全文获取类型
收费全文 | 9621篇 |
免费 | 693篇 |
国内免费 | 306篇 |
专业分类
电工技术 | 361篇 |
综合类 | 381篇 |
化学工业 | 1576篇 |
金属工艺 | 522篇 |
机械仪表 | 614篇 |
建筑科学 | 501篇 |
矿业工程 | 171篇 |
能源动力 | 313篇 |
轻工业 | 458篇 |
水利工程 | 149篇 |
石油天然气 | 298篇 |
武器工业 | 30篇 |
无线电 | 1433篇 |
一般工业技术 | 1566篇 |
冶金工业 | 885篇 |
原子能技术 | 92篇 |
自动化技术 | 1270篇 |
出版年
2024年 | 42篇 |
2023年 | 131篇 |
2022年 | 250篇 |
2021年 | 332篇 |
2020年 | 266篇 |
2019年 | 271篇 |
2018年 | 264篇 |
2017年 | 260篇 |
2016年 | 256篇 |
2015年 | 343篇 |
2014年 | 407篇 |
2013年 | 592篇 |
2012年 | 546篇 |
2011年 | 592篇 |
2010年 | 491篇 |
2009年 | 515篇 |
2008年 | 459篇 |
2007年 | 455篇 |
2006年 | 413篇 |
2005年 | 397篇 |
2004年 | 271篇 |
2003年 | 267篇 |
2002年 | 258篇 |
2001年 | 249篇 |
2000年 | 211篇 |
1999年 | 260篇 |
1998年 | 268篇 |
1997年 | 217篇 |
1996年 | 181篇 |
1995年 | 162篇 |
1994年 | 135篇 |
1993年 | 105篇 |
1992年 | 94篇 |
1991年 | 80篇 |
1990年 | 62篇 |
1989年 | 67篇 |
1988年 | 58篇 |
1987年 | 46篇 |
1986年 | 38篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1974年 | 19篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen 相似文献
2.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach. 相似文献
3.
4.
5.
We report a case of pulmonary carcinosarcoma. Surgery is required for this rare mixed type, biphasic tumor. It is generally considered to be a malignant formation issuing from a single cell line but with a two-way differentiation into epithelial and conjunctive components. There is a differentiation continuum between spindle-cell carcinomas (also called monophasic sarcomatoid carcinoma) and carcinosarcoma (or biphasic sarcomatoid carcinoma) leading to debate concerning the immunohistochemical and ultrastructural features. 相似文献
6.
Extracellular single-unit discharges were obtained from 165 spontaneously active neurons within the region of the rostral ventrolateral medulla (RVLM) by glass microelectrode from 89 brain slices of the Sprague-Dawley rats. The units could be divided into three types: regular (61.8%), irregular (24.2%) and silent (14%). Acetylcholine (ACh, 0.1, 0.3 mumol/L) showed four kinds of effects on spontaneous discharges of RVLM neurons: excitatory, inhibitory, biphasic and non-responsive, counting respectively 41.8%, 20%, 3% and 35.2% of the neurons tested. The excitatory effect of ACh was dose-dependent. The effects, either excitatory or inhibitory, of ACh (n = 49) were mostly blocked by atropine (0.3 mumol/L, n = 42). The excitatory effect of ACh (n = 14) could be blocked mainly by selective antagonist of M1 receptor, pirenzepine (PZ, 30 nmol/L, n = 9), but not by selective antagonist of M2 receptor, methoctramine (MT) and AFDX-116. The inhibitory effect of ACh (n = 10) could be blocked mostly by M2 receptor antagonist MT (30 nmol/L, n = 7); and this inhibitory effect (n = 9) could be blocked mostly by another M2 receptor antagonist AFDX-116 (30 nmol/L, n = 6), but not by M1 receptor antagonist PZ. 相似文献
7.
Arafa M. Fay P. Ismail K. Chu J.O. Meyerson B.S. Adesida I. 《Electron Device Letters, IEEE》1996,17(3):124-126
We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (fT) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (gm) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K 相似文献
8.
9.
A simple measurement method for the absolute Raman scattering cross-section of an optical fibre is presented. This method does not require a high power pump laser and it measures the fibre directly. It is also shown that the calculation of the cross-section depends on the fibre structure, such as its refractive index profile and the differential attenuation between the pump wavelength and Raman wavelength.<> 相似文献
10.
Ultraviolet (UV) disinfection is becoming increasingly popular as an alternative disinfection technology to chlorination in recent years. In this study, we investigated the photoreactivation of Escherichia coli following medium-pressure (MP) UV disinfection of synthetic water by a bench-scale collimated beam apparatus. The UV doses ranged from 1.6 -19.7 mWs/cm2 and photoreactivation was investigated for 6 hours under fluorescent light. In addition, chloramination was applied after UV disinfection to investigate its ability to control photoreactivation. It was found that photoreactivation occurred for all UV doses tested and the increase in bacteria numbers ranged from 0.04 to 1.35 log10. However, the degree of photoreactivation decreased with increased UV doses. Chloramination experiments revealed that the addition of 0.5 mg/l of monochloramine resulted in suppression of photoreactivation for 1 hour only. An increased monochloramine dose of 1 mg/l was found to prevent photoreactivation for the entire duration of the experiment. The results of this study have shown that photoreactivation occurs even after MP UV disinfection, although it is of a lesser extent at higher UV doses. This study has also established that secondary chloramination can effectively suppress and eliminate photoreactivation with a chloramine dose of 1 mg/l. 相似文献