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91.
The heat flow model previously developed for a pure metal is extended to the solidification of an alloy over a range of temperatures.
The eq11Ations are then applied to rapid surface melting and solidification of an alloy substrate. The substrate is subjected
to a pulse of stationary high intensity heat flux over a circular region on its bounding surface. The finite difference form
of the heat transfer eq11Ation is written in terMs of dimensionless nodal temperature and enthalpy in an oblate spheroidal coordinate system. A numerical solution technique
is developed for an alloy which precipitates a eutectic at the end of solidification. Generalized solutions are presented
for an Al-4.5 wt pct Cu alloy subjected to a uniform heat flux distribution over the circular region. Dimensionless temperature
distributions, size and location of the “mushy” zone, and average cooling rate during solidification are calculated as a function
of the product of absorbed heat flux,q, the radius of the circular region,a, and time. General trends established show that for a given product ofqa all isotherMs are located at the same dimensionless distance for identical Fourier numbers. The results show that loss of superheat and
shallower temperature gradients during solidification result in significantly larger “mushy” zone sizes than during melting.
Furthermore, for a given set of process parameters, the average cooling rate increases with distance solidified from the bottom
to the top of the melt pool. 相似文献
92.
93.
Since the discovery of bulk Zr-Ti-Cu-Ni-Be[1] and Pd-Ni-Cu-P[2] metallic glasses with ex-traordinary high glass forming (GFA) ability and critical cooling rate lower than 100 K/s, great attention has been paid to the structure of BMG alloys. Experimental results of X-ray and neutron diffraction or scattering have provided ample evidence that there is a short-range order in BMG alloys. Metallic glasses always exhibit strong compound forming tendency and the corresponding anomalies of t… 相似文献
94.
95.
为了能更好地揭示脂肪烃的气相色谱保留指数与结构的关系,通过对412个脂肪烃类化合物在不同固定相、不同柱温下的1742个样本集的气相色谱保留指数值(RI)与其部分参数相关性的研究,发现RI与拓扑指数(mQ)、分子杂化状态指数(MHSI)、碳原子数(N)、固定液极性(CP)及柱温(T)的关系可表示为:RI=46.6537 15.83520Q 6.02101Q 49.9215MHSI- 62.4378N 2.2836CP 0.6159T(R=0.9954)此式不仅在一定程度上阐明了脂肪烃类化合物RI与其分子结构信息、固定液极性及柱温之间的关系,同时也提供了一种预测脂肪烃类化合物在各种色谱分离条件(不同固定相、不同温度)下RI的新方法。继以留一法(leave-one-out,LOO)进行交互检验,相关系数RLOO=0.9953,说明所建模型具有良好的稳定性和预测能力,较好地揭示了脂肪烃类化合物在不同固定相、不同柱温下气相色谱保留指数的变化规律。 相似文献
96.
Owing to long serving time and huge numbers of clients, Internet services can easily suffer from transient faults. Although restarting a service can solve this problem, information of the on‐line requests will be lost owing to the service restart, which is unacceptable for many commercial or transaction‐based services. In this paper, we propose an approach to achieve the goal of zero‐loss restart for Internet services. Under this approach, a kernel subsystem is responsible for detecting the transient faults, retaining the I/O channels of the service, and managing the service restart flow. In addition, some straightforward modifications to the service should be made to take advantage of the kernel support. To demonstrate the feasibility of our approach, we implemented the subsystem in the Linux kernel. Moreover, we modified a Web server and a CGI program to take advantage of the kernel support. According to the experimental results, our approach incurs little runtime overhead (i.e. less than 3.2%). When the service crashes, it can be restarted quickly (i.e. within 210 μs) with no information loss. Furthermore, the performance impact due to the service crash is small. These results show that the approach can efficiently achieve the goal of zero‐loss restart for Internet services. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
97.
Chiou J.-C. Kou C.-F. Lin Y.-J. 《IEEE journal of selected topics in quantum electronics》2007,13(2):297-303
A micromirror with large rotation angle and vertical displacement is proposed and developed. The proposed micromirror is actuated by newly developed prestress comb drive actuators, which exhibit no pull-in, no hysteresis, and large vertical displacement range characteristics. The micromirror was fabricated using commercially available PolyMUMPs. Experimental results indicated that the maximum rotation angle and vertical displacement of the device are 26 and 45 mum, respectively 相似文献
98.
Xite?WangEmail author Derong?Shen Mei?Bai Tiezheng?Nie Yue?Kou Ge?Yu 《Frontiers of Computer Science》2015,9(1):128-141
MapReduce is a popular parallel data-processing system, and task scheduling is one of the kernel techniques in MapReduce. In many applications, users have requirements that their MapReduce jobs should be completed before specific deadlines. Hence, in this paper, a novel scheduling algorithm based on the most effective sequence (SAMES) is proposed for deadline-constraint jobs in MapReduce. First, according to the characteristics of MapReduce, we propose a novel sequence-based execution strategy for MapReduce jobs and a new concept, the effective sequence (ES). Then, we design some efficient approaches for finding ESes and choose the most effective sequence (MES) for job execution. We also propose methods for MES-updates and exception handling. Finally, we verify the effectiveness of SAMES through experiments. The experimental results show that SAMES is an efficient scheduling algorithm for deadline-constraint jobs in MapReduce. 相似文献
99.
ABSTRACTMapping scale is an essential issue in land use and land cover (LULC) data production, which always involves the minimum mapping unit (MMU) that stipulated in the product specification. Since the application of MMUs will inevitably cause some inappropriate classification problems, a technique is needed to evaluate the impact on the data outputs. In this study, a novel method is proposed to investigate the classification uncertainty brought by MMUs on LULC data. The omission errors are predicted based on an assumption of the skewed frequency distribution of the LULC patch size, and the commission errors are subsequently computed through the conversion possibilities among different land classes, which can be deduced from the generalization rule. A test is conducted on real data to verify the underlying assumption on the patch size distribution, and the accuracy of the prediction of omission errors is evaluated through a simulation experiment. A case study is also presented to demonstrate the efficiency and feasibility of the proposed method. At the end of this article, the advantages and notes of this method are discussed for further study and application. 相似文献
100.
部分用户存在因某些时段功率因数过低,引发无功功率倒送电网的情况,会给电网运行和用户自身带来不利的影响。以某高速公路路灯线路的无功功率倒送电网作为案例,分析了问题产生的原因,提出了解决方法。 相似文献