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   60763篇
  免费   5223篇
  国内免费   2658篇
电工技术   3500篇
技术理论   8篇
综合类   3629篇
化学工业   9429篇
金属工艺   2933篇
机械仪表   3273篇
建筑科学   3980篇
矿业工程   1505篇
能源动力   1754篇
轻工业   3493篇
水利工程   1097篇
石油天然气   2830篇
武器工业   646篇
无线电   6950篇
一般工业技术   6771篇
冶金工业   8273篇
原子能技术   697篇
自动化技术   7876篇
  2024年   255篇
  2023年   908篇
  2022年   1802篇
  2021年   2459篇
  2020年   1819篇
  2019年   1521篇
  2018年   1694篇
  2017年   1805篇
  2016年   1623篇
  2015年   2278篇
  2014年   2702篇
  2013年   3434篇
  2012年   3573篇
  2011年   3787篇
  2010年   3322篇
  2009年   3228篇
  2008年   3109篇
  2007年   2948篇
  2006年   2980篇
  2005年   2472篇
  2004年   1856篇
  2003年   1619篇
  2002年   1672篇
  2001年   1531篇
  2000年   1319篇
  1999年   1495篇
  1998年   2827篇
  1997年   1905篇
  1996年   1378篇
  1995年   1003篇
  1994年   788篇
  1993年   739篇
  1992年   369篇
  1991年   327篇
  1990年   253篇
  1989年   240篇
  1988年   212篇
  1987年   154篇
  1986年   142篇
  1985年   139篇
  1984年   34篇
  1983年   37篇
  1982年   64篇
  1981年   61篇
  1980年   76篇
  1979年   24篇
  1978年   23篇
  1977年   171篇
  1976年   359篇
  1975年   16篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
113.
PURPOSE: Nitric oxide (NO) is generated in mammalian tissue by the conversion of L-arginine to L-citrulline. The reaction is catalyzed by nitric oxide synthase (NOS). NO has been suggested to have a dual role in tumor biology with both antitumor and tumor promoter activity. Furthermore, it has been proposed that NO contributes to interleukin-2-induced antitumor activity. Since interleukin-2 is used in the treatment of renal cell carcinoma (RCC) it was of interest to study the NOS activity in the human kidney and in RCC and its correlation to tumor grade. Furthermore, the effect of cytokine treatment on NOS activity and the effect of NO donor application was studied in cultured cells. MATERIALS AND METHODS: The effect of cytokine treatment on NOS activity and the effect of NO donor application on cell proliferation was studied in cultured human proximal tubular cells and in RCC cell lines HN4 and HN51. NOS activity was measured by the L-arginine to L-citrulline conversion assay. RESULTS: Calcium-dependent NOS activity was found in all non-malignant kidney tissues (486+/-63 pmol. min(-1) g(-1) tissue). The activity was significantly lower in RCC (24+/-6 pmol. min(-1) g(-1) tissue) and correlated with tumor grade; thus high grade tumors showed lower activity than low grade tumors. Calcium-independent NOS activity was not detected in non-malignant kidney tissue or in RCC tissue. In cultured proximal tubular cells and RCC cell lines HN4 and HN51, cytokine treatment induced a marked increase in NOS activity and NO exerted cytostatic effects on these cell lines. Conclusions: The NOS activity was higher in non-malignant kidney tissue than in RCC tissue and was inversely correlated with tumor grade. Furthermore, cytokine treatment induced a marked increase in NOS activity and NO exerted cytostatic effects on cultured proximal tubular cells and RCC cell lines.  相似文献   
114.
Cheng  D. 《Electronics letters》1996,32(6):529-530
A triaxial omega medium, which can be artificially realised by embedding three types of omega-shaped particles in an isotropic host medium, is proposed. The Green dyadic and the electromagnetic field of a dipole radiator are presented, by introducing a set of auxiliary fields and coordinate transformation  相似文献   
115.
This paper reports a simple I-V method for the first time to determine the lateral lightly-doped source/drain (S/D) profiles (n- region) of LDD n-MOSFETs. One interesting result is the direct observation of the reverse-short-channel effect (RSCE). It is observed that S/D n- doping profile is channel length dependent if reverse short-channel effect exists as a result of the interstitial imperfections caused by Oxide Enhanced Diffusion (OED) or S/D implant. Not only the lateral profiles for long-channel devices but also for short-channel devices can be determined. One other practical application of the present method for device drain engineering has been demonstrated with a LATID MOS device drain engineering work. It is convincible that the proposed method is well suited for the characterization and optimization of submicron and deep-submicron MOSFETs in the current ULSI technology  相似文献   
116.
A case of Macrozamia riedlei seed poisoning is described in a young Dachshund. Vomiting and depression commenced within 6 h of ingestion; other signs that developed included severe hepatopathy, jaundice, abdominal pain that was unresponsive to analgesics, severe gastro-intestinal haemorrhage and thrombocytopenia as well as crystalluria and marrow dyserythropoiesis. The dog was euthanased 6 days after ingestion of the seeds.  相似文献   
117.
本文利用可控平均冷却速度的单向凝固实验炉测定了45号钢在不同平均冷却速度下的冷却曲线,由此得到其在凝固期间的平均冷却速度R,相应地测量了不同平均冷却速度下试样的二次枝晶臂间距S2,通过回归,得到了如下关系式:S2=727R-0.41,并将引式成功地应用于实际生产中。  相似文献   
118.
119.
120.
高文学  陈桂林 《爆破》1994,11(2):29-32
文章通过对洋浦电厂海水冷却箱涵沟槽预裂(深孔)爆破技术的研究,提出了复杂地质条件下合理的控制爆破参数及微差起爆方式。针对砂层地段难以钻、爆的特点。笔者进行了有益的探讨。  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