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   3157篇
  免费   54篇
  国内免费   3篇
电工技术   19篇
综合类   1篇
化学工业   377篇
金属工艺   30篇
机械仪表   80篇
建筑科学   119篇
矿业工程   2篇
能源动力   64篇
轻工业   229篇
水利工程   14篇
石油天然气   3篇
无线电   303篇
一般工业技术   401篇
冶金工业   1247篇
原子能技术   29篇
自动化技术   296篇
  2021年   22篇
  2019年   29篇
  2018年   27篇
  2017年   26篇
  2016年   34篇
  2015年   23篇
  2014年   32篇
  2013年   105篇
  2012年   64篇
  2011年   88篇
  2010年   65篇
  2009年   59篇
  2008年   93篇
  2007年   86篇
  2006年   75篇
  2005年   73篇
  2004年   56篇
  2003年   61篇
  2002年   72篇
  2001年   60篇
  2000年   63篇
  1999年   90篇
  1998年   327篇
  1997年   207篇
  1996年   146篇
  1995年   84篇
  1994年   93篇
  1993年   92篇
  1992年   44篇
  1991年   36篇
  1990年   39篇
  1989年   42篇
  1988年   54篇
  1987年   45篇
  1986年   34篇
  1985年   45篇
  1984年   41篇
  1983年   31篇
  1982年   40篇
  1981年   47篇
  1980年   38篇
  1979年   29篇
  1978年   34篇
  1977年   56篇
  1976年   76篇
  1975年   32篇
  1974年   29篇
  1973年   17篇
  1971年   19篇
  1970年   20篇
排序方式: 共有3214条查询结果,搜索用时 15 毫秒
21.
22.
In a prospective study of adolescent depression, adolescents (N?=?1,508) were assessed at Time 1 and after 1 yr (Time 2) on psychosocial variables hypothesized to be associated with depression. Most psychosocial variables were associated with current (n?=?45) depression. Formerly depressed adolescents (n?=?217) continued to differ from never depressed controls on many of the psychosocial variables. Many of the depression-related measures also acted as risk factors for future depression (n?=?112), especially past depression, current other mental disorders, past suicide attempt, internalizing behavior problems, and physical symptoms. Young women were more likely to be, to become, and to have been depressed. Controlling for the psychosocial variables eliminated the gender difference for current and future but not for past depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
23.
24.
25.
Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation. On the basis of the crystal structure of TGF-beta 2, we have designed and synthesized two mutant TGF-beta s, TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73). Although both of these molecules inhibited the growth of Mv1Lu mink lung epithelial cells and LS1034 colorectal cancer cells, which are affected equally by TGF-beta 1 and TGF-beta 2, TGF-beta 1 (delta 69-73) was much less potent than TGF-beta 1 or TGF-beta 1 (71 Trp) at inhibiting the growth of LS513 colorectal cancer cells which are growth-inhibited by TGF-beta 1 but not TGF-beta 2. Both TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73) increased levels of mRNAs for fibronectin and plasminogen activator inhibitor with Mv1Lu cells, whereas only TGF-beta 1 (71 Trp) and not TGF-beta 1 (delta 69-73) up-regulated the mRNA level of carcinoembryonic antigen in LS513 cells. The expression level of carcinoembryonic antigen mRNA in LS1034 cells was not altered by either wild-type or mutant TGF-beta s. Receptor labeling experiments demonstrated that TGF-beta 1 (71 Trp) bound with high affinity to the cell-surface receptors of Mv1Lu, LS1034, and LS513 cells while TGF-beta 1 (delta 69-73) bound effectively to the receptors of Mv1Lu and LS1034 cells but much less to the receptors on LS513 cells.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
26.
PURPOSE: The phenoxyacetic acid, ethacrynic acid (ECA), has potential use in glaucoma therapy because it acts to increase aqueous outflow in vivo and in vitro. In human trabecular meshwork (HTM) cell culture, ECA acts to change cell shape and attachment, effects that have been correlated with microtubule (MT) alterations and chemical sulfhydryl (SH) reactivity. To further explore these actions, we evaluated two non-SH reactive phenoxyacetic acids, inadcrinone and ticrynafen, and the MT-disrupting drug vinblastine. METHODS: Excised bovine and porcine eyes were perfused and outflow facility measured. Calf pulmonary artery endothelial and HTM cells were grown in culture and cytoskeletal effects evaluated after drug treatment. RESULTS: Indacrinone, ticrynafen, and vinblastine all caused an increase in outflow facility. In contrast with ECA, the outflow effects of indacrinone and ticrynafen were not blocked by excess cysteine. Although indacrinone and ticrynafen produced changes in cell shape in vitro, the beta-tubulin staining pattern of treated cells was not altered. Vinblastine caused cell shape change and the expected MT disruption. CONCLUSIONS: Phenoxyacetic acids can increase aqueous outflow facility and alter HTM cell shape and attachment in vitro by a non-SH, non-MT mechanism (which is probably shared also by ECA). These findings suggest the possibility of a broader class of glaucoma drugs that may be directed at the HTM. An understanding of the cellular target for these drugs has implications both for potential glaucoma therapy and for the cytoskeletal mechanisms involved in normal outflow function.  相似文献   
27.
28.
29.
The authors examine some key data processing applications to be used in conjunction with the voice and facsimile services as a platform for deploying ISDN (integrated services digital network) in North America. Special emphasis is placed on the emerging standards of both Accredited Standards Committees (ACS) T1 and X3 in an attempt to harmonize the computer and telecommunication industries towards providing the user with an integrated platform that is vendor-transparent and ubiquitous. This generic platform, which spans a large spectrum of businesses, is presented as a base context for defining user-specific needs and incubating the applications that directly relate to businesses. Distributed transaction processing, electronic data interchange, information retrieval, electronic mail, and file transfer together with seven supplementary services for voice and G4 facsimile are proposed for ISDN deployment in the marketplace. The authors describe how the relevant standards may be exercised through the various ISDN channels and emphasize the value of the North American ISDN User's Forum for commercializing this platform  相似文献   
30.
Deuterated scintillators (NE230) can provide, without time-of-flight, usable neutron energy spectra for neutrons E n⩾1 MeV. The authors have assembled and calibrated several of these detectors and used them in experiments searching for d+d fusion-neutron emission (En, 2.5 MeV) in Pd+D 2O electrolysis and Ti+D2 adsorption at LN temperatures. The detectors yielded direct fusion-neutron spectra and set limits in the Pd+D and Ti+D experiments of <7×10-24 fusion n/s/dd pair and <3×10-24 fusion n/s/dd pair respectively. In addition, these detectors have been used for in-beam accelerator experiments requiring coincidence between fast neutrons and scattered ions  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