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   340101篇
  免费   2963篇
  国内免费   364篇
化学   162637篇
晶体学   4876篇
力学   17558篇
综合类   4篇
数学   50566篇
物理学   107787篇
  2021年   3571篇
  2020年   4058篇
  2019年   4804篇
  2018年   7086篇
  2017年   7230篇
  2016年   9475篇
  2015年   4820篇
  2014年   8135篇
  2013年   14889篇
  2012年   12748篇
  2011年   14285篇
  2010年   11666篇
  2009年   11593篇
  2008年   13572篇
  2007年   13192篇
  2006年   11752篇
  2005年   10438篇
  2004年   9931篇
  2003年   9088篇
  2002年   9194篇
  2001年   8540篇
  2000年   6919篇
  1999年   5087篇
  1998年   4744篇
  1997年   4507篇
  1996年   4283篇
  1995年   3684篇
  1994年   3810篇
  1993年   3775篇
  1992年   3805篇
  1991年   4140篇
  1990年   4191篇
  1989年   4118篇
  1988年   3865篇
  1987年   3920篇
  1986年   3607篇
  1985年   4238篇
  1984年   4450篇
  1983年   3779篇
  1982年   3977篇
  1981年   3670篇
  1980年   3373篇
  1979年   3838篇
  1978年   3912篇
  1977年   4082篇
  1976年   4147篇
  1975年   3855篇
  1974年   3730篇
  1973年   3905篇
  1972年   3301篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Russian Journal of General Chemistry - A method was developed for the synthesis of an organofluorine derivative of β-D-ribofuranoside. Biological tests revealed high insecticidal activity and...  相似文献   
122.
Journal of Analytical Chemistry - Studies on the separation of the Se and Te trace components from Co, Ni, Cu, Fe, Cr, Mo, and W macrocomponents for their determination by inductively coupled...  相似文献   
123.
ABSTRACT

The authors present the results of an investigation in Fe–Ni-Cr austenitic alloys of the low-temperature deformation-induced segregations of nickel that form in the micro regions being (i) located close to grain- and subgrain boundaries and (ii) characteristic of the concentration and magnetic inhomogeneities indicated by the appearance of a dark diffraction contrast at the electron diffraction patterns taken from these regions typical (at the same time) of an enhanced value of Curie temperature. The observed effects were connected with the micro distortions caused by the local change of lattice parameter because of an increase in nickel concentration, as well as in the result of a magnetostriction dilatation. Using methods of the X-ray energy dispersive spectroscopy (XEDS) and atomic-probe body-section radiography (tomography – APT) has made it possible to determine the borders of those regions of austenite that were characteristic of an enhanced concentration of nickel in the fields of the localisation of a deformation-induced segregation of nickel in the vicinity of grain (subgrain) boundaries of austenitic alloys of the types Fe–13Cr–30Ni and Fe–37Ni–3Ti.  相似文献   
124.
125.
126.
Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces with different curvature radii in a perfect nanocrystal passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to an external energy flux with subsequent development of a strong rotational field.  相似文献   
127.
128.
Molecular Diversity - Hypertension is a medical condition that affects millions of people worldwide. Despite the high efficacy of the current antihypertensive drugs, they are associated with...  相似文献   
129.
Journal of Experimental and Theoretical Physics - The nature of the training effect in exchange-biased compounds is studied. This effect consists in a decrease in the exchange bias field (HEB)...  相似文献   
130.
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000–1252 K and pressure range of 1.5–5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H5I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO → products (R1) and C3H5 + NO2 → products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5–5.0 bar, indicating that the measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm3/molecule/s):k1(C3H5+NO)=1.49×10?10exp(?6083.6KT)(1017?1252K)k2(C3H5+NO2)=1.71×10?10exp(?3675.7KT)(1062?1250K)To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions. The reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels.  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