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   3669篇
  免费   115篇
  国内免费   2篇
电工技术   31篇
综合类   1篇
化学工业   704篇
金属工艺   51篇
机械仪表   33篇
建筑科学   190篇
矿业工程   6篇
能源动力   63篇
轻工业   577篇
水利工程   28篇
石油天然气   10篇
无线电   177篇
一般工业技术   555篇
冶金工业   957篇
原子能技术   30篇
自动化技术   373篇
  2023年   18篇
  2022年   33篇
  2021年   86篇
  2020年   50篇
  2019年   39篇
  2018年   69篇
  2017年   60篇
  2016年   69篇
  2015年   53篇
  2014年   79篇
  2013年   193篇
  2012年   189篇
  2011年   203篇
  2010年   184篇
  2009年   173篇
  2008年   188篇
  2007年   182篇
  2006年   136篇
  2005年   140篇
  2004年   119篇
  2003年   123篇
  2002年   105篇
  2001年   64篇
  2000年   55篇
  1999年   73篇
  1998年   120篇
  1997年   111篇
  1996年   99篇
  1995年   72篇
  1994年   67篇
  1993年   54篇
  1992年   46篇
  1991年   39篇
  1990年   45篇
  1989年   41篇
  1988年   25篇
  1987年   36篇
  1986年   35篇
  1985年   33篇
  1984年   26篇
  1983年   18篇
  1982年   28篇
  1981年   14篇
  1980年   26篇
  1979年   20篇
  1978年   14篇
  1977年   21篇
  1976年   25篇
  1975年   11篇
  1973年   11篇
排序方式: 共有3786条查询结果,搜索用时 78 毫秒
71.
Allowing users to actively participate in the development and implementation of a new IS is supposed to increase their satisfaction with it. This type of participation, representing aspects relating to distributive and procedural justice, is increasingly impractical in current organizational settings, because many IS are used by thousands of employees and having them involved is impossible. Nonetheless, there are still benefits to be gained in other ways. Extrapolating from interactional justice, we proposed a passive participation method of engaging users. Its effect was tested in a large company in the USA and proved effective. Interactional justice, the perception of fairness in the way that people were treated at an interpersonal level, was found to increase user assessment of the value of their IS. Implications and expansions to interactional justice theory and how this antecedent affects IS implementation are discussed.  相似文献   
72.
Understanding the world we live in requires access to a large amount of background knowledge: the commonsense knowledge that most people have and most computer systems don't. Many of the limitations of artificial intelligence today relate to the problem of acquiring and understanding common sense. The Open Mind Common Sense project began to collect common sense from volunteers on the Internet starting in 2000. The collected information is converted to a semantic network called ConceptNet. Reducing the dimensionality of ConceptNet's graph structure gives a matrix representation called AnalogySpace, which reveals large-scale patterns in the data, smoothes over noise, and predicts new knowledge. Extending this work, we have created a method that uses singular value decomposition to aid in the integration of systems or representations. This technique, called blending, can be harnessed to find and exploit correlations between different resources, enabling commonsense reasoning over a broader domain.  相似文献   
73.
As computer technologies become increasingly ubiquitous, so must supporting digital forensics tools and techniques for efficiently and effectively analyzing associated systems' behavior. Live analysis is a logical and challenging step forward in this area and a method that has recently received increased R&D focus. This article describes some live analysis approaches as well as tools and techniques for live analysis on real and virtual machines. The discussion includes research challenges and open problems.  相似文献   
74.
One of the major stumbling blocks that prevents rapid structure determination using x-ray crystallography is macromolecular crystal growth. There are many examples where crystallization takes longer than structure determination. In some cases, it is impossible to grow useful crystals on earth. Recent experiments conducted in conjunction with NASA on various Space Shuttle missions have demonstrated that protein crystals often grow larger and display better internal molecular order than their earth-grown counterparts. This paper reports results from three Shuttle flights using the Protein Crystallization Facility (PCF). The PCF hardware produced large, high-quality insulin crystals by using a temperature change as the sole means to affect protein solubility and thus, crystallization. The facility consists of cylinders/containers with volumes of 500, 200, 100, and 50 ml. Data from the three Shuttle flights demonstrated that larger, higher resolution crystals (as evidenced by x-ray diffraction data) were obtained from the microgravity experiments when compared to earth-grown crystals.  相似文献   
75.
The objective of this paper is to propose an architecture for aCAble TeleVision (CATV) network, capable of supporting two-way transmission. This evolution is necessary for the survival of the CATV industry in an era of deregulation and of the development of the B-ISDN by the telecommunications companies. A communication transactional service is then considered and performance analysis is done under realistic assumptions.  相似文献   
76.
We have reported that acute cardiac allograft rejection is associated with increased numbers of donor-reactive helper T lymphocytes (HTL) in the peripheral blood of patients. Further, increased frequencies of circulating donor-reactive HTL may predict allograft rejection episodes diagnosed by endomyocardial biopsy. The present study evaluates the relationship between donor-reactive HTL and allograft "acceptance" in cardiac transplant recipients bearing long-term allografts (> 1 year). Patients were categorized as either long-term acceptors or persistent rejecters based on the number of rejection episodes and the ability to withdraw steroid therapy. Limiting dilution analysis for IL-2-producing HTL was utilized, with cadaver donor splenocytes as a source of donor alloantigens. Donor-reactive HTL frequencies were determined from peripheral blood samples obtained before transplant, and at 1 month and 1 year after transplant. Individuals who accommodated their allografts and were withdrawn from steroid therapy had reduced numbers of donor-reactive HTL at 1 year after transplant as compared with earlier time points. Further, PBMC obtained from these individuals at 1 year after transplant responded weakly to donor alloantigens in a mixed lymphocyte response (MLR). This relationship between donor-reactive HTL and allograft accommodation was exemplified in a cardiac/liver transplant patient who was diagnosed with progressive multifocal leukoencephalopathy and removed from all immunosuppression. No subsequent rejection episodes were diagnosed. Donor-reactive HTL were not detectable and this individual failed to mount an MLR to donor alloantigens. However, a vigorous donor-reactive response was observed when MLR cultures were supplemented with exogenous IL-2. Therefore, nonresponsiveness to the allograft appeared to be due to a deficit in IL-2 production. In contrast, patients who experienced persistent rejection episodes and required continued steroid therapy maintained large numbers of donor-reactive HTL at 1 year after transplant. PBMC from these individuals responded vigorously to donor alloantigens in an MLR. Hence, monitoring donor-reactive HTL may identify individuals who have accommodated their graft and may tolerate a reduction in immunosuppression.  相似文献   
77.
Deterministic lateral displacement (DLD) devices enable to separate nanometer to micrometer‐sized particles around a cutoff diameter, during their transport through a microfluidic channel with slanted rows of pillars. In order to design appropriate DLD geometries for specific separation sizes, robust models are required to anticipate the value of the cutoff diameter. So far, the proposed models result in a single cutoff diameter for a given DLD geometry. This paper shows that the cutoff diameter actually varies along the DLD channel, especially in narrow pillar arrays. Experimental and numerical results reveal that the variation of the cutoff diameter is induced by boundary effects at the channel side walls, called the wall effect. The wall effect generates unexpected particle trajectories that may compromise the separation efficiency. In order to anticipate the wall effect when designing DLD devices, a predictive model is proposed in this work and has been validated experimentally. In addition to the usual geometrical parameters, a new parameter, the number of pillars in the channel cross dimension, is considered in this model to investigate its influence on the particle trajectories.  相似文献   
78.
79.
A 53-year-old man died of sporadic Creutzfeldt-Jakob disease (CJD) after a 1.5-year clinical course. Four and a half years later, his then 55-year-old widow died from CJD after a 1-month illness. Both patients had typical clinical and neuropathologic features of the disease, and pathognomonic proteinase-resistant amyloid protein ("prion" protein, or PrP) was present in both brains. Neither patient had a family history of neurologic disease, and molecular genetic analysis of their PrP genes was normal. No medical, surgical, or dietary antecedent of CJD was identified; therefore, we are left with the unanswerable alternatives of human-to-human transmission or the chance occurrence of sporadic CJD in a husband and wife.  相似文献   
80.
Thin and thick YBCO Films have been grown by Aerosol Assisted as well as by thermal MOCVD. The Aerosol Assisted MOCVD technique allows the growth of YBCO films from a single liquid source at deposition rates of up to 10m/h.Transport measurements (I-V) on etched microbridges using a single pulse technique have been performed. The angular magnetic field dependence Jc() of the critical current density from Tc down to 50 K has been measured. Transport properties are reported and discussed with respect to the microstructural features as determined by X-ray diffraction and electron microscopy.  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