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   271012篇
  免费   2546篇
  国内免费   621篇
化学   144590篇
晶体学   3376篇
力学   12105篇
综合类   9篇
数学   30231篇
物理学   83868篇
  2019年   2358篇
  2018年   3212篇
  2017年   3176篇
  2016年   4609篇
  2015年   2821篇
  2014年   4425篇
  2013年   10987篇
  2012年   8420篇
  2011年   10238篇
  2010年   7313篇
  2009年   7014篇
  2008年   9638篇
  2007年   9809篇
  2006年   9157篇
  2005年   8344篇
  2004年   7667篇
  2003年   6944篇
  2002年   6847篇
  2001年   7419篇
  2000年   5772篇
  1999年   4416篇
  1998年   3930篇
  1997年   3897篇
  1996年   3661篇
  1995年   3372篇
  1994年   3530篇
  1993年   3229篇
  1992年   3710篇
  1991年   3692篇
  1990年   3544篇
  1989年   3403篇
  1988年   3495篇
  1987年   3411篇
  1986年   3215篇
  1985年   4320篇
  1984年   4621篇
  1983年   3824篇
  1982年   3960篇
  1981年   3891篇
  1980年   3859篇
  1979年   3835篇
  1978年   4175篇
  1977年   4094篇
  1976年   4165篇
  1975年   3822篇
  1974年   3886篇
  1973年   4026篇
  1972年   2828篇
  1971年   2352篇
  1970年   2169篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Research on Chemical Intermediates - A series of quinoxaline derivatives were efficiently synthesized by convenient and simple procedure in excellent yields using 1 wt.% of titanium silicate (TS-1)...  相似文献   
82.
Physics of Atomic Nuclei - Improved mechanical properties of oxide dispersion strengthened (ODS) steels, the advanced materials for the reactor core, are due to the high density of uniformly...  相似文献   
83.
84.
Galkina  E. G.  Zaspel  C. E.  Ivanov  B. A.  Kulagin  N. E.  Lerman  L. M. 《JETP Letters》2019,110(7):481-486
JETP Letters - The motion of domain walls in GdFeCo-type ferrimagnets near the point of compensation of sublattice spins s1 and s2, when the effects of the exchange increase in the limiting wall...  相似文献   
85.
86.
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease.  相似文献   
87.
Sukhorukova  O. S.  Tarasenko  A. S.  Tarasenko  S. V.  Shavrov  V. G. 《JETP Letters》2020,112(7):420-427
JETP Letters - At the resonant passage of a plane elastic shear wave through an acoustically continuous heterostructure consisting of magnetic and nonmagnetic layers in a symmetric nonmagnetic...  相似文献   
88.
89.
Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the...  相似文献   
90.
Droplet evaporation characterization, although of great significance, is still challenging. The recently developed phase rainbow refractometry (PRR) is proposed as an approach to measuring the droplet temperature, size as well as evaporation rate simultaneously, and is applied to a single flowing n-heptane droplet produced by a droplet-on-demand generator. The changes of droplet temperature and evaporation rate after a transient spark heating are reflected in the time-resolved PRR image. Results show that droplet evaporation rate increases with temperature, from ?1.28×10?8 m2/s at atmospheric 293 K to a range of (?1.5, ?8)×10?8 m2/s when heated to (294, 315) K, agreeing well with the Maxwell and Stefan–Fuchs model predictions. Uncertainty analysis suggests that the main source is the indeterminate gradient inside droplet, resulting in an underestimation of droplet temperature and evaporation rate. With the demonstration on simultaneous measurements of droplet refractive index as well as droplet transient and local evaporation rate in this work, PRR is a promising tool to investigate single droplet evaporation in real engine conditions.  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