全文获取类型
收费全文 | 113774篇 |
免费 | 2565篇 |
国内免费 | 439篇 |
专业分类
电工技术 | 1078篇 |
综合类 | 2369篇 |
化学工业 | 18000篇 |
金属工艺 | 5271篇 |
机械仪表 | 3568篇 |
建筑科学 | 3988篇 |
矿业工程 | 636篇 |
能源动力 | 1958篇 |
轻工业 | 6203篇 |
水利工程 | 1554篇 |
石油天然气 | 506篇 |
武器工业 | 3篇 |
无线电 | 11371篇 |
一般工业技术 | 21898篇 |
冶金工业 | 7783篇 |
原子能技术 | 456篇 |
自动化技术 | 30136篇 |
出版年
2023年 | 252篇 |
2022年 | 348篇 |
2021年 | 689篇 |
2020年 | 506篇 |
2019年 | 594篇 |
2018年 | 14981篇 |
2017年 | 13892篇 |
2016年 | 10716篇 |
2015年 | 1399篇 |
2014年 | 1239篇 |
2013年 | 2095篇 |
2012年 | 4736篇 |
2011年 | 11345篇 |
2010年 | 9631篇 |
2009年 | 6895篇 |
2008年 | 8390篇 |
2007年 | 9242篇 |
2006年 | 1546篇 |
2005年 | 2408篇 |
2004年 | 2188篇 |
2003年 | 2086篇 |
2002年 | 1429篇 |
2001年 | 635篇 |
2000年 | 695篇 |
1999年 | 586篇 |
1998年 | 534篇 |
1997年 | 472篇 |
1996年 | 500篇 |
1995年 | 446篇 |
1994年 | 435篇 |
1993年 | 436篇 |
1992年 | 395篇 |
1991年 | 251篇 |
1990年 | 319篇 |
1989年 | 321篇 |
1988年 | 279篇 |
1987年 | 296篇 |
1986年 | 286篇 |
1985年 | 306篇 |
1984年 | 267篇 |
1983年 | 256篇 |
1982年 | 239篇 |
1981年 | 209篇 |
1980年 | 175篇 |
1979年 | 182篇 |
1978年 | 165篇 |
1977年 | 135篇 |
1976年 | 122篇 |
1975年 | 134篇 |
1974年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 812 毫秒
111.
Linking Entrepreneurship to Growth: The Case of West Germany 总被引:1,自引:0,他引:1
112.
113.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献
114.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献
115.
In response to an interpretation made by Moore and Akgerman of data taken from a recent publication, previously unexplainable phenomena are accounted for, based on new experimental results. These relate to a thermodynamic equilibrium reaction involving saturation of aromatic hydrocarbons in synthetic crude middle distillates. 相似文献
116.
Mathematical models have been developed which predict the composition, molecular weight, and melt rheological properties for vinyl chloride/vinyl acetate copolymers of inherent viscosity range 0.4–0.7 dL/g and bound vinyl acetate levels of 3.8–17.4%. The effect of polymer long chain branching on the viscous/elastic moduli ratio is discussed as well as the comparison of Tinius–Olsen melt index measurements vs. mechanical spectrometer results. The reactivity ratio for vinyl chloride/vinyl acetate comonomer pairs was remeasured and found to be significantly different from literature values. 相似文献
117.
The effects of monomer refluxing on both resin properties and reactor fouling of suspension PVC have been studied in a laboratory-scale 14-L reactor. Process control equations were developed which related the particle properties to the reflux condenser operation by controlling the parameters of (1) the time at which refluxing is begun and (2) the rate profile of heat removal from the condenser. An operating envelope has been developed for laboratory scale operations which optimizes the cycle time of polymerization while minimizing the adverse effects on particle properties. These operating conditions may have application to production scale operations when the proper scaling factors are employed. 相似文献
118.
A model is presented for the thermal shock damage in plates subjected to a sudden rise in temperature. Spalling is assumed to follow localized buckling caused by the thermally induced compressive stresses above subsurface flaws. The minimum size o flaw required to cause spalling is determined as a function of the material properties of the plate, the temperature rise, the position of the paw, and the time after the thermal shock. 相似文献
119.
Previous solid state analyses of sintering in Ti4+ -doped-commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2 O3 −TiO3 −Na2 Ophase diagram at least by 1350° C, a temperature lower than that at which "solid state" studies were conducted. It is suggested that liquid-phase sintering is a much more common occurrence than was realized formerly. 相似文献
120.
Nietzel Michael T.; Russell Robert L.; Hemmings Kelly A.; Gretter Monica L. 《Canadian Metallurgical Quarterly》1987,55(2):156
[Correction Notice: An erratum for this article was reported in Vol 55(3) of Journal of Consulting and Clinical Psychology (see record 2008-10745-001). The data presented in Table 2 were incorrect because a row and a column were inadvertently omitted. The corrected Table 2 appears in the erratum.] This study used meta-analysis to study the clinical significance of psychotherapy for symptoms of unipolar depression. The following questions were addressed: How similar is the posttherapy adjustment of depressed adults to that of nondepressed adults? Is this adjustment maintained at follow-up? What dimensions of treatment, therapists, or design are associated with clinical significance? Using the Beck Depression Inventory (BDI), we calculated composite BDI norms from 28 published studies. Sixty effect sizes (from 31 outcome studies utilizing the BDI) were calculated. The results indicated that psychotherapy produces outcomes that have moderate clinical significance and that are well-maintained at follow-up, that individual therapy is associated with greater clinical significance than group treatment, and that type of therapy is not related to improvement. Alternative approaches for operationalizing clinical significance as the return of individuals to normal levels of functioning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献