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   7819篇
  免费   390篇
  国内免费   67篇
化学   5827篇
晶体学   73篇
力学   226篇
综合类   1篇
数学   644篇
物理学   1505篇
  2023年   33篇
  2022年   95篇
  2021年   139篇
  2020年   141篇
  2019年   159篇
  2018年   87篇
  2017年   89篇
  2016年   220篇
  2015年   205篇
  2014年   287篇
  2013年   475篇
  2012年   568篇
  2011年   681篇
  2010年   434篇
  2009年   378篇
  2008年   536篇
  2007年   410篇
  2006年   397篇
  2005年   390篇
  2004年   346篇
  2003年   279篇
  2002年   306篇
  2001年   179篇
  2000年   187篇
  1999年   110篇
  1998年   95篇
  1997年   68篇
  1996年   89篇
  1995年   72篇
  1994年   68篇
  1993年   64篇
  1992年   38篇
  1991年   49篇
  1990年   45篇
  1989年   45篇
  1988年   31篇
  1987年   31篇
  1986年   33篇
  1985年   49篇
  1984年   36篇
  1983年   39篇
  1982年   26篇
  1981年   35篇
  1980年   19篇
  1979年   22篇
  1978年   20篇
  1977年   28篇
  1976年   29篇
  1975年   22篇
  1974年   17篇
排序方式: 共有8276条查询结果,搜索用时 15 毫秒
951.
952.
The effect of various organic compounds on the Nafion/chelating agent mercury film electrodes (NCAMFEs) in square-wave anodic-stripping voltammetry (SWASV) is explored. Two chelating agents used to prepare the NCAMFEs are dimethylglyoxime and 2,2'-bipyridyl. Triton X-100, sodium dodecyl sulfate, albumin, gelatin, starch, camphor, and humic acid are used as model organic compounds, while cadmium, lead, and copper are used as test metal ions. The NCAMFEs are considerably more resistant to organic interferences than the Nafion-coated mercury film electrode. The implications of these interferences for the reliability and feasibility of stripping measurements using the NCAMFEs in real samples are discussed. Results presented for untreated urine and natural water samples demonstrate the analytical utility of the NCAMFEs in SWASV.  相似文献   
953.
Theoretical expressions and convergence conditions are developed here for the output of a feedback holographic associative memory. It is shown that a feedback holographic associative memory becomes a pinhole holographic associative memory under certain conditions, and thus is a generalization of the pinhole holographic associative memory. The crosstalk in the output of a feedback holographic associative memory can also be removed by a threshold device or controlled by the overall optical efficiency of the memory. A simulation is provided to verify the theoretical results shown here. Using the theoretical results and simulation verification, a feedback holographic associative memory can be designed efficiently. In addition, if a threshold device is used, optical elements with high optical efficiency can be used in a feedback holographic associative memory.  相似文献   
954.
955.
A computational scheme using the Chimera grid method is presented for simulation of three‐dimensional motion and aggregation of two red blood cells (RBCs) in a narrow tube. The cells are modelled as rigid ellipsoidal particles; the computational scheme is applicable to deformable fluid‐filled particles. Attractive energy between two RBCs is modelled by a depletion interaction theory and used for simulating aggregation of two cells. Through the simulation, we show that the Chimera grid method is applicable to the simulation of three‐dimensional motion and aggregation of multiple RBCs in a microvessel and microvascular network. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
956.
957.
Journal of the Operational Research Society - The classical no-shortage inventory policy is examined for the case of deteriorating items having a deterministic demand pattern with a linear...  相似文献   
958.
The kinetic distribution of64Cu,75Se, and69mZn radioactive tracers were determined in tissues of mice bearing ascites tumors and healthy ones. The HPGe gamma-ray spectrometric detection system was used for radionuclide analysis in tissues which were sampled at various periods after tracer injection during ascitic tumor growth. Significantly different distribution of64Cu,75Se, and69mZn were found in colon, small intestine, and liver of tumor-bearing mice. There was a dcerease of75Se in ascites and blood of tumor-bearing mice. The64Cu and69mZn concentration varied significantly in kidneys, and a similar effect was observed in the spleen for64Cu, too. A distinct variation of tracer distribution is also found at different stages after treatment. The results are discussed within the context of a correlation between elemental concentration and tumor-growth.  相似文献   
959.
Two new extended self‐polymerizable AB monomers, N‐(4‐fluorobenzoyl)‐4‐amino‐4′‐hydroxydiphenylether and N‐(4‐fluorobenzoyl)‐4‐amino‐4′‐hydroxybiphenyl, were prepared. The monomers were homopolymerized and copolymerized to high‐molecular‐weight, linear poly(arylether amides) in N‐methylpyrrolidone (NMP)/toluene in the presence of potassium carbonate at elevated temperature. The polymers retained NMP up to 200 °C. Samples containing small amounts of the solvent (5–10 wt %) were soluble in polar aprotic solvents. However, after complete removal of the NMP, the polymers were only soluble in strong acids such as sulfuric acid and methanesulfonic acid (MSA). The polymers, which had intrinsic viscosities of 0.57–1.49 dL/g (30.1 ± 0.1 °C in MSA), were semicrystalline with melting temperatures above 400 °C. Two new self‐polymerizable AB2 amide monomers, N,N′‐bis(4‐fluorobenzoyl)‐3,4‐diamino‐4′‐hydroxydiphenylether and N,N′‐bis(4‐fluorobenzoyl)‐3,5‐diamino‐4′‐hydroxybenzophenone, were also prepared and polymerized to give a hyperbranched poly(arylether amide) and a hyperbranched poly(aryletherketone) amide. The arylfluoride‐terminated, amorphous polymers had intrinsic viscosities of 0.34 and 0.24 dL/g (30.0 ± 0.1 °C in m‐cresol), glass‐transition temperatures of 210–269 °C, and were soluble in a wide variety of organic solvents. Matrix‐assisted laser desorption/ionization time‐of‐flight analysis indicated that the components of the low‐molecular‐weight fractions contained cyclic structures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2374–2389, 2003  相似文献   
960.
A DBSA (n‐dodecylbenzene sulfate)‐complexed aniline formaldehyde [AF(DBSA)1.0] was successfully synthesized with excess aniline (compared with formaldehyde) in the presence of n‐dodecylbenzene sulfonic acid (HDBSA), which was complexed with aniline monomer before polymerization. The resin was carefully characterized with 1H and 13C NMR, electron spectroscopy for chemical analysis, and Fourier transform infrared and was demonstrated to be a polymer in which anilines were all complexed with HDBSA and became anilinium salts. A drastic decrease of the maximum absorption wavelength (ultraviolet–visible spectra) of DBSA‐doped polyaniline [PANI(DBSA)0.5] was found when AF(DBSA)1.0 was mixed, and this resulted from the reduced conjugation length. A similar effect on PANI(DBSA)0.5 was found when free HDBSAs were mixed with PANI(DBSA)0.5. Visual inspection with an optical microscope revealed that PANI(DBSA)0.5/AF(DBSA)1.0 gave uniform morphologies in various compositions, showing possible miscibility for this system. X‐ray diffraction patterns of PANI(DBSA)0.5/AF(DBSA)1.0 showed that the layered structure of PANI(DBSA)0.5 was still present but became shorter in the polyblend because of the presence of AF(DBSA)1.0. Solid‐state 13C NMR spectra revealed that the reduced conjugation length was derived from the interaction of alkyl groups between HDBSA, complexed DBSA, and dopant DBSAs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3116–3125, 2005  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