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   2226篇
  免费   39篇
  国内免费   7篇
电工技术   11篇
综合类   16篇
化学工业   24篇
金属工艺   22篇
机械仪表   7篇
建筑科学   6篇
矿业工程   6篇
能源动力   1篇
轻工业   16篇
水利工程   8篇
石油天然气   4篇
无线电   16篇
一般工业技术   56篇
冶金工业   2058篇
自动化技术   21篇
  2024年   6篇
  2023年   4篇
  2022年   4篇
  2021年   7篇
  2020年   6篇
  2019年   5篇
  2018年   6篇
  2017年   3篇
  2015年   6篇
  2014年   7篇
  2013年   8篇
  2012年   12篇
  2011年   19篇
  2010年   13篇
  2009年   17篇
  2008年   15篇
  2007年   14篇
  2006年   5篇
  2005年   12篇
  2004年   2篇
  2003年   11篇
  2002年   8篇
  2001年   4篇
  2000年   2篇
  1999年   73篇
  1998年   630篇
  1997年   365篇
  1996年   234篇
  1995年   135篇
  1994年   121篇
  1993年   143篇
  1992年   13篇
  1991年   18篇
  1990年   9篇
  1989年   16篇
  1988年   27篇
  1987年   21篇
  1986年   15篇
  1985年   16篇
  1982年   8篇
  1981年   13篇
  1980年   21篇
  1978年   4篇
  1977年   62篇
  1976年   112篇
  1975年   7篇
  1972年   4篇
  1966年   2篇
  1955年   1篇
  1954年   1篇
排序方式: 共有2272条查询结果,搜索用时 15 毫秒
41.
From Mr T A Weaver Sir, I read with interest the above publication [J. S. D. C., 96 (June 1980) 305], and feel that observations arising from our own experience in supplying stenters over a number of years may be appropriate.  相似文献   
42.
Two cases of vesicoureteral reflux into intact, orthotopic ureteroceles are described. A review of the literature failed to reveal any similar reports. Insufficient submucosal ureteral length was thought to be the cause in each of the cases. Both patients were satisfactorily managed with standard ureteroneocystostomy after resection of the ureterocele.  相似文献   
43.
We previously reported a HPLC assay method using fluorimetric detection for the simultaneous determination of urinary N2-(3-aminopropyl)biopterin (oncopterin, a natural pteridine newly found in urine from cancer patients), biopterin and neopterin. We now have observed that an unknown substance, which may be derived from methotrexate, in urine from a patient with stomach cancer interfered with the assay of oncopterin and demonstrated that oncopterin could be completely separated from the unidentified substance by HPLC using a Nucleosil 100-5SA strong cation-exchange column. Furthermore, oncopterin was not detectable by this HPLC-fluorimetric method in urine samples from patients with stomach cancer who were not treated with methotrexate. The content of urinary oncopterin from cancer patients is supposed to be very low, with less than 1 mumol/mol creatinine. The present results indicate that the peak found with elution from the C18 column was a methotrexate-derived compound and co-eluted with the analyte oncopterin.  相似文献   
44.
45.
In substantia nigra from patients with Parkinson's disease, there are decreased levels of reduced glutathione (GSH) and diminished activities of mitochondrial complex I and alpha-ketoglutarate dehydrogenase (alpha-KGDH), along with increased activity of superoxide dismutase (SOD). However, the interrelationship among these events is uncertain. We now report the effect of decreased brain GSH levels on SOD and mitochondrial respiratory enzyme activity in rat brain. In addition, we have investigated the ability of thioctic acid, an endogenous antioxidant, to alter these parameters. Unilateral or bilateral intracerebroventricular (ICV) administration of buthionine sulphoximine (BSO; 1 x 3.2 mg or 2 x 1.6 mg) over a 48-hr period reduced cortical GSH by 55-70%. There was no change in the activity of complex I, II/III, or IV or of citrate synthase in cortex. Similarly, there was no alteration of mitochondrial or cytosolic SOD activity. Thioctic acid (50 or 100 mg/kg IP) alone had no effect on cortical GSH levels in control animals and did not reverse the decrease in GSH levels produced by unilateral or bilateral ICV BSO administration. Thioctic acid (50 or 100 mg/kg IP) had no overall effect on complex I, II/III, or IV or on citrate synthase activity in control animals. Thioctic acid also did not alter cortical mitochondrial respiratory enzyme activity in BSO-treated rats. At the lower dose, thioctic acid tended to increase mitochondrial and cytosolic SOD activity in control animals and in BSO-treated rats. However, at the higher dose, thioctic acid tended to decrease mitochondrial SOD activity. Overall, there was no consistent effect of thioctic acid (50 or 100 mg/kg IP) on SOD activity in control or BSO-treated animals. This study shows that BSO-induced glutathione deficiency does not lead to alterations in mitochondrial respiratory enzyme activity or to changes in SOD activity. GSH depletion in Parkinson's disease therefore may not account for the alterations occurring in complex I and mitochondrial SOD in substantia nigra. Thioctic acid did not alter brain GSH levels or mitochondrial function. Interestingly, however, it did produce some alterations in SOD activity, which may reflect either its antioxidant activity or its ability to act as a thiol-disulphide redox couple.  相似文献   
46.
Leishmania is primarily characterized by existing in two stages in its life cycle, each occurs in a distinct host. The amastigote stage found in the cytoplasm of the reticulo- endothelial cells, monocytes and other phagocytic cells of the vertebrate host. The promastigote stage found in the gut of its insect vector. The leishmaniasis comprise several diseases of wide diversity of manifestations caused by different species of the genus Leishmania. Because of the virtual morphological identity of the organisms throughout the genus, they are classified according to the clinical conditions which they produce in man, under three main headings: (1) Cutaneous leishmaniasis (CL.), (2) Mucocutaneous leishmaniasis (MCL.), (3) Visceral leishmaniasis (VL). Generally speaking, leishmaniasis is an example of a zoonosis that reaches man through an insect vector. The great majority of the Leishmania species are maintained by mammalian reservoir hosts in natural foci of infection. Rodents, dogs, wild cats, jackals, foxes, sloths, hyraxes and other carnivores are the animal reservoirs which maintain the infection in nature. The insect vectors are over 50 species of the genus Phlebotomus in the Old World and genus Lutzomyia in the New World.  相似文献   
47.
Microbial pathogens may be transmitted to humans via food animals and food animal products. A quick reference table is presented to provide easy access to food safety information related to the major food animal product areas. Included in the table are the pathogens, mode of transmission, public health impact, and control and prevention strategies for poultry, beef, dairy products, and pork.  相似文献   
48.
Thromboembolic events frequently complicate the clinical course of patients with inflammatory bowel disease (IBD). Hereditary thrombophilia may contribute to this tendency. Resistance to activated protein C is the most recently described thrombophilic state and may account for up to 40% of patients with thrombophilia. Thirty-seven patients with IBD were studied (mean age 44 years, range 18-82 years). Three patients had a history of thrombotic episodes. The 37 controls included 23 men and 17 women (mean age 48 years, range 16-89 years). Disease activity was assessed using the Harvey Bradshaw index for patients with Crohn's disease and the Truelove and Witts grading system for patients with ulcerative colitis. Levels of fibrinogen, antithrombin III (ATIII), protein C, protein S, activated protein C resistance (APCR), and the presence of a lupus anticoagulant (LA) were determined. Median ATIII levels in patients with IBD were significantly lower than controls (98% vs 106%, P = 0.007), while fibrinogen was elevated (4.2 vs 3.3 g/liter, P = 0.026) despite quiescent disease activity. LA was detected in 7/37 patients in the IBD group compared to 0/37 controls. (chi2 = 5.68, P = 0.017). No significant difference was observed in levels of inherited thrombophilic factors and in particular APCR between IBD patients and controls. In conclusion, the presence of inherited thrombophilic defects, in particular APCR, is uncommon in patients with IBD and does not merit routine screening.  相似文献   
49.
50.
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