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   286899篇
  免费   6314篇
  国内免费   1062篇
电工技术   4571篇
综合类   231篇
化学工业   43439篇
金属工艺   8875篇
机械仪表   7956篇
建筑科学   7979篇
矿业工程   609篇
能源动力   7987篇
轻工业   33071篇
水利工程   2428篇
石油天然气   2015篇
武器工业   11篇
无线电   35624篇
一般工业技术   52511篇
冶金工业   54841篇
原子能技术   3569篇
自动化技术   28558篇
  2021年   2550篇
  2020年   1997篇
  2019年   2268篇
  2018年   3893篇
  2017年   3878篇
  2016年   4232篇
  2015年   3137篇
  2014年   4892篇
  2013年   14451篇
  2012年   8829篇
  2011年   11615篇
  2010年   8984篇
  2009年   9807篇
  2008年   10593篇
  2007年   10351篇
  2006年   9378篇
  2005年   8380篇
  2004年   8065篇
  2003年   7861篇
  2002年   7281篇
  2001年   7422篇
  2000年   6741篇
  1999年   7338篇
  1998年   18843篇
  1997年   12881篇
  1996年   9625篇
  1995年   7198篇
  1994年   6238篇
  1993年   6102篇
  1992年   4211篇
  1991年   3997篇
  1990年   3781篇
  1989年   3595篇
  1988年   3474篇
  1987年   2774篇
  1986年   2699篇
  1985年   3378篇
  1984年   2993篇
  1983年   2710篇
  1982年   2500篇
  1981年   2558篇
  1980年   2355篇
  1979年   2167篇
  1978年   1994篇
  1977年   2361篇
  1976年   3087篇
  1975年   1677篇
  1974年   1552篇
  1973年   1630篇
  1972年   1196篇
排序方式: 共有10000条查询结果,搜索用时 314 毫秒
41.
The Journal of Supercomputing - Infrastructure-as-a-service container-based virtualization is gaining interest as a platform for running distributed applications. With increasing scale of cloud...  相似文献   
42.
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation.  相似文献   
43.
44.
45.
46.
47.
48.
A contact layer element for large deformations   总被引:1,自引:0,他引:1  
  相似文献   
49.
The selenol group of selenocysteine is much more nucleophilic than the thiol group of cysteine. Selenocysteine residues in proteins thus offer reactive points for rapid post-translational modification. Herein, we show that selenoproteins can be expressed in high yield and purity by cell-free protein synthesis by global substitution of cysteine by selenocysteine. Complete alkylation of solvent-exposed selenocysteine residues was achieved in 10 minutes with 4-chloromethylene dipicolinic acid (4Cl-MDPA) under conditions that left cysteine residues unchanged even after overnight incubation. GdIII−GdIII distances measured by double electron–electron resonance (DEER) experiments of maltose binding protein (MBP) containing two selenocysteine residues tagged with 4Cl-MDPA-GdIII were indistinguishable from GdIII−GdIII distances measured of MBP containing cysteine reacted with 4Br-MDPA tags.  相似文献   
50.
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   
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