全文获取类型
收费全文 | 31027篇 |
免费 | 3178篇 |
国内免费 | 2453篇 |
专业分类
电工技术 | 3805篇 |
综合类 | 3800篇 |
化学工业 | 1990篇 |
金属工艺 | 1816篇 |
机械仪表 | 4371篇 |
建筑科学 | 1344篇 |
矿业工程 | 863篇 |
能源动力 | 1064篇 |
轻工业 | 793篇 |
水利工程 | 751篇 |
石油天然气 | 1299篇 |
武器工业 | 359篇 |
无线电 | 2996篇 |
一般工业技术 | 2580篇 |
冶金工业 | 815篇 |
原子能技术 | 305篇 |
自动化技术 | 7707篇 |
出版年
2024年 | 128篇 |
2023年 | 361篇 |
2022年 | 675篇 |
2021年 | 763篇 |
2020年 | 888篇 |
2019年 | 811篇 |
2018年 | 724篇 |
2017年 | 1001篇 |
2016年 | 1148篇 |
2015年 | 1206篇 |
2014年 | 2065篇 |
2013年 | 2151篇 |
2012年 | 2465篇 |
2011年 | 2496篇 |
2010年 | 1895篇 |
2009年 | 1939篇 |
2008年 | 1698篇 |
2007年 | 2114篇 |
2006年 | 1786篇 |
2005年 | 1641篇 |
2004年 | 1360篇 |
2003年 | 1203篇 |
2002年 | 1048篇 |
2001年 | 920篇 |
2000年 | 807篇 |
1999年 | 604篇 |
1998年 | 421篇 |
1997年 | 420篇 |
1996年 | 333篇 |
1995年 | 292篇 |
1994年 | 252篇 |
1993年 | 194篇 |
1992年 | 144篇 |
1991年 | 142篇 |
1990年 | 117篇 |
1989年 | 94篇 |
1988年 | 66篇 |
1987年 | 45篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 33篇 |
1983年 | 36篇 |
1982年 | 27篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1975年 | 4篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
51.
52.
53.
介绍了一种用于液压支架大流量、快速移架系统中的POCV——200/31.5型液控单向阀的工作原理和结构特点。分析了该阀的性能,并指出了其推广应用前景。 相似文献
54.
Morten
rregaard Nielsen 《时间序列分析杂志》2005,26(2):279-304
Abstract. We consider semiparametric estimation in time‐series regression in the presence of long‐range dependence in both the errors and the stochastic regressors. A central limit theorem is established for a class of semiparametric frequency domain‐weighted least squares estimates, which includes both narrow‐band ordinary least squares and narrow‐band generalized least squares as special cases. The estimates are semiparametric in the sense that focus is on the neighbourhood of the origin, and only periodogram ordinates in a degenerating band around the origin are used. This setting differs from earlier studies on time‐series regression with long‐range dependence, where a fully parametric approach has been employed. The generalized least squares estimate is infeasible when the degree of long‐range dependence is unknown and must be estimated in an initial step. In that case, we show that a feasible estimate which has the same asymptotic properties as the infeasible estimate, exists. By Monte Carlo simulation, we evaluate the finite‐sample performance of the generalized least squares estimate and the feasible estimate. 相似文献
55.
56.
57.
李静 《制冷与空调(北京)》2007,7(2):86-88
介绍新型节流装置——线性浮阀的结构、工作原理、特点及其在大型冷水机组中的应用以及实际使用中可能存在的问题,为在设计具有较高能效比的中大型冷水机组中,在节流机构选择应用上提供更大的选择空间。 相似文献
58.
This study is concerned with the stability of a two-dimensional incompressible conducting liquid film surrounded by a passive
conducting medium, when an electric field is applied in a direction parallel to the initially flat bounding fluid interfaces.
Currents generate charges at the bounding interfaces which in turn affect the stress balances there. In the absence of an
electric field, the viscous liquid film is stable (instability can be induced by the inclusion of van der Waals forces for
ultra thin films). A complete model is presented, at arbitrary Reynolds number, which accounts for conductivity and permittivity
contrasts between the fluid and surrounding medium, as well as surface tension. The linear stability of the system is considered
for arbitrary Reynolds numbers and it is shown that the stable film can become unstable if, (i) σ
R
ɛ
p
>1, or (ii) σ
R
ɛ
p
<1 and (σ
R
−1)(1−ɛ
p
)<0, where σ
R
is the ratio of outer to inner conductivity and ε
p
is the ratio of inner to outer permittivity. Instability is possible only if the electric field is non-zero and the scalings
near bifurcation points that can be used to construct nonlinear theories are calculated. Several asymptotic limits are also
considered including zero Reynolds numbers and short or long waves. The instability criteria given above are constructed explicitly
in the case of Stokes flow. 相似文献
59.
Residual stress as measured quantity in quality assurance The x‐ray method is used in the Volkswagen Automotive Group at different world‐wide locations as a standard procedure to determine residual stress. As an important measured quantity in the quality assurance residual stresses are specified in drawings of different components (e.g. gears, coil springs). Measurements are carried out during quality assurance, production, damage analyse, technical development department and design control of components from suppliers. An optimum efficiency can be achieved, if it exists a unique correlation between residual stress values and loading capacity of components, and if the processes to introduce residual stress can be optimized using residual stress measurements during the production. 相似文献
60.
CAO Wei-feng WANG Wen-boBeijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2005,12(4)
1IntroductionCurrently,smart antenna technology can greatly en-hance system performance and i mprove the system ca-pacity so that it has been considered as a keytechnologyinthe third generation wireless communicationsystems .The researches on channel model , beamforming algo-rithms and receive algorithms have been widely carriedout and a great many of proposition have beensubmittedtothe 3th Generation Project Partner (3GPP) . Fromthe viewpoint of link-level and system-level research,many asp… 相似文献