全文获取类型
收费全文 | 205200篇 |
免费 | 25954篇 |
国内免费 | 23413篇 |
专业分类
电工技术 | 19088篇 |
技术理论 | 8篇 |
综合类 | 13920篇 |
化学工业 | 41740篇 |
金属工艺 | 12025篇 |
机械仪表 | 12813篇 |
建筑科学 | 9059篇 |
矿业工程 | 2355篇 |
能源动力 | 6031篇 |
轻工业 | 14866篇 |
水利工程 | 2497篇 |
石油天然气 | 4390篇 |
武器工业 | 2044篇 |
无线电 | 29742篇 |
一般工业技术 | 25886篇 |
冶金工业 | 4410篇 |
原子能技术 | 3495篇 |
自动化技术 | 50198篇 |
出版年
2024年 | 467篇 |
2023年 | 3038篇 |
2022年 | 5180篇 |
2021年 | 7124篇 |
2020年 | 6700篇 |
2019年 | 6062篇 |
2018年 | 5657篇 |
2017年 | 7810篇 |
2016年 | 8819篇 |
2015年 | 10495篇 |
2014年 | 10545篇 |
2013年 | 13719篇 |
2012年 | 15436篇 |
2011年 | 18503篇 |
2010年 | 13490篇 |
2009年 | 13329篇 |
2008年 | 14270篇 |
2007年 | 15524篇 |
2006年 | 14439篇 |
2005年 | 12552篇 |
2004年 | 10820篇 |
2003年 | 8694篇 |
2002年 | 6695篇 |
2001年 | 4582篇 |
2000年 | 3582篇 |
1999年 | 3052篇 |
1998年 | 2484篇 |
1997年 | 1969篇 |
1996年 | 1666篇 |
1995年 | 1440篇 |
1994年 | 1269篇 |
1993年 | 934篇 |
1992年 | 765篇 |
1991年 | 606篇 |
1990年 | 518篇 |
1989年 | 382篇 |
1988年 | 302篇 |
1987年 | 189篇 |
1986年 | 187篇 |
1985年 | 248篇 |
1984年 | 214篇 |
1983年 | 152篇 |
1982年 | 213篇 |
1981年 | 126篇 |
1980年 | 108篇 |
1979年 | 30篇 |
1978年 | 24篇 |
1977年 | 30篇 |
1976年 | 16篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A phaser-based processing technique was adopted in an UWB over fiber system employing SOA. The target is to simultaneously reduce the ASE noise impact and nonlinear effects inherent to optical amplification. Experimental results prove the effectiveness of chirping in terms of cross correlation and bit error rate. 相似文献
992.
Chemotherapy is the mainstream treatment of anaplastic large cell lymphoma (ALCL). However, chemotherapy can cause severe adverse effects in patients because it is not ALCL‐specific. In this study, a multifunctional aptamer‐nanomedicine (Apt‐NMed) achieving targeted chemotherapy and gene therapy of ALCL is developed. Apt‐NMed is formulated by self‐assembly of synthetic oligonucleotides containing CD30‐specific aptamer and anaplastic lymphoma kinase (ALK)‐specific siRNA followed by self‐loading of the chemotherapeutic drug doxorubicin (DOX). Apt‐NMed exhibits a well‐defined nanostructure (diameter 59 mm) and stability in human serum. Under aptamer guidance, Apt‐NMed specifically binds and internalizes targeted ALCL cells. Intracellular delivery of Apt‐NMed triggers rapid DOX release for targeted ALCL chemotherapy and intracellular delivery of the ALK‐specific siRNA induced ALK oncogene silencing, resulting in combined therapeutic effects. Animal model studies reveal that upon systemic administration, Apt‐NMed specifically targets and selectively accumulates in ALCL tumor site, but does not react with off‐target tumors in the same xenograft mouse. Importantly, Apt‐NMed not only induces significantly higher inhibition in ALCL tumor growth, but also causes fewer or no side effects in treated mice compared to free DOX. Moreover, Apt‐NMed treatment markedly improves the survival rate of treated mice, opening a new avenue for precision treatment of ALCL. 相似文献
993.
In recent years, finite element analyses have increasingly been utilized for slope stability problems. In comparison to limit equilibrium methods, numerical analyses do not require any definition of the failure mechanism a priori and enable the determination of the safety level more accurately. The paper compares the performances of strength reduction finite element analysis (SRFEA) with finite element limit analysis (FELA), whereby the focus is related to non-associated plasticity. Displacement-based finite element analyses using a strength reduction technique suffer from numerical instabilities when using non-associated plasticity, especially when dealing with high friction angles but moderate dilatancy angles. The FELA on the other hand provides rigorous upper and lower bounds of the factor of safety (FoS) but is restricted to associated flow rules. Suggestions to overcome this problem, proposed by Davis (1968), lead to conservative FoSs; therefore, an enhanced procedure has been investigated. When using the modified approach, both the SRFEA and the FELA provide very similar results. Further studies highlight the advantages of using an adaptive mesh refinement to determine FoSs. Additionally, it is shown that the initial stress field does not affect the FoS when using a Mohr-Coulomb failure criterion. 相似文献
994.
通过水热合成法成功地制备了丙三醇改性Ni/Al型水滑石(GMH),并通过批量处理法和静态吸附法考察了在固体投加量、溶液pH、离子强度、腐殖酸、接触时间和温度等因素影响下,溶液中Eu(Ⅲ)和U(Ⅵ)在GMH上的吸附行为。采用扫描电镜(SEM)、红外光谱(FTIR)、X射线衍射(XRD)等表征手段对材料吸附前后进行分析,结合吸附动力学和热力学模型对吸附机理进行探讨。结果表明,溶液pH值对Eu(Ⅲ)和U(Ⅵ)在GMH上的吸附行为影响显著,在pH=7.0左右时吸附率达到最大;准二级动力学模型和Langmuir等温线模型可以很好地描述Eu(Ⅲ)和U(Ⅵ)在GMH上的吸附过程,且此过程是自发的、吸热的过程;实验条件下,GMH对溶液中的Eu(Ⅲ)和U(Ⅵ)的最大理论吸附量分别为511 mg/g和441 mg/g;GMH对溶液中Eu(Ⅲ)的吸附主要是通过静电相互作用、内层表面络合以及离子交换相互作用实现;而对U(Ⅵ)的吸附主要是通过静电相互作用和内层表面络合作用实现的。实验表明,合成材料在含低放废水的有效净化和修复方面具有很大的应用前景。 相似文献
995.
针对0.2m高分辨率数字聚焦双侧向测井仪器的理论条件和工程需要,设计了发射电路,包括信号源与功率控制、基于电流源输出的模式1(35 Hz)和模式3(140 Hz)信号发射、基于电压源输出的模式2(280 Hz)信号发射、辅助监督等单元电路,确保三种模式同时工作、互不干扰以及辅助聚焦,三个模式的信号发射功率能够自动控制。室内测试与现场应用均表明,所设计的发射电路适用于0.2 m高分辨率数字聚焦双侧向测井仪器,测量值准确可靠,能够为油田薄层识别、饱和度求取以及水淹层判别提供准确可靠的高分辨率电阻率测井资料。 相似文献
996.
Seyed Ali Mohajeran Ghosheh Abed Hodtani 《International Journal of Communication Systems》2020,33(14)
In this paper, the power allocation problem in a wireless sensor network (WSN) with binary distributed detection is considered. It is assumed that the sensors independently transmit their local decisions to a fusion center (FC) through a slow fading orthogonal multiple access channel (OMAC), where, in every channel, the interferences from other devices are considered as correlated noises. In this channel, the associated power allocation optimization problem with equal power constraint is established between statistical distributions under different hypotheses by using the Jeffrey divergence (J‐divergence) as a performance criterion. It is shown that this criterion for the power allocation problem is more efficient compared to other criteria such as mean square error (MSE). Moreover, several numerical simulations and examples are presented to illustrate the effectiveness of the proposed approach. 相似文献
997.
《Advanced Powder Technology》2020,31(3):1125-1139
In this research, a novel impregnated nano-zeolite (NAASMS-Z) was synthesized and characterized using different characterization techniques. Excellent properties, such as high specific surface area (~502.77 m2/g), low pore size (~8.92 Å) and the existence of numerous functional groups caused the efficient elimination of Sr2+ and Cs+ cations from aquatic systems. The sorption performance of the nano-particles was enhanced by impregnation up to 60% in the aquatic media. The kinetic study indicated that the elimination process of both the concerned cations is controlled by external film mass transfer through the boundary within the first 30 min then controlled by intra-particle diffusion. The sorption equilibrium data suggested that the sorption process occurs on the heterogeneous sorbent surface. Parameters affecting the elimination of Sr2+ and Cs+ from a single metal sorption system, such as pH, initial contaminant concentration (Ci) and contact time (t), were investigated and optimized. A predictive model based on an Adaptive Neuro-Fuzzy Inference system (ANFIS) analysis was applied to evaluate the experimental parameters affecting the elimination of Sr2+ and Cs+ cations from aquatic system. A Mamdani-type FIS was employed to justify a collection of 16 rules (If-Then format) by means of centroid membership functions. The suggested fuzzy model revealed high predictive concert with high correlation coefficient (R2) and satisfactory deviation from the experimental data, affirming its appropriateness to predict Sr2+ and Cs+ elimination efficacy from the studied system. Rooted in experimental data and statistical analysis, the synthetized material was effective for treating contaminated aquatic solutions containing Sr2+ and Cs+ cations. 相似文献
998.
999.
1000.
M.A. Abbas M.A. Lajis D.R. Abbas O.M. Merzah M.H. Kadhim A.A. Shamran 《Materialwissenschaft und Werkstofftechnik》2020,51(6):719-724
The quality of the machined surface resulted from the electrical discharge machining (EDM) environment is not efficient according to the previous studies. One of the significant problems is the impedance of dielectric fluid, where it is contributing to focusing the plasma channel in a limited area. Hence, this behavior leads to appearing deep craters on the machined zone. The researchers have attempted to enhance the average of surface roughness by employing powder particles or surfactant as the additive materials in the dielectric fluid. Unfortunately, these studies did not present a comparison between these additive materials in this environment. Therefore, the present study aims to compare the performance of the average of surface roughness (Ra) for AISI D2 steel by utilizing Nano chromium powder (NCP) and Span-20. The present work has proved that the behavior of the average of surface roughness for this steel is dropping at the maximum level of Nano chromium powder concentration and pulse duration as compared to the behavior with the Span-20. Moreover, the best roughness was produced by this steel with Nano chromium powder at 2 g/L and 20 μs for this powder and the pulse duration. 相似文献