全文获取类型
收费全文 | 71927篇 |
免费 | 12604篇 |
国内免费 | 13843篇 |
专业分类
化学 | 52234篇 |
晶体学 | 1603篇 |
力学 | 4394篇 |
综合类 | 1145篇 |
数学 | 9333篇 |
物理学 | 29665篇 |
出版年
2024年 | 144篇 |
2023年 | 1247篇 |
2022年 | 2057篇 |
2021年 | 2633篇 |
2020年 | 2884篇 |
2019年 | 2722篇 |
2018年 | 2409篇 |
2017年 | 2693篇 |
2016年 | 3186篇 |
2015年 | 3556篇 |
2014年 | 4233篇 |
2013年 | 5522篇 |
2012年 | 6389篇 |
2011年 | 6656篇 |
2010年 | 5211篇 |
2009年 | 5083篇 |
2008年 | 5432篇 |
2007年 | 4995篇 |
2006年 | 4609篇 |
2005年 | 4010篇 |
2004年 | 3071篇 |
2003年 | 2301篇 |
2002年 | 2249篇 |
2001年 | 2025篇 |
2000年 | 1949篇 |
1999年 | 1623篇 |
1998年 | 1166篇 |
1997年 | 1075篇 |
1996年 | 1053篇 |
1995年 | 955篇 |
1994年 | 869篇 |
1993年 | 736篇 |
1992年 | 626篇 |
1991年 | 502篇 |
1990年 | 435篇 |
1989年 | 369篇 |
1988年 | 257篇 |
1987年 | 238篇 |
1986年 | 223篇 |
1985年 | 180篇 |
1984年 | 142篇 |
1983年 | 128篇 |
1982年 | 90篇 |
1981年 | 77篇 |
1980年 | 48篇 |
1979年 | 46篇 |
1978年 | 22篇 |
1977年 | 21篇 |
1976年 | 26篇 |
1975年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
951.
大肠杆菌有限生长的微量热及非线性动力学研究 总被引:2,自引:0,他引:2
The finite growth of Escherichia coli was studied by using a LKB 2277 BioActivity Mollitor. We found that the finite growth is a nonliear dynamic process. The nonlinear dynamic behaviour in the finite growth process and the nonlinear dynamic models describing the process were discovered and established. The curve of logistic map corresponding to the finite growth thermogram of Escherichia coli was obtained and the nonlinear dynamic parameters were calculated by means of a computer. Moreover, we also discussed the nonlinear dynamic characters of Escherichia colt in its finite growth process. 相似文献
952.
953.
954.
Determination of impurities in highly pure platinum by inductively coupled plasma-atomic emission spectrometry 总被引:1,自引:0,他引:1
In this work, a cyclone spray chamber system is used in conjunction with an inductively coupled plasma-atomic emission spectrometer instead of the conventional Scott-type chamber system to reduce the lower limit of detection achieved by the instrument, and an internal standard element (Y) is introduced to eliminate the effects caused by the drift in the plasma background level. An ICP-AES method for the determination of 13 impurity elements in a highly pure platinum sample has been developed. In this method, it is not necessary either to add a platinum matrix to the calibration standard or to separate and concentrate the elements to be determined in the samples. The effect of the platinum matrix on the elements to be analyzed is corrected for by a background equivalent concentration subtraction method. The determination ranges of the method are as follows: 0.00010-0.0050% for Mg, Mn, Cu, Ag, Fe and Zn; 0.00030-0.015% for Au, Ir, Ni and Pb; 0.00050-0.025% for Rh and Al; and 0.00080-0.040% for Pd. The method is simple, rapid and accurate, and can be applied to the analysis of 99.9–99.995% pure platinum. 相似文献
955.
设计合成了两种新型的以聚类吡唑硼酸盐为配体的钒氧配合物VO(acac)[HB(pz)3](1)和VO(acac)[HB(3,5-Me2pz)3]·CH3CN(2). 运用元素分析、 红外光谱和紫外光谱对所合成的配合物进行了表征, 并用X射线衍射测定了它们的晶体结构. 同时, 采用量子化学的Hartree Fock方法和自然轨道分析方法(NBO), 使用3-21G*(6d, 7f)基组计算得到了两个分子体系的分子轨道、原子电荷以及键级, 并对其结构进行了分析. 相似文献
956.
研究了在硫酸介质中,微量铁(Ⅲ)催化过氧化氢氧化亚甲基蓝的褪色反应,建立了测定痕量铁方法.灵敏度为8.0×10-8g/mL,线性范围为0~1.000 0g/mL,用于自来水中铁的测定,结果与实际接近,相对标准偏差为0.67%. 相似文献
957.
958.
近年来,化学修饰电极以其独特的优越性,在分析测试中具有广阔的应用前景[1-6],因此对于新的修饰剂的研究,以及用修饰电极探讨灵敏度高,选择性好的测定方法具有重要的意义。2[2,3,5-三氮唑偶氮]-5-乙酰基氨基苯酚(2-(2,3,5-triazolylazo)-5-acetam idophenol,简称TZAAP)是一种新合成的有机化合物,其结构式为:由于TZAAP可以和金属离子形成稳定的配合物,在光谱法中可以作为显色剂用于环境及生物样品中微量元素的测定[7,8]。Nafion是一种优良的阳离子交换剂,用作电极修饰材料具有良好的离子交换特性[9]。本文作者制备了TZAAP-Nafion修饰… 相似文献
959.
Yong Zhao Xianliang Sheng Jin Zhai Lei Jiang Chunhe Yang Zhongwei Sun Yongfang Li Daoben Zhu 《Chemphyschem》2007,8(6):856-861
Titanium dioxide (TiO(2)) photoelectrodes with micro/nano hierarchical branched inner channels have been prepared by an electrohydrodynamic (EHD) technique and assembled to form dye-sensitized solar cells (DSSCs). Excellent penetration of ionic-liquid electrolytes and enhanced light harvesting in the longer wavelength region are realized within the composite-structure electrode, thus a better fill factor (ff) of 75.3 % and higher conversion efficiency (eta) of 7.1 % are obtained for viscous ionic-liquid electrolytes compared to pure nanostructured films. Hierarchical branched channels in the photoanodes can efficiently improve the transport properties of redox-active species in viscous electrolytes, which is demonstrated by electrical impedance spectroscopy (EIS). The incident monochromatic photon-to-electron conversion efficiency (IPCE) shows that enhanced light scattering in the composite film is of benefit for light harvesting and thus for solar energy conversion efficiency. 相似文献
960.
Piezoelectric diffuse reflectance spectroelectrochemistry (PDRSEC), a new technique of diffuse reflectance spectroelectrochemistry (DRSEC) in combination with electrochemical quartz crystal microbalance (EQCM), was developed to study the electrochemical copolymerization of aniline and o-anthranilic acid in 1.0 mol l(-1) HClO4 and the properties of these copolymers. The DRSEC using an integral sphere was proven to possess a higher optical sensitivity at the unpolished piezoelectric quartz crystal electrodes used than the mirror reflectance spectroelectrochemistry mode. The copolymers grown from the copolymerization bath of different molar fractions of o-anthranilic acid (F1, relative to the total amount of the two monomers) showed intermediate properties between those of the homopolymers, which varied gradually with F1. The swelling/dissolution behavior of the copolymers vs solution pH was traced via the EQCM frequency and resistance signals, and its large dependence on F1 was found and discussed. In a HAc-NaAc buffer solution at pH 5.6, the amount of adsorbed lysozyme was found to be positively correlated with F1, via an EQCM impedance investigation, demonstrating the feasibility of using poly(aniline-co-o-anthranilic acid) as a load-adjustable immobilization matrix for cationic proteins. The novel PDRSEC method proposed is highly recommended for surface electrochemistry studies at relatively rough electrodes. 相似文献