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   424464篇
  免费   4024篇
  国内免费   1252篇
化学   210411篇
晶体学   4987篇
力学   20176篇
综合类   7篇
数学   60215篇
物理学   133944篇
  2019年   2555篇
  2018年   11287篇
  2017年   12040篇
  2016年   8704篇
  2015年   4254篇
  2014年   5102篇
  2013年   15154篇
  2012年   14821篇
  2011年   25213篇
  2010年   15564篇
  2009年   15225篇
  2008年   21909篇
  2007年   25222篇
  2006年   11583篇
  2005年   17485篇
  2004年   12893篇
  2003年   11670篇
  2002年   9072篇
  2001年   9546篇
  2000年   7102篇
  1999年   5336篇
  1998年   4407篇
  1997年   4608篇
  1996年   4380篇
  1995年   4463篇
  1994年   4150篇
  1993年   4114篇
  1992年   4575篇
  1991年   4579篇
  1990年   4275篇
  1989年   4275篇
  1988年   4332篇
  1987年   4261篇
  1986年   4031篇
  1985年   5591篇
  1984年   5856篇
  1983年   4841篇
  1982年   5400篇
  1981年   5157篇
  1980年   5098篇
  1979年   5141篇
  1978年   5502篇
  1977年   5185篇
  1976年   5373篇
  1975年   4964篇
  1974年   4919篇
  1973年   5442篇
  1972年   3318篇
  1971年   2544篇
  1968年   2516篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Li  Zh.  Zhang  Y.  Wang  R.  Jiang  D. 《Journal of Applied Spectroscopy》2022,89(2):371-380
Journal of Applied Spectroscopy - The concentration of heavy metals in drinking water is an important standard for water quality evaluation and water pipeline corrosion detection. This research...  相似文献   
2.
Mathematical Programming - Scenario generation is the construction of a discrete random vector to represent parameters of uncertain values in a stochastic program. Most approaches to scenario...  相似文献   
3.
Fuzzy Optimization and Decision Making - Cost-allocation problems in a fixed network are concerned with distributing the costs for use by a group of clients who cooperate in order to reduce such...  相似文献   
4.

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   
5.
Syrovatka  R. A.  Lipaev  A. M.  Naumkin  V. N.  Klumov  B. A. 《JETP Letters》2022,116(12):869-874
JETP Letters - A quasi-two-dimensional plasma crystal in (3 + 1) dimensions has been experimentally observed for the first time; i.e., three spatial coordinates of each microparticles of the...  相似文献   
6.
Avchyan  B. R.  Ghazaryan  A. G.  Sargsyan  K. A.  Sedrakian  Kh. V. 《JETP Letters》2022,116(7):428-435
JETP Letters - We present results of numerical investigations of high-order wave mixing/harmonic generation (HWM/HHG) with many-body interaction processes derived by a strong two-frequency circular...  相似文献   
7.
Theoretical and Mathematical Physics - We discuss the gravitational collapse of a spherically symmetric perfect fluid distribution of uniformly contracting stars. In a uniformly contracting star,...  相似文献   
8.
Annals of Operations Research - Selecting a vegetation layer design goes along with determining its future irrigation need. Therefore, it is essential to take a design decision that is minimising...  相似文献   
9.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems.  相似文献   
10.
Journal of Applied Spectroscopy - The aromaticity in the lowest triplet T1-state of NH-tautomers of corrole free bases with different peripheral substitution architecture was investigated using...  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