全文获取类型
收费全文 | 143907篇 |
免费 | 14115篇 |
国内免费 | 9059篇 |
专业分类
电工技术 | 11565篇 |
技术理论 | 2篇 |
综合类 | 17884篇 |
化学工业 | 16396篇 |
金属工艺 | 6269篇 |
机械仪表 | 10366篇 |
建筑科学 | 18141篇 |
矿业工程 | 6554篇 |
能源动力 | 4788篇 |
轻工业 | 7925篇 |
水利工程 | 6475篇 |
石油天然气 | 6126篇 |
武器工业 | 1979篇 |
无线电 | 9787篇 |
一般工业技术 | 18802篇 |
冶金工业 | 5667篇 |
原子能技术 | 2300篇 |
自动化技术 | 16055篇 |
出版年
2024年 | 609篇 |
2023年 | 1776篇 |
2022年 | 3274篇 |
2021年 | 3927篇 |
2020年 | 4412篇 |
2019年 | 3803篇 |
2018年 | 3637篇 |
2017年 | 4605篇 |
2016年 | 5115篇 |
2015年 | 5331篇 |
2014年 | 8678篇 |
2013年 | 8273篇 |
2012年 | 11031篇 |
2011年 | 11147篇 |
2010年 | 8645篇 |
2009年 | 8960篇 |
2008年 | 8244篇 |
2007年 | 10232篇 |
2006年 | 8960篇 |
2005年 | 7561篇 |
2004年 | 6214篇 |
2003年 | 5340篇 |
2002年 | 4453篇 |
2001年 | 3711篇 |
2000年 | 3290篇 |
1999年 | 2857篇 |
1998年 | 2242篇 |
1997年 | 1956篇 |
1996年 | 1646篇 |
1995年 | 1481篇 |
1994年 | 1247篇 |
1993年 | 912篇 |
1992年 | 813篇 |
1991年 | 570篇 |
1990年 | 469篇 |
1989年 | 474篇 |
1988年 | 340篇 |
1987年 | 195篇 |
1986年 | 161篇 |
1985年 | 66篇 |
1984年 | 68篇 |
1983年 | 35篇 |
1982年 | 42篇 |
1981年 | 55篇 |
1980年 | 30篇 |
1979年 | 36篇 |
1978年 | 17篇 |
1976年 | 13篇 |
1975年 | 16篇 |
1959年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
分析实现永州电力通信交换网集中操作和维护的必要性,介绍了实现程控交换机远程操作和维护的两种方式,总结在实践过程中所得到的经验和教训。 相似文献
102.
建立了AMl级别的最大重迭对称性分子轨道计算方案(MOSMO)。采用通常的半经验分子轨道方法AMl级别中完全相同的参数,计算了各种分子的几何参数等。所得计算结果与实验值及HF/6-31G*从头算方法计算结果相符,说明提出的计算方案是可行的。同时,由于提出的计算方案过程简单,更易推广使用到从头算方法难以解决的大分子体系和超分子体系的结构和性质研究。 相似文献
103.
This paper explains the manufacturing process of a composite train carbody with a sandwich composite structure for bodyshell and a stainless steel structure for the under frame. In addition, the structural behavior and safety of the composite carbody of the Korean tilting train was investigated by the static load tests. From the test results, the stiffness of the composite carbody met the specified design. In the aspect of strength, the maximum stress of the composite bodyshell was of 12.2% of strength of CF1263 carbon/epoxy. 相似文献
104.
105.
106.
Facile synthesis of ordered nanocrystalline alumina thin films with tunable mesopore structures 总被引:1,自引:0,他引:1
Lijuan Wan Honggang Fu Keying Shi Xiqiang Tian 《Microporous and mesoporous materials》2008,115(3):301-307
Mesoporous alumina layers have attracted attention for their potential use in ultrafiltration of salts, as a heterogeneous catalyst support, an adsorbent in environmental cleanup, and in petroleum refinement. The ability to control the fast hydrolysis rate of the inorganic precursors using simple and inexpensive routes is important for that potential to be realized. Herein, we introduce a novel and facile route to synthesize mesoporous alumina thin films from the combination of inexpensive and commercially available copolymer with aluminum chloride or nitrate (salts) in an EtOH–surfactant–NH3 · H2O–salts (EsNs) system through the evaporation-induced self-assembly (EISA) method. Mesoporous alumina layers obtained utilizing the EsNs system have ordered and tunable pore structures. The ability to easily control the mesophases of the alumina layers within a short time provides distinct advantages over previously reported synthesis procedures. Most importantly, we demonstrate that the binding of surfactant and NH3 · H2O for the formation of hydrogen bond between them in the EsNs system controls the fast hydrolysis rate of the inorganic species. This allows for the synthesis of nanocrystalline alumina layers via the aluminum oxo-clusters’ assembly with the surfactant. Such simple route may be applied in the synthesis of other non-silica mesostructured oxides. 相似文献
107.
Patrick Musonda 《Computational statistics & data analysis》2008,52(4):1942-1957
Second-order expressions for the asymptotic bias and variance of the log relative incidence estimator are derived for the self-controlled case series model in a simplified scenario. The dependence of the bias and variance on factors such as the relative incidence and ratio of risk to observation period are studied. Small-sample performance of the estimator in realistic scenarios is investigated using simulations. It is found that, in scenarios likely to arise in practice, asymptotic methods are valid for numbers of cases in excess of 20-50 depending on the ratio of the risk period to the observation period and on the relative incidence. The application of Monte Carlo methods to self-controlled case series analyses is also discussed. 相似文献
108.
Collinear magnetooptic interaction with magnetostatic surface waves (MSSW) can be used for wavelength‐selective switches, wavelength filters, and frequency shifters in wavelength‐division‐multiplexed (WDM) photonic networks and optical processing systems. The switching efficiency can be improved with a multilayer waveguide structure. To investigate the dynamic switching characteristics, the FDTD method was employed. The mode conversion between TE and TM mode was successfully demonstrated with FDTD simulation. The filtering characteristics were also evaluated. The FDTD results were compared with the result from the coupled mode theory, and good agreement was obtained. Switching of an optical pulse was also demonstrated by the FDTD method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 40–47, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20501 相似文献
109.
D.E. Kvasov D. Menniti A. Pinnarelli Y.D. Sergeyev N. Sorrentino 《Electric Power Systems Research》2008
In this paper, the problem of global tuning of fuzzy power-system stabilizers (FPSSs) present in a multi-machine power system in order to damp the power system oscillations is considered. In particular, it is formulated as a problem of global minimization of a multiextremal black-box function over a multidimensional hyperinterval. A global optimization technique, recently proposed, is used for solving the stated problem: the search hyperinterval is partitioned into smaller hyperintervals and the objective function is evaluated only at two vertices corresponding to the main diagonal of the generated hyperintervals, thus avoiding unnecessary ponderous simulations. Then, the performances of this technique are numerically compared with ones of a genetic algorithm (GA). 相似文献
110.