全文获取类型
收费全文 | 1200篇 |
免费 | 26篇 |
国内免费 | 32篇 |
专业分类
电工技术 | 31篇 |
综合类 | 43篇 |
化学工业 | 150篇 |
金属工艺 | 37篇 |
机械仪表 | 40篇 |
建筑科学 | 70篇 |
矿业工程 | 4篇 |
能源动力 | 7篇 |
轻工业 | 64篇 |
水利工程 | 16篇 |
石油天然气 | 15篇 |
武器工业 | 2篇 |
无线电 | 34篇 |
一般工业技术 | 26篇 |
冶金工业 | 690篇 |
原子能技术 | 2篇 |
自动化技术 | 27篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2015年 | 21篇 |
2014年 | 68篇 |
2013年 | 49篇 |
2012年 | 30篇 |
2011年 | 97篇 |
2010年 | 25篇 |
2009年 | 53篇 |
2008年 | 30篇 |
2007年 | 37篇 |
2006年 | 28篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 16篇 |
1998年 | 198篇 |
1997年 | 118篇 |
1996年 | 81篇 |
1995年 | 58篇 |
1994年 | 34篇 |
1993年 | 43篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1985年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1978年 | 7篇 |
1977年 | 27篇 |
1976年 | 52篇 |
1975年 | 8篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 3篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有1258条查询结果,搜索用时 15 毫秒
91.
92.
The partition of free fatty acids (FFA) to egg-phosphatidylcholine (egg-PC) and egg-phosphatidylethanolamine (egg-PE) vesicles was studied. Upon the addition of FFA to the suspension of vesicles, the pH of the aqueous phase changed depending on the length and saturation of the FFA hydrocarbon chain, as well as on the vesicle composition. The medium pH decreased faster if FFA was added to egg-PE as compared to egg-PC vesicles. The fluorescent free fatty acid indicator (ADIFAB) was used to measure the amount of FFA remaining in the aqueous phase. Most of the FFA added to the suspension of egg-PE vesicles remained in the aqueous phase, whereas in the presence of egg-PC vesicles the FFA partitioned preferentially into the lipid phase. The amount of FFA incorporated into the lipid bilayers was estimated by measuring the changes of pH at the lipid bilayer surface, using fluorescein-PE. At high surface concentrations of FFA, decreasing pH at the bilayer surface caused the protonation of FFA, and raised the pK of FFA at the bilayer surface from 5 to about 7. The partition of FFA in egg-PE vesicles was an order of magnitude lower than that in egg-PC vesicles. The incorporation amount was determined more by the molecular packing than by the nature of lipid headgroups, because steroylcaprioyl-PE, which preferred the bilayer structure, behaved more like egg-PC than egg-PE. Understanding FFA partition characteristics would help to interpret the hydrolysis measurements of phospholipids, and to explain many biological activities of FFA. 相似文献
93.
94.
95.
96.
97.
VG Savchenko EN Parovichnikova VG Isaev IA Demidova RG Kuliev EO Gribanova GA Kliasova RA Kucher AN Sokolov KS Momotiuk IuV Ol''shanskaia NG Tiurina LIu Tikhonova GM Galstian VM Budianski? EA Belousov VA Lapin SV Voloshin TS Konstaninova LB Filatov ON Porokhina EA Smirnova 《Canadian Metallurgical Quarterly》1998,70(7):5-11
98.
JA Esteban NG Walter G Kotzorek JE Heckman JM Burke 《Canadian Metallurgical Quarterly》1998,95(11):6091-6096
The RNA cleavage reaction catalyzed by the hairpin ribozyme shows biphasic kinetics, and chase experiments show that the slow phase of the reaction results from reversible substrate binding to an inactive conformational isomer. To investigate the structural basis for the heterogeneous kinetics, we have developed an enzymatic RNA modification method that selectively traps substrate bound to the inactive conformer and allows the two forms of the ribozyme-substrate complex to be separated and analyzed by using both physical and kinetic strategies. The inactive form of the complex was trapped by the addition of T4 RNA ligase to a cleavage reaction, resulting in covalent linkage of the 5' end of the substrate to the 3' end of the ribozyme and in selective and quantitative ablation of the slow kinetic phase of the reaction. This result indicates that the inactive form of the ribozyme-substrate complex can adopt a conformation in which helices 2 and 3 are coaxially stacked, whereas the active form does not have access to this conformation, because of a sharp bend at the helical junction that presumably is stabilized by inter-domain tertiary contacts required for catalytic activity. These results were used to improve the activity of the hairpin ribozyme by designing new interfaces between the two domains, one containing a non-nucleotidic orthobenzene linkage and the other replacing the two-way junction with a three-way junction. Each of these modified ribozymes preferentially adopts the active conformation and displays improved catalytic efficiency. 相似文献
99.
R McNerney SM Wilson AM Sidhu VS Harley Z al Suwaidi PM Nye T Parish NG Stoker 《Canadian Metallurgical Quarterly》1998,149(7):487-495
There is still an urgent requirement for more sensitive, cost-effective methods for detection and susceptibility testing of mycobacteria in clinical samples. We have been investigating a simple bacteriophage-based system which could be used for both purposes. As this depends upon the detection of phages which have successfully infected cells, a key step is the efficient removal or inactivation of phages remaining free in the culture medium. We demonstrate here the use of ferrous ammonium sulphate as an effective agent for the inactivation of mycobacteriophage D29 without impairing phage replication in previously infected host bacteria. Using this property, we report the detection of viable Mycobacterium smegmatis, M. bovis BCG and M. tuberculosis using simple low-cost technology. The method is highly sensitive, since it is able to detect 10 colony-forming units of M. smegmatis. It is also rapid, with the detection of M. tuberculosis in sputum specimens within 48 h. 相似文献
100.
B Burwinkel G Miglierini DE Jenne DJ Gilbert NG Copeland NA Jenkins HZ Ring U Francke MW Kilimann 《Canadian Metallurgical Quarterly》1998,49(3):462-466
OBJECTIVES: To assess the correlation of total prostatic size and prostate transition zone dimensions with various measurements of the severity of bladder outlet obstruction secondary to benign prostatic hyperplasia. METHODS: Prostate-specific antigen, creatinine, American Urological Association symptom score, bother score, urinary history, uroflowmetry, and post-void residual urine volume determination was followed by measurement of the prostate gland and transition zone on transrectal ultrasound images in 136 men undergoing systematic prostate biopsies. Patients were divided into five groups based on past urinary tract treatment history and the presence of prostate cancer on the biopsies. The total prostate and transition zone dimensions, as well as calculated prostate and transition zone volumes, were compared by Pearson correlation with both the subjective and objective voiding parameters in each patient group. RESULTS: The transition zone dimensions correlated positively with American Urological Association symptom score, bother score, and post-void residual urine volume and correlated negatively with maximum and mean flow rates, particularly in patients with no history of prostate surgery, alpha-blocker administration, urinary infections, irritative voiding symptoms, or prostate cancer. CONCLUSIONS: Transrectal ultrasound measurements of transition zone dimensions correlate better than total prostatic dimensions or calculated prostatic or transition zone volumes with the severity of benign prostatic hyperplasia. Of these, the transverse transition zone dimension demonstrated the best correlation; however, this correlation is probably not adequate for clinical utility. 相似文献