全文获取类型
收费全文 | 12628篇 |
免费 | 1110篇 |
国内免费 | 679篇 |
专业分类
化学 | 8550篇 |
晶体学 | 530篇 |
力学 | 114篇 |
综合类 | 20篇 |
数学 | 47篇 |
物理学 | 5156篇 |
出版年
2024年 | 19篇 |
2023年 | 113篇 |
2022年 | 226篇 |
2021年 | 298篇 |
2020年 | 347篇 |
2019年 | 272篇 |
2018年 | 230篇 |
2017年 | 256篇 |
2016年 | 438篇 |
2015年 | 272篇 |
2014年 | 367篇 |
2013年 | 936篇 |
2012年 | 769篇 |
2011年 | 741篇 |
2010年 | 642篇 |
2009年 | 804篇 |
2008年 | 828篇 |
2007年 | 1011篇 |
2006年 | 936篇 |
2005年 | 690篇 |
2004年 | 662篇 |
2003年 | 520篇 |
2002年 | 408篇 |
2001年 | 311篇 |
2000年 | 279篇 |
1999年 | 250篇 |
1998年 | 248篇 |
1997年 | 178篇 |
1996年 | 245篇 |
1995年 | 212篇 |
1994年 | 201篇 |
1993年 | 158篇 |
1992年 | 115篇 |
1991年 | 91篇 |
1990年 | 79篇 |
1989年 | 45篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 33篇 |
1985年 | 36篇 |
1984年 | 30篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 246 毫秒
961.
含铁化合物的Fe2p和Fe3s电子能谱研究 总被引:6,自引:0,他引:6
选择了十几种常见的含铁化合物,分另采集了它们的Fe2p和Fe3s谱。从峰位和峰形上讨论了它们各自的特点,结果表明Fe2p和Fe3s峰的峰形分析(如,shake-up卫星峰及多重分裂峰)像其结合能值一样可以提供化学状态分析的重要信息。 相似文献
962.
为探究便携式X射线荧光光谱法(Portable X-ray fluorescence spectrometry method, PXRF)测定结果的不确定度, 应用PXRF法和传统实验室方法对湖南某典型有色金属污染场地及周边土壤中的重金属进行测定,通过建立线性回归模型对比分析两种方法的测定数据,探究了PXRF法测定数据的准确程度和置信区间。结果表明,PXRF法原位、异位测定值与传统实验室方法测定值均能呈现较好的线性相关性,As、Cu、Pb、Cd等元素的决定性系数(R2)均大于0.70,其检测数据质量均能达到定量水平;PXRF法与实验室方法测定值间比率的置信区间结果显示,Cd元素的准确性最好,其次为Pb、Cu、As,比率置信区间分别为(0.57, 1.89)、(0.38, 2.22)、(0.31, 2.25)、(0.20, 4.53)。由此可见,PXRF法是一种方便快捷且相对准确的土壤重金属现场检测方法,可广泛地应用于污染场地调查和土壤修复工程实践中。 相似文献
963.
Depending on the solvothermal reaction conditions, we obtained three different metal-organic frameworks with yttrium(III) as metal component and 2,5-dihdyroxyterepthalic acid (H4dhtp) as bifunctional organic linker: Y2(H2dhtp)3(dmf)4 · (dmf)2 (CPO-29) contains dinuclear, paddle-wheel like inorganic secondary building units (SBUs) connected by the organic linker to a network with α-Po topology, while Y2(H2dhtp)(dhtp)(dmf)2 (CPO-30) and Y2(H2dhtp)(dhtp)(dmf)2(H2O)2 · (H2O)4 (CPO-31) contain one-dimensional inorganic SBUs that differ in how the half- and fully deprotonated ligands are connected to and arranged around them. Only the carboxylic acid groups of the organic linker are deprotonated in CPO-29, while CPO-30 and CPO-31 contain both 2,5-dihydroxyterephthalate (H2dhtp2–) linkers and fully deprotonated 2,5-dioxidoterephthalate (dhtp4–) linkers. All three compounds contain large volumes filled with solvent, but we were able to demonstrate permanence of porosity only for CPO-30. Variable temperature powder X-ray diffraction reveals that CPO-29 and CPO-31 undergo discontinuous phase transitions upon heating, and the flexibility of the framework structure indicated by these might be the reason for the inability to access the pore volume. Desolvated CPO-30 and CPO-31 are polymorphs, whose network structures differ in whether the H2dhtp2– and dhtp4– linkers are located in cis or trans arrangement around the inorganic SBU. 相似文献
964.
965.
Porous Organic Molecular Frameworks with Extrinsic Porosity: A Platform for Carbon Storage and Separation 下载免费PDF全文
Dr. Jian Lü Prof. Dr. Rong Cao 《Angewandte Chemie (International ed. in English)》2016,55(33):9474-9480
The assembly of porous organic molecular frameworks (POMFs), which typically evidence common feasibility and compatibility, purification, and regeneration at practical conditions, remains a strategic challenge in modern materials science and is crucial for their favorable applications in biological, medical, and environmental realms. However, instructive knowledge of well‐organized POMF assembly by supramolecular interactions is, in general, ambiguous to date. Nevertheless, a significant advance in controlled POMF assembly has been recently achieved. This Minireview highlights these approaches, with a particular focus on the design of molecular constituents and assembly strategies. We also look beyond the field of solid‐state POMF materials into the assembly and recognition in solution, thus covering recent advances in POMFs based on material design and applications in carbon storage and separation. 相似文献
966.
Dr. Ines E. Collings Dr. Elena Bykova Dr. Maxim Bykov Dr. Sylvain Petitgirard Dr. Michael Hanfland Dr. Damian Paliwoda Prof. Leonid Dubrovinsky Prof. Natalia Dubrovinskaia 《Chemphyschem》2016,17(21):3369-3372
The incorporation of noble gas atoms, in particular neon, into the pores of network structures is very challenging due to the weak interactions they experience with the network solid. Using high‐pressure single‐crystal X‐ray diffraction, we demonstrate that neon atoms enter into the extended network of ammonium metal formates, thus forming compounds Nex[NH4][M(HCOO)3]. This phenomenon modifies the compressional and structural behaviours of the ammonium metal formates under pressure. The neon atoms can be clearly localised within the centre of [M(HCOO)3]5 cages and the total saturation of this site is achieved after ~1.5 GPa. We find that by using argon as the pressure‐transmitting medium, the inclusion inside [NH4][M(HCOO)3] is inhibited due to the larger size of the argon. This study illustrates the size selectivity of [NH4][M(HCOO)3] compounds between neon and argon insertion under pressure, and the effect of inclusion on the high‐pressure behaviour of neon‐bearing ammonium metal formates. 相似文献
967.
Flupirtine maleate,a pharmaceutical compound for treating psychotic disease in clinics,has seven polymorphs.Form A,with better crystal stability and bioavailability,has been widely used as the pharmaceutical crystal form.Unfortunately,it is usually found in a polymorphic mixture with form B.In this study,pure crystal forms of A and B were prepared and characterized by X-ray powder diffraction (XRPD),Fourier transform infrared spectroscopy (FT-IR) and thermal analysis.An XRPD-based method for the quantitative determination of the amount of the flupirtine maleate polymorphs form A and form B was also established through a systematic optimization of instrumental parameters.The results of the analytical methodology validation showed that the XPRD method had a broad quantitative range of 0-100%(w/w),good linear relationship,with R2=0.999,excellent repeatability and precision and low limits of detection (LoD) of 0.15%(w/w) and quantification (LoQ) of 0.5%(w/w).The results also showed that the single-peak method was not as good as the whole pattern in reducing the influence of the preferred orientation,but this can be compensated for by a systematic optimization of instrumental parameters and validating the analytical methodology to reduce errors and obtain a good,repeatable,sensitive,and accurate method.This XRPD method can be used to analyze mixtures of flupirtine maleate polymorphs (forms A and B) quantitatively and control the quality of the bulk drug. 相似文献
968.
Uniform-sized fluorescent molecularly imprinted polymers were prepared by one-step swelling and suspension polymerization, while chlorpyrifos, methacrylic acid, ethylene glycol dimethacrylate, and oil-soluble CdSe/ZnS quantum dots were used as the carrier, template molecule, functional monomer, cross-linker, and fluorophor, respectively. The morphology, adsorption dynamics, binding ability, and selectivity of quantum dot-labeled molecularly imprinted polymers were evaluated. The dosage of quantum dots for labeling the molecularly imprinted polymers was optimized. The results showed that the optimized dose of quantum dots was 200?µL using a concentration of 8.0?µM. The microsphere size was approximately 10?µm with a honeycombed surface. The quantum dot-labeled molecularly imprinted polymers had an even brightness and a high selectivity. In the presence of different concentrations of chlorpyrifos, a decrease in the fluorescence intensity of the quantum dot-labeled molecularly imprinted polymer was clearly identified by flow cytometry. The whole detection process was accomplished within 2?h including pretreatment. This method was used for the determination of chlorpyrifos in tap water samples. 相似文献
969.
Behnaz Afzalian Joel T. Mague Maryam Mohamadi S. Yousef Ebrahimipour Behjat Pour amiri Esmat Tavakolinejad Kermani 《催化学报》2015,(7):1101-1108
Three complexes containing 2-pyrazinecarboxylate (pzca–), including [Ni(pzca)2(H2O)2], [Co(pzca)2(H2O)2], and [Cu(pzca)2(H2O)2], have been synthesized and characterized using physico-chemical and spectroscopic methods. Furthermore, the structure of each complex was determined by single-crystal X-ray diffraction. All three complexes have an octahedral geometry, where the metal ion chelated by two carboxylate oxygens, two nitrogen atoms belonging to pyrazinic acid molecules, and two oxygen atoms of two water molecules. The catalytic activities of these complex-es were also investigated in the green synthesis of 2H-indazolo[2,1-b]phthalazine-triones by the reaction of hydrazine hydrate with an arylaldehyde, phthalic anhydride, and dimedone in acetic acid. 相似文献
970.
Dr. Igor L. Dalinger Dr. Irina A. Vatsadze Dr. Tatyana K. Shkineva Dr. Alexandr V. Kormanov Dr. Marina I. Struchkova Dr. Kyrill Yu. Suponitsky Dr. Anatoly A. Bragin Dr. Konstantin A. Monogarov Dr. Valery P. Sinditskii Dr. Aleksei B. Sheremetev 《化学:亚洲杂志》2015,10(9):1987-1996
A new family of energetic compounds, nitropyrazoles bearing a trinitromethyl moiety at the nitrogen atom of the heterocycle, was designed. The desirable high‐energy dense oxidizers 3,4‐dinitro‐ and 3,5‐dinitro‐1‐(trinitromethyl)pyrazoles were synthesized in good yields by destructive nitration of the corresponding 1‐acetonylpyrazoles. All of the prepared compounds were fully characterized by multinuclear NMR and IR spectroscopy, as well as by elemental analysis. Single‐crystal X‐ray diffraction studies show remarkably high density. Impact sensitivity tests and thermal stability measurements were also performed. All of the pyrazoles possess positive calculated heats of formation and exhibit promising energetic performance that is the range of 1,3,5‐trinitroperhydro‐1,3,5‐triazine and pentaerythritol tetranitrate. The new pyrazoles exhibit positive oxygen balance and are promising candidates for new environmentally benign energetic materials. 相似文献