全文获取类型
收费全文 | 8970篇 |
免费 | 767篇 |
国内免费 | 222篇 |
专业分类
系统科学 | 1228篇 |
丛书文集 | 95篇 |
教育与普及 | 84篇 |
理论与方法论 | 306篇 |
现状及发展 | 892篇 |
研究方法 | 14篇 |
综合类 | 7340篇 |
出版年
2024年 | 19篇 |
2023年 | 46篇 |
2022年 | 79篇 |
2021年 | 116篇 |
2020年 | 63篇 |
2019年 | 27篇 |
2018年 | 764篇 |
2017年 | 793篇 |
2016年 | 488篇 |
2015年 | 131篇 |
2014年 | 161篇 |
2013年 | 135篇 |
2012年 | 406篇 |
2011年 | 1086篇 |
2010年 | 929篇 |
2009年 | 591篇 |
2008年 | 686篇 |
2007年 | 898篇 |
2006年 | 152篇 |
2005年 | 166篇 |
2004年 | 210篇 |
2003年 | 235篇 |
2002年 | 129篇 |
2001年 | 85篇 |
2000年 | 104篇 |
1999年 | 176篇 |
1998年 | 159篇 |
1997年 | 153篇 |
1996年 | 149篇 |
1995年 | 140篇 |
1994年 | 107篇 |
1993年 | 86篇 |
1992年 | 94篇 |
1991年 | 94篇 |
1990年 | 73篇 |
1989年 | 79篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 24篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1967年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9959条查询结果,搜索用时 31 毫秒
991.
Pure CoAPO-36 crystal grains were synthesized by hydrothermal reaction. Porous α-Al2O3, stainless steel and K2Ti6O13 supported CoAPO-36 films were fabricated using in situ crystallization for the first time. SEM images and XRD measurements demonstrate that a continuous CoAPO-36 film was obtained
on the K2Ti6O13 substrate. Diffuse reflectance UV-Vis spectra indicate that Co2+ has been incorporated into the ATS framework. Both CoAPO-36 crystal grains and the K2Ti6O13 supported CoAPO-36 film exhibit satisfactory catalytic activities for the oxidation of cyclohexane. 相似文献
992.
The distributed detection of botnets may induce heavy computation and communication costs to network devices. Each device in related scheme only has a regional view of Internet, so it is hard to detect botnet comprehensively. In this paper, we propose a lightweight real-time botnet detection framework called Bot-Guard, which uses the global landscape and flexible configurability of software defined network (SDN) to identify botnets promptly. SDN, as a new network framework, can make centralized control in botnet detection, but there are still some challenges in such detections. We give a convex lens imaging graph (CLI-graph) to depict the topology characteristics of botnet, which allows SDN controller to locate attacks separately and mitigate the burden of network devices. The theoretical and experimental results prove that our scheme is capable of timely botnet detecting in SDNs with the accuracy higher than 90% and the delay less than 56 ms. 相似文献
993.
Tsjalling Swierstra 《Foundations of Science》2017,22(2):275-278
In this review I argue that Puech draws on two important currents in modern thought: the criticism of the ontological and social priority of conflict, and the rehabilitation of praxis vis-à-vis theoria. Still, his plea for a non-confrontational art of living leaves important questions unanswered. What is the problem exactly? What does exactly count as (non)confrontational? What is non-confrontation exactly meant to solve? What is the antiposition here? And: how does this new (or rather: old) art of living relate to the political and ethical varieties of Technology Assessment? 相似文献
994.
This paper considers the mixed covolume method for the second-order elliptic equations over quadrilaterals.Superconvergence results are established in this paper on quadrilateral grids satisfying the h~2-parallelogram condition when the lowest-order Raviart-Thomas space is employed in the mixed covolume method.The authors prove O(h~2) accuracy between the approximate velocity or pressure and a suitable projection of the real velocity or pressure in the L~2 norm.Numerical experiments illustrating the theoretical results are provided. 相似文献
995.
This paper studies a maximum likelihood estimator (MLE) of the parameter for a continuous one-parameter exponential family under ranked set sampling (RSS). The authors first find the optimal RSS according to the character of the family, viz, arrange the RSS based on quasi complete and sufficient statistic of independent and identically distributed (iid) samples. Then under this RSS, some sufficient conditions for the existence and uniqueness of the MLE, which are easily used in practice, are obtained. Using these conditions, the existence and uniqueness of the MLEs of the parameters for some usual distributions in this family are proved. Numerical simulations for these distributions fully support the result from the above two step optimizations of the sampling and the estimation method. 相似文献
996.
997.
Artificial neural network has been used successfully to develope the automatic spike extraction. In order to address some of the problems before the wireless transmission of the implantable chip, the automatic spike sorting method with low complexity and high efficiency is proposed based on the hybrid neural network with the principal component analysis network (PCAN) and normal boundary response (NBR) self-organizing mapping (SOM) network classifier. An automatic PCAN technique is used to reduce the dimension and eliminate the correlation of the spike signal. The NBR-SOM network performs the spike sorting challenge and improves the classification performance. The experimental results show that based on the hybrid neural network, the spike sorting method achieves the accuracy above 97.91% with signals containing five classes. The proposed NBR-SOM network classifier is to further improve the stability and effectiveness of the classification system. 相似文献
998.
潘之波 《江西科技师范学院学报》2010,(2):98-100
在市场经济迅猛发展的今天,"旅游信用危机"越来越成为社会关注的焦点.本文通过对目前我国旅游行业诚信建设和导游管理现状进行分析,提出应从积极构建旅游诚信体系,规范旅游行政管理部门行为,充分发挥旅游行业协会的沟通协调作用,建立诚信教育与培训制度,注重旅游企业自身的诚信建设,保障导游的生存发展空间以及做理智的旅游消费者等方面牢同树立"共铸诚信"的观念,才能为旅游业的健康发展保驾护航,最终实现旅游业的可持续发展. 相似文献
999.
Elena C. Gianulis Chantelle Labib Gintautas Saulis Vitalij Novickij Olga N. Pakhomova Andrei G. Pakhomov 《Cellular and molecular life sciences : CMLS》2017,74(9):1741-1754
Tumor ablation by nanosecond pulsed electric fields (nsPEF) is an emerging therapeutic modality. We compared nsPEF cytotoxicity for human cell lines of cancerous (IMR-32, Hep G2, HT-1080, and HPAF-II) and non-cancerous origin (BJ and MRC-5) under strictly controlled and identical conditions. Adherent cells were uniformly treated by 300-ns PEF (0–2000 pulses, 1.8 kV/cm, 50 Hz) on indium tin oxide-covered glass coverslips, using the same media and serum. Cell survival plotted against the number of pulses displayed three distinct regions (initial resistivity, logarithmic survival decline, and residual resistivity) for all tested cell types, but with differences in LD50 spanning as much as nearly 80-fold. The non-cancerous cells were less sensitive than IMR-32 neuroblastoma cells but more vulnerable than the other cancers tested. The cytotoxic efficiency showed no apparent correlation with cell or nuclear size, cell morphology, metabolism level, or the extent of membrane disruption by nsPEF. Increasing pulse duration to 9 µs (0.75 kV/cm, 5 Hz) produced a different selectivity pattern, suggesting that manipulation of PEF parameters can, at least for certain cancers, overcome their resistance to nsPEF ablation. Identifying mechanisms and cell markers of differential nsPEF susceptibility will critically contribute to the proper choice and outcome of nsPEF ablation therapies. 相似文献
1000.
Aquaporins are implicated in a wide variety of plant physiological processes, although the mechanisms involved in their regulation are not fully understood. To gain further insight into the regulatory factors involved in this process, we used a yeast two-hybrid system to screen for potential binding partners to the Arabidopsis tonoplast intrinsic protein (TIP) AtTIP1;1. This was the first protein identified to be associated with high water permeability in vacuolar membranes from Arabidopsis thaliana. Using ... 相似文献