全文获取类型
收费全文 | 2165篇 |
免费 | 32篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 7篇 |
综合类 | 2篇 |
化学工业 | 100篇 |
金属工艺 | 9篇 |
机械仪表 | 20篇 |
建筑科学 | 4篇 |
能源动力 | 34篇 |
轻工业 | 74篇 |
水利工程 | 5篇 |
石油天然气 | 1篇 |
无线电 | 67篇 |
一般工业技术 | 120篇 |
冶金工业 | 1654篇 |
原子能技术 | 6篇 |
自动化技术 | 98篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 26篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 25篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 41篇 |
2012年 | 25篇 |
2011年 | 17篇 |
2010年 | 16篇 |
2009年 | 25篇 |
2008年 | 33篇 |
2007年 | 26篇 |
2006年 | 19篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 14篇 |
1999年 | 50篇 |
1998年 | 471篇 |
1997年 | 284篇 |
1996年 | 186篇 |
1995年 | 115篇 |
1994年 | 105篇 |
1993年 | 114篇 |
1992年 | 16篇 |
1991年 | 36篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 44篇 |
1976年 | 117篇 |
1975年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有2201条查询结果,搜索用时 234 毫秒
121.
Breast Cancer Therapy: Defined Host–Guest Chemistry on Nanocarbon for Sustained Inhibition of Cancer (Small 42/2016) 下载免费PDF全文
122.
123.
GL Grunewald VH Dahanukar RK Jalluri KR Criscione 《Canadian Metallurgical Quarterly》1999,42(1):118-134
7-Substituted-1,2,3,4-tetrahydroisoquinolines (7-substituted-THIQs) are potent inhibitors of phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28), the enzyme involved in the biosynthesis of epinephrine. Unfortunately, most of these compounds also exhibit strong affinity for the alpha2-adrenoceptor. To design a selective (PNMT vs alpha2-adrenoceptor affinity) inhibitor of PNMT, the steric and electrostatic factors responsible for PNMT inhibitory activity and alpha2-adrenoceptor affinity were investigated by evaluating a number of 7-substituted-THIQs. A classical quantitative structure-activity relationship (QSAR) study resulted in a three-parameter equation for PNMT (PNMT pKi = 0.599pi - 0.0725MR + 1. 55sigmam + 5.80; n = 27, r = 0.885, s = 0.573) and a three-parameter equation for the alpha2-adrenoceptor (alpha2 pKi = 0.599pi - 0. 0542MR - 0.951sigmam + 6.45; n = 27, r = 0.917, s = 0.397). These equations indicated that steric effects and lipophilicity play a similar role at either active site but that electronic effects play opposite roles at either active site. Two binding orientations for the THIQs were postulated such that lipophilic and hydrophilic 7-substituents would not occupy the same region of space at either binding site. Using these two binding orientations, based on the lipophilicity of the 7-substituent, comparative molecular field analysis (CoMFA) models were developed that showed that the steric and electrostatic interactions at both sites were similar to those previously elaborated in the QSAR analyses. Both the QSAR and the CoMFA analyses showed that the steric interactions are similar at the PNMT active site and at the alpha2-adrenoceptor and that the electrostatic interactions were different at the two sites. This difference in electrostatic interactions might be responsible for the selectivity of THIQs bearing a nonlipophilic electron-withdrawing group at the 7-position. These QSAR and CoMFA results will be useful in the design of potent and selective (PNMT vs alpha2-adrenoceptor affinity) inhibitors of PNMT. 相似文献
124.
K Ouriel CK Shortell KA Illig RK Greenberg RM Green 《Canadian Metallurgical Quarterly》1999,29(1):82-7; discussion 87-9
PURPOSE: With a diminishing rate of cardiac and neurologic events after carotid endarterectomy, intracerebral hemorrhage is gaining increasing importance as a cause of perioperative morbidity and mortality. To date, information has been largely anecdotal, and there has been no comparison with a control group of patients. METHODS: The records of all patients experiencing symptomatic intracerebral hemorrhage after carotid endarterectomy were reviewed and compared with data from 50 randomly selected patients who did not experience intracranial bleeding. Univariate analyses were performed, using the Fisher exact test for dichotomous data and the Student t test for continuous data. RESULTS: During a 6-year period, symptomatic intracranial hemorrhage developed in 11 (0.75%) of 1471 patients undergoing carotid endarterectomy, accounting for 35% of the 31 total perioperative neurologic events. Hemorrhage occurred a median of 3 days postoperatively (range, 0 to 18 days). Signs and symptoms included hypertension in all 11 patients, headache in 7 conscious patients (64%), and bradycardia in 6 patients (55%). Massive hemorrhage with herniation and death occurred in 4 patients (36%). Moderate hemorrhage developed in 5 patients (45%); 3 of these patients had partial recovery, and 2 had complete recovery. Petechial hemorrhage occurred in the remaining 2 patients (18%), 1 with partial and 1 with complete recovery. In comparison with the control group, there were no differences in respect to sex, indication for operation, smoking or diabetic history, and antiplatelet therapy or perioperative heparin management. Patients with intracranial hemorrhage were, however, younger, more frequently hypertensive, had a higher degree of ipsilateral and contralateral carotid stenosis, and had a higher rate of contralateral carotid occlusion. CONCLUSION: Intracranial hemorrhage occurs with notable frequency after carotid endarterectomy and accounts for a significant proportion of neurologic morbidity and mortality. Younger patients, hypertensive patients, and patients with severe cerebrovascular occlusive disease appear to be at greatest risk for the complication. 相似文献
125.
In this work, the process for producing polystyrene particles surface functionalized with a thin shell of ATRP initiator polymerized alone or along with styrene and a crosslinker, is presented. Copolymerization of styrene and acrylic end-capped ATRP initiator to generate a thin shell on the fully polymerized core particles suffered from secondary nucleation owing to their possible incompatibility with the core particles and their own colloidal stability. One step functionalization processes, where the shell forming monomers are added directly to the 70% polymerized core particles, lead to significant changes in the resulting particle morphologies. The shot addition of these monomers led to a very uniform surface morphology without any secondary nucleation owing to quick coalescence of the secondary particles on the soft surface of the seed particles. Addition of crosslinker to the system helped in effectively eliminating the smaller particles generated due to secondary nucleation along with the chemical networking. 相似文献
126.
RK Nesbet 《Canadian Metallurgical Quarterly》1990,41(8):4948-4952
127.
128.
129.
130.
H Kashiwagi AD Spigelman IC Talbot HS Debinski AB McKie NR Lemoine RK Phillips 《Canadian Metallurgical Quarterly》1997,84(6):826-829
BACKGROUND: The genetic alterations in patients with familial adenomatous polyposis (FAP) and duodenal adenomas are poorly characterized when compared with data relating to colorectal tumorigenesis in the same patients. METHODS: Point mutation of the K-ras oncogene and point mutation and overexpression of the TP53 tumour suppressor gene were investigated in 32 duodenal polyps (seven without mucosal pathology, 23 with mildly dysplastic adenomas and two with moderately dysplastic adenomas) from 21 patients with FAP. RESULTS: K-ras mutation, TP53 mutation or positive p53 staining were not found in duodenal polyps without histological abnormality. Of 25 duodenal adenomas, K-ras mutation was found in three (two mildly dysplastic, one moderately dysplastic), 20 showed positive p53 immunostaining, and mutation of the TP53 gene was found in one moderately dysplastic adenoma. p53 protein overexpression in duodenal adenomas was significantly more frequent than mutation of either K-ras or TP53 (P < 0.01). CONCLUSION: p53 dysfunction is a hallmark of duodenal adenomas in patients with FAP. Overexpression may indicate DNA damage and thus an early step in tumorigenesis. 相似文献