全文获取类型
收费全文 | 20549篇 |
免费 | 3879篇 |
国内免费 | 3008篇 |
专业分类
化学 | 9581篇 |
晶体学 | 177篇 |
力学 | 1506篇 |
综合类 | 145篇 |
数学 | 1370篇 |
物理学 | 9540篇 |
无线电 | 5117篇 |
出版年
2024年 | 124篇 |
2023年 | 423篇 |
2022年 | 584篇 |
2021年 | 792篇 |
2020年 | 989篇 |
2019年 | 782篇 |
2018年 | 730篇 |
2017年 | 878篇 |
2016年 | 1009篇 |
2015年 | 967篇 |
2014年 | 1324篇 |
2013年 | 1686篇 |
2012年 | 1312篇 |
2011年 | 1407篇 |
2010年 | 1184篇 |
2009年 | 1336篇 |
2008年 | 1358篇 |
2007年 | 1346篇 |
2006年 | 1300篇 |
2005年 | 1038篇 |
2004年 | 907篇 |
2003年 | 849篇 |
2002年 | 692篇 |
2001年 | 616篇 |
2000年 | 573篇 |
1999年 | 500篇 |
1998年 | 426篇 |
1997年 | 350篇 |
1996年 | 293篇 |
1995年 | 251篇 |
1994年 | 218篇 |
1993年 | 166篇 |
1992年 | 137篇 |
1991年 | 143篇 |
1990年 | 95篇 |
1989年 | 92篇 |
1988年 | 82篇 |
1987年 | 64篇 |
1986年 | 61篇 |
1985年 | 58篇 |
1984年 | 41篇 |
1983年 | 23篇 |
1982年 | 37篇 |
1981年 | 35篇 |
1980年 | 32篇 |
1979年 | 31篇 |
1978年 | 16篇 |
1977年 | 23篇 |
1976年 | 12篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
162.
扫描透射电子显微术是目前应用最广泛的电子显微表征手段之一,具有分辨率高、对化学成分敏感和图像直观易解释等特点。其中高分辨扫描电子显微镜可以直接获得原子分辨率的Z 衬度像,结合X射线能谱(EDS)和电子能量损失谱(EELS),可在亚埃尺度上对材料的原子和电子结构进行分析。文章简述了扫描透射电子显微镜的基本原理及其应用现状,重点论述了高角环形暗场(HAADF)和环形明场(ABF)像的成像原理、特征和应用。此外,文中还对原子尺度分辨率的X射线能谱及电子能量损失谱元素分析方法进行了简述。 相似文献
163.
We propose a six-parameter exponential-type potential (SPEP),which has been shown to be a shapeinvariant potential with a translation of parameters.For this reducible potential,the exact energy levels are obtained by using the supersymmetric shape invariance technique.Choosing appropriate parameters,four classes of exponential-type potentials and their exact energy spectra are reduced from the SPEP and a general energy level formula,respectively.Each class shows the identity except for the different definitions of parameters. 相似文献
164.
L.P. Kaptari B. Kämpfer S.S. Semikh S.M. Dorkin 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):119-132
The exclusive charge exchange reaction pD↦n(pp) at intermediate and high energies is studied within the Bethe-Salpeter formalism. The final-state interaction in the detected
pp pair at nearly zero excitation energy is described by the 1
S
0 component of the Bethe-Salpeter amplitude. Results of numerical calculations of polarization observables and differential
cross-section persuade that, as in the non-relativistic case, this reaction i) can be utilized as a “relativistic deuteron
polarimeter” and ii) delivers further information about the elementary nucleon-nucleon charge exchange amplitude.
Received: 26 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003 相似文献
165.
Jung-Hui Hsu 《Applied Surface Science》2010,256(6):1769-121
This study presents the surface adhesion between hexagonal boron nitride nanotube (BNNT) and silicon based on lateral manipulation in an atomic force microscope (AFM). The BNNT was mechanically manipulated by the lateral force of an AFM pyramidal silicon probe using the scan mechanism in the imaging mode. With a controlled normal force of the AFM probe and the lateral motion, the lateral force applied to the BNNT could overcome the surface adhesion between BNNT and silicon surface. The individual BNNT is forced to slide and rotate on the silicon surface. Based on the recorded force curve, the calculated shear stress due to surface adhesion is 0.5 GPa. And the specific sliding energy loss is 0.2 J/m2. Comparing BNNTs and carbon nanotube (CNT), the shear stress and specific sliding energy loss of BNNT are an order of magnitude larger than that of CNT. Therefore, the results show that the surface adhesion between BNNT and silicon surface is higher than that of CNT. 相似文献
166.
Molecular dynamics simulations of nanoimprint lithography (NIL) were performed to investigate the effects of three critical process parameters in NIL: stamp shape, adhesive energy between the stamp and polymer film, and imprint temperature. The proposed simulation model of the NIL process consists of an amorphous SiO2 stamp with a line pattern, an amorphous poly(methylmethacrylate) film, and a Si substrate under the periodic boundary condition in the horizontal direction to simulate a real NIL process imprinting periodical line patterns. The behavior of polymer deformation and the effects of adhesion on pattern transfer were investigated by observing the deformation process, calculating the imprint and separation forces, and analyzing the density and stress distribution inside the polymer film. In addition, their dependency on the process parameters is also discussed with reference to the changes in pattern shape, adhesive energy between the stamp and polymer atoms, and imprint temperature of the polymer film. During the imprint process, the rectangular pattern shows inferior cavity filling and higher stress concentration compared to trapezoidal and triangular patterns because it requires much larger flow and deformation of the polymer film. Low imprint temperature also produces high stress concentration and large imprint force due to the lower fluidity of polymer film. In the separation process, the rectangular pattern generates the largest separation force and causes the most serious defects of the transferred pattern and even the polymer film, while the triangular pattern shows the most satisfactory pattern transfer. In addition, the adhesive energy between the stamp and the polymer film also strongly influences the adhesion between the stamp and the polymer film. Low adhesive energy reduces the separation force of the stamp and transferred pattern defects, and therefore enhances the quality of pattern transfer. 相似文献
167.
Nakao’s stochastic integrals for continuous additive functionals of zero energy are extended from the symmetric Dirichlet forms setting to the non-symmetric Dirichlet forms setting.It? ’s formula in terms of the extended stochastic integrals is obtained. 相似文献
168.
本文提出了分析速调管束波互作用能量转换的二维模型和假设,详细描述了在能量转换过程中的电子运动方程,并指出了能量转换的二维数值分析可能会对速调管基础理论的发展有所贡献的方面。 相似文献
169.
Stephen Fox 《Entropy (Basel, Switzerland)》2021,23(2)
Active inference is a physics of life process theory of perception, action and learning that is applicable to natural and artificial agents. In this paper, active inference theory is related to different types of practice in social organization. Here, the term social organization is used to clarify that this paper does not encompass organization in biological systems. Rather, the paper addresses active inference in social organization that utilizes industrial engineering, quality management, and artificial intelligence alongside human intelligence. Social organization referred to in this paper can be in private companies, public institutions, other for-profit or not-for-profit organizations, and any combination of them. The relevance of active inference theory is explained in terms of variational free energy, prediction errors, generative models, and Markov blankets. Active inference theory is most relevant to the social organization of work that is highly repetitive. By contrast, there are more challenges involved in applying active inference theory for social organization of less repetitive endeavors such as one-of-a-kind projects. These challenges need to be addressed in order for active inference to provide a unifying framework for different types of social organization employing human and artificial intelligence. 相似文献
170.
Experimental results concerning the interaction between a variety of nanocrystalline metals (gold, silver, nickel and chromium) and both crystalline polymer [poly-DCH (1,6-di (N-carbazolyl)-2,4-hexadiene)] and amorphous carbon substrates, are presented and analyzed. Attention is focused on aspects of the interaction that concern interfacial bonding, its correlation with the cohesive energies of the various metals and the energy of the interfaces. Experimental contributions include qualitative estimates of the magnitude of interfacial energies for the crystalline polymer/metal and amorphous carbon/metal interfaces and a direct measurement of the interfacial energies for gold and silver nanocrystals deposited on the amorphous carbon substrate. The sequence of interfacial energy values for the polymer/metal and amorphous carbon/metal systems is also determined. The interfacial energies for both the poly-DCH and amorphous carbon substrates decreases in the order silver, gold, nickel, and chromium, as expected from cohesive energy, melting point and surface energy data for these elements. The crystalline polymer/metal interfaces were examined for the presence of orientation relationships using selected area diffraction and optical diffractometry of high-resolution TEM images. No orientation relationships were found for any of the polymer/metal combinations spanning a large range of metal reactivities. Lack of atomic matching or some as yet unknown surface condition on the polymer may be responsible for this effect. 相似文献