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951.
Young Beom Kim Ki Hyun Bae Seung-Schik Yoo Tae Gwan Park HyunWook Park 《Magnetic resonance imaging》2009
Objective
The objective of this study was to investigate a method to generate positive contrast, selective to superparamagnetic iron oxide (SPIO) labeled cells, using the susceptibility-weighted echo-time encoding technique (SWEET).Materials and Methods
SPIO-labeled human epidermal carcinoma (KB) cells were placed in a gel phantom. Positive contrast from the labeled cells was created by subtraction between conventional spin-echo images and echo-time shifted susceptibility-weighted images. SPIO-labeled cells were injected into the left dorsal flank and hind limb of nude mice, and unlabeled cells were placed on the right side as controls. Tumor growth was monitored using the proposed method, and a histological analysis was used to confirm the presence of the labeled cells.Results
Based on in vitro testing, we could detect 5000 labeled cells at minimum and the number of pixels with positive contrast increased proportionally to the number of labeled cells. Animal experiments also revealed the presence of tumor growth from SPIO-loaded cells.Conclusions
We demonstrated that the proposed method, based on the simple principle of echo-time shift, could be readily implemented in a clinical scanner to visualize the magnetic susceptibility effects of SPIO-loaded cells through a positive-contrast mechanism. 相似文献952.
郭本瑜 《应用数学学报(英文版)》2001,17(2):218-232
1. IntroductionIn studying many problems arising in science and engineering, we need to estimate parameters in governing differential equations. Some theoretical results for this kind of inverseproblems can be found in various literatu-res, e.g., see [1-4]. Also, there have been a lot ofwork concerning their numerical approalmations, e.g., see [5-10]. One of numerical methods is the so-called optimization method as in is]. To do this, we first guess the unknownparameters in some ways, and the… 相似文献
953.
Base metal catalyzed regioselective cage B–H functionalization has been achieved. Under the assistance of a bidentate directing group, Cu-catalyzed [4+2] annulation of carboranyl amides with internal alkynes affords unprecedented C,B-substituted carborane-fused-pyridone derivatives, whereas the use of terminal alkynes leads to B–H/C(sp)–H dehydrocoupling products. The isolation and structural identification of a notably stable Cu(Ⅰ) intermediate shed light on the reaction mechanism, which is proposed to involve a Cu(Ⅲ) intermediate. 相似文献
954.
Qidong Tai Xuyun Guo Guanqi Tang Peng You Tsz‐Wai Ng Dong Shen Jiupeng Cao Chun‐Ki Liu Naixiang Wang Ye Zhu Chun‐Sing Lee Feng Yan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):816-820
Tin‐based perovskites with excellent optoelectronic properties and suitable band gaps are promising candidates for the preparation of efficient lead‐free perovskite solar cells (PSCs). However, it is challenging to prepare highly stable and efficient tin‐based PSCs because Sn2+ in perovskites can be easily oxidized to Sn4+ upon air exposure. Here we report the fabrication of air‐stable FASnI3 solar cells by introducing hydroxybenzene sulfonic acid or its salt as an antioxidant additive into the perovskite precursor solution along with excess SnCl2. The interaction between the sulfonate group and the Sn2+ ion enables the in situ encapsulation of the perovskite grains with a SnCl2–additive complex layer, which results in greatly enhanced oxidation stability of the perovskite film. The corresponding PSCs are able to maintain 80 % of the efficiency over 500 h upon air exposure without encapsulation, which is over ten times longer than the best result reported previously. Our results suggest a possible strategy for the future design of efficient and stable tin‐based PSCs. 相似文献
955.
Manh Linh Nguyen Jaeduk Byun Suwoong Kim June Won Hyun Kahyun Hur Tae Joo Shin Byoung‐Ki Cho 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(9):2775-2779
The 1,2,3‐triazole molecule, which is a product of click chemistry, possesses a high dipole moment and can be a useful polar motif for ferroelectric columnar liquid crystal (LC) materials—though it has not been used to date. Herein, we report the helical assembly and ferroelectric switching properties of a columnar liquid crystal comprising a naphthalene core and 1,2,3‐triazolyl linkages. The molecule assembles into a double‐stranded helical columnar LC structure (Colhel). The X‐ray simulations of cisoid and transoid columnar models suggest that the helical assembly comprises cisoid conformers with a non‐zero dipole moment. The helical columns in the Colhel phase are aligned homeotropically under an electric field. The ferroelectric switching of the axial polarization can be observed in the temperature range of 105–115 °C in the Colhel phase, wherein the triazolyl hydrogen bonding along the column axis is weakened. The ferroelectric switching event is attributed to the rotation of the polar triazolyl units in response to the electric field. 相似文献
956.
The often used “Boussinesq equations” for the determination of the coupled flow and temperature field in natural convection are systematically deduced by an asymptotic approach. With the nondimensional temperature difference that drives the flow, ?, as a perturbation parameter the leading order equations are identified as the appropriate equations, named “asymptotic Boussinesq equations”. These equations appear as the distinguished limit $\varepsilon\rightarrow0The often used “Boussinesq equations” for the determination of the coupled flow and temperature field in natural convection
are systematically deduced by an asymptotic approach. With the nondimensional temperature difference that drives the flow,
ɛ, as a perturbation parameter the leading order equations are identified as the appropriate equations, named “asymptotic
Boussinesq equations”. These equations appear as the distinguished limit e?0\varepsilon\rightarrow0 and Ec? 0{Ec}\rightarrow 0 with Ec/e = const.{Ec}/\varepsilon =const. The equations are compared to “Boussinesq equations” of other studies and used to calculate Nusselt numbers in laminar and
turbulent flows in infinite vertical channels as an example and for the justification of the asymptotic approach. 相似文献
957.
An axisymmetric boundary element method (BEM) has been developed to simulate atomization processes in a pressure-swirl atomizer. Annular ligaments are pinched from the parent sheet and presumed to breakup via the linear stability model due to Ponstein. Corrections to Ponstein’s result are used to predict satellite droplet sizes formed during this process. The implementation provides a first-principles capability to simulate drop size distributions for low viscosity fluids. Results show reasonable agreement with measured droplet size distributions and the predicted SMD is 30–40% smaller than experiment. The model predicts a large number of very small droplets that cannot typically be resolved in an experimental observation of the spray. A quasi-3-D spray visualization is presented by tracking droplets in a Lagrangian fashion from their formation point within the ring-shaped ligaments. A complete simulation is provided for a case generating over 80,000 drops. 相似文献
958.
Nematic lyomesophases with discotic (N D) and cylindrical (N C) micelles in complex multicomponent lyotropic systems based on alkyltrimethylammonium bromide detergents have been identified by the 1H-2H-, and 13C-NMR methods and polarizationoptical microscopy. The difference in the structures of the N D and N C nematic phases is especially pronounced in the 13C-NMR spectra. Addition of chiral dopants to the lyomixture facilitates formation of the Ch D and Ch C cholesteric phases. According to the 13C-NMR spectra, the micellar mobility in the cholesteric lyomesophases decreases in comparison with the nematic ones. The alignment of lyocholesterics under the action of an external magnetic field is found. 相似文献
959.
Sung Young Park Yuhan Lee Ki Hyun Bae Cheol‐Hee Ahn Tae Gwan Park 《Macromolecular rapid communications》2007,28(10):1172-1176
The Pluronic F127 triblock copolymer was end‐capped by carboxyl groups using a degradable oligolactide as a spacer to confer pH‐ and thermo‐sensitive properties. With increasing chain length of the oligolactide, the temperature‐dependent sol‐gel transition curve was significantly shifted to higher concentration with concomitant narrowing of the gelation temperature range. Carboxylic acid end‐capped Pluronic also exhibited a peculiar pH‐dependent sol‐gel transition behavior. At 37 °C, sharp gel‐to‐sol and sol‐to‐gel transitions were observed around pH = 4.8 and 8.2, respectively. The pH‐dependent phase transition was caused by introduction of carboxylic acid groups at the ends of Pluronic F127.
960.
Byung Kwon Park Min Soo Lee Min Ki Woo Yong-Su Kim Sang-Wook Han Sung Moon 《中国科学:物理学 力学 天文学(英文版)》2017,60(6):060311
We develop a quantum key distribution (QKD) system with fast active optical path length compensation. A rapid and reliable active optical path length compensation scheme is proposed and applied to a plug-and-play QKD system. The system monitors changes in key rates and controls it is own operation automatically. The system achieves its optimal performance within three seconds of operation, which includes a sifted key rate of 5.5 kbps and a quantum bit error rate of less than 2% after an abrupt temperature variation along the 25 km quantum channel. The system also operates well over a 24 h period while completing more than 60 active optical path length compensations. 相似文献