全文获取类型
收费全文 | 21171篇 |
免费 | 2174篇 |
国内免费 | 1599篇 |
专业分类
电工技术 | 1286篇 |
技术理论 | 1篇 |
综合类 | 1624篇 |
化学工业 | 4539篇 |
金属工艺 | 1457篇 |
机械仪表 | 818篇 |
建筑科学 | 1251篇 |
矿业工程 | 616篇 |
能源动力 | 1019篇 |
轻工业 | 1067篇 |
水利工程 | 553篇 |
石油天然气 | 1345篇 |
武器工业 | 307篇 |
无线电 | 2160篇 |
一般工业技术 | 3348篇 |
冶金工业 | 732篇 |
原子能技术 | 625篇 |
自动化技术 | 2196篇 |
出版年
2024年 | 76篇 |
2023年 | 512篇 |
2022年 | 593篇 |
2021年 | 739篇 |
2020年 | 807篇 |
2019年 | 698篇 |
2018年 | 696篇 |
2017年 | 830篇 |
2016年 | 888篇 |
2015年 | 838篇 |
2014年 | 1151篇 |
2013年 | 1419篇 |
2012年 | 1389篇 |
2011年 | 1616篇 |
2010年 | 1200篇 |
2009年 | 1171篇 |
2008年 | 1166篇 |
2007年 | 1329篇 |
2006年 | 1188篇 |
2005年 | 1026篇 |
2004年 | 873篇 |
2003年 | 731篇 |
2002年 | 574篇 |
2001年 | 538篇 |
2000年 | 430篇 |
1999年 | 400篇 |
1998年 | 308篇 |
1997年 | 285篇 |
1996年 | 262篇 |
1995年 | 203篇 |
1994年 | 178篇 |
1993年 | 136篇 |
1992年 | 116篇 |
1991年 | 112篇 |
1990年 | 96篇 |
1989年 | 91篇 |
1988年 | 62篇 |
1987年 | 38篇 |
1986年 | 38篇 |
1985年 | 33篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The influence of network density on the strain hardening behaviour of amorphous polymers is studied. The network density of polystyrene is altered by blending with poly(2,6-dimethyl-1,4-phenylene-oxide) and by cross-linking during polymerisation. The network density is derived from the rubber-plateau modulus determined by dynamic mechanical thermal analysis. Subsequently uniaxial compression tests are performed to obtain the intrinsic deformation behaviour and, in particular, the strain hardening modulus. At room temperature, the strain hardening modulus proves to be proportional to the network density, irrespective of the nature of the network, i.e. physical entanglements or chemical cross-links. With increasing temperature, the strain hardening modulus is observed to decrease. This decrease appears to be related to the influence of thermal mobility of the chains, determined by the distance to the glass-transition temperature (T−Tg). 相似文献
32.
33.
针对车用柴油酸度等性质测定过程繁琐,采用衰减全反射样品池测定车用柴油的红外光谱,用偏最小二乘法(PLS)建立红外光谱测定车用柴油酸度、密度、闪点和凝点的4个校正模型,验证标准误差分别为0.46 mg/(100 mL),0.77kg/m3,2.60 ℃,2.77 ℃,该方法符合标准方法再现性要求。与标准方法相比,该方法具有无需预处理、操作简单、测量快速、重复性好等优点。 相似文献
34.
低阻VDMOSFET的优化设计与制造 总被引:1,自引:1,他引:0
文章对9926型双N沟增强型VDMOSFET进行了结构和版图的优化设计。给出了该器件的纵横向结构参数,材料的物理参数和版图总体结构。单胞结构的优化设计使单胞密度达到204万个/cm2,比国际市场现有产品的单胞密度(156万个/cm2)提高了30%。这种设计采用浅n+注入工艺可使器件生产成本下降31%。最后对研制结果进行了分析讨论。 相似文献
35.
The period and damping of the free motion of a body oscillating in a fluid depend on the fluid's viscosity and density. Commonly, a working equation which expresses the damping as a function of the viscosity and density is solved for the viscosity, the damping being measured and the density being treated as an independently supplied parameter. Another working equation exists for the period, and, in general, the period depends on a combination of the viscosity and the density which is linearly independent of the combination that appears in the damping equation. It is, therefore, in principle, possible to determine both the viscosity and the density by a simultaneous solution of the two coupled working equations, since the period also is measured. In this paper, the working equations that describe the oscillating-disk viscometer are reviewed and their simultaneous solution is considered. The effect of fixed plates symmetrically located above and below the oscillating disk is of specific interest. The paper's main result is that fixed plates can dramatically increase the independence of the damping and period working equations, so that it becomes indeed feasible to determine the viscosity and the density of a fluid simultaneously from the damping and period of oscillating motion. A price is paid, however, because the instrument's working equations when plates are present have multiple solutions. Under special conditions, these multiple solutions can coalesce, and then one can only deduce the viscosity from the damping equation if the density is known a priori. 相似文献
36.
37.
As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is
desirable to have a clear picture of the errors introduced by currently popular approximate exchange-correlation functionals.
We have performed ab initio density functional theory and density functional perturbation theory calculations to investigate
the thermal properties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation
(GGA). Thermal effects are treated within the quasiharmonic approximation. We find that the LDA and GGA errors for anharmonic
quantities are an order of magnitude smaller than for harmonic quantities; we argue that this might be a general feature.
We also obtain much closer agreement with experiment than earlier, more approximate calculations. 相似文献
38.
This paper proposes an original method for obtaining analytical approximations of the invariant probability density function of multi-dimensional Hamiltonian dissipative dynamic systems under Gaussian white noise excitations, with linear non-conservative parts and nonlinear conservative parts. The method is based on an exact result and a heuristic argument. Its pertinence is attested by numerical tests. 相似文献
39.
40.
西部地区深井井身结构设计技术探讨 总被引:3,自引:2,他引:1
科学合理地确定井身结构及钻井液密度是深井超深井钻井的关键环节之一,其基础是准确建立地层孔隙压力、地应力、破裂压力、坍塌压力的钻前预测剖面。分析了西部地区目前深井井身结构的缺点和进行井身结构应考虑的问题,介绍了深探井井身结构的设计方法,并针对西部复杂地区的地层特点,建议采用3种增加技术套管的井身结构方案。塔河油田钻井实践表明,采用这3种井身结构方案后,深井机械钻速得到提高,钻井周期缩短,而且降低了钻井成本。 相似文献