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   293784篇
  免费   5219篇
  国内免费   1209篇
电工技术   4939篇
综合类   829篇
化学工业   41801篇
金属工艺   8867篇
机械仪表   8416篇
建筑科学   7663篇
矿业工程   972篇
能源动力   7652篇
轻工业   30649篇
水利工程   2658篇
石油天然气   1912篇
武器工业   9篇
无线电   35277篇
一般工业技术   50503篇
冶金工业   65201篇
原子能技术   3552篇
自动化技术   29312篇
  2021年   1883篇
  2020年   1358篇
  2019年   1711篇
  2018年   3594篇
  2017年   3756篇
  2016年   4150篇
  2015年   3056篇
  2014年   4121篇
  2013年   12345篇
  2012年   8869篇
  2011年   12160篇
  2010年   8095篇
  2009年   9148篇
  2008年   9517篇
  2007年   9543篇
  2006年   8813篇
  2005年   11567篇
  2004年   10198篇
  2003年   9404篇
  2002年   7432篇
  2001年   7734篇
  2000年   6582篇
  1999年   7349篇
  1998年   21480篇
  1997年   14543篇
  1996年   10686篇
  1995年   7797篇
  1994年   6621篇
  1993年   6525篇
  1992年   4212篇
  1991年   4040篇
  1990年   3833篇
  1989年   3623篇
  1988年   3540篇
  1987年   2796篇
  1986年   2664篇
  1985年   3314篇
  1984年   2856篇
  1983年   2628篇
  1982年   2460篇
  1981年   2552篇
  1980年   2375篇
  1979年   2105篇
  1978年   1970篇
  1977年   2756篇
  1976年   3974篇
  1975年   1670篇
  1974年   1526篇
  1973年   1601篇
  1972年   1183篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Photonic Network Communications - Optical packet switching is a prominent technology proposing not only a reduction in the energy consumption by the elimination of numerous...  相似文献   
22.
23.
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape.  相似文献   
24.
25.
26.
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019  相似文献   
27.
28.
The Journal of Supercomputing - Infrastructure-as-a-service container-based virtualization is gaining interest as a platform for running distributed applications. With increasing scale of cloud...  相似文献   
29.
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.  相似文献   
30.
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