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991.
Kendra V. Sharp David Hill Daniel Troolin Geoffrey Walters Wing Lai 《Experiments in fluids》2010,48(1):167-183
Volumetric three-component velocimetry measurements have been taken of the flow field near a Rushton turbine in a stirred
tank reactor. This particular flow field is highly unsteady and three-dimensional, and is characterized by a strong radial
jet, large tank-scale ring vortices, and small-scale blade tip vortices. The experimental technique uses a single camera head
with three apertures to obtain approximately 15,000 three-dimensional vectors in a cubic volume. These velocity data offer
the most comprehensive view to date of this flow field, especially since they are acquired at three Reynolds numbers (15,000,
107,000, and 137,000). Mean velocity fields and turbulent kinetic energy quantities are calculated. The volumetric nature
of the data enables tip vortex identification, vortex trajectory analysis, and calculation of vortex strength. Three identification
methods for the vortices are compared based on: the calculation of circumferential vorticity; the calculation of local pressure
minima via an eigenvalue approach; and the calculation of swirling strength again via an eigenvalue approach. The use of two-dimensional
data and three-dimensional data is compared for vortex identification; a ‘swirl strength’ criterion is less sensitive to completeness
of the velocity gradient tensor and overall provides clearer identification of the tip vortices. The principal components
of the strain rate tensor are also calculated for one Reynolds number case as these measures of stretching and compression
have recently been associated with tip vortex characterization. Vortex trajectories and strength compare favorably with those
in the literature. No clear dependence of trajectory on Reynolds number is deduced. The visualization of tip vortices up to
140° past blade passage in the highest Reynolds number case is notable and has not previously been shown. 相似文献
992.
Z. Pei L. S. Lai H. P. Hwang Y. T. Tseng C. S. Liang M. -J. Tsai 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):554
For the first time in the literature, we report the monolithic integration of SiGe near-infrared phototransistor and planar hetero-junction bipolar transistor (HBT). The phototransistor is made with SiGe/Si multi-quantum well structure (MQW_PHT). At room temperature, the MQW_PHT reveals an optical responsivity of 1904 mW/A at 0.85 μm and 1.25 mW/A at 1.3 μm under the reversed bias of VCE=1.5 V. For electrical DC and microwave performance, the SiGe HBT has a current gain of 160 and a cut-off frequency (fT) of 25 GHz, respectively. 相似文献
993.
二值化梯形透过率光栅是一种具有离轴衍射级次的二维光栅,其各衍射点光强信息和位置信息的确定对该新型光栅的实际应用具有重要意义。然而,目前尚无相关解析理论对其进行合理的描述。为了解决上述问题,通过二维傅里叶变换方法获得了该光栅各个衍射级次光强分布的解析表达式,并根据二维光栅的结构特征给出了在透射式和反射式情况下该光栅满足的光栅方程。这为该新型光栅的光线追迹计算打下了理论基础。最后,将解析表达式计算结果与采用X-Lab软件标量衍射模块计算的数值模拟结果进行比较,验证解析理论的正确性。 相似文献
994.
利用超高真空化学气相淀积系统, 基于低温缓冲层和插入应变超晶格的方法, 在Si(100)衬底上外延出厚度约为880 nm的纯Ge层. 采用X射线双晶衍射、高分辨透射电镜、原子力显微镜和光致发光谱分别表征了其结构及光学性质. 测试结果显示外延Ge的X射线双晶衍射曲线半高宽为273", 表面均方根粗糙度为0.24 nm, 位错密度约为1.5×106 cm2. 在室温下观测到外延Ge的直接带跃迁光致发光, 发光峰值位于1540 nm. 表明生长的Si基Ge材料具有良好的结晶质量, 可望在Si基光电子器件中得到应用. 相似文献
995.
996.
In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein type resonance across which an x-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to a unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized x rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magnetic field and geometry. 相似文献
997.
998.
Li‐Hong Zhang Tao Jiang Dr. Lian‐Bin Wu Dr. Jun‐Hua Wan Dr. Chih‐Hsien Chen Dr. Yong‐Bing Pei Dr. Hua Lu Yuan Deng Gao‐Feng Bian Prof. Hua‐Yu Qiu Prof. Guo‐Qiao Lai 《化学:亚洲杂志》2012,7(7):1583-1593
A series of linear 2,5‐tetraphenylsilole‐vinylene‐type polymers were successfully synthesized for the first time. The tetraphenylsilole moieties were linked at their 2,5‐positions through a vinylene bridge with p‐dialkoxybenzenes to obtain polymer PSVB and with 3,6‐carbazole to obtain polymer PSVC . For comparison, 2,5‐tetraphenylsilole‐ethyne‐type polymer PSEB was also synthesized, in which the vinylene bridge of PSVB was replaced with an ethyne bridge. Very interestingly, the bridging group (vinylene or ethyne) had a significant effect on the photophysical properties of the corresponding polymers. The fluorescence peak of PSEB at 504 nm in solution originated from the emission of its silole moieties, whereas PSVB and PSVC emitted yellow light and no blueish–green emission from the silole moieties was observed, thus demonstrating that the emissions of PSVB and PSVC were due to their polymer backbones. More importantly, the 2,5‐tetraphenylsilole‐ethyne polymer exhibited a pronounced aggregation‐enhanced emission (AEE) effect but the 2,5‐tetraphenylsilole‐vinylene polymer was AEE‐inactive. Moreover, both AEE‐active 2,5‐tetraphenylsilole‐ethyne polymer and AEE‐inactive 2,5‐tetraphenylsilole‐vinylene polymers were successfully applied as fluorescent chemosensors for the detection of explosive compounds. 相似文献
999.