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   725826篇
  免费   11565篇
  国内免费   3648篇
电工技术   14642篇
技术理论   7篇
综合类   2788篇
化学工业   111605篇
金属工艺   28356篇
机械仪表   21596篇
建筑科学   19036篇
矿业工程   4200篇
能源动力   18817篇
轻工业   64574篇
水利工程   7518篇
石油天然气   14410篇
武器工业   370篇
无线电   80822篇
一般工业技术   137395篇
冶金工业   139232篇
原子能技术   14352篇
自动化技术   61319篇
  2022年   4674篇
  2021年   7247篇
  2020年   5230篇
  2019年   6448篇
  2018年   10426篇
  2017年   10260篇
  2016年   10817篇
  2015年   8185篇
  2014年   13056篇
  2013年   33352篇
  2012年   20849篇
  2011年   28193篇
  2010年   22367篇
  2009年   24544篇
  2008年   25552篇
  2007年   25311篇
  2006年   22354篇
  2005年   20014篇
  2004年   18608篇
  2003年   18061篇
  2002年   17499篇
  2001年   17564篇
  2000年   16293篇
  1999年   17119篇
  1998年   42092篇
  1997年   29934篇
  1996年   22886篇
  1995年   17162篇
  1994年   15183篇
  1993年   14726篇
  1992年   10826篇
  1991年   10143篇
  1990年   10026篇
  1989年   9798篇
  1988年   9092篇
  1987年   7991篇
  1986年   7922篇
  1985年   8803篇
  1984年   8354篇
  1983年   7453篇
  1982年   6932篇
  1981年   7155篇
  1980年   6686篇
  1979年   6711篇
  1978年   6433篇
  1977年   7456篇
  1976年   9867篇
  1975年   5681篇
  1974年   5284篇
  1973年   5440篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
This article presents the results of a pilot-study conducted on a small sample of women with breast cancer and the members of their social support system. The purpose was to determine the potential link between the mental health of the breast cancer patient and their support system. Mental health was assessed with the SCL-90-R (Derogatis, 1977), a self-report scale composed of 90 items divided into nine categories, offering three global indicators of distress: the Global Severity Index (GSI); the Positive Symptom Distress Index (PSDI), and the Positive Symptom Total (PST). The SCL-90-R was distributed to a sample of 14 subjects: seven women treated for breast cancer and seven significant others (social support). The results led to the definition of symptoms such as hostility, phobic anxiety and psychosis specific to either the woman or the support system.  相似文献   
142.
This paper focuses on the hydrodynamics of third sound on a superfluid 3 He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range.  相似文献   
143.
The Frizzled genes encode receptors for WNTs, secreted glycoproteins implicated in development as well as in carcinogenesis. In this paper, we report molecular cloning of Hfz6, the human homologue of Mfz6. Nucleotide sequence analysis showed that the Hfz6 gene encodes the 706 amino-acid protein with seven transmembrane domains, a cystein-rich domain in the N-terminal extracellular region, two N-linked glycosylation sites, and two cystein residues in the second and third extracellular loops. Hfz6 mRNA 4.4-kb in size was detected in various normal adult and fetal tissues, and a larger amount of Hfz6 mRNA was detected in both fetal lung and fetal kidney. The Hfz6 gene has been mapped to human chromosome 8q22.3-q23.1. In conclusion, we have cloned Hfz6, which encodes a seven-transmembrane receptor with the cystein-rich domain in the N-terminal extracellular region, but without the Ser/Thr-X-Val motif in the C-terminus.  相似文献   
144.
PURPOSE: We investigated Sertoli cells in testicular biopsies with carcinoma in situ (CIS) in respect to cytokeratin expression to elucidate the status of Sertoli cell differentiation adjacent to CIS in human testes. Cytokeratin 18 intermediate filaments indicate a state of undifferentiation usually observed in Sertoli cells of prepubertal testes. MATERIALS AND METHODS: 29 testicular biopsies presenting CIS were investigated by means of immunohistochemistry, using a polyclonal antibody against placental-alkaline phosphatase to detect CIS cells and a monoclonal antibody against human cytokeratin 18 to show expression of cytokeratin 18 intermediate filaments in Sertoli cells. RESULTS: All tubules bearing CIS showed positive cytokeratin expression of Sertoli cells if tubules were devoid of normal germ cells. However, a total of 13 specimen revealed CIS cells together with normal germ cells. In the presence of CIS cells together with round or elongated spermatids, adjacent Sertoli cells did not express cytokeratin immunoreactivity. In the case of combined presence of CIS and spermatogonia and primary spermatocytes, Sertoli cells could be found either immunopositive or immunonegative, and were positive in tubules with CIS and spermatogonia only. CONCLUSIONS: Sertoli cells associated with CIS cells undergo a process of dedifferentiation, seen by the re-expression of cytokeratin intermediate filaments. We suggest that this dedifferentiation results in a loss of Sertoli cell function and leads to a cessation of spermatogenic activity.  相似文献   
145.
An implicit assumption of several causal reasoning models is that readers adopt the goals of a narrative's protagonist during text comprehension. In apparent violation of this assumption, readers participating in Experiment 1 of the present study drew inferences relevant to a protagonist's goal even when that goal was already satisfied from the perspective of the protagonist. In Experiments 2 and 3, participants were explicitly asked to view the text situation from the point of view of the protagonist. In this case, the goals of the reader and the protagonist should be the same. In these experiments, participants focused on the goals of the protagonist only when those goals had not been satisfied from the perspective of the protagonist. These results are discussed in terms of reader- and character-based perspectives and in terms of text characteristics that cue perspective taking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
146.
147.
148.
The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels  相似文献   
149.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well  相似文献   
150.
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