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   3866篇
  免费   61篇
  国内免费   1篇
电工技术   84篇
综合类   1篇
化学工业   410篇
金属工艺   20篇
机械仪表   37篇
建筑科学   47篇
矿业工程   2篇
能源动力   25篇
轻工业   107篇
水利工程   9篇
石油天然气   5篇
无线电   335篇
一般工业技术   417篇
冶金工业   1826篇
原子能技术   29篇
自动化技术   574篇
  2021年   28篇
  2020年   21篇
  2019年   32篇
  2018年   29篇
  2017年   33篇
  2016年   20篇
  2015年   31篇
  2014年   23篇
  2013年   132篇
  2012年   64篇
  2011年   82篇
  2010年   87篇
  2009年   85篇
  2008年   94篇
  2007年   74篇
  2006年   82篇
  2005年   68篇
  2004年   48篇
  2003年   74篇
  2002年   76篇
  2001年   68篇
  2000年   55篇
  1999年   108篇
  1998年   433篇
  1997年   268篇
  1996年   195篇
  1995年   150篇
  1994年   135篇
  1993年   138篇
  1992年   66篇
  1991年   54篇
  1990年   76篇
  1989年   62篇
  1988年   66篇
  1987年   49篇
  1986年   67篇
  1985年   68篇
  1984年   40篇
  1983年   49篇
  1982年   45篇
  1981年   51篇
  1980年   37篇
  1979年   27篇
  1978年   38篇
  1977年   56篇
  1976年   105篇
  1975年   26篇
  1974年   31篇
  1972年   21篇
  1970年   18篇
排序方式: 共有3928条查询结果,搜索用时 15 毫秒
1.
2.
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well.  相似文献   
3.
4.
This paper describes a fully integrated digital-spread spectrum transceiver chip fabricated through MOSIS in 1.2 μm CMOS. It includes a baseband spread spectrum transmitter and a coherent intermediate frequency (IF) receiver consisting of a Costas loop, an acquisition loop for the pseudo-noise (PN) sequence, and a clock recovery loop with a 406.4 MHz onchip numerically controlled oscillator (NCO). The transceiver is capable of operating at a maximum IF sampling rate of 50.8 MS/s and a maximum chip rate of 12.7 R Mchips/s (Mcps) with selectable data rates of 100, 200, 400, and 800 kbps. At the maximum operating speed of 50.8 R MS/s, it dissipates 1.1 W. In an additive white Gaussian noise channel the IF receiver achieves a receiver output SNR within 1 dB of theory and can acquire code with a wide range of input SNR from -17 dB to over 30 dB. The transceiver chip has been interfaced to an RF up/down converter to demonstrate a wireless voice/data/video link operating in the 902-928 MHz band  相似文献   
5.
The purpose of this study is to present three patients with multifocal primary neuroblastoma, to review the literature, and describe the radiographic findings. SUBJECTS AND METHODS: Three children with multifocal neuroblastoma have been identified. The case histories and imaging findings in these patients are reviewed. RESULTS: Two children had synchronous and one child had metachronous multifocal primary neuroblastoma. The primary tumors were both in the abdomen in one patient, both in the chest in another patient, and in the chest and abdomen in the third patient. Evidence for multifocal origin of these tumors, rather than metastatic spread, is presented. CONCLUSION: Multifocal primary neuroblastomas can occur. The tumors maybe synchronous or metachronous. Awareness of this disorder may prevent errors in diagnosis and staging. Although not identified in our patients there is a strong familial incidence of neuroblastomas in those patients with multifocal tumors.  相似文献   
6.
A predictive analogy of turbulent mass transfer across wavy, sheared air-water interface, in deep water bodies is proposed. The theory is based on the formulation of a theoretical eddy diffusivity profile in the surface region, and it applies to the non-breaking wave regime. The predictions for a water-side friction velocity range of 0.5–6 cm/s are in excellent agreement with laboratory data from wind-wave facilities with an average error of 15.4%.  相似文献   
7.
8.
9.
This study examined the degree to which different types of communication disturbances in the speech of 48 schizophrenia patients and 28 controls were variable and state related versus stable and traitlike. Clinically rated formal thought disorder and 5 types of referential disturbance showed substantial stability within participants over time. The sixth type of referential disturbance, the vague reference, was not stable over time. Formal thought disorder was associated with the severity of core psychotic symptoms in patients, whereas referential disturbances showed little or no association with positive or negative symptom severity. Furthermore, changes in psychotic symptoms over time were accompanied by corresponding changes in formal thought disorder but not referential disturbances. These results support the idea that some types of referential disturbances are traitlike and may be reflective of vulnerability as well as manifest illness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
10.
Four experiments examined 10-mo-old infants' causal event perception. Exp 1 replicated previous studies except that the specific objects used as agent and recipient varied from trial to trial. Under these conditions infants did not process the causality. Instead they keyed on specific temporal and spatial differences among the events. Exp 2 showed that infants notice a change in the particular agent performing either a causal or noncausal action. Exp 3 showed that infants do not notice a change in the type of action done to a particular recipient. Exp 4 demonstrated that infants do not pay attention to the object used as a recipient. As a whole, the results indicate that 10-mo-old infants perceive the causality of simple events by associating a specific agent with the causal action. These results provide more support for an information-processing view than for the view that infants have a causal module. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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