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   2767篇
  免费   94篇
  国内免费   14篇
电工技术   17篇
综合类   34篇
化学工业   269篇
金属工艺   56篇
机械仪表   101篇
建筑科学   42篇
矿业工程   6篇
能源动力   62篇
轻工业   118篇
水利工程   10篇
石油天然气   22篇
无线电   218篇
一般工业技术   328篇
冶金工业   1425篇
原子能技术   9篇
自动化技术   158篇
  2023年   17篇
  2022年   23篇
  2021年   41篇
  2020年   35篇
  2019年   39篇
  2018年   37篇
  2017年   52篇
  2016年   30篇
  2015年   29篇
  2014年   74篇
  2013年   87篇
  2012年   97篇
  2011年   99篇
  2010年   71篇
  2009年   83篇
  2008年   71篇
  2007年   61篇
  2006年   69篇
  2005年   50篇
  2004年   30篇
  2003年   48篇
  2002年   46篇
  2001年   34篇
  2000年   31篇
  1999年   59篇
  1998年   492篇
  1997年   310篇
  1996年   176篇
  1995年   109篇
  1994年   78篇
  1993年   91篇
  1992年   28篇
  1991年   34篇
  1990年   38篇
  1989年   26篇
  1988年   26篇
  1987年   20篇
  1986年   15篇
  1985年   15篇
  1984年   4篇
  1983年   5篇
  1982年   4篇
  1981年   5篇
  1980年   13篇
  1978年   5篇
  1977年   19篇
  1976年   40篇
  1974年   4篇
  1968年   1篇
  1944年   1篇
排序方式: 共有2875条查询结果,搜索用时 0 毫秒
1.
Low temperature wafer direct bonding   总被引:11,自引:0,他引:11  
A pronounced increase of interface energy of room temperature bonded hydrophilic Si/Si, Si/SiO2, and SiO2/SiO 2 wafers after storage in air at room temperature, 150°C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and/or silicon at the interface at temperatures below 110°C and the formation of stronger siloxane bonds above 110°C appear to be the main mechanisms responsible for the increase in the interface energy. After prolonged storage, interface bubbles are detectable by an infrared camera at the Si/Si bonding seam. Desorbed hydrocarbons as well as hydrogen generated by a reaction of water with silicon appear to be the major contents in the bubbles. Design guidelines for low temperature wafer direct bonding technology are proposed  相似文献   
2.
The objectives of this study were to evaluate the possible mechanisms involved in prolongation of bleeding time in pre-eclamptic patients receiving a magnesium sulfate infusion to prevent convulsions. Eighteen pre-eclamptic patients near term or at term (4 cases 33 to 35 weeks; the remainder > 36 weeks) were studied. Fifteen of them received magnesium sulfate infusion; 3 did not and served as controls. Bleeding time (modified Ivy method with Surgicutt), platelet count, platelet aggregation pattern, as well as serum arachidonic acid metabolites [thromboxane B2 (TxB2) and 6-Keto-prostaglandin F1 alpha (6-Keto-PGF1 alpha)] werde done on admission to the labor floor (before magnesium infusion) and repeated at discontinuation of the infusion, 12-24 hours postpartum; the controls received the second test 24 hours postpartum. Thirteen of 15 patients receiving magnesium sulfate had an increase in bleeding time from an average of 6 minutes 31 seconds to 11 minutes 56 seconds, an 82% rise (p < 0.004). In 2 there was a decrease. Among the 3 controls the averages were 6 minutes 38 seconds and 6 minutes 3 seconds. The total magnesium given ranged from 52.5 to 145 grams. Platelet counts averaged 251,000/mm3 (range 145,000-519,000). Platelet aggregation pattern done in 11 patients and was normal and unchanged after magnesium in 10 of the patients with increased bleeding time and one control. TxB2 and 6-Keto-PGF1 alpha levels did not change significantly either after magnesium administration (688 and 135 pgm/ml, to 654 and 117) or in controls (695 and 230 pgm/ml, to 445 and 225). Likewise, the ratio of these 2 substances did not change in either group (6.3 to 6.6, and 4.2 to 2.2). There was no correlation between duration of infusion or total magnesium given and directions of small changes observed. This study confirms a prior preliminary observation that magnesium sulfate infusion, as currently used to prevent eclamptic convulsions, induces a significant prolongation of bleeding time. This effect is mediated neither by changes in platelets count or aggregation pattern, nor by changing the level or ratios of serum arachidonic acid metabolites (TxB2 and 6-Keto-PGF1 alpha). Further studies are needed to clarify the mechanism of this clinically important observation of increased bleeding following magnesium sulfate infusion.  相似文献   
3.
4.
面向企业信息化实现管理现代化   总被引:1,自引:0,他引:1  
为适应社会信息化技术的发展,必须积极推行企业信息化,企业信息化引发管理革命,从而丰富了企业管理现代化的内容。本文论述了上述三方面的内部及演化关系,指出只有面向企业信息化,才能充分实现企业管理现代化。  相似文献   
5.
The effect exerted by transplantation of the 5 day culture of testicles from newly born piglets on the hypogonadal state of mature X-ray irradiated (3 Gy) rats was studied. It has been found that a month after transplantation (two months after irradiation) the hypogonadal state disappeared for a while, which is confirmed by normalization of the weight of seminal vesicles, content of testosterone and biologically active lutropine, restoration of the reproductive function of rats. No significant changes in steroidogenesis activity have been found, which proves a substituent character of transplantation. The effect disappears three months later but certain restoration of the content of nucleic acids in the testicles is observed.  相似文献   
6.
7.
We examined the molecular mechanism of metronidazole resistance by constructing a lambda-Zap II phagemid expression library with genomic DNA from a metronidazole-resistance strain of Helicobacter pylori. Twenty-two clones were found to have elevated MTZ resistances in XLOLR strain of E. coli. Phagemids belonging to the twenty two clones were extracted and then retransformed into the XLOLR strain of E. coli. After MTZ selection, five clones could confer metronidazole resistance consistently. According to Southern hybridization and DNA sequencing, the five clones contained a same locus, recA. In addition, transforming the five clones into BL21 strain of E. coli produced a higher resistance to MTZ. Interestingly, electroporation of one of the five phagemid clones into two MTZ sensitive H. pylori yielded MTZ resistant strains. Comparing amino acid sequence in MTZ resistant with sensitive isolates revealed two point mutations at this locus. Above results suggest that mutation in recA may be associated with metronidazole resistance of H. pylori.  相似文献   
8.
The pre- and postnatal findings of a fetus with a de novo del(13)(pter-->q21:) and an occipital encephalocoele are described. Maternal serum alpha-fetoprotein (AFP) screening at 19 weeks' gestation demonstrated a high level of 2.5 multiples of the median (MOM) and ultrasonography at 27 weeks' gestation showed severe intrauterine growth retardation, cardiomegaly, an occipital encephalocoele, and a calvarial defect. Genetic amniocentesis revealed a karyotype of 46,XX,del(13)(pter-->q21:). The proband postnatally displayed additional abnormalities such as microphthalmia, hypertelorism, large low-set ears, and micrognathia. We discuss the association of central nervous system (CNS) malformations with 13q deletions and emphasize that pregnancies with neural tube defects warrant cytogenetic analysis, especially when additional fetal abnormalities and neonatal dysmorphism are observed.  相似文献   
9.
Tramadol hydrochloride is a centrally acting synthetic analgesic in widespread clinical use. Despite different degrees of opioid-like characteristics in preclinical tests, it is characterized by lack of full naloxone reversibility or naloxone-precipitated withdrawal in humans. To investigate this apparent discrepancy, the present study measured the affinity of tramadol (and its enantiomers) and an active O-desmethyl metabolite (M1) (and its enantiomers) to cloned human opioid receptors of the mu, delta and kappa type stably expressed in HN9.10 neuroblastoma cells. At mu sites, the Ki values for tramadol, its (+) and (-) enantiomers, M1, and its (+) and (-) enantiomers were 17000, 15700, 28800, 3190, 153 and 9680 nM, respectively, compared to 7.1 nM for morphine. These results are consistent with the suggestion of a non-opioid contribution to the clinical profile of tramadol.  相似文献   
10.
BACKGROUND: Aortic aneurysm anatomy is crucial when considering patients for endovascular repair. The aim of this study was to determine the proportion of patients with aortic aneurysm suitable for endovascular repair with three different graft-stent systems. METHODS: Spiral computed tomographic angiography was used to assess the anatomy of 154 abdominal aortic aneurysms. Measurements were made of aneurysm neck length and diameter, renal artery to aortic bifurcation length, common iliac artery diameter and length, and external iliac artery diameter. Aneurysms were assessed for anatomical suitability for currently available aortoaortic, aortobi-iliac and aortouni-iliac devices. RESULTS: Six patients (4 per cent) had a distal aortic neck suitable for implantation of a straight aortic graft. Fifteen patients (10 per cent) had arterial anatomy suitable for implantation of a bifurcated graft and 85 (55 per cent) patients were suitable for endovascular repair with an aortouni-iliac graft. The primary reasons for unsuitability were: proximal neck length less than 1.5 cm (44 patients), proximal neck diameter greater than 3.0 cm (12), and angulation of the proximal neck (three). A further ten patients were considered unsuitable for an aortouni-iliac graft because of bilateral common iliac artery aneurysms (four), tortuous iliac arteries (four) and narrow external iliac arteries (two). CONCLUSION: The aortouni-iliac device has the widest applicability of the currently available endovascular systems but open repair remains the only option for a large proportion of patients.  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