全文获取类型
收费全文 | 15692篇 |
免费 | 3631篇 |
国内免费 | 1558篇 |
专业分类
化学 | 7161篇 |
晶体学 | 177篇 |
力学 | 989篇 |
综合类 | 108篇 |
数学 | 410篇 |
物理学 | 5524篇 |
无线电 | 6512篇 |
出版年
2024年 | 80篇 |
2023年 | 233篇 |
2022年 | 424篇 |
2021年 | 567篇 |
2020年 | 702篇 |
2019年 | 656篇 |
2018年 | 641篇 |
2017年 | 751篇 |
2016年 | 861篇 |
2015年 | 878篇 |
2014年 | 1057篇 |
2013年 | 1441篇 |
2012年 | 1216篇 |
2011年 | 1128篇 |
2010年 | 921篇 |
2009年 | 847篇 |
2008年 | 865篇 |
2007年 | 927篇 |
2006年 | 881篇 |
2005年 | 733篇 |
2004年 | 663篇 |
2003年 | 586篇 |
2002年 | 554篇 |
2001年 | 498篇 |
2000年 | 461篇 |
1999年 | 374篇 |
1998年 | 295篇 |
1997年 | 288篇 |
1996年 | 269篇 |
1995年 | 214篇 |
1994年 | 188篇 |
1993年 | 131篇 |
1992年 | 124篇 |
1991年 | 78篇 |
1990年 | 55篇 |
1989年 | 57篇 |
1988年 | 57篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 5篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
In this letter, the constant driving power reduction ratio has been achieved for column drivers regardless of the input image by incorporating a new static power reduction scheme into the previous dynamic power reduction method. The measured power reduction ratio is around 50% for a 120 Hz liquid crystal display panel in such cases of still input video and fallback. 相似文献
952.
《Journal of separation science》2017,40(19):3763-3770
We have developed an efficient procedure and detection method using reversed‐phase high‐performance liquid chromatography for the simultaneous measurement of uracil and dihydrouracil in human plasma. The procedure, including chromatographic conditions and sample preparation, was optimized and validated. Optimization of the sample preparation included deproteinization, extraction, and cleanup. A new sample preparation method which resulted in an improved extraction yield of analytes and significantly reduced interference at low‐wavelength UV detection was developed. The developed method was validated for specificity, linearity, limits of detection and quantitation, precision, and accuracy. All calibration curves showed excellent linear regression (R 2 > 0.9990) within the testing range. The limit of detection for uracil and dihydrouracil was 2.5 and 5.0 ng/mL, respectively. The extraction yields were >94% for uracil and 91% for dihydrouracil. Intra‐ and interassay precision and accuracy for uracil and dihydrouracil were lower than 8% at all tested concentrations. The proposed method was successfully applied to measure plasma concentrations of uracil and dihydrouracil in colorectal cancer patients scheduled to receive fluoropyrimidine‐based chemotherapy. 相似文献
953.
A high‐order convection‐bounded scheme is constructed by combining the total variational diminishing constraint and convection boundedness criterion condition in the normalized variable formulation. It employs the Hermite polynomial interpolation to design its characteristic line in the normalized variable diagram. Numerical results of the convection‐dominated problems with smooth or discontinuous initial distributions demonstrate the present scheme possesses high resolution and good robustness. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
954.
955.
In this paper, we present a spatial perturbation method to control the optical patterns in semiconductor microresonators in the far‐field configuration. We propose a fast all‐optical switch which operates at a low light level. The switching beam controls the behavior of output beams with strong intensities. The method has been applied successfully to different optical patterns such as rolls, squares, and hexagons. 相似文献
956.
《Biomedical chromatography : BMC》2017,31(9)
A new, simple, accurate and precise high‐performance thin‐layer chromatographic method has been developed and validated for simultaneous determination of an anthelmintic drug, albendazole, and its active metabolite albendazole, sulfoxide. Planar chromatographic separation was performed on aluminum‐backed layer of silica gel 60G F254 using a mixture of toluene–acetonitrile–glacial acetic acid (7.0:2.9:0.1, v /v/v) as the mobile phase. For quantitation, the separated spots were scanned densitometrically at 225 nm. The retention factors (R f) obtained under the established conditions were 0.76 ± 0.01 and 0.50 ± 0.01 and the regression plots were linear (r 2 ≥ 0.9997) in the concentration ranges 50–350 and 100–700 ng/band for albendazole and albendazole sulfoxide, respectively. The method was validated for linearity, specificity, accuracy (recovery) and precision, repeatability, stability and robustness. The limit of detection and limit of quantitation found were 9.84 and 29.81 ng/band for albendazole and 21.60 and 65.45 ng/band for albendazole sulfoxide, respectively. For plasma samples, solid‐phase extraction of analytes yielded mean extraction recoveries of 87.59 and 87.13% for albendazole and albendazole sulfoxide, respectively. The method was successfully applied for the analysis of albendazole in pharmaceutical formulations with accuracy ≥99.32%. 相似文献
957.
《应用有机金属化学》2017,31(12)
Palladium nanocrystals with a variety of shapes have received particular interest in recent years due to their unique properties in catalysis. Herein, Pd concave nanocubes with high‐index facets (Pd‐CNs) was synthesized by a simple water‐based route without seeds using L‐ascorbic acid (AA) as the reduction agent in the presence of CTAB. X‐ray diffraction and transmission electron microscopy were employed to demonstrate the formation of concave structures with high‐index facets of the Pd‐CNs with an average size of 17.5 nm. The as‐prepared Pd‐CNs presented significantly higher catalytic activity than commercial Pd/C (an average particle size of 4.7 nm) in the electro‐oxidation of methanol, but exhibited weaker property in Suzuki coupling reaction, which provided an evidence for the effect of shape and size on different reactions. 相似文献
958.
959.
Improvement of the weighted essentially nonoscillatory scheme based on the interaction of smoothness indicators 下载免费PDF全文
The weighted essentially nonoscillatory scheme is improved by introducing new smoothness indicators that evaluate the interactions among the classical smoothness indicators suggested by Jiang and Shu. The effect of the key parameters in the new smoothness indicators on the scheme is systematically investigated. The improved scheme has smaller dissipation with larger weight assignment to the discontinuous stencils and higher numerical accuracy with weights closer to the ideal weights. To verify the theory, benchmark problems governed by the linear transport equation, the 1‐dimensional nonlinear Burgers equation, and the Euler equations are conducted and analyzed, respectively. Better computational performances both on numerical resolution and accuracy are shown in the comparisons with other classical weighted essentially nonoscillatory schemes. 相似文献
960.
Novel correction method for X-ray beam energy fluctuation of high energy DR system with a linear detector 总被引:1,自引:0,他引:1
A high energy digital radiography (DR) testing system has generated diverse scientific and technological interest in the field of industrial non-destructive testing. However, due to the limitations of manufacturing technology for accelerators, an energy fluctuation of the X-ray beam exists and leads to bright and dark streak artifacts in the DR image. Here we report the utilization of a new software-based method to correct the fluctuation artifacts. The correction method is performed using a high pass filtering operation to extract the high frequency information that reflects the X-ray beam energy fluctuation, and then subtracting it from the original image. Our experimental results show that this method is able to rule out the artifacts effectively and is readily implemented on a practical scanning system. 相似文献