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   112134篇
  免费   8194篇
  国内免费   4218篇
电工技术   5874篇
技术理论   11篇
综合类   6618篇
化学工业   18991篇
金属工艺   5856篇
机械仪表   6698篇
建筑科学   8666篇
矿业工程   3092篇
能源动力   3104篇
轻工业   6644篇
水利工程   1722篇
石油天然气   6251篇
武器工业   693篇
无线电   13992篇
一般工业技术   14289篇
冶金工业   5910篇
原子能技术   1251篇
自动化技术   14884篇
  2024年   445篇
  2023年   1755篇
  2022年   2918篇
  2021年   4041篇
  2020年   3077篇
  2019年   2606篇
  2018年   3004篇
  2017年   3384篇
  2016年   2949篇
  2015年   3878篇
  2014年   4919篇
  2013年   6275篇
  2012年   6581篇
  2011年   7198篇
  2010年   6267篇
  2009年   6180篇
  2008年   6180篇
  2007年   5764篇
  2006年   6046篇
  2005年   5414篇
  2004年   3694篇
  2003年   3200篇
  2002年   2856篇
  2001年   2755篇
  2000年   2871篇
  1999年   3384篇
  1998年   2917篇
  1997年   2550篇
  1996年   2287篇
  1995年   1922篇
  1994年   1555篇
  1993年   1220篇
  1992年   965篇
  1991年   738篇
  1990年   600篇
  1989年   500篇
  1988年   390篇
  1987年   294篇
  1986年   206篇
  1985年   176篇
  1984年   108篇
  1983年   81篇
  1982年   87篇
  1981年   57篇
  1980年   47篇
  1979年   32篇
  1978年   25篇
  1977年   25篇
  1976年   40篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
A modified CIECAM02 colour appearance model, named CIECAM02‐m2, is proposed to enable CIECAM02 to predict the simultaneous contrast effect. The structure of the CIECAM02‐m2 is a development from CIECAM02, and contains two different procedures for modifying the reference white; one is for lightness and the other is for hue. The model was tested using a data set accumulated in this study and the LUTCHI data. The CV values for three colour attributes between predictions and experimental data were used to evaluate the accuracy of the model. The low CV values obtained show the performance of the CIECAM02‐m2 model to predict the simultaneous contrast effect satisfactorily. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 121 – 129, 2007  相似文献   
63.
HREM and FEG TEM were emphasized and extensively used to follow the most subtle changes in the structure and composition of ball-milled Cu, Fe-Cu, and thermally decomposed Fe60Cu40. Some significant results are obtained and summarized as follows: HREM shows that the deformation of ball-milled copper proceeds mainly by twinning and shear bands (SBs) formation. The nano-grains formed during ball milling (BM) contain a high density of dislocations. The grain boundaries (GBs) of nanocrystalline (NC) Cu prepared by BM are ordered, curved, and strained, but disordering, lattice distortion, and nanovoids in local regions were frequently observed. Nanoscale composition analysis on mechanically alloyed Fe16Cu84 shows that the average Fe content in both the interior of grains and the GBs is close to the designed composition, which proves that a supersaturated solid solution has really formed. However, the Fe content is rather inhomogeneous between the larger and smaller grains, which infers the inhomogeneous mixing of Fe and Cu during mechanical alloying (MA). NC structure and the mechanical force-enhanced fast diffusion are the reasons of the formation of supersaturated solid solutions in immiscible systems with positive enthalpy of mixing. HREM observations carried out with the thermally decomposed Fe60Cu40 solid solution show that the Nishiyama (N-W) or Kurdyumov-Sachs (K-S) orientation relationships exist between alpha-Fe and Cu. Energy dispersive X-ray spectra (EDXS) results show that the Cu content in these alpha-Fe grains reaches as high as 9.5 at.% even after heating to 1,400 degrees C, which is even higher than the maximum solubility of Cu in gamma-Fe at 1,094 degrees C.  相似文献   
64.
酞菁光敏剂对S180移植瘤的疗效   总被引:1,自引:0,他引:1  
研究了GaS_4PC,ZnS_2PC两种酞菁在激光照射下对S180肉瘤的疗效,并讨论了其他酞菁光敏剂对癌细胞的杀伤效果。  相似文献   
65.
Lysophosphatidylcholine (LPC) is formed by hydrolysis of PC in low density lipoprotein (LDL) and cell membranes by phospholipase A2 or by oxidation. Oxidized (ox) LDL activates endothelial cells, an effect mimicked by LPC. oxLDL also has the capacity to activate T and B cells, and antibody titers to oxLDL are related to the degree of atherosclerosis. The antigen in oxLDL responsible for its immune-stimulatory capacity is not well characterized, and we hypothesized that LPC was involved. We demonstrate herein the presence of antibodies against LPC, both of the IgG and IgM isotype, in 210 healthy individuals. This antibody reactivity was not specifically related to oxidation of the fatty acid moiety in LPC, since LPC containing only palmitic acid showed antibody titers equivalent to those of LPC containing unsaturated fatty acids. Antibody titers to PC were low compared with LPC, and hydrolysis of PC at the sn-2 position is thus essential for immune reactivity. There was a close correlation between anti-oxLDL and anti-LPC antibodies. Furthermore, LPC competitively inhibited anti-oxLDL reactivity, which indicates that LPC may explain a significant part of the immune-stimulatory properties of oxLDL. LPC, being a lipid, is not likely to be an antigen itself. Instead, LPC could form immunogenic complexes with peptides, which may induce and potentiate immune reactions in the vessel wall. This study adds to the evidence that LPC is an important component of oxLDL and emphasizes the potential role of phospholipase A2 in atherosclerosis.  相似文献   
66.
67.
Diagnosis and treatment of 17 patients who sustained 20 iatrogenic ureteral injuries were analyzed. Primary operations in which ureteral injury occurred are almost gynecologic procedures and general surgery. Injuries were managed by ureteroureterostomy in four, ureteral stent in one, removal suture ligation and ureteral double J-catheter in one, ureteroneocystostomy in ten, psoas-hitch technique and ureteroneocystostomy in one, nephrectomy in two. All patients with appropriate repair were followed-up periods of three to five years. Renal function of these patients had optimal results. When ureteral injury occurs, B-US, IVU, cystoscopy, retrograde ureterography or infusion of dye may be useful. An appropriate repair should be chosen according to length and position of ureteral injuries. Reoperation was optimal in two to three weeks. Immediate recognition of accidental ureteral injury provides optimal results. Patients with unrecognized injuries had suboptimal results.  相似文献   
68.
69.
实验表明,EC浓度与配体交换反应速度常数无关,体系的pH值对速度常数和99mTc-EC的标记率影响较大。测定并计算了不同pH值的交换反应速度常数。结果表明,为保证用配体交换法制备99mc-EC时99mc-EC的标记率大于90%,体系的pH值必须≥8。  相似文献   
70.
新型高性能脉冲峰值保持电路   总被引:10,自引:7,他引:3  
本文介绍了两种新型跨导型脉冲峰值保持器,分别用于多丝正比室(MWPC)和复合晶体闪烁探测器(Phoswich)输出脉冲信号的形状和幅度分析。电路的跨导放大级采用跨导型集成运算放大器,使电路结构简单化,且性能优良可靠,能响应输入脉冲最小上升时间分别为50ns(Phoswich)和500ns(MWPC)的信号,在40dB的动态范围内,两电路的积分非线性均好于0.1%,特别适用于空间γ射线观测。  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