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   4041篇
  免费   600篇
  国内免费   456篇
化学   2940篇
晶体学   40篇
力学   231篇
综合类   35篇
数学   473篇
物理学   1378篇
  2024年   10篇
  2023年   99篇
  2022年   102篇
  2021年   139篇
  2020年   190篇
  2019年   166篇
  2018年   142篇
  2017年   110篇
  2016年   174篇
  2015年   184篇
  2014年   172篇
  2013年   286篇
  2012年   292篇
  2011年   301篇
  2010年   215篇
  2009年   215篇
  2008年   244篇
  2007年   196篇
  2006年   194篇
  2005年   195篇
  2004年   179篇
  2003年   120篇
  2002年   117篇
  2001年   111篇
  2000年   113篇
  1999年   102篇
  1998年   86篇
  1997年   81篇
  1996年   85篇
  1995年   62篇
  1994年   72篇
  1993年   50篇
  1992年   44篇
  1991年   34篇
  1990年   41篇
  1989年   25篇
  1988年   24篇
  1987年   25篇
  1986年   18篇
  1985年   22篇
  1984年   13篇
  1983年   3篇
  1982年   7篇
  1981年   10篇
  1980年   7篇
  1979年   4篇
  1973年   3篇
  1972年   2篇
  1969年   2篇
  1967年   2篇
排序方式: 共有5097条查询结果,搜索用时 15 毫秒
941.
Xiao J  Zhao Y  Mao F  Liu J  Wu M  Yu X 《The Analyst》2012,137(1):195-201
The effect of a ZnO#ZnS QDs heterojunction (O#SQDs) on the binding affinities of flavonoid glycosides for bovine serum albumin (BSA) was investigated. The fluorescence intensities of BSA decreased remarkably with increasing concentration of O#SQDs. The magnitudes of the binding constants of flavonoid glycosides for BSA in the presence of O#SQDs were in the range of 10(5)-10(7) L mol(-1), and the number of binding sites per BSA (n) was determined as 1.24 ± 0.17. O#SQDs increased the affinities of flavonoid glycosides for BSA by about 2.96% to 114.68% depending on their structures. O#SQDs in blood will enhance the transportation of flavonoid glycosidegs in blood and improve their pharmacology effects. From this point, O#SQDs are a perfect candidate for flavonoid glycosides delivery applications.  相似文献   
942.
Li S  Mao L  Tian Y  Wang J  Zhou N 《The Analyst》2012,137(4):823-825
A spectrophotometric method for the detection of tyrosinase activity is developed by utilizing the product-triggered aggregation of boronic acid-functionalized gold nanoparticles. Based on the changes of absorbance in UV-visible spectra, the assay shows extremely high sensitivity and lowered limit of detection of 1 × 10(-10) u mL(-1).  相似文献   
943.
Single‐crystalline Ni2P nanotubes (NTs) were facilely synthesized by using a Ni nanowire template. The mechanism for the formation of the tubular structures was related to the nanoscale Kirkendall effect. These NTs exhibited a core/shell structure with an amorphous carbon layer that was grown in situ by employing oleylamine as a capping agent. Galvanostatic charge/discharge measurements indicated that these Ni2P/C NTs exhibited superior high‐rate capability and good cycling stability. There was still about 310 mAh g?1 retained after 100 cycles at a rate of 5 C. Importantly, the tubular nanostructures and the single‐crystalline nature of the Ni2P NTs were also preserved after prolonged cycling at a relatively high rate. These improvements were attributed to the stable nanotubular structure of Ni2P and the carbon shell, which enhanced the conductivity of Ni2P, suppressed the aggregation of active particles, and increased the electrode stability during cycling.  相似文献   
944.
The first examples of lanthanide(III) organoarsonates, Ln(L(1))(H(2)O)(3) (Ln = La (1), H(3)L(1) = 4-hydroxy-3-nitrophenylarsonic acid), Ln(L(1))(H(2)O)(2) (Ln = Nd (2), Gd (3)), and mixed-ligand lanthanide(III) organoarsonates, Ln(2)(HL(1))(2)(C(2)O(4))(H(2)O)(2) (Ln = Nd (4), Sm (5), Eu (6)), were hydrothermally synthesized and structurally characterized. Compounds 1-3 feature a corrugated lanthanide arsonate layer, in which 1D lanthanide arsonate inorganic chains are further interconnected via bridging L(1)(3-) ligands. Compounds 4-6 exhibit a complicated 3D network. The interconnection of the lanthanide(III) ions by the bridging arsonate ligand leads to the formation of a novel 3D framework with long narrow 1D tunnels along the a-axis, with the oxalate anions are located at the above tunnels and bridging with lanthanide(III) ions. Compounds 2 and 4 exhibit the characteristic emission bands of the Nd(III) ion, whereas compound 6 displays the characteristic emission bands of the Eu(III) ion. The magnetic properties of compounds 3-6 were also investigated.  相似文献   
945.
Columnar grains can lead to detrimental surface ridging and an inhomogeneous microstructure, although their {1 0 0}〈0 v w〉 texture is considered desirable due to their good magnetic properties in non-oriented silicon steel. Based on the hereditary tendency of {1 0 0}〈0 v w〉 texture, the effects of lubrication and heating rate on texture and on final magnetic properties were investigated using a cast slab containing 100% columnar grains. Hot rolling with lubrication, normalization at low heating rate, two-stage cold rolling, and final annealing at 1000 °C helped achieve high performance. As a result, a new non-oriented silicon steel with high magnetic induction (B50=1.82 T) and low core loss (P1.5=2.35 W/kg) was prepared. The possibility of further performance optimization was also discussed.  相似文献   
946.
Diffusion on random systems above and at their percolation threshold in three dimensions is carried out by a molecular trajectory method and a simple lattice random walk method, respectively. The classical regimes of diffusion on percolation near the threshold are observed in our simulations by both methods. Our Monte Carlo simulations by the simple lattice random walk method give the conductivity exponent μ/ν=2.32±0.02 for diffusion on the incipient infinite clusters and μ/ν=2.21±0.03 for diffusion on a percolating lattice above the threshold. However, while diffusion is performed by the molecular trajectory algorithm either on the incipient infinite clusters or on a percolating lattice above the threshold, the result is found to be μ/ν=2.26±0.02. In addition, it takes less time step for diffusion based on the molecular trajectory algorithm to reach the asymptotic limit comparing with the simple lattice random walk.  相似文献   
947.
Volatility series (defined as the magnitude of the increments between successive elements) of five different meteorological variables over China are analyzed by means of detrended fluctuation analysis (DFA for short). Universal scaling behaviors are found in all volatility records, whose scaling exponents take similar distributions with similar mean values and standard deviations. To reconfirm the relation between long-range correlations in volatility and nonlinearity in original series, DFA is also applied to the magnitude records (defined as the absolute values of the original records). The results clearly indicate that the nonlinearity of the original series is more pronounced in the magnitude series.  相似文献   
948.
PurposeIron deficiency anemia (IDA) and thalassemia (THAL) are two types of microcytic anemia, and both of these conditions disturb the morphology and function of erythrocytes at the molecular level. The ability to distinguish between thalassemic and iron deficiency anemia microcytosis has important clinical implications. The purpose of this study was to show that pathophysiological changes to erythrocytes could be detected at the nanometer scale, which is important for the early diagnosis of anemia and for distinguishing between IDA and THAL.MethodsBlood samples were taken from six healthy volunteers and six patients with either iron deficiency anemia or thalassemia. Changes in the morphological of erythrocytes were studied at the nanometer level using atomic force microscopy (AFM).ResultsThere were dramatic overall shape and surface membrane deformations of the erythrocytes associated with iron deficiency anemia and thalassemia compared to healthy erythrocytes. Healthy and pathological erythrocytes of iron deficiency anemia and thalassemia could be distinguished by the morphologic parameters of width, length, the ratio of length to width, valley, peak, valley-to-peak, standard deviations, and surface fluctuation. These AFM parameters of erythrocyte morphology differed greatly between iron deficiency anemia and thalassemia.ConclusionAFM was found to be an extremely useful tool for detecting and distinguishing between iron deficiency anemia and thalassemia. Erythrocyte morphology is an important determinant for diagnosing and distinguishing IDA and THAL.  相似文献   
949.
Tin (Sn) crystal growth on Sn-based anodes in lithium ion batteries is hazardous for reasons such as possible short-circuit failure by Sn whiskers and Sn-catalyzed electrolyte decomposition, but the growth mechanism of Sn crystals during battery cycling is not clear. Here we report different growth mechanisms of Sn crystal during the lithiation and delithiation processes of SnO(2) nanowires revealed by in situ transmission electron microscopy (TEM). Large spherical Sn nanoparticles with sizes of 20-200nm grew instantaneously upon lithiation of a single-crystalline SnO(2) nanowire at large current density (j>20A/cm(2)), which suppressed formation of the Li(x)Sn alloy but promoted agglomeration of Sn atoms. Control experiments of Joule-heating (j≈2400A/cm(2)) the pristine SnO(2) nanowires resulted in melting of the SnO(2) nanowires but not Sn particle growth, indicating that the abnormal Sn particle growth was induced by both chemical reduction (i.e., breaking the SnO(2) lattice to produce Sn atoms) and agglomeration of the Sn atoms assisted by Joule heating. Intriguingly, Sn crystals grew out of the nanowire surface via a different "squeeze-out" mechanism during delithiation of the lithiated SnO(2) nanowires coated with an ultra-thin solid electrolyte LiAlSiO(x) layer. It is attributed to the negative stress gradient generated by the fast Li extraction in the surface region through the Li(+)-conducting LiAlSiO(x) layer. Our previous studies showed that Sn precipitation does not occur in the carbon-coated SnO(2) nanowires, highlighting the effect of nanoengineering on tailoring the electrochemical reaction kinetics to suppress the hazardous Sn whiskers or nanoparticles formation in a lithium ion battery.  相似文献   
950.
以对氨基酚、对硝基氯苯、8-羟基喹啉、4-硝基邻苯二甲腈以及醋酸锌为主要原料,合成了不对称2(3)-[二(对硝基苯基)氨基苯氧基]-9(10),16(17),23(24)-三(8-喹啉氧)锌酞菁(TQPc).用核磁、红外、元素分析等表征TQPc以及前驱化合物结构,TQPc的电子吸收光谱表现出了强烈的π-π*跃迁现象.利用紫外光谱研究了其N,N-二甲基甲酰胺(DMF)和CH2Cl2溶液的吸收光谱性质,结果表明在DMF中主要以单体的形式存在,浓度在0.223×10-5~2.587×10-5mol/L时,TQPc在CH2Cl2溶液中有二聚体的存在,经计算得到平衡常数为0.24×105L/mol.用循环伏安法研究了TQPc的氧化还原行为,结合差分伏安数据计算了能级结构,LUMO(-1.04 V vs SCE)和HOMO(0.78 V vs SCE)与纳米TiO2导带能级匹配,可作为性能较好的电荷传输材料用于染料敏化太阳能电池.  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