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   7176篇
  免费   186篇
  国内免费   17篇
电工技术   305篇
综合类   5篇
化学工业   1524篇
金属工艺   166篇
机械仪表   183篇
建筑科学   169篇
矿业工程   1篇
能源动力   204篇
轻工业   679篇
水利工程   37篇
石油天然气   8篇
无线电   620篇
一般工业技术   1264篇
冶金工业   1399篇
原子能技术   222篇
自动化技术   593篇
  2023年   39篇
  2022年   64篇
  2021年   143篇
  2020年   67篇
  2019年   80篇
  2018年   128篇
  2017年   91篇
  2016年   161篇
  2015年   87篇
  2014年   166篇
  2013年   379篇
  2012年   260篇
  2011年   367篇
  2010年   252篇
  2009年   313篇
  2008年   329篇
  2007年   254篇
  2006年   264篇
  2005年   230篇
  2004年   214篇
  2003年   220篇
  2002年   209篇
  2001年   147篇
  2000年   122篇
  1999年   175篇
  1998年   533篇
  1997年   371篇
  1996年   272篇
  1995年   153篇
  1994年   157篇
  1993年   168篇
  1992年   72篇
  1991年   69篇
  1990年   68篇
  1989年   67篇
  1988年   57篇
  1987年   43篇
  1986年   67篇
  1985年   72篇
  1984年   48篇
  1983年   52篇
  1982年   41篇
  1981年   45篇
  1980年   43篇
  1979年   29篇
  1978年   20篇
  1977年   36篇
  1976年   50篇
  1975年   16篇
  1973年   14篇
排序方式: 共有7379条查询结果,搜索用时 203 毫秒
981.
Protein and mRNA expression of transforming growth factor-beta (TGF-beta) receptor type I (TbetaRI), type II (TbetaRII), and type III (TbetaRIII) were studied in serial sections of kidney samples obtained from patients with glomerulonephritis. In minimal change disease, weak expression of TbetaRI and TbetaRII was observed mainly in glomerular endothelial cells, peritubular capillaries, and interstitial arteriolar endothelial cells, whereas TbetaRIII expression was found mainly in the interstitium. Expression of all three TGF-beta receptors (TbetaR) was increased remarkably in glomerular and Bowman's capsular cells comprising the tuft adhesions to Bowman's capsules in glomerulonephritis with increased matrix accumulation, including IgA nephropathy, lupus nephritis, focal and segmental glomerulosclerosis, myeloperoxidase-antineutrophil cytoplasmic antibody-associated crescentic glomerulonephritis, and membranoproliferative glomerulonephritis. Increased expression of the three TbetaR was also seen in glomerular epithelial cells in the vicinity of glomerulosclerotic lesions, in crescent cells, and in some tubules and infiltrative mononuclear cells found in the periglomerular and tubulointerstitial lesions with increased matrix deposition. In contrast, no remarkable TbetaRII expression was noted in mesangial proliferative lesions in IgA nephropathy, lupus nephritis, and membranoproliferative glomerulonephritis. These data suggest that distinctive modulation of TbetaR expression may be involved in the development of adhesive, sclerotic, and proliferative renal lesions in human glomerulonephritis.  相似文献   
982.
The interaction between CD28 and its ligands, CD80 and CD86, is crucial for an optimal activation of antigen-specific T cells. However, the requirement of CD80 or CD86 co-stimulation in Th2 cell differentiation and activation is controversial. Freshly isolated murine CD4+ and CD8+ T cells were incubated with P815 transfectants expressing a similar level of either CD80 or CD86 in the presence of anti-CD3 mAb. Both CD80 and CD86 co-stimulated the proliferation of CD4+ and CD8+ T cells at comparable time-kinetics and magnitude, but CD86 alone was able to co-stimulate IL-4 and especially IL-10 production in CD4+ T cells. In typical Th2-dependent immune responses elicited by Nippostrongylus brasillensis infection, the anti-CD86 mAb treatment but not the anti-CD80 mAb treatment efficiently inhibited antigen-specific IgE and IgG1 production, which was accompanied with the reduced IL-4 production. Our results suggest that CD86 co-stimulation plays a dominant role not only in the primary activation of Th2 cells but also in the secondary interaction between antigen-primed Th2 cells and B cells.  相似文献   
983.
This study used an intracerebral self-administration paradigm in rats to determine if blockade of GABAA receptors in the ventral tegmental area (VTA) has a reinforcing effect. Rats quickly learned to self-infuse a picrotoxin solution into the anterior VTA; rats discriminated the lever that produced picrotoxin infusions from the lever without consequences; and when the response requirement was increased, rats increased response levels for picrotoxin infusion. The reinforcing effect of picrotoxin was site-specific: Anterior VTA regions supported vigorous self-infusions, but not the posterior VTA, substantia nigra, or lateral hypothalamus. Muscimol, a GABAA agonist, disrupted picrotoxin self-infusion, but bicuculline, a GABAA antagonist, was self-infused into the VTA. The results suggest that blockade of GABAA receptors in the anterior VTA is reinforcing and that functional organization of the GABA systems within the VTA is heterogeneous. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
984.
BACKGROUND: Subpopulations of c-Kit immunopositive cells in the muscle coat of the gastrointestinal tract are considered pacemaker cells and have been investigated in human tissue relating to motility disorder. However, the morphology of c-kit immunopositive cells in intact human tissue is still unclear. METHODS: The authors studied the distribution of c-Kit immunopositive cells in the normal human colon and their cellular configuration by confocal microscopy on whole-mount preparations. The authors then compared them with six cases of Hirschsprung's disease (HD; two of short segment aganglionosis, three of extensive aganglionosis, and one of total aganglionosis). RESULTS: In the normal colon regional differences were found in the distribution of c-Kit immunopositive cells. The population in the muscle layers and at the submucosal border was larger in the anal part than in the oral part. Accumulation of positive cells at the myenteric plexus level was prominent only at the descending colon. In the descending colon of HD the authors could not demonstrate any differences in c-Kit immunopositive cells on aganglionic segments compared with the corresponding area of intact tissue. CONCLUSION: More attention must be paid to these regional differences of distribution, and identical regions of affected and unaffected bowels must be compared when discussing the relation between the abnormality of c-Kit-positive cells and motility disorders including HD.  相似文献   
985.
Two new alcoholic aroma precursors, cis- and trans-linalool, 3,7-oxides 6-O-beta-D-apiofuranosyl-beta-D-glucopyranosides (1 and 2), as well as two already known compounds, (Z)-3-hexenyl beta-D-glucopyranoside (3) and methyl salicylate 6-O-beta-D-xylopyranosyl-beta-D-glucopyranoside (beta-primeveroside: 4), and another new monoterpendiol glycoside, 8-hydroxygeranyl beta-primeveroside (5) have recently been isolated as aroma precursors in tea leaves (Camellia sinensis var. sinensis cv. Maoxie) ready for oolong tea processing.  相似文献   
986.
A molybdenum single crystal with an optional shape was produced by the secondary recrystallization method. First, a specimen with an optional shape was mechanically fabricated by drilling, punching or bending from a hot-rolled sheet doped with CaO and MgO. Then the specimen was isothermally annealed at 2300°C for 1 h.  相似文献   
987.
988.
Transmission loss increase of optical glass fibre caused by hydrogen diffusion is measured as a function of temperature and partial pressure of hydrogen gas. The activation energy of hydroxyl group formation from the diffused molecular hydrogen was found to be 15.9 kcal/mole. Also the hydroxyl absorption loss increase at 200°C was found to be proportional to the square root of the partial pressure of hydrogen gas.  相似文献   
989.
990.
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