全文获取类型
收费全文 | 4186篇 |
免费 | 103篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 42篇 |
综合类 | 3篇 |
化学工业 | 741篇 |
金属工艺 | 92篇 |
机械仪表 | 98篇 |
建筑科学 | 164篇 |
矿业工程 | 24篇 |
能源动力 | 92篇 |
轻工业 | 301篇 |
水利工程 | 27篇 |
石油天然气 | 14篇 |
无线电 | 380篇 |
一般工业技术 | 725篇 |
冶金工业 | 1062篇 |
原子能技术 | 43篇 |
自动化技术 | 487篇 |
出版年
2022年 | 35篇 |
2021年 | 67篇 |
2020年 | 50篇 |
2019年 | 35篇 |
2018年 | 49篇 |
2017年 | 48篇 |
2016年 | 68篇 |
2015年 | 53篇 |
2014年 | 83篇 |
2013年 | 219篇 |
2012年 | 114篇 |
2011年 | 172篇 |
2010年 | 115篇 |
2009年 | 143篇 |
2008年 | 136篇 |
2007年 | 142篇 |
2006年 | 137篇 |
2005年 | 120篇 |
2004年 | 132篇 |
2003年 | 103篇 |
2002年 | 90篇 |
2001年 | 62篇 |
2000年 | 73篇 |
1999年 | 92篇 |
1998年 | 195篇 |
1997年 | 151篇 |
1996年 | 122篇 |
1995年 | 86篇 |
1994年 | 83篇 |
1993年 | 104篇 |
1992年 | 70篇 |
1991年 | 64篇 |
1990年 | 50篇 |
1989年 | 68篇 |
1988年 | 58篇 |
1987年 | 51篇 |
1986年 | 63篇 |
1985年 | 65篇 |
1984年 | 61篇 |
1983年 | 39篇 |
1982年 | 42篇 |
1981年 | 51篇 |
1980年 | 40篇 |
1979年 | 40篇 |
1978年 | 43篇 |
1977年 | 51篇 |
1976年 | 68篇 |
1975年 | 24篇 |
1974年 | 29篇 |
1973年 | 22篇 |
排序方式: 共有4295条查询结果,搜索用时 15 毫秒
991.
The dynamic online job shop scheduling problem (JSSP) is formulated based on the classical combinatorial optimization problem – JSSP with the assumption that new jobs continuously arrive at the job shop in a stochastic manner with the existence of unpredictable disturbances during the scheduling process. This problem is hard to solve due to its inherent uncertainty and complexity. This paper models this class of problem as a multi-objective problem and solves it by hybridizing the artificial intelligence method of artificial immune systems (AIS) and priority dispatching rules (PDRs). The immune network theory of AIS is applied to establish the idiotypic network model for priority dispatching rules to dynamically control the dispatching rule selection process for each operation under the dynamic environment. Based on the defined job shop situations, the dispatching rules that perform best under specific environment conditions are selected as antibodies, which are the key elements to construct the idiotypic network. Experiments are designed to demonstrate the efficiency and competitiveness of this model. 相似文献
992.
In this work, we present a non‐photorealistic rendering technique to create stylized abstractions from color images and videos. Our approach is based on adaptive line integral convolution in combination with directional shock filtering. The smoothing process regularizes directional image features while the shock filter provides a sharpening effect. Both operations are guided by a flow field derived from the structure tensor. To obtain a high‐quality flow field, we present a novel smoothing scheme for the structure tensor based on Poisson's equation. Our approach effectively regularizes anisotropic image regions while preserving the overall image structure and achieving a consistent level of abstraction. Moreover, it is suitable for per‐frame filtering of video and can be efficiently implemented to process content in real‐time. 相似文献
993.
994.
Large collections of communities such as those found in complex control systems necessitate sophisticated techniques for high-level human supervision due to their requirements of influence spanning over individuals, communities, and global system behaviours. We have developed psycho-socio-cultural models for mediation of system-level behaviours and interactions. The ensuing lowered human cognitive load will enable supervisors to effectively guide large systems with competing objectives. This model paves the way for developing the ‘Man On The Loop’ (MOTL) paradigm, a phrase we are proposing for a novel human supervision role that contrasts with typical micromanagement. We have highlighted and validated MOTL parameters through the implementation of a domain-neutral simulation and compared our results with those found in natural systems. 相似文献
995.
Sathananthan AH Selvaraj K Girijashankar ML Ganesh V Selvaraj P Trounson AO 《Microscopy research and technique》2006,69(6):396-407
The fine structure of human oogonia and growing oocytes has been reviewed in fetal and adult ovaries. Preovulatory maturation and the ultrastructure of stimulated oocytes from the germinal vesicle (GV) stage to metaphase II (MII) stage are also documented. Oogonia have large nuclei, scanty cytoplasm with complex mitochondria. During folliculogenesis, follicle cell processes establish desmosomes and deep gap junctions at the surface of growing oocytes, which are retracted during the final stages of maturation. The zona pellucida is secreted in secondary follicles. Growing oocytes have mitochondria, Golgi, rough endoplasmic reticulum (RER), ribosomes, lysosomes, and lipofuscin bodies, often associated with Balbiani bodies and have nuclei with reticulated nucleoli. Oocytes from antral follicles show numerous surface microvilli and cortical granules (CGs) separated from the oolemma by a band of microfilaments. The CGs are evidently secreted by Golgi membranes. The GV oocytes have peripheral Golgi complexes associated with a single layer of CGs close to the oolemma. They have many lysosomes, and nuclei with dense compact nucleoli. GV breakdown occurs by disorganization of the nuclear envelope and the oocyte enters a transient metaphase I followed by MII, when it is arrested and ovulated. Maturation of oocytes in vitro follows the same pattern of meiosis seen in preovulatory oocytes. The general organization of the human oocyte conforms to that of most other mammals but has some unique features. The MII oocyte has the basic cellular organelles such as mitochondria, smooth endoplasmic reticulum, microfilaments, and microtubules, while Golgi, RER, lysosomes, multivesicular, residual and lipofuscin bodies are very rare. It neither has yolk nor lipid inclusions. Its surface has few microvilli, and 1-3 layers of CGs, aligned beneath the oolemma. Special reference has been made to the reduction and inactivation of the maternal centrosome during oogenesis. The MII spindle, often oriented perpendicular to the oocyte surface, is barrel-shaped, anastral and lacks centrioles. Osmiophilic centrosomes are not demonstrable in human eggs, since the maternal centrosome is nonfunctional. However, oogonia and growing oocytes have typical centrioles, similar to those of somatic cells. The sperm centrosome activates the egg and organizes the sperm aster and mitotic spindles of the embryo, after fertilization. 相似文献
996.
D. Wang A. Ueckermann A. Schacht M. Oeser B. Steinauer B. N. J. Persson 《Tribology Letters》2014,56(2):397-402
When a rubber block is squeezed against a nominal flat but rough surface, the rubber bottom surface will penetrate into the substrate roughness profile. The relation between penetration depth \(w\) (or the average interfacial separation \(\bar{u}\) ) and the applied squeezing pressure \(p\) determines the (perpendicular) contact stiffness \(K=\hbox {d}p/\hbox {d}w=-\hbox {d}p/\hbox {d}\bar{u}\) , which is important for many applications. We have measured the relation between \(p\) and \(\bar{u}\) for a rubber block squeezed against 28 different concrete and asphalt road surfaces. We find a linear relation between \({\mathrm{log}}p\) and \(\bar{u}\) , in agreement with theory predictions. The measured stiffness values correlate rather well with the theory prediction. 相似文献
997.
To study cellular shapes, growth patterns, and fine structure during early stages of CNS development in rat embryos, preparative procedures were evaluated and modified to meet two criteria: (1) Coronal semithin sections should reveal undeformed telencephalic hemispheres that were symmetrically expanded on both sides of midline structures and were surrounded by contiguous mesenchyme. (2) In electron micrographs, cells should have intact, undistorted surface membranes, evenly distributed nucleoplasm and well preserved cytoplasmic organelles. To meet these criteria, 378 fetuses with a gestational age of 11–20 days (E11–E20) were used to test and modify procedures for anesthesia, embryo removal and handling, dissection, fixation, dehydration, and embedding of the embryonic CNS. Most specimens were in an early stage of development (E11–E13), which, in case of the neopallial wall, is the preneural period. The tests produced methods that met the above criteria and identified the most common artifacts and their causes. Deformities of the cerebral hemispheres and separations between the brain and its coverings were usually caused by trauma during embryo removal and during handling before fixation. Changes in cellular volumes, especially swelling during fixation and dehydration, were the most important causes of histological artifacts. The procedures and methods that consistently produced the best light and electron microscopic preservation of the E11–E13 rat CNS are described. Fixation was best when the brains were treated with glutaraldehyde and s-collidine buffer, followed by osmium tetroxide in s-collidine buffer. A surprisingly beneficial effect of sodium chloride in the dehydrating alcohol was noted. 相似文献
998.
Devaux F. Dorgeuille F. Ougazzaden A. Huet F. Carre M. Carenco A. Henry M. Sorel Y. Kerdiles J.-F. Jeanney E. 《Photonics Technology Letters, IEEE》1993,5(11):1288-1290
The authors have fabricated a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsP multiple quantum wells. The drive voltage for 12-dB extinction ratio is 1.2 V, and the frequency response is flat within 2 dB from DC to 20 GHz. Operation at 20 Gb/s is reported. Extensive data concerning the parasitic phase modulation (chirping) are obtained as a function of applied bias acid operating wavelength 相似文献
999.
We address analytically and numerically the problem of crack path prediction in the model system of a crack propagating under
thermal loading. We show that one can explain the instability from a straight to a wavy crack propagation by using only the
principle of local symmetry and the Griffith criterion. We then argue that the calculations of the stress intensity factors
can be combined with the standard crack propagation criteria to obtain the evolution equation for the crack tip within any
loading configuration. The theoretical results of the thermal crack problem agree with the numerical simulations we performed
using a phase field model. Moreover, it turns out that the phase-field model allows to clarify the nature of the transition
between straight and oscillatory cracks which is shown to be supercritical. 相似文献
1000.
Hydrogenation of stigmasterol 总被引:1,自引:0,他引:1
Hydrogenations of stigmasterol over 5% Pd/C, 5% Ru/C, Pt, Raney Ni, Raney Co, Ni/kieselguhr, and tris(triphenylphosphine)chlororhodium
catalysts and with diimide generated from hydrazine andp-toluenesulfonylhydrazide were studied to determine the best conditons for the selective reduction of the Δ22 double bond. The best results (maximum stigmasterol reduction, minimum stigmastanol formation) were obtained with Raney nickel
at room temperature and atmospheric pressure.
Contribution No. 1889 University of Arizona Agricultural Experiment Station. 相似文献