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81.
82.
Gerhard Angermüller 《manuscripta mathematica》1986,54(3):349-359
Let f:AmAn be a polynomial map between affine spaces. We give some sufficient conditions for the connectedness of the difference kernel of f and relate this to the Jacobian Conjecture. 相似文献
83.
The rapid-scanning capability of FTIR instrumentation has revitalized the field of vibrational spectroscopy in polymer research and will be discussed with reference to the study of polyurethane kinetics, the temperature dependence of hydrogen bonding in polyamide 6 and strain-induced crystallization in a polydimethylsiloxane elastomer. 相似文献
84.
By use of salt elimination, the transition metal substituted oligosilanes (η5-C5Me4Et)Fe(CO)2SiMe2SiMe2Cl 1, (η5-C5Me4Et)Mo(CO)3SiMe2SiMe2Br 2, (η5-C5Me4Et)Fe(CO)2(SiMe2)6(CO)2Fe(η5-C5Me4Et) 3 and (η5-C5Me4Et)Fe(CO)2(SiMe2)6Br 4 were prepared and characterized. Compound 1 is well crystallized from pentane and its structure has been determined by X-ray diffraction analysis. 相似文献
85.
Katleen Boussu Jérémie De Baerdemaeker Charles Dauwe Marc Weber Kelvin G Lynn Diederik Depla Steliana Aldea Ivo F J Vankelecom Carlo Vandecasteele Bart Van der Bruggen 《Chemphyschem》2007,8(3):370-379
This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly. 相似文献
86.
The solubility of argon in pure liquid water was measured at ca. 100 kPa and from 2 to 40°C using an analytical method characterized by an imprecision of about ±0.05%. From the experimental results, Henry fugacities H
2,1
(T,P
s,1
) (also known as Henry's Law constants or Henry coefficients) at the vapor pressure P
s,1
of water as well as Ostwald coefficients L
2,1
at infinite dilution were obtained. Measurements were made at roughly 0.5°C and/or 1° intervals between 2 and 8°C (region I), and at 5°C intervals above 10°C (region II). A difference plot lnH
2,1
/T suggests an unusual temperature dependence in region I, i.e., between 2 and 8°C. Because of this, the data were treated separately in two parts corresponding to these two regions. Our results are compared with the recent high-precision data of Krause and Benson (Henry fugacities), and with calorimetrically determined quantities (enthalpies and heat capacities of solution). Finally, experimental results are compared with values calculated via scaled particle theory.Communicated in part at the 2nd International Symposium on Solubility Phenomena in Newark, New Jersey, August 12–15, 1986, and at the 4th ISSP in Troy, New York, July 20–August 3, 1990. 相似文献
87.
We explore here an approach to mimic the structures and biological functions of protein loops in small synthetic molecules, by grafting the loop of interest onto an organic template comprising a bicyclic diketopiperazine, prepared by the formal coupling of (2S,4S)-4-aminoproline (Pro(NH2)) and aspartic acid (Asp). The Fmoc-protected template 4 is used to prepare cyclo(-Ala1-Asn2-Pro3-Asn4-Ala5- Ala6-Temp-) ( 5 ) and cyclo(-Ala1-Arg2-Gly3-Asp4-Temp-) ( 6 ) (where Temp = template derived from 4 ), containing the Asn-Pro-Asn-Ala (NPNA) and Arg-Gly-Asp (RGD) motifs. The conformational properties of these molecules are studied in aqueous solution by NMR and simulated-annealing methods. The NPNA motif, an immunodominant epitope on the circumsporozoite surface protein of the malaria parasite Plasmodium falciparum, is shown to adopt a stable type-I β-turn in 5 . The template in 5 adopts a preferred conformation with Pro(NH2)χ1 ≈? ?35° and the Asp moiety χ1 ≈? 70°. A different template conformation is inferred for 6 , with Pro(NH2)χ1 ≈? 0°, but the ARGD loop appears by NMR to undergo rapid conformational averaging. Solid-phase binding assays reveal that 6 displays modest antagonist activity towards both the integrin αIIbβ3 and αvβ3 receptors. 相似文献
88.
The 1-ferrocenyl-2-methyl-1-propylamine (2a)is the most effective chiral template in asymmetrically induced peptide synthesis by stereoselective four component condensation (4CC). Two routes for the synthesis of this amine via its N,N-dimethyl derivative (12a) an described. One route involves the conversion of 12a into the corresponding azide 14a by treatment with methyl iodide/sodium azide in diglyme/water and subsequent reduction of the azide. The preferred other route consists of treating 12a with thioglycolic acid/formic acid to yield the carboxymethylmercapto derivative 9a and transformation of the latter into 2a with aqueous ammonia/ammonium chloride/mercuric chloride. Some related reactions are also discussed. 相似文献
89.
Gerhard Klebe Thomas Mietzner Frank Weber 《Journal of computer-aided molecular design》1994,8(6):751-778
Summary A relative comparison of the binding properties of different drug molecules requires their mutual superposition with respect to various alignment criteria. In order to validate the results of different alignment methods, the crystallographically observed binding geometries of ligands in the pocket of a common protein receptor have been used. The alignment function in the program SEAL that calculates the mutual superposition of molecules has been optimized with respect to these references. Across the reference data set, alignments could be produced that show mean rms deviations of approximately 1 Å compared to the experimental situation. For structures with obvious skeletal similarities a multiple-flexible fit, linking common pharmacophoric groups by virtual springs, has been incorporated into the molecular mechanics program MOMO. In order to combine conformational searching with comparative alignments, the optimized SEAL approach has been applied to sets of conformers generated by MIMUMBA, a program for conformational analysis. Multiple-flexible fits have been calculated for inhibitors of ergosterol biosynthesis. Sets of different thrombin and thermolysin inhibitors have been conformationally analyzed and subsequently aligned by a combined MIMUMBA/SEAL approach. Since for these examples crystallographic data on their mutual alignment are available, an objective assessment of the computed results could be performed. Among the generated conformers, one geometry could be selected for the thrombin and thermolysin inhibitors that approached reasonably well the experimentally observed alignment. 相似文献
90.
THE EFFECTS OF THROMBOXANE INHIBITORS ON THE MICROVASCULAR AND TUMOR RESPONSE TO PHOTODYNAMIC THERAPY 总被引:9,自引:0,他引:9
Victor H. Fingar Kimberly A. Siegel T. Jeffery Wieman Karola Weber Doak 《Photochemistry and photobiology》1993,58(3):393-399
Abstract— Vascular stasis and tissue ischemia are known to cause tumor cell death in several experimental models after photodynamic therapy (PDT); however, the mechanisms leading to this damage remain unclear. Because previous studies indicated that thromboxane release is implicated in vessel damage, we further examined the role of throm-boxane in PDT. Rats bearing chondrosarcoma were injected with 25 mg/kg Photofrin® (intravenously) 24 h before treatment. Light (135 J/cm 2 , 630 nm) was delivered to thc tumor area after injection of one of the following inhibitors: (1) R68070: a thromboxane synthetase inhibitor; (2) SQ-29548: a thromboxane receptor antagonist; and (3) Flunarizine: an inhibitor of platelet shape change. Systemic thromboxane levels were determined. Vessel constriction and leakage were evaluated by intravital microscopy. Tumor response was assessed after treatment. Thromboxane levels were decreased more than 50% with SQ-29548 as compared to controls. Thromboxane levels in animals given R68070 and Flunarizine remained at baseline levels. SQ-29548 and R68070 reduced vessel constriction compared to controls, while Flunarizine totally prevented vessel constriction. R68070 and SQ-29548 inhibited vessel permeability compared to PDT controls; Flunarizine did not. Animals given these inhibitors showed markedly reduced tumor cure. These results indicate that the release of thromboxane is linked to the vascular response in PDT. 相似文献