首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18557篇
  免费   2804篇
  国内免费   2192篇
化学   13130篇
晶体学   236篇
力学   1120篇
综合类   120篇
数学   2412篇
物理学   6535篇
  2024年   80篇
  2023年   426篇
  2022年   711篇
  2021年   698篇
  2020年   724篇
  2019年   733篇
  2018年   635篇
  2017年   628篇
  2016年   926篇
  2015年   918篇
  2014年   1115篇
  2013年   1375篇
  2012年   1620篇
  2011年   1688篇
  2010年   1140篇
  2009年   1031篇
  2008年   1214篇
  2007年   995篇
  2006年   944篇
  2005年   778篇
  2004年   688篇
  2003年   513篇
  2002年   531篇
  2001年   390篇
  2000年   326篇
  1999年   442篇
  1998年   305篇
  1997年   224篇
  1996年   250篇
  1995年   245篇
  1994年   191篇
  1993年   165篇
  1992年   144篇
  1991年   144篇
  1990年   145篇
  1989年   102篇
  1988年   71篇
  1987年   57篇
  1986年   49篇
  1985年   45篇
  1984年   34篇
  1983年   28篇
  1982年   20篇
  1981年   16篇
  1980年   6篇
  1979年   6篇
  1978年   7篇
  1976年   5篇
  1975年   5篇
  1973年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Mediterranean Journal of Mathematics - We study the multifractal analysis of dimension spectrum for almost additive potentials in a class of one-dimensional non-uniformly hyperbolic dynamic systems.  相似文献   
942.
The usage of full-color imaging in digital pathology produces significant results. Compared with a grayscale image or a pseudocolor image containing contrast information, a full-color image can identify and detect the target object better with color texture information. Fourier ptychographic microscopy(FPM) is a high-throughput computational imaging technique that breaks the tradeoff between high resolution(HR) and a large field of view. It also eliminates the artifacts of scanning and stitching in digital pathology and improves its imaging efficiency. However, the conventional full-color digital pathology based on FPM is still time-consuming because of the repeated experiments with tri-wavelengths. A color transfer FPM approach termed "CFPM" was reported. The color texture information of a low-resolution full-color pathologic image is directly transferred to the HR grayscale FPM image captured by only a single wavelength. Both of the color space of FPM based on the standard CIE-XYZ color model and the display based on the standard RGB color space were established. Different FPM colorization schemes were analyzed and compared with 30 biological samples. Three types of evaluation approaches were provided, including the root-mean-square error(RMSE), the difference maps, and the image histogram cosine similarity. The average RMSE values of the conventional method and CFPM compared with the ground truth were 5.3% and 5.7%, respectively. Therefore, the reconstruction time is significantly reduced by 2/3 with the sacrifice of precision of only 0.4%. The CFPM method is also compatible with advanced fast FPM approaches to further reduce computation time.  相似文献   
943.
由环的P-性质所确定的根   总被引:1,自引:0,他引:1  
王尧  杨军 《数学研究》1999,32(3):305-309
定义了环的P根P、弱拟P根Pw 和拟P根PQ,证明它们均为Am itsurKurosh 根且P= Pw 为特殊根,给出了P半单环的结构定理和P根的模刻划  相似文献   
944.
In this paper we first establish global pointwise time-space estimates of the fundamental solution for Schr?dinger equations, where the symbol of the spatial operator is a real non-degenerate elliptic polynomial. Then we use such estimates to establish related L p ?CL q estimates on the Schr?dinger solution. These estimates extend known results from the literature and are sharp. This result was lately already generalized to a degenerate case (cf. [4]).  相似文献   
945.
Li  Han  Jintao  Feng  Wang  Zhen  Jia  Yan  Li  Peng  Yao  Cuixia  Qu  Zongjin 《Journal of fluorescence》2022,32(5):1825-1832

The development of fluorescent probes for nitroreductase (NTR) has received intense attention because of its biological significance and wide application. In this work, a novel fluorescent probe for the detection of NTR in aqueous solution was designed and synthesized on a 1,8-naphthalimide scaffold. In the presence of NTR and nicotinamide adenine dinucleotide (NADH) under physiological conditions, the probe was converted into a 4-hydroxy-1,8-naphthalimide derivative and exhibited a sharp fluorescence enhancement at 550 nm, with a high selectivity for NTR over various analytes. The detection limit for NTR was determined to be 9.8 ng/ml by this probe. Due to its low signal background, this probe showed?>?70-fold fluorescence enhancement. Theoretical calculations revealed that the reason for the fluorescence quenching of this probe is the photoinduced electron transfer (PET) from both the nitrobenzene and morpholine groups to the naphthalimide fluorophore.

  相似文献   
946.
1 IntroductionIn this paPer, we collsider the initial and boundaxy value probIem of linear and sentilillearScl1r5dinger equation as fOllows:l ie(x):5:i".,'<">"'>.'<",,'>,"=' 1:!\:?0t:)t>, (l1)wllere E > 0, fl C RN is a bounded open dolllain and T is an ar…  相似文献   
947.
Two-level injection-locked opto-electronic oscillator is proposed for low phase noise. Dielectric resonator oscillator (DRO) is used as the first injection source, injection locking a long-fiber loop based opto-electronic oscillator, then its output is injection locking another long-fiber opto-electronic oscillator for getting a lower-phase noise output carrier. After the first injection, the single side band (SSB) phase noise at 10 kHz offset frequency decreases from −123 dBc/Hz to −135 dBc/Hz, then through the second injection the SSB phase noise drops down to −146 dBc/Hz.  相似文献   
948.
949.
We investigate the pairing symmetry of the Kondo-Heisenberg model on triangular lattice, which is believed to capture the core competition of Kondo screening and local magnetic exchange interaction in heavy electron compounds. On the dominant background of the heavy fermion state, the introduction of the Heisenberg antiferromagnetic interaction (J H ) leads to superconducting pairing instability. Depending on the strength of the interactions, it is found that the pairing symmetry favours an extended s-wave for small J H and high conduction electron density but a chiral \(d_{x^2 - y^2 } + id_{xy}\)-wave for large J H and low conduction electron density, which provides a phase diagram of pairing symmetry from the calculations of the ground-state energy. The transition between these two pairing symmetries is found to be first-order. Furthermore, we also analyze the phase diagram from the pairing strengths and find that the phase diagram obtained is qualitatively consistent with that based on the ground-state energy. In addition, we propose an effective single-band BCS Hamiltonian, which is able to describe the low-energy thermodynamic behaviors of the heavy fermion superconducting states. These results further deepen the understanding of the antiferromagnetic interaction which results in a geometric frustration for the model studied. Our work may provide a possible scenario to understand the pairing symmetry of the heavy fermion superconductivity, which is one of active issues in very recent years.  相似文献   
950.
为了研究硬质合金表面激光微织构对其表面润湿性的影响,利用光纤激光不同功率(3,5,7,9,10 W)及不同加工次数(1,2,3,4,5)加工微凹坑,采用VHX1000c超景深三维显微镜、光学显微镜分析微凹坑形貌,利用CAM 200光学接触角仪测量表面微织构(微凹坑直径、深度和织构密度)与润湿性之间的关系。结果表明:随着激光功率的增大,微凹坑深度增加,直径变化不明显;硬质合金表面的亲水性能随着微凹坑深度的增加而减小;随着微凹坑直径的增大,亲水性增强;随着微织构密度的增加,亲水性出现极值。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号