全文获取类型
收费全文 | 702252篇 |
免费 | 9718篇 |
国内免费 | 2244篇 |
专业分类
电工技术 | 12538篇 |
综合类 | 692篇 |
化学工业 | 105155篇 |
金属工艺 | 25590篇 |
机械仪表 | 20153篇 |
建筑科学 | 17511篇 |
矿业工程 | 2710篇 |
能源动力 | 19696篇 |
轻工业 | 65293篇 |
水利工程 | 6596篇 |
石油天然气 | 10903篇 |
武器工业 | 41篇 |
无线电 | 82807篇 |
一般工业技术 | 133119篇 |
冶金工业 | 137691篇 |
原子能技术 | 12769篇 |
自动化技术 | 60950篇 |
出版年
2021年 | 6065篇 |
2020年 | 4463篇 |
2019年 | 5660篇 |
2018年 | 9483篇 |
2017年 | 9327篇 |
2016年 | 9885篇 |
2015年 | 7003篇 |
2014年 | 11627篇 |
2013年 | 32738篇 |
2012年 | 18879篇 |
2011年 | 26469篇 |
2010年 | 20717篇 |
2009年 | 23241篇 |
2008年 | 24013篇 |
2007年 | 23660篇 |
2006年 | 21039篇 |
2005年 | 19201篇 |
2004年 | 18419篇 |
2003年 | 18189篇 |
2002年 | 17194篇 |
2001年 | 17426篇 |
2000年 | 16137篇 |
1999年 | 17244篇 |
1998年 | 44041篇 |
1997年 | 30751篇 |
1996年 | 23399篇 |
1995年 | 17618篇 |
1994年 | 15333篇 |
1993年 | 15030篇 |
1992年 | 10773篇 |
1991年 | 10114篇 |
1990年 | 9819篇 |
1989年 | 9469篇 |
1988年 | 8917篇 |
1987年 | 7688篇 |
1986年 | 7510篇 |
1985年 | 8651篇 |
1984年 | 8025篇 |
1983年 | 7151篇 |
1982年 | 6716篇 |
1981年 | 6860篇 |
1980年 | 6423篇 |
1979年 | 6201篇 |
1978年 | 5866篇 |
1977年 | 7062篇 |
1976年 | 9180篇 |
1975年 | 5061篇 |
1974年 | 4743篇 |
1973年 | 4941篇 |
1972年 | 3928篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
M Valenti G Cimoli S Parodi GL Mariani M Venturini P Conte P Russo 《Canadian Metallurgical Quarterly》1993,(8):1157-1161
Synergism between recombinant human tumour necrosis factor (rHuTNF) and DNA topoisomerase II inhibitor VP16 during the killing of cells has been studied in six human ovarian cancer cell lines (A2774, A2780, SW626, IGROV-1, SKOV3, Pa1) and a cervical carcinoma cell line (Me180). Studies were performed using an assay of colony formation inhibition (drug treatment for 1 h) and a growth inhibition assay (continuous exposure for 20 h). Concomitant treatment of cells with VP16+rHuTNF enhanced cell killing in all the cell lines tested--an effect observed in both short- and long-term cytotoxicity assays. This study suggests that the activity of VP16 in ovarian cancer cell lines might be enhanced by rHuTNF in in vitro models. 相似文献
252.
HG Tiselius C Berg AM Fornander MA Nilsson 《Canadian Metallurgical Quarterly》1993,7(1):381-9; discussion 389-90
Urinary citrate appears to be an important factor in the crystallization process of calcium oxalate and calcium phosphate. The urinary excretion of citrate was found to be significantly lower in patients with calcium oxalate stone disease as compared with normal subjects, and about 30 per cent of the calcium stone formers can be considered as hypocitraturic. The lowest excretion of citrate was recorded in urine collected during the night. Citrate has significant effects on supersaturation with respect to both calcium oxalate and calcium phosphate, it also inhibits the growth of these crystals. In addition, citrate appears to be capable of inhibiting the aggregation of crystals composed of calcium oxalate, brushite, and hydroxyapatite. The heterogenous growth of calcium oxalate on calcium phosphate is also counteracted by citrate. As a consequence of the crucial role of citrate in these processes, stone prevention with alkaline citrate has become an attractive form of treatment in patients with recurrent stone formation. Single evening dose administration of sodium potassium citrate resulted in an of sodium potassium citrate resulted in an increased excretion of citrate, reduced levels of the calcium/citrate ratio as well as supersaturation with respect to calcium oxalate and a decreased rate of stone formation. However, conflicting results of stone preventive treatment with alkaline citrate have been reported by different groups, and long-term follow-up of patients treated in a randomized way is necessary to definitely assess the efficacy of alkaline citrate. 相似文献
253.
B Blanc P Laloi D Atlan C Gilbert R Portalier 《Canadian Metallurgical Quarterly》1993,139(7):1441-1448
Lactobacillus helveticus ITGL1 is able to hydrolyse many amino-acyl and dipeptidyl-p-nitroanilides. Analysis of heat inactivation kinetics, metal ion and protease inhibitor effects, and the subcellular location of aminopeptidase activities in both the parental strain and mutants deficient in lysyl-p-nitroanilide hydrolysis, led to the characterization of two cell-wall-associated aminopeptidases, APII and APIV. APII, which catalysed L-lysine p-nitroanilide hydrolysis, was purified about 28-fold to homogeneity from cell-wall extracts of L. helveticus ITGL1 and characterized. The purified enzyme appeared to be monomeric, with a molecular mass of 97 kDa. Aminopeptidase activity was greatest at pH 6.5 and 50 degrees C. APII was completely inhibited by bestatin, chelating agents such as EDTA or 1,10-phenanthroline and the divalent cations Zn2+ and Cu2+. The activity of the EDTA-treated enzyme was restored by Co2+, Ca2+ or Mn2+. Although APII was able to degrade several dipeptides and tripeptides with hydrophobic N-terminal amino acid (Leu, Ala), it was inactive on peptides containing Pro or Gly, and may thus contribute to the development of cheese flavour by processing bitter peptides. 相似文献
254.
A multilayer theory has been developed for unidirectional/cross-ply unbalanced laminates subjected to surface shear tractions, using the assumption of plane strain. The analytical solution for the stress field in the laminate is obtained and it is shown that the stresses in each layer are in good agreement with the results of a three-dimensional finite element analysis. Approximate formulae for the analytical stresses are also derived for a laminate subjected to an offset distributed force at one end. The accuracy of this solution is shown by comparison with a three-dimensional finite element analysis. 相似文献
255.
J. Jiang M. D. Olson 《International journal for numerical methods in engineering》1993,36(13):2219-2243
Numerical investigations are carried out to verify the new super element model developed in Reference 1 for non-linear analysis of stiffened box structures. The results presented here are obtained from a variety of examples which are chosen to illustrate the accuracy and convergence of the model in various applications. Good agreement is obtained for most of the problems considered and the present formulation is found to be accurate and economical for preliminary engineering design. 相似文献
256.
The use of patent titles for identifying the topics of invention and forecasting trends 总被引:7,自引:0,他引:7
Co-word analysis applied to patents through WPIL normalized title words appears to give a useful picture of a given field: we obtain both qualitative (themes) and quantitative information (weight of themes). It also gives information about the strategic aspects of the themes. Furthermore, in some cases, it is an indication of the future of certain themes that may help forecasting and management studies. Finally, it provides information about what could be a real technology growth process, in relation to the so-called translation model used in co-word analysis. 相似文献
257.
F. Cioffi E. M. Cohen Richard Badick 《Drug development and industrial pharmacy》1993,19(14):1741-1746
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well. 相似文献
258.
259.
260.