全文获取类型
收费全文 | 21227篇 |
免费 | 2323篇 |
国内免费 | 1350篇 |
专业分类
电工技术 | 738篇 |
技术理论 | 3篇 |
综合类 | 2290篇 |
化学工业 | 3474篇 |
金属工艺 | 450篇 |
机械仪表 | 766篇 |
建筑科学 | 1355篇 |
矿业工程 | 611篇 |
能源动力 | 656篇 |
轻工业 | 3781篇 |
水利工程 | 412篇 |
石油天然气 | 636篇 |
武器工业 | 166篇 |
无线电 | 1663篇 |
一般工业技术 | 2090篇 |
冶金工业 | 1287篇 |
原子能技术 | 166篇 |
自动化技术 | 4356篇 |
出版年
2024年 | 154篇 |
2023年 | 526篇 |
2022年 | 799篇 |
2021年 | 921篇 |
2020年 | 864篇 |
2019年 | 803篇 |
2018年 | 732篇 |
2017年 | 745篇 |
2016年 | 796篇 |
2015年 | 843篇 |
2014年 | 1250篇 |
2013年 | 1281篇 |
2012年 | 1367篇 |
2011年 | 1546篇 |
2010年 | 1118篇 |
2009年 | 1190篇 |
2008年 | 1136篇 |
2007年 | 1343篇 |
2006年 | 1162篇 |
2005年 | 1024篇 |
2004年 | 913篇 |
2003年 | 752篇 |
2002年 | 624篇 |
2001年 | 515篇 |
2000年 | 401篇 |
1999年 | 353篇 |
1998年 | 240篇 |
1997年 | 188篇 |
1996年 | 199篇 |
1995年 | 176篇 |
1994年 | 145篇 |
1993年 | 120篇 |
1992年 | 101篇 |
1991年 | 65篇 |
1990年 | 50篇 |
1989年 | 37篇 |
1988年 | 39篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1965年 | 16篇 |
1964年 | 17篇 |
1963年 | 21篇 |
1961年 | 21篇 |
1960年 | 19篇 |
1959年 | 25篇 |
1958年 | 17篇 |
1957年 | 19篇 |
1956年 | 22篇 |
1955年 | 27篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Hashim A.
Hashim 《国际强度与非线性控制杂志
》2020,30(10):3848-3870
》2020,30(10):3848-3870
This paper introduces two novel nonlinear stochastic attitude estimators developed on the Special Orthogonal Group with the tracking error of the normalized Euclidean distance meeting predefined transient and steady‐state characteristics. The tracking error is confined to initially start within a predetermined large set such that the transient performance is guaranteed to obey dynamically reducing boundaries and decrease smoothly and asymptotically to the origin in probability from almost any initial condition. The proposed estimators produce accurate attitude estimates with remarkable convergence properties using measurements obtained from low‐cost inertial measurement units. The estimators proposed in continuous form are complemented by their discrete versions for the implementation purposes. The simulation results illustrate the effectiveness and robustness of the proposed estimators against uncertain measurements and large initialization error, whether in continuous or discrete form. 相似文献
3.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. 相似文献
4.
5.
The motional transition and heterogeneity of semi‐interpenetrating networks (SIPNs) based on polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin probe method. The concentration of functional groups in both prepolymers varied from 0 to 0.45 mmol g?1. Spin‐probed SIPNs show that the temperature‐dependent spectra are sensitive to polymer interactions imposed by functional groups. These interactions determine the free volume distribution in the matrix and temperature at which motional transition takes place. The fraction of free volume increases with functional group concentration and reaches its maximum at 0.25 mmol g?1. Further increases in the functional group concentration reduce the free volume. The results of the networks with strong interactions are discussed in terms of the interference of the plasticizing effect of the PU component and the formation of possible cluster cross‐links, which restricts segmental motions. Copyright © 2003 Society of Chemical Industry 相似文献
6.
The present empirical investigation had a 3-fold purpose: (a) to cross-validate L. R. Offermann, J. K. Kennedy, and P. W. Wirtz's (1994) scale of Implicit Leadership Theories (ILTs) in several organizational settings and to further provide a shorter scale of ILTs in organizations; (b) to assess the generalizability of ILTs across different employee groups, and (c) to evaluate ILTs' change over time. Two independent samples were used for the scale validation (N1 = 500 and N2 = 439). A 6-factor structure (Sensitivity, Intelligence, Dedication, Dynamism, Tyranny, and Masculinity) was found to most accurately represent ELTs in organizational settings. Regarding the generalizability of ILTs, although the 6-factor structure was consistent across different employee groups, there was only partial support for total factorial invariance. Finally, evaluation of gamma, beta, and alpha change provided support for ILTs' stability over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
This study investigated the ability of the Millon Clinical Multiaxial Inventory--Third Edition (MCMI-III) to discriminate students malingering psychopathology (n=106) from bona fide psychiatric inpatients (n=202). Students were randomly assigned to a fake-bad or an honest-responding condition. Analyses investigated the ability of the modifier indices to discriminate fake-bad group participants from the psychiatric inpatients. Scale X raw cutoff score >178 yielded a positive predictive power (PPP) of 0.0, a negative predictive power (NPP) of 63.1, and a hit rate of 63.1%. Optimal cutoff scores were developed. Scale X Base Rate (BR) >84 provided a PPP of 55.6, an NPP of 72.1, and a hit rate of 65.2%. Scale Y BR 相似文献
8.
The Lambda Library (LL) adds a form of lambda functions to C++, which are common in functional programming languages. The LL is implemented as a template library using standard C++; thus no language extensions or preprocessing is required. The LL consists of a rich set of tools for defining unnamed functions. In particular these unnamed functions work seamlessly with the generic algorithms in the C++ Standard Library. The LL offers significant improvements, in terms of generality and ease of use, compared to the current tools in the C++ Standard Library. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
9.
César I. Beristain Ebner Azuara Hugo S. Garcia & Eduardo J. Vernon-Carter 《International Journal of Food Science & Technology》1996,31(5):379-386
The water and oil uptake of mesquite and arabic gums in powdered form was studied at temperatures of 23, 35 and 45°C. A previously proposed equation to predict osmotic equilibrium was tested using the experimental data with both gums and a good statistical fit was obtained. Mesquite gum showed the highest water and oil absorption at all temperatures studied. Temperature dependence of the reciprocal of the S1 and WL∞ were determined using an Arrhenius equation. The activation energy for water and oil absorption for gum arabic was 21.98 and 39.57 kJ mol−1 , compared to that of mesquite gum having values of 15.79 and 46.16 kJ mol−1 , respectively. A second order kinetic model was obtained for water and oil absorption for both gums. 相似文献
10.