high cytotoxicity on two cancer cells, especially for Hep3B, and show no significant effect on normal cells. The Res/HP-CD complex shows higher cytotoxicity on the two cancer cells than that of the Res/β-CD complex. The inhibition of lipid peroxidation induced by Fe2+/ascorbate of the two inclusion complexes has been determined by thiobarbituric acid assay. The inhibition rate shows a linear increase with the increase of CDs concentration, and the Res/HP-CD complex shows stronger inhibition activity than that of the Res/β-CD complex. The results of this work indicate a potential for using the Res/CD complexes to inhibit human cancer growth and lipoproteins peroxidation.  相似文献   
994.
A versatile one‐step method for the general synthesis of metal oxide hollow nanostructures is demonstrated. This method involves the controlled deposition of metal oxides on shaped α‐Fe2O3 crystals which are simultaneously dissolved. A variety of uniform SnO2 hollow nanostructures, such as nanococoons, nanoboxes, hollow nanorings, and nanospheres, can be readily generated. The method is also applicable to the synthesis of shaped TiO2 hollow nanostructures. As a demonstration of the potential applications of these hollow nanostructures, the lithium storage capability of SnO2 hollow structures is investigated. The results show that such derived SnO2 hollow structures exhibit stable capacity retention of 600–700 mAh g?1 for 50 cycles at a 0.2 C rate and good rate capability at 0.5–1 C, perhaps benefiting from the unique structural characteristics.  相似文献   
995.
996.
We report on a biosensor for the electrochemical detection of the damage of DNA and of antioxidant protecting DNA. The biosensor was constructed by co-immobilization of DNA and glucose oxidase (GOx) on a glassy carbon electrode. Under aerobic conditions, GOx catalyzes the oxidation of glucose, and the hydrogen peroxide produced reacts with ferrous ions in a Fenton-type reaction to generate hydroxy radical. This was validated by UV–vis spectroscopy. The hydroxy radical can cause serious oxidative damage to DNA, and this can be detected by square wave voltammetry of the electroactive indicator Co(bpy) 3 3+ . The effects of pH value, incubation time, and the concentration of glucose and ferrous ion were optimized. The effects of the antioxidants ascorbic acid and aloe emodin on DNA damage were also investigated within the concentration range from 0.05 to 200?μM. This work provides an in-vitro model system to mimic the processes in oxidative DNA damage by a simple electrochemical approach.
Figure
Schematic diagram for working principle of SWV detection of in situ DNA damage for DNA-GOx film.  相似文献   
997.
998.
We propose a scheme to generate multiple-atom entangled states in separate cavities. In our scheme, only weak cross-Kerr mediums, homodyne measurement, and some linear elements are employed. With the help of homodyne measurement, four-atom GHZ state can be obtained with high probability and fidelity, and the proposal can be easily scaled to prepare multiple-atom GHZ state. Under ideal conditions, the success probability will not be affected by atomic numbers.  相似文献   
999.
In order to well study the influence of the thickness and doping concentration on optical properties of transmission-mode GaAs photocathode, three exponential-doping and one uniform-doping photocathode modules were prepared by molecular beam epitaxy with a structure of glass/Si3N4/Ga1 ? xAlxAs/GaAs. By use of the spectrophotometer, the optical properties were separately measured including the reflectivity and transmissivity curves. Based on thin film optical principles, the optical properties and their integral values are calculated by matrix formula for the four-layer photocathode module. The result shows that the antireflection and window layers affect the peak and valley of the optical property curves and the active layer influences the absorptivity values of the transmission-mode cathode modules. The photocathode module has high absorptivity within the response waveband when the optimal module has the Si3N4 antireflection layer of 0.1 μm, the Ga1 ? xAlxAs window layer of more than 0.4 μm, and the GaAs active layer of 1.5 μm–2 μm and low average doping concentration.  相似文献   
1000.
We performed off-lattice Monte Carlo simulations of links of two model ring chains with chain length N up to 32,768 in the theta solution or amorphous bulk state by using a random walk model (Model I), and molecular dynamics simulations of two model ring chains in solution with excluded volume interaction (Model II) to investigate topological effects on the geometry of link and ring conformation. In the case of Model I, the mean squared linking number, its distribution, and the size of two chains with fixed linking number are investigated. Our simulation results confirm the previous theoretical prediction that the mean squared linking number decays as pe(-qs(2)) with the distance of centers of chain mass s, where p and q are found to be chain length dependent and q asymptotically approaches to 0.75 as chain length increases. The linking number distribution of two chains has a universal form for long chains, but our simulation results clearly show that the distribution function deviates from the Gaussian distribution, a fact not predicted by any previous theoretical work. A scaling prediction is proposed to predict the link size, and is checked for our simulations for the Model II. The simulation results confirmed the scaling prediction of the blob picture that the link with linking number m occupies a compact volume of m blobs, and the size of the link is asymptotic to R(L) ≈ bN(ν)m(1/3-ν), where N is the chain length, and v is the Flory exponent of polymer in solutions.  相似文献   
[首页] « 上一页 [95] [96] [97] [98] [99] 100 下一页 » 末  页»
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