全文获取类型
收费全文 | 34436篇 |
免费 | 1377篇 |
国内免费 | 37篇 |
专业分类
化学 | 23689篇 |
晶体学 | 262篇 |
力学 | 629篇 |
数学 | 4835篇 |
物理学 | 6435篇 |
出版年
2023年 | 272篇 |
2022年 | 214篇 |
2021年 | 426篇 |
2020年 | 588篇 |
2019年 | 559篇 |
2018年 | 726篇 |
2017年 | 671篇 |
2016年 | 1322篇 |
2015年 | 1067篇 |
2014年 | 1128篇 |
2013年 | 2242篇 |
2012年 | 2472篇 |
2011年 | 2669篇 |
2010年 | 1535篇 |
2009年 | 1306篇 |
2008年 | 2207篇 |
2007年 | 2167篇 |
2006年 | 1888篇 |
2005年 | 1721篇 |
2004年 | 1388篇 |
2003年 | 1083篇 |
2002年 | 983篇 |
2001年 | 720篇 |
2000年 | 628篇 |
1999年 | 468篇 |
1998年 | 337篇 |
1997年 | 262篇 |
1996年 | 378篇 |
1995年 | 258篇 |
1994年 | 251篇 |
1993年 | 296篇 |
1992年 | 266篇 |
1991年 | 183篇 |
1990年 | 164篇 |
1989年 | 151篇 |
1988年 | 153篇 |
1987年 | 143篇 |
1986年 | 141篇 |
1985年 | 196篇 |
1984年 | 184篇 |
1983年 | 142篇 |
1982年 | 131篇 |
1981年 | 114篇 |
1980年 | 95篇 |
1979年 | 105篇 |
1978年 | 102篇 |
1977年 | 99篇 |
1976年 | 91篇 |
1975年 | 83篇 |
1973年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Pártay L Jedlovszky P Vincze A Horvai G 《The journal of physical chemistry. B》2005,109(43):20493-20503
Monte Carlo simulation of the vapor-liquid interface of water-methanol mixtures of different compositions, ranging from pure water to pure methanol, have been performed on the canonical (N, V, T) ensemble at 298 K. The analysis of the systems simulated has revealed that the interface is characterized by a double layer structure: methanol is strongly adsorbed at the vapor side of the interface, whereas this adsorption layer is followed at its liquid side by a depletion layer of methanol of lower concentration than in the bulk liquid phase of the system. The dominant feature of the interface has been found to be the adsorption layer in systems of methanol mole fractions below 0.2, and the depletion layer in systems of methanol mole fractions between 0.25 and 0.5. The orientation of the molecules located at the depletion layer is found to be already uncorrelated with the interface, whereas the methanol molecules of the adsorption layer prefer to align perpendicular to the interface, pointing straight toward the vapor phase by their methyl group. Although both the preference of the molecular plane for a perpendicular alignment with the interface and the preference of the methyl group for pointing straight to the vapor phase are found to be rather weak, the preference of the methyl group for pointing as straight toward the vapor phase as possible within the constraint imposed by the orientation of the molecular plane is found to be fairly strong. One of the two preferred orientations of the interfacial water molecules present in the neat system is found to disappear in the presence of methanol, because methanol molecules aligned in their preferred orientation can replace these water molecules in the hydrogen-bonding pattern of the interface. 相似文献
992.
The preparation of ethyl 4-(2-bromoethyl)thieno[2,3-b]pyrrole-5-carboxylate and ethyl 6-(2-bromoethyl)thieno[3,2-b]pyrrole-5-carboxylate by reaction of t-butyl 2-(2-thienyl)carbazate and t-butyl 2-(3-thienyl)carbazate with ethyl-5-bromo-2-oxopentanoate are described. 相似文献
993.
Chemical compounds containing platinum have been employed since 1978 as drugs to beat certain type of tumours. Nevertheless, besides of their exceptional antitumoral properties, these drugs also have important deleterious side effects, such as, nephrotoxicity and ototoxicity.A study of Pt accumulation and a speciation analysis has been performed by ICP-MS in samples from kidney and inner ear in a controlled population of Wistar rats treated with, either, cisplatin, carboplatin or oxaliplatin. The results on Pt accumulation point out to drug structure and not only to Pt content as the responsible for the alteration of organ functionality.Speciation studies in the samples from kidney and inner ear were performed coupling two-dimensional liquid chromatography (2D-LC) to ICP-MS. Size exclusion (SEC) and anion exchange fast protein liquid chromatography (FPLC) was employed for 2D orthogonal separation. After these separations, free drug peaks were not observed in any of the samples.The binding of Pt to biomolecules was demonstrated by SEC and, independently of the drug used, Pt eluted as two main bands with molecular weights of 12 kDa and 25-65 kDa for inner ear samples, and as two different bands with 20 kDa and 50-60 kDa in the samples from kidney. However, the relative band intensity presented important differences for the three drugs. Using the same chromatographic conditions, it was shown that a metallothionein (MT) standard eluted in the same position as some of the cytosolic Pt-biomolecules.High Pt-containing fractions eluting from the SEC column were analysed by anion exchange FPLC after a preconcentration step. Among the different preconcentration methods tested, sample focusing on the head of the FPLC column shows main advantages. In this way, the separation by 2D chromatography of the high molecular Pt-species has been considerably improved. 相似文献
994.
This paper describes the experimental studies carried out to determine (238)Pu, (239/40)Pu, (241)Pu, (241)Am, (242)Cm and (244)Cm in samples from nuclear power plants (mainly spent ion exchange resins and evaporator concentrates) using an organophosphorus compound immobilized on an inert support. These materials are commercially available under the name TRU Resin (for Transuranium Specific) from Eichrom Industries, Darien, IL. An attempt is made to develop a rapid, accurate method of analysis, with minimum waste generation. Standard solutions of Pu and Am and one sample of spent ion exchange resin that contains fission, activation products, Pu, Am and Cm were analyzed to study the separation factors and interferences in the measurement of Pu, Am and Cm isotopes. 相似文献
995.
Chromatographic retention data and thermodynamic properties of six pine terpenes (α-pinene, β-pinene, camphene, limonene, α-phellandrene and p-cymene) on six different liquid phases, with a wide range of polarity, are reported at temperatures from 80 to 120 °C. The retention behaviour and selectivity of liquid phases for the separation of binary solute systems are discussed in terms of activity coefficients and specific interactions. Solubility parameters for the liquid phases are reported using the regular solution theory and the Takamiya equation and a good correlation between polarity and solubility parameters is observed. 相似文献
996.
Villar-Rodil S. Paredes J. I. Martínez-Alonso A. Tascón J.M.D. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):37-43
The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to
get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main
stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and
morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR)
and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
Summary A comparison of three binary mobile phases in LC separation of C60 and C70 fullerences on chemically bonded 2,4-dinitroanilinopropyl (DNAP) stationary phase was carried out, n-Hexane-benzene has been found to be the best mobile phase for efficient separation of the all-carbon molecules permitting high loads in preparative LC. 相似文献
998.
M. N. Moreno-Carretero J. M. Salas-Peregrín 《Journal of Thermal Analysis and Calorimetry》1984,29(5):1053-1059
The following cadmium(II) complexes of deprotonated 6-amino-5-nitroso-uracil (AH), deprotonated 6-amino-3-methyl-5-nitroso-uracil (BH) and neutral 6-amino-1-methyl-5--nitroso-uracil (CH) have been prepared and their thermal behaviour studied by TG and DSC techniques: CdA2 · 3 H2O, CdB2 · 2 H2O, CdB2 and CdCl2(CH)2 · 2 H2O.Dehydration processes of these complexes take place in only one step and the enthalpy values associated with them are comprised in the 42.7–80.5 kJ · mole–1 H2O range. The pyrolytic reactions finish in the 630–900 C temperature range, remaining as final residue in the case of CdA2 · 3 H2O, CdB2 · 2 H2O and CdB2 complexes, cadmium oxide. The pyrolytic decomposition of CdCl2(CH)2 · 2 H2O complex does not yield any residue, due to the elimination of cadmium chloride.
Zusammenfassung Folgende Cadmium(II)-Komplexe von deprotoniertem 6-Amino-5-nitrosouracil (AH), deprotoniertem 6-Amino-3-methyl-5-nitroso-uracil (BH) und neutralem 6-Amino-1-methyl-5-nitroso-uracil (CH) wurden hergestellt: CdA2 · 3 H2O, CdB2· 2 H2O, CdB2 und CdCl2(CH)2 · 2 H2O. Das thermische Verhalten dieser Komplexe wurde mittels TG und DSC untersucht. Die Dehydratisierung der Komplexe verlÄuft in nur einem Schritt. Die Enthalpiewerte für diese Prozesse liegen im Bereich von 42.7–80.5 kJ · mol–1 H2O. Die pyrolytischen Reaktionen verlaufen im Temperaturbereich von 630–900C zu Ende, wobei im Falle der Komplexe CdA2 · 3 H2O, CdB2 · 2 H2O und CdB2 Cadmiumoxid als Rückstand zurückbleibt. Die pyroytische Zersetzung von CdCl2(CH)2 · 2 H2O verlÄuft wegen der Flüchtigkeit von CdCl2 rückstandslos.
CdA2 · 3 H2O, CdB2 · 2 H2O, CdB2 CdCl2(CH)2 · 2 H2O, A — 6--5-, B — 6--3--5- CH — 6--1--5- . . 42.7–80.5 · –1. 630–900, . CdCl2(CH)2 · 2 H2O - , .相似文献
999.
Liquid—liquid extraction of divalent palladium by solutions of the hexachloroderivate of cobalt dicarbolide (HBCl6) in the mixture of solvents (30 v/v % nitrobenzene+20 v/v % n-dodecane +50 v/v/ % toluene) from nitric acid medium has been studied. Besides HBCl6 the organic phase contained also 2,2′-dipyridyl (dipy). The yield of palladium extraction from 0.5M HNO3 is greater than 99.0%. The species extracted into the organic phase corresponds to the formula [Pd(dipy)2] (BCl6)2. 相似文献
1000.
An analytical potential energy surface (PES) representation of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+)) system was developed by fitting around 600 CCSD(T)/cc-pVQZ ab initio points. Rate constant calculations for this reaction and its isotopic variants (D(2) and HD) were performed using the quasiclassical trajectory (QCT) method, obtaining a good agreement with experimental data. Calculations conducted to determine the cross section of the title reaction, considering collision energies (E(T)) below 0.3 eV, also led to good accord with experiments. This PES appears to be suitable for kinetics and dynamics studies. Moreover, the QCT results show that, although the hypotheses of a widely used capture model are not satisfied, the resulting expression for the cross section can be applied within a suitable E(T) interval, due to errors cancellation. This could be a general situation regarding the application of this simple model to ion-molecule processes. 相似文献