全文获取类型
收费全文 | 4090篇 |
免费 | 564篇 |
国内免费 | 499篇 |
专业分类
化学 | 3235篇 |
晶体学 | 35篇 |
力学 | 233篇 |
综合类 | 54篇 |
数学 | 402篇 |
物理学 | 1194篇 |
出版年
2024年 | 25篇 |
2023年 | 112篇 |
2022年 | 181篇 |
2021年 | 196篇 |
2020年 | 223篇 |
2019年 | 194篇 |
2018年 | 153篇 |
2017年 | 151篇 |
2016年 | 201篇 |
2015年 | 186篇 |
2014年 | 256篇 |
2013年 | 310篇 |
2012年 | 321篇 |
2011年 | 355篇 |
2010年 | 229篇 |
2009年 | 209篇 |
2008年 | 205篇 |
2007年 | 196篇 |
2006年 | 175篇 |
2005年 | 169篇 |
2004年 | 124篇 |
2003年 | 104篇 |
2002年 | 111篇 |
2001年 | 90篇 |
2000年 | 85篇 |
1999年 | 93篇 |
1998年 | 82篇 |
1997年 | 56篇 |
1996年 | 63篇 |
1995年 | 48篇 |
1994年 | 47篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有5153条查询结果,搜索用时 15 毫秒
51.
Study of Tea Digitized Chromatographic Fingerprint Spectra Using Micellar Electrokinetic Chromatography 总被引:1,自引:0,他引:1
IntroductionTeaisthemostwidelyconsumedbeverageinpeople’slife .Theheightenedpopularityofthisbeveragethroughouttheworldinrecentyearsmaybedueinparttotheevidenceofarelationshipbetweenteaconsumptionandpreventionofcertainformsofhumandisease .Themaincomponentsofteaarepolyphenoliccompounds ,commonlyknownascatechins ,whichrepresentagroupofcom poundsbelongingtotheflavonoidfamily .Thesecom poundsarewidelydistributedinthetealeavesandconsti tuteupto 30 %ofthedryleafweight.1Muchinteresthasbeenfocusedoncat… 相似文献
52.
高效液相色谱法测定血浆中7种灭鼠剂 总被引:12,自引:0,他引:12
建立了血浆中7种缓效灭鼠剂的反相高效液相色谱分析方法,选择了样品提取与测定条件,考察了有关化合物对测定的影响,在色谱工作站上建立了灭鼠剂的紫餐吸收光谱库,根据吸收光谱与tR值进行库检索,提出了定性的准确度。方法的线性范围为2-10μL/L血浆,最低检测浓度为1μL/mL血浆。 相似文献
53.
化学衍生-高效液相色谱法测定硫氰酸根阴离子 总被引:4,自引:0,他引:4
以α-溴-2,3,4,5,6-五氟甲苯作柱前衍生试剂,经优化衍生和色谱条件,实现了用高效液相色谱法测定硫氰酸根离子。在ODS柱上,用甲醇-水(80:20)作流动相,于254nm检测,得到线性关系良好的工作曲线,最小检测限为4.7ng。分析了吸烟者唾液样品,回收率为93.7%~101.4%。 相似文献
54.
A new method for the synthesis of eight-membered heterocyclic 1,4,5-oxadiazocines has been described from β-diketone and β,β,β-triketone with an acidic α-hydrogen. The method entails the reaction of a di- or triketone with 2-hydroxyethylhydrazine and an aldehyde in the presence of acetic acid providing respectable yield. 相似文献
55.
56.
57.
Xian Zhao Daren Guan Xizhang Yi Guibao Xu Minhua Jiang 《International journal of quantum chemistry》2003,93(5):335-343
A dynamic Lie algebraic (DLA) formulation is applied to the study of nonlinear optical properties of the substituted benzenes. We have described the generation of the dynamic Lie algebra for the model Hamiltonian used in the present study. In terms of these elements of the dynamic algebra we express the evolution operator as a function of the group parameters, which can be determined by means of solving a system of coupled nonlinear differential equations. Thus, in terms of the density matrix operator formalism in statistical mechanics we obtain the statistical averages of the electric polarization and then derive readily an expression for the hyperpolarizability of the paradisubstituted benzenes. Comparisons with experimental observations and other quantum calculations of the hyperpolarizabilities for the paradisubstituted benzenes are made qualitatively and quantitatively. These results imply that the DLA method appears useful in describing the nonlinear optical phenomena in the substituted benzene molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 335–343, 2003 相似文献
58.
59.
Jingqi Guan ShuBo Jing Shujie Wu Haiyan Xu Zhenlv Wang Qiubin Kan 《Reaction Kinetics and Catalysis Letters》2007,90(1):27-33
A series of MoV0.3Tex (x = 0−0.3) mixed oxides were prepared and investigated for the selective oxidation of isobutane. Among them, MoV0.3Te0.23 showed the best methacrolein and methacrylic acid selectivity (as high as 17% and 16%, respectively), and the yield to methacrolein
and methacrylic acid reached 3.6% and 3.5%, respectively, at 21.3% isobutane conversion at 440°C. 相似文献
60.
Zhang X Young MA Lyandres O Van Duyne RP 《Journal of the American Chemical Society》2005,127(12):4484-4489
A rapid detection protocol suitable for use by first-responders to detect anthrax spores using a low-cost, battery-powered, portable Raman spectrometer has been developed. Bacillus subtilis spores, harmless simulants for Bacillus anthracis, were studied using surface-enhanced Raman spectroscopy (SERS) on silver film over nanosphere (AgFON) substrates. Calcium dipicolinate (CaDPA), a biomarker for bacillus spores, was efficiently extracted by sonication in nitric acid and rapidly detected by SERS. AgFON surfaces optimized for 750 nm laser excitation have been fabricated and characterized by UV-vis diffuse reflectance spectroscopy and SERS. The SERS signal from extracted CaDPA was measured over the spore concentration range of 10(-14)-10(-12) M to determine the saturation binding capacity of the AgFON surface and to calculate the adsorption constant (Kspore=1.7 x 10(13) M(-1)). At present, an 11 min procedure is capable of achieving a limit of detection (LOD) of approximately 2.6 x 10(3) spores, below the anthrax infectious dose of 10(4) spores. The data presented herein also demonstrate that the shelf life of prefabricated AgFON substrates can be as long as 40 days prior to use. Finally, these sensing capabilities have been successfully transitioned from a laboratory spectrometer to a field-portable instrument. Using this technology, 10(4) bacillus spores were detected with a 5 s data acquisition period on a 1 month old AgFON substrate. The speed and sensitivity of this SERS sensor indicate that this technology can be used as a viable option for the field analysis of potentially harmful environmental samples. 相似文献