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121.
L1 β-Lactamase催化反应机理研究 总被引:1,自引:0,他引:1
用混合量子力学和分子力学(QM/MM)方法和密度泛函理论讨论了L1 β-Lactamase催化Nitrocefin水解的过程, 研究结果表明, 反应为多步反应: 第一步亲核进攻反应为反应的决速步骤, 并且伴随着酰胺键的断裂, 第二步反应为质子迁移反应. 同时讨论了金属锌在反应中的作用. 相似文献
122.
Yijia Wang Yuansong Huang Yue Guo Lili Wang Zhihai Cao Minghua Wu 《无机化学与普通化学杂志》2020,646(11-12):526-531
TPE-TCF, a simple TPE-derivative with red-emission was used to detect cyanide in the condition of single dispersion as well as under aggregate state. It could be found that TPE-TCF exhibited excellent fluorescent response to cyanide in both situations, and the mechanism was supposed to be the reaction between cyanide and the double bond in TPE-TCF as well as the aggregation induced emission property of the reacted TPE-TCF molecules. What's more, TPE-TCF could distinguish cyanide with other species, such as common anions and biotiol well, which indicated it as a potential indicator for cyanide with good selectivity and specificity. 相似文献
123.
We have synthesized the tetrabutylammonium ([Bu4N]+), tetraethylammonium ([Et4N]+), guanidinium ([C(NH2)3]+), and methylguanidinium ([C(N3H5CH3)]+) salts of the [BH3(NH2BH2)2H]− anion, a five-membered B/N anionic chain, in high yields by the metathesis reactions of Na[BH3(NH2BH2)2H] with the corresponding halides and characterized them by NMR (11B, 11B{1H}, 1H, 1H{11B}, 13C), IR, elemental analysis, TGA-DSC, and TGA-MS. These complexes behave like ionic liquids (ILs), in which the melting point of the [Bu4N][BH3(NH2BH2)2H] is the lowest (−51 °C). The dehydrogenation of these ILs have been studied through the thermal decomposition and catalytic hydrolysis in aqueous solution using the noble or non-noble metals or their salts as catalysts, and the results indicate that these ILs of five-membered B/N anionic chain are promising hydrogen storage materials. 相似文献
124.
复合分子筛催化微晶纤维素水解 总被引:1,自引:0,他引:1
采用水热晶化法制备了HY/ZSM-5复合分子筛。通过XRD、SEM、N2-吸附脱附、NH3-TPD及吡啶吸附红外光谱等手段表征催化剂的结构和性质。结果表明,HY与HZSM-5复合后HY型分子筛完全被HZSM-5紧密包裹,形成致密的核壳结构。与机械混合物相比,复合分子筛微孔比表面积及孔体积均有所减少,总酸量略高,弱酸量小,而强酸量大,Br9nsted酸量与之相似,而Lewis酸量有所减少。将所制备的HY/ZSM-5复合分子筛催化剂应用于以离子液体氯化1-乙基-3-甲基咪唑鎓([Emim]Cl)为溶剂的纤维素水解反应中,与HY催化的纤维素水解相比,HY/ZSM-5催化纤维素水解反应获得的最佳葡萄糖收率由28.04%提高到38.78%,葡萄糖选择性由28.91%提高至48.29%。 相似文献
125.
Summary Human lipoprotein-associated coagulation inhibitor (LACI) is a serum protein containing three Kunitz domains. We displayed the first domain (LACI-D1) on the III protein of phage M13 and made libraries of this domain. We iteratively varied 13 residues in the region corresponding to the BPTI-trypsin interface and selected for binding to human plasmin (PLA) and human plasma kallikrein (pKAL). For PLA, our first-round best binder, EPI-P211, had KD=2 nM. Using information from the first selection, we made a PLA-biased library containing 500 000 proteins and selected from these a protein, EPI-P302, having a KD for PLA of 87 pM. EPI-P302 inhibits pKAL with KD=250 nM (2800-fold higher than for PLA) and KD values for other proteases are higher yet. From the same initial LACI-D1 library, we selected an inhibitor of pKAL, EPI-K401, with a KD for pKAL of 287 pM. We used information from this selection to construct a pKAL-biased library from which we selected EPI-K502, which has a KD for pKAL of 40 pM. EPI-K502 inhibits PLA with KD20 nM (500-fold higher than for pKAL); KD values for other proteases are much higher. For both targets and for both selections, there are families of proteins having a few differences and a range of affinities for their targets. These proteins are candidate drugs and imaging agents for indications involving excess PLA or pKAL. Structure-activity relationships of PLA and pKAL binders will allow design of small molecules that are specific for these targets.Abbreviations APP-I-D1
Kunitz domain of amyloid precursor protein-I
- BPTI
bovine pancreatic trypsin inhibitor
- F.VIIa
Factor VIIa
- F.XIa
Factor XIa
- FIR
fraction of input recovered
- hNE
human neutrophil elastase
- LACI-D1
lipoprotein-associated coagulation inhibitor, first Kunitz domain
- pKAL
human plasma kallikrein
- PLA
human plasmin
- RT
room temperature
- THBN
human thrombin
- Vg
variegated
- w.t.
wild-type
- %RIA
percent residual inhibitory activity
- ::
fusion (gene or protein) 相似文献
126.
Darla Graff Thompson Jill C. Osborn Jon R. Schoonover 《Polymer Degradation and Stability》2006,91(12):3360-3370
A polyester polyurethane, was subjected to humid and dry aging conditions at 70 °C with 75% and 0% relative humidity, respectively. Differences in molecular weight and quasi-static tensile strength between humid- and dry-aged samples are attributed to hydrolysis of the humid-aged polymers. A phase-separation study was performed on selected samples from the aging matrix. Polymer samples were subjected to 110 °C for 10 min, by mixing the polyester (soft) and the polyurethane (hard) domains, then rapidly cooled to room temperature, initiating the phase-separation process. Uniaxial tension, dynamic shear and infrared spectra of these samples were measured as a function of time providing insight into the effects of hydrolytic degradation and the relationship of mechanical and molecular-level properties. An Avrami-type analysis shows two distinct processes whose characteristics vary as a function of increased hydrolysis. LA-UR 04-6447. 相似文献
127.
Toluene diamines (TDAs) in urine have been used widely to determine the amount of toluene diisocyanate (TDI) absorbed by humans. Conventional hydrolysis to prepare a sample of urine takes approximately 16 h. An attempt is made to apply microwave-assisted heating (MAH) to reduce the duration of analysis. Urine collected from rats exposed to a mixture of 2,4- and 2,6-TDI was diluted with non-exposed human urine 1/1250-, 1/500- and 1/250-fold. The urine samples were hydrolyzed by both conventional heating and MAH. The hydrolysis efficiency obtained using MAH significantly exceeded that obtained using conventional heating. Hydrolysis by MAH required only 20 min, 48 times faster than with conventional heating. The use of the MAH method in hydrolysis was demonstrated to be reproducible, timesaving and efficient technique in measuring the concentration of urinary TDAs. 相似文献
128.
Isopropyl and p-nitrophenyl α- and β-d-glucopyranosides, restrained in a conformation close to B2,5 via an oxymethylene bridge have been synthesized. These four glucopyranosides were found to be hydrolyzed at similar rates, close to those observed for the parent unconstrained glucosides. In such derivatives, either α or β, the exocyclic cleaved bond is synperiplanar to an endocyclic oxygen lone pair. This conformationally locked glucopyranosyl moiety was also incorporated into a disaccharide, affording a conformationally restrained cellobiose analogue which was assayed against various glycosidases. 相似文献
129.
A comparison of steric and anchimeric effects on the hydrolytic stability of polyesters was studied. Twelve monomers were selected based on their propensity toward steric and anchimeric interactions: adipic acid, isophthalic acid, phthalic anhydride, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, maleic anhydride, ethylene glycol, 1,2-propanediol, 1,3-propanediol 1,4-butanediol, 1,5-pentanediol, and neopentyl glycol. Hydroxyl terminated oligoesters consisting of one diacid and one diol and one hydroxyl terminated oligoester consisting of two diacids and one diol were prepared. The hydrolytic stability was evaluated in an acetone/water solution. The acid number was monitored as a function of time. It was found that telechelic groups favor anchimeric interactions, while steric groups determine the rate of hydrolysis for the main chain. 相似文献
130.
Minoru Kuniyoshi Masahide Takahashi Yomei Tokuda Toshinobu Yoko 《Journal of Sol-Gel Science and Technology》2006,39(2):175-183
The effects of acid catalyst, water content and reaction temperature on the hydrolysis and polycondensation of phenyltriethoxysilane
(PhTES) were studied using 29Si NMR spectroscopy. The sol catalyzed by hydrochloric acid showed the simultaneous progress of hydrolysis and polycondensation.
In addition, the reaction rate was almost independent of reaction temperature. On the other hand, the polycondensation in
the PhTES-derived sol mixed with an excess amount of water and acetic acid as a catalyst proceeded after completion of the
hydrolysis. In the acetic acid-catalyzed system, the degree of the hydrolysis and polycondensation largely depends on the
reaction temperature. 相似文献