全文获取类型
收费全文 | 4329篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 249篇 |
金属工艺 | 51篇 |
机械仪表 | 36篇 |
建筑科学 | 126篇 |
矿业工程 | 7篇 |
能源动力 | 66篇 |
轻工业 | 204篇 |
水利工程 | 14篇 |
石油天然气 | 10篇 |
无线电 | 174篇 |
一般工业技术 | 372篇 |
冶金工业 | 2798篇 |
原子能技术 | 13篇 |
自动化技术 | 226篇 |
出版年
2022年 | 14篇 |
2021年 | 13篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 115篇 |
2012年 | 55篇 |
2011年 | 86篇 |
2010年 | 70篇 |
2009年 | 59篇 |
2008年 | 71篇 |
2007年 | 78篇 |
2006年 | 68篇 |
2005年 | 71篇 |
2004年 | 62篇 |
2003年 | 63篇 |
2002年 | 43篇 |
2001年 | 49篇 |
2000年 | 47篇 |
1999年 | 109篇 |
1998年 | 836篇 |
1997年 | 480篇 |
1996年 | 298篇 |
1995年 | 223篇 |
1994年 | 183篇 |
1993年 | 198篇 |
1992年 | 57篇 |
1991年 | 55篇 |
1990年 | 49篇 |
1989年 | 50篇 |
1988年 | 46篇 |
1987年 | 43篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 34篇 |
1981年 | 38篇 |
1980年 | 38篇 |
1979年 | 24篇 |
1978年 | 28篇 |
1977年 | 82篇 |
1976年 | 142篇 |
1975年 | 17篇 |
1974年 | 13篇 |
1973年 | 19篇 |
1972年 | 14篇 |
1968年 | 13篇 |
排序方式: 共有4363条查询结果,搜索用时 15 毫秒
41.
SW Qian JK Burmester PD Sun A Huang DJ Ohlsen L Suardet KC Flanders D Davies AB Roberts MB Sporn 《Canadian Metallurgical Quarterly》1994,33(40):12298-12304
Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation. On the basis of the crystal structure of TGF-beta 2, we have designed and synthesized two mutant TGF-beta s, TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73). Although both of these molecules inhibited the growth of Mv1Lu mink lung epithelial cells and LS1034 colorectal cancer cells, which are affected equally by TGF-beta 1 and TGF-beta 2, TGF-beta 1 (delta 69-73) was much less potent than TGF-beta 1 or TGF-beta 1 (71 Trp) at inhibiting the growth of LS513 colorectal cancer cells which are growth-inhibited by TGF-beta 1 but not TGF-beta 2. Both TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73) increased levels of mRNAs for fibronectin and plasminogen activator inhibitor with Mv1Lu cells, whereas only TGF-beta 1 (71 Trp) and not TGF-beta 1 (delta 69-73) up-regulated the mRNA level of carcinoembryonic antigen in LS513 cells. The expression level of carcinoembryonic antigen mRNA in LS1034 cells was not altered by either wild-type or mutant TGF-beta s. Receptor labeling experiments demonstrated that TGF-beta 1 (71 Trp) bound with high affinity to the cell-surface receptors of Mv1Lu, LS1034, and LS513 cells while TGF-beta 1 (delta 69-73) bound effectively to the receptors of Mv1Lu and LS1034 cells but much less to the receptors on LS513 cells.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
42.
Clonality in T-cell malignancy was investigated using T-cell receptor (TcR) V beta 1-20 family primers and polymerase chain reaction amplification (PCR) of cDNA prepared from tissue biopsies and blood involved with tumour. Secondary PCR amplification of the VDJ joints of primary PCR products was performed to distinguish clonal from polyclonal products, and clonal V beta gene products were confirmed by direct PCR sequencing in the majority of cases. In eight T-cell malignancies including T-cell acute lymphoblastic leukaemia (T-ALL) and T-cell chronic lymphocytic leukaemia (T-CLL) shown to be clonal by Southern blot analysis, one or two primary PCR products were identified and shown to be clonal. In five cases of peripheral T-cell lymphoma (PTCL) all V beta 1-20 families were identified after primary PCR amplification, and clonal products were identified in two cases after secondary amplification; TcR V beta clonal families could not be demonstrated in the remaining three cases. These data were in agreement with previous Southern blot analysis of these cases, and confirmed the presence of reactive T cells in PTCL as well as providing further evidence for the genotypic heterogeneity of this entity. In the remaining case, a blood lymphocytosis, primary PCR amplification produced predominant TcR V beta 6 and V beta 12 family products, of which the V beta 6 family proved clonal after secondary PCR amplification. There was no evidence for overrepresentation of TCR V beta families by the tumour populations in this study, furthermore the data confirm the involvement of reactive cells in T-cell malignancy and the genetic heterogeneity of PTCL. 相似文献
43.
44.
45.
46.
Multisite microprobes for neural recordings 总被引:1,自引:0,他引:1
Blum N.A. Carkhuff B.G. Charles H.K. Jr. Edwards R.L. Meyer R.A. 《IEEE transactions on bio-medical engineering》1991,38(1):68-74
Multisite, passive microprobes have been developed to allow simultaneous recording of action potential activity from multiple neurons at different locations in the brain. The microprobes were fabricated using standard integrated circuit techniques. The probe is a planar structure that consists of gold electrodes sandwiched between two polyimide dielectric layers and bonded to a molybdenum structural support. Windows in the top dielectric layer expose the electrode sites and bonding pads. In two distinct versions of the probe four or six recordings sites, respectively, of approximately 25 microns 2 are arranged on a dagger-shaped structure which can penetrate the pia. The bonding pads and interconnect wires at the probe head are entirely encapsulated in a tubular fixture that is packed with silicone RTV and sealed with epoxy to protect the interconnections from contact with body fluids. The site impedances at 1 kHz are typically between 2 and 4 M omega. Probe lifetimes for continuous immersion in physiological saline solution, as measured by impedance, have exceeded 750 h. The failure mechanism is believed to be due to moisture and ion absorption in the top dielectric layer. In acute neurophysiological experiments using the four site probes, action potential activity was recorded from physiologically identified neurons in the dorsal column nuclei of anesthetized rat. 相似文献
47.
H.W. Choi C.W. Jeon M.D. Dawson P.R. Edwards R.W. Martin 《Photonics Technology Letters, IEEE》2003,15(4):510-512
High-performance, two-dimensional arrays of parallel-addressed InGaN blue micro-light-emitting diodes (LEDs) with individual element diameters of 8, 12, and 20 /spl mu/m, respectively, and overall dimensions 490 /spl times/490 /spl mu/m, have been fabricated. In order to overcome the difficulty of interconnecting multiple device elements with sufficient step-height coverage for contact metallization, a novel scheme involving the etching of sloped-sidewalls has been developed. The devices have current-voltage (I-V) characteristics approaching those of broad-area reference LEDs fabricated from the same wafer, and give comparable (3-mW) light output in the forward direction to the reference LEDs, despite much lower active area. The external efficiencies of the micro-LED arrays improve as the dimensions of the individual elements are scaled down. This is attributed to scattering at the etched sidewalls of in-plane propagating photons into the forward direction. 相似文献
48.
Radkovskaya A. Sydoruk O. Shamonin M. Shamonina E. Stevens C.J. Faulkner G. Edwards D.J. Solymar L. 《Microwaves, Antennas & Propagation, IET》2007,1(1):80-83
Magnetoinductive waves propagating along a line consisting of two kinds of metamaterial elements are studied. Both elements are made up by the same metallic loop but are loaded by different capacitors resulting in different resonant frequencies. The dispersion characteristics are derived from phase and amplitude measurements for the cases when the line consists of (i) identical elements and (ii) of alternating elements. Both planar (elements in the same plane as the axis of the line) and axial (elements perpendicular to the axis of the line) configurations are investigated. It is shown that in the bi-periodic arrangement of the elements, the dispersion curves have a forward wave in the lower frequency branch and a backward wave in the upper frequency branch independent of the configuration whether it is planar or axial. Comparisons between theoretical and experimental results show good agreement 相似文献
49.
E Totsuka S Todo Y Zhu N Ishizaki Y Kawashima MB Jin A Urakami T Shimamura TE Starzl 《Canadian Metallurgical Quarterly》1998,187(3):276-286
Workplace AIDS training is a recent addition to many corporations' occupational health agenda. However, little is known about the objectives, content, and practices of AIDS training programs. A survey of 126 workplace AIDS trainers was conducted to determine the impact of the trainer's organizational affiliation (in-house, consultant, union, etc.) and personal motives on training program objectives, content, and practices. Results indicate that the organizational affiliation of trainers is significantly related to training objectives, topics, and practices, whereas strong personal motives for becoming an AIDS trainer is significantly associated with an emphasis on more controversial content areas and training practices. Findings are discussed in terms of applicability to other values-oriented training topics, applications to practice, and future research needs. 相似文献
50.
CD Holyoak M Stratford Z McMullin MB Cole K Crimmins AJ Brown PJ Coote 《Canadian Metallurgical Quarterly》1996,62(9):3158-3164
The weak acid sorbic acid transiently inhibited the growth of Saccharomyces cerevisiae in media at low pH. During a lag period, the length of which depended on the severity of this weak-acid stress, yeast cells appeared to adapt to this stress, eventually recovering and growing normally. This adaptation to weak-acid stress was not due to metabolism and removal of the sorbic acid. A pma1-205 mutant, with about half the normal membrane H+-ATPase activity, was shown to be more sensitive to sorbic acid than its parent. Sorbic acid appeared to stimulate plasma membrane H+-ATPase activity in both PMA1 and pma1-205. Consistent with this, cellular ATP levels showed drastic reductions, the extent of which depended on the severity of weak-acid stress. The weak acid did not appear to affect the synthesis of ATP because CO2 production and O2 consumption were not affected significantly in PMA1 and pma1-205 cells. However, a glycolytic mutant, with about one-third the normal pyruvate kinase and phosphofructokinase activity and hence a reduced capacity to generate ATP, was more sensitive to sorbic acid than its isogenic parent. These data are consistent with the idea that adaptation by yeast cells to sorbic acid is dependent on (i) the restoration of internal pH via the export of protons by the membrane H+-ATPase in an energy-demanding process and (ii) the generation of sufficient ATP to drive this process and still allow growth. 相似文献