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   18490篇
  免费   474篇
  国内免费   18篇
电工技术   240篇
综合类   9篇
化学工业   3638篇
金属工艺   282篇
机械仪表   317篇
建筑科学   1120篇
矿业工程   109篇
能源动力   519篇
轻工业   1438篇
水利工程   163篇
石油天然气   194篇
武器工业   1篇
无线电   1090篇
一般工业技术   2914篇
冶金工业   4274篇
原子能技术   170篇
自动化技术   2504篇
  2022年   149篇
  2021年   223篇
  2020年   174篇
  2019年   228篇
  2018年   271篇
  2017年   266篇
  2016年   326篇
  2015年   243篇
  2014年   386篇
  2013年   1120篇
  2012年   680篇
  2011年   894篇
  2010年   699篇
  2009年   685篇
  2008年   865篇
  2007年   885篇
  2006年   694篇
  2005年   731篇
  2004年   573篇
  2003年   580篇
  2002年   517篇
  2001年   336篇
  2000年   308篇
  1999年   310篇
  1998年   353篇
  1997年   324篇
  1996年   310篇
  1995年   342篇
  1994年   274篇
  1993年   313篇
  1992年   277篇
  1991年   168篇
  1990年   241篇
  1989年   285篇
  1988年   206篇
  1987年   215篇
  1986年   215篇
  1985年   266篇
  1984年   262篇
  1983年   229篇
  1982年   219篇
  1981年   216篇
  1980年   173篇
  1979年   187篇
  1978年   176篇
  1977年   179篇
  1976年   148篇
  1975年   180篇
  1974年   165篇
  1973年   134篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Synthetic aggregation pheromones ofCarpophilus hemipterus (L.) andCarpophilus mutilatus Erichson were field tested during a 10-month period in southern New South Wales stone fruit orchards to determineCarpophilus spp. phenology and the effect of two pheromone doses on attraction. Aggregation pheromones synergize the attraction of host volatiles toCarpophilus spp. Four major species,C. hemipterus, C. mutilatus, C. davidsoni Dobson andC. (Urophorus) humeralis (F.), were trapped, with greater numbers of each species inC. hemipterus pheromone/fermenting whole-wheat breaddough-baited traps, than in dough-only-traps. InC. mutilatus pheromone/ fermenting-dough-baited traps, onlyC. mutilatus andC. davidsoni responded in greater numbers than to dough-only traps. Beetles first appeared in traps in late September (early spring) when daily maximum temperatures averaged 17.5C. Trappings reached a peak during October and declined to very low levels in November–December (late spring-early summer). Numbers trapped of all species increased during February–March (late summer–early autumn), presumably due to the presence of abundant host resources (ripening and fallen fruit), and continued at high levels until May (late autumn). An 18-week study demonstrated significantly greater responses byCarpophilus spp. to 5000-g than to 500-g doses of C.hemipterus andC. mutilatus pheromones. Greatest responses to 5000g were recorded forC. hemipterus andC. mutilatus responding to their own pheromones (increased attraction over dough alone of 259x and 21.2x respectively). Implications of the study and the potential for using synthetic aggregation pheromones for managingCarpophilus spp. populations in Australian stone fruit are discussed.  相似文献   
63.
In this paper we report the results of Quantum Monte Carlo (QMC) simulations of a tight binding, correlated electron model consisting of two 2D Hubbard sheets hybridized by an intersheet hopping t. As t increases, a ground state with long range antiferromagnetic order gives way to a spin liquid phase.  相似文献   
64.
65.
This paper describes a method for rounding edges and corners of arbitrary polyhedra that uses a fast approximation to convolutional filtering. The approximation defines an implicit surface, which is rendered with a specialised ray-tracing algorithm. By varying the radius of the smoothing filter, a wide range of effects can be obtained, from perfect polyhedra to blobby models. Small rounding radii give polyhedra a softer, more natural look, with edges well delineated by shadows and highlights. The rounded surfaces are much easier to specify and compute than those obtained by traditional filleting and surface-blending techniques, and are far more economical in storage.  相似文献   
66.
According to the human factors paradigm for patient safety, health care work systems and innovations such as electronic medical records do not have direct effects on patient safety. Instead, their effects are contingent on how the clinical work system, whether computerized or not, shapes health care providers’ performance of cognitive work processes. An application of the human factors paradigm to interview data from two hospitals in the Midwest United States yielded numerous examples of the performance-altering effects of electronic medical records, electronic clinical documentation, and computerized provider order entry. Findings describe both improvements and decrements in the ease and quality of cognitive performance, both for interviewed clinicians and for their colleagues and patients. Changes in cognitive performance appear to have desirable and undesirable implications for patient safety as well as for quality of care and other important outcomes. Cognitive performance can also be traced to interactions between work system elements, including new technology, allowing for the discovery of problems with “fit” to be addressed through design interventions.  相似文献   
67.
We revisit the problem of determining confidence interval widths for the comparison of means. For the independent two-sample (two-sided) case, Goldstein and Healy (1995) draw attention to the fact that comparisons based on 95% error bars are not very effective in assessing the statistical significance of the difference in means and derive the correct confidence interval for such a comparison. We provide an extension to Goldstein and Healy (1995) to account for the correlation structure and unequal variances. We use the results to develop rules of thumb for evaluating differences, in an exploratory manner, like Moses (1987) and Cumming (2009), from the independent case. We illustrate the method for the simple comparison of two means in a real data set, provide R code that may be easily implemented in practice, and discuss the extension of the method to other applied problems.  相似文献   
68.
69.
70.
In this paper, we present a thorough mathematical analysis of the use of neural networks to solve a specific classification problem consisting of a bilinear boundary. The network under consideration is a three-layered perceptron with two hidden neurons having the sigmoid serving as the activation function. The analysis of the hidden space created by the outputs of the hidden neurons will provide results on the network’s capacity to isolate two classes of data in a bilinear fashion, and the importance of the value of the sigmoid parameter is highlighted. We will obtain an explicit analytical function describing the boundary generated by the network, thus providing information on the effect each parameter has on the network’s behavior. Generalizations of the results are obtained with additional neurons, and a theorem concerned with analytical reproducibility of the boundary function is established.  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