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   70702篇
  免费   3302篇
  国内免费   107篇
电工技术   598篇
综合类   65篇
化学工业   14740篇
金属工艺   1396篇
机械仪表   1377篇
建筑科学   3051篇
矿业工程   185篇
能源动力   2111篇
轻工业   9227篇
水利工程   766篇
石油天然气   276篇
武器工业   5篇
无线电   3925篇
一般工业技术   11164篇
冶金工业   13582篇
原子能技术   495篇
自动化技术   11148篇
  2023年   434篇
  2022年   842篇
  2021年   1628篇
  2020年   1129篇
  2019年   1435篇
  2018年   1898篇
  2017年   1766篇
  2016年   2003篇
  2015年   1714篇
  2014年   2306篇
  2013年   4782篇
  2012年   3626篇
  2011年   4260篇
  2010年   3346篇
  2009年   3237篇
  2008年   3328篇
  2007年   3151篇
  2006年   2651篇
  2005年   2338篇
  2004年   2043篇
  2003年   1878篇
  2002年   1757篇
  2001年   1197篇
  2000年   1043篇
  1999年   1148篇
  1998年   2940篇
  1997年   2103篇
  1996年   1610篇
  1995年   1144篇
  1994年   1009篇
  1993年   1030篇
  1992年   680篇
  1991年   463篇
  1990年   562篇
  1989年   563篇
  1988年   465篇
  1987年   482篇
  1986年   422篇
  1985年   573篇
  1984年   515篇
  1983年   402篇
  1982年   393篇
  1981年   388篇
  1980年   370篇
  1979年   326篇
  1978年   296篇
  1977年   399篇
  1976年   540篇
  1975年   236篇
  1973年   205篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification.  相似文献   
22.
Seed processing technologies are essential for seed safety and functionality through protection of physicochemical quality, pathogen inactivation, aflatoxin detoxification and alleviation of mutagenicity. Design of a pilot-scale unit of pulsed electric fields (PEF) to treat sesame seeds with respect to quality parameters, Aspergillus parasiticus inactivation and aflatoxin reduction as well as alleviation of aflatoxin mutagenicity were prompted in this study. PEF energy ranged from 0.97 to 17.28 J achieved maximum reductions of peroxide value and acidity number of 67.4 and 85.7%, respectively, and did not change color L*, a*, b* and hue values. A 60% reduction of A. parasiticus counts occurred at the maximum PEF energy. Aflatoxins G1, G2, B1, and B2 contents decreased by 94.7, 92.7, 86.9, and 98.7%, respectively. Except for the samples treated by 2.16 J with 100 μg/plate and by 6.80 J with 10 μg/plate, PEF treatment provided elimination of aflatoxin mutagenity. It is concluded that PEF treatment can be used to treat sesame seeds with preservation of physicochemical properties, inactivation of A. parasiticus and decomposition of aflatoxins with reduced mutagenicity.  相似文献   
23.
Urbano  Cristóbal  Ardanuy  Jordi 《Scientometrics》2020,124(1):575-602
Scientometrics - The interdisciplinary nature of library and information science (LIS) research has been highlighted for some time now. The term “interdisciplinary” is used primarily in...  相似文献   
24.
Neural Computing and Applications - This study presents the design of a tenth-order multiple feedback Chebyshev low-pass filter (MF-C-LPF). Component selection and gain calculation of filters are...  相似文献   
25.
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   
26.
Zinc (Zn), the second-most necessary trace element, is abundant in the human body. The human body lacks the capacity to store Zn; hence, the dietary intake of Zn is essential for various functions and metabolism. The uptake of Zn during its transport through the body is important for proper development of the three major accessory sex glands: the testis, epididymis, and prostate. It plays key roles in the initial stages of germ cell development and spermatogenesis, sperm cell development and maturation, ejaculation, liquefaction, the binding of spermatozoa and prostasomes, capacitation, and fertilization. The prostate releases more Zn into the seminal plasma during ejaculation, and it plays a significant role in sperm release and motility. During the maternal, labor, perinatal, and neonatal periods, the part of Zn is vital. The average dietary intake of Zn is in the range of 8–12 mg/day in developing countries during the maternal period. Globally, the dietary intake of Zn varies for pregnant and lactating mothers, but the average Zn intake is in the range of 9.6–11.2 mg/day. The absence of Zn and the consequences of this have been discussed using critical evidence. The events and functions of Zn related to successful fertilization have been summarized in detail. Briefly, our current review emphasizes the role of Zn at each stage of human reproduction, from the spermatogenesis process to childbirth. The role of Zn and its supplementation in in vitro fertilization (IVF) opens opportunities for future studies on reproductive biology.  相似文献   
27.
28.
29.
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