全文获取类型
收费全文 | 17276篇 |
免费 | 1651篇 |
国内免费 | 989篇 |
专业分类
电工技术 | 1114篇 |
综合类 | 1244篇 |
化学工业 | 2525篇 |
金属工艺 | 932篇 |
机械仪表 | 1137篇 |
建筑科学 | 1359篇 |
矿业工程 | 507篇 |
能源动力 | 462篇 |
轻工业 | 1153篇 |
水利工程 | 354篇 |
石油天然气 | 932篇 |
武器工业 | 204篇 |
无线电 | 2097篇 |
一般工业技术 | 2018篇 |
冶金工业 | 944篇 |
原子能技术 | 180篇 |
自动化技术 | 2754篇 |
出版年
2024年 | 62篇 |
2023年 | 267篇 |
2022年 | 510篇 |
2021年 | 742篇 |
2020年 | 546篇 |
2019年 | 461篇 |
2018年 | 502篇 |
2017年 | 549篇 |
2016年 | 514篇 |
2015年 | 759篇 |
2014年 | 874篇 |
2013年 | 1001篇 |
2012年 | 1086篇 |
2011年 | 1262篇 |
2010年 | 1152篇 |
2009年 | 1065篇 |
2008年 | 1127篇 |
2007年 | 1064篇 |
2006年 | 1066篇 |
2005年 | 879篇 |
2004年 | 592篇 |
2003年 | 438篇 |
2002年 | 525篇 |
2001年 | 519篇 |
2000年 | 380篇 |
1999年 | 344篇 |
1998年 | 308篇 |
1997年 | 262篇 |
1996年 | 219篇 |
1995年 | 190篇 |
1994年 | 163篇 |
1993年 | 137篇 |
1992年 | 84篇 |
1991年 | 54篇 |
1990年 | 40篇 |
1989年 | 40篇 |
1988年 | 29篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1971年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
The kinetics of substrate removal by the liver and the resulting nonlinear changes in unbound fraction along the flow path at varying input drug concentrations were examined by a model simulation study. Specifically, we varied the binding association constant, KA, and the Michaelis-Menten constants (Km and Vmax) to examine the steady state drug removal (expressed as hepatic extraction ratio E) and changes in drug binding for (i) unienzyme systems and (ii) simple, parallel metabolic pathways; zonal metabolic heterogeneity was also added as a variable. At low KA, E declined with increasing input drug concentration, due primarily to saturation of enzymes; only small differences in binding were present across the liver. At high KA, a parabolic profile for E with concentration was observed; changes in unbound fraction between the inlet and the outlet of the liver followed in parallel fashion. Protein binding was the rate-determining step at low input drug concentrations, whereas enzyme saturation was the rate-controlling factor at high input drug concentration. Heterogeneous enzymic distribution modulated changes in unbound fraction within the liver and at the outlet. Despite marked changes in unbound fraction occurring within the liver for different enzymic distributions, the overall transhepatic differences were relatively small. We then investigated the logarithmic average unbound concentration and the length averaged concentration as estimates of substrate concentration in liver in the presence of nonlinear drug binding. Fitting of simulated data, with and without assigned random error (10%), to the Michaelis-Menten equation was performed; fitting was repeated for simulated data obtained with presence of a specific inhibitor of the high-affinity, anteriorly distributed pathway. Results were similar for both concentration terms: accurate estimates were obtained for anterior, high affinity pathways; an overestimation of parameters was observed for the lower affinity posteriorly distributed pathways. Improved estimations were found for posteriorly distributed pathways upon inhibition with specific inhibitors; with added random error, however, the improvement was much decreased. We applied the method for fitting of several sets of metabolic data obtained from rat liver perfusion studies performed with salicylamide (SAM) (i) without and (ii) with the presence of 2,6-dichloro-4-nitrophenol (DCNP), a SAM sulfation inhibitor. The fitted results showed that SAM sulfation was a high-affinity high-capacity pathway; SAM glucuronidation was of lower affinity but comparable capacity as the sulfation pathway, whereas SAM hydroxylation was of lower affinity and lower capacity. 相似文献
22.
23.
24.
25.
苯磺隆干悬浮剂技术浅析 总被引:1,自引:0,他引:1
通过对苯磺隆干悬浮剂项目的研究,进一步了解干悬浮剂的加工工艺和配方中各种助剂的相互作用;剖析助剂对主要技术指标的影响。 相似文献
26.
挤压力对晶体生长速度及枝晶间距的影响 总被引:4,自引:4,他引:0
研究了挤压铸造时挤压力对宏观晶体生长速度的影响,给出了晶体生长速度表达式。结果表明:挤压力对合金宏观晶体生长速度的影响除与合金成分有关外,在某些挤压条件下,当形核率的增加幅度超过长大速度时,则挤压力可使宏观晶粒细化;反之,会使宏观晶粒变粗。随着挤压力的提高,合金凝固速度加快,一次枝晶间距和二次枝晶间距都随之减小,从而细化了树枝晶。 相似文献
27.
28.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
29.
30.
根据滑坡发生的初始条件、滑坡成因及方式表象,对常见的蠕变倾覆滑坡、卸荷滑坡、震动液化平推滑坡、潜蚀塌陷滑坡、溶蚀下陷滑坡、孔隙水压浮动滑坡和人工切蚀或冲(浪)蚀—加载滑坡等机理进行了分析. 相似文献