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971.
短穗柽柳花内蜜腺的解剖学研究 总被引:2,自引:0,他引:2
短穗柽柳的花内蜜腺位于花冠基部与子房之间的花盘上,属于花盘蜜腺。蜜腺组织由分泌表皮、产蜜组织以及维管束三部分组成。分泌表皮具有较厚的角质层,但其上没有气孔器分布,产蜜组织在蜜腺发育过程中,其液泡和淀粉粒随蜜腺的发育有一定的消长规律。来自花托的维管束一直通入产蜜组织内。维管组织中只有韧皮部,原蜜汁可能由韧皮部提供。 相似文献
972.
We demonstrate collective atomic recoil motion with a dilute, ultracold, degenerate fermion gas in a single spin state. By utilizing an adiabatically decompressed magnetic trap with an aspect ratio different from that of the initial trap, a momentum-squeezed fermion cloud is achieved. With a single pump pulse of the proper polarization, we observe, for the first time, multiple wave-mixing processes that result in distinct collective atomic recoil motion modes in a degenerate fermion cloud. Contrary to the case with Bose condensates, no pump-laser detuning asymmetry is present. 相似文献
973.
We report on the development of a laser source in the mid-infrared spectral region based on difference-frequency generation (DFG) in a periodically poled LiNbO3 (PPLN) crystal. Continuously tunable coherent radiation from 2.75 to 4.78 μm was produced by optical parametric interaction between a diode-pumped monolithic continuous-wave (CW) Nd:YAG laser operating at 1.064 μm and a CW Ti:Sapphire laser tunable from 767 to 871 nm. Temperature-dependent quasi-phase-matched DFG wavelength acceptance bandwidth was studied and characterized. An empiric formula is given to estimate the phase-matched wavelength acceptance bandwidth as a function of the crystal temperature at Λ = 22.5 μm. A large frequency scan of 128 cm−1 (about 78 cm−1 above 1 μW) near 4.2 μm was achieved. The whole absorption spectrum of the P and R branches of the ν3 band of atmospheric carbon dioxide has been recorded with a single phase-matched frequency scan. 相似文献
974.
975.
报道了N-{4-{N-甲基-N-[2-羟基-3-(2,4-二氧代-1,2,3,4-四氢嘧啶-5-基)氨基]丙基}氨基-3-溴}苯甲酰基-L-谷氨酸二乙酯及其衍生物的简便合成方法. 分别以4-氨基苯甲酸乙酯和4-氨基苯甲酰基-L-谷氨酸二乙酯为起始物, 经甲基化、烯丙基化、溴羟基化、环氧化、开环、脱保护等反应首次合成了6个新型5-取代氨基嘧啶类化合物, 并通过1H NMR, 13C NMR 和MS对其化学结构进行了表征. 初步生物活性结果表明, 苯环侧链的L-谷氨酸酯部分是此类化合物抑制人重组二氢叶酸还原酶的必需结构. 相似文献
976.
977.
978.
Shuang Qiu Wannan Li Tao Deng Angzhi Bi Yang Yang Xi Jiang Dr. Jie P. Li 《Angewandte Chemie (International ed. in English)》2023,62(28):e202303014
Intercellular proximity labeling has emerged as a promising approach to enable the study of cell-cell interactions (CCIs), but the efficiency of current platforms is limited. Here, we use Ru(bpy)32+ to construct an efficient photocatalytic proximity labeling (PPL) system on the cell surface that allows the highly discriminative CCI detection with spatiotemporal resolution. Through the mechanism study and quantitative characterization on living cells, we demonstrate that the singlet-oxygen (1O2) mechanism is more efficient and specific than the single electron transfer (SET) mechanism in Ru-mediated PPL. Ru(bpy)32+ catalysts with different cell-anchoring moieties are prepared to facilitate the catalyst loading on primary cells. Finally, based on this system, we develop a “live” T cell receptor (TCR) multimer with TCR-T cells that could sensitively identify and discriminate cells presenting antigens of different affinity, providing a powerful tool to better understand the heterogeneity of antigen presenting cells. 相似文献
979.
980.
Qian Deng Mejdi Kammoun Alper Erturk Pradeep Sharma 《International Journal of Solids and Structures》2014
One of the most tantalizing applications of piezoelectricity is to harvest energy from ambient mechanical vibrations for powering micro and nano devices. However, piezoelectricity is restricted only to certain materials and is severely compromised at high temperatures. In this article, we examine in detail, the possibility of using the phenomenon of flexoelectricity for energy harvesting. The flexoelectric effect is universally present in all dielectrics and exhibits a strong scaling with size. Using a simple beam-based paradigmatical design, we theoretically and computationally examine flexoelectric energy harvesting under harmonic mechanical excitation. We find that the output power density and conversion efficiency increase significantly when the beam thickness reduces from micro to nanoscale and flexoelectricity-based energy harvesting can be a viable alternative to piezoelectrics. Specifically, the conversion efficiency in flexoelectric transduction at sub-micron thickness levels is observed to increase by two orders of magnitude as the thickness is reduced by an order of magnitude. The flexoelectric energy harvester works even for a single layer beam with a symmetric cross section which is not possible in piezoelectric energy harvesting. Our results also pave the way for exploration of high temperature energy harvesting since unlike piezoelectricity, flexoelectricity persists well beyond the Curie temperatures of the high electromechanical coupling ferroelectrics that are often used. 相似文献