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   80657篇
  免费   2135篇
  国内免费   350篇
化学   44943篇
晶体学   1221篇
力学   2921篇
综合类   2篇
数学   9354篇
物理学   24701篇
  2023年   954篇
  2022年   809篇
  2021年   1113篇
  2020年   1643篇
  2019年   1270篇
  2018年   2286篇
  2017年   2627篇
  2016年   2369篇
  2015年   1556篇
  2014年   2838篇
  2013年   6792篇
  2012年   4459篇
  2011年   5497篇
  2010年   3918篇
  2009年   3927篇
  2008年   3957篇
  2007年   4060篇
  2006年   3446篇
  2005年   2824篇
  2004年   2180篇
  2003年   2054篇
  2002年   1677篇
  2001年   1596篇
  2000年   1171篇
  1999年   1133篇
  1998年   505篇
  1997年   527篇
  1996年   493篇
  1995年   513篇
  1994年   555篇
  1993年   503篇
  1992年   483篇
  1991年   509篇
  1990年   498篇
  1989年   575篇
  1988年   529篇
  1987年   570篇
  1986年   515篇
  1985年   850篇
  1984年   946篇
  1983年   495篇
  1982年   766篇
  1981年   717篇
  1980年   759篇
  1979年   652篇
  1978年   608篇
  1977年   604篇
  1976年   567篇
  1975年   386篇
  1973年   464篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.

The machining process is primarily used to remove material using cutting tools. Any variation in tool state affects the quality of a finished job and causes disturbances. So, a tool monitoring scheme (TMS) for categorization and supervision of failures has become the utmost priority. To respond, traditional TMS followed by the machine learning (ML) analysis is advocated in this paper. Classification in ML is supervised based learning method wherein the ML algorithm learn from the training data input fed to it and then employ this model to categorize the new datasets for precise prediction of a class and observation. In the current study, investigation on the single point cutting tool is carried out while turning a stainless steel (SS) workpeice on the manual lathe trainer. The vibrations developed during this activity are examined for failure-free and various failure states of a tool. The statistical modeling is then incorporated to trace vital signs from vibration signals. The multiple-binary-rule-based model for categorization is designed using the decision tree. Lastly, various tree-based algorithms are used for the categorization of tool conditions. The Random Forest offered the highest classification accuracy, i.e., 92.6%.

  相似文献   
4.
5.
Plasmodium parasites causing malaria have developed resistance to most of the antimalarials in use, including the artemisinin-based combinations, which are the last line of defense against malaria. This necessitates the discovery of new targets and the development of novel antimalarials. Plasmodium falciparum alanyl aminopeptidase(PfA-M1) and leucyl aminopeptidase(PfA-M17) belong to the M1 and M17 family of metalloproteases respectively and play critical roles in the asexual erythrocytic stage o...  相似文献   
6.
We report, for the first time, a detailed crystallographic study of the supramolecular arrangement for a set of zinc(II) Schiff base complexes containing the ligand 2,6-bis((E)-((2-(dimethylamino)ethyl)imino)methyl)-4-R-phenol], where R=methyl/tert-butyl/chloro. The supramolecular study acts as a pre-screening tool for selecting the compartmental ligand R of the Schiff base for effective binding with a targeted protein, bovine serum albumin (BSA). The most stable hexagonal arrangement of the complex [Zn − Me] (R=Me) stabilises the ligand with the highest FMO energy gap (ΔE=4.22 eV) and lowest number of conformations during binding with BSA. In contrast, formation of unstable 3D columnar vertebra for [Zn − Cl] (R=Cl) tend to activate the system with lowest FMO gap (3.75 eV) with highest spontaneity factor in molecular docking. Molecular docking analyses reported in terms of 2D LigPlot+ identified site A, a cleft of domains IB, IIIA and IIIB, as the most probable protein binding site of BSA. Arg144, Glu424, Ser428, Ile455 and Lys114 form the most probable interactions irrespective of the type of compartmental ligands R of the Schiff base whereas Arg185, Glu519, His145, Ile522 act as the differentiating residues with ΔG=−7.3 kcal mol−1.  相似文献   
7.
As the application of electrocatalyst continues to expand, envisaging the hidden mechanisms occurring at various length scale affecting the catalytic efficiency became important. To enhance the stability of electrocatalyst and reduce the cost, it is of paramount importance to reveal the active site's dynamics (using in situ techniques for getting the real-time information) which directly affect the reactions such as oxygen evolution reaction, hydrogen evolution reaction, and so on. Since such reactions are crucial for many engineering and scientific applications, in situ characterization techniques are required, which could capture such reactions happening at a different length and time scale. This article analyzes the recent progress made in the field of electrocatalyst's characterization using in situ neutron techniques. The article also paves the future path and has delineated the future challenges involved in multiscale correlative techniques (e.g., neutron techniques in the combination of synchrotron or microscopic techniques) used for getting the multiscale (atomic to micrometer range) mechanistic information about the electrocatalyst's working and degradation.  相似文献   
8.
9.
Effect of induced magnetic field is critical as a result of much controlled and focused on liquid flow is wanted in numerous modern and clinical procedures for example electromagnetic casting, drug delivery and cooling of nuclear reactors. Hence this investigation explains the behaviour of hybrid carbon nanotubes (CNTs) flow through slipped surface with induced magnetic field. Accumulation of SWCNTs (single wall) and MWCNTs (multi wall) nanomaterial with water base liquid is considered. Thermal performance is analyzed with regular heat source/sink effect. Chemical reaction and activation energy impacts are incorporated in mass equation. Solution of the similarity equations are obtained by adopting RKF45 method. Influence of flow variables are illustrated through graphs and computational values of drag force, Nusselt number and Sherwood number are presented in tables. It is noted that activation energy enhance the concentration field whereas opposite behaviour for reaction rate. Also induce magnetic field boosted with the larger values of magnetic Prandtl number. Furthermore it is observed that hybrid CNTs nanomaterial having higher rate of heating/cooling compare to singular CNTs nanomaterial.  相似文献   
10.
In this paper we investigated the stability of fractional order fuzzy cellular neural networks with leakage delay and time varying delays. Based on Lyapunov theory and applying bounded techniques of fractional calculation, sufficient criterion are established to guarantee the stability. Hybrid feedback control is applied to derive the proposed results. Finally, numerical examples with simulation results are given to illustrate the effectiveness of the proposed method.  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