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   2083篇
  免费   32篇
  国内免费   5篇
电工技术   79篇
综合类   2篇
化学工业   452篇
金属工艺   92篇
机械仪表   50篇
建筑科学   32篇
能源动力   103篇
轻工业   131篇
水利工程   1篇
石油天然气   2篇
无线电   174篇
一般工业技术   398篇
冶金工业   385篇
原子能技术   62篇
自动化技术   157篇
  2022年   12篇
  2021年   20篇
  2020年   11篇
  2019年   13篇
  2018年   26篇
  2017年   20篇
  2016年   32篇
  2015年   8篇
  2014年   29篇
  2013年   97篇
  2012年   65篇
  2011年   86篇
  2010年   82篇
  2009年   71篇
  2008年   78篇
  2007年   77篇
  2006年   77篇
  2005年   55篇
  2004年   61篇
  2003年   73篇
  2002年   60篇
  2001年   61篇
  2000年   44篇
  1999年   42篇
  1998年   150篇
  1997年   83篇
  1996年   80篇
  1995年   54篇
  1994年   49篇
  1993年   54篇
  1992年   31篇
  1991年   34篇
  1990年   25篇
  1989年   21篇
  1988年   26篇
  1987年   18篇
  1986年   29篇
  1985年   28篇
  1984年   24篇
  1983年   26篇
  1982年   29篇
  1981年   23篇
  1980年   21篇
  1979年   17篇
  1978年   16篇
  1977年   21篇
  1976年   18篇
  1975年   8篇
  1974年   5篇
  1970年   5篇
排序方式: 共有2120条查询结果,搜索用时 31 毫秒
121.
122.
Given the multiple impairments in host defense that occur during HIV infection, patients with AIDS are at risk for a variety of pleural infections and neoplasms. Of infectious causes, bacterial parapneumonic effusions and empyemas and tuberculous pleurisy occur more frequently than effusions caused by P. carinii. In each case, therapy is directed at eradication of the causative organisms. In the setting of systemic Kaposi's sarcoma, pleural involvement is common, although diagnosis is difficult and therapeutic options are limited. Pleural effusions caused by non-Hodgkin's lymphoma often occur in the setting of pulmonary parenchymal disease and can be diagnosed cytologically. The recently described entity of primary effusion lymphoma occurs in the absence of solid-organ involvement. The development of a spontaneous pneumothorax in a HIV-infected individual should prompt a search for P. carinii infection. Although these pneumothoraces often recur and are difficult to manage, recent series suggest that surgical approaches to bronchopleural fistulas are reasonable in selected patients.  相似文献   
123.
In order to investigate the relationship between various temporomandibular joint (TMJ) pain levels and the detection of high signal intensity (joint effusion) on T2 weighted magnetic resonance imaging (MRI), 19 consecutive patients who complained of unilateral painful TMJ hypomobility (closed locking) were involved in this study. All patients were clinically examined in a routine manner, and all patients rated their pain levels by a visual analogue scale and eight pain questionnaire prior MRI study. T1 and T2 weighted MRI was taken in sagittal section at unilateral affected joint side. The presence or absence of a high signal intensity spot within the TMJ compartment were judged by three examiners. The high signal intensity was detected in 10 joints, but not in 9 joints. In between these two groups, the pain ratio was calculated and compared. The data showed that there was no significant statistical correlation between pain levels and the presence of high signals. This study disclosed that the MRI detection of high signal intensity in the closed locking TMJ did not directly relate to the presence of TMJ pain nor the increased pain level. These indicate the need of further larger studies.  相似文献   
124.
125.
o-Nitrophenyl sulfenyl-modified ACTH (NPS-ACTH) stimulated steroidogenesis acutely in bovine fasciculata-reticularis cells without increase in cellular cAMP synthesis. Application of NPS-ACTH to the cultured cells induced Ca2+ signals in individual cells as detected by video-enhanced microscopic fluorescence measurements. The percentage of Ca2+ signaling cells corresponded well with the increase of steroidogenesis induced by NPS-ACTH below 1 nM. Treatment of the cells with nicardipine, a Ca2+ channel blocker, suppressed the Ca2+ signals except for the transient increase just after the addition of NPS-ACTH and also blocked completely the stimulative effect on the steroidogenesis of NPS-ACTH below 1 nM. At a dosage of NPS-ACTH higher than 10 nM, the stimulative effect of steroidogenesis was partly suppressed by nicardipine and also by AA-861, a lipoxygenase inhibitor. The action of NPS-ACTH might be mediated by both Ca2+ and lipoxygenase metabolite(s) of arachidonic acid as dual second messengers. The effect of ACTH in pM range on the steroidogenesis was suppressed completely by the treatment with nicardipine and AA-861 at the same time, indicating that the action was mediated by both Ca2+ and the lipoxygenase metabolite(s) but not by cAMP. cAMP plays a significant role as a second messenger for ACTH action only at ACTH concentrations greater than 10 pM.  相似文献   
126.
It is important to determine what kind of antigen is involved in atopic asthma for appropriate management as well as diagnosis. We can measure total IgE and antigen specific IgE antibodies by means of RIA and EIA in vitro. Antigen specific IgE antibodies can be detected more sensitively by skin tests consisting of intradermal, prick and scratch tests, among which the intradermal test is most sensitive. To study if the antibody thus detected is functional, there are in vivo tests such as the provocation test and eye reaction with the corresponding antigen and in vitro tests such as the histamine release assay and CAST. In Japan we tend to prefer in vitro assays, while the skin test has been recommended more than in vitro assays in the United States.  相似文献   
127.
The properties of high-field domains in GaxIn1-xSb Gunn diodes (0.4 < x < 0.82) have been studied by measuring the surface potential on the diodes. The domain velocities vary with the Ga composition x, 5.3?6.1×106 cm/s for0.8 > x > 0.55 and 10×106 cm/s for x = 0.4, but they are almost independent of the applied voltage, even if the electron concentration is increased by the impact ionisation in the domain at high applied voltages for the small-x samples.  相似文献   
128.
Transparent La0.33NbO3 flakes were fabricated by a rapid quenching technique. The quenched La0.33NbO3 phase takes a simple cubic perovskite structure and cation vacancies are randomly distributed on the A sites. The cubic La0.33NbO3 phase is a new modification which is different from the well-known orthorhombic phase with ordered A-site vacancies. Transparent flakes were found to show the predominant orientation of (110) and (220) planes.  相似文献   
129.
Comparison between a petroleum energy system and a solar-hydrogen energy system is studied in the case where an industry is newly introduced to an isolated island. Assuming a hybrid energy system composed of petroleum, solar energy, hydrogen energy and electric energy, we investigate an optimum economy with the use of computer-aided LP (Linear Programming) and QP (Quadratic Programming) models taking account of the cost functions originated from the acquisition prices of the primary energy and the transport prices. Furthermore, the modified LP model makes it possible to take account of the uncertainties arising from the acquisition instability and environmental protection. Some conditions are clarified under which the introduction of a solar-hydrogen energy system is highly feasible.  相似文献   
130.
Summary The chlorine in poly(epichlorohydrin) was found to be substituted by diethyldithiocarbamate (ETC) group by the reaction with NaETC in tetrahydrofuran at 60°C. The reaction product was analyzed by RI-UV dual-detector GPC. The composition i.e. the percentage of the chlorine replaced by the ETC group was found to be invariant with the elution count. This result might indicate the absence of polymer effect in the carbamation of poly(epichlorohydrin).  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