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   21958篇
  免费   1675篇
  国内免费   315篇
电工技术   538篇
综合类   361篇
化学工业   4851篇
金属工艺   906篇
机械仪表   1286篇
建筑科学   1033篇
矿业工程   251篇
能源动力   699篇
轻工业   1879篇
水利工程   148篇
石油天然气   564篇
武器工业   60篇
无线电   2978篇
一般工业技术   4035篇
冶金工业   1927篇
原子能技术   265篇
自动化技术   2167篇
  2024年   50篇
  2023年   298篇
  2022年   492篇
  2021年   711篇
  2020年   543篇
  2019年   581篇
  2018年   624篇
  2017年   729篇
  2016年   786篇
  2015年   724篇
  2014年   1054篇
  2013年   1443篇
  2012年   1318篇
  2011年   1629篇
  2010年   1209篇
  2009年   1174篇
  2008年   1162篇
  2007年   932篇
  2006年   851篇
  2005年   735篇
  2004年   618篇
  2003年   590篇
  2002年   503篇
  2001年   424篇
  2000年   393篇
  1999年   495篇
  1998年   692篇
  1997年   538篇
  1996年   354篇
  1995年   279篇
  1994年   260篇
  1993年   238篇
  1992年   156篇
  1991年   146篇
  1990年   123篇
  1989年   123篇
  1988年   82篇
  1987年   73篇
  1986年   67篇
  1985年   83篇
  1984年   77篇
  1983年   49篇
  1982年   48篇
  1981年   47篇
  1980年   47篇
  1979年   40篇
  1977年   53篇
  1976年   83篇
  1975年   42篇
  1973年   33篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
商品混凝土目前价格偏高 ,用户不情愿接受 ,影响了它的推广应用。针对这一问题 ,本文提出了用“活化填料”、“活化水泥”配制高性能商品混凝土的技术路线并分析了其技术经济效益  相似文献   
32.
It is believed that DOPA-negative melanocytes in the outer root sheath of the human hair follicle are activated, become identifiable by DOPA staining, and migrate into the epidermis during the repigmenting phase of vitiligo. These cells are difficult to identify, however, and otherwise have not been characterized. These cells are readily identified by immunofluorescence, immunohistochemistry, and immunoelectronmicroscopy using the antibodies NKI/beteb and A4F11, which recognize premelanosome-related antigens. The majority of the outer root sheath melanocytes were found in the mid to the upper portion of the hair follicle. Double staining revealed that these cells were distinct from HLA-DR-bearing dendritic cells. Further immunohistochemical investigation using alpha-PEP-7, alpha-PEP-1, or TMH-1 and alpha-PEP-8 antibodies revealed that outer root sheath melanocytes cannot be identified by antibodies to tyrosinase, TRP-1, or TRP-2, respectively. These cells also did not react with HMB45 antibody, which recognizes a melanosome-associated cytoplasmic antigen. We believe that the inactive outer root sheath melanocytes contain some of the early structural proteins but not any of the enzymatic proteins necessary for melanogenesis. Therefore, activation is the process whereby outer root sheath melanocytes acquire all of the structural and enzymatic proteins necessary for melanogenesis.  相似文献   
33.
34.
35.
The feasibility of a new alloy design concept utilizing the principle of ‘tungsten bronze effect’ is critically evaluated for the development of metallic bipolar plates for proton exchange membrane fuel cell (PEMFC). An austenitic stainless steel (ASS) is modified with W and La to improve the stability of the passive film in an acidic environment as well as to reduce the contact resistance by the tungsten bronze effect. The experimental ASS containing W and La was evaluated in a simulated PEMFC environment of H3PO4 and H2SO4 solutions at 80 °C, and the electrical property was evaluated by performing a contact resistance test. The test results show that the ASS modified with W and La has good passive film stability for corrosion resistance and low contact resistance. The X-ray photoelectron spectroscopy (XPS) analysis clearly suggests the possibility of the tungsten bronze effect from the change in valency state of W6+ to W5+ in the passive film formed on the modified ASS. The feasibility of a new alloy design concept utilizing the ‘tungsten bronze effect’ is well demonstrated; however, more study is highly required for the development of metallic bipolar plates of PEMFC.  相似文献   
36.
37.
Central temperature is usually tightly regulated in human beings. Anesthesia alters the normal thermoregulatory controls of the body. Intraoperatively, mild degrees of hypothermia may provide some cerebral protection. However, the risk of organ dysfunction and shivering require that the anesthesiologist be prepared to treat severe hypothermia. Appropriate measures such as warning the operating room and using forced air blankets can prevent both intraoperative hypothermia and postoperative shivering. The use of temperature measurement is not limited to the operative and immediate recovery periods. Anesthesiologists practicing in intensive care units and in pain clinics use temperature monitoring as a diagnostic tool in a variety of situations.  相似文献   
38.
We present a simple and efficient approach for continuous collision detection of deforming triangles based on conservative advancement. The efficiency of our approach is due to a sequence of simple collision-free conditions for deforming triangles. In our experiment, we show that our CCD algorithm achieves 2-30 times performance improvement over existing algorithms for triangle primitives.  相似文献   
39.
本文以选票统计问题为例,讨论了3种查找计数方法(顺序法、二分法、插值法)在统计中的应用,提出了一种新颖的查找计数方法——一次到位法,给出了用FOXPLUS数据库语言编写的算法子程序,并比较了它们各自的特点和适用范围。  相似文献   
40.
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