全文获取类型
收费全文 | 3229篇 |
免费 | 342篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 44篇 |
化学工业 | 814篇 |
金属工艺 | 136篇 |
机械仪表 | 101篇 |
建筑科学 | 77篇 |
矿业工程 | 20篇 |
能源动力 | 162篇 |
轻工业 | 720篇 |
水利工程 | 15篇 |
石油天然气 | 10篇 |
无线电 | 165篇 |
一般工业技术 | 660篇 |
冶金工业 | 65篇 |
原子能技术 | 9篇 |
自动化技术 | 577篇 |
出版年
2024年 | 7篇 |
2023年 | 31篇 |
2022年 | 25篇 |
2021年 | 123篇 |
2020年 | 117篇 |
2019年 | 141篇 |
2018年 | 225篇 |
2017年 | 211篇 |
2016年 | 243篇 |
2015年 | 191篇 |
2014年 | 253篇 |
2013年 | 419篇 |
2012年 | 234篇 |
2011年 | 180篇 |
2010年 | 158篇 |
2009年 | 178篇 |
2008年 | 128篇 |
2007年 | 106篇 |
2006年 | 67篇 |
2005年 | 35篇 |
2004年 | 49篇 |
2003年 | 45篇 |
2002年 | 37篇 |
2001年 | 13篇 |
2000年 | 26篇 |
1999年 | 13篇 |
1998年 | 19篇 |
1997年 | 12篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1990年 | 15篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 31篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有3575条查询结果,搜索用时 15 毫秒
141.
Ultrastructural and developmental toxicity of potato and tomato leaf extracts to beet armyworm,Spodoptera exigua (lepidoptera: noctuidae) 下载免费PDF全文
Zbigniew Adamski Katarzyna Radtke Agnieszka Kopiczko Szymon Chowański Paweł Marciniak Monika Szymczak Marta Spochacz Patrizia Falabella Filomena Lelario Laura Scrano Sabino A. Bufo 《Microscopy research and technique》2016,79(10):948-958
Beet Armyworm, Spodoptera exigua is a herbivorous moth and a serious pest of many economically important plants, which are used as food sources. Because of rigorous standards of food quality, usage of synthetic insecticides in crop protection, against pests, is limited. Solanaceae plant extracts may be a relatively cheap source of efficient natural insecticides that can limit usage of synthetic substances. Their biological activity is not fully known. In particular, ultrastructural studies, using transmission electron microscopy, are not usual. In the present article we describe the effects of sublethal concentrations of tomato and potato leaf extracts against S. exigua. Acute lethal effects were not observed. Both extracts exerted similar effects within midgut and fat body cells. Midgut cells were not significantly altered while fat body cells showed prominent swelling of nuclear envelope and endoplasmic reticulum, vacuolization of mitochondria and fusion of fat droplets. These changes were much more intensive within groups exposed to potato than tomato extracts at highest concentration at least. Light microscopy was used to observe and document developmental alterations of S. exigua exposed to potato and tomato leaf extracts. Potato leaf extracts significantly decreased hatching success and caused morphological malformations of imagoes. Among them, malformations of wings were the most prominent. Interestingly, these effects were not observed within populations exposed to tomato extracts at highest concentration at least. 相似文献
142.
143.
The issue of computing (co)homology generators of a cell complex is gaining a pivotal role in various branches of science. While this issue may be rigorously solved in polynomial time, it is still overly demanding for large scale problems. Drawing inspiration from low-frequency electrodynamics, this paper presents a physics inspired algorithm for first cohomology group computations on three-dimensional complexes. The algorithm is general and exhibits orders of magnitude speed up with respect to competing ones, allowing to handle problems not addressable before. In particular, when generators are employed in the physical modeling of magneto-quasistatic problems, this algorithm solves one of the most long-lasting problems in low-frequency computational electromagnetics. In this case, the effectiveness of the algorithm and its ease of implementation may be even improved by introducing the novel concept of lazy cohomology generators. 相似文献
144.
The finite satisfiability problem for guarded fixpoint logic is decidable and complete for 2ExpTime (resp. ExpTime for formulas of bounded width). 相似文献
145.
Effects of the spray drying conditions of chokeberry (Aronia melanocarpa L.) juice concentrate on the physicochemical properties of powders 下载免费PDF全文
Jolanta Gawałek Ewa Domian Antoni Ryniecki Sławomir Bakier 《International Journal of Food Science & Technology》2017,52(9):1933-1941
A semi‐industrial spray drying process of chokeberry juice concentrate using maltodextrin was analysed. The influence of the content and dextrose equivalent (DE) of maltodextrin, inlet air temperature and rotary disc atomiser speed was studied on the physicochemical properties of the obtained powders. The size and structure of the powder particles, bulk density, moisture content, flowability, yield and total polyphenol content were analysed. An increase in carrier content from 50% to 70% caused a 4.9% increase in total polyphenol retention, better flowability (Hausner ratio decrease of 0.17) and greater yield of the powder (60%). An increase in the drying temperature (150–170 °C) caused larger particle size and improved powder flowability but also resulted in greater loss of total polyphenols. A decrease in rotary atomiser speed (11 000–15 000 rpm) had a moderate influence on particle size and improvement in flowability but had no effect on polyphenol retention. Changes in the DE (8–22) of maltodextrin as a carrier indicated a moderate growing dependence on particle size and worse flowability. 相似文献
146.
Linear poly(l ‐lactides) (PLLAs ) and poly(d ‐lactides) (PDLAs ) with M n in the range 2000 ? 4300 containing a different number and placement of carboxyl groups were obtained via cationic ring‐opening polymerization and post‐polymerization functionalization. PLA stereoisomers (PLLA ‐(COOH )x and PDLA ‐(COOH )x , where x = 1 ? 3) were used for the investigation of stereocomplexation in solution performed in the presence of metal cations such as Ca2+, Mg2+, Zn2+, Fe3+. Spherical microparticles with a diameter in the range 0.7 ? 3.0 µm were obtained in all cases which was confirmed on the basis of scanning electron microscopy (SEM ) analysis. The microsphere size and homogeneity were analyzed depending on the stereocomplexation conditions and the molecular weight as well as the number of carboxyl end groups in the PLLA and PDLA used for stereocomplexation. The PLA microspheres obtained were analyzed by Fourier transform IR spectroscopy, wide angle X‐ray spectroscopy and energy‐dispersive X‐ray spectroscopy methods which confirmed the presence of metal cations inside. The application of regular microspheres with metal ions as drug delivery systems is considered. © 2016 Society of Chemical Industry 相似文献
147.
The article presents a new approach to the analysis of light propagation in photorefractive materials. The discussed numerical method can be used for an analysis of the dynamics of nonlinear effects taking place in those media in which an analytical approach requires the use of approximations or is impossible. As an example of how the method works, the results of simulation are shown, illustrating the process of spatial solitary wave formation in two materials: a photorefractive semiconductor and a ferroelectric crystal. 相似文献
148.
The paper presents a new form of the electrothermal model of the ferromagnetic core for SPICE and the way, in which the parameters of the model are determined. The manner of determining magnetic, geometric and thermal parameters of this model is described. The correctness of the proposed model and the manner of determining the values of the parameters are verified by comparing the calculated and measured characteristics of the selected ferromagnetic cores. 相似文献
149.
150.
We report on electron spin resonance (ESR) investigations of a FeVO4 single crystal. Temperature and angular dependences of ESR resonance positions were measured and calculated in temperature range of 35–100 K. The spectra show rich angular dependences of the linewidth, the shape and the resonance field. They consist of a single broad line with asymmetric distortion. Due to the low symmetry of the crystal lattice this distortion can be explained by taking into account the influence of non diagonal dynamic susceptibility. 相似文献