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   152693篇
  免费   1349篇
  国内免费   384篇
化学   81960篇
晶体学   2028篇
力学   6657篇
综合类   7篇
数学   15279篇
物理学   48495篇
  2020年   1111篇
  2019年   1171篇
  2018年   1475篇
  2017年   1451篇
  2016年   2467篇
  2015年   1545篇
  2014年   2422篇
  2013年   6314篇
  2012年   4925篇
  2011年   6256篇
  2010年   4277篇
  2009年   4289篇
  2008年   5690篇
  2007年   5763篇
  2006年   5403篇
  2005年   4992篇
  2004年   4409篇
  2003年   3852篇
  2002年   3882篇
  2001年   4333篇
  2000年   3316篇
  1999年   2573篇
  1998年   2241篇
  1997年   2184篇
  1996年   1981篇
  1995年   1897篇
  1994年   1888篇
  1993年   1726篇
  1992年   1991篇
  1991年   2119篇
  1990年   1917篇
  1989年   1916篇
  1988年   1856篇
  1987年   1755篇
  1986年   1692篇
  1985年   2192篇
  1984年   2324篇
  1983年   1897篇
  1982年   2078篇
  1981年   1964篇
  1980年   1888篇
  1979年   2029篇
  1978年   2197篇
  1977年   2068篇
  1976年   2112篇
  1975年   2019篇
  1974年   2072篇
  1973年   2060篇
  1972年   1354篇
  1971年   1210篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Transpiration is a technique in which extra non-physical normal flows are created on an aerofoil surface in order to form a new streamline pattern such that the surface streamlines no longer follow the aerofoil surface under inviscid flow. The transpiration model is an important technique adopted in aerofoil design either to avoid mesh regeneration when aerofoil profile co-ordinates are adjusted or to find shape corrections in inverse design methods. A first-order approximation (with respect to the normal streamline displacement) to the transpiration model is commonly adopted; it is shown that this can be a poor approximation especially in regions of high curvature. In this paper more accurate approximations are developed to address this problem and improve the accuracy.  相似文献   
92.
93.
A combined approach based on solid-phase optosensing and multicommutation principles has been applied to develop a method for the simultaneous analysis of two pharmaceuticals (naproxen and salicylic acid) in biological fluids. The multicommuted flow-through optosensor was based on direct native fluorescence measurements of both analgesics using a non-polar sorbent (C18 silica gel) as a solid sensing zone. The flow system was controlled by Java-written home-made software and designed using three-way solenoid valves for an independent automated manipulation of sample and carrier solutions. Using an optimized sampling time, the method was calibrated in the range of 1 - 25 and 5 - 200 ng mL(-1). The obtained detection limits were 0.3 and 1.3 ng mL(-1) for naproxen and salicylic acid, respectively, with RSD (%) values of better than 2% for both analytes. The proposed methodology was successfully applied to urine, serum and pharmaceutical preparations. Recovery percentages ranging from 96.1 to 104% were obtained for both analytes.  相似文献   
94.
The breakup of suspended, agglomerated submicron particles was studied by exposing the aerosol to weak shock waves of varying strength under conditions 400 ms?1?v?880 ms?1. A newly developed laser light-scattering diagnostic employing a top hat laser profile was used to size the particles passing through a very small scattering volume. By Comparing the optically measured particle size in front of and behind shock waves, the breakup of agglomerated particles could be clearly identified. The experiments indicate that the aerodynamic forces behind an incident shock overcome the particle binding force resulting in disintegration of the submicron agglomerates. The results are presented in form of a modified Weber number.  相似文献   
95.
96.
97.
Excited states of73Se have been investigated up to spin, 21/2 using techniques of in-beamγ-ray spectroscopy in connection with the70Ge(α, n) reaction. Mean lifetimes of 12 levels have been determined applying Doppler-shift andγ-RF-methods. Five different bands have been identified that reflect a variety of different excitation modes. The decoupled 9/2+ band is likely to correspond to an oblate deformation while the 5/2+ band is interpreted as a strongly coupled prolate band built on the Nilsson configuration [422] 5/2+. The 3/2? band is a strongly coupled band built on the [301] 3/2} configuration.Nuclear reactions:70Ge(α,n),E=14, 16, 18, 19, 20MeV; measuredE γ,I γ,σ(E γ,θ),γγ-coin, linear polarization, DSA,γ(t).75Se deduced levels,I, π, τ, δ(E2/M1), B(σλ). Enriched targets, Ge detectors.  相似文献   
98.
The determination of doxazosin by high-performance liquid chromatography with fluorescence detection is described. Propanolol was used as the internal standard. Plasma samples were treated with methanol to precipitate the proteins. Doxazosin was isolated with C18 reversed-phase extraction columns. The determination limit is 1 ng/ml of plasma, while the extraction columns can be reused frequently. The method is applied to clinical trial samples.  相似文献   
99.
100.
Electron energy distribution functions (eedf) in CO2 laser discharge (He—CO2—N2—CO mixture) have been calculated by solving the Boltzmann equation in the presence of given concentrations of excited (vibrational and electronic) states. The results show a well structured eedf as a result of second kind collisions coming from metastable electronic states of N2 and He as well as a strong dependence of rate coefficients for CO2 dissociation and for the ionization of the different species.  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