全文获取类型
收费全文 | 3929篇 |
免费 | 559篇 |
国内免费 | 269篇 |
专业分类
化学 | 817篇 |
晶体学 | 17篇 |
力学 | 993篇 |
综合类 | 71篇 |
数学 | 615篇 |
物理学 | 2244篇 |
出版年
2024年 | 12篇 |
2023年 | 32篇 |
2022年 | 101篇 |
2021年 | 99篇 |
2020年 | 108篇 |
2019年 | 85篇 |
2018年 | 79篇 |
2017年 | 124篇 |
2016年 | 138篇 |
2015年 | 100篇 |
2014年 | 200篇 |
2013年 | 286篇 |
2012年 | 175篇 |
2011年 | 242篇 |
2010年 | 198篇 |
2009年 | 222篇 |
2008年 | 240篇 |
2007年 | 239篇 |
2006年 | 226篇 |
2005年 | 209篇 |
2004年 | 202篇 |
2003年 | 172篇 |
2002年 | 159篇 |
2001年 | 160篇 |
2000年 | 148篇 |
1999年 | 102篇 |
1998年 | 98篇 |
1997年 | 77篇 |
1996年 | 82篇 |
1995年 | 65篇 |
1994年 | 43篇 |
1993年 | 46篇 |
1992年 | 49篇 |
1991年 | 45篇 |
1990年 | 25篇 |
1989年 | 33篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
排序方式: 共有4757条查询结果,搜索用时 0 毫秒
71.
六十年代后期,在Hartree-Fock-Slater法的基础上,提出了Xα法[1].用于原子结构计算的Xα法与HF(Hartree-Fock)法的主要区别在于:用简单的统计平均交换势替代了HF法中计算最为困难的电子交换势,从而在保持较高理论严谨性和计算精确度的同时,大大减少了计算工作量,近年来获得了广泛的应用.我们尝试用经过适当修改的Xα方法,计算原子参数,解决分子结构中的某些问题.用原子参数解决分子问题,历来是化学和物理工作者常用的方法.本工作的意图是引入一个比HF法简单的容易在微机上实现的某种表现原子参数的计算方法,提供… 相似文献
72.
Rani Angineni Venkataswamy Perala Ramaswamy Kadari Srilekha Pallati Sreenu Kurra Vithal Muga 《印度化学会志》2022,99(6):100495
One of the well-known ways of increasing the visible light absorption capability of semiconducting materials is cation doping. This study aims to use Gd doping to tailor the bandgap energy of K2Ta2O6 (KTO) for photocatalytic degradation of organic pollutants under visible light irradiation. Accordingly, the parent KTO and Gd-doped KTO with different Gd concentrations (K2-3xGdxTa2O6; x = 0.025, 0.05, 0.075 and 0.1 mol%) were synthesized by hydrothermal and facile ion-exchange methods, respectively. The powder XRD, FT-IR, SEM-EDS, TEM-SAED, N2 adsorption-desorption, XPS, UV–Vis DRS, PL and ESR techniques were used to investigate the effect of Gd dopant concentration on the structural and photocatalytic properties of KTO. The photocatalytic activity of these samples was investigated for the photocatalytic degradation of methylene blue (MB) dye in an aqueous solution at room temperature under visible light irradiation. The experimental results show that all Gd-doped KTO samples exhibit enhanced photocatalytic activity compared with parent KTO toward MB degradation. In particular, Gd-KTO obtained by doping of 0.075 mol% shows the highest photocatalytic activity among the Gd-doped samples and the degradation efficiency of MB was 79% after 180 min of visible light irradiation, which is approximately 1.5 times as high as that by parent KTO (53%). In addition, trapping experiments and electron spin resonance (ESR) analysis demonstrated that the hydroxyl radicals (?OH) have played a crucial role in the photocatalytic degradation of MB. The reusability and stability of Gd doped-KTO with a Gd content of 0.075 mol% against MB degradation were examined for five cycles. Based on the present study results, a visible light induced photocatalytic mechanism has been proposed for Gd0075-KTO sample. 相似文献
73.
Xiao Zhao Shinobu Takao Takuma Kaneko Yasuhiro Iwasawa 《Chemical record (New York, N.Y.)》2019,19(7):1337-1353
It remains a big challenge to remarkably improve both oxygen reduction reaction (ORR) activity and long‐term durability of Pt?M bimetal electrocatalysts simultaneously in the harsh cathode environment toward widespread commercialization of polymer electrolyte fuel cells (PEFC). In this account we found double‐promotional effects of carbon micro coil (CMC) support on ORR performance and durability of octahedral Pt3Ni nanoparticles (Oh Pt3Ni/CMC). The Oh Pt3Ni/CMC displayed remarkable improvements of mass activity (MA; 13.6 and 34.1 times) and surface specific activity (SA; 31.3 and 37.0 times) compared to those of benchmark Pt/C (TEC10E20E) and Pt/C (TEC10E50E‐HT), respectively. Notably, the Oh Pt3Ni/CMC revealed a negligible MA loss after 50,000 triangular‐wave 1.0–1.5 VRHE (startup/shutdown) load cycles, contrasted to MA losses of 40 % (TEC10E20E) and 21.5 % (TEC10E50E‐HT) by only 10,000 load cycles. It was also found that the SA increased exponentially with the decrease in the CO stripping peak potential in a series of Pt?M/carbon (M: Ni and Co), which predicts a maximum SA at the curve asymptote. Key factors for simultaneous improvements of performance and durability of core‐shell Pt3Ni/carbon electrocatalysts toward superior PEFC is also discussed. 相似文献
74.
Theoretical expressions for the covalence reduction factors of orbital angular momentum and spin-orbit coupling in pseudo-tetrahedral four-coordinated paramagnetic complexes withD 2d symmetry, denoted ask's andR's respectively, have been derived. p ]The mixing coefficients in the antibonding MO's for the CuCl 4 2- ion in three complexes are estimated using suitable approximations. It is shown thatk's must be less thanR's in Tinkham's approximation. Certain misconceptions existing in the literature regarding the value of the integral 〈p u |???u|s〉 have been clarified. 相似文献
75.
Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying
ionic states (1, 22Π, and 1, 22Σ+) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and
double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians
have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic
states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states
are also presented and are compared with the photoelectron spectrum.
Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001 相似文献
76.
大气汽溶胶微粒子光学特性的研究 总被引:5,自引:0,他引:5
根据Mie微粒子光散射理论计算了汽溶胶大气模型的光学特性,得到了汽溶胶的散射截面、吸收截面和消光截面以及红外波段散射强度分布,同时计算了汽溶胶大气的发射率光谱,为研究大气红外传输提供了计算方法。 相似文献
77.
YU Jian-Chang WANG Chang-Yun 《结构化学》2007,26(10):1139-1144
In this paper,zinc acetate,manganese acetate and thiacetamide are used as raw materials to successfully synthesize monodispersed ZnS:Mn2+ microspheres by using hydrothermal method and taking P123 surfactant as a template. The products were characterized by XRD,STEM,FT-IR and N2 adsorption-desorption. And the results show that the diameter of this microsphere is 1.0 μm or so,which is larger than that of ZnS microsphere without Mn2+ doping,and it has monodispersion,smooth surface and uniform size. The doping of Mn2+ does not obviously change the structure of monodispersed ZnS microsphere. The photoluminescence peak lies in a wide band ranging from 450 to 650 nm,and the microspheres emit orange light; with the increase of Mn2+ concentration,fluorescence intensity of ZnS:Mn2+ microsphere changes,and when the mole ratio of Mn2+:Zn2+ is 0.3:1,the fluorescence intensity is the strongest. 相似文献
78.
《Physics and Chemistry of Liquids》2012,50(3):318-336
We know that vinblastine, as one of the vinca alkaloids, has played a major role in cancer chemotherapy by inhibiting the polymerisation of tubulin into microtubules. We present an in-depth investigation of the structural, infrared (IR) spectra of vinblastine. The structure of vinblastine is theoretically investigated using the density functional theory and Hartree–Fock levels of theory with the standard 6-31g* and 6-31g** basis sets. The vibrational spectral data obtained from IR spectra are assigned modes based on the results of the theoretical calculations as intensity and frequency curves. The fundamental vibrational modes were characterised depending on the stability of vinblastine in different dielectric constants. Thermodynamic analysis of data demonstrates good correlation of vinblastine at various media by SCRF–Onsager model with linear coefficient (R 2). Thus, the goal of this article is to evaluate and quantify the molecular basis for vinblastine structure in variant positions. 相似文献
79.
《Analytical letters》2012,45(2):257-280
Abstract A procedure for selection of wavelength range and number of factors to be used in partial least square calibration that involves the calculation of prediction residual sum of squares (PRESS) in different conditions is proposed. The best model takes into account the minimum PRESS value that does not show significant differences with respect to the corresponding model with fewer factors. The ability of the proposed method to minimize errors in partial least squares (PLS) prediction is demonstrated by applying it to the resolution of phenytoine (DPH) and phenobarbital (PB) binary mixtures with errors less than 2.8%; the results are compared with those obtained using another wavelength selection procedure. The ensuing method, which was validated by high performance liquid chromatography (HPLC), also gives good results with real samples (pharmaceutical preparations). 相似文献
80.
Jorge A. Vila Yelena A. Arnautova Osvaldo A. Martin Harold A. Scheraga 《Journal of computational chemistry》2014,35(4):309-312
The goal of this study is twofold. First, to investigate the relative influence of the main structural factors affecting the computation of the 13C′ shielding, namely, the conformation of the residue itself and the next nearest‐neighbor effects. Second, to determine whether calculation of the 13C′ shielding at the density functional level of theory (DFT), with an accuracy similar to that of the 13Cα shielding, is feasible with the existing computational resources. The DFT calculations, carried out for a large number of possible conformations of the tripeptide Ac‐G XY ‐NMe, with different combinations of X and Y residues, enable us to conclude that the accurate computation of the 13C′ shielding for a given residue X depends on the: (i) (?,ψ) backbone torsional angles of X ; (ii) side‐chain conformation of X ; (iii) (?,ψ) torsional angles of Y ; and (iv) identity of residue Y . Consequently, DFT‐based quantum mechanical calculations of the 13C′ shielding, with all these factors taken into account, are two orders of magnitude more CPU demanding than the computation, with similar accuracy, of the 13Cα shielding. Despite not considering the effect of the possible hydrogen bond interaction of the carbonyl oxygen, this work contributes to our general understanding of the main structural factors affecting the accurate computation of the 13C′ shielding in proteins and may spur significant progress in effort to develop new validation methods for protein structures. © 2013 Wiley Periodicals, Inc. 相似文献