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   738191篇
  免费   6796篇
  国内免费   2032篇
化学   369331篇
晶体学   10625篇
力学   37387篇
综合类   19篇
数学   105471篇
物理学   224186篇
  2021年   5925篇
  2020年   6488篇
  2019年   7438篇
  2018年   13819篇
  2017年   14105篇
  2016年   15853篇
  2015年   8238篇
  2014年   12926篇
  2013年   31054篇
  2012年   25653篇
  2011年   34749篇
  2010年   24198篇
  2009年   24103篇
  2008年   31683篇
  2007年   33549篇
  2006年   24072篇
  2005年   24670篇
  2004年   21515篇
  2003年   19805篇
  2002年   18639篇
  2001年   19107篇
  2000年   14909篇
  1999年   11500篇
  1998年   9914篇
  1997年   9797篇
  1996年   9263篇
  1995年   8442篇
  1994年   8292篇
  1993年   8135篇
  1992年   8645篇
  1991年   9161篇
  1990年   8769篇
  1989年   8684篇
  1988年   8536篇
  1987年   8260篇
  1986年   7951篇
  1985年   10299篇
  1984年   10775篇
  1983年   9041篇
  1982年   9557篇
  1981年   9001篇
  1980年   8615篇
  1979年   9132篇
  1978年   9578篇
  1977年   9233篇
  1976年   9407篇
  1975年   8809篇
  1974年   8753篇
  1973年   9246篇
  1972年   6490篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The thermodynamic properties of the Ln2BaO4 phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.  相似文献   
992.
The title compound [systematic name: 8‐chloro‐11‐(piperidin‐4‐yl­idene)‐6,11‐dihydro‐5H‐benzo[4,5]cyclo­hepta­[2,1‐b]pyridine], C19H19ClN2, was crystallized from ethyl acetate. The inter­esting feature of the reported structure is that it does not contain any strong hydrogen bonds, although the mol­ecule contains a secondary NH group, which is a good hydrogen‐bond donor.  相似文献   
993.
994.
995.
996.
Errors in the programs of winding pressure vessels can lead to an asymmetric reinforcement structure, which affects the equilibrium shape of their domes and the tension in the left and right families of filaments. In this paper, equations determining the equilibrium shape of the domes, the tension in filaments, and the shear stresses between layers are obtained. Examples with winding trajectories in the form of geodesics and constant-deviation lines are considered. It is found that, for pressure vessels, in the absence of external torque, the tension levels in filaments of the left and right families differ considerably. It is also revealed that, for actual friction coefficients in winding, the shear stresses taken up by the binder are insignificant. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 743–752, November–December, 2005.  相似文献   
997.
Mo2Ni3Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo2Ni3Si primary dendrites and the interdendritic Mo2Ni3Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo2Ni3Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance.  相似文献   
998.
999.
Summary Studies performed by the Brazilian Nuclear Corporation (NUCLEBRAS), in collaboration with the Geological Survey Company of Brazil (CPRM), identified high levels of natural uranium in the districts of Pedra and Venturosa, in the rural region of the state of Pernambuco (PE) - Brazil, where the maximum value found in rocks was 22,000 mg.  相似文献   
1000.
Some polythermal sections of the Ni-Bi-Se system have been investigated by DTA, X-ray powder diffraction, microstructural analysis, and microhardness measurements. The liquidus surface has been constructed for this system. The compounds NiBi2Se4 and Ni3Bi2Se2 are formed by dystectic reactions and melt at 1088 and 980 K, respectively. The regions of primary and joint phase crystallization have been determined. A commutation of Bi2Se3-based thermoelements with a metal nickel bus-bar has been proposed.  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