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   677篇
  免费   21篇
  国内免费   4篇
电工技术   19篇
综合类   1篇
化学工业   175篇
金属工艺   23篇
机械仪表   14篇
建筑科学   12篇
能源动力   23篇
轻工业   54篇
水利工程   2篇
无线电   66篇
一般工业技术   124篇
冶金工业   105篇
原子能技术   12篇
自动化技术   72篇
  2023年   8篇
  2022年   12篇
  2021年   11篇
  2020年   4篇
  2019年   10篇
  2018年   14篇
  2017年   8篇
  2016年   17篇
  2015年   15篇
  2014年   21篇
  2013年   33篇
  2012年   31篇
  2011年   38篇
  2010年   24篇
  2009年   35篇
  2008年   28篇
  2007年   32篇
  2006年   25篇
  2005年   22篇
  2004年   22篇
  2003年   16篇
  2002年   24篇
  2001年   13篇
  2000年   13篇
  1999年   19篇
  1998年   30篇
  1997年   31篇
  1996年   14篇
  1995年   15篇
  1994年   10篇
  1993年   19篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1988年   5篇
  1987年   4篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1983年   9篇
  1982年   4篇
  1981年   7篇
  1980年   2篇
  1979年   8篇
  1978年   3篇
  1977年   4篇
  1976年   8篇
  1974年   2篇
  1973年   3篇
排序方式: 共有702条查询结果,搜索用时 156 毫秒
61.
Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
62.
BACKGROUND: We postulated that pathophysiologic processes under nonpulsatile circulation are related to the behavior of the sympathetic nerve activity that regulates tissue perfusion. METHODS: Pulsatile and nonpulsatile pumps were installed in parallel in the left heart bypass circuit of anesthetized goats (n = 9) so that pulsatile circulation could be converted to nonpulsatile circulation instantly. At 5 minutes before and after systemic depulsation, we measured hemodynamic indices, renal nerve activity, and regional blood flow of the brain, heart, and renal cortex. RESULTS: Renal nerve activity was significantly elevated after systemic depulsation (15.6 +/- 9.3 versus 19.4 +/- 9.8 microV), when mean aortic pressure remained almost constant. The renal cortical flow was significantly reduced after depulsation (3.61 +/- 1.23 versus 2.93 +/- 1.19 mL.min-1.g-1), whereas no significant difference was found in the regional blood flow of the brain or the heart. CONCLUSIONS: The significant reduction of renal cortical blood flow after systemic depulsation is associated with a significant increase in renal nerve activity. Our results suggest that increased renal nerve activity plays an important role in the reduction of renal function after systemic depulsation.  相似文献   
63.
The effectiveness of the ab(ad)sorption and the subsequent reduction (abbreviated as ASR hereafter) system for the removal of highly dilute NO has been examined using a flow-type reaction system. The ASR system comprises two serial processes: first, NO is absorbed into (and/or adsorbed on) the system in the presence of O2 until saturation, and then the absorbed NO is decomposed, for example, by reduction at a higher temperature in the presence of propene and oxygen. YBa2Cu3Oy (YBC) and Ce-ZSM-5 were chosen in this study as materials for absorption and reduction, respectively. Efficient removal of NO was attained when the first layer consisting of a mixture of YBC and Ce-ZSM-5 was combined with the second layer of Ce-ZSM-5, and propene was additionally introduced between the two layers during the reductive decomposition. By this ASR system, the amount of NO absorption reached 1.5 mol per mole of YBC at 573 K and 60% of the NO absorbed was selectively decomposed to N2 at 623 K in 9 h (N balance, 75%; N2 selectivity, 79%).  相似文献   
64.
We discuss the properties of comb-like dispersion profiled fiber (CDPF) for an optical soliton transmission. It is found that the CDPF in which the standard single-mode fiber is placed both at the first and at the end of each section is more suitable to reduce dispersive waves if chirp-free transform limited optical pulse is used as a light source. A 10-ps optical soliton transmission experiment is performed in such a CDPF over 1000 km with the amplifier spacing of 80 km that corresponds to 3.1 times the dispersion distance.  相似文献   
65.
A 3-D virtual analysis system to analyze the motion of control rod drive mechanism (CRDM) was developed. The analysis system consists of a 3-D model established as per the actual dimensions and interfaces of CRDM parts and a routine to calculate the forces acting on the mechanism, and was verified by mock-up test using the same equipment as the actual product. The analysis system is useful for functional evaluation in maintenance or to factor out root causes in the case of malfunction of CRDM.  相似文献   
66.
We describe some details of a new experimental setup for torsional oscillator (TO) measurement of $^4$ He monolayers adsorbed on a graphite surface. This setup is designed to seek for the possible supersolid phase, in which crystalline order coexists with superfluidity, in two dimensional (2D) solid $^4$ He below 300 mK. Among such 2D solids, the commensurate phase in the second layer on graphite is the most hopeful candidate for the novel supersolid phase since it is the lowest-density quantum solid ever found. An exfoliated graphite substrate we used is ZYX which has at least ten times longer surface coherence length compared to Grafoil, an exfoliated graphite most commonly used in previous experiments. The first version of TO we made has the resonant frequency of 786.8 Hz and the Q value of $1.1\times 10^5$ at $T \le 10$  mK. The resonant frequency of this particular TO without any He samples ( $f_{\mathrm {cell}}$ ) showed unexpectedly large temperature variation and non-reproducibility below 1 K as well as sudden jumps when mechanical shocks are applied to the experimental apparatus. We found the stability of $f_{\mathrm {cell}}$ is highly correlated with the temperature stability of 1 K pot in dilution refrigerator.  相似文献   
67.
We describe the enantioselective epoxidation of straight‐chain aliphatic alkenes using a biocatalytic system containing styrene monooxygenase from Rhodococcus sp. ST‐10 and alcohol dehydrogenase from Leifsonia sp. S749. The biocatalyzed enantiomeric epoxidation of 1‐hexene to (S)‐1,2‐epoxyhexane (>44.6 mM) using 2‐propanol as the hydrogen donor was achieved under optimized conditions. The biocatalyst had broad substrate specificity for various aliphatic alkenes, including terminal, internal, unfunctionalized, and di‐ and tri‐substituted alkenes. Here, we demonstrate that this biocatalytic system is suitable for the efficient production of enantioenriched (S)‐epoxyalkanes.

  相似文献   

68.
Temperature characteristics of the open-circuit voltage (Voc) were investigated in the temperature range from 30°C to 240°C for the InGaP/InGaAs/Ge triple-junction cells. Also, single-junction cells that had the similar structure to the subcells in the triple-junction cells were studied. In the high-temperature range (from 170°C to 240°C), the temperature coefficients of Voc of the InGaP/InGaAs/Ge triple-junction solar cell (dVoc/dT) were different from those in the low-temperature range (from 30°C to 100°C). This is because photo-voltage from the Ge subcell becomes almost 0 V in the high-temperature range. It was found that the open-circuit voltage of a Ge single-junction cell reduced to almost 0 V temperatures over 120°C under 1 sun condition.  相似文献   
69.
After a laser annealing experiment on Si wafer, we found an asymmetric sheet resistance on the surface of the wafer. Periodic nano-strip grating lines (nano-SGLs) were self-organized along the trace of one-time scanning of the continuous wave (CW) laser. Depending on laser power, the nano-trench formed with a period ranging from 500 to 800 nm with a flat trough between trench structures. This simple method of combining the scanning laser with high scanning speed of 300 m min(-1) promises a large area of nanostructure fabrication with a high output. As a demonstration of the versatile method, concentric circles were drawn on silicon substrate rotated by a personal computer (PC) cooling fan. Even with such a simple system, the nano-SGL showed iridescence from the concentric circles.  相似文献   
70.
The long-term performance of a bioaugmented membrane bioreactor (MBR) containing a GAC-packed anaerobic zone for treatment of textile wastewater containing structurally different azo dyes was observed. A unique feeding strategy, consistent with the mode of evolution of separate waste streams in textile plants, was adopted to make the best use of the GAC-zone for dye removal. Dye was introduced through the GAC-zone while the rest of the colorless media was simultaneously fed through the aerobic zone. Preliminary experiments confirmed the importance of coupling the GAC-amended anaerobic zone to the aerobic MBR and also evidenced the efficacy of the adopted feeding strategy. Following this, the robustness of the process under gradually increasing dye-loading was tested. The respective average dye concentrations (mg/L) in the sample from GAC-zone and the membrane-permeate under dye-loadings of 0.1 and 1 g/L.d were as follows: GAC-zone (3, 105), permeate (0, 5). TOC concentration in membrane-permeate for the aforementioned loadings were 3 and 54 mg/L, respectively. Stable decoloration along with significant TOC removal during a period of over 7 months under extremely high dye-loadings demonstrated the superiority of the proposed hybrid process.  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