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   410722篇
  免费   7944篇
  国内免费   2944篇
电工技术   8723篇
技术理论   2篇
综合类   2599篇
化学工业   63163篇
金属工艺   14771篇
机械仪表   13357篇
建筑科学   13297篇
矿业工程   1803篇
能源动力   11223篇
轻工业   44072篇
水利工程   3489篇
石油天然气   4958篇
武器工业   209篇
无线电   53205篇
一般工业技术   73172篇
冶金工业   69121篇
原子能技术   5555篇
自动化技术   38891篇
  2022年   2286篇
  2021年   3805篇
  2020年   2795篇
  2019年   3202篇
  2018年   4355篇
  2017年   4594篇
  2016年   4888篇
  2015年   4330篇
  2014年   6781篇
  2013年   19453篇
  2012年   11270篇
  2011年   15562篇
  2010年   12323篇
  2009年   13561篇
  2008年   14449篇
  2007年   14584篇
  2006年   13543篇
  2005年   12319篇
  2004年   11458篇
  2003年   11102篇
  2002年   10621篇
  2001年   10853篇
  2000年   10064篇
  1999年   10782篇
  1998年   22707篇
  1997年   16439篇
  1996年   12989篇
  1995年   10140篇
  1994年   8970篇
  1993年   8566篇
  1992年   6570篇
  1991年   6177篇
  1990年   5851篇
  1989年   5692篇
  1988年   5396篇
  1987年   4487篇
  1986年   4337篇
  1985年   5346篇
  1984年   4793篇
  1983年   4448篇
  1982年   4156篇
  1981年   4109篇
  1980年   3812篇
  1979年   3646篇
  1978年   3392篇
  1977年   3993篇
  1976年   4989篇
  1975年   2945篇
  1974年   2707篇
  1973年   2776篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal  相似文献   
54.
The transjugular intrahepatic portosystemic shunt procedure is an accepted treatment for adults with complications of portal hypertension. We performed a retrospective review of all pediatric TIPS placements performed at the University of California, San Francisco between 1990 and 1996. Twelve procedures were attempted in nine children, with a mean age (+/- SD) of 9.4 +/- 3.9 years (range, 5 to 15 years) and a mean weight of 31 +/- 18 kg (range, 16 to 70 kg). The indications for TIPS placement were portal hypertension complicated by chronic variceal hemorrhage not controlled with sclerotherapy (n = 7) and hypersplenism with thrombocytopenia (n = 2). TIPS placement was successfully completed initially in seven of nine (78%) patients. Unfavorable vascular anatomy was the cause of failure in two cases. The seven patients who underwent successful TIPS placement were followed up for an average of 136 days (range, 1 to 800 days); two still have patent shunts, three underwent liver transplantation, one had a splenorenal shunt after stenosis, and one died of underlying liver disease. Variceal bleeding was controlled in four of five patients who successfully underwent TIPS placement. Shunt occlusion occurred in four patients; patency was restored by transjugular shunt revision in three, and a splenorenal shunt was performed in one.  相似文献   
55.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel.  相似文献   
56.
57.
A case of traumatic extracranial vertebral arterial dissection leading to vertebrobasilar thrombosis and respiratory compromise requiring mechanical ventilation was managed with intraarterial thrombolysis and stenting of the vertebral intimal dissection. In contrast to similar, previously reported cases, this critically ill patient made a full recovery, returning to his job as a secondary school teacher.  相似文献   
58.
A subpopulation of rabbit polyclonal anti-idiotypic antibody (anti-Id) was previously produced to a murine monoclonal antibody (mAb) (M1875) specific for the bluetongue virus core protein VP7. In this report, mimicry of VP7 by this anti-Id (designated RAb2-A) was functionally analyzed through immunization of Balb/c mice with RAb2-A or purified VP7. Animals immunized with RAb2-A were able to produce an M1875-like Ab3 antibody response with idiotype and epitope specificity resembling that of M1875 without subsequent exposure to the nominal antigen. This conclusion was supported by experiments showing that the RAb2-A-induced Ab3 antibodies (i) reacted specifically with the immunizing anti-Id; (ii) were capable of binding VP7; (iii) inhibited M1875 from binding to VP7; and (iv) inhibited M1875 from binding to RAb2-A. Similarly, mice immunized with purified VP7 also produced antibodies that exhibited characteristics such as idiotype and epitope specificity in common with M1875. No antibody response to VP7 was detected in control groups of mice immunized with either normal rabbit IgG or BHK-21 cell components. Therefore, it can be concluded that rabbit anti-Id RAb-2-A mimics an M1875-defined VP7 epitope sufficiently to function as a surrogate antigen for inducing an anti-bluetongue virus response.  相似文献   
59.
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay.  相似文献   
60.
In a prospective study we found good results concerning postoperative complications (21%), perioperative lethality (3.2%) and lethality during hospital stay (6.5%) after implantation of dynamic hip screws (DHS) in patients with per- and subtrochanteric fractures of the femur. The ability to walk, as well as housing and social care postoperatively and follow-up for at least six months after dismissal demonstrates the importance of these fractures for the elderly. One of three patients needs professional care, 21% at home, 13% in nursing homes. Six months after operation the lethality is nearly 20%, i.e. three times higher than in hospital. These are the essential data for all techniques of osteosynthesis used in patients with these fractures, which could only be documented in prospective studies.  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