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   2986篇
  免费   56篇
  国内免费   13篇
电工技术   168篇
综合类   23篇
化学工业   633篇
金属工艺   67篇
机械仪表   65篇
建筑科学   53篇
能源动力   94篇
轻工业   270篇
水利工程   19篇
石油天然气   7篇
无线电   355篇
一般工业技术   433篇
冶金工业   649篇
原子能技术   41篇
自动化技术   178篇
  2023年   11篇
  2022年   30篇
  2021年   42篇
  2020年   13篇
  2019年   25篇
  2018年   31篇
  2017年   29篇
  2016年   32篇
  2015年   34篇
  2014年   55篇
  2013年   120篇
  2012年   103篇
  2011年   99篇
  2010年   90篇
  2009年   97篇
  2008年   104篇
  2007年   112篇
  2006年   99篇
  2005年   94篇
  2004年   82篇
  2003年   83篇
  2002年   91篇
  2001年   81篇
  2000年   51篇
  1999年   86篇
  1998年   251篇
  1997年   186篇
  1996年   130篇
  1995年   68篇
  1994年   79篇
  1993年   80篇
  1992年   43篇
  1991年   57篇
  1990年   41篇
  1989年   46篇
  1988年   28篇
  1987年   29篇
  1986年   39篇
  1985年   49篇
  1984年   33篇
  1983年   32篇
  1982年   20篇
  1981年   23篇
  1980年   23篇
  1979年   19篇
  1978年   11篇
  1977年   23篇
  1976年   20篇
  1973年   6篇
  1972年   9篇
排序方式: 共有3055条查询结果,搜索用时 0 毫秒
81.
Male Fischer 344 rats were subcutaneously injected with azoxymethane (AOM) twice weekly at a dose of 15 mg/kg and were fed with freeze-dried (FD) samples of beer brewed without hops (non-hops beer), beer with hops at 4 times the amount of regular lager beer (x 4-hops beer), and isomerized hop extract (IHE) for the whole experimental period (I/PI) or for the post-initiation period (PI) only. Feeding FD beer samples at a dose of 1% significantly decreased the number of aberrant cryp foci (ACF) in the PI protocol over five weeks.x4-hops beer showed stronger inhibitory effects on the development of the numbers of aberrant crypts per focus and large ACF with four or more crypts than non-hops beer. Feeding IHE to rats at a dose of 0.01% or 0.05% in either the I/PI or PI experiment significantly reduced the numbers of ACF. Prostaglandin E2 (PGE2) levels in colonic mucosa of AOM-treated rats were significantly reduced by feeding of IHE. PGE2 production induced by lipopolysaccharide/interferon-gamma (LPS/IFN-gamma) in RAW264.7 cells was also reduced by treatment with IHE and isohumulone in a dose-dependent manner. These observations suggest that isohumulones show chemopreventive effects on ACF formation in rat colon by inhibiting the production of PGE2.  相似文献   
82.
The effect of low-molecular-weight polyphenols extracted from lychee (Oligonol) on metabolic syndrome characterized by abdominal obesity was examined. We performed a clinical trial for Oligonol conducted by randomized double-blind, placebo-controlled study. Eighteen (male, 14; female, 4) adult volunteers with abdominal circumference over 85 cm were enrolled and divided into two groups, Oligonol and placebo groups. All subjects took two capsules of Oligonol (50 mg/capsule) or placebo twice a day for 10 weeks. Physical and haematological examinations as well as a CT scan of the abdomen were carried out, before (control) and 10 weeks after Oligonol intake. Clinical parameters of body weight, abdominal circumference and visceral fat volume were significantly decreased in the Oligonol group compared to the control. Insulin resistance was improved by Oligonol in conjunction with elevation of serum adiponectin. These results suggest that Oligonol ameliorates metabolic syndrome by reducing visceral fat obesity.  相似文献   
83.
Additive effects of glass powder upon the product yields and chlorine distribution after liquefaction of hydrothermally pretreated mixed waste (HMW) are compared with liquefaction of HMW with any one of water, quartz sand, or glass powder plus water. As a result, addition of either water or quartz sand did not affect liquefaction and dechlorination of HMW. Further, water (5 g) addition did not enhance liquefaction and dechlorination of HMW with glass powder. On the other hand, after liquefaction of HMW with glass powder, the yields of chlorine in the gas and water insoluble constituents decreased and the chlorine yield in the water-soluble constituent increased significantly. Because sodium in glass powder dissolved in a small amount (0.5 g) of water resulted from dehydration of HMW during liquefaction. Further, hydrogen chloride derived from polyvinylchloride in HMW was neutralized by ion exchange between H(+) and Na(+) dissolved in a small amount of water forming NaCl in the Residue (water-soluble) constituent. Therefore, most of chlorine in HMW was removed easily by water extraction of the Residue constituent after liquefaction of HMW with glass powder. Further, upgrading of HMW into the oil constituent was enhanced due to inhibition of production of chlorine containing organic compounds. Accordingly, it was clarified that glass powder was the most effective additive for liquefaction and dechlorination of HMW.  相似文献   
84.
The glucosyl transfer reaction of kojibiose phosphorylase (KP; EC 2.4.1.230) was examined using glycerol or myo-inositol as an acceptor. In the case of glycerol, KP produced two main transfer products: saccharides A and B. The structure of saccharide A was O-alpha-D-glucopyranosyl-(1-->1)-glycerol and that of saccharide B was O-alpha-D-glucopyranosyl-(1-->2)-O-alpha-D-glucopyranosyl-(1-->1)-glycerol. These results show that KP transferred a glucose residue to the hydroxyl group at position 1 of glycerol. On the other hand, when myo-inositol was used as an acceptor, KP produced four transfer products: saccharides 1-4. The structures of saccharides 1 and 2 were O-alpha-D-glucopyranosyl-(1-->1)- and O-alpha-D-glucopyranosyl-(1-->5)-myo-inositol, respectively; those of saccharides 3 and 4 were O-alpha-D-glucopyranosyl-(1-->2)-O-alpha-D-glucopyranosyl-(1-->1)- and O-alpha-D-glucopyranosyl-(1-->2)-O-alpha-D-glucopyranosyl-(1-->5)-myo-inositol, respectively. KP transferred a glucose residue to the hydroxyl group at position 1 or 5 of myo-inositol. On the basis of the structures of their glucosyl transfer products, glycerol and myo-inositol were found to have a common structure with three hydroxyl groups corresponding to the hydroxyl group of the glucose molecule at positions 2, 3 and 4. The conformation of these three hydroxyl groups in the structure is equatorial. This structure is the substrate recognition site of KP. It has been suggested that KP strictly recognizes the structures of glycerol and myo-inositol, and catalyzes the transfer reaction of a glucose residue to the hydroxyl group at position 1 in glycerol, and at position 1 or 5 in myo-inositol, corresponding to position 2 in glucose.  相似文献   
85.
86.
A novel repeated batch operation mode was proposed for ethanol fermentation, where the fermenter beer was periodically exchanged between the fermenter with biomass recycle and the distillation unit, to promote the selective removal of ethanol. Using the mathematical model developed, as based on the experimental results, the optimal operation of the proposed method was shown to attain high performance, with a productivity of about 12 g dm−3 h−1 and a product concentration of 400 g dm−3.  相似文献   
87.
88.
The promotional effects of Co in CoMoAl2O3 hydrodesulfurization (HDS) catalysts were studied by means of X-ray photoelectron spectroscopy. The higher MoO3-content MoAl2O3 catalysts (10 and 20 wt% MoO3) contain mobile Mo, which migrates from the pores to the outermost surface layers of the catalysts and segregates to form less active crystalline MoS2 during the HDS reaction, while in the case of MoAl2O3 (5 wt% MoO3) catalyst: no migration of Mo was observed. It is revealed that the Co in CoMoAl2O3 catalyst inhibits the migration and segregation of Mo and that it keeps Mo effective for the HDS reaction, since no surface enrichment of Mo was observed. It is concluded that stabilization of the Mo monomolecular layer is the main role of Co. The active species of Mo is suggested to have the composition of S/Mo(IV) = 1 on the basis of the sulfur contents of the catalysts under the mild HDS reaction conditions.  相似文献   
89.
Mouse embryonic stem (ES) cells have the pluripotent ability to differentiate in vitro into various cell lineages, including neurons. Adding chick dorsal root ganglion (DRG) conditioned medium (CM) to the culture medium promotes the differentiation of ES cells into neurons. We determined the types of neurons that differentiate from ES cells. The addition of DRG-CM caused nearly half of all ES cells on the periphery of the colony sphere to differentiate into neurons. Immunofluorescence analysis showed that the neurons that differentiated from ES cells were mainly motor, GABAergic, serotonergic, and cholinergic neurons. Of particular note, flow cytometry showed that approximately 50% of betaIII-tubulin-positive neurons were motor neurons. This indicates that DRG-CM induces ES cells to differentiate into motor neurons as target of DRG neurons (sensory neurons).  相似文献   
90.
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