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91.
根据Flory热力学统计理论和比容-熔融热作国法,由DSC结果得到了不同联苯含量的聚醚醚酮酮-含联苯聚醚醚酮酮(PEEKK-PEBEKK)共聚物的熔融热,两种方法获得的结果吻合。在此基础上给出了PEEKK-PEBEKK共聚物不同联苯含量的熔点计算表达式。结果还表明,随着联苯含量nB,的变化,明显改变;当nB=0.35时,PEEKKPEBEKK共聚物的值最小。 相似文献
92.
The technique of temperature waves to measure the complex thermophysical characteristics of materials has been proposed. The relations for the moduli and arguments of these characteristics for the case of plane temperature waves have been calculated. The temperature dependences of the moduli and arguments of complex thermophysical characteristics of polyvinylacetate (PVAc) at different frequencies and also the temperature dependences of its vibrational and configurational heat capacities have been determined. It has been shown that the vibrational heat capacity of PVAc in the region of softening grows sharply and its configurational heat capacity goes through a peak. The segmental mobility has been found to affect the heat transfer in the polymer in an ambivalent way causing both a decrease and increase of thermal conductivity.
Zusammenfassung Zur Bestimmung der komplexen thermophysischen Eigenschaften von Stoffen wurde eine Temperaturwellentechnik vorgeschlagen. Für den Fall zweidimensionaler Temperatur-wellen wurden die Verhältnisse von Moduli und Argumenten dieser Eigenschaften berechnet. Die Temperaturabhängigkeit von Moduli und Argumenten der komplexen thermophysischen Eigen-schaften von Polyvinylacetat (PVAc) bei verschiedenen Frequenzen und auch die Temperatur-abhängigkeit seiner Vibrations- und Konfigurations-Wärmekapazitäten wurden bestimmt. Es wurde gezeigt, daß die Vibrations-Wärmekapazität von PVAc im Erweichungsbereich scharf zunimmt und die Konfigurations-Wärmekapazität durch einen Peak geht. Man fand, daß die Segment-Mobilität den Wärmetransport im Polymer auf eine ambivalente Weise beeinflußt, in dem die Wärmeleit-fähigkeit entweder gesenkt oder angehoben wird.相似文献
93.
Seto Y. Umemoto K. Arii T. Masuda Y. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):165-177
New solid complex of nitrilotriacetic acid and bismuth trichloride was synthesized by a solid phase reaction of nitrilotriacetic
acid and bismuth trichloride at room temperature. The composition of the sample is BiCl3[N(CH2COOH)3]2.5. The crystal structure of the complex belongs to triclinic system with the lattice parameters: α=0.7849 nm, β=0.9821 nm,
χ=2.0021 nm, α=96.50°, β=98.76° and γ=90.49°. The far-infrared spectra show the bonding between the Bi ion and N atom of nitrilotriacetic
acid. The thermal analysis also demonstrates the complex formation between the bismuth ion and nitrilotriacetic acid. The
gaseous pyrolysis product and the final residue in the thermal decomposition process are determined to check the thermal decomposition
reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
94.
95.
Pucci V Bugamelli F Mandrioli R Ferranti A Kenndler E Raggi MA 《Biomedical chromatography : BMC》2004,18(1):37-44
An accurate and precise high-performance liquid chromatographic method using diode array detection for the determination of the novel antiepileptic, Levetiracetam, has been developed. Three clean-up procedures for the analysis of Levetiracetam in human plasma were implemented and evaluated, namely solid-phase extraction, deproteinization by addition of organic solvents and formation of insoluble salts. Adenosine was used as the internal standard for all three sample pretreatment procedures. Among the several cartridges used for solid-phase extraction, the hydrophilic-lypophilic balance (Oasis) HLB) phase provides the best extraction yield of Levetiracetam, together with high precision. With the two other clean-up procedures involving plasma deproteinization by addition of methanol or zinc sulphate, lower sensitivity and precision of the assays were obtained. However, they are cheaper and faster when compared with the solid-phase extraction procedure. 相似文献
96.
Shaginian A Rosen MC Binkowski BF Belshaw PJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4334-4340
We describe the first solid-phase synthesis of dihydrovirginiamycin S(1), a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1', 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure-activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities. 相似文献
97.
Using the Picker flow microcalorimeter, excess heat capacities have been obtained at 25°C throughout the concentration range for 2,2-dimethylbutane,n-hexane, and cyclohexane each mixed with a series of hexadecane isomers of increasing degrees of orientational order, as determined by depolarized Rayleigh scattering. The isomers are 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4-, and 2-methylpentadecane, andn-hexadecane. Thec
p
E
values are negative, increasing rapidly in magnitude with increase of orientational order, and are not predicted by the Prigogine—Flory theory which neglects order. Values ofc
p
E
are obtained at 10, 25, and 55°C for cyclohexane +6-, 4-, and 2-methylpentadecane which with other literature data lead to the temperature dependence of the thermodynamic excess functions for cyclohexane solutions of the five C16 isomers. The excess enthalpy and entropy vary with the C16 isomer and with temperature, but the corresponding variation of the excess free energy is small, indicating a high degree of enthalpy-entropy compensation. This is consistent with a rapid decrease with temperature of orientational order in the C16 isomers. 相似文献
98.
C. Auguet J. L. Seguin F. Martorell F. Moll V. Torra J. Lerchner 《Journal of Thermal Analysis and Calorimetry》2006,86(2):521-529
Micro-calorimetric
devices using Si-based sensors are very useful for the study of gas–solid
reactions, in which very low mass of reactants are necessary. But in fact
the consequence of using flat detectors is an increase of the uncertainty
in the measured energy. In this work a calorimetric gas sensor based on Xensor
chip is analysed studying the local x–y
contributions of dissipation to the sensitivity related to the value in the
centre. We study also the effects of the gas-flow on the sensitivity, comparing
the results obtained with two Xensor type chips. Finally we carry out a deeper
analysis of the x–y effects on the
calorimetric detector for dissipations in the reactant shell extremely close
to the detector surface to visualize the link between the power density distribution
and the output signal. 相似文献
99.
Brunsveld L Watzke A Durek T Alexandrov K Goody RS Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2756-2772
Prenylated proteins with non-native functionalities are generally very difficult to obtain by recombinant or enzymatic means. The semisynthesis of preparative amounts of prenylated Rab guanosine triphosphatases (GTPases) from recombinant proteins and synthetic prenylated peptides depends largely on the availability of functionalised prenylated peptides corresponding to the proteins' native structure or modifications thereof. Here, we describe and compare solution-phase and solid-phase strategies for the generation of peptides corresponding to the prenylated C terminus of Rab7 GTPase. The solid-phase with utilisation of a hydrazide linker emerges as the more favourable approach. It allows a fast and practical synthesis of pure peptides and gives a high degree of flexibility in their modification. To facilitate the analysis of semisynthetic proteins, the synthesised peptides were equipped with a fluorescent group. Using the described approach, we introduced fluorophores at several different positions of the Rab7 C terminus. The position of the incorporated fluorescent groups in the peptides did not influence the protein-ligation reaction, as the generated peptides could be ligated onto thioester-tagged Rab7. However, it was found that the positioning of the fluorescent group had an influence on the functionality of the Rab7 proteins; analysis of the interaction of the semisynthetic Rab7 proteins with REP (Rab escort protein) and GDI (guanosine diphosphate dissociation inhibitor) molecules revealed that modification of the peptide side chains or of the C-terminal isoprenoid did not significantly interfere with complex formation. However, functionalisation of the C terminus was found to have an adverse effect on complex formation and stability, possibly reflecting low structural flexibility of the Rab GDI/REP molecules in the vicinity of the lipid-binding site. 相似文献
100.
E. Tomaszewicz 《Thermochimica Acta》2006,447(1):69-74
Reactivity in the solid state between CoWO4 and some rare-earth metal tungstates RE2WO6 (RE = Sm, Eu, Gd) was investigated by the XRD method. Two families of new isostructural cobalt and rare-earth metal tungstates, Co2RE2W3O14 and CoRE4W3O16, were synthesized. The Co2RE2W3O14 phases are formed by heating in air the CoWO4 and RE2WO6 compounds mixed at the molar ratio 2:1, while the CoRE4W3O16 phases are synthesized at the molar ratio of CoWO4/RE2WO6 equals to 1:2. The Co2RE2W3O14 phases as well as the CoRE4W3O16 compounds crystallize in the orthorhombic system. The Co2RE2W3O14 and CoRE4W3O16 compound melt above 1150 °C. A melting manner of the Co2RE2W3O14 and CoRE4W3O16 compounds was determined in an inert atmosphere. The formation of CoWO4−x phase was observed during heating in an inert atmosphere. 相似文献