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   19833篇
  免费   1796篇
  国内免费   1241篇
电工技术   1550篇
综合类   1744篇
化学工业   2330篇
金属工艺   869篇
机械仪表   1185篇
建筑科学   1115篇
矿业工程   516篇
能源动力   492篇
轻工业   1958篇
水利工程   407篇
石油天然气   396篇
武器工业   247篇
无线电   2049篇
一般工业技术   1736篇
冶金工业   3288篇
原子能技术   329篇
自动化技术   2659篇
  2024年   86篇
  2023年   262篇
  2022年   562篇
  2021年   732篇
  2020年   531篇
  2019年   386篇
  2018年   407篇
  2017年   468篇
  2016年   411篇
  2015年   679篇
  2014年   847篇
  2013年   1109篇
  2012年   1333篇
  2011年   1334篇
  2010年   1316篇
  2009年   1241篇
  2008年   1284篇
  2007年   1293篇
  2006年   1065篇
  2005年   961篇
  2004年   692篇
  2003年   497篇
  2002年   464篇
  2001年   420篇
  2000年   377篇
  1999年   223篇
  1998年   828篇
  1997年   453篇
  1996年   352篇
  1995年   232篇
  1994年   215篇
  1993年   223篇
  1992年   102篇
  1991年   75篇
  1990年   93篇
  1989年   84篇
  1988年   81篇
  1987年   67篇
  1986年   61篇
  1985年   79篇
  1984年   62篇
  1983年   75篇
  1982年   62篇
  1981年   55篇
  1980年   67篇
  1979年   49篇
  1978年   47篇
  1977年   98篇
  1976年   175篇
  1975年   39篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The available surgical and non-surgical therapy options for treatment of gallstone disease are presented. Conventional cholecystectomy is regarded as standard therapy of symptomatic cholecystolithiasis. Other modes of therapy may be indicated under certain circumstances, depending on the results of imaging procedures. In this context conventional X-ray examination, oral and intravenous cholecystography, sonography, computed tomography, endoscopic retrograde cholangiography/cholecystography, and magnetic resonance imaging are discussed and their influence on therapeutic decisions is explained.  相似文献   
42.
The North Carolina Research and Education Network (NC-REN), formerly known as CONCERT, is an existing video and data network, owned and operated by MCNC. NC-REN's purpose has been to provide network-based support for collaboration in the research community within the state since 1985. The first major application planned for the North Carolina Information Highway (NCIH) is an interactive video distance learning system. A secondary application proposed is the use of Switched Multimegabit Data Service (SMDS) as a means of providing data communications services over NCIH. The user community currently supported by NC-REN has come to expect high levels of service, reliability, interoperability and performance for data and video communications. MCNC is committed to see that NC-REN users receive service that is equal to or better than what is currently provided by the existing network. The prospect of migrating NC-REN-provided services to NCIH-provided transport has raised challenging technical and unique service issues  相似文献   
43.
攀钢转炉炼钢用碳化硅提温的试验研究   总被引:1,自引:1,他引:0  
戈文荪  杜德信 《钢铁钒钛》1994,15(3):16-19,26
低品位碳化硅是转炉炼钢的有效提高温剂。工业性试验结果表明,碳化硅加入8.0kg/t钢水提温40.3-70.3℃(平均48.4℃);渣中TFe降低1.3%;加提温剂有利于转炉内造渣脱硫和碱少炉渣对耐火砖的侵蚀。文中还给出了攀钢转炉半钢冶炼铸用钢不水时加与不加碳化硅的tλ,[C]λ区域。  相似文献   
44.
We report an unusual case of a 1 cm papillary renal cell carcinoma arising from the outer surface of the free wall of a radiographically simple renal cyst. Most malignancies arising from the wall of a renal cyst are present along the inner surface, usually adjacent to underlying renal parenchyma. While this is a rare occurrence, it does reinforce the need to explore even small solid renal masses.  相似文献   
45.
In several chronic diseases, lesions are more severe in LEW rats than in F344 rats. To determine whether or not acute viral diseases also are more severe in LEW rats than in F344 rats, we inoculated 6-7-week-old LEW and F344 rats with 10(7.2) cell culture infective units of sialodacryoadenitis virus or 10(4.7) infective units of Sendai virus. Twenty-four rats of each strain were given each virus. Lesions in nasal passages, tracheas, intrapulmonary airways, and pulmonary alveoli in 6 or 12 rats inoculated with each virus were assessed by scoring 5, 10, and 14 days after inoculation. Both viruses caused typical patchy necrotizing rhinitis, tracheitis, bronchitis, and bronchiolitis, with multifocal pneumonitis, in rats of both strains. Mean lesion indices for LEW rats given sialodacryoadenitis virus were significantly different from those for F344 rats for nasal passages on days 10 (0.999 vs. 0.680) and 14 (0.736 vs. 0.278), bronchi on day 5 (0.479 vs. 0.361), and alveoli on day 5 (0.677 vs. 0.275). Lesion indices for LEW rats given Sendai virus were significantly different from those for F344 rats for nasal passages on days 10 (1.000 vs. 0.611) and 14 (0.778 vs. 0.583); trachea on day 10 (0.625 vs. 0.028); bronchi on days 5 (0.476 vs. 0.331), 10 (0.123 vs. 0.013), and 14 (0.038 vs. 0); and alveoli on days 5 (0.413 vs. 0.114) and 10 (0.185 vs. 0.020). Thus, at the tested doses, both viruses caused more severe respiratory tract lesions in LEW rats than in F344 rats.  相似文献   
46.
47.
地域通信网的干扰技术研究   总被引:1,自引:0,他引:1  
本文在分析地域通信网结构及组成的基础上,研究了对地域通信网实施的节点破坏、末端信息封锁、局部阻塞瘫痪等对抗方法,并使用干扰地域通信网的程度、节点干扰率、末端节点封锁率和传递信息误差率等指标对干扰效果进行评估。  相似文献   
48.
ECAP细化晶粒法的仿真与分析   总被引:7,自引:0,他引:7  
ECAP(Equal Channel Angular Extrusion)方法,是实现材料纯剪切变形的有效方法。本文采用有限元(FEA)分析软件ANSYS对Al的挤压过程进行仿真与分析。分析结果表明:外切角Φ、圆角半径、试样与凹模之间的摩擦系数、凹模本身的特性(如弹性模量、泊松比等)等等,对材料的变形量都有不同程度的影响。  相似文献   
49.
Recent developments in III-V nitride thin-film materials for electronic and optoelectronic applications are reviewed. The problems that are limiting the development of these materials and devices made from them are discussed. The properties of cubic boron nitride, aluminum nitride, gallium nitride, AlN/GaN solid solutions and heterostructures, and indium nitride are discussed. It is pointed out that the lack of a suitable substrate, with the possible exception of SiC for AlN, is a problem of considerable magnitude. This is compounded by the presence of shallow donor bands in GaN and InN which are apparently caused by N vacancies. The question of whether these vacancies occur (if they do) as a result of intrinsic or extrinsic (as a result of deposition) nonstoichiometry has not been answered. However, the recent advances in the fabrication of p-type GaN and a p-n junction light emitting diode via the electron beam stimulation of the Mg dopant are very encouraging and may considerably advance the technology of this material. This would indicate that self-compensation effects, similar to those observed in ZnO and ZnSe, may not be present in the III-V nitrides, since cubic BN (cBN) AlN and now GaN have been reportedly doped both n- and p-type  相似文献   
50.
A gait analysis system is described. It is designed for clinical use as well as research purposes. The system is simple to operate and can be used by non-computer specialist. The design philosophy is straightforward and allows for easy adaptation to other systems. Samples of the output are presented.  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