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   614353篇
  免费   6119篇
  国内免费   1442篇
化学   308108篇
晶体学   8979篇
力学   30830篇
综合类   20篇
数学   84983篇
物理学   188994篇
  2021年   4862篇
  2020年   5315篇
  2019年   5940篇
  2018年   13123篇
  2017年   13527篇
  2016年   13911篇
  2015年   7184篇
  2014年   10905篇
  2013年   24862篇
  2012年   21849篇
  2011年   30995篇
  2010年   21457篇
  2009年   21597篇
  2008年   28305篇
  2007年   30340篇
  2006年   20020篇
  2005年   21568篇
  2004年   18518篇
  2003年   16896篇
  2002年   15659篇
  2001年   16735篇
  2000年   12741篇
  1999年   9837篇
  1998年   8323篇
  1997年   7963篇
  1996年   7753篇
  1995年   6975篇
  1994年   6883篇
  1993年   6705篇
  1992年   7263篇
  1991年   7616篇
  1990年   7256篇
  1989年   7147篇
  1988年   7051篇
  1987年   6942篇
  1986年   6589篇
  1985年   8492篇
  1984年   8596篇
  1983年   6948篇
  1982年   7101篇
  1981年   6985篇
  1980年   6475篇
  1979年   7085篇
  1978年   7319篇
  1977年   7247篇
  1976年   7292篇
  1975年   6710篇
  1974年   6678篇
  1973年   6839篇
  1972年   4977篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
Optics and Spectroscopy - 10.1134/S0030400X17050095  相似文献   
183.
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   
184.
Silver-mediated α-dC–Ag+–β-dC hybrid base pairs decorated with 5-iodo- or 5-octadiynyl residues are well accommodated in duplex DNA. A strong Tm increase and favorable thermodynamic data for duplex DNA were observed after addition of silver ions. The phenomenon is particularly obvious when both nucleobases of the base pairs are functionalized. Neither the position of the base pair, nor the type of 5-substituent had a negative influence. On the contrary, functionalization of conventional silver-mediated β-dC–Ag+–β-dC homo base pairs showed a negative impact induced by the bulky substituents. To this end, cytosine modified 12-mer oligodeoxynucleotides were prepared by solid-phase synthesis employing new α-anomeric 2′-deoxycytidine phosphoramidites. A multigram scale synthesis was developed for 5-iodo-α-d -2′-deoxycytidine ( 1 ) employing the direct glycosylation of cytosine with Hoffer's α-d -halogenose followed by separation of anomeric DMT nucleosides. Regarding base-pair stability and functionalization silver-mediated α/β-dC hybrid base pairs were found to be superior to β/β-dC homo pairs. According to their extraordinary properties, they might find applications in DNA diagnostics, material science, or nanotechnology.  相似文献   
185.
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   
186.
187.
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.  相似文献   
188.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  相似文献   
189.
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained...  相似文献   
190.
International Applied Mechanics - Problems of parametric optimization of rod structure stated in terms of the nonlinear programming problem are considered. Use is made of the method of projection...  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