全文获取类型
收费全文 | 9769篇 |
免费 | 418篇 |
国内免费 | 82篇 |
专业分类
电工技术 | 194篇 |
综合类 | 89篇 |
化学工业 | 1623篇 |
金属工艺 | 218篇 |
机械仪表 | 296篇 |
建筑科学 | 351篇 |
矿业工程 | 13篇 |
能源动力 | 279篇 |
轻工业 | 463篇 |
水利工程 | 38篇 |
石油天然气 | 44篇 |
武器工业 | 2篇 |
无线电 | 1759篇 |
一般工业技术 | 1596篇 |
冶金工业 | 2142篇 |
原子能技术 | 88篇 |
自动化技术 | 1074篇 |
出版年
2023年 | 94篇 |
2022年 | 136篇 |
2021年 | 193篇 |
2020年 | 147篇 |
2019年 | 131篇 |
2018年 | 193篇 |
2017年 | 192篇 |
2016年 | 192篇 |
2015年 | 195篇 |
2014年 | 289篇 |
2013年 | 536篇 |
2012年 | 445篇 |
2011年 | 484篇 |
2010年 | 385篇 |
2009年 | 446篇 |
2008年 | 450篇 |
2007年 | 409篇 |
2006年 | 374篇 |
2005年 | 321篇 |
2004年 | 301篇 |
2003年 | 305篇 |
2002年 | 255篇 |
2001年 | 230篇 |
2000年 | 212篇 |
1999年 | 225篇 |
1998年 | 756篇 |
1997年 | 449篇 |
1996年 | 309篇 |
1995年 | 213篇 |
1994年 | 183篇 |
1993年 | 201篇 |
1992年 | 97篇 |
1991年 | 97篇 |
1990年 | 84篇 |
1989年 | 71篇 |
1988年 | 74篇 |
1987年 | 72篇 |
1986年 | 77篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 44篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 27篇 |
1977年 | 54篇 |
1976年 | 84篇 |
1974年 | 12篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
FR Matuschka TW Schinkel B Klug A Spielman D Richter 《Canadian Metallurgical Quarterly》1998,64(8):3089-3091
To define conditions promoting inherited infection by Lyme disease spirochetes in Ixodes ticks, we variously infected ticks with Borrelia afzelii and examined their progenies by dark-field microscopy, immunofluorescence, PCR, and serial passage. No episode of inherited infection was evident, regardless of instar or gender infected or frequency of exposure. We suggest that these spirochetes rarely, if ever, are inherited by vector ticks. 相似文献
92.
KJ Barakat K Cheng WW Chan BS Butler TM Jacks KD Schleim DF Hora GJ Hickey RG Smith AA Patchett RP Nargund 《Canadian Metallurgical Quarterly》1998,8(11):1431-1436
A new class of potent, orally active phenyl piperazine-based GH secretagogues have been discovered from attempts to mimic the arrangement of the phenyl substituent in the spiroindanyl piperidine and spiroindoline sulfonamide privileged structures of 4 and 1, respectively. The best of these compounds, 18 (EC50 = 2.8 nM) is nearly as potent as MK-0677 for releasing GH from rat pituitary cells. 相似文献
93.
94.
95.
Meraj Talha Rauf Hafiz Tayyab Zahoor Saliha Hassan Arslan Lali M. IkramUllah Ali Liaqat Bukhari Syed Ahmad Chan Shoaib Umar 《Neural computing & applications》2021,33(17):10737-10750
Neural Computing and Applications - Lung cancer is a deadly disease if not diagnosed in its early stages. However, early detection of lung cancer is a challenging task due to the shape and size of... 相似文献
96.
The influence of the mobility reduction factor on the dominant third-harmonic distortion and effective transconductance in CMOS differential pair transconductors is examined. Analytical expressions are developed which are suitable for hand calculation and generate realistic estimates for distortion and transconductance. The results produced have been tested against SPICE simulations over a wide range of parameter values and show excellent agreement. The analysis highlights the importance of mobility degradation and reveals that the linearity of the source-coupled differential pair is actually improved as the mobility reduction factor increases. This surprising finding suggests that where 0.15, for example, acceptably low distortion levels (<60 dB for V
i
=1 V
pp
) should be achievable with the basic long-tailed pair and that complex linearization schemes may be unnecessary.This work is supported by a grant of the Science and Engineering Research Council. 相似文献
97.
Effects of Stearic Acid on the Injection Molding of Alumina 总被引:1,自引:0,他引:1
This research investigated the influence of stearic acid on the injection molding of alumina, by varying the concentration of stearic acid. The interaction between stearic acid and alumina was identified using transmission infrared spectroscopy, indicating stearic acid preferentially adsorbed onto the alumina powder surface. In addition to slightly modifying the intrinsic binder viscosity, stearic acid adsorbed onto the powder surface changed the flow behavior of the mixtures from dilatant flow to pseudoplastic flow at low temperatures. As a result, inhomogeneous distribution of binder in the injection-molded parts was minimized with increased stearic acid concentration. However, the possibility of forming bubbles in the mixtures arising from vaporization of stearic acid was enhanced. Additionally, the binder burnout temperature range was broadened with the increase of stearic acid concentration. 相似文献
98.
The Lovász ?-function (Lovász in IEEE Trans. Inf. Theory, 25:1–7, 1979) of a graph G=(V,E) can be defined as the maximum of the sum of the entries of a positive semidefinite matrix X, whose trace Tr(X) equals 1, and X ij =0 whenever {i,j}∈E. This function appears as a subroutine for many algorithms for graph problems such as maximum independent set and maximum clique. We apply Arora and Kale’s primal-dual method for SDP to design an algorithm to approximate the ?-function within an additive error of δ>0, which runs in time $O(\frac{\vartheta ^{2} n^{2}}{\delta^{2}} \log n \cdot M_{e})$ , where ?=?(G) and M e =O(n 3) is the time for a matrix exponentiation operation. It follows that for perfect graphs G, our primal-dual method computes ?(G) exactly in time O(? 2 n 5logn). Moreover, our techniques generalize to the weighted Lovász ?-function, and both the maximum independent set weight and the maximum clique weight for vertex weighted perfect graphs can be approximated within a factor of (1+?) in time O(? ?2 n 5logn). 相似文献
99.
The phenomenon of slow stable crack growth in polyethylene is investigated using notched specimens subject to constant load and the concepts of fracture mechanics. The effect of specimen geometry and dimension, the loading and the mode of loading on the applied stress intensity factor versus crack speed () curves has been studied to demonstrate that Kc is the controlling stress parameter for crack growth under suitable conditions. curves are obtained for a high density polyethylene homopolymer in distilled water and in a diluted detergent solution at four different temperatures. Results are also obtained for a much tougher medium density polyethylene copolymer whenever possible. Several mechanisms can be identified from the form of the curves. Two, in particular, have been observed but not explained before: (i) crack growth with a time dependence of 0.25, and (ii) the high slopes for crack growth in a tough copolymer. With the help of scanning electron microscopic studies of the fracture surfaces, (i) is postulated to be due to diffusion controlled void growth process and (ii) is considered to be the result of crack tip blunting effects. From the temperature dependence of crack growth, the activation energy of the diffusion controlled crack growth process is found to coincide with that of the x-relaxation process in polyethylene implying that diffusion controlled crack growth may be related to the motion of main chains in the polymer. 相似文献
100.
The onset of hydrodynamical instability induced by impulsive spin-down to rest in a cylinder containing a Newtonian fluid
is analyzed by using propagation theory. It is well-known that the primary transient swirl flow is laminar, but with initial
high velocities secondary motion sets in at a certain time. The dimensionless critical time Τc to mark the onset of instability is presented here as a function of the Reynolds number Re. Available experimental data indicate
that for large Re deviation of the velocity profiles from their momentum diffusion occurs starting from a certain time Τ≈4Τc. This means that secondary motion is detected at this characteristic time. It seems evident that during Τc⪯Τ⪯4Τc, secondary motion is relatively very weak and the primary diffusive momentum transfer is dominant. 相似文献