全文获取类型
收费全文 | 42173篇 |
免费 | 541篇 |
国内免费 | 790篇 |
专业分类
电工技术 | 724篇 |
综合类 | 52篇 |
化学工业 | 6378篇 |
金属工艺 | 3094篇 |
机械仪表 | 1386篇 |
建筑科学 | 863篇 |
矿业工程 | 151篇 |
能源动力 | 1429篇 |
轻工业 | 2265篇 |
水利工程 | 356篇 |
石油天然气 | 1386篇 |
无线电 | 3976篇 |
一般工业技术 | 10667篇 |
冶金工业 | 7218篇 |
原子能技术 | 788篇 |
自动化技术 | 2771篇 |
出版年
2021年 | 342篇 |
2020年 | 276篇 |
2019年 | 373篇 |
2018年 | 665篇 |
2017年 | 657篇 |
2016年 | 743篇 |
2015年 | 539篇 |
2014年 | 807篇 |
2013年 | 2388篇 |
2012年 | 1405篇 |
2011年 | 1884篇 |
2010年 | 1489篇 |
2009年 | 1781篇 |
2008年 | 1624篇 |
2007年 | 1768篇 |
2006年 | 1400篇 |
2005年 | 1226篇 |
2004年 | 1178篇 |
2003年 | 1078篇 |
2002年 | 1066篇 |
2001年 | 1119篇 |
2000年 | 964篇 |
1999年 | 999篇 |
1998年 | 2115篇 |
1997年 | 1657篇 |
1996年 | 1440篇 |
1995年 | 983篇 |
1994年 | 757篇 |
1993年 | 774篇 |
1992年 | 597篇 |
1991年 | 572篇 |
1990年 | 524篇 |
1989年 | 485篇 |
1988年 | 369篇 |
1987年 | 402篇 |
1986年 | 364篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 349篇 |
1979年 | 341篇 |
1978年 | 294篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1974年 | 292篇 |
1973年 | 311篇 |
1972年 | 272篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.<> 相似文献
152.
Dianov E.M. Grudinin A.B. Gurjanov A.N. Gusovsky D.D. Harutjunian Z.E. Ignatev S.V. Smirnov O.B. 《Lightwave Technology, Journal of》1992,10(2):118-124
The reproducible technology for producing high-birefringence fibers with stress-induced elliptical cladding and circular core is described. The authors have obtained fibers that have a birefringence of about (1-3) 10-4, a mode coupling parameter of about (2-7) 10 -5 m-1, and loss of less than 0.5 dB/km at 1.6 μm. The authors have found effects restricting the capability of test fibers to maintain the state of linear polarization 相似文献
153.
Z. M. Sun Z. G. Wang H. Hdl B. Weiss R. Sticker 《Materialwissenschaft und Werkstofftechnik》1995,26(9):483-487
The deformation behavior of pure recrystallized molybdenum under cyclic and static loads was investigated in the temperature range between 30°C and 10O°C, for stress amplitudes between 100 MPa and 250 MPa and for static loads up to 200 MPa. The results show that in spite of the low test temperatures and stress levels the Mo material exhibits considerable plastic strains which depend sensitively on frequenez and small changes in temperature.The activation energy deduced for the static and dynamic deformation is less than 0.98 eV which indicates thermally activated processes, to be explained by a dislocation kink model as described in the literature. The low-temperature fatigue behavior appears strongly influenced by creep-fatigue interaction phenomena. 相似文献
154.
Under serum-free conditions the beta-glucan receptor of mouse macrophages mediates phagocytosis of beta-1,3-D-glucan-coated microbeads (diameter 2 microns). IFN-gamma increases the phagocytic function of the beta-glucan receptor in a dose-dependent manner, giving the plateau level at 100 U/ml. Maximum activity appears 9 h after addition of IFN-gamma to the cells. The effect disappears within 24 h. The effect of IFN-gamma may be a result of augmented receptor synthesis since treatment with cycloheximide reduces the phagocytosis. IL-1 also increases the phagocytic function of the beta-glucan receptor giving a dose-dependent response and with the plateau level reached at 10 U/ml. Maximum activity is found 4 h after addition of IL-1 to macrophages. The effect disappears within 24 h. TNF does not alter the phagocytic function of the beta-glucan receptor, but TNF together with IL-1 prolongs the effect of IL-1. PGE2 reduces the phagocytic function of the beta-glucan receptor. Maximum reduction is achieved with 8 ng/ml. Time-course studies show the lowest phagocytic activity 9 h after addition of PGE2 to the cells. 相似文献
155.
M Eberstadt B Huang Z Chen RP Meadows SC Ng L Zheng MJ Lenardo SW Fesik 《Canadian Metallurgical Quarterly》1998,392(6679):941-945
When activated, membrane-bound receptors for Fas and tumour-necrosis factor initiate programmed cell death by recruiting the death domain of the adaptor protein FADD to the membrane. FADD then activates caspase 8 (also known as FLICE or MACH) through an interaction between the death-effector domains of FADD and caspase 8. This ultimately leads to the apoptotic response. Death-effector domains and homologous protein modules known as caspase-recruitment domains have been found in several proteins and are important regulators of caspase (FLICE) activity and of apoptosis. Here we describe the solution structure of a soluble, biologically active mutant of the FADD death-effector domain. The structure consists of six antiparallel, amphipathic alpha-helices and resembles the overall fold of the death domains of Fas and p75. Despite this structural similarity, mutations that inhibit protein-protein interactions involving the Fas death domain have no effect when introduced into the FADD death-effector domain. Instead, a hydrophobic region of the FADD death-effector domain that is not present in the death domains is vital for binding to FLICE and for apoptotic activity. 相似文献
156.
Continuing our work on the immunosuppressive activity of cyclolinopeptide A (CLA), a cyclic nonapeptide of the sequence: c-(-Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe), we synthesized a series of 6 linear analogs of CLA, successively shortened at the N-terminus of the peptide chain. Immunosuppressive activity of acetates as well as trifluoroacetates of these peptides was investigated using PFC (humoral immunity) and DTH (cellular immunity) tests. It was found that the immunosuppressive potency of the peptides examined diminishes with shortening of the peptide chain. Octapeptide I with the sequence Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe was found to be the most active of the whole series. The immunosuppressive activity increased again for a tripeptide fragment of CLA of the sequence Pro-Phe-Phe. The immunosuppressive activity of octapeptide probably depends on the suppression of IL-1, IL-6 and TNF production by the cells involved in immune and inflammatory response. 相似文献
157.
R. Z. Gataulin 《Chemical and Petroleum Engineering》1992,28(8):519-521
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 8, pp. 31–32, August, 1992. 相似文献
158.
159.
By using a mRNA differential display technique to search for salicylate suppressible genes, we identified a cDNA in human foreskin fibroblasts, which by GenBankTM DNA data base search shows sequence homology to the recently reported cullin/Cdc53 (CUL) family genes, especially CUL-3. We have cloned the full-length human CUL-3 (Hs-CUL-3) cDNA. It encodes a 768-amino acid polypeptide and has a predicted molecular weight of 88,939. The amino acid sequence of Hs-CUL-3 shows 46% homology to that of its Caenorhabditis elegans ortholog, Ce-CUL-3, and 27 and 23% to that of Hs-CUL-1 and Hs-CUL-2, respectively. Northern blot analysis showed that phorbol 12-myristate 13-acetate increased the expression of Hs-CUL-3 mRNA in a concentration- and time-dependent manner, and this increase was inhibited by sodium salicylate. Hs-CUL-3 widely expressed in human tissues and its expression in cultured COLO205 colon cancer cells was increased when compared with that in normal colon cells. It is likely that Hs-CUL-3 is involved in cell proliferation control. 相似文献
160.