全文获取类型
收费全文 | 45317篇 |
免费 | 15681篇 |
国内免费 | 54篇 |
专业分类
化学 | 55237篇 |
晶体学 | 46篇 |
力学 | 2030篇 |
数学 | 2661篇 |
物理学 | 1078篇 |
出版年
2024年 | 372篇 |
2023年 | 4082篇 |
2022年 | 1432篇 |
2021年 | 2472篇 |
2020年 | 4617篇 |
2019年 | 2302篇 |
2018年 | 2271篇 |
2017年 | 591篇 |
2016年 | 5562篇 |
2015年 | 5518篇 |
2014年 | 4935篇 |
2013年 | 5117篇 |
2012年 | 3167篇 |
2011年 | 1008篇 |
2010年 | 3394篇 |
2009年 | 3349篇 |
2008年 | 1009篇 |
2007年 | 730篇 |
2006年 | 94篇 |
1997年 | 80篇 |
1996年 | 79篇 |
1995年 | 141篇 |
1994年 | 85篇 |
1993年 | 211篇 |
1992年 | 96篇 |
1988年 | 114篇 |
1987年 | 99篇 |
1986年 | 81篇 |
1985年 | 101篇 |
1984年 | 114篇 |
1983年 | 105篇 |
1982年 | 132篇 |
1981年 | 157篇 |
1980年 | 201篇 |
1979年 | 189篇 |
1978年 | 195篇 |
1977年 | 313篇 |
1976年 | 362篇 |
1975年 | 459篇 |
1974年 | 473篇 |
1973年 | 286篇 |
1972年 | 373篇 |
1971年 | 355篇 |
1970年 | 541篇 |
1969年 | 413篇 |
1968年 | 457篇 |
1967年 | 117篇 |
1966年 | 89篇 |
1965年 | 84篇 |
1963年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Dr. J. Kegel 《Analytical and bioanalytical chemistry》1972,276(1):45-50
The direct determination of CO2 is often faulty because of certain contents of the natural water. Due to this reason a specific method was worked out. The water to be analysed and distilled water are placed side by side in a gas-tight vessel with an atmosphere free of CO2, whereby mixing is avoided but gas-exchange is possible. After adjustment to the gas-equilibration the CO2 content of the distilled water is determined e.g. by titration, measuring of conductivity or other methods, from where the CO2 content in the natural water is calculated. 相似文献
102.
Qiang Xu Prof. Dr. Nobuko Tsumori Prof. Dr. Ling Jiang Masanobu Kondo Ryuichi Arakawa Prof. Dr. 《化学:亚洲杂志》2007,2(5):599-608
Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and ‐molybdate‐(II) anions, [fac‐M(CO)(NO)2(SO3F)3]? (M=W, Mo), which are novel weakly coordinating anions that contain a metal carbonyl/nitrosyl moiety, have been generated in fluorosulfonic acid and completely characterized by multinuclear NMR, IR, and Raman spectroscopy as well as ESI mass spectrometry. ESI MS measurements performed for the first time on a superacidic solution system unambiguously reveal the formation of the monoanionic, mononuclear W and Mo complexes formulated as [M(CO)(NO)2(SO3F)3]? (M=W, Mo). Multinuclear NMR spectroscopic studies at natural abundance and 13C and 15N enrichment clearly indicate the presence of one CO ligand, two equivalent NO ligands, and two types of nonequivalent SO3F? groups in a 2:1 ratio. The IR and Raman spectra reveal that the two equivalent NO ligands have a cis conformation, thus indicating a fac structure. Density functional calculations at the B3LYP level of theory predict that these anions have a singlet ground state (1A′) with a Cs symmetry along with C–O and N–O vibrational frequencies that are in agreement with the experimental observations. Mulliken population analysis shows that the monovalent negative charge is dispersed on the bulky sphere, the surface of which is covered by all the negatively charged O and F atoms with charge densities much lower than SO3F?, suggesting that [fac‐M(CO)(NO)2(SO3F)3]? (M=W, Mo) are weakly nucleophilic and poorly coordinating anions. 相似文献
103.
O. Reuter R. Langley Dr. Wan Manshol Bin W. Zn 《Radiation Physics and Chemistry》1998,52(1-6):429-432
This paper presents anew design concept for a gamma irradiation plant for the continuous processing of pumpable liquids. Typical applications of such a plant include
- • * the irradiation vulcanisation of natural latex rubber
- • * disinfection of municipal sewage sludge for agricultural use
- • * sterilisation of liquids in the pharmaceutical and cosmetics industries
- • * industrial processing of bulk liquids
The authors describe the design and operation of the latex irradiator now operating on a small production scale in Malaysia and proposed developments.
The design allows irradiation processing to be carried out under an inert or other gaseous environment.
State-of-the-art computer control system ensures the fully automatic processing operation needed by industrial computers. 相似文献
104.
Dr. Bhagwan Swaroop 《Colloid and polymer science》1978,256(5):482-486
Summary The depressions in freezing point measurements in quaternary solubilized solutions or micro-emulsion in sodium oleate + phenol + benzene + water are measured. Maxima and minima were observed, Gibbs' phase rule was applicable, eutectic points were detected, congruent melting points were obtained, loose combination of molecules or clusters, were formed, phases of the system transferred and finally unstable emulsion separated out. This is contrary to the views ofMcBain who called these solutions as thermodynamically stable. The results were compared with the conductivity, stability and heat of solubilization-concentration measurements.
With 5 figures and 1 table 相似文献
Zusammenfassung Es wird die Gefrierpunktserniedrigung von quaternären solubilisierten Lösungen im System Natriumoleat-Phenol-Benzol-Wasser gemessen. Die verschiedenen Befunde (Maxima und Minima des Gefrierpunktes in Abhängigkeit von der Zusammensetzung, Anwendbarkeit der Gibbs'schen Phasenregel, Auftreten von Eutektika, kongruente Schmelzpunkte etc.) dienen zum Beweis, daß diese Lösungen thermodynamisch instabil sind.
With 5 figures and 1 table 相似文献
105.
Prof. Dr. H. G. Kilian 《Colloid and polymer science》1977,255(8):740-754
Summary A thermodynamic treatment of homo-polymer systems out of linear chains with folded chain crystals is developed outgoing from appropriate models for single component systems. An expansion of thermodynamics to multi-micro-phase systems the structure of which is partially or totaly frozen is indispensable. General properties of melt crystallized homopolymers with folded chain crystals can be recognized indeed when the thermodynamic formalisms developed are applied.
Notation g c (y);g m (Y) molar Gibbs-free energy of a chain of a lengthy within an extended chain crystal and the melt rsp - g o c ;g o m molar free enthalpy of the unit in the crystal lattice and the melt rsp - g(y,y, f) molar Gibbs-function of an ideally folded chain crystal with the fold heighty f - gco(y, y ef,y f) molar free enthalpy of the crystal corey co - g 0 ex ((yef) excess free enthalpy of the longitudinal layers of folded chain crystals - g f(yef,g o ex ) molar free enthalpy of the longitudinal layers of the folded chain crystals - g tot molar free enthalpy of a chain of the lengthy within a folded chain crystal with longitudinal layers - h o 1c ,h o m molar enthalpy of the chain unit within the crystal lattice and the melt rsp - h =h o m -h o c molar heat of fusion of the unit - C p=C p m -C p c difference of the molar specific heat of a unit within the melt and within the chain crystal - h D molar defect enthalpy of local defects within the crystal lattice - h D molar defect enthalpy of the unit - s o c ,s o m molar entropy of the chain unit within the crystal lattice and the melt rsp - s c m conformational entropy of a chain in the melt - s gk conformational entropy of a chain of lengthy within a super-lattice as indicated in figure 5, - s molar entropy of fusion of the melt - s n c nematic configurational entropy - T absolute temperature - T M melting temperature of extended chain crystals of infinite size - T M(y) melting temperature of extended chain crystals containing only chains of the lengthy - T M (y, y f) melting temperatureof folded chain crystals of the thicknessy f composed of chains of the lengthy - T M(y f) melting temperature of folded chain crystals of the thicknessy fy - eh excess free enthalpy of the chain ends occupying crystallographic places - ef excess free enthalpy of a single fold loop - z coordination number of the lattice - 7 Euler's constant - R Boltzmann's constant - y number of chain units - y f height of lamelliform folded chain crystals - f=(y/y f - 1) number of fold loops of a chain of a lengthy when being built into a folded chain crystal of the thicknessy f - y co thickness of the crystal core of the simplified twophase model - y et average thickness of the surface layers of folded chain crystals - N c number of crystallized units of a chain of the lengthy - x c molar number of crystallized units of a chain of the lengthy - x nc molar number of noncrystallized units - excess free enthalpy parameter - (y f) thickness distribution of the fold heightsy f With 15 figures and 2 tables 相似文献
Zusammenfassung Das Schmelzen in polymeren Einteilchensystemen mit Faltungskristallen einheitlicher Dicke kann thermodynamisch als Umwandlung 1. Ordnung in einer Richtung behandelt werden, wenn die Faltungslänge bis zur Umwandlungstemperatur konstant bleibt (Faltungslänge als innerer Zusatzparameter). Eine wesentliche begriffliche Erweiterung ist für eine phänomenologische Beschreibung mit den Mitteln der Thermodynamik unumgänglich, wenn eine Faltungskristallit-Dickenverteilung existiert, weil dann prinzipiell nur noch partielle Koexistenz bestimmter Fraktionen metastabiler autonomer Mikrophasen mit der Schmelze möglich ist. Partielles Aufschmelzen und Rektistallisation können so dann auch in Betracht genommen werden. Die entwickelten Konzeptionen bewähren sich in der Anwendung auf bekannte Experimente.
Notation g c (y);g m (Y) molar Gibbs-free energy of a chain of a lengthy within an extended chain crystal and the melt rsp - g o c ;g o m molar free enthalpy of the unit in the crystal lattice and the melt rsp - g(y,y, f) molar Gibbs-function of an ideally folded chain crystal with the fold heighty f - gco(y, y ef,y f) molar free enthalpy of the crystal corey co - g 0 ex ((yef) excess free enthalpy of the longitudinal layers of folded chain crystals - g f(yef,g o ex ) molar free enthalpy of the longitudinal layers of the folded chain crystals - g tot molar free enthalpy of a chain of the lengthy within a folded chain crystal with longitudinal layers - h o 1c ,h o m molar enthalpy of the chain unit within the crystal lattice and the melt rsp - h =h o m -h o c molar heat of fusion of the unit - C p=C p m -C p c difference of the molar specific heat of a unit within the melt and within the chain crystal - h D molar defect enthalpy of local defects within the crystal lattice - h D molar defect enthalpy of the unit - s o c ,s o m molar entropy of the chain unit within the crystal lattice and the melt rsp - s c m conformational entropy of a chain in the melt - s gk conformational entropy of a chain of lengthy within a super-lattice as indicated in figure 5, - s molar entropy of fusion of the melt - s n c nematic configurational entropy - T absolute temperature - T M melting temperature of extended chain crystals of infinite size - T M(y) melting temperature of extended chain crystals containing only chains of the lengthy - T M (y, y f) melting temperatureof folded chain crystals of the thicknessy f composed of chains of the lengthy - T M(y f) melting temperature of folded chain crystals of the thicknessy fy - eh excess free enthalpy of the chain ends occupying crystallographic places - ef excess free enthalpy of a single fold loop - z coordination number of the lattice - 7 Euler's constant - R Boltzmann's constant - y number of chain units - y f height of lamelliform folded chain crystals - f=(y/y f - 1) number of fold loops of a chain of a lengthy when being built into a folded chain crystal of the thicknessy f - y co thickness of the crystal core of the simplified twophase model - y et average thickness of the surface layers of folded chain crystals - N c number of crystallized units of a chain of the lengthy - x c molar number of crystallized units of a chain of the lengthy - x nc molar number of noncrystallized units - excess free enthalpy parameter - (y f) thickness distribution of the fold heightsy f With 15 figures and 2 tables 相似文献
106.
Prof. Dr. G. Zigeuner W. Galatik W. -B. Lintschinger F. Wede 《Monatshefte für Chemie / Chemical Monthly》1975,106(5):1219-1233
The title compounds7 are formed in a general reaction by heating β-isothiocyanoketones3 with primary amines in inert solvents, or by thermal elimination of water from tetrahydro-6-hydroxy-6-methyl-2(1H)-pyrimidinethiones5, also in inert solvents. The 1-alkyl compounds can also be prepared under similar conditions from α,β-unsaturated ketones by reaction with alkylammonium rhodanides. The NMR-spectra show that the 1-substituted dihydro-6-methyl-2(1H)-pyrimidinethiones are in tautomeric equilibrium with the tetrahydro-6-methylene-2(1H)-pyrimidinethiones13. The reactivity of 1-alkyl and 1-aryldihydro-6-methyl-2(1H)-pyrimidinethiones is similar to that of dihydro-4,4,6-trimethyl-2(1H)-pyrimidinethione7 j, although their ring stability is certainly less. 相似文献
107.
Prof. Dr. E. Nachbaur A. Popitsch P. Burkert 《Monatshefte für Chemie / Chemical Monthly》1974,105(4):822-833
According to spectroscopic (IR, broadline proton NMR) and chemical (alkylation) investigations of disilver sulphamide the following molecular structure is assumed: $$\begin{gathered} O \hfill \\ || \hfill \\ H_2 N\_\_S\_\_NAg| \hfill \\ OAg \hfill \\ \end{gathered}$$ From the IR and NMR data deduction concerning the nature of the chemical bonds in this compound is possible. The instability of the still unknown mono-and trisilver sulphamide is discussed with regard to the structure of disilver sulphamide. 相似文献
108.
The annealing induced morphological changes in isotropic block copoly(etherester)s are investigated by small angle X-ray scattering methods. The observed results are consistent with a lamellar model which is comprised of a crystalline core of thickness 35 to 45 Å, a diffuse boundary zone of width 9 Å, and an amorphous layer which is varying strongly in thickness. The enhanced crystallinity of the samples annealed at higher temperatures is mainly due the lateral growth of the lamellae; the long period increases by not more than 20%. The scattering power of the samples is explained by means of an equivalent two-phase model in which the crystalline phase has the same structure as theα-form of poly(butylene terephthalate), whereas the amorphous phase is a mixture of the uncrystallized ester segments and the ether segments. The crystallinity determined from the scattering power is very much higher than that determined from thermoanalytical investigations. 相似文献
109.
The crystal structure of Ru2Si3 has been refined by leastsquares using three-dimensional X-ray data from a twinned crystal (1355 reflections,R=5.8%). Ru2Si3 is isostructural with Ru2Ge3 and like this compound a member of the Mn11Si19 structure family. The lattice parameters of the orthorhombic unit cell (Pnca—D
14
2h
) are:a=5.530 (1),b=11.060 (2) andc=8.952 (2) Å.
Mit 1 Abbildung 相似文献
Mit 1 Abbildung 相似文献
110.
Prof. Dr. Maximilian Pöhm Harald Kolassa Kurt Jentzsch 《Monatshefte für Chemie / Chemical Monthly》1977,108(2):393-395
It is well known that in the ergot alkaloids of the peptide type the proline appears in thel-configuration. Different methods of acid hydrolysis may lead to various cleavage products; hydrolysis by HCl yieldsd-proline, on the other hand hydrolytic cleavage by means of strongly acid cation exchange resin preserved the orginall-configuration.
Teilveröffentlichung der Dissertation vonH. Kolassa, Univ. Wien, 1973. 相似文献
Teilveröffentlichung der Dissertation vonH. Kolassa, Univ. Wien, 1973. 相似文献