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931.
Multivariate statistical design modeling and the Derringer-Suich desirability function analysis were applied to micellar electrokinetic chromatography (MEKC) results with anionic surfactant to separate carbohydrates (CHOs) in different food matrices. This strategy has been studied with success to analyze compounds of difficult separation, but has not been explored for carbohydrates. Six procedures for the analysis of different sets of CHOs present in six food matrices were developed. The effects of pH, electrolyte and surfactant concentrations on the separation of the compounds were investigated using a central composite design requiring 17 experiments. The simultaneous optimization of the responses for separation of six sets of CHOs was performed employing empirical models for prediction of optimal resolution conditions in six matrices, condensed milk, orange juices, rice bran, red wine, roasted and ground coffee and breakfast cereal samples. The results indicate good separation for the samples, with appropriate detectability and selectivity, short analysis time, low reagent cost and little waste generation, demonstrating that the proposed technique is a viable alternative for carbohydrate analysis in foods. 相似文献
932.
Barbaro P Bianchini C Dal Santo V Meli A Moneti S Psaro R Scaffidi A Sordelli L Vizza F 《Journal of the American Chemical Society》2006,128(21):7065-7076
The complex Rh(cod)(sulfos) (Rh(I); sulfos = (-)O(3)S(C(6)H(4))CH(2)C(CH(2)PPh(2))(3); cod = cycloocta-1,5-diene), either free or supported on silica, does not catalyze the hydrogenation of benzene in either homogeneous or heterogeneous phase. However, when silica contains supported Pd metal nanoparticles (Pd(0)/SiO(2)), a hybrid catalyst (Rh(I)-Pd(0)/SiO(2)) is formed that hydrogenates benzene 4 times faster than does Pd(0)/SiO(2) alone. EXAFS and DRIFT measurements of in situ and ex situ prepared samples, batch catalytic reactions under different conditions, deuterium labeling experiments, and model organometallic studies, taken together, have shown that the rhodium single sites and the palladium nanoparticles cooperate with each other in promoting the hydrogenation of benzene through the formation of a unique entity throughout the catalytic cycle. Besides decreasing the extent of cyclohexa-1,3-diene disproportionation at palladium, the combined action of the two metals activates the arene so as to allow the rhodium sites to enter the catalytic cycle and speed up the overall hydrogenation process by rapidly reducing benzene to cyclohexa-1,3-diene. 相似文献
933.
Basseem Radwan Adriana Adamczyk Szymon Tott Krzysztof Czamara Katarzyna Kaminska Ewelina Matuszyk Malgorzata Baranska 《Molecules (Basel, Switzerland)》2020,25(23)
Endothelial cells (EC) constitute a single layer of the lining of blood vessels and play an important role in maintaining cardiovascular homeostasis. Endothelial dysfunction has been recognized as a primary or secondary cause of many diseases and it manifests itself, among others, by increased lipid content or a change in the lipid composition in the EC. Therefore, the analysis of cellular lipids is crucial to understand the mechanisms of disease development. Tumor necrosis factor alpha (TNF-α)-induced inflammation of EC alters the lipid content of cells, which can be detected by Raman spectroscopy. By default, lipid detection is carried out in a label-free manner, and these compounds are recognized based on their spectral profile characteristics. We consider (3S,3′S)-astaxanthin (AXT), a natural dye with a characteristic resonance spectrum, as a new Raman probe for the detection of lipids in the EC of various vascular beds, i.e., the aorta, brain and heart. AXT colocalizes with lipids in cells, enabling imaging of lipid-rich cellular components in a time-dependent manner using laser power 10 times lower than that commonly used to measure biological samples. The results show that AXT can be used to study lipids distribution in EC at various locations, suggesting its use as a universal probe for studying cellular lipids using Raman spectroscopy. The use of labeled Raman imaging of lipids in the EC of various organs could contribute to their easier identification and to a better understanding of the development and progression of various vascular diseases, and it could also potentially improve their diagnosis and treatment. 相似文献
934.
The conformations of monomeric 1,2-dichloropropane isolated in low temperature xenon matrix were characterized experimentally using FTIR spectroscopy. The interpretation of the experimental spectra was aided by ab initio MP2/6-311++G(3df,3pd) calculations. Relative energies of three structures, differing by the orientation of the Cl−C−C−Cl dihedral angle, fall within 0–6 kJ mol−1 range. The spectral signatures of all three conformers were identified experimentally. Infrared irradiation of the matrix isolated compound resulted in selective conversion of the most stable Trans conformer into the higher energy Gauche+ rotamer, while the Gauche− conformer remained unaffected. This result was interpreted in terms of calculated energy barriers and dipole moments. 相似文献
935.
A simple and rapid high-performance liquid chromatographic method was developed and validated for the analysis in rat plasma of BOL-303225-A, a new coumarin-based anti-inflammatory drug. Liquid-liquid extraction was used for sample preparation. Chromatographic separation was achieved on a C(18) column using acetonitrile and water containing 1% triethylamine pH 3.5, adjusted with orthophosphoric acid (35.5:64.5 v/v) as mobile phase. The UV detector was set at 324 nm. The method proved to be linear (r(2) > 0.99) and precise (RSD < 7%) over the concentration range 29-940 ng/mL, and was suitable for the support of pharmacokinetic studies in rats. 相似文献
936.
Gilles A. Francfort Adriana Garroni 《Archive for Rational Mechanics and Analysis》2006,182(1):125-152
Under time-dependent loading an elastic material undergoes the simplest form of damage in which it passes from its original
state to a weaker elastic state. Elaborating on prior work [14], we establish the existence of a relaxed variational evolution
where, at each time, the two states of the material combine to form a fine mixture, optimal from the standpoint of the applied
load at that time, yet preserving the irreversibility of the damaging process. 相似文献
937.
Adriana De Stefanis Giorgio Perez Anthony A.G. Tomlinson 《Reaction Kinetics and Catalysis Letters》2003,79(2):227-232
Reactions of primary aliphatic C2-C8 alcohols on alumina and iron-aluminium-oxides pillared montmorillonite and beidellite
indicate that dehydration reaction occurs on Lewis sites of pillars, while clays are responsible of cracking.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
938.
Wanderley de Souza Adriana Lanfredi-Rangel Loraine Campanati 《Microscopy and microanalysis》2004,10(5):513-527
Giardia lamblia is a flagellated protozoan of great medical and biological importance. It is the causative agent of giardiasis, one of the most prevalent diarrheal disease both in developed and third-world countries. Morphological studies have shown that G. lamblia does not present structures such as peroxisomes, mitochondria, and a well-elaborated Golgi complex. In this review, special emphasis is given to the contribution made by various microscopic techniques to a better knowledge of the biology of the protozoan. The application of video microscopy, immunofluorescence confocal laser scanning microscopy, and several techniques associated with transmission electron microscopy (thin section, enzyme cytochemistry, freeze-fracture, deep-etching, fracture-flip) to the study of the cell surface, peripheral vesicles, endoplasmic reticulum-Golgi complex system, and of the encystation vesicles found in trophozoites and during the process of trophozoite-cyst transformation are discussed. 相似文献
939.
Tommasina Coviello Laura Bertolo Pietro Matricardi Antonio Palleschi Gianfranco Bocchinfuso Adriana Maras Franco Alhaique 《Colloid and polymer science》2009,287(4):413-423
The peculiar unidirectional elongation observed during swelling of tablets prepared with scleroglucan (Sclg) and borax was
compared with that of other synthetic and natural polymers capable of physical/chemical interactions with borate ions. A dynamomechanical
characterization of “squared” Sclg/borax tablets was carried out to study the differences detectable on the two sides of the
matrix corresponding to the two directions, respectively, the parallel and perpendicular one with respect to the applied compression
force. Different compression forces were used and, in some cases, a second compression was applied on the tablets along a
direction perpendicular to the first one. Birefringence experiments were carried out on the swelled tablets along the two
directions. Obtained results allow correlating the anisotropic swelling behavior with the detected dynamomechanical and optical
properties of the Sclg/borax system. Among the various tested polymers, only guar gum and, to a lesser extent, locust bean
gum, showed an anisotropic elongation during swelling. 相似文献
940.
Whole‐Cell‐Catalyzed Multiple Regio‐ and Stereoselective Functionalizations in Cascade Reactions Enabled by Directed Evolution 下载免费PDF全文
Dr. Aitao Li Dr. Adriana Ilie Dr. Zhoutong Sun Dr. Richard Lonsdale Prof. Dr. Jian‐He Xu Prof. Dr. Manfred T. Reetz 《Angewandte Chemie (International ed. in English)》2016,55(39):12026-12029
Biocatalytic cascade reactions using isolated stereoselective enzymes or whole cells in one‐pot processes lead to value‐added chiral products in a single workup. The concept has been restricted mainly to starting materials and intermediate products that are accepted by the respective wild‐type enzymes. In the present study, we exploited directed evolution as a means to create E. coli whole cells for regio‐ and stereoselective cascade sequences that are not possible using man‐made catalysts. The approach is illustrated using P450‐BM3 in combination with appropriate alcohol dehydrogenases as catalysts in either two‐, three‐, or four‐step cascade reactions starting from cyclohexane, cyclohexanol, or cyclohexanone, respectively, leading to either (R,R)‐, (S,S)‐, or meso‐cyclohexane‐1,2‐diol. The one‐pot conversion of cyclohexane into (R)‐ or (S)‐2‐hydroxycyclohexanone in the absence of ADH is also described. 相似文献