全文获取类型
收费全文 | 2814篇 |
免费 | 134篇 |
国内免费 | 663篇 |
专业分类
化学 | 3390篇 |
晶体学 | 33篇 |
力学 | 11篇 |
综合类 | 26篇 |
物理学 | 151篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 67篇 |
2021年 | 56篇 |
2020年 | 65篇 |
2019年 | 58篇 |
2018年 | 66篇 |
2017年 | 104篇 |
2016年 | 103篇 |
2015年 | 88篇 |
2014年 | 130篇 |
2013年 | 332篇 |
2012年 | 160篇 |
2011年 | 163篇 |
2010年 | 164篇 |
2009年 | 158篇 |
2008年 | 173篇 |
2007年 | 185篇 |
2006年 | 182篇 |
2005年 | 186篇 |
2004年 | 152篇 |
2003年 | 150篇 |
2002年 | 104篇 |
2001年 | 94篇 |
2000年 | 90篇 |
1999年 | 94篇 |
1998年 | 69篇 |
1997年 | 60篇 |
1996年 | 66篇 |
1995年 | 54篇 |
1994年 | 39篇 |
1993年 | 39篇 |
1992年 | 34篇 |
1991年 | 20篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有3611条查询结果,搜索用时 31 毫秒
141.
Shahram Mehdipour-Ataei 《European Polymer Journal》2005,41(1):65-71
Terephthalic acid bis(carboxydiphenyl methyl)ester (TBE) as a new monomer for the preparation of polyamides was synthesized through the nucleophilic substitution reaction of benzilic acid with terephthaloyl chloride. This diester-diacid (TBE) was characterized using conventional spectroscopic methods. Polycondensation reactions of TBE with different aromatic and semi-aromatic diamines via Yamazaki method resulted different poly(ester amide)s. All the polymers were characterized and their physical and thermal properties were studied. 相似文献
142.
Christian K. Riener Andreas Ebner Alex A. Gall Yuri L. Lyubchenko Hermann J. Gruber 《Analytica chimica acta》2003,479(1):59-75
We have established an easy-to-use test system for detecting receptor-ligand interactions on the single molecule level using atomic force microscopy (AFM). For this, avidin-biotin, probably the best characterized receptor-ligand pair, was chosen. AFM sensors were prepared containing tethered biotin molecules at sufficiently low surface concentrations appropriate for single molecule studies. A biotin tether, consisting of a 6 nm poly(ethylene glycol) (PEG) chain and a functional succinimide group at the other end, was newly synthesized and covalently coupled to amine-functionalized AFM tips. In particular, PEG800 diamine was glutarylated, the mono-adduct NH2-PEG-COOH was isolated by ion exchange chromatography and reacted with biotin succinimidylester to give biotin-PEG-COOH which was then activated as N-hydroxysuccinimide (NHS) ester to give the biotin-PEG-NHS conjugate which was coupled to the aminofunctionalized AFM tip. The motional freedom provided by PEG allows for free rotation of the biotin molecule on the AFM sensor and for specific binding to avidin which had been adsorbed to mica surfaces via electrostatic interactions. Specific avidin-biotin recognition events were discriminated from nonspecific tip-mica adhesion by their typical unbinding force (∼40 pN at 1.4 nN/s loading rate), unbinding length (<13 nm), the characteristic nonlinear force-distance relation of the PEG linker, and by specific block with excess of free d-biotin. The convenience of the test system allowed to evaluate, and compare, different methods and conditions of tip aminofunctionalization with respect to specific binding and nonspecific adhesion. It is concluded that this system is well suited as calibration or start-up kit for single molecule recognition force microscopy. 相似文献
143.
I. Strakova A. Strakovs M. Petrova S. Belyakov 《Chemistry of Heterocyclic Compounds》2007,43(12):1512-1518
The [3+2] cycloaddition reactions of a series of 1,3-substituted 5-diazo-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles with
maleic anhydride and dimethyl acetylenedicarboxylate gave 1′,3′-substituted 3-spiro[4,6-dioxo-4,6,3a,6a-tetrahydro-3H-furo[3,4-c]pyrazole]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles]
and 1′,3′-substituted 3-spiro[4,5-di(methoxycarbonyl)-3H-pyrazole]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles]
respectively. When heated the former eliminate nitrogen and are transformed into 1′,3′-substituted 6-spiro[2,4-dioxo-3-oxabicyclo[3.1.0]hexane]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles].
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1784–1791, December, 2007. 相似文献
144.
《Arabian Journal of Chemistry》2020,13(1):1198-1228
Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds. 相似文献
145.
146.
The synthesis of some new N‐[1‐(2,5‐dichlorophenyl)‐5‐methyl‐1,2,3‐triazol‐4‐yl]‐carbamic acid ester derivatives are reported in this paper. The yielded products 6a‐l were confirmed by Elemental analyses, NMR, MS, and IR spectra. 相似文献
147.
1 INTRODUCTION Coordination polymers are a family of materials composed of 1D chains, 2D sheets, and 3D networks of metal-organic building blocks connected via co- valent and hydrogen bonds. Recently, they have re- ceived increasing attention for their fascinating struc- tures and topological features[1~4]. The complex as ligands approach is one of the best strategies to de- sign and synthesize polynuclear species, and a good example of ‘complex ligand’ is represented by mono- nuclear… 相似文献
148.
Fatty acid methyl esters from various fats and oils were separated by comprehensive two-dimensional supercritical fluid chromatography with conventional packed columns and FID detection. The first dimension was a silica gel column and the second dimension was an ODS column. This combination was largely orthogonal for the separation of fatty acid methyl esters. The first dimension separations were primarily based on the number of double bonds while the second dimension separations were based on the chain length. The highly-ordered chromatograms and improved resolution allowed the easy detection and identification of minor components. Although the first dimension separations were performed under isobaric conditions where the peak width increased in proportion to the retention, the programming of the sampling duration allowed us to maintain the optimum re-injection frequency (3–4 times) per peak into the second dimension and so to minimize the total analysis time without deteriorating the resolution. 相似文献
149.
An intercrosslinked network of cyanate ester (CE)-bismaleimide (BMI) modified epoxy matrix system was made by using epoxy resin, 1,3-dicyanatobenzene and bismaleimide (N,N′-bismaleimido-4,4′-diphenyl methane) with diaminodiphenylmethane as curing agent. BMI-CE-epoxy matrices were characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. The matrices, in the form of castings, were characterised for their mechanical properties such as tensile strength, flexural strength and unnotched Izod impact test as per ASTM methods. Mechanical studies indicated that the introduction of cyanate ester into epoxy resin improves the toughness and flexural strength with reduction in tensile strength and glass transition temperature, whereas the incorporation of bismaleimide into epoxy resin influences the mechanical and thermal properties according to its percentage content. DSC thermograms of cyanate ester as well as BMI modified epoxy resin show an unimodal reaction exotherm. Electrical properties were studied as per ASTM method and the morphology of the BMI modified epoxy and CE-epoxy systems were studied by scanning electron microscope. 相似文献
150.
《Journal of Coordination Chemistry》2012,65(21):3764-3771
The crystal structure of [Zn2(2-pmOpe)2Cl4] (2-pmOpe?=?diethyl (pyridin-2-ylmethyl)phosphate) was determined by X-ray-diffraction method. The compound was also characterized by IR, far-IR, 1H, and 31P NMR spectroscopy. In this compound, 2-pmOpe is a bidentate N,O-bridging ligand and Zn(II) are slightly distorted tetrahedral ZnNOCl2. Zn(II) ions are doubly bridged by the 2-pmOpe ligands, resulting in a dinuclear species. The structure is stabilized by intermolecular C–H?···?O and C–H?···?Cl hydrogen bonds. The spectral properties are in agreement with the structural data. 相似文献