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121.
Raymundo Cea-Olivares Rubn Alfredo Toscano Marcela Lpez Patricia García 《Heteroatom Chemistry》1993,4(4):313-317
Three 1,1-dithioacids containing an additional functional group, 2-pyrrolidone-1-carbodithioic acid, 2-hydroxycyclopentene-1-carbodithioic acid, and 2-pyrrolidone-1,3-bis(carbodithioic) acid, were reacted with the Group 15 heterocycles 2-chloro-1,3-dithia-2-arsa- and stiba-cyclopentanes (CIMS2C2H4; M = As, Sb). The dithiocomplexes obtained were characterized by spectroscopic methods and elemental analyses. The X-ray structure determination of the 2-pyrrolidonedithiocarbamate of 1,3-dithia-arsacyclopentane shows a monodentate behavior of the dithiocarbamate entity and the absence of participation of the carbonyl oxygen in the coordination. 相似文献
122.
Parts molded from reground BPA polycarbonate (PC) resin recovered from used objects do not always give the desired physical properties as parts molded from virgin resin. This loss of properties appears due to a surface hydrolysis of the PC which results in a reduction in molecular weight and formation of bis-phenol-A (BPA). The hydrolysis appears to be aided by exposure to uv-light and humidity. If the surface of the PC is washed with caustic solution, BPA and low MW oligomers are removed and many of the physical properties of the PC are restored. 相似文献
123.
lvaro Fernndez-Ochoa María de la Luz Cdiz-Gurrea Patricia Fernndez-Moreno Alejandro Rojas-García David Arrez-Romn Antonio Segura-Carretero 《Molecules (Basel, Switzerland)》2022,27(3)
The study of the bioavailability of bioactive compounds is a fundamental step for the development of applications based on them, such as nutraceuticals, functional foods or cosmeceuticals. It is well-known that these compounds can undergo metabolic reactions before reaching therapeutic targets, which may also affect their bioactivity and possible applications. All recent studies that have focused on bioavailability and metabolism of phenolic and terpenoid compounds have been developed because of the advances in analytical chemistry and metabolomics approaches. The purpose of this review is to show the role of analytical chemistry and metabolomics in this field of knowledge. In this context, the different steps of the analytical chemistry workflow (design study, sample treatment, analytical techniques and data processing) applied in bioavailability and metabolism in vivo studies are detailed, as well as the most relevant results obtained from them. 相似文献
124.
Hairy roots of Brugmansia candida produce the tropane alkaloids scopolamine and hyoscyamine. In an attempt to divert the carbon flux from competing pathways
and thus enhance productivity, the polyamine biosynthesis inhibitors cyclohexylamine (CHA) and methylglyoxal-bis-guanylhy,
drazone (MGBG) and the phenylalamine-ammonia-lyase inhibitor cinnamic acid were used. CHA decreased the specific productivity
of both alkaloids but increased significantly the release of scopolamine (approx 500%) when it was added in the mid-exponential
phase. However, when CHA was added for only 48 h during the exponential phase, the specific productivity of both alkaloids
increased (approx 200%), favoring scopolamine. Treatment with MGBG was detrimental to growth but promoted release into the
medium of both alkaloids. However, when it was added for 48 h during the exponential phase, MGBG increased the specific productivity
(approx 200%) and release (250–1800%) of both alkaloids. Cinnamic acid alone also favored release but not specific productivity.
When a combination of CHA or MGBG with cinnamic acid was used, the results obtained were approximately the same as with each
polyamine biosynthesis inhibitor alone, although to a lesser extent. Regarding root morphology, CHA inhibited growth of primary
roots and ramification. However, it had a positive effect on elongation of lateral roots. 相似文献
125.
Two new marine sediment standard reference materials (SRMs) for the determination of organic contaminants 总被引:3,自引:0,他引:3
Wise SA Poster DL Schantz MM Kucklick JR Sander LC Lopez de Alda M Schubert P Parris RM Porter BJ 《Analytical and bioanalytical chemistry》2004,378(5):1251-1264
Two new marine sediment standard reference materials (SRMs), SRM 1941b Organics in Marine Sediment and SRM 1944 New York/New Jersey Waterway Sediment, have been recently issued by the National Institute of Standards and Technology (NIST) for the determination of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, and chlorinated pesticides. Both sediment SRMs were analyzed using multiple analytical methods including gas chromatography/mass spectrometry (GC/MS) on columns with different selectivity, reversed-phase liquid chromatography with fluorescence detection (for PAHs only), and GC with electron capture detection (for PCBs and pesticides only). SRM 1941b has certified concentrations for 24 PAHs, 29 PCB congeners, and 7 pesticides, and SRM 1944 has certified concentrations for 24 PAHs, 29 PCB congeners, and 4 pesticides. Reference concentrations are also provided for an additional 58 (SRM 1941b) and 39 (SRM 1944) PAHs, PCB congeners, and pesticides. SRM 1944, which was collected from multiple sites within New York/New Jersey coastal waterways, has contaminant concentrations that are generally a factor of 10–20 greater than SRM 1941b, which was collected in the Baltimore (Maryland) harbor. These two SRMs represent the most extensively characterized marine sediment certified reference materials available for the determination of organic contaminants.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material. 相似文献
126.
Patricia W. Stege Germán A. Messina Guillermo Bianchi Roberto A. Olsina 《Journal of fluorescence》2010,20(2):517-523
Enzyme activities can provide indication for quantitative changes in soil organic matter (SOM). It is known that the activities
of most enzymes increase as native SOM content reflecting larger microbial communities and stabilization of enzymes on humic
materials. β-Gucosidase (β-Glu) activities have been frequently used as indicators of changes in quantity and quality of SOM.
In this study we propose a simple and very sensitive method, which has lower limit of detection compared with classic spectrophotometric
method with the aim of determinate the β-Glu activity in soil samples using Fluorescein mono-β-D-glucopyranoside (FMGlc) as
a substrate. The fluorescein released by the enzymatic reaction was quantified by capillary electrophoresis-laser induced
fluorescence (CE-LIF) method. The background electrolyte (BGE) consisted in 40 mM phosphate buffer, pH 6. The LOD and LOQ
for fluorescein were 1.3 10−7 mg mL−1 and 6.4 10−6 mg mL−1, respectively. This work deals with the minimization of the mixture for the enzymatic reaction and with the optimization
conditions of CE separation. To the best of our knowledge, this is the first time that an enzymatic activity was detected
in soil using CE-LIF system. 相似文献
127.
Cucurbituril‐mediated immobilization of fluorescent proteins on supramolecular biomaterials 下载免费PDF全文
Olga J. G. M. Goor Ralph P. G. Bosmans Luc Brunsveld Patricia Y. W. Dankers 《Journal of polymer science. Part A, Polymer chemistry》2017,55(21):3607-3616
The reversible introduction of functionality at material surfaces is of interest for the development of functional biomaterials. In particular, the use of supramolecular immobilization strategies facilitates mild reaction and processing conditions, as compared to other covalent analogues. Here, the engineering of multicomponent supramolecular materials, beyond the use of a single supramolecular entity is proposed. Cucurbit[8]uril (Q8) mediated host–guest chemistry is combined with hydrogen bonding supramolecular 2‐ureido‐4‐pyrimidinone (UPy)‐based materials. The modular incorporation of a UPy‐additive that presents one guest to incorporate into the Q8 host allows for selective supramolecular functionalization at the water–polymer material interface. Supramolecular ternary complex formation at the material surface was studied by X‐ray photoelectron spectroscopy, which as a result of large overlap in atomic composition of the different components showed minor changes is surface composition upon complex formation. Surface MALDI‐ToF MS measurements revealed useful insights in the formation of complexes. Protein immobilization was monitored using both fluorescence spectroscopy and quartz crystal microbalance with dissipation monitoring, which successfully demonstrated ternary complex formation. Although proteins could selectively be immobilized onto the surfaces, control of the system's stability remains a challenge as a result of the dynamicity of the host–guest assembly. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3607–3616 相似文献
128.
Laura C. Carpi Osvaldo A. Rosso Patricia M. Saco Martín Gómez Ravetti 《Physics letters. A》2011,375(4):801-804
A methodology to analyze dynamical changes in complex networks based on Information Theory quantifiers is proposed. The square root of the Jensen-Shannon divergence, a measure of dissimilarity between two probability distributions, and the MPR Statistical Complexity are used to quantify states in the network evolution process. Three cases are analyzed, the Watts-Strogatz model, a gene network during the progression of Alzheimer's disease and a climate network for the Tropical Pacific region to study the El Niño/Southern Oscillation (ENSO) dynamic. We find that the proposed quantifiers are able not only to capture changes in the dynamics of the processes but also to quantify and compare states in their evolution. 相似文献
129.
130.
Gorga MP Neely ST Dorn PA Dierking D Cyr E 《The Journal of the Acoustical Society of America》2002,112(6):2910-2920
Measurements of DPOAE level in the presence of a suppressor were used to describe a pattern that is qualitatively similar to population studies in the auditory nerve and to behavioral studies of upward spread of masking. DPOAEs were measured in the presence of a suppressor (f3) fixed at either 2.1 or 4.2 kHz, and set to each of seven levels (L3) from 20 to 80 dB SPL. In the presence of a fixed f3 and L3 combination, f2 was varied from about 1 oct below to at least 1/2 oct above f3, while L2 was set to each of 6 values (20-70 dB SPL). L1 was set according to the equation L1 = 0.4L2 + 39 [Janssen et al., J. Acoust. Soc. Am. 103, 3418-3430 (1998)]. At each L2, L1 combination, DPOAE level was measured in a control condition in which no suppressor was presented. Data were converted into decrements (the amount of suppression, in dB) by subtracting the DPOAE level in the presence of each suppressor from the DPOAE level in the corresponding control condition. Plots of DPOAE decrements as a function of f2 showed maximum suppression when f2 approximately = f3. As L3 increased, the suppressive effect spread more towards higher f2 frequencies, with less spread towards lower frequencies relative to f3. DPOAE decrement versus L3 functions had steeper slopes when f2 > f3, compared to the slopes when f2 < f3. These data are consistent with other findings that have shown that response growth for a characteristic place (CP) or frequency (CF) depends on the relation between CP or CF and driver frequency, with steeper slopes when driver frequency is less than CF and shallower slopes when driver frequency is greater than CF. For a fixed amount of suppression (3 dB), L3 and L2 varied nearly linearly for conditions in which f3 approximately = f2, but grew more rapidly for conditions in which f3 < f2, reflecting the basal spread of excitation to the suppressor. The present data are similar in form to the results observed in population studies from the auditory nerve of lower animals and in behavioral masking studies in humans. 相似文献