全文获取类型
收费全文 | 3225篇 |
免费 | 50篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 28篇 |
综合类 | 2篇 |
化学工业 | 448篇 |
金属工艺 | 38篇 |
机械仪表 | 44篇 |
建筑科学 | 87篇 |
矿业工程 | 17篇 |
能源动力 | 36篇 |
轻工业 | 210篇 |
水利工程 | 13篇 |
石油天然气 | 6篇 |
无线电 | 292篇 |
一般工业技术 | 349篇 |
冶金工业 | 1364篇 |
原子能技术 | 32篇 |
自动化技术 | 326篇 |
出版年
2021年 | 26篇 |
2019年 | 21篇 |
2018年 | 30篇 |
2016年 | 27篇 |
2015年 | 26篇 |
2014年 | 25篇 |
2013年 | 132篇 |
2012年 | 62篇 |
2011年 | 113篇 |
2010年 | 62篇 |
2009年 | 63篇 |
2008年 | 89篇 |
2007年 | 110篇 |
2006年 | 92篇 |
2005年 | 85篇 |
2004年 | 65篇 |
2003年 | 61篇 |
2002年 | 66篇 |
2001年 | 44篇 |
2000年 | 67篇 |
1999年 | 51篇 |
1998年 | 252篇 |
1997年 | 158篇 |
1996年 | 128篇 |
1995年 | 98篇 |
1994年 | 76篇 |
1993年 | 89篇 |
1992年 | 54篇 |
1991年 | 23篇 |
1990年 | 54篇 |
1989年 | 52篇 |
1988年 | 53篇 |
1987年 | 47篇 |
1986年 | 49篇 |
1985年 | 51篇 |
1984年 | 53篇 |
1983年 | 53篇 |
1982年 | 43篇 |
1981年 | 46篇 |
1980年 | 33篇 |
1979年 | 30篇 |
1978年 | 52篇 |
1977年 | 55篇 |
1976年 | 83篇 |
1975年 | 38篇 |
1974年 | 31篇 |
1973年 | 27篇 |
1972年 | 25篇 |
1970年 | 24篇 |
1964年 | 20篇 |
排序方式: 共有3292条查询结果,搜索用时 15 毫秒
1.
Meghelli M. Rylyakov A.V. Zier S.J. Sorna M. Friedman D. 《Solid-State Circuits, IEEE Journal of》2003,38(12):2147-2154
A 43-Gb/s receiver (Rx) and transmitter (Tx) chip set for SONET OC-768 transmission systems is reported. Both ICs are implemented in a 0.18-/spl mu/m SiGe BiCMOS technology featuring 120-GHz f/sub T/ and 100 GHz f/sub max/. The Rx includes a limiting amplifier, a half-rate clock and data recovery unit, a 1:4 demultiplexer, a frequency acquisition aid, and a frequency lock detector. Input sensitivity for a bit-error rate less than 10/sup -9/ is 40 mV and jitter generation better than 230 fs rms. The IC dissipates 2.4 W from a -3.6-V supply voltage. The Tx integrates a half-rate clock multiplier unit with a 4:1 multiplexer. Measured clock jitter generation is better than 170 fs rms. The IC consumes 2.3 W from a -3.6-V supply voltage. 相似文献
2.
3.
The convexity and continuity of fuzzy mappings are defined through a linear ordering and a metric on the set of fuzzy numbers. The local-global minimum property of real-valued convex functions is extended to convex fuzzy mappings. It is proved that a strict local minimizer of a quasiconvex fuzzy mapping is also a strict global minimizer. Characterizations for convex fuzzy mappings and quasiconvex fuzzy mappings are given. In addition, the Weirstrass theorem is extended from real-valued functions to fuzzy mappings. 相似文献
4.
MJ Glantz PC Burger AH Friedman RA Radtke EW Massey SC Schold 《Canadian Metallurgical Quarterly》1994,44(11):2020-2027
When radiation is used to treat nervous system cancer, exposure of adjacent normal nervous system tissue is unavoidable, and radiation-induced injury may occur. Acute injury is usually mild and transient, but late forms of radiation-induced nervous system injury are usually progressive and debilitating. Treatment with corticosteroids, surgery, and antioxidants is often ineffective. We treated 11 patients with late radiation-induced nervous system injuries (eight with cerebral radionecrosis, one with a myelopathy, and two with plexopathies, all unresponsive to dexamethasone and prednisone) with full anticoagulation. Some recovery of function occurred in five of the eight patients with cerebral radionecrosis, and all the patients with myelopathy or plexopathy. Anticoagulation was continued for 3 to 6 months. In one patient with cerebral radionecrosis, symptoms recurred after discontinuation of anticoagulation and disappeared again after reinstitution of treatment. We hypothesize that anticoagulation may arrest and reverse small-vessel endothelial injury--the fundamental lesion of radiation necrosis--and produce clinical improvement in some patients. 相似文献
5.
K Tordjman N Stern G Ouaknine Y Yossiphov N Razon M Nordenskj?ld E Friedman 《Canadian Metallurgical Quarterly》1993,77(3):765-769
The majority of pituitary tumors are of monoclonal origin; however, the molecular basis for their formation is poorly understood. Somatic mutations in the alpha-subunit of the GTP-binding protein, Gs alpha (gsp oncogene) have been found in about one third of GH-secreting tumors. Mutations in another alpha-subunit of a GTP-binding protein, Gi2 alpha (gip mutations) have been described in other endocrine tumors. In this study, we examined 21 nonfunctioning pituitary tumors and 4 macroprolactinomas for gsp mutations and 27 nonfunctioning tumors and 4 macroprolactinomas for gip mutations. Using the polymerase chain reaction and denaturing gradient gel electrophoresis, 2 nonfunctioning pituitary tumors displayed migration abnormalities when the Gs alpha-gene was analyzed. Sequence analysis of these abnormally migrating polymerase chain reaction products revealed two previously known gsp mutations: arginine at codon 201 altered to cysteine, and glutamine at codon 227 changed to leucine. No gip mutations could be demonstrated. These findings emphasize the monoclonal origin of nonfunctioning pituitary tumors and suggest that cAMP may play a role in tumorigenesis of nonfunctioning pituitary tumors. 相似文献
6.
Interviewed 120 sunbathing and nonsunbathing beachgoers about their health practices, knowledge about skin cancer, moods, and social rewards obtained through sunbathing. Ss also completed personality questionnaires. Data were considered using a theoretical perspective combining aspects of health belief, social influence, social learning, and risk-taking models. Results indicate that sunbathing was related to having a positive attitude toward risk taking, having little knowledge about skin cancer, reporting a relaxed mood, having friends who sunbathe, and engaging in activities related to maintaining a positive physical appearance. Sunscreen use was related to sex, having knowledge about skin cancer, knowing people who have had cancer, and reporting high levels of anxiety. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
Yikun Huang Nehorai A. Friedman G. 《Antennas and Propagation, IEEE Transactions on》2003,51(6):1307-1314
Coupling between two collocated orthogonal circular thin-wire loops is analyzed in this paper. Two coupled integral equations for the loop currents are derived and their solution in general form is found in terms of Fourier series. An analytical expression for currents induced through the mutual coupling is obtained for the case when all loop current harmonics higher than first can be ignored. It is found that strong coupling can exist for all loop current harmonics, except for the fundamental. It is also found that coupling for orthogonal collocated loop antennas depends on the relative locations of the loop terminals. 相似文献
8.
The results of applying enhanced-surface-area packed-bed (ESAP) electrodes in electrogenerative SO2/O2 cells are reported to illustrate their utility and potential applications. Mathematical analysis with parameters pertinent
to the experimental conditions shows that all electrocatalyst sites in these electrodes are expected to be uniformly utilized
for electrochemical SO2 oxidation. Experimental results showed that ESAP electrodes (1 mg Pt/cm2) could provide at least 5 times higher SO2 conversion at given cell voltages than graphite sheet electrodes (1.5 mg Pt/cm2). 相似文献
9.
10.