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281.
A single-laboratory validation study was conducted for a liquid chromatographic/mass spectrometric (LCIMS) method for the simultaneous determination of the free carnitine and total choline in milk-based infant formula and health-care products. The sample preparation used for both carnitine and choline was adapted from AOAC Official Method 999.14, with an acidic and enzymatic hydrolysis of esterified forms of choline. Carnitine and choline were quantified by ion-pair chromatography with single-quadrupole MS detection, using their respective deuterated internal standards. The repeatability relative standard deviation was < or =2.5 and 2.1%, respectively, for carnitine and choline. The intermediate reproducibility relative standard deviation was <4.7 and 2.4%, respectively, for carnitine and choline. The ranges of the average product-specific recoveries were 92-98 and 94-103%, respectively, for carnitine and choline. Choline concentration determined in infant formula reference material SRM 1846 was in agreement with the reference value. The proposed method was compared with the enzymatic methods for a range of products; good correlation (r = 0.99) was obtained, although a significant bias was observed for both analytes. The method, with a short chromatographic run time (7 min), is convenient for routine analysis to enhance analytical throughput and is a good alternative to enzymatic assays. 相似文献
282.
Ntaganda R Milovic T Tiburcio J Thadani AN 《Chemical communications (Cambridge, England)》2008,(34):4052-4054
N-Acyl-alpha-amino amides were prepared, without the necessity of chromatographic purification, in a single step by heating the corresponding alpha-keto ester in methanolic ammonia. 相似文献
283.
Dr. Oleksandr Ivanenko Tamara Pavlenko Dr. Yuliia Pohorenko Dr. Valeriy Bykov 《欧洲无机化学杂志》2023,26(28):e202300295
The article presents the results of research on the hydrothermal synthesis of nanoscale oxide of cobalt and zirconium and their mixed oxide compositions. The synthesized samples have been characterized by the X-ray phase, scanning electron microscopy and nitrogen adsorption-desorption methods; the composition of the samples has been determined by chemical analysis methods, and their catalytic activity in the decomposition of hydrogen peroxide has been studied. It has been shown that during synthesis, highly dispersed cobalt and zirconium oxide are formed, and the sample of the composition (mol %): Co3O4(88)−ZrO2(12) has the highest specific surface area (181.2 m2/g) and the highest activity (K=6.18 ⋅ 10−2 s−1) against the decomposition of hydrogen peroxide. The increasing of the ZrO2 content in oxide compositions reduces their catalytic activity. The particle size in the synthesized samples is 7–38 nm. 相似文献
284.
Let L be a lattice of finite length, ξ = (x 1,…, x k )∈L k , and y ∈ L. The remoteness r(y, ξ) of y from ξ is d(y, x 1)+?+d(y, x k ), where d stands for the minimum path length distance in the covering graph of L. Assume, in addition, that L is a graded planar lattice. We prove that whenever r(y, ξ) ≤ r(z, ξ) for all z ∈ L, then y ≤ x 1∨?∨x k . In other words, L satisfies the so-called c 1 -median property. 相似文献
285.
Katherine N. Clayton Stuart J. Williams Xudong Pan Tamara Kinzer‐Ursem Steve Wereley 《Electrophoresis》2016,37(4):658-665
Rapid electrokinetic patterning (REP) is an emerging optoelectric technique that takes advantage of laser‐induced AC electrothermal flow and particle‐electrode interactions to trap and translate particles. The electrothermal flow in REP is driven by the temperature rise induced by the laser absorption in the thin electrode layer. In previous REP applications 350–700 nm indium tin oxide (ITO) layers have been used as electrodes. In this study, we show that ITO is an inefficient electrode choice as more than 92% of the irradiated laser on the ITO electrodes is transmitted without absorption. Using theoretical, computational, and experimental approaches, we demonstrate that for a given laser power the temperature rise is controlled by both the electrode material and its thickness. A 25‐nm thick Ti electrode creates an electrothermal flow of the same speed as a 700‐nm thick ITO electrode while requiring only 14% of the laser power used by ITO. These results represent an important step in the design of low‐cost portable REP systems by lowering the material cost and power consumption of the system. 相似文献
286.
Density fingering of the chlorite-tetrathionate reaction has been studied experimentally in a periodically heterogeneous Hele-Shaw cell where the heterogeneity is introduced in the form of spatial modulation of gap width along the front. Depending on the spatial wavelength, gap width, and chemical composition, three types of cellular structures have been observed. The initial evolution is characterized by dispersion curves, while the long time behavior is described by the change in the autocorrelation function of the front profile and in the mixing length of the patterns. 相似文献
287.
Bae S Mah H Chaturvedi S Jeknic TM Baird WM Katz AK Carrell HL Glusker JP Okazaki T Laali KK Zajc B Lakshman MK 《The Journal of organic chemistry》2007,72(20):7625-7633
1,4-Difluorobenzo[c]phenanthrene (1,4-DFBcPh) and its putative metabolites, the dihydrodiol and diol epoxides, have been synthesized and structurally characterized, and the extent of DNA binding by the metabolites has been assessed. 1,4-DFBcPh and 1,4-difluoro-10-methoxybenzo[c]phenanthrene were prepared by photochemical cyclization of appropriate naphthylphenylethylenes. The dihydrodiol was synthesized from 1,4-difluoro-10-methoxybenzo[c]phenanthrene, and the diol epoxides were diastereoselectively synthesized from the dihydrodiol. Interesting differences were noted in 1H NMR spectra of the series 1 (syn) diol epoxides of benzo[c]phenanthrene (BcPh) and 1,4-DFBcPh; the BcPh diol epoxide displays a quasi-diequatorial orientation of the hydroxyl groups, but in the 1,4-DFBcPh case these are diaxially disposed. This difference probably stems from the presence of the fjord-region fluorine atom in 1,4-DFBcPh. A through-space, fjord-region H-F coupling has also been observed for 1,4-DFBcPh and its derivatives. Comparative X-ray crystallographic analyses of BcPh and 1,4-DFBcPh and their dihydrodiols show that introduction of fluorine increases the molecular distortion by about 6-7 degrees . As a guide to estimating the molecular distortion and its effects, and for comparison with the X-ray structures in known cases, optimized structures of BcPh, 1,4-DFBcPh, and 1,4-DMBcPh (the dimethyl analogue) as well as their dihydrodiols and diol epoxides were computed. Relative aromaticities of these compounds were assessed by nucleus-independent chemical shift calculations, and 13C NMR chemical shifts were computed by gauge-inducing atomic orbital calculations. 1,4-DFBcPh and its dihydrodiol were subjected to metabolism, and the amount of DNA binding in human breast cancer MCF-7 cells was assessed. The extent of DNA binding was then compared with that for BcPh and its dihydrodiol and the potent carcinogen benzo[a]pyrene. The 1,4-DFBcPh series 2 (anti) diol epoxide-derived DNA adducts were also compared with those arising from intracellular oxidation of the dihydrodiol with subsequent DNA binding. These experiments showed that increased molecular distortion decreased metabolic activation to the terminal metabolites but that diol epoxide metabolites that are formed are the DNA-damaging species. 相似文献
288.
Powers DC Leber PA Gallagher SS Higgs AT McCullough LA Baldwin JE 《The Journal of organic chemistry》2007,72(1):187-194
At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate. 相似文献
289.
Maryam Bayat Meisam Zargar Tamara Astarkhanova Elena Pakina Sergey Ladan Marina Lyashko Sergey I. Shkurkin 《Molecules (Basel, Switzerland)》2021,26(10)
In this investigation, for the first time, we used Fragaria ananassa (strawberry) leaf extract as a source of natural reducing, capping or stabilizing agents to develop an eco-friendly, cost-effective and safe process for the biosynthesis of metal-based nanoparticles including silver, copper, iron, zinc and magnesium oxide. Calcinated and non-calcinated zinc oxide nanoparticles also synthesized during a method different from our previous study. To confirm the successful formation of nanoparticles, different characterization techniques applied. UV-Vis spectroscopy, X-ray Diffraction (XRD) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS), Photon Cross-Correlation Spectroscopy (PCCS) and Fourier Transformed Infrared Spectroscopy (FT-IR) were used to study the unique structure and properties of biosynthesized nanoparticles. The results show the successful formation of metal-based particles in the range of nanometer, confirmed by different characterization techniques. Finally, the presented approach has been demonstrated to be effective in the biosynthesis of metal and metal oxide nanoparticles. 相似文献
290.
Carbonylation of heterocycles by homogeneous catalysts 总被引:1,自引:0,他引:1
Church TL Getzler YD Byrne CM Coates GW 《Chemical communications (Cambridge, England)》2007,(7):657-674
This article summarizes the recent developments (particularly the uses of homogeneous organometallic catalysts) in ring-opening carbonylations, ring-opening carbonylative polymerizations and ring-expansion carbonylations of heterocycles such as epoxides, aziridines, lactones and oxazolines. 相似文献