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   290548篇
  免费   2923篇
  国内免费   1588篇
化学   123009篇
晶体学   3397篇
力学   17369篇
综合类   45篇
数学   63787篇
物理学   87452篇
  2018年   18283篇
  2017年   18921篇
  2016年   10509篇
  2015年   2958篇
  2014年   2080篇
  2013年   5750篇
  2012年   11259篇
  2011年   25699篇
  2010年   14948篇
  2009年   15129篇
  2008年   20303篇
  2007年   25532篇
  2006年   4749篇
  2005年   12582篇
  2004年   8549篇
  2003年   8409篇
  2002年   5237篇
  2001年   3877篇
  2000年   3111篇
  1999年   2185篇
  1998年   1841篇
  1997年   1893篇
  1996年   1978篇
  1995年   1936篇
  1994年   1672篇
  1993年   1666篇
  1992年   1845篇
  1991年   1820篇
  1990年   1754篇
  1989年   1769篇
  1988年   1781篇
  1987年   1761篇
  1986年   1674篇
  1985年   2253篇
  1984年   2377篇
  1983年   1979篇
  1982年   2302篇
  1981年   2114篇
  1980年   2156篇
  1979年   2189篇
  1978年   2302篇
  1977年   2104篇
  1976年   2160篇
  1975年   2097篇
  1974年   1928篇
  1973年   2198篇
  1972年   1323篇
  1971年   1000篇
  1968年   1160篇
  1967年   1140篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
1.
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   
2.
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   
3.
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   
4.
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   
5.
Ultrasound has been recognized as an exciting tool to enhance the therapeutic efficacy in tumor chemotherapy owing to the triggered drug release, facilitated intracellular drug delivery, and improved spatial precision. Aiming for a precise localized drug delivery, novel dendritic polyurethane-based prodrug (DOX-DPU-PEG) was fabricated with a drug content of 18.9% here by conjugating DOX onto the end groups of the functionalized dendritic polyurethane via acid-labile imine bonds. It could easily form unimolecular micelles around 38 nm. Compared with the non-covalently drug-loaded unimolecular micelles (DOX@Ph-DPU-PEG), they showed excellent pH/ultrasound dual-triggered drug release performance, with drug leakage of only 4% at pH 7.4, but cumulative release of 14% and 88% at pH 5.0 without and with ultrasound, respectively. The ultrasound responsiveness was attributed to the unique strawberry-shaped topological structure of the DOX-DPU-PEG, in which DOX was embedded in the skin layer of the hydrophobic DPU cores. With ultrasound, the DOX-DPU-PEG unimolecular micelles possessed enhanced tumor growth inhibition than free DOX but showed no obvious cytotoxicity on the tumor cells without ultrasound. Such feature makes them promising potential for precise localized drug delivery.  相似文献   
6.
Journal of Applied Mechanics and Technical Physics - A self-equilibrated stress field for an incompressible sphere is constructed based on a non-Euclidean continuum model. The...  相似文献   
7.
Li  Y.  Shi  W. H.  Dong  L. M.  Xu  S. X.  Huang  H. J.  Yin  J. R. 《Journal of Applied Spectroscopy》2022,89(3):534-541
Journal of Applied Spectroscopy - Sr3B2O6:Dy3+, Eu3+ single-matrix white-light-emitting materials are prepared using the high-temperature solid-state method. The microstructure, emission spectrum,...  相似文献   
8.
Chen  R. J.  Chen  W.  Kong  F. L. 《Analysis Mathematica》2022,48(1):19-28

Restricted testing conditions were considered recently. For the maximal operator, Hytönen, Li and Sawyer [8] first obtained parental testing condition. Later, they [9] showed that it suffices to restrict testing to doubling cubes. Chen and Lacey [3] gave a similar restricted testing condition. In our paper, we discuss a version of the latter in the multilinear setting.

  相似文献   
9.
Guo  W.  Wang  Z.  Safonova  I. N.  Skiba  A. N. 《Mathematical Notes》2022,111(3-4):534-543
Mathematical Notes - All the groups considered in this paper are finite, and $$G$$ always denotes a finite group; $$\sigma$$ is a partition of the set $$\mathbb{P}$$ of all primes, i.e.,...  相似文献   
10.
A nonlinear damage model based on the combination of deformation and hysteretic energy and its validation with experiments are presented. Also, a combination parameter is defined to consider the mutual effect of deformation and hysteretic energy for different types of components in different loading stages. Four reinforced concrete (RC) columns are simulated and analyzed using the nonlinear damage model. The results indicate that the damage evolution evaluated by the model agrees well with the experimental phenomenon. Furthermore, the seismic damage evolution of a six-story RC frame was analyzed, revealing four typical failure modes according to the interstory drift distribution of the structure; the damage values calculated using the nonlinear damage model agree well with the four typical failure modes.  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