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   1459528篇
  免费   26988篇
  国内免费   6903篇
电工技术   34806篇
综合类   6332篇
化学工业   270796篇
金属工艺   65267篇
机械仪表   42930篇
建筑科学   44824篇
矿业工程   11641篇
能源动力   50169篇
轻工业   104219篇
水利工程   14611篇
石油天然气   38190篇
武器工业   138篇
无线电   196945篇
一般工业技术   279574篇
冶金工业   130646篇
原子能技术   34306篇
自动化技术   168025篇
  2021年   15464篇
  2020年   11743篇
  2019年   14508篇
  2018年   17434篇
  2017年   17078篇
  2016年   21884篇
  2015年   17377篇
  2014年   28564篇
  2013年   87793篇
  2012年   34455篇
  2011年   47754篇
  2010年   43689篇
  2009年   52470篇
  2008年   44351篇
  2007年   41854篇
  2006年   43034篇
  2005年   38905篇
  2004年   40625篇
  2003年   40348篇
  2002年   39420篇
  2001年   35569篇
  2000年   34364篇
  1999年   32849篇
  1998年   33749篇
  1997年   32614篇
  1996年   30939篇
  1995年   28067篇
  1994年   26734篇
  1993年   26620篇
  1992年   25563篇
  1991年   22529篇
  1990年   22976篇
  1989年   22074篇
  1988年   20489篇
  1987年   18897篇
  1986年   18206篇
  1985年   21537篇
  1984年   22006篇
  1983年   19946篇
  1982年   19023篇
  1981年   19102篇
  1980年   17673篇
  1979年   18267篇
  1978年   17523篇
  1977年   16845篇
  1976年   16941篇
  1975年   15850篇
  1974年   15393篇
  1973年   15457篇
  1972年   12940篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
321.
Bile acids have been reported as important cofactors promoting human and murine norovirus (NoV) infections in cell culture. The underlying mechanisms are not resolved. Through the use of chemical shift perturbation (CSP) NMR experiments, we identified a low-affinity bile acid binding site of a human GII.4 NoV strain. Long-timescale MD simulations reveal the formation of a ligand-accessible binding pocket of flexible shape, allowing the formation of stable viral coat protein–bile acid complexes in agreement with experimental CSP data. CSP NMR experiments also show that this mode of bile acid binding has a minor influence on the binding of histo-blood group antigens and vice versa. STD NMR experiments probing the binding of bile acids to virus-like particles of seven different strains suggest that low-affinity bile acid binding is a common feature of human NoV and should therefore be important for understanding the role of bile acids as cofactors in NoV infection.  相似文献   
322.
Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.  相似文献   
323.
Combined photochemical arylation, “nuisance effect” (SNAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with SNAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.  相似文献   
324.
This work investigates the performance of the inverted-T (IT) junctionless (JL) FinFET with selective buried oxide (SELBOX) topology. The electrical charac  相似文献   
325.
326.
A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.  相似文献   
327.
The machining of metal surfaces and the application of functional coatings by means of a flexible tool (a rotating wire brush) is considered. Frictional cladding may be applied on metal-cutting machines by means of simple attachments or manual angle grinders.  相似文献   
328.
329.
330.
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