全文获取类型
收费全文 | 35855篇 |
免费 | 2913篇 |
国内免费 | 1471篇 |
专业分类
电工技术 | 2160篇 |
技术理论 | 1篇 |
综合类 | 2118篇 |
化学工业 | 6125篇 |
金属工艺 | 1854篇 |
机械仪表 | 2390篇 |
建筑科学 | 2783篇 |
矿业工程 | 1169篇 |
能源动力 | 939篇 |
轻工业 | 2212篇 |
水利工程 | 652篇 |
石油天然气 | 2299篇 |
武器工业 | 254篇 |
无线电 | 4211篇 |
一般工业技术 | 4364篇 |
冶金工业 | 1741篇 |
原子能技术 | 406篇 |
自动化技术 | 4561篇 |
出版年
2024年 | 206篇 |
2023年 | 683篇 |
2022年 | 1071篇 |
2021年 | 1520篇 |
2020年 | 1119篇 |
2019年 | 954篇 |
2018年 | 1092篇 |
2017年 | 1139篇 |
2016年 | 1017篇 |
2015年 | 1376篇 |
2014年 | 1770篇 |
2013年 | 2055篇 |
2012年 | 2238篇 |
2011年 | 2315篇 |
2010年 | 2011篇 |
2009年 | 1969篇 |
2008年 | 1801篇 |
2007年 | 1818篇 |
2006年 | 1935篇 |
2005年 | 1737篇 |
2004年 | 1108篇 |
2003年 | 997篇 |
2002年 | 947篇 |
2001年 | 817篇 |
2000年 | 933篇 |
1999年 | 1003篇 |
1998年 | 811篇 |
1997年 | 733篇 |
1996年 | 687篇 |
1995年 | 547篇 |
1994年 | 451篇 |
1993年 | 333篇 |
1992年 | 263篇 |
1991年 | 205篇 |
1990年 | 156篇 |
1989年 | 122篇 |
1988年 | 102篇 |
1987年 | 53篇 |
1986年 | 36篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 24篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper presents a novel approach to computing tight upper bounds on the processor utilization for general real-time systems where tasks are composed of subtasks and precedence constraints may exist among subtasks of the same task. By careful analysis of preemption effects among tasks, the problem is formulated as a set of linear programming (LP) problems. Observations are made to reduce the number of LP problem instances required to be solved, which greatly improves the computation time of the utilization bounds. Furthermore, additional constraints are allowed to be included under certain circumstances to improve the quality of the bounds. 相似文献
62.
Arachidonic acid (AA)-induced platelet chemiluminescence (CL) was measured with a lumiphotometer. Quercetin remarkably inhibited the CL, the IC50 of quercetin was 3 mumol.L-1. When quercetin plus aspirin, which inhibits only cyclooxygenase, was added, the inhibitory rate of platelet-CL obviously increased (P < 0.01). On the other hand, the quercetin had a scavenging effect on superoxide anion radical using alkaline sodium dithionite solution generation. The IC50 was 20.9 mumol.L-1. In addition, superoxide dismutase of 0.1 mg.ml-1 inhibited the platelet-CL by 97.8%, while mannitol, a hydroxyl radical scavenger, only by 43.3% at a concentration of 80 mg.ml-1. These results suggest that the mechanism of the inhibiting AA-induced platelet-CL by quercetin was associated with scavenging the superoxide anion radical directly and with inhibiting the cyclooxygenase. 相似文献
63.
交联型聚醚聚氨酯的表征、力学性能及其碱金属盐络合物的导电性能 总被引:1,自引:0,他引:1
采用三羟甲基丙烷(TMP)作交联剂与聚乙二醇(PEO-1540)和甲苯二异氰酸酯(TDI)反应,得到了具有较好力学性能的交联型聚醚聚氨酯(PEU),该聚合物与LiClO4的结合物具有较高的室温电导率(σ30℃=1.87×10 ̄(-4)S/cm)。采用全反射红外光谱(ATR-IR)对聚合物的结构进行了表征。对聚合物的组成、不同TDI类型及络合盐浓度对聚合物力学性能及其络合物电导率的影响进行了探讨。低度交联聚合物的络合物,其电导率与温度的关系符合建立在自由体积理论上的VTF方程,表明络合物中离子的传导主要是在无定形区域进行,与自由体积有关。 相似文献
64.
Adenomatous polyps are considered as the dominant precursor lesion of colorectal cancer. A phase III colorectal cancer prevention trial, conducted by the Arizona Cancer Center, concerns the ability of wheat bran fibre supplement to reduce the recurrence of adenomatous polyps. All participants in the study are to have had colorectal polyps detected and removed during a baseline (qualifying) colonoscopy within three months prior to enrolment. In this paper, our interest focuses on occurrence of adenomatous polyps at the baseline colonoscopy. We use a truncated Poisson model to fit these types of data. We develop a regression model to assess the effects of explanatory factors on the positive counting variable. We fit truncated Poisson parameters by a log-linear regression model and estimate regression parameters by the maximum likelihood procedure. Finally, we apply it to the baseline colonoscopy data from the Wheat Bran Fiber study. 相似文献
65.
66.
In this paper we propose a new protocol called time-space label switching protocol (TSL-SP) in optical burst switching (OBS), and define the terms time-space label (TSL) and time-space routing (TSR). An important concept of response time is introduced in the time label mechanism. The TSL-SP is a new technology that can quickly and efficiently forward data with a label on the optical networks. A two-dimension label switched path (TD-LSP) can be set up, that is maintained and deleted by the TSL-SP. For clearly illuminating the operation principles of the TSL-SP, we propose a new approach of orthogonal time-space coordinates in which the vertical coordinate is the space label and the horizontal coordinate is the time label. The proposed TD-LSP can dramatically reduce the routing failure probability and greatly improve the link network efficiency compared with other signaling protocols. Moreover, we define the time-space label control plane that can achieve the higher efficiency. When the TSL-SP is applied to networks, switching performance can be improved by two orders compared to the switching performance with the conventional OBS signaling protocols. The fundamental goal of TSL-SP is to band the signaling and routing functions together closely. Also, the TSL-SP can reduce the complexity of the network, support automatic service offering, and provide traffic engineering. 相似文献
67.
Basic data of four fractions, PM1, PM6, PM7and PM8, derived from Pingshuo bituminous coal were obtained by ultimate analyses, mean molecular weight measure, GC/MS, 13C-NM R, 1H-NM R and FTIR technigues. A method of calculating the average molecular parameters of the fractions is introduced. Based on the calculated parameters, the molecular structure models of the fractions of PM6, PM;and PM8are constructed. Significant structural information about the saturated hydrocarbon and aromatic hydrocarbon with heteroatom groups is given also. 相似文献
68.
本文先将倒虹吸管的管径计算公式整理成等式左边只含管径的一次方法,右边含有管径高阶非线性的迭代函数,然后证明该迭代函数收敛,最后利用数学迭代原理给迭代函数右边赋初值,计算左边的管径。继续迭代下去,就能求出倒虹吸管的管径。 相似文献
69.
报道了以茈为荧光探针,探讨小剂量~(60)Co γ射线照射后小鼠胸腺细胞膜流动性的变化。结果表明,剂量在0.25-1.00Gy范围,胸腺细胞膜流动性降低与剂量之间呈明显线性关系。从0.50Gy起,辐照组荧光强度比值I_1/I_2与I_3/I_2与对照组的比较存有显著差异(P<0.05)。提示淋巴细胞膜流动性的变化可作为小剂量辐照早期效应的敏感指标。 相似文献
70.
An observer-based robust adaptive nonlinear position and speed tracking controller is developed for a permanent magnet synchronous motor with initial rotor angle uncertainty. The unknown initial rotor position is treated as a constant motor parameter in the development of the controller. An incremental encoder, which provides relative position variation of the rotor, is used along with stator current signals to achieve stable control. However, the controller does not require the knowledge of motor parameters and it only assumes friction, external disturbances, and model uncertainties are bounded. By using state observers, the measurement of acceleration and load torque, which is required usually in the nonlinear controller design with high tracking performance, is avoided. The stability of the control system and tracking convergence are guaranteed using Lyapunov theory. Finally, the stability and efficacy of the proposed drive system are verified by experimental results. 相似文献