全文获取类型
收费全文 | 2917篇 |
免费 | 108篇 |
国内免费 | 13篇 |
专业分类
化学 | 2153篇 |
晶体学 | 8篇 |
力学 | 32篇 |
数学 | 433篇 |
物理学 | 412篇 |
出版年
2022年 | 23篇 |
2021年 | 22篇 |
2020年 | 52篇 |
2019年 | 45篇 |
2018年 | 24篇 |
2016年 | 76篇 |
2015年 | 72篇 |
2014年 | 82篇 |
2013年 | 104篇 |
2012年 | 141篇 |
2011年 | 154篇 |
2010年 | 101篇 |
2009年 | 69篇 |
2008年 | 114篇 |
2007年 | 152篇 |
2006年 | 150篇 |
2005年 | 140篇 |
2004年 | 90篇 |
2003年 | 83篇 |
2002年 | 96篇 |
2001年 | 62篇 |
2000年 | 45篇 |
1999年 | 47篇 |
1998年 | 42篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 42篇 |
1994年 | 41篇 |
1993年 | 32篇 |
1992年 | 48篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 31篇 |
1988年 | 42篇 |
1987年 | 41篇 |
1986年 | 33篇 |
1985年 | 45篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 29篇 |
1980年 | 35篇 |
1979年 | 23篇 |
1978年 | 30篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1975年 | 34篇 |
1974年 | 36篇 |
1973年 | 34篇 |
1971年 | 21篇 |
排序方式: 共有3038条查询结果,搜索用时 15 毫秒
21.
The Catalysed Volatilization of Red Phosphorus and of Claudetite The catalysis of the volatilization of Pred (as P4) by AlCl3,g, and of the volatilization of claudetite (as As4O6) by I2,g is observed by mass spectrometry. 相似文献
22.
Reicher Fany Leitner Sirlei C. S. Sierakowski Maria R. Fontana Jose D. Correa Joao B. C. 《Applied biochemistry and biotechnology》1991,28(1):353-361
Stryphnodendron barbatiman (barbatimão) is a native tree that is found throughout the “Cerrados,” a region of Central Brazil. Plant seeds, on water extraction, furnished 28 g% galactomannan (dryweight basis), the monosaccharide composition of which (galactose to mannose ratio, 1.0:1.5) fits in the legume heteromannan group. This seed gum, after Sevag deproteinization, still retained 6 g% of associated protein and had a molecular weight of about 1.8 MD on gel filtration. A high intrinsic viscosity (1300 cP) was observed for the polysaccharide sample obtained after reflux of the crushed seeds in 80% aqueous methanol.
相似文献23.
Keller Hildegard Langer Elisabeth Lehner Harald Derflinger Gerhard 《Theoretical chemistry accounts》1978,49(2):93-100
The Algebraic Theory of Chirality Functions is derived by means of exclusively qualitative considerations. Hence, the significance of quantitative results is questionable. Moreover the construction of “Näherungsansätze” (”Approximation-Ansatz”), which may be interpreted as semiempirical methods, is achieved on the basis of plausibility and mathematical simplicity. Since physical arguments are not included, the consistency or inconsistency of “Näherungsansätze” with experimental results do not justify direct physical conclusions. 相似文献
24.
The 1D- and 2D-6Li, 6Li-INADEQUATE experiments are described as new tools for the detection of scalar coupled nonequivalent 6Li nuclei in organolithium clusters. Practical applications of these sequences are demonstrated for the 6Li-NMR spectra of (E)-1-lithio-2-(2-lithiophenyl)-1-phenylhex-1-ene ( 1 ) and (E)-2-lithio-1-(2-lithiophenyl)-1-phenylpent-1-ene ( 2 ), where signals due to dimers and monomers can be distinguished. The performance of the 2D-6Li, 6Li-INADEQUATE and the 6Li, 6Li-COSY-45-LR experiment are compared. The 6Li chemical shifts of 1 and 2 are discussed. 相似文献
25.
Hiller W Brüll A Argyropoulos D Hoffmann E Pasch H 《Magnetic resonance in chemistry : MRC》2005,43(9):729-735
The application of HPLC-NMR for the analysis of a mixture of fatty alcohol ethoxylates (FAEs) is described. The use of the new generation, cryogenically cooled probes is investigated in respect of the sensitivity advantage that they provide. The FAE mixture is separated using liquid chromatography at the critical point of adsorption. The ability of the method to differentiate between the different end groups and the degree of polymerization of the mixture constituents is investigated. Both on-flow and stop-flow HPLC-NMR techniques were used together with two-dimensional NMR spectroscopy. The results are compared with those obtained by using an evaporative light scattering detector for the HPLC. 相似文献
26.
Harald Schfer 《无机化学与普通化学杂志》1974,410(3):269-273
The Chemical Transport of Platinum with Chlorine Experiments show that the chemical transport of platinum by means of chlorine within a temperature gradient at temperatures below ≈ 1000°K goes into the hot temperature region, but at higher temperatures in the reverse direction. From the thermodynamic discussion it can be seen, that the platinum content of the gas phase at low temperatures is governed by the exothermic formation of Pt6Cl12,g, and at higher temperatures by the endothermic formation of PtCl3,g and PtCl2,g. The platinum content of the gas phase passes a minimum at ≈ 1000°K, if P(Cl2) = 3.5 atm. This result is in agreement with the observed inversion of the transport direction. 相似文献
27.
Mass Spectroscopic Observations and Chemical Transport Experiments with the Systems VCl3/Al2Cl6 and VCl2/Al2Cl6 By mass spectrometry the equilibrium VCl3,s + 0.5 Al2Cl6,g ? VAlCl6,g has been determined: ΔH°(298) = 25.6(±0.5) kcal; ΔS°(298) = 23.0(±3) cal/K, ΔCp (assumed) = ?4 cal/K. This is approximately in agreement with results determined by ligand field spectroscopy by ANUNDSKÅS and ØYE (A. and Ø.). For the dimerization of VCl3,g values for ΔH and ΔS have been derived. The molecule VAl2Cl9 assumed by A. and Ø. could not been observed by mass spectrometry. For the VCl2/Al2Cl6 complex, observed by chemical transport, A. and Ø. give the formula VAl3Cl11. This molecule could not been observed by mass spectrometry. This suggests a smaller concentration, compared with the results of A. and Ø. Stabilization of VCl2,s (by metal-nietal-bonds) shifts the reaction to the left, whith explains the lower complex concentration as well as the larger molecular weight of the complex. With chlorides stabilized by stronger metal-metal bonds (MoCl3, MoCl2, Nb3Cl8) AlCl3 complexes are not formed in observable concentrations. The chemical transport of VCl2 with Al2Cl6 needs relatively high temperatures (973 → 873 K). In this case the addition of SiCl4 hinders the attack of the quartz ampoule by Al2Cl6. Using a VCl3 + VCl2 mixture, VCl3 is transported by Al2Cl6 (673 → 623 K) into the colder region. If afterwords the ampoule is reversed, VCl3 again moves into the colder region, but the thermal decomposition of VCl3 at the same time causes that a VCl2-residue remains in the hot region. 相似文献
28.
Franz Andreas Mautner Harald Krischner Christoph Kratky 《Monatshefte für Chemie / Chemical Monthly》1988,119(11):1245-1249
[N(CH3)4]Ca(N3)3,M=240.29, was prepared from aqueous solutions of tetramethylammoniumazide with calciumazide at 298 K. The crystals are tetragonala=936.6(7) pm,c=694.7(5)pm, space group P4/nmm,Z=2, (x)=1.31Mgm–3. The crystal structure was determined by single crystal x-ray diffraction (234 Mo-K-reflections, =0.469 mm–1,R=0.064). Calcium is octahedrally coordinated to six azide groups. The octahedra are connected via azide groups to a threedimensional array with the complex ammonium ions between. The terminal nitrogen atoms of the azide groups and the methyl groups are considerably disordered. 相似文献
29.
Gas Molecules Pd2Al2Cl10 and PdAlCl5 as Accompanists of PdAl2Cl8 Mass spectrometric observations using a double cell showed that the reaction of gaseous Al2Cl6 with solid PdCl2 besides the known gaseous complex PdAl2Cl8 gives PdAlCl5 and the unexpected complex Pd2Al2Cl10. For the equilibrium (with ΔCp? ?1 cal/K) ΔH°(298) = 7.5 kcal/Mol and ΔS°(298) = 5.3 ± 2 cl have been obtained. 相似文献
30.
Analytical procedures for quantification of peptides in pharmaceutical research by liquid chromatography–mass spectrometry 总被引:6,自引:0,他引:6
John H Walden M Schäfer S Genz S Forssmann WG 《Analytical and bioanalytical chemistry》2004,378(4):883-897
Peptide quantification by liquid chromatography–mass spectrometry (LC–MS) combines the high resolving power of reversed-phase (RP) chromatography with the excellent selectivity and sensitivity of mass spectrometric detection. On the basis of comprehensive practical experience in the analysis of small molecules, pharmaceutical research is developing technologies for analysis of a growing number of peptidic drug candidates. This article is a detailed review of procedures based on LC–MS techniques for quantitative determination of peptides. With the focus on pharmaceutical applications several technologies for sample preparation, various aspects of peptide chromatography, important characteristics of ESI–MS, selectivity of MS-detection modes, the large variability of internal standards, and modern instrumentation are discussed. The demand for reliable, robust, sensitive, and accurate methods is discussed using numerous examples from the literature, complemented by experiments and results from our laboratory. 相似文献