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   855篇
  免费   12篇
  国内免费   2篇
电工技术   48篇
综合类   8篇
化学工业   291篇
金属工艺   20篇
机械仪表   16篇
建筑科学   12篇
能源动力   48篇
轻工业   28篇
水利工程   2篇
无线电   58篇
一般工业技术   125篇
冶金工业   147篇
原子能技术   29篇
自动化技术   37篇
  2022年   8篇
  2021年   8篇
  2020年   3篇
  2019年   7篇
  2018年   15篇
  2017年   4篇
  2016年   11篇
  2015年   10篇
  2014年   10篇
  2013年   24篇
  2012年   21篇
  2011年   32篇
  2010年   17篇
  2009年   33篇
  2008年   26篇
  2007年   21篇
  2006年   27篇
  2005年   18篇
  2004年   18篇
  2003年   28篇
  2002年   25篇
  2001年   17篇
  2000年   16篇
  1999年   33篇
  1998年   57篇
  1997年   34篇
  1996年   29篇
  1995年   30篇
  1994年   23篇
  1993年   26篇
  1992年   20篇
  1991年   12篇
  1990年   11篇
  1989年   11篇
  1988年   4篇
  1987年   19篇
  1986年   15篇
  1985年   18篇
  1984年   15篇
  1983年   10篇
  1982年   9篇
  1981年   13篇
  1980年   9篇
  1979年   20篇
  1978年   12篇
  1977年   4篇
  1976年   14篇
  1975年   7篇
  1972年   5篇
  1968年   2篇
排序方式: 共有869条查询结果,搜索用时 15 毫秒
161.
A 71-year-old man was admitted to our hospital with massive GI bleeding and followed by acute myocardial infarction. Severe three vessel coronary artery disease with poor left ventricular performance (EF: 40%) was demonstrated by coronary angiography. He was referred for CABG. He had also cholecystitis, which needed surgical treatment simultaneously. Combined CABG and cholecystectomy were performed without using gastroepiploic artery as a bypass graft, and through separate median sternotomy and through right upper transrectal laparotomy. Postoperative course was uneventful. This combined procedure is beneficial for the patients with acute cholecystitis and unstable angina.  相似文献   
162.
Copper amine oxidase contains an organic redox cofactor, 2,4, 5-trihydroxyphenylalaninequinone (topaquinone, TPQ), derived by the post-translational modification of a specific tyrosyl residue. To identify amino acid residues participating in the biogenesis of TPQ in the recombinant phenylethylamine oxidase from Arthrobacter globiformis, we have modified the copper/TPQ-less apoenzyme and the copper/TPQ-containing holoenzyme with 4-fluoro-7-nitrobenzo-2-oxa-1, 3-diazole (NBD-F). In the apoenzyme modification, the Cu2+-dependent, self-processing formation of the TPQ cofactor was retarded in accordance with the amount of NBD incorporated. The holoenzyme was also rapidly inactivated by incubation with NBD-F. The inactivation was prevented almost completely in the presence of an oxidation product from phenylethylamine, phenylacetaldehyde. Furthermore, the reaction of an inhibitor, phenylhydrazine, with TPQ was much slower in the NBD-labeled holoenzyme than in the native holoenzyme. Sequence analysis of the NBD-labeled holoenzyme has identified Lys184 and Lys354 as the labeled sites. The two Lys residues are located close to the entrance to a channel, which has been found by recent X-ray crystallographic studies to be suitable for the movement of substrates and products to and from the Cu2+/TPQ-active site buried in the protein interior (Wilce, M. C. J., et al. (1997) Biochemistry 36, 16116-16133). However, site-specific mutant enzymes for Lys184, Lys354, and the neighboring invariant His355 had normal capacities for the TPQ formation in apoenzyme. These residues were also found to be dispensable for catalytic activity of holoenzyme. Thus, modification of Lys184 and Lys354 with NBD-F presumably causes structural perturbations of the substrate channel or steric hindrance for the access of small molecules to the active site through the channel.  相似文献   
163.
The relationship between chemical properties of anti-DNA antibodies (Abs) and lupus nephritis was investigated. The anti-DNA Abs in sera from systemic lupus erythematosus (SLE) patients were separated by two-dimensional electrophoresis (2-DE) and immunoblotting with goat anti-human IgG Abs. Highly cationic anti-DNA Abs were detected in deoxyribonuclease I (DNase I)-treated sera from patients with lupus nephritis (in 8 of 9 cases) but not in the sera from SLE patients without nephritis (in 0 of 9 cases), normal subjects, or patients with other renal diseases (in 0 of 7 cases). The mean titers of anti-dsDNA Abs in patients with lupus nephritis were not significantly different from those in SLE patients without nephritis. The highly cationic anti-DNA Abs in the sera disappeared after incubation with heparin-Sepharose. These results suggest that highly cationic anti-DNA Abs are specific for lupus nephritis and may be involved in development of lupus nephritis via the binding to glycosaminoglycans on the endothelial cell surface.  相似文献   
164.
We report herein the case of a 59-year-old woman who developed a local recurrence of rectal cancer which showed extremely rapid growth. The patient had undergone a curative low anterior resection with total mesoexcision, and was discharged on postoperative day 25 after an uneventful recovery. However, 2 months after the operation, she developed bleeding from the rectum during defecation, the quantity of which gradually increased. A colonoscopy performed during the fifth postoperative month revealed a circular tumor at the suture line. The tumor was unresectable because it had firmly invaded not only the sacrum, but also the right ureter. Despite the administration of 5-fluorouracil and leucovorin, the patient died of cancer 18 months after her initial surgery. Considering that local recurrence of rectal cancer does not usually occur within 1 year after surgery, this case is unusual because the local recurrence developed very early and showed extremely rapid growth, occupying the entire lumen of the rectum by the time it was detected by colonoscopy during the fifth postoperative month.  相似文献   
165.
Novel brominated and halogen-less azaphilone (oxoisochromane) derivatives, 5-bromoochrephilone and dechloroisochromophilone IV, and known derivatives, dechloroisochromophilone III and isorotiorin, were isolated from the culture broth of a producing organism of isochromophilones I and II (azaphilones inhibiting gp120-CD4 binding), Penicillium multicolor FO-2338, fermented in a medium containing potassium bromide. Nineteen azaphilone-related compounds isolated from the above strain and from other fungi were tested for the inhibition of gp120-CD4 binding and the structure-activity relationship is discussed. Consequently, 5-bromoochrephilone is the strongest inhibitor (IC50, 2.5 microM). A halogen atom at C-5, a proton at C-8 and a diene structure in C-3 side chain of 6-oxoisochromane ring are necessary for gp120-CD4 binding.  相似文献   
166.
New porous solids from alumina-pillared fluorine micas (APMs), which were obtained from synthetic Na-tetrasilicic fluorine mica [NaMg2.5Si4O10F2], were prepared by sulfuric acid-treatment under mild conditions at 25 °C. The products were investigated by XRD, ICP, SEM, TEM and N2 adsorption–desorption isotherm at 77 K. XRD measurements indicated that the interlayer pillared structure having a large basal spacing collapsed during the early stages of the acid-treatment. ICP analyses indicated that Al3+ and Mg2+ ions were leached out from the pillared micas during the acid-treatment. The pore properties of the leached products were found to differ from those of the mother pillared micas: the acid leaching of the pillared micas leads to the formation of mesopores around 3.2 nm in diameter. The correlation between the change in pore properties and cation elution behavior suggests that the mesopore formation results from the leaching of Mg2+ ions from the octahedral sheet of the pillared micas. The leached products thus obtained retained the flaky morphology of the mother pillared micas. These results show that the mild acid-treatment using APMs provides a novel route for obtaining unique mesopore solids having the large particle sizes of the mother micas.  相似文献   
167.
LEAlB14 (orthorhombic, Imam) (LE = Li, Mg) crystals were grown using metal salts (Li2CO3, LiF, LiI, MgO, MgF2, MgI2) and crystalline boron from a high-temperature aluminium metal flux. The growth conditions for growing LEAlB14 were established using the starting mixtures of B/LE = 2.0, and Al metal was added to each mixture at a mass ratio of 1:15–20. LEAlB14 crystals from the Al-self flux using metal salts could be obtained from all the different salts. The maximum dimensions of LiAlB14 and MgAlB14 crystals were approximately 18 and 12 mm for the crystals obtained from LiF and MgF2. The unit-cell parameters of as-grown LEAlB14 are as follows: for LiAlB14, obtained from LiF, a = 0.5846 (2) nm, b = 0.8144 (2) nm, c = 1.0355 (3) nm, V = 0.4930 (2) nm3: for MgAlB14, obtained from MgF2, a = 0.5845 (2) nm, b = 0.8114 (2) nm, c = 1.0330 (3) nm, V = 0.4899 (3) nm3. Microhardness, oxidation resistance and magnetic susceptibility of these materials are described in detail.  相似文献   
168.
ABSTRACT

Carbon fiber reinforced thermoplastic (CFRTP) has a good electromagnetic shielding property due to its higher conductivity and broad absorption frequency bandwidth while presenting high specific strength and stiffness, their easy process-ability, cost-effectiveness, and recyclability. In the present study, laminated CFRTP made of carbon fiber-polyamide 6 unidirectional tape (UD tape) were fabricated with different laminate configurations and arrangements (unidirectional, bidirectional, and quasi–isotropic) and then were compared with randomly chopped-tape CFRTP. Thereafter, estimated electromagnetic interference shielding effectiveness (EMI-SE) using Simon formalism and flexural properties of CFRTP were evaluated. The result showed a remarkable total EMI-SE of 31–44 dB in the Ultra High Frequency (UHF) range and strongly correlated with the laminate configuration of CFRTP. Whereas, randomly chopped-tape CFRTP has a lower total EMI-SE of 23–27 dB in the same frequency range. In addition, the flexural test result showed the flexural strength and modulus are strongly influenced by the tape layer configuration in the laminated CFRTP. Moreover, microscopy analysis was also conducted to verify the interlaminar structure and fiber-to-fiber contact in the composite. In conclusion, laminated CFRTP made of UD tape can be considered as electromagnetic interference shielding material for both functional and structural applications.  相似文献   
169.
The paper deals with a compensation method of the rotor-resistance variation in induction motor drives using high-performance slip-frequency control. Our proposed method is based on a discrete-type model reference adaptive system (MRAS), and it is implemented in an 8086 microprocessor. When an induction motor is driven by a controlled current source, the system sensitivity to the rotor resistance variation is increased. In the MRAS, the value of the rotor resistance is estimated and the slip-frequency gain is adjusted. Experimental and numerical results show that even if the value of the rotor resistance varies from its nominal value, the secondary flux level is maintained constant by using this compensation method. These results point out the validity of our proposed method.  相似文献   
170.
High-speed operations up to 35 Gb/s were demonstrated for a resonant tunneling (RT) logic gate monostable-bistable transition logic element (MOBILE). The test circuit consisted of a MOBILE and a DCFL-type output buffer, and it was fabricated using InP-based resonant tunneling diode/HEMT integration technology. This operation bit rate is close to the cutoff frequency of the 0.7-μm gate HEMTs used in the circuit, and was obtained after improvement of the output buffer design. This result indicates the high-speed potential of the MOBILE, though the speed is still limited by the buffer. The power dissipation of the MOBILE was also discussed based on a simple equivalent circuit model of RTDs. This revealed that the power dissipation is as small as 2 mW/gate over a wide range of operation bit rates  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