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   4577篇
  免费   78篇
  国内免费   7篇
电工技术   216篇
综合类   7篇
化学工业   988篇
金属工艺   110篇
机械仪表   93篇
建筑科学   78篇
能源动力   166篇
轻工业   294篇
水利工程   12篇
石油天然气   9篇
无线电   587篇
一般工业技术   780篇
冶金工业   957篇
原子能技术   103篇
自动化技术   262篇
  2023年   23篇
  2022年   20篇
  2021年   54篇
  2020年   26篇
  2019年   29篇
  2018年   43篇
  2017年   43篇
  2016年   63篇
  2015年   51篇
  2014年   83篇
  2013年   161篇
  2012年   93篇
  2011年   201篇
  2010年   138篇
  2009年   162篇
  2008年   195篇
  2007年   131篇
  2006年   132篇
  2005年   125篇
  2004年   102篇
  2003年   129篇
  2002年   126篇
  2001年   116篇
  2000年   89篇
  1999年   150篇
  1998年   412篇
  1997年   240篇
  1996年   198篇
  1995年   135篇
  1994年   129篇
  1993年   94篇
  1992年   70篇
  1991年   80篇
  1990年   74篇
  1989年   67篇
  1988年   65篇
  1987年   48篇
  1986年   61篇
  1985年   40篇
  1984年   55篇
  1983年   56篇
  1982年   34篇
  1981年   38篇
  1980年   49篇
  1979年   44篇
  1978年   36篇
  1977年   34篇
  1976年   45篇
  1973年   14篇
  1972年   14篇
排序方式: 共有4662条查询结果,搜索用时 796 毫秒
121.
122.
123.
A low speed single barrel pellet injector, using a mechanical punch device has been developed for alternative injection in the large helical device. A pellet is injected by the combined operation of a mechanical punch and a pneumatic propellant system. The pellet shape is cylindrical, 3 mm in diameter and 3 mm in length. Using this technique the speed of the pellet can be controlled flexibly in the range of 100-450 m/s, and a higher speed can be feasible for a higher gas pressure. The injector is equipped with a guide tube selector to direct the pellet to different injection locations. Pellets are exposed to several curved parts with the curvature radii R(c) = 0.8 and 0.3 m when they are transferred in guided tubes to the respective injection locations. Pellet speed variation with pressure at different pellet formation temperatures has been observed. Pellet intactness tests through these guide tubes show a variation in the intact speed limit over a range of pellet formation temperatures from 6.5 to 9.8 K. Pellet speed reduction of less than 6% has been observed after the pellet moves through the curved guide tubes.  相似文献   
124.
Although many neural network controllers have been proposed, we still have to tune several parameters of neural networks in order to obtain a better learning performance in practical applications. Our tracking method provides a new aspect of this tuning of neural network parameters. It has been applied to adaptive and learning-type neural network direct controllers, and an adaptive-type neural network feed-forward feed-back controller. This work applied it to a learning-type neural network feed-forward feed-back controller. Simulation results confirmed its usefulness, and we discuss a transformation of the track on a 2D plane to one-dimensional values.  相似文献   
125.
In some animals, such as mice and guinea pigs, a hormonally controlled mechanism increases the flexibility of the pubic symphysis and enhances the cervical remodeling necessary for safe delivery. Cervical ripening during pregnancy is associated with a paradoxical influx of leukocytes. However, the changes in cell metabolism during relaxation of the mouse pubic symphysis for delivery have not been extensively studied. In this work, we used light microscopy and transmission and scanning electron microcopy, as well as immunohistochemistry and Western blotting for MMP-8, to investigate the involvement of granulocytes or resident stromal cells in the relaxation of the virgin pubic symphysis during late pregnancy (days 18 and 19, before delivery) in vivo and in explanted joints. MMP-8 was studied because this collagenase is a hallmark for cervical ripening associated with the influx of granulocytes during late pregnancy. Extensive dissolution and disorganization of the extracellular matrix was seen around fibroblastic-like cells in late pregnancy. In contrast to the cervix (positive control), morphological and immunohistochemical analyses revealed that there was no characteristic cellular inflammatory response in the interpubic tissue. Staining for MMP-8 was observed in chondroid and fibroblastic-like cells of virgin and relaxed interpubic ligament, respectively. However, no granulocytes were seen during the extensive remodeling of the pubic joint in late pregnancy. These results indicate that constitutive stromal cells may have an important role in tissue relaxation during remodeling of the pubic symphysis in pregnancy.  相似文献   
126.
In an attempt to study "manic-depressive" affairs associated with endocrine and mental disorders, our clinical data are analyzed before and after appropriate treatment in Cushing's disease, Cushing's syndrome, hyperthyroid Graves' disease and primary hypothyroidism. Although our data do not provide definite findings on manic-depressive affairs associated with Cushing's disease and syndrome, review data by others indicated a high incidence of depression under untreated condition and its disappearance after appropriate treatment. In contrast, patients with adrenocortical insufficiency did have a depression but this was cleared after supplemental therapy. In hyperthyroid Graves' disease, a number of emotional and mental instability and irritability were noticed before the treatment, but these abnormalities all disappeared after appropriate treatment for 3-6 months. In contrast, patients with primary hypothyroidism did show lethargy and apathy, and these abnormalities disappeared after appropriate treatment. From the data accumulated, it is concluded that adrenal steroid and thyroid hormone do affect the functions of nervous system and, as a result, cause a number of clinical symptoms. The exact biochemical processes underlying these abnormalities are not known and remains for further investigations.  相似文献   
127.
Large single crystals of (La1–x Ca x )2CaCu2O6 were synthesized by the travelling solvent floating zone (TSFZ) technique. The dimension of the grown boules was typically 4 mm×30 mm long with thec-axis perpendicular to the growth direction. After oxygen loading at 1080°C in 400 atm of O2, they became superconductive with a sharp transition at around 50 K. The resistivity was metallic both along thec-axis and within theab-plane, with an anisotropy ratio of 2( c/ ab ) 50 which is almost independent of temperature. Details of the crystal growth, heat treatment procedures, and the results of electrical and magnetic property measurements are presented.  相似文献   
128.
OBJECTIVE: For resuscitation of hemorrhagic hypovolemia, we compared the effectiveness of (1) isotonic lactated Ringer's solution (LRS), (2) 2400 mOsm of 7.5% NaCl:6% dextran 70 (HSD), and (3) 2400 mOsm of 7.9% sodium acetate:1.9% NaCl:6% dextran 70 (HAD). DESIGN: In six randomized, blinded experiments for each solution, conscious instrumented adult sheep were hemorrhaged by removing approximately 1.8 L (42 +/- 3 mL/kg) of blood, while maintaining the mean arterial pressure (MAP) at 50 mm Hg for 2 hours. METHODS: Test solutions were infused as needed to restore the cardiac index to baseline. RESULTS: Volume requirements with HAD (236 +/- 29 mL) and HSD (244 +/- 39 mL) were significantly less (p < 0.05) than LRS (3463 +/- 234 mL). Mean arterial pressure was normalized with HSD and LRS, but not with HAD, which resulted in MAPs of 20 to 25 mm Hg less than baseline resulting from a reduced peripheral resistance. Oxygen delivery, however, was significantly higher with HAD during the resuscitation period. Acid-base balance (pH) and oxygen consumption were normalized within 5 minutes of infusion only with HAD. CONCLUSIONS: Small-volume infusion with HAD resulting in "high-flow-low-pressure" resuscitation may offer unique hemodynamic and metabolic advantages for the initial treatment of hemorrhage from trauma.  相似文献   
129.
Hydrogen is a promising alternative to fossil fuels that can reduce greenhouse gas emissions. Decoupled water electrolysis system using a reversible proton storage redox mediator, where the oxygen evolution reaction and hydrogen evolution reaction are separated in time and space, is an effective approach to producing hydrogen gas with high purity, high flexibility, and low cost. To realize fast hydrogen production in such a system, a redox mediator capable of releasing protons rapidly is required. Herein, α-MoO3, with an ultrafast proton transfer property that can be explained by a dense hydrogen bond network in the lattice oxygen arrays of HxMoO3, is examined as a high-rate redox mediator for fast hydrogen production in acidic electrolytes. The α-MoO3 redox mediator shows both a large capacity of 204 mAh g−1 and fast hydrogen production at a current rate of 10 A cm−2(≈153 A g−1), outperforming most of the previously reported solid-state redox mediators.  相似文献   
130.
Pouliquen  M.  Denoual  M.  Jorel  C.  Radu  C.  Robbes  D.  Grand  J.  Awala  H.  Mintova  S.  Harnois  M.  Sagazan  O. de  Inoue  S.  Lebrasseur  E.  Yamada  K.  Okamoto  Y.  Mita-Tixier  A.  Mita  Y. 《Microsystem Technologies》2022,28(6):1313-1319
Microsystem Technologies - We demonstrate a new operation mode of thermal gas sensor based on thermal capacity extraction with identification algorithm. The system is a silicon microstructure...  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