全文获取类型
收费全文 | 2431篇 |
免费 | 75篇 |
专业分类
化学 | 1702篇 |
晶体学 | 33篇 |
力学 | 17篇 |
数学 | 264篇 |
物理学 | 490篇 |
出版年
2023年 | 15篇 |
2022年 | 46篇 |
2021年 | 118篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 79篇 |
2017年 | 62篇 |
2016年 | 139篇 |
2015年 | 88篇 |
2014年 | 108篇 |
2013年 | 227篇 |
2012年 | 119篇 |
2011年 | 165篇 |
2010年 | 114篇 |
2009年 | 94篇 |
2008年 | 133篇 |
2007年 | 115篇 |
2006年 | 87篇 |
2005年 | 88篇 |
2004年 | 82篇 |
2003年 | 72篇 |
2002年 | 49篇 |
2001年 | 40篇 |
2000年 | 24篇 |
1999年 | 18篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 18篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1929年 | 5篇 |
1927年 | 5篇 |
排序方式: 共有2506条查询结果,搜索用时 15 毫秒
61.
Marcin Marczak Lidia Wolska Wojciech Chrzanowski Jacek Namieśnik 《Mikrochimica acta》2006,155(3-4):331-348
Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants.
Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic
parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile
organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned
pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages
of these techniques are discussed and novel developments are also taken into consideration. 相似文献
62.
Ewa Bulska Katarzyna Wróbel Adam Hulanicki 《Fresenius' Journal of Analytical Chemistry》1992,342(9):740-743
Summary The optimal conditions for the determination of aluminium and chromium in blood serum are proposed. Several sample pretreatment procedures for the purpose are compared. The best results are obtained by sample dilution with nitric acid (0.1 mol/l) and addition of Mg(NO3)2 as modifier with a magnesium concentration of 0.2 mg/ml. This procedure has been used for studying the intestinal intake of aluminium by patients after oral administration of aluminium compounds. 相似文献
63.
Piotr Podleś 《Communications in Mathematical Physics》1992,150(1):167-179
Exterior algebras of differential forms on quantum 2-spheresS
qc
2
,q[–1, 1]/{0},c[0, ] (c=0 forq=±1), are classified. In the definition of exterior algebras we assume the invariance w.r.t. the action of the quantumSU(2) group and dimensionality conditions (which imply that we deal with two-dimensional manifolds). The exterior algebras exist only forc=0 and are unique in that case. The corresponding generalized directional derivatives are provided. 相似文献
64.
It is shown that generic small data Robinson-Trautman space-times cannot beC
123 extended beyond the r=2m Schwarzschild-like event horizon. This implies that an observer living in such a space-time can determine by local measurements whether or not he has crossed the event-horizon of the black-hole. 相似文献
65.
A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions n
, n
, S
z
n
, S
z
n
, S
z (n
–n
), n
n
and S
+
a
+
a
as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic.The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors. 相似文献
66.
Mieczysław Jaroniec Jarosław Ościk Anna Deryło Ryszard Kusak Janusz Czarniecki 《Monatshefte für Chemie / Chemical Monthly》1982,113(1):29-35
An equation for multilayer adsorption from multicomponent liquid mixtures on solid surfaces1 has been examined. For this purpose experimental adsorption data for four alcohols from benzene/n-heptane mixture on silica gel have been measured. Average number of the adsorbed layers, heterogeneity parameter and capacity of the surface phase have been evaluated by using the equation mentioned above.
Mehrschichten-Adsorption von Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel
Zusammenfassung Eine Gleichung für Mehrschichten-Adsorption an festen Oberflächen1 aus Mehrkomponentenlösungen wurde getestet. Zu diesem Zweck wurden experimentelle Daten für die Adsorption von vier Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel herangezogen. Der Mittelwert für die Anzahl der Adsorptionsschichten, der Heterogenitätsparameter und die Kapazität der Oberflächenphase wurde aus dieser Gleichung berechnet.相似文献
67.
Chmielewski MK Marchán V Cieślak J Grajkowski A Livengood V Münch U Wilk A Beaucage SL 《The Journal of organic chemistry》2003,68(26):10003-10012
Thermolytic groups structurally related to well-studied heat-sensitive phosphate/thiophosphate protecting groups have been evaluated for 5'-hydroxyl protection of deoxyribonucleosides as carbonates and for potential use in solid-phase oligonucleotide synthesis. The spatial arrangement of selected functional groups forming an asymmetric nucleosidic 5'-O-carbonic acid ester has been designed to enable heat-induced cyclodecarbonation reactions, which would result in the release of carbon dioxide and the generation of a nucleosidic 5'-hydroxyl group. The nucleosidic 5'-O-carbonates 3-8, 10-15, and 19-21 were prepared and were isolated in yields ranging from 45 to 83%. Thermolytic deprotection of these carbonates is preferably performed in aqueous organic solvent at 90 degrees C under near neutral conditions. The rates of carbonate deprotection are dependent on the nucleophilicity of the functional group involved in the postulated cyclodecarbonation reaction and on solvent polarity. Deprotection kinetics increase according to the following order: 4 < 5 < 10 < 6 < 12 < 7 < 13 < 8 < 14 congruent with 19-21 and CCl4 < dioxane < MeCN < t-BuOH < MeCN:phosphate buffer (3:1 v/v, pH 7.0) < EtOH:phosphate buffer (1:1 v/v, pH 7.0). Complete thermolytic deprotection of carbonates 7, 8, 13, and 14 is achieved within 20 min to 2 h under optimal conditions in phosphate buffer-MeCN. The 2-(2-pyridyl)amino-1-phenylethyl and 2-[N-methyl-N-(2-pyridyl)]aminoethyl groups are particularly promising for 5'-hydroxyl protection of deoxyribonucleosides as thermolytic carbonates. 相似文献
68.
Surface properties of the binary mixed systems of alkylpyridinium halides and sodium alkylsulfonates 总被引:1,自引:0,他引:1
Danuta Gralczyk Katarzyna H
c Pawe
Wydro 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,220(1-3):55-60
Surface properties of the binary mixed systems of decyl- and dodecylpyridinium chloride or bromide and sodium pentyl- and heptylsulfonate have been investigated. The surface tension of solutions of equimolar mixtures of surfactants and individual surfactants was measured, and the composition of mixed monolayers and surface interaction parameter β were calculated with the regular solution theory. Our results indicate that the properties of mixed films depend on both ionic strength and the kind of added inorganic electrolyte. With the increase of inorganic electrolyte concentration, the content of more surface active ions in the adsorption films enhances and is the highest in the presence of NaI and the smallest when solutions contain NaCl. Mutual interactions in mixed adsorbed films were found to be attractive. However, the strength of interaction weakens with the increase of ionic strength and depends on the kind of inorganic ions in the order: Cl−>Br−>I−. 相似文献
69.
Magdalena Kurdziel Elżbieta Szczepaniec-Cięciak Barbara Dąbrowska Wojciech Nitek Katarzyna Paliś Edyta Ślusarska 《Journal of solution chemistry》2003,32(7):601-615
The solubilities of solid 2,3-dimethylbutane and cyclopentene in liquid argon at a temperature of 87.3 K and in liquid nitrogen at 77.4 K have been measured by the filtration method. The hydrocarbon contents in solutions were determined using gas chromatography. GC–MS was used to identify impurities in solutes. The experimental value of the mole fraction solubility of solid 2,3-dimethyl-butane in liquid argon at 87.3 K is (8.26 ± 1.60) × 10–6 and (2.77 ± 0.94) × 10–8 in liquid nitrogen at 77.4 K. The experimental value of the mole fraction solubility of solid cyclopentene in liquid argon at 87.3 K is (5.11 ± 0.44) × 10–6 and (4.60 ± 0.76) × 10–8 in liquid nitrogen at 77.4 K. The Preston–Prausnitz method was used for calculation of the solubilities of solid hydrocarbons in liquid argon in the temperature range 84.0–110.0 K and in liquid nitrogen from 64.0 to 90.0 K. The solvent–solute interaction parameters l
12 were also calculated. At 90.0 K liquid argon is a better solvent for investigated solid hydrocarbons than is liquid nitrogen. 相似文献
70.
Buchachenko AA Tscherbul TV Kłos J Szcześniak MM Chałasiński G Webb R Viehland LA 《The Journal of chemical physics》2005,122(19):194311
Interaction potentials of the iodine atom, atomic cation, and anion with light rare-gas atoms from He to Ar are calculated within the unified ab initio approach using the unrestricted coupled-cluster with singles and doubles and perturbative treatment of triples correlation treatment, relativistic small-core pseudopotential, and an extended basis set. Ab initio points are fit to a flexible analytical function. The calculated potentials are compared with available literature data, assessed in the I(-)-and I+-ion mobility calculations and the Ar-I(-)-anion zero electron kinetic-energy spectra simulations, and analyzed using the correlation rules. The results indicate a high precision of the reported potentials. 相似文献