全文获取类型
收费全文 | 6351篇 |
免费 | 356篇 |
国内免费 | 235篇 |
专业分类
化学 | 601篇 |
晶体学 | 9篇 |
力学 | 945篇 |
综合类 | 46篇 |
数学 | 2855篇 |
物理学 | 2486篇 |
出版年
2024年 | 4篇 |
2023年 | 86篇 |
2022年 | 140篇 |
2021年 | 170篇 |
2020年 | 184篇 |
2019年 | 198篇 |
2018年 | 194篇 |
2017年 | 192篇 |
2016年 | 212篇 |
2015年 | 190篇 |
2014年 | 320篇 |
2013年 | 474篇 |
2012年 | 332篇 |
2011年 | 377篇 |
2010年 | 328篇 |
2009年 | 456篇 |
2008年 | 382篇 |
2007年 | 382篇 |
2006年 | 297篇 |
2005年 | 291篇 |
2004年 | 249篇 |
2003年 | 229篇 |
2002年 | 158篇 |
2001年 | 136篇 |
2000年 | 138篇 |
1999年 | 119篇 |
1998年 | 133篇 |
1997年 | 93篇 |
1996年 | 80篇 |
1995年 | 55篇 |
1994年 | 74篇 |
1993年 | 48篇 |
1992年 | 49篇 |
1991年 | 51篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有6942条查询结果,搜索用时 15 毫秒
991.
992.
激光诱导等离子体的实验研究及其在光谱分析中的应用 总被引:2,自引:2,他引:0
综述了近几年国内外在激光诱导等离子体方面的实验研究进展 ,及其在光谱分析中的应用。着重阐明了在不同的条件下 (气体种类、环境气压、激光能量、波长、脉宽、功率密度、观测高度 )激光诱导等离子体的形成、辐射、电子温度、电子密度和扩散速度方面的实验研究 ;另外 ,激光诱导等离子体用于物质成分分析中 ,主要阐述了直接采集等离子体的辐射进行固态、液态和气态样品的分析以及激光烧蚀与ICP光源联用进行的光谱化学分析两个方面 ,并对影响分析精确度和检出限的因素进行了简要讨论 相似文献
993.
对流占优扩散方程的一种特征差分算法 总被引:3,自引:0,他引:3
A new kind of characteristic-difference scheme for convection-diffusion equations is constructed by characteristic method and bilinear interpolation method. The convergence of the scheme is proved. The advantages of this scheme are to obtain the solutions of the convection diffusion equations with variable coefficient expediently and to reduce the numerical oscillations of the convectiondominanted diffusion equations effectively. 相似文献
994.
利用多元转移概率流图及转移概率母函数,对带有中止检查规则的调整型抽样方案进行了讨论,分别在(1)当检查始于正常检查时,(2)当检查始于加严检查时和(3)当检查始于放宽检查时,得到了三个复合OC函数. 相似文献
995.
The new complex bis(2-bromobenzoato-O,O′)-bis(methyl-3-pyridylcarbamate-N)-zinc(II), [Zn(2-BrC6H4COO)2mpc2] (1), has been prepared and characterized by elemental analysis, IR spectroscopy, thermal analysis and single-crystal X-ray diffraction. The bonding between the ligands and the central atom was investigated by DFT studies. The theoretical infrared spectrum of 1 was compared with the experimental data. The complex proved to be thermally stable up to 165 °C. Volatile intermediate products of its thermal decomposition were identified by mass spectrometry. The coordination environment of the zinc atom consists of two nitrogen atoms of two methyl-3-pyridylcarbamate ligands and is chelated by four oxygen atoms of two 2-bromobenzoate ligands (ZnO4N2 – chromophore). 相似文献
996.
Shereena M. Arif John D. Holliday Peter Willett 《Journal of computer-aided molecular design》2009,23(9):655-668
Current systems for similarity-based virtual screening use similarity measures in which all the fragments in a fingerprint
contribute equally to the calculation of structural similarity. This paper discusses the weighting of fragments on the basis
of their frequencies of occurrence in molecules. Extensive experiments with sets of active molecules from the MDL Drug Data Report and the World of Molecular Bioactivity databases, using fingerprints encoding Tripos holograms, Pipeline Pilot ECFC_4 circular substructures and Sunset Molecular
keys, demonstrate clearly that frequency-based screening is generally more effective than conventional, unweighted screening.
The results suggest that standardising the raw occurrence frequencies by taking the square root of the frequencies will maximise
the effectiveness of virtual screening. An upper-bound analysis shows the complex interactions that can take place between
representations, weighting schemes and similarity coefficients when similarity measures are computed, and provides a rationalisation
of the relative performance of the various weighting schemes. 相似文献
997.
Comparison of two laser-induced breakdown spectroscopy techniques for total carbon measurement in soils 总被引:1,自引:0,他引:1
M.V. Belkov V.S. Burakov A. De Giacomo V.V. Kiris S.N. Raikov N.V. Tarasenko 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
The potentials of two advanced laser-induced breakdown spectroscopy (LIBS) techniques which are used to determine the total carbon content in soils have been examined. The first one is the combination of a single-pulse laser ablation with spark excitation of plasma plume triggering the gap between electrodes close to the target surface. The second one is a more conventional double-pulse LIBS. In both modes the calibration graphs have a nonlinear trend in the actual range of carbon contents and present a good R2 value (0.97). In the combined laser-spark approach, using low-cost and portable laser instrumentation is possible, as well as inducing a micro-damage on the target surface. Certain regularities in the spectral line intensities of soil nutritious elements have been detected and appear to be connected to the total carbon content and to the soil origin. 相似文献
998.
探讨了铌-铬天青S配合物与牛血清白蛋白(BSA)结合反应体系.在pH 4.6的邻苯二甲酸氢钾-NaOH(Clark-Lubs)缓冲溶液中,在OP存在下,铌-铬天青S配合物与牛血清白蛋白进一步形成复合物,其最大吸收峰位于595 nm,且随着BSA量的增加,体系在595 nm波长处吸收峰也随着增大.据此建立以铌-铬天青S配合物为光谱探针,分光光度法测定蛋白质含量的新方法.牛血清白蛋白含量在0~0.32 mg/mL的范围内符合比尔定律,摩尔吸光系数ε595为 4.4×105 L·mol-1·cm-1,相关系数为γ=0.9996,生物体内的常见物质基本上不干扰测定,方法可用于人血清蛋白中蛋白质的测定. 相似文献
999.
Two new flavanone glycosides 1 and 2 were isolated from the aerial parts oi Macrothelypteris torresiana(Gaud.)Ching.The structures of two products were identified as(2S)-5,7,2',5'-tetrahydroxyfiavanone-2'-O-β-D-6"-O-acetylglucopyranoside and(2S)- 5,7,2',5'-tetrahydroxyflavanone-2'-O-β-D-glucopyranoside on the basis of their chemical and spectral analysis,respectively. 相似文献
1000.
A spectral similarity measure was developed that can differentiate subtle differences between two spectra. The spectra are digitalized into a vector. The difference between the two spectra is defined by a difference vector, which is one spectrum minus the other. The spectral similarity measure is transformed into a hypothesis test of the similarities and differences between the two spectra. The scalar mean of the difference vector is used as the statistical variable for the hypothesis test. A threshold for the hypothesis that the spectra are different was proposed. The Bayesian prior odds ratio was estimated from multiple spectra of the same sample. The posterior odds ratio was used to quantity the spectral similarity measure of the two spectra. Diffuse reflectance near-infrared spectra of tobacco samples of two formulations were used to demonstrate this method. The results show that this new method can detect subtle differences between the spectra. 相似文献