全文获取类型
收费全文 | 44196篇 |
免费 | 3916篇 |
国内免费 | 2018篇 |
专业分类
电工技术 | 2484篇 |
技术理论 | 2篇 |
综合类 | 2503篇 |
化学工业 | 7693篇 |
金属工艺 | 2609篇 |
机械仪表 | 2932篇 |
建筑科学 | 3021篇 |
矿业工程 | 1296篇 |
能源动力 | 1275篇 |
轻工业 | 2858篇 |
水利工程 | 647篇 |
石油天然气 | 2478篇 |
武器工业 | 337篇 |
无线电 | 5397篇 |
一般工业技术 | 5973篇 |
冶金工业 | 2484篇 |
原子能技术 | 492篇 |
自动化技术 | 5649篇 |
出版年
2024年 | 246篇 |
2023年 | 878篇 |
2022年 | 1511篇 |
2021年 | 2170篇 |
2020年 | 1577篇 |
2019年 | 1462篇 |
2018年 | 1513篇 |
2017年 | 1547篇 |
2016年 | 1451篇 |
2015年 | 1897篇 |
2014年 | 2261篇 |
2013年 | 2694篇 |
2012年 | 2779篇 |
2011年 | 3156篇 |
2010年 | 2481篇 |
2009年 | 2442篇 |
2008年 | 2456篇 |
2007年 | 2184篇 |
2006年 | 2291篇 |
2005年 | 1838篇 |
2004年 | 1333篇 |
2003年 | 1197篇 |
2002年 | 1124篇 |
2001年 | 981篇 |
2000年 | 948篇 |
1999年 | 998篇 |
1998年 | 838篇 |
1997年 | 714篇 |
1996年 | 631篇 |
1995年 | 527篇 |
1994年 | 411篇 |
1993年 | 277篇 |
1992年 | 228篇 |
1991年 | 205篇 |
1990年 | 169篇 |
1989年 | 156篇 |
1988年 | 101篇 |
1987年 | 88篇 |
1986年 | 57篇 |
1985年 | 51篇 |
1984年 | 37篇 |
1983年 | 37篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
31.
Herein, we report an efficient process for preparing monodisperse Au@SiO2 nanoparticles using homogeneous shaking and without the use of surface‐coupling silane agents or large stabilizers. The resulting pure‐silica surface of the Au@SiO2 nanoparticles is very important for straightforward surface functionalization with different functional groups via well‐established silica surface chemistry. Subsequent covalent bioconjugation of the aldehyde‐functionalized Au@SiO2 nanoparticles with various biomolecules is successfully employed to make robust nanoprobes for fast, colorimetric DNA and protein detection based on the sequence‐specific hybridization properties of DNA and the specific binding affinity between proteins, respectively. 相似文献
32.
Diagnosis and treatment of 17 patients who sustained 20 iatrogenic ureteral injuries were analyzed. Primary operations in which ureteral injury occurred are almost gynecologic procedures and general surgery. Injuries were managed by ureteroureterostomy in four, ureteral stent in one, removal suture ligation and ureteral double J-catheter in one, ureteroneocystostomy in ten, psoas-hitch technique and ureteroneocystostomy in one, nephrectomy in two. All patients with appropriate repair were followed-up periods of three to five years. Renal function of these patients had optimal results. When ureteral injury occurs, B-US, IVU, cystoscopy, retrograde ureterography or infusion of dye may be useful. An appropriate repair should be chosen according to length and position of ureteral injuries. Reoperation was optimal in two to three weeks. Immediate recognition of accidental ureteral injury provides optimal results. Patients with unrecognized injuries had suboptimal results. 相似文献
33.
The employment of the Zn(Se,Te) pseudo-graded contacting scheme to p-type ZnSe-based alloys contributes directly to the recent
demonstration of room temperature continuous-wave operation of II– VI green-blue laser diodes. Contact ohmicity is maintained
down to cryogenic temperatures which enabled the investigation of electrical transport properties associated with the p-type
nitrogen-doped ZnSe, Zn(S,Se), and (Zn,Mg)(S,Se). The observation of both persistent photoconductivity and a metastable population
of holes which are in thermodynamic equilibrium with hydrogenic acceptors having reduced activation energy suggests the presence
of a DX-like behavior for holes in p-type (Zn,Mg)(S,Se). 相似文献
34.
韩玉涛 《计算机光盘软件与应用》2012,(2):199+205
在高职院校的软件项目实训环节中,大多项目需要团体协作进行编程。针对如果有效提高学生的协同编程效率、团队合作意识以及合作学习能力的问题,提出了基于Dillenbourg原则的协同编程方法。通过实践证明,该方法取得了良好的实训效果。 相似文献
35.
Han Y Liu G 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2012,42(3):827-837
Localized multiple kernel learning (LMKL) is an attractive strategy for combining multiple heterogeneous features in terms of their discriminative power for each individual sample. However, models excessively fitting to a specific sample would obstacle the extension to unseen data, while a more general form is often insufficient for diverse locality characterization. Hence, both learning sample-specific local models for each training datum and extending the learned models to unseen test data should be equally addressed in designing LMKL algorithm. In this paper, for an integrative solution, we propose a probability confidence kernel (PCK), which measures per-sample similarity with respect to probabilistic-prediction-based class attribute: The class attribute similarity complements the spatial-similarity-based base kernels for more reasonable locality characterization, and the predefined form of involved class probability density function facilitates the extension to the whole input space and ensures its statistical meaning. Incorporating PCK into support-vectormachine-based LMKL framework, we propose a new PCK-LMKL with arbitrary l(p)-norm constraint implied in the definition of PCKs, where both the parameters in PCK and the final classifier can be efficiently optimized in a joint manner. Evaluations of PCK-LMKL on both benchmark machine learning data sets (ten University of California Irvine (UCI) data sets) and challenging computer vision data sets (15-scene data set and Caltech-101 data set) have shown to achieve state-of-the-art performances. 相似文献
36.
Qiyong Han Xiaodong Zhang Dong Chen Pengfei Wang 《Metallurgical and Materials Transactions B》1988,19(4):617-622
The equilibrium Ca3P2(s) = 3[Ca] + 2[P] was studied at 1600 ° by equilibrating liquid iron, saturated with Ca3P2, and contained in a TiN crucible, with Ca vapor. The source of Ca was liquid Ca contained in an Mo crucible, and the vapor
pressure of Ca was varied by varying the position of the Mo crucible in the temperature gradient of a vertical tube furnace.
A least-squares analysis of the data gave and. The simultaneous equilibria CaO(s) = [Ca] + [O] and CaS(s) = [Ca] + [S] were studied at 1600 ° by equilibrating liquid iron, contained in a pressed and sintered CaO-CaS crucible with
Ca vapor. The advantage of this technique is that two equilibrium constants,K
cas andK
cao, and two interaction coefficients, and can be determined from one set of experiments. It was determined that, at 1600 °,K
cas = 5.9 × 10−8
K
cao = 5.5 × 10−9,, and.
Formerly Graduate Students 相似文献
37.
研究了一种制造低电电压氧化锌压敏电阻器的方法。在基本成分的基础上适当加入二氧化钛可降低梯度电压(V1mA/mm),适量掺硼和改进热处理工艺可减小元件的漏电流和提高其稳定性。 相似文献
38.
Silicon - In this paper, an analytical model for negative capacitance double gate field effect transistor (NC-DG-FET) is proposed. This model includes interface traps and temperature effects, which... 相似文献
39.
Chang Dae Han 《应用聚合物科学杂志》1974,18(2):481-490
An annular die has been designed having a very thin gap distance between two coaxial cylinders. The die was then used to measure wall normal stresses along the longitudinal direction of polymer melts flowing through the thin annulus. The materials investigated were high-density polyethylene, low-density polyethylene, polypropylene, and polystyrene. Also investigated were blends of polystyrene and polypropylene, and blends of polystyrene and high-density polyethylene The measurements of wall normal stresses were used to determine the rheological properties of the melts, namely, the melt viscosity from the slope of axial wall normal stress profiles and the melt elasticity from exit pressures. The interpretation of the experimental data was made possible by the fact that the narrow-gap annular die can be considered as a substitute for a thin slit die. It has been found that the results obtained in the present study are consistent with those reported earlier by the author, who at that time used both capillary and slit dies. 相似文献
40.
Guerbet十四醇的合成与表征 总被引:4,自引:1,他引:4
以正庚醇为原料 ,通过Guerbet反应合成Guerbet十四醇 (2 戊基壬醇 ,C14 GA)。用IR、NMR和元素分析测定了C14 GA的结构 ,并研究了反应温度和用料比对其产率的影响。实验结果如下 :(1)在较优化的反应条件下 (正庚醇的总加入量为 1mol,在实验过程中 ,先加入 1/ 3mol庚醇和 1/ 4mol的KOH ,在 16 0℃下反应 2h ,然后再加入剩下的 2 / 3mol庚醇和 4g 5 %Pd -C催化剂 ,在 15 5℃下反应 6h)合成产物 ,其产率可达到 5 4 2 0 % ;(2 )所合成的产物与试图要得到的Guerbet十四醇 (2 戊基壬醇 ,C14 GA)含有相同的基团 (2×—CH3、10×—CH2 —、1×CH、1×—CH2 —O—和 1×—OH) ,而且 ,所合成的产物中 ,w (C) =79 0 6 % ,w (H ) =13 6 2 % ,与从Guerbet十四醇分子式计算的理论值w(C) =78 5 0 % ,w (H) =14 0 1%基本一致。可见所合成的产物正是Guerbet十四醇 (C14 GA) 相似文献