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991.
为给岩溶覆盖区盖层土体的稳定性判别方法提供更多的有效途径,以岩溶疏干区典型圆柱状盖层土体为研究对象,基于传统的极限平衡法,首先建立了处于一定覆盖层厚度、土体重度、降雨积水深度及岩溶空腔跨度等条件下的覆盖层土柱 临界线,在覆盖层土柱的渐进破坏过程中,土体的黏聚强度和内摩擦角发挥作用的大小和顺序是不同的,根据潘家铮原理假设二者沿着距离 临界线最短的路径折减,然后利用强度折减法确定了黏聚强度和内摩擦角的折减系数,进而获得了岩溶覆盖区盖层土体的稳定系数计算式,定义了覆盖层土体稳定状态的可靠域及失效域。最后指出在圆柱状塌陷坑形成后由于应力重新分布和集中,塌陷坑有继续塌陷的可能,通过分析建立了塌陷坑稳定性判据系数,为圆柱状塌陷坑是否二次发育继续塌陷提供了判定依据。实例分析表明,基于强度折减法建立的稳定系数计算结果及利用塌陷坑稳定性判据系数对已有塌陷坑稳定性进行判定的结果与现实情况吻合良好,为岩溶覆盖区盖层土体的稳定性分析提供了理论依据。 相似文献
992.
本文采用离子快速注入法,在低温条件下利用微量NiO物种对TiO_2光催化剂表面微结构进行了修饰和改性,构建了NiO光催化反应活性中心。研究结果表明,Ni物种是以TiO_2-NiO-H形式存在于TiO_2表面;相对于未修饰的TiO_2光催化剂,NiO的修饰很大程度上提高了其光催化析氢性能,在最佳条件下,放氢速率由1.1μmol·h~(-1)提高到241.4μmol·h~(-1)。另外,Ni物种含量,热处理温度,乙醇电子给体浓度,催化剂悬浮浓度对光催化析氢性能也有明显的影响。光电化学实验结果表明,NiO的表面修饰能够产生有效的光催化反应活性中心,增强了光生电子-空穴电子对的分离效果。所制备的光催化剂采用X射线粉末衍射(XRD),光电子能谱(XPS)等技术进行表征。 相似文献
993.
994.
In the thermochemical water-splitting iodine–sulfur process for hydrogen production, new polymer electrolyte membranes were applied in an electro-membrane process (electro-electrodialysis, EED) to increase the HI molality of HIx solution (HI + I2 + H2O mixture) to be over quasi-azeotropic. Radiation grafting of a styrene monomer into a poly(ethylene-co-tetrafluoroethylene) base film and subsequent sulfonation provided electrolyte membranes that had ion exchange capacities (IECs) of 1.1–1.6 mmol/g. With the EED of the HIx solutions using [HI] = [I2] = 10 mol/kg at 40 °C the transport number of protons, ratio of permeated quantities of water to the protons, and current efficiency all appeared to depend on the IEC of the resulting membranes. When compared to Nafion, the self-made membranes exhibited lower electric cell resistance, and thereby decreasing up to 32% of the overall energy required in the concentration operation. 相似文献
995.
Ce掺杂K_2La_2Ti_3O_(10)催化剂的可见光高效催化制氢的研究 总被引:1,自引:0,他引:1
采用高温固相法合成了铈掺杂的K2La2Ti3O10催化剂,利用X射线衍射(XRD)、紫外-可见漫反射(UV-visDRS)、透射电镜(TEM)和X射线光电子能谱(XPS)对催化剂进行了表征.考察了催化剂的可见光催化分解甲醇水溶液制氢的活性,并对可见光催化机理进行了分析.研究表明,铈的掺杂没有改变K2La2Ti3O10的微晶结构,并使催化剂粒径有所减小.紫外可见漫反射分析表明禁带宽度为2.3eV左右,对可见光具有较高吸收.XPS表明La和Ti为+3和+4价,而Ce则是+3和+4的混合价态.担载2wt%Pt后,在可见光下光催化活性大大提高,当铈的掺杂量为0.5mol%(即Ce取代La的摩尔百分量)时,光催化活性达到最大,产氢速率为0.05mmol/h;光照5h后产氢量为0.22mmol,而纯K2La2Ti3O10的产氢量只有0.037mmol. 相似文献
996.
An overview of spectroscopic diagnostics techniques for low temperature plasmas is presented with an emphasis to electron number density — Ne measurement. Stark broadening of non-hydrogenic atom and positive ion spectral lines is given. The attention is drawn to experimental techniques used for line intensity and line profile measurement. Self-absorption test, importance of Abel inversion, deconvolution of experimental line profiles and measurement of line asymmetry are treated in some detail in order to improve Ne measurements. Finally the sources of theoretical and experimental Stark broadening data are reviewed and some details discussed. 相似文献
997.
John V. Hanna Dr. Kevin J. Pike Dr. Thibault Charpentier Dr. Thomas F. Kemp Dr. Mark E. Smith Prof. Bryan E. G. Lucier Robert W. Schurko Prof. Lindsay S. Cahill Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(10):3222-3239
A variable B0 field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high‐precision measurement of 93Nb NMR interaction parameters such as the isotropic chemical shift (δiso), quadrupole coupling constant and asymmetry parameter (CQ and ηQ), chemical shift span/anisotropy and skew/asymmetry (Ω/Δδ and κ/ηδ) and Euler angles (α, β, γ) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR‐CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from NbV in most oxo environments, this study emphasises that a thorough variable B0 approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (?1/2?+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these 93Nb broadline data. These measurements reveal that the 93Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the NbV positions, with CQ values in the 0 to >80 MHz range being measured; similarly, the δiso (covering an approximately 250 ppm range) and Ω values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the Nb? O bond angles and distances defining the immediate NbV oxo environment is complicated by longer‐range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the 93Nb NMR interaction parameters generated here are the all‐electron WIEN2k and the gauge included projector augmented wave (GIPAW) NMR‐CASTEP DFT approaches, which account for the short‐ and long‐range symmetries, periodicities and interaction‐potential characteristics for all elements (and particularly the heavy elements) in comparison with Gaussian 03 methods, which focus on terminated portions of the total structure. 相似文献
998.
Noureddine Issaoui Najeh Rekik Brahim Oujia Marek J. Wójcik 《International journal of quantum chemistry》2010,110(14):2583-2602
In this article, we extend a previous work toward presenting a theoretical study of the effects of Fermi resonances and the fundamental anharmonic coupling parameter α between the high‐frequency mode and the H‐bond bridge. The model incorporates (i) both intrinsic anharmonicities of the fast mode (double well potential) and the H‐bond Bridge (Morse potential), (ii) strong anharmonic coupling theory, (iii) Fermi resonances by the aid of an anharmonic coupling between the fast mode and one or several harmonic bending modes, (iv) quadratic modulation of both the angular frequency and the equilibrium position of the X? …Y stretching mode on the intermonomer ? H… motions, and (v) the quantum direct (fast and bending modes) and indirect dampings (slow mode). The IR spectral density is obtained by Fourier transform of the autocorrelation function of the transition dipole moment operator of the X? H bond. The numerical calculation shows that Fermi resonances generate very complicated profiles with multisubstructure and also provide a direct evidence of Fermi resonances which were predicted to be a major feature of H‐bonds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
999.
An effective method for producing methyl 4-bromo-3-hydroxybutyrate enantiomers was developed using an engineered protein. Escherichia coli transformant cells containing a mutant β-keto ester reductase (KER-L54Q) from Penicillium citrinum and a cofactor-regeneration enzyme such as glucose dehydrogenase (GDH) or Leifsonia sp. alcohol dehydrogenase (LSADH) were used to produce methyl (S)-4-bromo-3-hydroxybutyrate from methyl 4-bromo-3-oxobutyrate. On the other hand, the production of methyl (R)-4-bromo-3-hydroxybutyrate was achieved by asymmetric reduction of methyl 4-bromo-3-oxobutyrate with a mutant phenylacetaldehyde reductase (PAR-HAR1) from Rhodococcus sp. ST-10. 相似文献
1000.
The environment of Eu3+ in zinc-thallium-tellurite glass of the molar composition 60TeO2-30TlO0.5-9.9ZnO-0.1Eu2O3 was investigated by laser-induced fluorescence line narrowing (FLN) techniques using Eu3+ as a local site probe. From the site selective luminescence spectra of Eu3+ at 7 K, the energies of the Stark components of the 7F1 and 7F2 states were recorded and then the crystal field parameters Bnm were calculated assuming a C2v site symmetry. The ratios B22/B20 and B44/B40 for each excitation energy within 7F0-5D0 transition were obtained and compared with the values calculated for Eu3+ in other types of glasses. 相似文献