全文获取类型
收费全文 | 12262篇 |
免费 | 537篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 121篇 |
综合类 | 5篇 |
化学工业 | 2377篇 |
金属工艺 | 181篇 |
机械仪表 | 239篇 |
建筑科学 | 676篇 |
矿业工程 | 30篇 |
能源动力 | 393篇 |
轻工业 | 972篇 |
水利工程 | 120篇 |
石油天然气 | 46篇 |
无线电 | 906篇 |
一般工业技术 | 2315篇 |
冶金工业 | 2284篇 |
原子能技术 | 63篇 |
自动化技术 | 2092篇 |
出版年
2023年 | 78篇 |
2022年 | 148篇 |
2021年 | 258篇 |
2020年 | 205篇 |
2019年 | 240篇 |
2018年 | 263篇 |
2017年 | 263篇 |
2016年 | 274篇 |
2015年 | 253篇 |
2014年 | 379篇 |
2013年 | 733篇 |
2012年 | 618篇 |
2011年 | 847篇 |
2010年 | 565篇 |
2009年 | 533篇 |
2008年 | 664篇 |
2007年 | 585篇 |
2006年 | 498篇 |
2005年 | 444篇 |
2004年 | 385篇 |
2003年 | 371篇 |
2002年 | 321篇 |
2001年 | 199篇 |
2000年 | 205篇 |
1999年 | 196篇 |
1998年 | 389篇 |
1997年 | 301篇 |
1996年 | 277篇 |
1995年 | 213篇 |
1994年 | 183篇 |
1993年 | 154篇 |
1992年 | 115篇 |
1991年 | 106篇 |
1990年 | 117篇 |
1989年 | 103篇 |
1988年 | 89篇 |
1987年 | 96篇 |
1986年 | 79篇 |
1985年 | 107篇 |
1984年 | 86篇 |
1983年 | 91篇 |
1982年 | 83篇 |
1981年 | 69篇 |
1980年 | 56篇 |
1979年 | 61篇 |
1978年 | 52篇 |
1977年 | 68篇 |
1976年 | 75篇 |
1975年 | 38篇 |
1974年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Kim Khoa Nguyen Mohamed Cheriet Mathieu Lemay Victor Reijs Andrew Mackarel Alin Pastrama 《Computer Networks》2012,56(10):2538-2550
Cloud computing services have recently become a ubiquitous service delivery model, covering a wide range of applications from personal file sharing to being an enterprise data warehouse. Building green data center networks providing cloud computing services is an emerging trend in the Information and Communication Technology (ICT) industry, because of Global Warming and the potential GHG emissions resulting from cloud services. As one of the first worldwide initiatives provisioning ICT services entirely based on renewable energy such as solar, wind and hydroelectricity across Canada and around the world, the GreenStar Network (GSN) was developed to dynamically transport user services to be processed in data centers built in proximity to green energy sources, reducing Greenhouse Gas (GHG) emissions of ICT equipments. Regarding the current approach, which focuses mainly in reducing energy consumption at the micro-level through energy efficiency improvements, the overall energy consumption will eventually increase due to the growing demand from new services and users, resulting in an increase in GHG emissions. Based on the cooperation between Mantychore FP7 and the GSN, our approach is, therefore, much broader and more appropriate because it focuses on GHG emission reductions at the macro-level. This article presents some outcomes of our implementation of such a network model, which spans multiple green nodes in Canada, Europe and the USA. The network provides cloud computing services based on dynamic provision of network slices through relocation of virtual data centers. 相似文献
122.
Garbage collection can be done in vector mode on supercomputers like the CRAY-2 and the Cyber 205. Both copying collection and mark-and-sweep can be expressed as breadth-first searches in which the queue can be processed in parallel. We have designed a copying garbage collector whose inner loop works entirely in vector mode. We give performance measurements of the algorithm as implemented for Lisp CONS cells on the Cyber 205. Vector-mode garbage collection performs up to nine times faster than scalar-mode collection-a worthwhile improvement.Supported in part by NSF Grants DCR-8603543 and CCR-8806121, and by a Digital Equipment Corp. Faculty Incentive Grant.Supported by the NSF Research Experiences for Undergraduates program. 相似文献
123.
LetR be a unidirectional asynchronous ring ofn identical processors each with a single input bit. Letf be any cyclic nonconstant function ofn boolean variables. Moran and Warmuth (1986) prove that anydeterministic algorithm that evaluatesf onR has communication complexity (n logn) bits. They also construct a family of cyclic nonconstant boolean functions that can be evaluated inO(n logn) bits by a deterministic algorithm.This contrasts with the following new results:
相似文献
1. | There exists a family of cyclic nonconstant boolean functions which can be evaluated with expected complexity bits by arandomized algorithm forR. |
2. | Anynondeterministic algorithm forR which evaluates any cyclic nonconstant function has communication complexity bits. |
124.
N. Klein U. D?hne U. Poppe N. Tellmann K. Urban S. Orbach S. Hensen G. Müller H. Piel 《Journal of Superconductivity》1992,5(2):195-201
We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR
s
of 1×1 cm2 superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE01 oscillation mode the highly reproducible quality factor of about 105 results in a sensitivity of ±50 forR
s
measurements. The temperature dependence ofR
s
can be measured up to values as high as 1 . We have investigated several YBa2Cu3O7 thin films prepared by high oxygen pressure d.c. sputtering on LaAlO3 and NdGaO3. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivity(T) with(300K)/(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT
c
, a further strong decrease ofR
s
at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForTTc/2 these films exhibit an exp (–T
c/T) dependence ofR
s
with-values around 0.4. These observations may be explained by a superconducting energy gap with 2/kT
c0.8 for charge carriers localized in the CuO chains for YBa2Cu3O7. 相似文献
125.
Measurements are reported of the dielectric properties of two semiconducting glasses of composition SiO2 · Na2O with admixtures of Sb2O
5 and SnO2, covering a wide range of temperatures and a range of six decades of frequency 10–2 to 104 Hz. Both glasses show a gradual evolution of growing low frequency dispersion (LFD) with increasing temperature, with both the real and imaginary components of the complex susceptibility following a power law of the type
n–1, with n 1 at the lowest frequencies. There are also clear indications of reversible phase transitions taking place which manifest themselves by changes in the spectral shape of the dielectric response. 相似文献
126.
Several related algorithms are presented for computing logarithms in fieldsGF(p),p a prime. Heuristic arguments predict a running time of exp((1+o(1))
) for the initial precomputation phase that is needed for eachp, and much shorter running times for computing individual logarithms once the precomputation is done. The running time of the precomputation is roughly the same as that of the fastest known algorithms for factoring integers of size aboutp. The algorithms use the well known basic scheme of obtaining linear equations for logarithms of small primes and then solving them to obtain a database to be used for the computation of individual logarithms. The novel ingredients are new ways of obtaining linear equations and new methods of solving these linear equations by adaptations of sparse matrix methods from numerical analysis to the case of finite rings. While some of the new logarithm algorithms are adaptations of known integer factorization algorithms, others are new and can be adapted to yield integer factorization algorithms. 相似文献
127.
128.
Kvin Nay William J. Smiles Jacqueline Kaiser Luke M. McAloon Kim Loh Sandra Galic Jonathan S. Oakhill Andrew L. Gundlach John W. Scott 《International journal of molecular sciences》2021,22(8)
As life expectancy has increased, particularly in developed countries, due to medical advances and increased prosperity, age-related neurological diseases and mental health disorders have become more prevalent health issues, reducing the well-being and quality of life of sufferers and their families. In recent decades, due to reduced work-related levels of physical activity, and key research insights, prescribing adequate exercise has become an innovative strategy to prevent or delay the onset of these pathologies and has been demonstrated to have therapeutic benefits when used as a sole or combination treatment. Recent evidence suggests that the beneficial effects of exercise on the brain are related to several underlying mechanisms related to muscle–brain, liver–brain and gut–brain crosstalk. Therefore, this review aims to summarize the most relevant current knowledge of the impact of exercise on mood disorders and neurodegenerative diseases, and to highlight the established and potential underlying mechanisms involved in exercise–brain communication and their benefits for physiology and brain function. 相似文献
129.
Natasha M. van Poppelen Jolique A. van Ipenburg Quincy van den Bosch Jolanda Vaarwater Tom Brands Bert Eussen Frank Magielsen Hendrikus J. Dubbink Dion Paridaens Erwin Brosens Nicole Naus Annelies de Klein Emine Kili Robert M. Verdijk 《International journal of molecular sciences》2021,22(11)
The aim of this study was exploration of the genetic background of conjunctival melanoma (CM) and correlation with recurrent and metastatic disease. Twenty-eight CM from the Rotterdam Ocular Melanoma Study group were collected and DNA was isolated from the formalin-fixed paraffin embedded tissue. Targeted next-generation sequencing was performed using a panel covering GNAQ, GNA11, EIF1AX, BAP1, BRAF, NRAS, c-KIT, PTEN, SF3B1, and TERT genes. Recurrences and metastasis were present in eight (29%) and nine (32%) CM cases, respectively. TERT promoter mutations were most common (54%), but BRAF (46%), NRAS (21%), BAP1 (18%), PTEN (14%), c-KIT (7%), and SF3B1 (4%) mutations were also observed. No mutations in GNAQ, GNA11, and EIF1AX were found. None of the mutations was significantly associated with recurrent disease. Presence of a TERT promoter mutation was associated with metastatic disease (p-value = 0.008). Based on our molecular findings, CM comprises a separate entity within melanoma, although there are overlapping molecular features with uveal melanoma, such as the presence of BAP1 and SF3B1 mutations. This warrants careful interpretation of molecular data, in the light of clinical findings. About three quarter of CM contain drug-targetable mutations, and TERT promoter mutations are correlated to metastatic disease in CM. 相似文献
130.
Liza-Anastasia DiCecco Andrew D'Elia Chelsea Miller Prof. Dr. Kyla N. Sask Prof. Dr. Leyla Soleymani Prof. Dr. Kathryn Grandfield 《Chembiochem : a European journal of chemical biology》2021,22(15):2488-2506
For biological imaging using electron microscopy (EM), the use of room-temperature ionic liquids (RTILs) has been proposed as an alternative to traditional lengthy preparation methods. With their low vapor pressures and conductivity, RTILs can be applied onto hard-to-image soft and/or wet samples without dehydration – allowing for a more representative, hydrated state of material and opening the possibility for visualization of in situ physiological processes using conventional EM systems. However, RTILs have yet to be utilized to their full potential by microscopists and microbiologists alike. To this end, this review aims to provide a comprehensive summary of biological applications of RTILs for EM to bridge the RTIL, in situ microscopy, and biological communities. We outline future research avenues for the use of RTILs for the EM observation of biological samples, notably i) RTIL selection and optimization, ii) applications for live cell processes and iii) electron beam and ionic liquid interaction studies. 相似文献