首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7057篇
  免费   201篇
  国内免费   28篇
电工技术   106篇
综合类   2篇
化学工业   1435篇
金属工艺   291篇
机械仪表   188篇
建筑科学   109篇
矿业工程   8篇
能源动力   339篇
轻工业   269篇
水利工程   58篇
石油天然气   14篇
无线电   999篇
一般工业技术   1531篇
冶金工业   861篇
原子能技术   72篇
自动化技术   1004篇
  2023年   70篇
  2022年   151篇
  2021年   184篇
  2020年   162篇
  2019年   153篇
  2018年   244篇
  2017年   203篇
  2016年   199篇
  2015年   108篇
  2014年   206篇
  2013年   414篇
  2012年   239篇
  2011年   317篇
  2010年   241篇
  2009年   281篇
  2008年   256篇
  2007年   207篇
  2006年   216篇
  2005年   155篇
  2004年   128篇
  2003年   129篇
  2002年   129篇
  2001年   126篇
  2000年   129篇
  1999年   112篇
  1998年   264篇
  1997年   183篇
  1996年   131篇
  1995年   130篇
  1994年   105篇
  1993年   133篇
  1992年   108篇
  1991年   97篇
  1990年   84篇
  1989年   75篇
  1988年   72篇
  1987年   75篇
  1986年   88篇
  1985年   106篇
  1984年   99篇
  1983年   95篇
  1982年   78篇
  1981年   63篇
  1980年   50篇
  1979年   46篇
  1978年   49篇
  1977年   62篇
  1976年   82篇
  1975年   43篇
  1973年   42篇
排序方式: 共有7286条查询结果,搜索用时 0 毫秒
51.
A model for transitional breakage probability of droplets in agitated lean fiquid-liquid dispersions is proposed based on the mechanism of breakage of droplets due to their oscillations resulting from relative velocity fluctuations. A universal transitional breakage probability in terms of non-dimensionalized drop diameter is derived for all dispersed phases whose density and viscosity are almost the same as that of continuous phase. The maximum stable drop diameter ds derived from the model, shows a dependence of NWe?0.6. It is shown that a “power law” approximation Kvn is valid for transitional breakage probability for d/ds up to 2. The exponent 2.67, predicted by this model corresponds rather well with an estimate of 2, obtained from experimental observations. A functional relation for the rate constant K in terms of the parameters and physical properties of the system is derived. A universal non-dimensionalized equilibrium drop-size distribution for agitated lean liquid-liquid dispersions is derived by analytical solution of a population balance equation simplified by order of magnitude estimates. Interestingly enough, this analytical solution is the same as the Gaussian distribution suggested empirically by Chen and Middleman.  相似文献   
52.
This paper addresses the flow shop batching and scheduling problem where sequence-dependent family setup times are present and the objective is to minimize makespan. We consider violating the group technology assumption by dividing product families into batches. In order to reduce setup times, inconsistent batches are formed on different machines, which lead to non-permutation schedules. To the best of our knowledge, this is the first time that the splitting of job families into inconsistent batches has been considered in a flow shop system. A tabu search algorithm is developed which contains several neighbourhood functions, double tabu lists and a multilevel diversification structure. Compared to the state-of-the-art meta-heuristics for this problem, the proposed tabu search algorithm achieves further improvement when the group scheduling assumption is dropped. Also, various experiments conducted on the benchmark problem instances confirm the benefits of batching. Therefore, it will be prudent for the practitioners to consider adopting inconsistent batches and non-permutation schedules to improve their operational efficiency within a reasonable amount of computational effort.  相似文献   
53.
Crystallization of polypropylene (PP) in the blends of PP with styrene–ethylene butylene–styrene triblock copolymer (SEBS) is studied through differential thermal analysis (DTA) and X-ray diffraction measurements. Analysis of crystallization exotherm peaks in terms of crystallization nucleation and growth rates, crystallite size distribution, and crystallinity revealed differences in the morphology of PP component in the blend in the different regions of blend composition. Crystallinity determined by X-ray diffraction and DTA showed identical variations with blend composition. Variations in tensile properties of these blends with blend composition are also reported. Correlations of the various tensile properties with the crystallization parameters, viz., the crystallinity and crystallite size distribution, are presented, which confirm the influence of crystallization of PP component on the tensile properties of these blends.  相似文献   
54.
The univariant element, Q1 P0, and the multivariant elements, QP0 and R P0, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q1 P0 element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q P0 and R P0, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.  相似文献   
55.
Informally stated, we present here a randomized algorithm that given black-box access to the polynomial f computed by an unknown/hidden arithmetic formula ? reconstructs, on the average, an equivalent or smaller formula \({\hat{\phi}}\) in time polynomial in the size of its output \({\hat{\phi}}\) . Specifically, we consider arithmetic formulas wherein the underlying tree is a complete binary tree, the leaf nodes are labeled by affine forms (i.e., degree one polynomials) over the input variables and where the internal nodes consist of alternating layers of addition and multiplication gates. We call these alternating normal form (ANF) formulas. If a polynomial f can be computed by an arithmetic formula μ of size s, it can also be computed by an ANF formula ?, possibly of slightly larger size s O(1). Our algorithm gets as input black-box access to the output polynomial f (i.e., for any point x in the domain, it can query the black box and obtain f(x) in one step) of a random ANF formula ? of size s (wherein the coefficients of the affine forms in the leaf nodes of ? are chosen independently and uniformly at random from a large enough subset of the underlying field). With high probability (over the choice of coefficients in the leaf nodes), the algorithm efficiently (i.e., in time s O(1)) computes an ANF formula \({\hat{\phi}}\) of size s computing f. This then is the strongest model of arithmetic computation for which a reconstruction algorithm is presently known, albeit efficient in a distributional sense rather than in the worst case.  相似文献   
56.
Batch and continuous wet grinding experiments were carried out in a 40 × 40 cm grate-discharge ball bill. Well-distributed ?4 and ?20 mesh feeds of two complex pyritic ores were used. The vol. % solids in the pulp ranged from 30 to 40, the particle load from 5 to 8 kg, and the solids feed rate from 70 to 110 kg/h.Analysis of the experimental data showed that over the range of operating conditions investigated, a linearized model could be used to predict the size distributions of both the mill product as well as the mill hold-up of the solids, very accurately. The breakage rate parameters, Si, were found to be dependent on the mode of operation, independent of the percent solids in the pulp, and approximately inversely proportional to the mill hold-up weight of the solids. In the case of the continuous mode of operation, with decrease in particle size the rate parameter values became increasingly smaller by comparison with the corresponding expected batch operation values.  相似文献   
57.
Multimedia Tools and Applications - Prostate cancer (PCa) has become the second most dreadful cancer in men after lung cancer. Traditional approaches used for treatment of PCa were manual, time...  相似文献   
58.

Handwriting recognition is used for the prediction of various demographic traits such as age, gender, nationality, etc. Out of all the applications gender prediction is mainly admired topic among researchers. The relation between gender and handwriting can be seen from the physical appearance of the handwriting. This research work predicts gender from handwriting using the landmarks of differences between the two genders. We use the shape or visual appearance of the handwriting for extracting features of the handwriting such as slanteness (direction), area (no of pixels occupied by text), perimeter (length of edges), etc. Classification is carried out using the Support Vector Machine (SVM) as a classifier which transforms the nonlinear problem into linear using its kernel trick, logistic regression, KNN and at the end to enhance the classification rates we use Majority Voting. The experimental results obtained on a dataset of 282 writers with 2 samples per writer shows that the proposed method attains appealing performance on writer detection and text-independent environment.

  相似文献   
59.

Estimation of terrestrial water budget at global and regional scales are essential for efficient agricultural water management, flood predictions, and, hydrological modeling. In hydrological modeling, it is a challenging task to quantify the major hydrological components like runoff, evapotranspiration (ET), and total water storage (TWS) due to improper and limited availability of detailed meteorological datasets. Furthermore, there has been no consensus to answer a-decade-long critical question that a less data-intensive models can be an alternate to robust data-intensive models in data scarce conditions. This study aims at multi-model approach over the single models usage for representing the hydrological behaviour in the Kangsabati River Basin (KRB), India. It is done by applying the standard model selection criteria over various hydrological models. Two hydrological models are selected, a semi- distributed model, Variable Infiltration Capacity (VIC-3 L), and a conceptually lumped model, Identification of unit Hydrograph and Component flows from Rainfall, Evapotranspiration and Streamflow (IHACRES). Both models were calibrated against the observed daily discharge at the KRB outlet for the period of 2001–2006 and validated for 2008–2010. The results show that both VIC-3 L and IHACRES produce reasonable runoff estimates at daily and monthly time scale in the KRB. The ET estimates show that VIC-3 L and IHACRES captured the seasonal variations with the percent change of 0.4% and 6.6% respectively. As IHACRES is simpler, parsimonious, fewer parameters, and better performances, it can be useful for hydrological modeling in data-scarce regions.

  相似文献   
60.

Hydrological responses corresponding to the agricultural land use alterations are critical for planning crop management strategies, water resources management, and environmental evaluations. However, accurate estimation and evaluation of these hydrological responses are restricted by the limited availability of detailed crop classification in land use and land cover. An innovative approach using state-of-the-art Variable Infiltration Capacity (VIC) model is utilized by setting up the crop-specific vegetation parameterization and analyse the effect of uniform and heterogeneous agricultural land use over the hydrological responses of the basin, in the Kangsabati River Basin (KRB). Thirteen year simulations (1998–2010) based on two different scenarios i.e., single-crop in agricultural land use (SC-ALU) and multi-crop in agricultural land use (MC-ALU) patterns are incorporated in the model and calibrated (1998–2006) and validated (2007–2010) for the streamflow at Reservoir and Mohanpur in the KRB. The results demonstrated that the VIC model improved the estimates of hydrological components, especially surface runoff and evapotranspiration (ET) at daily and monthly timescales corresponding to MC-ALU than SC-ALU (NSC?>?0.7). Grid-scale ET estimates are improved after incorporating heterogeneous agricultural land use (NSC?>?0.55 and R2?>?0.55) throughout the period of 1998–2010. This study improves our understanding on how the change in agricultural land use in the model settings alters the basin hydrological characteristics, and to provide model-based approaches for best management practices in irrigation scheduling, crop water requirement, and management strategies in the absence of flux towers, eddy covariance, and lysimeters in the basin.

  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号