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   1493084篇
  免费   25793篇
  国内免费   6940篇
电工技术   34178篇
综合类   6354篇
化学工业   269941篇
金属工艺   63988篇
机械仪表   41809篇
建筑科学   45805篇
矿业工程   11346篇
能源动力   50242篇
轻工业   112325篇
水利工程   14869篇
石油天然气   37508篇
武器工业   128篇
无线电   195599篇
一般工业技术   282307篇
冶金工业   157002篇
原子能技术   33874篇
自动化技术   168542篇
  2021年   15490篇
  2020年   11787篇
  2019年   14572篇
  2018年   15137篇
  2017年   14351篇
  2016年   20968篇
  2015年   17220篇
  2014年   28592篇
  2013年   87640篇
  2012年   34924篇
  2011年   46840篇
  2010年   41772篇
  2009年   50372篇
  2008年   43935篇
  2007年   41056篇
  2006年   44317篇
  2005年   38776篇
  2004年   41225篇
  2003年   41118篇
  2002年   40310篇
  2001年   37122篇
  2000年   35651篇
  1999年   34528篇
  1998年   42604篇
  1997年   37849篇
  1996年   34606篇
  1995年   30351篇
  1994年   28576篇
  1993年   28337篇
  1992年   26207篇
  1991年   23301篇
  1990年   23612篇
  1989年   22693篇
  1988年   21271篇
  1987年   19478篇
  1986年   18923篇
  1985年   22306篇
  1984年   22446篇
  1983年   20450篇
  1982年   19306篇
  1981年   19406篇
  1980年   18000篇
  1979年   18632篇
  1978年   17792篇
  1977年   17605篇
  1976年   18623篇
  1975年   16050篇
  1974年   15601篇
  1973年   15658篇
  1972年   13160篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
This study evaluated several physical and sensory parameters of different types of cheese available in the Polish market. The measurements of textural properties were conducted in an Instron universal testing machine, while the colour properties of cheeses were measured using a Minolta chromameter. The chemical composition was determined by means of the near‐infrared spectroscopy (NIRs). Moreover, a trained sensory panel was invited to assess the cheese texture‐related properties. Generally, cheeses with reduced fat content were characterised by higher hardness, adhesiveness, cohesiveness and elasticity. Texture‐related parameters of cheese with canola oil were comparable to that of most of full‐fat cheeses. The correlation analysis between physical and sensory attributes related to cheese textural properties indicated the potential applications of TPA, shear and penetration tests (= 0.766, = 0.75 and = 0.765, respectively) for the evaluation of sensory properties related to the hardness. Meanwhile, the elasticity of cheese obtained from sensory evaluation was strongly correlated with the elasticity determined from the shear test (= 0.722) and moderately correlated with the elasticity from penetration test (= 0.588), indicating a need to refine the method of penetration test. In addition, cheeses exhibited higher meltability during convection heating at 230 °C than microwave heating. The values of meltability for cheese with reduced fat content were lower than those of full‐fat cheese.  相似文献   
182.
183.
In submerged cultures performed in chemically defined fermentation medium containing glucose and glutamate, the growth and production of water‐soluble red pigments and citrinin by the filamentous fungus Monascus ruber were studied under various carbon/nitrogen (C/N) ratios. The specific production of the red pigments was optimal at a glucose/glutamate ratio of about 10 and then steadily decreased at higher C/N ratio. In contrast, the production of the mycotoxin increased with increased C/N with an optimum in the range of 30–45. In a fed‐batch mode, it was also found that the production of pigments was not favoured in fed‐batch mode by feeding the medium with glucose while keeping the C/N ratio lower than 10. This low production likely resulted from concurrent high accumulation of L‐malic acid that was reported to inhibit this production. In contrast, this mode of cultivation was rather favourable for the production of the mycotoxin.  相似文献   
184.
185.
186.
187.
Hyperspectral imaging (HSI) is a spectroscopic method that uses densely sampled measurements along the electromagnetic spectrum to identify the unique molecular composition of an object. Traditionally HSI has been associated with remote sensing-type applications, but recently has found increased use in biomedicine, from investigations at the cellular to the tissue level. One of the main challenges in the analysis of HSI is estimating the proportions, also called abundance fractions of each of the molecular signatures. While there is great promise for HSI in the area of biomedicine, large variability in the measurements and artifacts related to the instrumentation has slow adoption into more widespread practice. In this article, we propose a novel regularization and variable selection method called the spatial LASSO (SPLASSO). The SPLASSO incorporates spatial information via a graph Laplacian-based penalty to help improve the model estimation process for multivariate response data. We show the strong performance of this approach on a benchmark HSI dataset with considerable improvement in predictive accuracy over the standard LASSO. Supplementary materials for this article are available online.  相似文献   
188.
189.
Lévy flights have gained prominence for analysis of animal movement. In a Lévy flight, step-lengths are drawn from a heavy-tailed distribution such as a power law (PL), and a large number of empirical demonstrations have been published. Others, however, have suggested that animal movement is ill fit by PL distributions or contend a state-switching process better explains apparent Lévy flight movement patterns. We used a mix of direct behavioural observations and GPS tracking to understand step-length patterns in females of two related butterflies. We initially found movement in one species (Euphydryas editha taylori) was best fit by a bounded PL, evidence of a Lévy flight, while the other (Euphydryas phaeton) was best fit by an exponential distribution. Subsequent analyses introduced additional candidate models and used behavioural observations to sort steps based on intraspecific interactions (interactions were rare in E. phaeton but common in E. e. taylori). These analyses showed a mixed-exponential is favoured over the bounded PL for E. e. taylori and that when step-lengths were sorted into states based on the influence of harassing conspecific males, both states were best fit by simple exponential distributions. The direct behavioural observations allowed us to infer the underlying behavioural mechanism is a state-switching process driven by intraspecific interactions rather than a Lévy flight.  相似文献   
190.
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