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   42332篇
  免费   5691篇
  国内免费   3458篇
电工技术   4176篇
综合类   5013篇
化学工业   5393篇
金属工艺   1766篇
机械仪表   2730篇
建筑科学   4633篇
矿业工程   1439篇
能源动力   2026篇
轻工业   2489篇
水利工程   2123篇
石油天然气   2491篇
武器工业   537篇
无线电   4645篇
一般工业技术   4392篇
冶金工业   1176篇
原子能技术   804篇
自动化技术   5648篇
  2024年   230篇
  2023年   701篇
  2022年   1334篇
  2021年   1443篇
  2020年   1678篇
  2019年   1456篇
  2018年   1361篇
  2017年   1702篇
  2016年   1816篇
  2015年   1918篇
  2014年   2508篇
  2013年   2940篇
  2012年   3176篇
  2011年   3299篇
  2010年   2346篇
  2009年   2542篇
  2008年   2459篇
  2007年   2861篇
  2006年   2443篇
  2005年   2076篇
  2004年   1746篇
  2003年   1360篇
  2002年   1218篇
  2001年   1063篇
  2000年   906篇
  1999年   784篇
  1998年   612篇
  1997年   569篇
  1996年   500篇
  1995年   459篇
  1994年   392篇
  1993年   277篇
  1992年   237篇
  1991年   205篇
  1990年   207篇
  1989年   146篇
  1988年   110篇
  1987年   70篇
  1986年   59篇
  1985年   52篇
  1984年   33篇
  1983年   22篇
  1982年   31篇
  1981年   22篇
  1980年   31篇
  1979年   11篇
  1978年   11篇
  1977年   8篇
  1959年   9篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
101.
A new method for prediction of Gurney velocity of explosives is introduced in which energy output is correlated with the heat of detonation, the number of moles of gaseous products of detonation per gram of explosive and the average molecular weight of gaseous products. It is assumed that the CHNO explosive reacts to form products composed of N2 , CO, H2O, CO2, H2,O2 and C(s) as determined by the oxygen balance of the unreacted compound. Good agreement is obtained between measured and calculated values of Gurney velocity as compared to previous correlations which assumed the reaction products to consist of N2 , H2O, CO2 and either C(s) or O2.  相似文献   
102.
二硫代磷酸硫化氧钼与硫,磷添加剂的复配特性研究   总被引:1,自引:0,他引:1  
研究了二烷基二硫代磷酸硫化氧钼(MoDTP)摩擦改进剂及其与硫、磷、硫-磷型添加剂复合的抗磨减摩性能。试验表明,经过适当复配后,这类合活性元素的添加剂对MoDTP的抗磨减摩性能均有增效作用,同一类型添加剂的活性愈高,增效作用愈显著。同时利用扫描电镜和X-射线能谱仪进行摩擦副表面膜的形貌照相及元素分析,对复合作用的机理进行了初步探讨。  相似文献   
103.
多元函数可微性的一个注记   总被引:1,自引:0,他引:1  
给出了Henle定理的简单证明,并指出该定理在n≥3时不再成立,进而又给出了一个当n≥3时,函数z=f(x1,x2,…,xn)在点M0可微的定理及其证明。  相似文献   
104.
克拉2气田储层岩石的应力敏感性及其对生产动态的影响   总被引:9,自引:2,他引:7  
克拉2气田是一个异常高压气藏,压力系数在2.0以上。在衰竭式开采条件下,其地层压力降幅可为普通气藏地层压力降幅的3倍以上,因此研究储层岩石应力敏感性及其对生产动态的影响意义重大。研究得出,岩石的应力敏感性特征主要有:岩石物性对应力的敏感性总体上不大,其中以孔隙度最小,渗透率次之,压缩系数最大;岩石物性随地层压力的下降而下降;在同一地层压降下.岩石物性下降幅度不是渗透率的连续函数,而是与渗透率分布范围有关,高渗透率范围,岩石物性下降幅度小,低渗透率范围,岩石物性下降幅度大。研究得出,克拉2气田岩石的应力敏感性对其生产动态的影响较小。  相似文献   
105.
Thermal Radiative Properties of Xonotlite Insulation Material   总被引:1,自引:0,他引:1  
Introduction Xonotlite-type calcium silicate (6CaO?6SiO2?H2O) is synthesized porous insulation material by hydrothermal processing with quartz powder and limestone as the raw material (with CaO/ SiO2≈1:1). Compared with fire- retardant fibre, xonotlite has more excellent insulating performance, such as low thermal conductivity, environment friendly, high intension, and wide applying temperature range, which has been emphasized in recent years by many scholars and widely used in many indu…  相似文献   
106.
Abstract. A pth‐order random coefficient integer‐valued autoregressive [RCINAR(p)] model is proposed for count data. Stationarity and ergodicity properties are established. Maximum likelihood, conditional least squares, modified quasi‐likelihood and generalized method of moments are used to estimate the model parameters. Asymptotic properties of the estimators are derived. Simulation results on the comparison of the estimators are reported. The models are applied to two real data sets.  相似文献   
107.
Solubility of dimethyl-2,6-naphthalene dicarboxylate in acetic acid, N,N-dimethylfonnamide, N,N-dimethyl acetamide, dimethyl sulphoxide, and N-methyl-2-ketopyrrolidine were determined using a dynamic method. The measured systems were correlated by UNIFAC group contribution method. A new main group (aromatic ester, ACCOO) was defined to express the activity coefficients of the aromatic ester. New interaction parameters of the ACCOO group were expressed as the first-order function of temperature and were determined from the experimental data. The calculated results for the new interaction parameters were satisfactory. The measured systems were also correlated with the Wilson and 2-h models, and the results were compared with those of the UNIFAC model.  相似文献   
108.
A simple, rapid and sensitive procedure for the simultaneous determination of total cholesterol, tocopherols and β-carotene in meat is described. The method involves a direct saponification of the meat, a single n-hexane extraction and the analysis of the extracted compounds by normal-phase HPLC, using fluorescence (tocopherols) and UV–Vis photodiode array (cholesterol and β-carotene) detections in tandem. Rates of recovery of spiked meat samples were 93% for cholesterol, 83–86% for (α-, β- and -γ) tocopherols and 89% for β-carotene. Repeatabilities were high (CV < 6%) for all determined compounds, except for δ-tocopherol. This tocopherol, which is not usually present in meat, showed a much lower recovery percentage (73%) and repeatability (12.8%). This methodology was applied for the quantification of total cholesterol, tocopherols and β-carotene in three muscles (longissimus thoracis, longissimus lumborum and semitendinosus) of the Portuguese traditional Barrosã-PDO veal, obtained from autochthonous calves fed extensively during summer (with the least abundant green pastures) and slaughtered in early autumn (October). Barrosã-PDO veal showed median contents of total cholesterol (0.50–0.56 mg/g) and, depending on the analysed muscle, moderate to high contents of α-tocopherol (3.3–3.9 μg/g) and β-carotene (0.07–0.09 μg/g), suggesting an high sensorial and hygienic quality.  相似文献   
109.
针对部分Q195冷轧板材存在轧制困难的现象,进行了现场检验与分析。带状组织、混晶现象严重导致变形强化系数偏高是造成轧制困难的主要原因。  相似文献   
110.
Principal component regression (PCR), partial least squares (PLS), StepWise ordinary least squares regression (OLS), and back‐propagation artificial neural network (BP‐ANN) are applied here for the determination of the propylene concentration of a set of 83 production samples of ethylene–propylene copolymers from their infrared spectra. The set of available samples was split into (a) a training set, for models calculation; (b) a test set, for selecting the correct number of latent variables in PCR and PLS and the end point of the training phase of BP‐ANN; (c) a production set, for evaluating the predictive ability of the models. The predictive ability of the models is thus evaluated by genuine predictions. The model obtained by StepWise OLS turned out to be the best one, both in fitting and prediction. The study of the breakdown number of samples to be included in the training set showed that at least 52 experiments are necessary to build a reliable and predictive calibration model. It can be concluded that FTIR spectroscopy and OLS can be properly employed for monitoring the synthesis or the final product of ethylene–propylene copolymers, by predicting the concentration of propylene directly along the process line. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  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