全文获取类型
收费全文 | 111911篇 |
免费 | 8761篇 |
国内免费 | 5675篇 |
专业分类
电工技术 | 4562篇 |
技术理论 | 8篇 |
综合类 | 9243篇 |
化学工业 | 20989篇 |
金属工艺 | 4759篇 |
机械仪表 | 3861篇 |
建筑科学 | 13610篇 |
矿业工程 | 5140篇 |
能源动力 | 6374篇 |
轻工业 | 6669篇 |
水利工程 | 18821篇 |
石油天然气 | 8017篇 |
武器工业 | 317篇 |
无线电 | 5423篇 |
一般工业技术 | 10414篇 |
冶金工业 | 3820篇 |
原子能技术 | 1491篇 |
自动化技术 | 2829篇 |
出版年
2024年 | 330篇 |
2023年 | 1198篇 |
2022年 | 2304篇 |
2021年 | 2870篇 |
2020年 | 3083篇 |
2019年 | 2634篇 |
2018年 | 2549篇 |
2017年 | 3236篇 |
2016年 | 3527篇 |
2015年 | 3521篇 |
2014年 | 6376篇 |
2013年 | 6641篇 |
2012年 | 8098篇 |
2011年 | 8525篇 |
2010年 | 6270篇 |
2009年 | 6595篇 |
2008年 | 5829篇 |
2007年 | 7701篇 |
2006年 | 7176篇 |
2005年 | 6453篇 |
2004年 | 5240篇 |
2003年 | 4676篇 |
2002年 | 4055篇 |
2001年 | 3383篇 |
2000年 | 2868篇 |
1999年 | 2241篇 |
1998年 | 1736篇 |
1997年 | 1428篇 |
1996年 | 1123篇 |
1995年 | 1015篇 |
1994年 | 806篇 |
1993年 | 631篇 |
1992年 | 477篇 |
1991年 | 364篇 |
1990年 | 259篇 |
1989年 | 272篇 |
1988年 | 167篇 |
1987年 | 159篇 |
1986年 | 109篇 |
1985年 | 108篇 |
1984年 | 103篇 |
1983年 | 61篇 |
1982年 | 37篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1959年 | 6篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
可交易水权改革若干问题的思考 总被引:4,自引:1,他引:3
从水权制度变迁理论分析入手,认定水权制度的改革不仅是一个简单的资源配置或生产力布局问题,更是涉及制度建设和一个国家管理体制的演化的问题。通过对已建立可交易水权为基础的水权制度改革作进一步探讨,提出了建立“准市场”和“地方政治民主协商”机制、构建合约化的水权交易市场、加快水权市场的布设与推广等相应的建议。 相似文献
212.
A photochromic nanocomposite based on Keggin structure phosphomolybdic acid (PMoA) well dispersed in polyethyleneglycol (PEG) was fabricated. TEM image showed that PMoA nanoparticles with narrow size distribution were finely dispersed in polymer matrix. FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and strong coulombic interaction was built between PMoA and polymer matrix. Under UV irradiation, the film was reduced photochemically to yield a blue species, which was in accordance with a charge-transfer mechanism. 相似文献
213.
用己二酸二酰肼(ADH)对透明质酸(HA)进行化学修饰,制备交联透明质酸(HA-ADH)薄膜。粘度法测试表明HA-ADH是一种可降解的生物材料,并且与HA相比,HA.ADH的降解速率减慢。在此基础上,研究了以疏水性的替硝唑(TDZ)和亲水性的头孢唑啉钠(CEZ)为模拟药物的HA-ADH药物载体薄膜的释药性能。紫外-可见(UV-Vis)吸收光谱检测表明,HA-ADH是一种疏水性药物TDZ的优良缓释制荆,这是由于TDZ的疏水性和HA-ADH薄膜的缓慢溶胀和降解性能的结合而得到的,药物的释放主要受扩散机制控制。 相似文献
214.
A lubrication-flow model for a free film in a corner is presented. The model, written in the hyperbolic coordinate system
ξ = x
2 −y
2, η = 2xy, applies to films that are thin in the η-direction. The lubrication approximation yields two coupled evolution equations
for the film thickness and the velocity field which, to lowest order, describes plug flow in the hyperbolic coordinates. A
free film in a corner evolving under surface tension and gravity is investigated. The rate of thinning of a free film is compared
to that of a film evolving over a solid substrate. Viscous shear and normal stresses are both captured in the model and are
computed for the entire flow domain. It is shown that normal stress dominates over shear stress in the far field, while shear
stress dominates close to the corner.
This revised version was published online in October 2005 with corrected page numbers. 相似文献
215.
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
216.
The dynamics of a thin liquid film falling down a uniformly heated wall is studied. The model introduced by Kalliadasis et al. [J. Fluid Mech. 475 (2003) 377] for the same problem is revisited and its deficiencies, namely the prediction of a critical
Reynolds number with 20% error, cured. For the energy equation a high-order Galerkin projection in terms of polynomial test
functions is developed. It is shown that not only does this more refined formulation correct the critical Reynolds number,
but it also gives, with an appropriate expansion close to criticality, the long-wave theory. Bifurcation diagrams for permanent
solitary waves are constructed and compared with the solution branches obtained from different models. It is shown that, in
all cases, the long-wave theory exhibits limit points and branch multiplicity, while the other models predict the continuing
existence of solitary waves. Time-dependent computations show that the free surface and interfacial temperature approach a
train of coherent structures that resemble the infinite-domain stationary solitary pulses. 相似文献
217.
Shuichi Yamamoto Teruaki Morihiro Koichi Ariyoshi Turkan Aktas 《Drying Technology》2005,23(6):1319-1330
As the surface properties of the drying materials are very important not only for the drying rate but also for the quality change during drying, the effects of surface concentration on the drying behavior of liquid foods (sugar solutions) were investigated by isothermal drying experiments and by numerical calculation experiments. The isothermal drying experiments with gelled sugar solution systems (sucrose and maltodextrin) were carried out at various relative humidity (RH) values (RH = 0 to 84%). Separate experiments were carried out for determination of the desorption isotherms.
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
218.
219.
220.
以水资源可持续发展为出发点,探讨了一种可以同时兼顾经济发展、水资源利用和社会效益的多目标水资源宏观经济模型的建立方法,通过引入带权2-模评价函数,将多目标优化问题转变成单目标优化问题。以2002年为现状水平年,对安徽省2010年的产业结构及产业规模进行优化分析。结果表明,多目标模型求得的总用水量较单目标模型明显降低,而两模型优化的产业规模与结构差别不大,体现了高用水效率行业优先发展的要求。 相似文献