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   87673篇
  免费   8928篇
  国内免费   5636篇
电工技术   6865篇
技术理论   8篇
综合类   7172篇
化学工业   13416篇
金属工艺   5152篇
机械仪表   5695篇
建筑科学   6435篇
矿业工程   2873篇
能源动力   2707篇
轻工业   7038篇
水利工程   2264篇
石油天然气   3874篇
武器工业   1147篇
无线电   10365篇
一般工业技术   9616篇
冶金工业   3957篇
原子能技术   1320篇
自动化技术   12333篇
  2024年   456篇
  2023年   1433篇
  2022年   3087篇
  2021年   4048篇
  2020年   2924篇
  2019年   2336篇
  2018年   2580篇
  2017年   2732篇
  2016年   2465篇
  2015年   3633篇
  2014年   4438篇
  2013年   5453篇
  2012年   6198篇
  2011年   6638篇
  2010年   5908篇
  2009年   5821篇
  2008年   5731篇
  2007年   5689篇
  2006年   5363篇
  2005年   4412篇
  2004年   3295篇
  2003年   2543篇
  2002年   2569篇
  2001年   2293篇
  2000年   1980篇
  1999年   1564篇
  1998年   1227篇
  1997年   1044篇
  1996年   840篇
  1995年   700篇
  1994年   538篇
  1993年   457篇
  1992年   355篇
  1991年   284篇
  1990年   205篇
  1989年   203篇
  1988年   156篇
  1987年   99篇
  1986年   99篇
  1985年   82篇
  1984年   38篇
  1983年   34篇
  1982年   39篇
  1981年   37篇
  1980年   26篇
  1979年   29篇
  1977年   16篇
  1976年   19篇
  1973年   14篇
  1951年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
乙烯-1-辛烯共聚物增韧应用研究   总被引:3,自引:0,他引:3  
介绍了聚烯烃系弹性体(POE)的特点及其在PP增韧改性中的应用,同时还报道了马来酸酐接枝的POE在极性聚合物复合体系中的应用研究。  相似文献   
72.
The change of foot length and width with age has been reported in a few anthropometric studies in the literature. However, the relationship with body height rarely is reported, and the dynamic effect of weightbearing on foot size has not been documented. In this series, 2829 children 3 to 18 years of age of equal gender distribution were included in the study. The foot length and width on weightbearing and nonweightbearing were measured with a special precision electronic caliper. The foot length and width were found to increase linearly from the age of 3 years until 12 years in girls and 15 years in boys. This was followed by a phase during which the increase plateaued. The foot length and width increased significantly on weightbearing at all ages in both genders with a mean of 2.1 to 4.4 mm or 3.1% to 4.8%, respectively. The foot length and width also were found to correlate significantly with the body height in both genders, with a correlation coefficient of 0.96 to 0.98. No significant differences were found between the sizes of the dominant and nondominant foot in either gender.  相似文献   
73.
A configurable nonlinear filter generator is proposed. The nonlinear function employed is key controllable. By changing the key, a different sequence will be obtained. Simulated results show that an optimal linear complexity profile of the sequence can be generated  相似文献   
74.
An adaptive morphological filter for image processing   总被引:6,自引:0,他引:6  
Novel types of opening operator (NOP) and closing operator (NCP) are proposed. An adaptive morphological filter is then constructed on the basis of the NOP and NCP. The filter can remove any details consisting of fewer pixels than a given number N, while preserving the other details. Efficient algorithms are also developed for the implementation of the NOP and NCP.  相似文献   
75.
The general volume equivalence theorem for bianisotropic scatterers is presented, where the equivalent electric and magnetic currents are determined by a pair of coupled vector integral equations. Moreover, using the general volume equivalence theorem and conventional image principle, image theory is developed for a bianisotropic body over an infinite perfect electric or magnetic conducting ground plane.  相似文献   
76.
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   
77.
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   
78.
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   
79.
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   
80.
Images stored in resist for soft X-ray lithography or microradiography were found to show a background noise which limits the resolution. This is due to the statistically variable spatial distribution of the photons incident on the resist surface. An estimate of the fundamental noise-limited resolution has been made from the experimental measurement of photon flux incident on the surface and the accurate development rate curves. Monochromatic radiation from a synchrotron source was used.  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