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   1252672篇
  免费   98714篇
  国内免费   1333篇
  2021年   17713篇
  2020年   12620篇
  2019年   16142篇
  2018年   18316篇
  2017年   17157篇
  2016年   28349篇
  2015年   42190篇
  2014年   50162篇
  2013年   76443篇
  2012年   33768篇
  2011年   22213篇
  2010年   43795篇
  2009年   45118篇
  2008年   21273篇
  2007年   19147篇
  2006年   24458篇
  2005年   25922篇
  2004年   24981篇
  2003年   22557篇
  2002年   20756篇
  2001年   26160篇
  2000年   23279篇
  1999年   25839篇
  1998年   24517篇
  1997年   24113篇
  1996年   23818篇
  1995年   21931篇
  1994年   21807篇
  1993年   20767篇
  1992年   22813篇
  1991年   21501篇
  1990年   20349篇
  1989年   21463篇
  1988年   19686篇
  1987年   18542篇
  1986年   17653篇
  1985年   19919篇
  1984年   20358篇
  1983年   17965篇
  1982年   19035篇
  1981年   18486篇
  1980年   17290篇
  1979年   16091篇
  1978年   15843篇
  1977年   15333篇
  1976年   14752篇
  1975年   14205篇
  1974年   14506篇
  1973年   14977篇
  1972年   12446篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Rechargeable graphite dual‐ion batteries (GDIBs) have attracted the attention of electrochemists and material scientists in recent years due to their low cost and high‐performance metrics, such as high power density (≈3–175 kW kg?1), energy efficiency (≈80–90%), long cycling life, and high energy density (up to 200 Wh kg?1), suited for grid‐level stationary storage of electricity. The key feature of GDIBs is the exploitation of the reversible oxidation of the graphite network with concomitant and highly efficient intercalation/deintercalation of bulky anionic species between graphene layers. In this review, historical and current research aspects of GDIBs are discussed, along with key challenges in their development and practical deployment. Specific emphasis is given to the operational mechanism of GDIBs and to unbiased and correct reporting of theoretical cell‐level energy densities.  相似文献   
972.
973.
Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks.  相似文献   
974.
975.
Summary The conditions required for the production of a polylysine-coated gold (PL-G) complex, which shows optimal sensitivity for the demonstration of tissue anionic sites, expressed under different conditions of pH have been investigated. Problems encountered with this complex have been compared with those found with other methods of conjugation of polylysine to colloidal gold. The performance of a bovine serum albumin (BSA)-stabilized PL-G complex was examined against other PL-G conjugates, including complexes that are commercially available, for the detection of heterogeneous glomerular anionic site populations, expressed at pH 2.5 and pH 7.0.  相似文献   
976.
977.
978.
Enumeration of denitrifying microbial populations in turf   总被引:2,自引:0,他引:2  
Summary Denitrifer populations of a silt and silt loam soil under a Kentucky bluegrass turf were enumerated using the most probable number (MPN) procedure. The influence of soil texture, soil depth, soil moisture, and additions of nitrate fertilizer on denitrifier populations were determined. Saturated soil conditions increased denitrifier populations 87-fold in the silt soil and 121-fold in the silt loam soil. Denitrifier populations did not differ significantly between soil depths and additions of fertilizer nitrate did not influence populations.  相似文献   
979.
980.
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