全文获取类型
收费全文 | 3590篇 |
免费 | 101篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 133篇 |
综合类 | 7篇 |
化学工业 | 798篇 |
金属工艺 | 74篇 |
机械仪表 | 59篇 |
建筑科学 | 66篇 |
矿业工程 | 4篇 |
能源动力 | 105篇 |
轻工业 | 349篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 401篇 |
一般工业技术 | 469篇 |
冶金工业 | 902篇 |
原子能技术 | 51篇 |
自动化技术 | 265篇 |
出版年
2023年 | 19篇 |
2022年 | 38篇 |
2021年 | 76篇 |
2020年 | 27篇 |
2019年 | 28篇 |
2018年 | 53篇 |
2017年 | 44篇 |
2016年 | 53篇 |
2015年 | 45篇 |
2014年 | 88篇 |
2013年 | 144篇 |
2012年 | 129篇 |
2011年 | 148篇 |
2010年 | 111篇 |
2009年 | 125篇 |
2008年 | 143篇 |
2007年 | 125篇 |
2006年 | 93篇 |
2005年 | 119篇 |
2004年 | 81篇 |
2003年 | 106篇 |
2002年 | 87篇 |
2001年 | 80篇 |
2000年 | 73篇 |
1999年 | 86篇 |
1998年 | 377篇 |
1997年 | 208篇 |
1996年 | 134篇 |
1995年 | 96篇 |
1994年 | 89篇 |
1993年 | 81篇 |
1992年 | 39篇 |
1991年 | 39篇 |
1990年 | 29篇 |
1989年 | 48篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 34篇 |
1985年 | 25篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 19篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 25篇 |
1978年 | 29篇 |
1977年 | 35篇 |
1976年 | 50篇 |
1975年 | 13篇 |
1974年 | 15篇 |
排序方式: 共有3693条查询结果,搜索用时 15 毫秒
101.
The potential protection of Picea glehnii seedlings from damping-off by seed-epiphytic Penicillium species was investigated. We studied the chemical response of seed-epiphytic Penicillium species (Pen. cyaneum, Pen. damascenum, and Pen. implicatum) to Pythium vexans, a damping-off fungus, in vitro. Penicillium species were cultured singly or cocultured with Pyt. vexans for 14 or 18 d, and mycelial growth, pH of culture filtrate, antifungal activity of the culture filtrate against Pyt. vexans, and the amount of antifungal compound produced by each Penicillium species, were examined. The filtrate of both the single culture of Penicillium and the coculture of Penicillium and Pyt. vexans showed antifungal activity against Pyt. vexans. In a coculture with Pyt. vexans, Pen. cyaneum produced an antifungal compound (patulin) as in the single culture. Pen. damascenum cocultured with Pyt. vexans produced an antifungal compound (citrinin), as it did in the single culture and in larger amounts on day 10. Pen. implicatum produced two antifungal compounds, frequentin and palitantin, and the ratio of frequentin (with higher antifungal activity than palitantin) to palitantin was higher in the coculture with Pyt. vexans than in the single culture. Our results indicate that these Penicillium species have the ability to produce antifungal compounds and to keep antifungal activity under competitive condition with Pyt. vexans. The chemical response of these Penicillium species to Pyt. vexans may contribute to protect P. glehnii seedlings from damage by Pyt. vexans. 相似文献
102.
T. Sasaki N. Yoneyama A. Suzuki I. Ito N. Kobayashi Y. Ikemoto H. Kimura N. Hanasaki H. Tajima 《Journal of Low Temperature Physics》2006,142(3-4):377-382
The electronic phase separation on macroscopic scale is studied in the organic Mott system κ-(BEDT-TTF)2Cu[N(CN)2]Br by means of scanning microregion infrared spectroscopy using the synchrotron radiation. The phase separation appears in
the vicinity of the Mott boundary in the single crystals of which the band width is controlled by partly substituting the
BEDT-TTF molecule with the deuterated one. The transport properties under the phase separation are considered to be influenced
by the percolation process of the domains. 相似文献
103.
104.
1Introduction Themostimportantrequirementofapercutaneous deviceisthepreventionofbacterialinfectionthroughtheinterfacebetweenthematerialandtheskin.Therefore,a percutaneousdevicehastoadherefirmlytoskintissueandpreventepidermaldowngrowth.Previously,Aokietalp… 相似文献
105.
Y. Sasaki E. Hayata T. Tanaka H. Ito T. Mizusaki 《Journal of Low Temperature Physics》2005,138(3-4):911-916
No Heading We have constructed an Ultra Low Temperature cryostat for Magnetic Resonance Imaging (ULT-MRI) applicable for various condensed phases of 3He at ultra low temperature, such as Nuclear Ordered Solid 3He or superfluid 3He. In contrast to conventional MRI for general use, where a pulsed-field gradient method is commonly used, we used a steady-field gradient method to avoid eddy current heating to metal parts at ultra low temperature. To avoid nonlinear response from the nuclear ordered spin system, which contradicts a principle of conventional MRI, we employed Free Induction Decay (FID) after a small tipping angle RF pulse to obtain the spectrum.PACS numbers: 07.20Mc, 67.57.Lm, 67.80.Jd, 76.60.Pc, 83.85.Fg 相似文献
106.
Many applications lead to a nonlinear elliptic interface problem in which the discontinuous coefficient depends on the solution and the material properties. A finite difference method based on Cartesian grids and the maximum principle preserving immersed interface method is proposed for the nonlinear elliptic interface problems discussed in this paper. Numerical experiments against the exact solutions reveal that our method is nearly second order accurate in the infinity norm. The method is applied to study the magneto-rheological field-responsive fluids that contain iron particles. Numerical experiments are performed against the results from the literature. 相似文献
107.
Suppose that some particular link in the Internet is currently
congested.
A natural solution is to try to make packets bypass that link.
This can be done by increasing the cost of that link intentionally,
say from a
1 to a
2, since the Internet uses shortest-path
routing. Unfortunately, however, this often causes temporary loops
for packet traveling, called routing loops. In this paper
we show that routing loops can be avoided by increasing the cost
of the link not directly from a
1 to a
2 but through an
intermediate value, a
3, i.e., from a
1 to a
3 and then
to a
2.
We may need several
intermediate values.
We show that in this case
the greedy strategy,
namely, raising the cost as much as possible in each step,
is optimal. 相似文献
108.
A simultaneous detecting circuit system of centers and lengths of some lines in one dimension is presented applying an electronic circuit model of the nervous axon with respect to signal transmission. This model consists of series of one basic section, and has functions of Neuristor. The circuit system has a paralell processing function. It is constructed by three layers. In the first layer each visual signal of lines is changed to electric pulse signal. In the second layer edges of each line are detected, and in the third layer these detected signals are converted into voltages which correspond to lengths of the lines. These functions were confirmed experimentally using its hardware. 相似文献
109.
NOx reduction from combustion flue gases by superimposed barrier discharge plasma reactors is experimentally investigated. The experiments are conducted for applied voltages from 0 to 28 kV, flue gas rates from 0.5 to 2 L/min, ammonia mixture concentrations from 0.7 to 2.65 stoichiometry, and applied voltage phase differences from 0° to 180°, where two 60-Hz AC power supplies are used. The results show the following: (1) NOx reduction rate decreases with increasing discharge power for surface discharge operations, however, NOx reduction rate increases with increasing discharge power for silent and superimposing discharge operating modes; (2) NOx reduction rate increases with increasing discharge power, gas flow rate and ammonia stoichiometry under in-phase operations; (3) NOx reduction rate for out-of-phase operations is much higher compared with in-phase operations, however, NOx reduction rate has an optimum condition on ammonia stoichiometry, discharge power, and gas flow rate; and (4) energy efficiency of NOx reduction increases with increasing ammonia mixture and gas flow rate and decreases with increasing discharge power 相似文献
110.
The generalization ability of feedforward neural networks (NNs) depends on the size of training set and the feature of the training patterns. Theoretically the best classification property is obtained if all possible patterns are used to train the network, which is practically impossible. In this paper a new noise injection technique is proposed, that is noise injection into the hidden neurons at the summation level. Assuming that the test patterns are drawn from the same population used to generate the training set, we show that noise injection into hidden neurons is equivalent to training with noisy input patterns (i.e., larger training set). The simulation results indicate that the networks trained with the proposed technique and the networks trained with noisy input patterns have almost the same generalization and fault tolerance abilities. The learning time required by the proposed method is considerably less than that required by the training with noisy input patterns, and it is almost the same as that required by the standard backpropagation using normal input patterns. 相似文献