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981.
982.
983.
Uwe Schön Josef Messinger Uwe Reinecker Manoj K.S. Prabhu 《Tetrahedron letters》2005,46(42):7111-7115
An efficient Pd(0)-catalyzed protocol for the rapid and efficient preparation of 3-aminoestrone via 3-benzylaminoestrone from estrone-triflate is described. The three step synthesis proceeds with an overall yield of about 55% using X-Phos as optimal ligand for the Pd(0)-catalyzed Buchwald-Hartwig amination. 相似文献
984.
Josef Vold?ich 《Journal of Mathematical Analysis and Applications》2002,272(2):582-595
In this paper, we deal with averaging over balls in EN and derive an equality describing a relation between scale and space dependence of the average function. We also show connections with equations of mathematical physics. 相似文献
985.
Julie Thevarpadam Irene Bessi Oliver Binas Dr. Diana P. N. Gonçalves Dr. Chavdar Slavov Dr. Hendrik R. A. Jonker Dr. Christian Richter Prof. Dr. Josef Wachtveitl Prof. Dr. Harald Schwalbe Prof. Dr. Alexander Heckel 《Angewandte Chemie (International ed. in English)》2016,55(8):2738-2742
The ability of three different bifunctional azobenzene linkers to enable the photoreversible formation of a defined intermolecular two‐tetrad G‐quadruplex upon UV/Vis irradiation was investigated. Circular dichroism and NMR spectroscopic data showed the formation of G‐quadruplexes with K+ ions at room temperature in all three cases with the corresponding azobenzene linker in an E conformation. However, only the para–para‐substituted azobenzene derivative enables photoswitching between a nonpolymorphic, stacked, tetramolecular G‐quadruplex and an unstructured state after E–Z isomerization. 相似文献
986.
The microwave heated Suzuki-Miyaura cross-coupling reaction of boronic acids, boronic esters and organotrifluoroborates served as a model reaction in a singlemode equipment. The reaction conditions were optimized with respect to temperature and reaction time and were transferred to multimode equipment which is well suited for multiparallel synthesis in a larger scale. The source of the Pd species chosen included immobilized Pd complexes and Pd particles. In fact the increased time to reach the required reaction time in multimode chambers suitable for 48 parallel reactions has to be taken into account. The nature of the boronic acid has no impact on the efficiency of the catalytic process. However, heterogenized Pd species perform less well in multimode chambers with larger vial volumes, which we ascribe to diffusion phenomena. 相似文献
987.
Vacek J Caskey DC Horinek D Shoemaker RK Stang PJ Michl J 《Journal of the American Chemical Society》2008,130(24):7629-7638
The rate of interconversion of the two inequivalent edges of the pyridine rings in the trigonal prism 3c, self-assembled from 3 equiv of the star connector, tetrakis[4-(4-pyridylethynyl)phenyl]cyclobutadienecyclopentadienylcobalt, and 6 equiv of a platinum linker, cis-(Me3P)2Pt(2+) 2 TfO(-), was determined by DNMR in nitromethane. It exhibits a highly unusual bilinear Eyring plot. In the low temperature regime, the activation enthalpy DeltaH(double dagger) is approximately 12 kcal/mol and an activation entropy DeltaS(double dagger) ranges from approximately -15 to approximately 0 cal/mol x K as a function of the nature and concentration of the anions present. The reaction is attributed to hindered rotation of the pyridine rings about the Pt-N bond, facilitated by a tight pairing with a counterion. Above a counterion-dependent limiting temperature, DeltaH(double dagger) and DeltaS(double dagger) change abruptly to approximately 35 kcal/mol and approximately 60 cal/mol x K, respectively. The changes largely compensate, such that the reactions have comparable rates in the two regimes, both amenable to DNMR measurement, but their mechanisms clearly differ. Several kinetic models for the involvement of ion pairing equilibria fit the observed data nearly equally well, and they all contain a reaction step with high DeltaH(double dagger) and DeltaS(double dagger) values in the high-temperature regime. Its mechanism is proposed to involve a counterion-assisted reversible dissociation of one or two adjacent Pt-N bonds, followed by nearly free rotation of the terminal pyridine ring or rings and subsequent bond reclosure, which is similar to the last presumed step in the initial prism assembly. An interpretation of the very high DeltaS(double dagger) value is suggested by molecular dynamics calculations: at equilibrium, there is a bubble of gaseous nitromethane solvent inside the prism, and it collapses when the prism opens as the transition state is reached. A simple calculation of the entropy of cavitation provides quantitative support for this tentative proposal. The presence of such voids might be generally important for the formation and properties of self-assembled cages. 相似文献
988.
Bakardjiev M Holub J Hnyk D Stíbr B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(21):6529-6533
Treatment of the nido-1-CB8H12 (1) carborane with NaBH4 in THF at ambient temperature led to the isolation of the stable [arachno-5-CB8H13]- (2(-)), which was isolated as Na+[5-CB8H13]-.1.5 THF and PPh4 +[5-CB8H13]- in almost quantitative yield. Compound 2(-) underwent a boron-degradation reaction with concentrated hydrochloric acid to afford the arachno-4-CB7H13 (3) carborane in 70 % yield, whereas reaction between 2(-) and excess phenyl acetylene in refluxing THF gave the [closo-2-CB6H7]- (4-) in 66 % yield. Protonation of the Cs+4(-) salt with concentrated H2SO4 or CF3COOH in CH2Cl2 afforded a new, highly volatile 2-CB6H8 (4) carborane in 95 % yield, the deprotonation of which with Et3N in CH2Cl2 leads quantitatively to Et3NH+[2-CB6H7](-) (Et3NH+4(-)). Both compounds 4- and 4 can be deboronated through treatment with concentrated hydrochloric acid in CH2Cl2 to yield the carbahexaborane nido-2-CB5H9 (5) in 60 % yield. New compounds 2-, 3, and 4 were structurally characterised by the ab initio/GIAO/MP2/NMR method. The method gave superior results to those carried out using GIAO-HF when relating the calculated 11B NMR chemical shifts to experimental data. 相似文献
989.
Regina Mikulíková Václav Švorčík Josef Náhlík Tomáš Sopuch Pavel Havelka 《Cellulose (London, England)》2008,15(3):473-479
We studied the physical–chemical properties of polyethylene (PE) films doped with calcium salt of 6-carboxycellulose (Ca-oxy)
in concentrations 0–20 wt.% and their interactions with cells. The interaction between the PE/Ca-oxy composite film and 3T3
cells has not been described so far. Modification by surface grinding to enhance material cytocompatibility was studied. The
surface wettability of doped films was tested by contact angle measurements and the surface morphology by SEM microscopy and
profilometry. Adhesion and proliferation of tissue cells (3T3 mouse fibroblasts) were studied in vitro on pristine and ground
doped PE films. The ground samples have a higher contact angle values and the number of proliferated cells is greater on the
ground samples than on pristine ones. The presence of Ca-oxy in PE film increases the adhesion of 3T3 cells on the doped substrate
and on ground samples adhere more cells than on pristine ones.
相似文献
Václav ŠvorčíkEmail: |
990.
Zimmermann M Takats J Kiel G Törnroos KW Anwander R 《Chemical communications (Cambridge, England)》2008,(5):612-614
The reaction of Ln(AlMe(4))(3) with bulky hydrotris(pyrazolyl)borate (Tp(t)(Bu,Me))H proceeds via a sequence of methane elimination and C-H bond activation, affording unprecedented rare-earth metal ligand moieties including Ln(Me)[(micro-Me)AlMe(3)] and X-ray structurally characterized "Tebbe-like" Ln[(micro-CH(2))(2)AlMe(2)]. 相似文献