全文获取类型
收费全文 | 10167篇 |
免费 | 820篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 70篇 |
综合类 | 5篇 |
化学工业 | 2396篇 |
金属工艺 | 101篇 |
机械仪表 | 284篇 |
建筑科学 | 431篇 |
矿业工程 | 20篇 |
能源动力 | 216篇 |
轻工业 | 1980篇 |
水利工程 | 68篇 |
石油天然气 | 18篇 |
无线电 | 682篇 |
一般工业技术 | 1737篇 |
冶金工业 | 1409篇 |
原子能技术 | 23篇 |
自动化技术 | 1557篇 |
出版年
2024年 | 35篇 |
2023年 | 140篇 |
2022年 | 116篇 |
2021年 | 325篇 |
2020年 | 270篇 |
2019年 | 272篇 |
2018年 | 346篇 |
2017年 | 355篇 |
2016年 | 465篇 |
2015年 | 419篇 |
2014年 | 544篇 |
2013年 | 988篇 |
2012年 | 857篇 |
2011年 | 644篇 |
2010年 | 468篇 |
2009年 | 467篇 |
2008年 | 490篇 |
2007年 | 422篇 |
2006年 | 391篇 |
2005年 | 246篇 |
2004年 | 225篇 |
2003年 | 196篇 |
2002年 | 191篇 |
2001年 | 121篇 |
2000年 | 118篇 |
1999年 | 103篇 |
1998年 | 375篇 |
1997年 | 270篇 |
1996年 | 178篇 |
1995年 | 128篇 |
1994年 | 118篇 |
1993年 | 103篇 |
1992年 | 41篇 |
1991年 | 44篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 40篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 37篇 |
1976年 | 65篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
ESR spin trapping was used to investigate the reaction of rabbit cytochrome P450 (P450) 1A2 with cumene hydroperoxide. Cumene hydroperoxide-derived peroxyl, alkoxyl, and carbon-centered radicals were formed and trapped during the reaction. The relative contributions of each radical adduct to the composite ESR spectrum were influenced by the concentration of the spin trap. Computer simulation of the experimental data obtained at various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations was used to quantitate the contributions of each radical adduct to the composite ESR spectrum. The alkoxyl radical was the initial radical produced during the reaction. Experiments with 2-methyl-2-nitrosopropane identified the carbon-centered adducts as those of the methyl radical, hydroxymethyl radical, and a secondary carbon-centered radical. The reaction did not require NADPH-cytochrome P450 reductase or NADPH. It is concluded that the reaction involves the initial homolytic scission of the peroxide O-O bond to produce the cumoxyl radical. Methyl radicals were produced from the beta-scission of the cumoxyl radical. The peroxyl adduct was not observed in the absence of molecular oxygen. We conclude that the DMPO peroxyl radical adduct detected in the presence of oxygen was due to the methylperoxyl radical formed by the reaction of the methyl radical with oxygen. At a higher P450 concentration, a protein-derived radical adduct was also detected. 相似文献
2.
Astrid Labidi Marie-Christine Salon Alessandro Gandini Hervé Cheradame 《Polymer Bulletin》1985,14(3-4):271-278
Summary 2-Furyl vinyl ketone was polymerised using anionic, cationic and free-radical initiators. Yields and molecular weights varied with the type of activation. Whereas radical polymerisation gave a product possessing a regular vinylic structure, other kinds of units were detected in the polymers prepared with anionic and cationic catalysts. 相似文献
3.
We compare two link analysis ranking methods of web pages in a site. The first, called Site Rank, is an adaptation of PageRank to the granularity of a web site and the second, called Popularity Rank, is based on the frequencies of user clicks on the outlinks in a page that are captured by navigation sessions of users through
the web site. We ran experiments on artificially created web sites of different sizes and on two real data sets, employing
the relative entropy to compare the distributions of the two ranking methods. For the real data sets we also employ a nonparametric
measure, called Spearman's footrule, which we use to compare the top-ten web pages ranked by the two methods. Our main result
is that the distributions of the Popularity Rank and Site Rank are surprisingly close to each other, implying that the topology
of a web site is very instrumental in guiding users through the site. Thus, in practice, the Site Rank provides a reasonable
first order approximation of the aggregate behaviour of users within a web site given by the Popularity Rank. 相似文献
4.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
5.
6.
M Schietroma A Risetti F Carlei MV Santirocco F Muzi G Maggi C De Santis CL Recchia D Iannucci R Rampa M Simi 《Canadian Metallurgical Quarterly》1996,48(4):43-46
Adhesions have been suggested as a possible cause of chronic abdominal pain, but the reports of their etiological role conflict. Lysis of adhesions has been proposed as the therapeutic modality of choice, although the reports of success are controversial. The aim our prospective study was to determine whether laparoscopic adhesiolysis ameliorates chronic abdominal pain in patients with abdominal adhesions. Forty-one patients with chronic abdominal pain lasting for more than 6 months, but with no abnormal findings other than adhesions found at laparoscopy, underwent laparoscopic adhesiolysis. 37 patients (90.2%) were available for follow-up after a median time interval of 18 months (range: 12-41 months). Twenty-two patients (59.4%) were free from abdominal pain and 9 (24.3%) patients reported significant amelioration of their pain. Six (16.2%) patients had no amelioration. In conclusion the laparoscopy is an effective tool for the evaluation of patients with chronic abdominal pain, and laparoscopic adhesiolysis cures of ameliorates chronic abdominal pain in more than 80% of patients. 相似文献
7.
OBJECTIVE: We report a case of candidiasis of the upper urinary tract that presented as acute renal failure associated with septic syndrome. The patient initially required hemodialysis. Right hydronephrosis and perirenal collection were observed on ultrasound examination. METHODS: A percutaneous nephrostomy was performed. Nephrostomy urine cytology and cultures were positive for Candida tropicalis. An anterograde pyelography showed a 'fungus ball' in the urinary tract. RESULTS: Therapy with oral fluconazole and percutaneous amphotericin B achieved excellent results. CONCLUSIONS: Candidiasic urinary infection of the upper urinary tract often produces obstructive uropathy requiring percutaneous nephrostomy, which can also be used to instill amphotericin B. Combination therapy with amphotericin B and fluconazole can achieve excellent results. 相似文献
8.
Ovarian failure is heterogeneous in etiology and may occur at various points in a woman's life. As such, it may interfere with fertility. Clinical presentation ranges from complete cessation of menses to oligomenorrhea to the continuation of menses with elevated gonadotropins. Various therapies have been used in an attempt to induce fertility, including sex steroids and gonadotropin-releasing hormone agonists to suppress circulating gonadotropin alone or in combination with estrogen or gonadotropin-releasing hormone agonists to induce ovulation. Corticosteroids are also used to overcome autoimmunity. Randomized therapeutic trials are rare and fail to demonstrate any significant improvement in ovulation and pregnancy rates. Donor oocytes have demonstrated high success rates and have proven to be useful in patients with both premature ovarian failure and natural menopause. Pregnancies have been initiated and maintained in women through 60 years of age. Thus, for those accepting of the technique, oocyte donation appears to be the treatment of choice for hypergonadotropic hypogonadism. 相似文献
9.
10.
G Gaffney MV Squier A Johnson V Flavell S Sellers 《Canadian Metallurgical Quarterly》1994,70(2):F101-F106
Neuropathological examinations were carried out at necropsy on 274 cases of intrauterine death or neonatal death at or before three days after birth. Fifty six (20.4%) subjects had evidence of prenatal ischaemic brain damage. On review of the maternal case notes to ascertain antenatal clinical associations there was an increased incidence of intrauterine growth retardation, either based on birth weight for gestational age (odds ratio (OR) 2.0; 95% confidence interval (CI) 1.1 to 3.7) or diagnosed antenatally (OR 2.7; 95% CI 1.3 to 5.6). Oligohydramnios was also more common (OR 2.9; 95% CI 1.2 to 7.0). The association of intrauterine growth retardation and white matter damage remained after excluding fetuses with a major congenital anomaly (OR 2.4; 95% CI 1.1 to 5.1). The findings suggest that chronic intrauterine hypoxia may be associated with damage to cerebral white matter among fetuses and infants who die. The relation between ischaemic white matter damage and cerebral palsy among survivors remains speculative. 相似文献