全文获取类型
收费全文 | 204071篇 |
免费 | 15521篇 |
国内免费 | 7674篇 |
专业分类
电工技术 | 11092篇 |
技术理论 | 14篇 |
综合类 | 11149篇 |
化学工业 | 34606篇 |
金属工艺 | 10440篇 |
机械仪表 | 11975篇 |
建筑科学 | 16239篇 |
矿业工程 | 4843篇 |
能源动力 | 5842篇 |
轻工业 | 12576篇 |
水利工程 | 3165篇 |
石油天然气 | 10889篇 |
武器工业 | 1345篇 |
无线电 | 25264篇 |
一般工业技术 | 26446篇 |
冶金工业 | 12153篇 |
原子能技术 | 2103篇 |
自动化技术 | 27125篇 |
出版年
2024年 | 559篇 |
2023年 | 3064篇 |
2022年 | 4717篇 |
2021年 | 7566篇 |
2020年 | 5639篇 |
2019年 | 4877篇 |
2018年 | 5320篇 |
2017年 | 6056篇 |
2016年 | 5597篇 |
2015年 | 7233篇 |
2014年 | 9458篇 |
2013年 | 12223篇 |
2012年 | 12225篇 |
2011年 | 13865篇 |
2010年 | 11613篇 |
2009年 | 11454篇 |
2008年 | 10872篇 |
2007年 | 10466篇 |
2006年 | 10858篇 |
2005年 | 9629篇 |
2004年 | 6563篇 |
2003年 | 5776篇 |
2002年 | 5250篇 |
2001年 | 4723篇 |
2000年 | 4868篇 |
1999年 | 5665篇 |
1998年 | 5737篇 |
1997年 | 4577篇 |
1996年 | 4106篇 |
1995年 | 3374篇 |
1994年 | 2821篇 |
1993年 | 2256篇 |
1992年 | 1684篇 |
1991年 | 1267篇 |
1990年 | 1016篇 |
1989年 | 876篇 |
1988年 | 680篇 |
1987年 | 492篇 |
1986年 | 386篇 |
1985年 | 333篇 |
1984年 | 193篇 |
1983年 | 180篇 |
1982年 | 159篇 |
1981年 | 148篇 |
1980年 | 149篇 |
1979年 | 97篇 |
1978年 | 70篇 |
1977年 | 113篇 |
1976年 | 176篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
对《任意曲线透视投影的逆变换》中作出的以下3项研究结果进行了探讨并提出了不同见解:(1)透视投影的逆变换基本方程;(2)根据长方体上一个矩形的投影确定其长宽高之比;(3)由实体的透视图象准确重建其三维信息。 相似文献
992.
本文论述了一种普及型电子式电能表的设计原理和实现方法,具体讨论了时分割乘法器和电流互感器的组成和误差分析,最后给出测试结果。 相似文献
993.
分析了WTG420铁路罐车用钢的组织结构和力学性能。提出了冶炼与轧制的技术关键,其一,添加稀土元素改善钢中夹杂物;其二,采用控轧控冷使铁素体晶粒细化。 相似文献
994.
The short-range order (SRO) structure of a Au-25 at. pct Fe single crystal was studied using wide-angle diffuse synchrotron
X-radiation scattering at room temperature. Two heat treatments were investigated: a 400 °C aging treatment for 2 days and
a 440 °C treatment for 5 days, both preceded by solution treatment in the single-phase field and water-quenched to room temperature.
Evolution of the SRO structure with aging was determined by fitting the two sets of Cowley-Warren (C-W) SRO parameters to
a pair of 140,608-atom models. The microstructures, although quite disordered, showed a trend with aging for an increasing
volume fraction of an Fe-enriched and an Fe-depleted environment. The Fe-enriched environment displayed a preference for Fe
segregation to the {110} and {100} face-centered cubic (fcc) matrix planes. A major portion of the Fe-depleted environment
was found to contain elements (and variations of these elements) of the Dla ordered superstructure. The SRO contained in the Fe-depleted environment may be best described in terms of the standing concentration
wave packet (SCWP) model. This study provides, for the first time, a quantitative real-space view of the atomic arrangements,
which make up both environments in the SRO structure of Au-25 at. pct Fe.
Formerly Graduate Research Assistant, University of Illinois, Urbana, IL. 相似文献
995.
Granules containing indomethacin crystals are coated with Eudragit solutions of different RL/RS ratios using a pan coating technique. The process is reproducible with regard to drug content, inexpensive and the formed granules were directly compressed into tablets. In vitro release of indomethacin from coated granules, tablets and capsules was studied as a function of different ratios of Eudragit RL/RS in the coating solution. The release of the drug was significantly reduced by the coating process in comparison with a formulation made from uncoated granules, prepared using 10 per cent gelatin solution as a binder. Release data were found to follow a diffusion-controlled model. 相似文献
996.
997.
S Whitman L Lacey D Ansell EH Chen J Dell CW Phillips 《Canadian Metallurgical Quarterly》1993,22(3):393-397
Magnetic resonance imaging allows a noninvasive assessment of myelination during normal brain maturation as well as the detection of genetically determined and acquired diseases that affect the synthesis and maintenance of myelin. If this high sensitivity of magnetic resonance imaging for white matter changes is completed by adequate clinical and biochemical information, a unique diagnostic tool is available to gain new insights in the formation of myelin and pathogenesis of myelin disorders. 相似文献
998.
Control of neuronal morphogenesis by homeoproteins: consequences for the making of neuronal networks
M Volovitch I le Roux AH Joliot E Bloch-Gallego A Prochiantz 《Canadian Metallurgical Quarterly》1993,1(3):133-138
The authors investigated the relationship between plasma lipids and the risk for cortical infarction (61 cases) and transient ischaemic attacks (TIA) (35 cases) compared with matched controls. They observed a maximal increase of total cholesterol, of very low-density lipoprotein and low-density lipoprotein (LDL), triglycerides, total apolipoprotein (Apo), B,LDL-Apo B and Apo-A1, and small size high-density lipoprotein (HDL) and large size HDL whose separation was not possible. In contrast they observed a decrease of HDL-ApoE, a distribution of LDL in a single fraction and the presence of LDL of low weight in the group with cortical infarction with or without cardiac arrhythmias. For the first time, we describe a decrease of the HDL-ApoE/total ApoE ratio. TIA differed from the former group by a low level of HDL and the lack of abnormalities of Apo-A1, distribution of small and large size HDL, and in the distribution and the weight of LDL. These data suggest that previously demonstrated differences in LDL-cholesterol and HDL-cholesterol levels between patients with ischaemic stroke and control subjects may apply to patients with cortical infarction, and that in TIA there are changes in the distribution and the weight of LDL. 相似文献
999.
A rigorous analysis of the 80/20 rule is made using an index for the observed values of the variables. Three important findings are identified. First, a sufficient condition is provided for Burrell's inverse relationship between minimum holdings and average circulation rate. Second, an indexed version of Lotka's law is used to derive a sufficient condition for Egghe's finding on the 80/20 rule. Third, through the computer simulations of the Simon-Yule model of Lotka's law, we identify the entry rate of new holdings as well as the number of circulations when the entry rate is a decreasing function to be crucial factors for the pattern of the 80/20-type curve. 相似文献
1000.
多人决策的一类相对均衡解 总被引:1,自引:0,他引:1
本文分析由于决策人偏好不同而引起决策差异的多人多目标决策问题,提出了这类决策问题的一类相对均衡解的概念和求取方法。相对均衡解以决策群体偏好的加权集结为基础,能最大程度地反映每个决策人的偏好。文中研究相对均衡解的SWT求取方法,并给出了求解的步骤。 相似文献